Laboratory and pilot-scale investigation of soil cations behavior in conjunction with electrokinetic remediation of inorganic pollutants

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Saudi, Mohamed A. Osman This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-8891372/v1 This work is licensed under a CC BY 4.0 License Status: Posted Version 1 posted You are reading this latest preprint version Abstract Soil electrokinetics (SEK) has a variety of applications, one of which is remediating contaminated soils that contain inorganic contaminants. The SEK remediation (SEKR), which is regarded as a physicochemical separation technique, is unable to distinguish between various ions in removal. In continuation with our recent publication in IJEST titled " Scaling up soil electrokinetic removal of inorganic contaminants based on lab chemical and biological optimizations " [ 1 ], which focused on the enhancement of SEKR of inorganic pollutants in real soils, these results are expanded upon in this article to show how cations linked to inorganic contaminants are removed. In the present investigation, the behavior/migration of six cations — Mg, Ca, Ba, Na, Li, and K — was illustrated. The findings demonstrated that the amount of Mg removed using the perforated cathode pipe SEKR system (PCPSS) under the influence of an electric field was proportionate to the rise in soil acidity. It was found that the best chemical to combine with soil to improve the removal of calcium was formic acid (pH 1). Compared to Mg, the amount of Ca removed was greater. The application of formic acid (pH 1) decreased the quantity of Ba accumulation spots/areas within the PCPSS apparatus. Using the recommended enhancing reagents, the content ratios with the removed Na had the lowest values, which exhibit the best rates of removal. In addition to decreasing the accumulation percentages around the cathode pipes (bottom layers), applying formic acid (pH 1) enhanced the amounts of Li removed from the surface layers as compared to the other treatments. After the pilot scale unit of the PCPSS was terminated, the removal percentages of the investigated cations were greatest for Na (lowest content ratios). Since Na is thought to be the primary obstacle to reclaiming salt-affected soil, it is highly recommended to recover salt-affected soil and remove inorganic pollutants simultaneously using the PCPSS pilot scale unit. Environmental Engineering Soil electrokinetics Process optimization/intensification The PCPSS Upscaling approach Cations removal Enhancement regents Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Figure 7 Figure 8 Figure 9 Figure 10 1. Introduction It is thought to be difficult to reclaim salt-affected soil, especially in arid and semi-arid areas where there aren't enough water resources for intermittent or continuous cleaning [ 2 ], [ 3 ]. Approximately 1–10 billion hectares of soil worldwide are influenced by salt, which can be classified as saline, sodic, or saline-sodic soils due to both natural and anthropogenic factors [ 4 ]. Extended reuse of marginal water, which is seen as a worldwide practice, together with altered precipitation patterns and increased temperatures brought on by climate change, complicate the reclamation process [ 4 ], [ 5 ]. To overcome salt-affected soil, hydraulic, chemical, and phytoremediation procedures are suggested methods [ 4 ]. One of the separation and purification technologies that may improve the removal of salt-affected soils is soil electrokinetic remediation (SEKR). Scientists established the fundamentals and basics of the SEKR at the beginning of 1990 [ 6 ], [ 7 ], [ 8 ], [ 9 ]. Since then, the SEKR has been used to accomplish certain goals in a variety of interesting domains. Aside from polluted soil remediation (mercury [ 10 ], [ 11 ], fluoride/fluorine [ 12 ], and PFAS [ 13 ]) SEK can be used for consolidation [ 14 ], [ 15 ], dewatering to accelerate dryness [ 16 ], [ 17 ], improving nutrients [ 18 ] (e.g., phosphorus) availability [ 19 ], sedimentation [ 20 ], [ 21 ], reclamation of saline soil [ 22 ], [ 23 ], prevention and control of pollutants [ 24 ], improved seed germination [ 25 ], phosphorus management in soils and sewage sludge [ 19 ], [ 26 ], [ 27 ], and so on. To accomplish a certain movement of elements, SEKR works by transferring a direct electric field (direct current, DC) via porous materials between a positively charged anode and a negatively charged cathode [ 28 ], [ 29 ]. The four processes/methods of electromigration, electroosmosis, diffusion, and electrophoresis are in charge of accomplishing the primary goals of SEKR [ 30 ]. Unsaturated zone formation, reverse electro-osmosis flow, cementation phenomenon near the electrode, temperature increases, pH variations near anodes and cathodes, pH-jumping zone formation, EO flow rate reduction with extended experimental duration, cracks in the treated soil, and current passing reduction were some of the challenges encountered during the application of SEKR [ 31 ], [ 32 ]. To solve these challenges and improve performance at the same time, several scientists suggested changes to the SEKR apparatus's design in addition to the addition of enhancement materials [ 33 ], [ 34 ]. In 2012, the PCPSS was introduced, a novel ex-situ SEKR method for the removal of inorganic pollutants. The PCPSS is part of the vertical SEK design [ 35 ]. By changing the anode placements and adding perforated nozzles, the PCPSS design was improved. Additionally, the PCPSS's potential to restore severely salinized soils was examined The current effort builds upon our previous article, which was entitled “ Scaling up soil electrokinetic removal of inorganic contaminants based on lab chemical and biological optimizations ” [ 1 ]. Throughout the enhancing and upscaling studies, the behavior of the cations Mg, Ca, Ba, Na, Li, and K was assessed. To optimize the reclamation process of salt-affected soils, it is crucial to investigate the behavior of cations during SEKR of inorganic pollutant-contaminated soils at the lab/bench and pilot scales. The results of our earlier investigation may be summarized as follows [ 1 ]: 1) the excellent efficiency of the PCPSS (laboratory scale) in removing inorganic pollutants was demonstrated when formic acid was mixed with actual contaminated soil, 2) the electroosmosis flow was improved by mixing nitric acid, formic acid, and biosurfactant bacterial broth culture with contaminated soil, 3) solar energy is a great alternative to the power source for the SEKR upscaling unit as it has proven to be capable of operating the PCPSS in the scale-up experiment. 2. Materials and Methods 2.1. The PCPSS's lab/bench size design As shown in Fig. 1 a, the PCPSS lab/bench scale design was constructed from transparent acrylic with a thickness of 1 cm in the shape of a rectangle [ 35 ]. The PCPSS apparatus measured 28 cm in height, 24 cm in width, and 4 cm in thickness. The PCPSS was operated without a continuous hydrostatic pressure above the anode rod or the top layer of contaminated soil. To guarantee the correct functioning of the PCPSS, the actual contaminated soil was sieved using a 2 mm sieve before filling the device with 20 cm in height of it. Inside the acrylic borders on the sides (2 cm thick), a titanium rod anode that was 28 cm long and 1.5 cm in diameter was fixed. The apparatus's bottom was equipped with stainless cylindrical cathode pipes, each measuring 10 cm in length and 1.5 cm in diameter. To allow electroosmosis flows to exit outside the PCPSS system, the stainless cylindrical cathode pipe was provided with about 12 holes spaced 3 cm apart. These holes were covered with two layers of cloth to prevent the clogging of the soil inside the holes. The perforated cathode pipe within the PCPSS setup had an effective length of 4 cm. Two cathode pipes with an internal spacing of 11 cm were placed downward within the PCPSS apparatus [ 35 ]. At the top of the PCPSS device, a rectangular acrylic sheet with the following measurements was placed: 28 cm in length, 4 cm in width, and 1 cm in thickness to prevent surface soil from drying while the studies are being conducted. The rectangular acrylic sheet was affixed to the top of the PCPSS device using an iron nail to facilitate the simple addition of water from the top. To supply a constant source of applied voltages (DC), power supplies (RXN-305D, 0-30V, made in China) and (RXN-3010, 30-60V, made in China) were used. Additionally, an electric organizer (TDGC2-0.5 and TDGC2-1, manufactured in China) supplied the power after a bridge was added to convert the alternating current (AC) to direct current (DC). An avometer (UT61E, manufactured in China) was placed inside the electric circle to guarantee the accurate detection of current flow. The 30-day testing period was in effect. The applied voltage was 1 V/cm (20 V), which is the optimal value for soil electrokinetics. Figure 2 depicts the sample locations. Thirty sections of the PCPSS-containing soil were separated for sampling after the soil electrokinetic experiments were finished. To determine the overall amount of inorganic elements, around 3 g of soil was taken from each section and dried at 75°C. After conducting electrokinetic tests, contour maps created with Surfer (version 10.1.561) were used to show the distribution of soil cations in actual contaminated soil. 2.2. The PCPSS pilot scale unit The PCPSS pilot scale, which is coupled to solar power to supply the applied voltage (DC), is photographed in Fig. 1 b. A durable plastic cylindrical cylinder measuring 57 cm in height and 2 mm in thickness served as the PCPSS's pilot unit. The plastic cylindrical container had a top diameter of 56 cm and a bottom diameter of 41 cm. A 46-cm-high plastic cylindrical container was filled with actual polluted soil. It was observed that the height of the actual polluted soil had decreased to 40 cm following the conclusion of the pilot investigation. To replicate the actual situation in the field, actual contaminated soil was utilized in the PCPSS pilot scale unit without sieving. There was an accumulation of gravel at the bottom of the PCPSS pilot unit after the pilot experiment was terminated. The PCPSS pilot unit was operated with solar electricity (SUNTECK, model no. STP 545S-C72/Vmh, 545W ± 5%, 29.1 kg) made in China with the following properties (~ 2.3 m long, ~ 1.1 m wide, and 3.5 cm thickness). The duration of the trial was sixty days. An electricity controller (MPPT, Solar Charge Controller, made in Turkey) was connected to the solar panels to provide a stable DC voltage of 48 ± 1 V when the trial was being conducted. Four batteries (Gel Deep Cycle, 12 V, 100 Ah, and C10, made in Büdingen, Germany) were linked in series with the solar electricity to guarantee a steady supply of power to the PCPSS pilot unit at night. The anode, which had a round form and was 41 cm in diameter and 2 mm in thickness, was composed of iron. Two sets of holes were supplied for the iron anode: a) five holes of 1.5 diameter and b) six holes of 0.8 diameter. These eleven holes were created to let water from the anode flow into the soil. The surface portion of the PCPSS plastic container (about 10 cm high) was refilled using tap water. Two iron rods (13 cm long, 5 mm in diameter) were attached to the surface of the iron anode to enable the correct electrical connection and prevent the anolyte from coming into direct contact with the copper wires, which may be readily sacrificed. As shown in Fig. 1 d, three 1.5 cm diameter stainless steel pipes were used as cathodes and placed at the bottom of the PCPSS container with an internal gap of around 8.5 cm. The dimensions of the right and left cathodes were 39 cm long (32.5 cm inside the PCPSS and 6.5 cm outside), and (33.5 cm inside the PCPSS and 5.5 cm outside), respectively. Nonetheless, the center cathode's dimensions were as follows: 39.5 cm within the PCPSS and 9.5 cm outside (it was 49 cm long). The cathode pipes were perforated with holes (30 holes per 20 cm long) to enable the disposal of electroosmosis flow. These holes were covered with two layers of cloth to prevent clogging inside the holes. A Chinese-made avometer (UT61E) was included in the electric circuit to precisely measure variations in current passage. For approximately 60 days, from 22 January 2023 to 23 March 2023, the pilot scale experiment was conducted. On January 22, the day lighting period lasted approximately 10.5 hours, with dawn at 6:51 am and sunset at 5:23 pm. On March 23, the day lighting period lasted approximately 12 hours, with sunrise at 5:57 am and sunset at 6:08 pm [ 36 ]. As a result, during the pilot PCPSS's operation, solar power can provide applied voltages for 10.5 to 12 hours each day; at night, batteries will provide the experiment with the necessary energy. Following the conclusion of the experiment, 10 samples were taken vertically from two sites (each 4 cm deep), as seen in Fig. 1 e. Samples were collected at the PCPSS pilot unit's center at the first site; in contrast, samples were collected at the second site from the region 11 cm behind the PCPSS pilot unit's center. 2.3. Adding chemical and biological materials to improve the lab-scale PCPSS's performance In this part, the impact of chemical and biological materials additions was examined in order to maximize the PCPSS's performance on a lab/bench scale. The PCPSS pilot-scale investigation's final condition was established based on the results that were released from this part. Six enhancement reagents' effects were assessed, including “a) HNO 3 (pH = 2), EDTA (0.1 M), addition of 50 ml L − 1 of biosurfactant containing bacterial broth culture (BCBBC, 50 ml L − 1 ), addition of 50 ml L − 1 of biosurfactant containing bacterial broth culture (BCBBC, 400 ml L − 1 ), powder of crud extracted biosurfactant (PCEB, 1 g L − 1 , dissolved in formic acid, pH = 1), and formic acid (pH = 1)” [ 1 ]. To simulate the low pH generated at the anode electrode during PCPSS operation, the pH of HNO 3 was adjusted to 2. Based on the values documented in relevant literature, an EDTA concentration of 0.1 M was chosen [ 37 ], [ 38 ], [ 39 ]. In soil electrokinetic experiments, surfactants have shown effectiveness [ 40 ], and adding biosurfactant-producing microorganisms enhanced Sr desorption while decreasing Pb availability [ 41 ]. In order to guarantee the sustainability of surfactant addition during the soil electrokinetic experiments, especially for the scale-up unit, biosurfactant additives were investigated. The process described in the literature was followed in the production of the biosurfactant [ 42 ], [ 43 ]. Before the start of the experiment, the enhancing reagents were mixed well with the actual contaminated soil and allowed to sit in the lab for 15 days. In our recent literature, specifics about reagent preparation are discussed [ 1 ]. 2.4. Analysis and collection of soil Excavating the surface (0–30 cm) and subsurface (30–60 cm) layers of the El-Gabal El-Asfar farm in Egypt allowed for the collection of soil samples. Horizon-based sampling was not feasible because horizon boundaries were not clearly distinguishable in the studied soils, and the experimental objective did not require horizon-specific analysis. There was good mixing of the soil of the surface and subsurface layers. The mixed soils had the following characteristics (Table 1 ) [ 44 ]: EC (1.2 dS m − 1 ), pH (7.2), organic matter (2.07%), CaCO 3 (0.70%), texture (Sandy Clay Loam), and very low hydraulic conductivity (0.0035 cm h − 1 ) according to the USDA classification [ 1 ]. The total cation contents (mean) were arranged in the following descending order: K (2793 mg kg − 1 ) > Mg (1761.6 mg kg − 1 ) > Ca (1642 mg kg − 1 ) > Na (529.5 mg kg − 1 ) > Li (13.6 mg kg − 1 ) > Ba (13.3 mg kg − 1 ). Based on the overall content measurements, the content ratio (CR) was calculated to show how cations comprising actual contaminated soil behaved during electrokinetic studies. There is no fluctuation in the ion content when the CR value is equal to 1. Ion accumulation is indicated by CR values greater than 1, whereas ion removal is shown by CR values less than 1. The CR was computed using the following formula: $$\:\text{C}\text{R}=\:\frac{The\:contnet\:ratio\:of\:ion\:after\:treatment}{\:\:The\:contnet\:ratio\:of\:ion\:before\:treatment}$$ 1 …………………………………….………………………… The collected samples were digested using a digestion mixture following the conclusion of the electrokinetic studies according to the procedure mentioned by Hagab et al . [ 45 ], and detected using the ICP-OES (iCAP PRO X Duo – Thermo Fisher). The following is a summary of the process: 10 ml of HNO 3 was added to a 100 ml Teflon beaker after 1 g of dry soil sample had been moistened with distilled water. The heating was turned on until there was very little left in the volume of the solution. A mixture of concentrated analytical-grade acids (10 mL HF, 5 mL HNO 3 , and 5 mL HClO 4 ) was used without dilution, and the mixture was heated (180–200 ºC) until vapors were formed. The Teflon beaker was fumed for thirty minutes on the heater. The liquid was then heated for ten minutes after 10 milliliters of HCl (1/1, v/v) were added. Distilled water was added to dilute the digest to 100 ml once it had cooled. To avoid obstructions inside the small ICP-OES nozzles, the solution was filtered using a syringe filter (PTFE, 0.45 µm, 25 mm) prior to ICP-OES detection. The soil cations were detected using the ICP-OES (iCAP PRO X Duo – Thermo Fisher). The detection limits of the iCAP PRO Series ICP-OES Duo Axial (iFR mode µg L − 1 ) are 0.02 for Ca, 0.01 for Mg, 2.7 for Na, 0.03 for Ba, and 0.42 for K [ 46 ]. Table 1 Physicochemical properties of the polluted soil under study. Parameter Value EC 1.2 dS m − 1 pH 7.2 Organic matter 2.07% CaCO 3 0.70% Texture Sandy Clay Loam Hydraulic conductivity 0.0035 cm h − 1 Total K 2793 mg kg − 1 Total Mg 1761.6 mg kg − 1 Total Ca 1642 mg kg − 1 Total Na 529.5 mg kg − 1 Total Li 13.6 mg kg − 1 Total Ba 13.3 mg kg − 1 3. Results and Discussion 3.1 The behavior of cations in the presence of an electric field utilizing the improved PCPSS at the laboratory/bench scale 3.1.1. Behavior of Mg The data in Fig. 3 illustrates how magnesium behaves when actual contaminated soil is remediated using the lab/bench scale of the improved PCPSS. Mg was removed from the surface layers and accumulated in the following layers by using the PCPSS without the addition of an improved reagent (Fig. 3 a). The content ratios of magnesium ranged from 0.92 to 1.1. Magnesium accumulated more around the cathode pipes than in the space between them. It was observed that the pulling forces played an effective role in the space between the cathode pipes. When compared to applying the optimal PCPSS without enhancement additives, the addition of an enhancement reagent (pH 2, nitric acid) enhanced the removal of magnesium from the whole apparatus. The magnesium content ratios ranged from 0.66 to 1.06. Above the cathode pipes, two areas/spots of magnesium accumulation were seen (Fig. 3 b). When compared to applying the optimal PCPSS without treatments, the content ratio gap increased (0.64 to 1.24) when EDTA (0.1 M) was added (Fig. 3 c). Magnesium accumulation was seen in the upper layers, however magnesium depletion was seen around the cathode pipes. When compared to using the optimal PCPSS design without treatments, the content ratio gap increased (0.76 to 1.2) when the BCBBC (50 ml L − 1 ) was added (Fig. 3 d). The addition of the BCBBC (50 ml L − 1 ) removed Mg from the surface layers close to that observed with nitric acid application, whereas, Mg was accumulated in the bottom layers. The degree of magnesium accumulation above the cathode pipes increased when the BCBBC dosage was raised from 50 to 400 ml L − 1 (Fig. 3 e). The addition of PCEB (1 g L − 1 ) to the actual polluted soil reduced the amount of accumulation around the cathode pipes and enhanced the amount of magnesium removed from the upper layers (Fig. 3 f). As seen in Fig. 3 g, applying formic (pH 1) improves the removal of magnesium in comparison to applying PCEB (1 g L − 1 ). Although using the optimal PCPSS without enhancement additives demonstrated the lowest removal rate, the aforementioned discussion indicates that raising acidity is the most essential aspect for improving the removal of magnesium from the actual polluted soils. 3.1.2. Behavior of Ca The distribution of Ca within the PCPSS apparatus with and without the addition of enhancing reagents is seen in the data in Fig. 4 . When the PCPSS was used without the addition of enhancing chemicals, Ca was removed from the surface layers and acclimated in the bottom layer, especially around the cathode pipes, as shown in Fig. 4 a. In line with our earlier findings, the pulling force was greater in the space between the cathode pipes than it was at the exit just above the cathode pipes [ 35 ]. The content ratios ranged from 0.3 to 1.15. The removal of calcium from the top layers was enhanced when nitric acid (pH 2) was mixed with the actual polluted soil. In comparison to the ideal PCPSS without treatments, as shown in Fig. 4 b, it reduced the amount of accumulation around the cathode pipes. The content ratios had the lowest and maximum values of 0.15 and 1, respectively, which are below the ideal PCPSS without treatment. When compared to the nitric acid treatment, the amount of Ca that was removed improved somewhat with the use of EDTA (0.1 M). As seen in Fig. 4 c, the content ratios of Ca ranged from 0.1 to 1.15. The response of the BCBBC (50 ml L − 1 ) application was similar to that of the nitric acid and EDTA treatments, as seen in Fig. 4 d, in which the content ratios of Ca ranged from 0.1 to 1.1. As seen in Fig. 4 e, the removed Ca from the center section of the PCPSS apparatus decreased when the BCBBC concentration was increased from 50 to 40 ml L − 1 . As shown in Fig. 4 e, the content ratios of Ca ranged from 0.1 to 1.15. Comparing the actual contaminated soil to the previous trials, the PCEB addition improved the migration of Ca from the surface layers and decreased the accumulation region near the cathode pipes (Fig. 4 f). As shown in Fig. 4 f, the content ratios of Ca ranged from 0.1 to 1.15. As seen in Fig. 4 g, using formic acid produced the greatest results from actual polluted soil; only above the right cathode pipe was the Ca accumulation visible. The content ratios ranged from a minimum of 0.15 to a maximum of 1.1. 3.1.3. Behavior of Ba Figure 5 shows the distribution of Ba inside the PCPSS apparatus both with and without treatments. With the exception of the region directly above the cathode pipes, the Ba was removed from the PCPSS apparatus when it was utilized untreated (Fig. 5 a). The content ratios varied from 0.2 to 3.2. The removal of Ba from the center of the PCPSS apparatus was enhanced by combining nitric acid (pH 2) with actual contaminated soil (Fig. 5 b); still, accumulation areas/spots were seen around the anode rod and cathode pipes. Figure 5 b shows that the content ratios varied from 0.3 to 2.2. When EDTA (1.0 M) was added, Ba accumulated around the cathode pipes. Figure 5 c shows that the content ratios varied from 0.4 to 2.8. The removal of Ba in the surface layer was unaffected by the application of BCBBC (50 ml L − 1 ); however, the middle apparatus and the area around the cathode pipes showed improvements. Figure 5 d shows that the content ratios varied from 0.5 to 2.5. The removed Ba did not significantly improve when the BCBBC concentration was increased from 50 to 400 ml L − 1 . As seen in Fig. 5 e, the content ratios varied from 0.5 to 3.3. The behavior of nitric acid (pH 2) and the addition of PCEB (1 g L − 1 ) exhibited a similar trend. Figure 3 f shows that the content ratios varied from 0.4 to 5. In comparison to earlier trials, Fig. 5 g illustrates the decrease in Ba accumulation spots. As was previously mentioned, the formic acid additive reduces the number of Ba accumulation spots in the PCPSS apparatus, demonstrating the treatment efficacy. 3.1.4. Behavior of Na In Fig. 6 , the response of Na to an electric field is shown using the enhanced PCPSS. When exposed to an electric field without any additional treatment, Na was not routinely removed. As seen in Fig. 6 a, the Na content ratios varied from 0.6 to 1.55. The addition of nitric acid (pH 2) resulted in the regular removal of Na. When compared to the ideal PCPSS without treatment, the content ratios, which varied from 0.14 to 0.215, showed high removal percentages. With the other treatments, large percentages of Na removal were also noted. The content ratios of the removed Na were (0.14 to 0.3), (0.175 to 0.315), (0.205 to 0.275), (0.19 to 0.28), and (0.19 to 0.295) for EDTA (0.1 M), the BCBBC (50 ml L − 1 ), the BCBBC (400 ml L − 1 ), the PCEB (1 g L − 1 ), and formic acid (pH 1), respectively. Accumulation of Na in the bottom layers was noticed by applying EDTA (0.1 M), the BCBBC (50 ml L − 1 ), the BCBBC (400 ml L − 1 ), and the PCEB (1 g L − 1 ). When compared to other treatments, the application of nitric acid (pH 2) produced the lowest content ratio values (0.14 to 0.215), despite the fact that other treatments significantly removed Na from the actual contaminated soil. 3.1.5. Behavior of Li Figure 7 illustrates the distribution of Li in actual polluted soils following the application of an electric field, both with and without treatments. Li that exists in the surface layers was irregularly removed when the PCPSS was applied without any treatments. Li accumulated in the middle of the PCPSS apparatus. As shown in Fig. 7 a, the Li content ratios varied from 0.84 to 1.36. When compared to the optimal PCPSS without treatment, the content ratio values improved with the addition of nitric acid (pH 2) (0.66 to 1.16). Additionally, the addition of nitric acid (pH 2) increased the removal of Li from the surface layers, and the accumulation volume from the center of the PCPSS apparatus was decreased (Fig. 7 b). Compared to the ideal PCPSS without treatment and nitric acid treatment, EDTA additions were able to decrease the amount of Li accumulation. When compared to nitric acid treatment, EDTA additives marginally decreased the amount of Li that was removed from the surface layers. As seen in Fig. 7 c, the content ratios varied from 0.6 to 1.45. The application of BCBBC (50 ml L − 1 ) exhibited behavior similar to that of the EDTA treatment, and as seen in Fig. 7 d, the content ratios of Li varied from 0.6 to 1.5. Nevertheless, the degree of symmetry of Li removal improved horizontally when the BCBBC concentrations were increased from 50 to 400 ml L − 1 , with content ratios ranging from 0.78 to 1.38 (Fig. 7 e). Li was removed irregularly with content ratios ranging from 0.64 to 1.12 after the PCEB (1 g L − 1 ) was applied (Fig. 7 f). In comparison to the earlier treatments, applying formic acid (pH 1) enhanced the volume of Li removed from the surface layers and decreased the accumulation percentages around the cathode pipes (bottom layers). According to the explanation above, the formic acid treatment had the greatest outcomes for removing Li from real polluted soils. 3.1.6. Behavior of K Figure 8 shows the distribution of K inside the PCPSS apparatus following the assessment of the PCPSS with and without treatments. The PCPSS was applied without treatment (Fig. 8 a), which led to the accumulation of K around the cathode pipes and the irregular removal of K from the PCPSS surface layers. As shown in Fig. 8 a, the content ratios ranged from 0.84 to 1.12. Applying nitric acid (pH 2) enhanced the K that was removed from the PCPSS surface layers. When nitric acid (pH 2) was used instead of PCPSS without treatments, the total removal of K was enhanced, with content ratios ranging from 0.52 to 0.9 (Fig. 8 b). Additionally, as compared to the ideal PCPSS without treatment, the addition of EDTA (0.1 M) enhanced the removal of K from the PCPSS's surface layers. The range of content ratios was 0.54 to 1.04. When compared to the whole apparatus, the addition of EDTA (0.1 M) enhanced the accumulation of K in the bottom layers (Fig. 8 c). In comparison to the ideal PCPSS without treatment, the addition of BCBBC (50 ml L − 1 ) increased the amount of K that was removed from the surface layers. Furthermore, the space between the cathode pipes was where K was most concentrated (Fig. 8 d). In comparison to the ideal PCPSS without treatment, the removed K from the entire PCPSS apparatus improved when the BCBBC concentration was increased from 50 to 400 ml L − 1 . According to Fig. 8 e, the content ratios varied from 0.68 to 1.06. Although the removal of K from the surface layers was enhanced by the PCEP (1 g L − 1 ) additions, this removal was not regular. Additionally, as seen in Fig. 8 f, the amount of accumulated K in the bottom layers decreased after the application of PCEP (1 g L − 1 ). The range of the accumulation ratios was 0.58 to 1.14. Although the application of formic acid (pH 1) resulted in an uneven removal of K from the surface layers, the content ratios were lower than those of the other treatments. Figure 8 g shows that the content ratios ranged from 0.6 to 0.94. Nitric acid (pH 2) and formic acid (pH 1) are the most effective treatments for the K that has been removed from the actual contaminated soil, according to the content ratio data. 3.2. Behavior of cations in the presence of an electric field utilizing the solar-powered pilot-scale PCPSS Both the center and the area behind the center (11 cm) of the pilot scale PCPSS device were used to assess the vertical distribution of cations (Figs. 9 and 10 ). Formic acid with a pH of 1.5 and applied voltages of 48 ± 1 V were used in the pilot scale experiment [ 1 ]. The distribution of Mg, Ca, Ba, Na, Li, and K inside the PCPSS pilot scale, where samples were taken vertically from the center, is shown in Fig. 9 . Among the cations under study, Na had the greatest removal ratios, while Ba had the lowest. The average removal of cations in the first 20 centimeters of the vertical distance from the PCPSS center was arranged as follows: Na (73%) > Ca (52.8%) > K (41.6%) > Mg (36.6%) > Li (25.1%) > Ba (2.3%). In the first 20 cm of the PCPSS pilot unit, the vertical oscillation removal of K and Mg was observed. The average cation removal from the vertical distance from the PCPSS pilot unit's center (20–40 cm) decreased as follows: Na (54.7%) > K (29.8%) > Mg (29.5%) > Li (28.9%) > Ca (22.7%) > Ba (16.2%). Cations that were vertically removed from 0–20 cm had higher removal efficiency than those that were found within 20–40 cm. The nearby anode may be the cause of the comparatively high ion removal ratios in the surface layers. The total average removal of cations (0–40 cm) from the PCPSS pilot unit's center was arranged in the following descending order: Na (63.9%) > Ca (37.8%) > K (35.7%) > Mg (33%) > Li (27%) > Ba (9.2%). The average vertical removal of cations from the second area, which was 11 cm behind the center and within the range of 0–20 cm, was arranged as follows: Na (74%) > Ca (56.4%) > K (42.7%) > Mg (33.8%) > Li (26.7%) > Ba (24.6%) as presented in Fig. 10 . Among the cations under study, Na had the greatest removal ratios, while Ba had the lowest. The average vertical cation removal from 0–20 cm (11 cm behind the center) was marginally superior to samples taken from the PCPSS pilot unit's center, with the exception of Ba, where the average removal percentage increased significantly from 2.3% to 24.6%. Within 20–40 cm, the average vertical cation removal from the region 11 cm behind the center was as follows: Na (70.7%) > Ca (35.9%) > K (32.8%) > Li (27.4%) > Mg (19.8%) > Ba (5.4%). For the whole PCPSS pilot unit, the average vertical cation removal from the area 11 cm behind the center was as follows: Na (72.3 %) > Ca (46.1 %) > K (37.7 %) > Li (27 %) > Mg (26.8 %) > Ba (15 %) Except for Mg and Li, the average removal of cations from the whole unit of the PCPSS pilot scale was much better in the area located 11 cm behind the center compared to samples collected from the center. Na, which is regarded as the primary challenge for recovering salt-affected soil, has the highest removal efficiency. Therefore, it is strongly advised to use the PCPSS pilot scale unit to concurrently remediate inorganic contaminants and restore salt-affected soil. 4. Soil rehabilitation after the application of soil electrokinetic remediation After the application of soil electrokinetic remediation, the treated soil will be subject to several modifications, particularly in the pH and ion concentrations [ 28 ]. Most of the investigations were focused on optimizing the performance, including modifying the current design [ 30 ], application of pulsed electric field technique [ 47 ], utilizing reverse polarity mode [ 48 ], incorporating nozzles and pipes [ 46 ], applying electrode approaching system [ 49 ], controlling the pH of soil, catholyte, and anolyte [ 28 ], integrated soil electrokinetic/electroosmosis-vacuum [ 30 ], avoiding soil cracking [ 50 ], utilizing permeable reactive barriers [ 51 ], [ 52 ], investigate the impact of electrode materials [ 53 ], etc. The rehabilitation program could be carried out through the operation of soil electrokinetics in which the fluctuation of pH could be controlled via several methods [ 28 ]. Some electrokinetic studies require the addition of a chemical (acid or base) to the polluted soil to increase the solubility of pollutants (inorganic or organic) inside the soil pores to make them subject to eventually change the soil pH. In this case, soil rehabilitation is required to return soil to its initial status, such as applying reverse polarity mode for the same period that was applied before, excavating the soil adjacent to the anode and cathode and mixing them, and mixing the pH-value-opposing solution with the treated soil (adding acid to soil that has been treated with base, and vice versa). All these challenges will be taken into consideration in our future research. 5. Conclusions One of the numerous applications for the soil electrokinetic is the remediation of contaminated soils with inorganic contaminants. Despite being regarded as a physicochemical separation technique, soil electrokinetic remediation is unable to distinguish between various ions during removal. We previously investigated the possibility of improving the soil electrokinetic remediation of inorganic pollutants using real contaminated soils at lab/bench and pilot levels by adding different enhancement chemical before scaling up. The behavior of soil cations, such as Mg, Ca, Ba, Na, Li, and K, is being investigated in the current study. The findings may be summed up as follows: Using the PCPSS, the results showed that acidity effectively improved the removed Mg when exposed to an electric field. The similar pattern was also seen in the way that Ca responded to the electric field, with formic acid (pH 1) being the most effective method of removing calcium. In addition to decreasing the accumulation percentages around the cathode pipes (bottom layers), applying formic acid (pH 1) increased the contents of Li removed from the surface layers as compared to the other treatments. The removed Mg was found to be less than the Ca. Applying formic acid (pH 1) decreased the quantity of Ba accumulation spots inside the PCPSS apparatus, however Ba accumulation spots were seen to emerge with various treatments. Na showed the lowest content ratio values (higher removal percentages) during the lab/bench scale enhancement experiments, while the other cations had the highest content ratios. Since Na is thought to be the primary obstacle to recovering salt-affected soil, the pilot PCPSS unit is a suggested method for doing so concurrently with contaminated soil remediation. Statements and Declarations Funding This work was supported by Science and Technology & Innovation Funding Authority (STIFA), previously known also as Science and Technology & Development Fund (STDF), Grant No. 39369. Competing Interests The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this review. Author contribution A.A.-S suggested the article topic, analyzed the results, prepared the figures and tables, and wrote the manuscript; and A.H., A.S., and M.A.O. improved the content, and revised the manuscript. 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Syst. , vol. 9, no. 3, p. 2400722, Mar. 2025, doi: https://doi.org/10.1002/adsu.202400722. U. Naseer, Z. Du, A. Ahmad, S. Farooq, M. Yousaf, and T. Yue, ‘Advanced Electrode Materials in Electrokinetic Technology for Remediation of Heavy Metal-Contaminated Soil: Recent Progress and Challenges’, Adv. Sustain. Syst. , vol. 9, no. 8, p. 2500197, Aug. 2025, doi: https://doi.org/10.1002/adsu.202500197. Additional Declarations The authors declare no competing interests. Cite Share Download PDF Status: Posted Version 1 posted You are reading this latest preprint version Research Square lets you share your work early, gain feedback from the community, and start making changes to your manuscript prior to peer review in a journal. As a division of Research Square Company, we’re committed to making research communication faster, fairer, and more useful. We do this by developing innovative software and high quality services for the global research community. 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Also discoverable on Platform About Our Team In Review Editorial Policies Advisory Board Help Center Resources Author Services Accessibility API Access RSS feed Manage Cookie Preferences © Research Square 2026 | ISSN 2693-5015 (online) Privacy Policy Terms of Service Do Not Sell My Personal Information {"props":{"pageProps":{"initialData":{"identity":"rs-8891372","acceptedTermsAndConditions":true,"allowDirectSubmit":true,"archivedVersions":[],"articleType":"Research Article","associatedPublications":[],"authors":[{"id":591997800,"identity":"d8d310fa-aebe-4793-a55f-f37fde64bb67","order_by":0,"name":"Ahmed Abou-Shady","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAAA7klEQVRIiWNgGAWjYDACCSBmbAAi9gYDUrXwHCBZi0QCkVr4Zzcfk/y5w052w83H2z78YKiVMzjAfPgFXkvuHEuT5j2TbLzhdlrxzB6G48YGB9jSLPBacyPHTJqxjTlxw+0cY2YGhmOJMxt4zPA6UR6oRfJnW33ihptnYFr4v+HVYgDUIsHbdjhxww0ekJaaxH4GHuYH+LQY3jmWbM3bdtx45pm0YsYegwPG/MxsZni9Ine7+eDNn23Vsn3HD29m+FFRJ8fG3vz4A149MKBwAOzOwwwMzAxsEkRpkW8AU3Uggpk4W0bBKBgFo2CkAABdY015jHwG2gAAAABJRU5ErkJggg==","orcid":"","institution":"Desert Research Center","correspondingAuthor":true,"prefix":"","firstName":"Ahmed","middleName":"","lastName":"Abou-Shady","suffix":""},{"id":591998862,"identity":"0a2b924b-7f70-4def-abad-18d072b2be95","order_by":1,"name":"Ashraf Habib","email":"","orcid":"","institution":"Desert Research Center","correspondingAuthor":false,"prefix":"","firstName":"Ashraf","middleName":"","lastName":"Habib","suffix":""},{"id":591998863,"identity":"78e852c9-a28e-4bc6-b582-65c923eb5161","order_by":2,"name":"Ahmed M. 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diagram illustrates the ideal/traditional design of a perforated cathode pipe SEKR system (PCPSS) for use in a lab or bench scale, after (Abou-Shady et al., [1])(A) (please take note that this is the original design that was introduced in 2012; we used it for illustration because it gives readers a clear picture), scaling up the PCPSS with solar energy (B), PCPSS's scaling up unit (C), a vertical view shows how cathode pipes are installed inside the PCPSS (D), and the sampling locations after the scaling up experiment has been terminated (E).\u003c/p\u003e","description":"","filename":"1.png","url":"https://assets-eu.researchsquare.com/files/rs-8891372/v1/c7d8223751e78b554e1d497f.png"},{"id":102963817,"identity":"87f3015c-c8f5-4d9d-9a36-5da17b244cba","added_by":"auto","created_at":"2026-02-19 04:20:38","extension":"png","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":330796,"visible":true,"origin":"","legend":"\u003cp\u003eA schematic diagram shows the sample locations after the soil electrokinetic process is terminated using a perforated cathode pipe SEK system (PCPSS).\u003c/p\u003e","description":"","filename":"2.png","url":"https://assets-eu.researchsquare.com/files/rs-8891372/v1/348400b620bc56e9171d6395.png"},{"id":102901540,"identity":"b28873a6-ee37-4234-86d1-21caf414512d","added_by":"auto","created_at":"2026-02-18 08:20:49","extension":"png","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":1543738,"visible":true,"origin":"","legend":"\u003cp\u003eMg removal from real polluted soil utilizing the improved lab/bench scale PCPSS: a) the control experiment, in which the ideal/traditional PCPSS operated without adding the enhanced chemical and biological additives, b) enhanced PCPSS with the addition of HNO\u003csub\u003e3\u003c/sub\u003e (pH 2), c) enhanced PCPSS with the addition of EDTA (0.1 M), d) enhanced PCPSS with the addition of BCBBC (50 ml L\u003csup\u003e-1\u003c/sup\u003e), e) enhanced PCPSS with the addition of BCBBC (400 ml L\u003csup\u003e-1\u003c/sup\u003e), f) enhanced PCPSS with the addition of PCEB (1 g L\u003csup\u003e-1\u003c/sup\u003e, pH = 1), and g) enhanced PCPSS with the addition of formic acid (pH = 1).\u003c/p\u003e","description":"","filename":"3.png","url":"https://assets-eu.researchsquare.com/files/rs-8891372/v1/4fdb2faea93ce825f784a0f1.png"},{"id":102964140,"identity":"dc903612-39b5-4f6a-9912-a8e58d30e286","added_by":"auto","created_at":"2026-02-19 04:21:35","extension":"png","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":1477907,"visible":true,"origin":"","legend":"\u003cp\u003eCa removal from real polluted soil utilizing the improved lab/bench scale PCPSS: a) the control experiment, in which the ideal/traditional PCPSS operated without adding the enhanced chemical and biological additives, b) enhanced PCPSS with the addition of HNO\u003csub\u003e3\u003c/sub\u003e (pH 2), c) enhanced PCPSS with the addition of EDTA (0.1 M), d) enhanced PCPSS with the addition of BCBBC (50 ml L\u003csup\u003e-1\u003c/sup\u003e), e) enhanced PCPSS with the addition of BCBBC (400 ml L\u003csup\u003e-1\u003c/sup\u003e), f) enhanced PCPSS with the addition of PCEB (1 g L\u003csup\u003e-1\u003c/sup\u003e, pH = 1), and g) enhanced PCPSS with the addition of formic acid (pH = 1).\u003c/p\u003e","description":"","filename":"4.png","url":"https://assets-eu.researchsquare.com/files/rs-8891372/v1/176ccad3b3a255b6f72d6d94.png"},{"id":102901543,"identity":"ff46608a-eb80-46bb-986f-54448d7d0127","added_by":"auto","created_at":"2026-02-18 08:20:49","extension":"png","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":1336344,"visible":true,"origin":"","legend":"\u003cp\u003eBa removal from real polluted soil utilizing the improved lab/bench scale PCPSS: a) the control experiment, in which the ideal/traditional PCPSS operated without adding the enhanced chemical and biological additives, b) enhanced PCPSS with the addition of HNO\u003csub\u003e3\u003c/sub\u003e (pH 2), c) enhanced PCPSS with the addition of EDTA (0.1 M), d) enhanced PCPSS with the addition of BCBBC (50 ml L\u003csup\u003e-1\u003c/sup\u003e), e) enhanced PCPSS with the addition of BCBBC (400 ml L\u003csup\u003e-1\u003c/sup\u003e), f) enhanced PCPSS with the addition of PCEB (1 g L\u003csup\u003e-1\u003c/sup\u003e, pH = 1), and g) enhanced PCPSS with the addition of formic acid (pH = 1).\u003c/p\u003e","description":"","filename":"5.png","url":"https://assets-eu.researchsquare.com/files/rs-8891372/v1/2a1a9b091ae0494dbc3f737e.png"},{"id":102901539,"identity":"6b3cc945-8bb0-43e2-974f-5b5a493493f4","added_by":"auto","created_at":"2026-02-18 08:20:49","extension":"png","order_by":6,"title":"Figure 6","display":"","copyAsset":false,"role":"figure","size":1481341,"visible":true,"origin":"","legend":"\u003cp\u003eNa removal from real polluted soil utilizing the improved lab/bench scale PCPSS: a) the control experiment, in which the ideal/traditional PCPSS operated without adding the enhanced chemical and biological additives, b) enhanced PCPSS with the addition of HNO\u003csub\u003e3\u003c/sub\u003e (pH 2), c) enhanced PCPSS with the addition of EDTA (0.1 M), d) enhanced PCPSS with the addition of BCBBC (50 ml L\u003csup\u003e-1\u003c/sup\u003e), e) enhanced PCPSS with the addition of BCBBC (400 ml L\u003csup\u003e-1\u003c/sup\u003e), f) enhanced PCPSS with the addition of PCEB (1 g L\u003csup\u003e-1\u003c/sup\u003e, pH = 1), and g) enhanced PCPSS with the addition of formic acid (pH = 1).\u003c/p\u003e","description":"","filename":"6.png","url":"https://assets-eu.researchsquare.com/files/rs-8891372/v1/756041425b4101c6805327ec.png"},{"id":102901541,"identity":"c52abe0e-4c8e-4185-accc-7b26ccc4ce8e","added_by":"auto","created_at":"2026-02-18 08:20:49","extension":"png","order_by":7,"title":"Figure 7","display":"","copyAsset":false,"role":"figure","size":2331932,"visible":true,"origin":"","legend":"\u003cp\u003eLi removal from real polluted soil utilizing the improved lab/bench scale PCPSS: a) the control experiment, in which the ideal/traditional PCPSS operated without adding the enhanced chemical and biological additives, b) enhanced PCPSS with the addition of HNO\u003csub\u003e3\u003c/sub\u003e (pH 2), c) enhanced PCPSS with the addition of EDTA (0.1 M), d) enhanced PCPSS with the addition of BCBBC (50 ml L\u003csup\u003e-1\u003c/sup\u003e), e) enhanced PCPSS with the addition of BCBBC (400 ml L\u003csup\u003e-1\u003c/sup\u003e), f) enhanced PCPSS with the addition of PCEB (1 g L\u003csup\u003e-1\u003c/sup\u003e, pH = 1), and g) enhanced PCPSS with the addition of formic acid (pH = 1).\u003c/p\u003e","description":"","filename":"7.png","url":"https://assets-eu.researchsquare.com/files/rs-8891372/v1/fef659ae468b060be57cb61c.png"},{"id":102963885,"identity":"ae16f621-ffa3-4156-9c73-249bf167f8d1","added_by":"auto","created_at":"2026-02-19 04:20:47","extension":"png","order_by":8,"title":"Figure 8","display":"","copyAsset":false,"role":"figure","size":1518038,"visible":true,"origin":"","legend":"\u003cp\u003eK removal from real polluted soil utilizing the improved lab/bench scale PCPSS: a) the control experiment, in which the ideal/traditional PCPSS operated without adding the enhanced chemical and biological additives, b) enhanced PCPSS with the addition of HNO\u003csub\u003e3\u003c/sub\u003e (pH 2), c) enhanced PCPSS with the addition of EDTA (0.1 M), d) enhanced PCPSS with the addition of BCBBC (50 ml L\u003csup\u003e-1\u003c/sup\u003e), e) enhanced PCPSS with the addition of BCBBC (400 ml L\u003csup\u003e-1\u003c/sup\u003e), f) enhanced PCPSS with the addition of PCEB (1 g L\u003csup\u003e-1\u003c/sup\u003e, pH = 1), and g) enhanced PCPSS with the addition of formic acid (pH = 1).\u003c/p\u003e","description":"","filename":"8.png","url":"https://assets-eu.researchsquare.com/files/rs-8891372/v1/90b1baeec2d2d31f58e4c3b0.png"},{"id":102901544,"identity":"e9ef9654-f68d-42d8-838e-df3934eedb2c","added_by":"auto","created_at":"2026-02-18 08:20:49","extension":"png","order_by":9,"title":"Figure 9","display":"","copyAsset":false,"role":"figure","size":149847,"visible":true,"origin":"","legend":"\u003cp\u003eThe distribution of cations (Mg, Ca, Ba, Na, Li, and K) during the soil electrokinetic remediation using the PCPSS pilot scale in which samples were collected from the center.\u003c/p\u003e","description":"","filename":"9.png","url":"https://assets-eu.researchsquare.com/files/rs-8891372/v1/01f15b3e8cbc95238f9331df.png"},{"id":102963952,"identity":"6fea0453-4e46-46a3-a07f-07106f0b0155","added_by":"auto","created_at":"2026-02-19 04:20:58","extension":"png","order_by":10,"title":"Figure 10","display":"","copyAsset":false,"role":"figure","size":1252647,"visible":true,"origin":"","legend":"\u003cp\u003eThe distribution of cations (Mg, Ca, Ba, Na, Li, and K) during the soil electrokinetic remediation using the PCPSS pilot scale in which samples were collected from area located behind the center (11 cm).\u003c/p\u003e","description":"","filename":"10.png","url":"https://assets-eu.researchsquare.com/files/rs-8891372/v1/649133d611ff0d407f7363fa.png"},{"id":102965670,"identity":"c94e377d-da32-408a-bb54-4cbbf6a7ba7d","added_by":"auto","created_at":"2026-02-19 04:32:20","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":14178227,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-8891372/v1/867a2abc-6bcb-48a5-abe1-e5e1201bbf4f.pdf"}],"financialInterests":"The authors declare no competing interests.","formattedTitle":"\u003cp\u003e\u003cstrong\u003eLaboratory and pilot-scale investigation of soil cations behavior in conjunction with electrokinetic remediation of inorganic pollutants\u003c/strong\u003e\u003c/p\u003e","fulltext":[{"header":"1. Introduction","content":"\u003cp\u003eIt is thought to be difficult to reclaim salt-affected soil, especially in arid and semi-arid areas where there aren't enough water resources for intermittent or continuous cleaning [\u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e], [\u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e]. Approximately 1\u0026ndash;10\u0026nbsp;billion hectares of soil worldwide are influenced by salt, which can be classified as saline, sodic, or saline-sodic soils due to both natural and anthropogenic factors [\u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e4\u003c/span\u003e]. Extended reuse of marginal water, which is seen as a worldwide practice, together with altered precipitation patterns and increased temperatures brought on by climate change, complicate the reclamation process [\u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e4\u003c/span\u003e], [\u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e]. To overcome salt-affected soil, hydraulic, chemical, and phytoremediation procedures are suggested methods [\u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e4\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eOne of the separation and purification technologies that may improve the removal of salt-affected soils is soil electrokinetic remediation (SEKR). Scientists established the fundamentals and basics of the SEKR at the beginning of 1990 [\u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e], [\u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e7\u003c/span\u003e], [\u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e], [\u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e]. Since then, the SEKR has been used to accomplish certain goals in a variety of interesting domains. Aside from polluted soil remediation (mercury [\u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e], [\u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e], fluoride/fluorine [\u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e12\u003c/span\u003e], and PFAS [\u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e]) SEK can be used for consolidation [\u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e14\u003c/span\u003e], [\u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e15\u003c/span\u003e], dewatering to accelerate dryness [\u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e16\u003c/span\u003e], [\u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e17\u003c/span\u003e], improving nutrients [\u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e18\u003c/span\u003e] (e.g., phosphorus) availability [\u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e19\u003c/span\u003e], sedimentation [\u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e20\u003c/span\u003e], [\u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e21\u003c/span\u003e], reclamation of saline soil [\u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e22\u003c/span\u003e], [\u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e23\u003c/span\u003e], prevention and control of pollutants [\u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e24\u003c/span\u003e], improved seed germination [\u003cspan citationid=\"CR25\" class=\"CitationRef\"\u003e25\u003c/span\u003e], phosphorus management in soils and sewage sludge [\u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e19\u003c/span\u003e], [\u003cspan citationid=\"CR26\" class=\"CitationRef\"\u003e26\u003c/span\u003e], [\u003cspan citationid=\"CR27\" class=\"CitationRef\"\u003e27\u003c/span\u003e], and so on. To accomplish a certain movement of elements, SEKR works by transferring a direct electric field (direct current, DC) via porous materials between a positively charged anode and a negatively charged cathode [\u003cspan citationid=\"CR28\" class=\"CitationRef\"\u003e28\u003c/span\u003e], [\u003cspan citationid=\"CR29\" class=\"CitationRef\"\u003e29\u003c/span\u003e]. The four processes/methods of electromigration, electroosmosis, diffusion, and electrophoresis are in charge of accomplishing the primary goals of SEKR [\u003cspan citationid=\"CR30\" class=\"CitationRef\"\u003e30\u003c/span\u003e]. Unsaturated zone formation, reverse electro-osmosis flow, cementation phenomenon near the electrode, temperature increases, pH variations near anodes and cathodes, pH-jumping zone formation, EO flow rate reduction with extended experimental duration, cracks in the treated soil, and current passing reduction were some of the challenges encountered during the application of SEKR [\u003cspan citationid=\"CR31\" class=\"CitationRef\"\u003e31\u003c/span\u003e], [\u003cspan citationid=\"CR32\" class=\"CitationRef\"\u003e32\u003c/span\u003e]. To solve these challenges and improve performance at the same time, several scientists suggested changes to the SEKR apparatus's design in addition to the addition of enhancement materials [\u003cspan citationid=\"CR33\" class=\"CitationRef\"\u003e33\u003c/span\u003e], [\u003cspan citationid=\"CR34\" class=\"CitationRef\"\u003e34\u003c/span\u003e]. In 2012, the PCPSS was introduced, a novel ex-situ SEKR method for the removal of inorganic pollutants. The PCPSS is part of the vertical SEK design [\u003cspan citationid=\"CR35\" class=\"CitationRef\"\u003e35\u003c/span\u003e]. By changing the anode placements and adding perforated nozzles, the PCPSS design was improved. Additionally, the PCPSS's potential to restore severely salinized soils was examined\u003c/p\u003e \u003cp\u003eThe current effort builds upon our previous article, which was entitled \u0026ldquo;\u003cem\u003eScaling up soil electrokinetic removal of inorganic contaminants based on lab chemical and biological optimizations\u003c/em\u003e\u0026rdquo; [\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e]. Throughout the enhancing and upscaling studies, the behavior of the cations Mg, Ca, Ba, Na, Li, and K was assessed. To optimize the reclamation process of salt-affected soils, it is crucial to investigate the behavior of cations during SEKR of inorganic pollutant-contaminated soils at the lab/bench and pilot scales. The results of our earlier investigation may be summarized as follows [\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e]: 1) the excellent efficiency of the PCPSS (laboratory scale) in removing inorganic pollutants was demonstrated when formic acid was mixed with actual contaminated soil, 2) the electroosmosis flow was improved by mixing nitric acid, formic acid, and biosurfactant bacterial broth culture with contaminated soil, 3) solar energy is a great alternative to the power source for the SEKR upscaling unit as it has proven to be capable of operating the PCPSS in the scale-up experiment.\u003c/p\u003e"},{"header":"2. Materials and Methods","content":"\u003cdiv id=\"Sec3\" class=\"Section2\"\u003e \u003ch2\u003e2.1. The PCPSS's lab/bench size design\u003c/h2\u003e \u003cp\u003eAs shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003ea, the PCPSS lab/bench scale design was constructed from transparent acrylic with a thickness of 1 cm in the shape of a rectangle [\u003cspan citationid=\"CR35\" class=\"CitationRef\"\u003e35\u003c/span\u003e]. The PCPSS apparatus measured 28 cm in height, 24 cm in width, and 4 cm in thickness. The PCPSS was operated without a continuous hydrostatic pressure above the anode rod or the top layer of contaminated soil. To guarantee the correct functioning of the PCPSS, the actual contaminated soil was sieved using a 2 mm sieve before filling the device with 20 cm in height of it. Inside the acrylic borders on the sides (2 cm thick), a titanium rod anode that was 28 cm long and 1.5 cm in diameter was fixed. The apparatus's bottom was equipped with stainless cylindrical cathode pipes, each measuring 10 cm in length and 1.5 cm in diameter. To allow electroosmosis flows to exit outside the PCPSS system, the stainless cylindrical cathode pipe was provided with about 12 holes spaced 3 cm apart. These holes were covered with two layers of cloth to prevent the clogging of the soil inside the holes. The perforated cathode pipe within the PCPSS setup had an effective length of 4 cm. Two cathode pipes with an internal spacing of 11 cm were placed downward within the PCPSS apparatus [\u003cspan citationid=\"CR35\" class=\"CitationRef\"\u003e35\u003c/span\u003e]. At the top of the PCPSS device, a rectangular acrylic sheet with the following measurements was placed: 28 cm in length, 4 cm in width, and 1 cm in thickness to prevent surface soil from drying while the studies are being conducted.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eThe rectangular acrylic sheet was affixed to the top of the PCPSS device using an iron nail to facilitate the simple addition of water from the top. To supply a constant source of applied voltages (DC), power supplies (RXN-305D, 0-30V, made in China) and (RXN-3010, 30-60V, made in China) were used. Additionally, an electric organizer (TDGC2-0.5 and TDGC2-1, manufactured in China) supplied the power after a bridge was added to convert the alternating current (AC) to direct current (DC). An avometer (UT61E, manufactured in China) was placed inside the electric circle to guarantee the accurate detection of current flow. The 30-day testing period was in effect. The applied voltage was 1 V/cm (20 V), which is the optimal value for soil electrokinetics. Figure\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e depicts the sample locations. Thirty sections of the PCPSS-containing soil were separated for sampling after the soil electrokinetic experiments were finished. To determine the overall amount of inorganic elements, around 3 g of soil was taken from each section and dried at 75\u0026deg;C. After conducting electrokinetic tests, contour maps created with Surfer (version 10.1.561) were used to show the distribution of soil cations in actual contaminated soil.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec4\" class=\"Section2\"\u003e \u003ch2\u003e2.2. The PCPSS pilot scale unit\u003c/h2\u003e \u003cp\u003eThe PCPSS pilot scale, which is coupled to solar power to supply the applied voltage (DC), is photographed in Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003eb. A durable plastic cylindrical cylinder measuring 57 cm in height and 2 mm in thickness served as the PCPSS's pilot unit. The plastic cylindrical container had a top diameter of 56 cm and a bottom diameter of 41 cm. A 46-cm-high plastic cylindrical container was filled with actual polluted soil. It was observed that the height of the actual polluted soil had decreased to 40 cm following the conclusion of the pilot investigation. To replicate the actual situation in the field, actual contaminated soil was utilized in the PCPSS pilot scale unit without sieving. There was an accumulation of gravel at the bottom of the PCPSS pilot unit after the pilot experiment was terminated. The PCPSS pilot unit was operated with solar electricity (SUNTECK, model no. STP 545S-C72/Vmh, 545W\u0026thinsp;\u0026plusmn;\u0026thinsp;5%, 29.1 kg) made in China with the following properties (~\u0026thinsp;2.3 m long, ~\u0026thinsp;1.1 m wide, and 3.5 cm thickness). The duration of the trial was sixty days. An electricity controller (MPPT, Solar Charge Controller, made in Turkey) was connected to the solar panels to provide a stable DC voltage of 48\u0026thinsp;\u0026plusmn;\u0026thinsp;1 V when the trial was being conducted. Four batteries (Gel Deep Cycle, 12 V, 100 Ah, and C10, made in B\u0026uuml;dingen, Germany) were linked in series with the solar electricity to guarantee a steady supply of power to the PCPSS pilot unit at night. The anode, which had a round form and was 41 cm in diameter and 2 mm in thickness, was composed of iron. Two sets of holes were supplied for the iron anode: a) five holes of 1.5 diameter and b) six holes of 0.8 diameter. These eleven holes were created to let water from the anode flow into the soil. The surface portion of the PCPSS plastic container (about 10 cm high) was refilled using tap water. Two iron rods (13 cm long, 5 mm in diameter) were attached to the surface of the iron anode to enable the correct electrical connection and prevent the anolyte from coming into direct contact with the copper wires, which may be readily sacrificed.\u003c/p\u003e \u003cp\u003eAs shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003ed, three 1.5 cm diameter stainless steel pipes were used as cathodes and placed at the bottom of the PCPSS container with an internal gap of around 8.5 cm. The dimensions of the right and left cathodes were 39 cm long (32.5 cm inside the PCPSS and 6.5 cm outside), and (33.5 cm inside the PCPSS and 5.5 cm outside), respectively. Nonetheless, the center cathode's dimensions were as follows: 39.5 cm within the PCPSS and 9.5 cm outside (it was 49 cm long). The cathode pipes were perforated with holes (30 holes per 20 cm long) to enable the disposal of electroosmosis flow. These holes were covered with two layers of cloth to prevent clogging inside the holes. A Chinese-made avometer (UT61E) was included in the electric circuit to precisely measure variations in current passage. For approximately 60 days, from 22 January 2023 to 23 March 2023, the pilot scale experiment was conducted. On January 22, the day lighting period lasted approximately 10.5 hours, with dawn at 6:51 am and sunset at 5:23 pm. On March 23, the day lighting period lasted approximately 12 hours, with sunrise at 5:57 am and sunset at 6:08 pm [\u003cspan citationid=\"CR36\" class=\"CitationRef\"\u003e36\u003c/span\u003e]. As a result, during the pilot PCPSS's operation, solar power can provide applied voltages for 10.5 to 12 hours each day; at night, batteries will provide the experiment with the necessary energy. Following the conclusion of the experiment, 10 samples were taken vertically from two sites (each 4 cm deep), as seen in Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003ee. Samples were collected at the PCPSS pilot unit's center at the first site; in contrast, samples were collected at the second site from the region 11 cm behind the PCPSS pilot unit's center.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec5\" class=\"Section2\"\u003e \u003ch2\u003e2.3. Adding chemical and biological materials to improve the lab-scale PCPSS's performance\u003c/h2\u003e \u003cp\u003eIn this part, the impact of chemical and biological materials additions was examined in order to maximize the PCPSS's performance on a lab/bench scale. The PCPSS pilot-scale investigation's final condition was established based on the results that were released from this part. Six enhancement reagents' effects were assessed, including \u0026ldquo;a) HNO\u003csub\u003e3\u003c/sub\u003e (pH\u0026thinsp;=\u0026thinsp;2), EDTA (0.1 M), addition of 50 ml L\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e of biosurfactant containing bacterial broth culture (BCBBC, 50 ml L\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e), addition of 50 ml L\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e of biosurfactant containing bacterial broth culture (BCBBC, 400 ml L\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e), powder of crud extracted biosurfactant (PCEB, 1 g L\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e, dissolved in formic acid, pH\u0026thinsp;=\u0026thinsp;1), and formic acid (pH\u0026thinsp;=\u0026thinsp;1)\u0026rdquo; [\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e]. To simulate the low pH generated at the anode electrode during PCPSS operation, the pH of HNO\u003csub\u003e3\u003c/sub\u003e was adjusted to 2. Based on the values documented in relevant literature, an EDTA concentration of 0.1 M was chosen [\u003cspan citationid=\"CR37\" class=\"CitationRef\"\u003e37\u003c/span\u003e], [\u003cspan citationid=\"CR38\" class=\"CitationRef\"\u003e38\u003c/span\u003e], [\u003cspan citationid=\"CR39\" class=\"CitationRef\"\u003e39\u003c/span\u003e]. In soil electrokinetic experiments, surfactants have shown effectiveness [\u003cspan citationid=\"CR40\" class=\"CitationRef\"\u003e40\u003c/span\u003e], and adding biosurfactant-producing microorganisms enhanced Sr desorption while decreasing Pb availability [\u003cspan citationid=\"CR41\" class=\"CitationRef\"\u003e41\u003c/span\u003e]. In order to guarantee the sustainability of surfactant addition during the soil electrokinetic experiments, especially for the scale-up unit, biosurfactant additives were investigated. The process described in the literature was followed in the production of the biosurfactant [\u003cspan citationid=\"CR42\" class=\"CitationRef\"\u003e42\u003c/span\u003e], [\u003cspan citationid=\"CR43\" class=\"CitationRef\"\u003e43\u003c/span\u003e]. Before the start of the experiment, the enhancing reagents were mixed well with the actual contaminated soil and allowed to sit in the lab for 15 days. In our recent literature, specifics about reagent preparation are discussed [\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e].\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec6\" class=\"Section2\"\u003e \u003ch2\u003e2.4. Analysis and collection of soil\u003c/h2\u003e \u003cp\u003eExcavating the surface (0\u0026ndash;30 cm) and subsurface (30\u0026ndash;60 cm) layers of the El-Gabal El-Asfar farm in Egypt allowed for the collection of soil samples. Horizon-based sampling was not feasible because horizon boundaries were not clearly distinguishable in the studied soils, and the experimental objective did not require horizon-specific analysis. There was good mixing of the soil of the surface and subsurface layers. The mixed soils had the following characteristics (Table\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e) [\u003cspan citationid=\"CR44\" class=\"CitationRef\"\u003e44\u003c/span\u003e]: EC (1.2 dS m\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e), pH (7.2), organic matter (2.07%), CaCO\u003csub\u003e3\u003c/sub\u003e (0.70%), texture (Sandy Clay Loam), and very low hydraulic conductivity (0.0035 cm h\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e) according to the USDA classification [\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e]. The total cation contents (mean) were arranged in the following descending order: K (2793 mg kg\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e)\u0026thinsp;\u0026gt;\u0026thinsp;Mg (1761.6 mg kg\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e)\u0026thinsp;\u0026gt;\u0026thinsp;Ca (1642 mg kg\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e)\u0026thinsp;\u0026gt;\u0026thinsp;Na (529.5 mg kg\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e)\u0026thinsp;\u0026gt;\u0026thinsp;Li (13.6 mg kg\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e)\u0026thinsp;\u0026gt;\u0026thinsp;Ba (13.3 mg kg\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e). Based on the overall content measurements, the content ratio (CR) was calculated to show how cations comprising actual contaminated soil behaved during electrokinetic studies. There is no fluctuation in the ion content when the CR value is equal to 1. Ion accumulation is indicated by CR values greater than 1, whereas ion removal is shown by CR values less than 1. The CR was computed using the following formula:\u003cdiv id=\"Equ1\" class=\"Equation\"\u003e\u003cdiv format=\"TEX\" class=\"mathdisplay\" id=\"FileID_Equ1\" name=\"EquationSource\"\u003e\n$$\\:\\text{C}\\text{R}=\\:\\frac{The\\:contnet\\:ratio\\:of\\:ion\\:after\\:treatment}{\\:\\:The\\:contnet\\:ratio\\:of\\:ion\\:before\\:treatment}$$\u003c/div\u003e\u003csub\u003e\u003c/sub\u003e\u003cdiv class=\"EquationNumber\"\u003e1\u003c/div\u003e\u003c/div\u003e\u0026hellip;\u0026hellip;\u0026hellip;\u0026hellip;\u0026hellip;\u0026hellip;\u0026hellip;\u0026hellip;\u0026hellip;\u0026hellip;\u0026hellip;\u0026hellip;\u0026hellip;\u0026hellip;.\u0026hellip;\u0026hellip;\u0026hellip;\u0026hellip;\u0026hellip;\u0026hellip;\u0026hellip;\u0026hellip;\u0026hellip;\u0026hellip;\u003c/p\u003e \u003cp\u003eThe collected samples were digested using a digestion mixture following the conclusion of the electrokinetic studies according to the procedure mentioned by Hagab \u003cem\u003eet al\u003c/em\u003e. [\u003cspan citationid=\"CR45\" class=\"CitationRef\"\u003e45\u003c/span\u003e], and detected using the ICP-OES (iCAP PRO X Duo \u0026ndash; Thermo Fisher). The following is a summary of the process: 10 ml of HNO\u003csub\u003e3\u003c/sub\u003e was added to a 100 ml Teflon beaker after 1 g of dry soil sample had been moistened with distilled water. The heating was turned on until there was very little left in the volume of the solution. A mixture of concentrated analytical-grade acids (10 mL HF, 5 mL HNO\u003csub\u003e3\u003c/sub\u003e, and 5 mL HClO\u003csub\u003e4\u003c/sub\u003e) was used without dilution, and the mixture was heated (180\u0026ndash;200 \u0026ordm;C) until vapors were formed. The Teflon beaker was fumed for thirty minutes on the heater. The liquid was then heated for ten minutes after 10 milliliters of HCl (1/1, v/v) were added. Distilled water was added to dilute the digest to 100 ml once it had cooled. To avoid obstructions inside the small ICP-OES nozzles, the solution was filtered using a syringe filter (PTFE, 0.45 \u0026micro;m, 25 mm) prior to ICP-OES detection. The soil cations were detected using the ICP-OES (iCAP PRO X Duo \u0026ndash; Thermo Fisher). The detection limits of the iCAP PRO Series ICP-OES Duo Axial (iFR mode \u0026micro;g L\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e) are 0.02 for Ca, 0.01 for Mg, 2.7 for Na, 0.03 for Ba, and 0.42 for K [\u003cspan citationid=\"CR46\" class=\"CitationRef\"\u003e46\u003c/span\u003e].\u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab1\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 1\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003ePhysicochemical properties of the polluted soil under study.\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"2\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e \u003cp\u003eParameter\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003eValue\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eEC\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e1.2 dS m\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003epH\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e7.2\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eOrganic matter\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e2.07%\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eCaCO\u003csub\u003e3\u003c/sub\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e0.70%\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eTexture\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eSandy Clay Loam\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eHydraulic conductivity\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e0.0035 cm h\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eTotal K\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e2793 mg kg\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eTotal Mg\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e1761.6 mg kg\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eTotal Ca\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e1642 mg kg\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eTotal Na\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e529.5 mg kg\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eTotal Li\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e13.6 mg kg\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eTotal Ba\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e13.3 mg kg\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003c/div\u003e"},{"header":"3. Results and Discussion","content":"\u003cp\u003e\u003cspan\u003e\u003c/span\u003e\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003e3.1 The behavior of cations in the presence of an electric field utilizing the improved PCPSS at the laboratory/bench scale\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003e\u003c/p\u003e\n\u003cdiv id=\"Sec8\" class=\"Section3\"\u003e\n \u003cdiv class=\"Heading\"\u003e\u003cstrong\u003e3.1.1. Behavior of Mg\u003c/strong\u003e\u003c/div\u003e\n \u003cp\u003eThe data in Fig. \u003cspan class=\"InternalRef\"\u003e3\u003c/span\u003e illustrates how magnesium behaves when actual contaminated soil is remediated using the lab/bench scale of the improved PCPSS. Mg was removed from the surface layers and accumulated in the following layers by using the PCPSS without the addition of an improved reagent (Fig. \u003cspan class=\"InternalRef\"\u003e3\u003c/span\u003ea). The content ratios of magnesium ranged from 0.92 to 1.1. Magnesium accumulated more around the cathode pipes than in the space between them. It was observed that the pulling forces played an effective role in the space between the cathode pipes. When compared to applying the optimal PCPSS without enhancement additives, the addition of an enhancement reagent (pH 2, nitric acid) enhanced the removal of magnesium from the whole apparatus. The magnesium content ratios ranged from 0.66 to 1.06. Above the cathode pipes, two areas/spots of magnesium accumulation were seen (Fig. \u003cspan class=\"InternalRef\"\u003e3\u003c/span\u003eb). When compared to applying the optimal PCPSS without treatments, the content ratio gap increased (0.64 to 1.24) when EDTA (0.1 M) was added (Fig. \u003cspan class=\"InternalRef\"\u003e3\u003c/span\u003ec). Magnesium accumulation was seen in the upper layers, however magnesium depletion was seen around the cathode pipes. When compared to using the optimal PCPSS design without treatments, the content ratio gap increased (0.76 to 1.2) when the BCBBC (50 ml L\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e) was added (Fig. \u003cspan class=\"InternalRef\"\u003e3\u003c/span\u003ed). The addition of the BCBBC (50 ml L\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e) removed Mg from the surface layers close to that observed with nitric acid application, whereas, Mg was accumulated in the bottom layers. The degree of magnesium accumulation above the cathode pipes increased when the BCBBC dosage was raised from 50 to 400 ml L\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e (Fig. \u003cspan class=\"InternalRef\"\u003e3\u003c/span\u003ee). The addition of PCEB (1 g L\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e) to the actual polluted soil reduced the amount of accumulation around the cathode pipes and enhanced the amount of magnesium removed from the upper layers (Fig. \u003cspan class=\"InternalRef\"\u003e3\u003c/span\u003ef). As seen in Fig. \u003cspan class=\"InternalRef\"\u003e3\u003c/span\u003eg, applying formic (pH 1) improves the removal of magnesium in comparison to applying PCEB (1 g L\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e). Although using the optimal PCPSS without enhancement additives demonstrated the lowest removal rate, the aforementioned discussion indicates that raising acidity is the most essential aspect for improving the removal of magnesium from the actual polluted soils.\u003c/p\u003e\n\u003c/div\u003e\n\u003cdiv id=\"Sec9\" class=\"Section3\"\u003e\n \u003cdiv class=\"Heading\"\u003e3.1.2. Behavior of Ca\u003c/div\u003e\n \u003cp\u003eThe distribution of Ca within the PCPSS apparatus with and without the addition of enhancing reagents is seen in the data in Fig. \u003cspan class=\"InternalRef\"\u003e4\u003c/span\u003e. When the PCPSS was used without the addition of enhancing chemicals, Ca was removed from the surface layers and acclimated in the bottom layer, especially around the cathode pipes, as shown in Fig. \u003cspan class=\"InternalRef\"\u003e4\u003c/span\u003ea. In line with our earlier findings, the pulling force was greater in the space between the cathode pipes than it was at the exit just above the cathode pipes [\u003cspan class=\"CitationRef\"\u003e35\u003c/span\u003e]. The content ratios ranged from 0.3 to 1.15. The removal of calcium from the top layers was enhanced when nitric acid (pH 2) was mixed with the actual polluted soil. In comparison to the ideal PCPSS without treatments, as shown in Fig. \u003cspan class=\"InternalRef\"\u003e4\u003c/span\u003eb, it reduced the amount of accumulation around the cathode pipes. The content ratios had the lowest and maximum values of 0.15 and 1, respectively, which are below the ideal PCPSS without treatment. When compared to the nitric acid treatment, the amount of Ca that was removed improved somewhat with the use of EDTA (0.1 M). As seen in Fig. \u003cspan class=\"InternalRef\"\u003e4\u003c/span\u003ec, the content ratios of Ca ranged from 0.1 to 1.15. The response of the BCBBC (50 ml L\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e) application was similar to that of the nitric acid and EDTA treatments, as seen in Fig. \u003cspan class=\"InternalRef\"\u003e4\u003c/span\u003ed, in which the content ratios of Ca ranged from 0.1 to 1.1. As seen in Fig. \u003cspan class=\"InternalRef\"\u003e4\u003c/span\u003ee, the removed Ca from the center section of the PCPSS apparatus decreased when the BCBBC concentration was increased from 50 to 40 ml L\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e. As shown in Fig. \u003cspan class=\"InternalRef\"\u003e4\u003c/span\u003ee, the content ratios of Ca ranged from 0.1 to 1.15. Comparing the actual contaminated soil to the previous trials, the PCEB addition improved the migration of Ca from the surface layers and decreased the accumulation region near the cathode pipes (Fig. \u003cspan class=\"InternalRef\"\u003e4\u003c/span\u003ef). As shown in Fig. \u003cspan class=\"InternalRef\"\u003e4\u003c/span\u003ef, the content ratios of Ca ranged from 0.1 to 1.15. As seen in Fig. \u003cspan class=\"InternalRef\"\u003e4\u003c/span\u003eg, using formic acid produced the greatest results from actual polluted soil; only above the right cathode pipe was the Ca accumulation visible. The content ratios ranged from a minimum of 0.15 to a maximum of 1.1.\u003c/p\u003e\n\u003c/div\u003e\n\u003cdiv id=\"Sec10\" class=\"Section3\"\u003e\n \u003cdiv class=\"Heading\"\u003e3.1.3. Behavior of Ba\u003c/div\u003e\n \u003cp\u003eFigure \u003cspan class=\"InternalRef\"\u003e5\u003c/span\u003e shows the distribution of Ba inside the PCPSS apparatus both with and without treatments. With the exception of the region directly above the cathode pipes, the Ba was removed from the PCPSS apparatus when it was utilized untreated (Fig. \u003cspan class=\"InternalRef\"\u003e5\u003c/span\u003ea). The content ratios varied from 0.2 to 3.2. The removal of Ba from the center of the PCPSS apparatus was enhanced by combining nitric acid (pH 2) with actual contaminated soil (Fig. \u003cspan class=\"InternalRef\"\u003e5\u003c/span\u003eb); still, accumulation areas/spots were seen around the anode rod and cathode pipes. Figure \u003cspan class=\"InternalRef\"\u003e5\u003c/span\u003eb shows that the content ratios varied from 0.3 to 2.2. When EDTA (1.0 M) was added, Ba accumulated around the cathode pipes. Figure \u003cspan class=\"InternalRef\"\u003e5\u003c/span\u003ec shows that the content ratios varied from 0.4 to 2.8. The removal of Ba in the surface layer was unaffected by the application of BCBBC (50 ml L\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e); however, the middle apparatus and the area around the cathode pipes showed improvements. Figure \u003cspan class=\"InternalRef\"\u003e5\u003c/span\u003ed shows that the content ratios varied from 0.5 to 2.5. The removed Ba did not significantly improve when the BCBBC concentration was increased from 50 to 400 ml L\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e. As seen in Fig. \u003cspan class=\"InternalRef\"\u003e5\u003c/span\u003ee, the content ratios varied from 0.5 to 3.3. The behavior of nitric acid (pH 2) and the addition of PCEB (1 g L\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e) exhibited a similar trend. Figure \u003cspan class=\"InternalRef\"\u003e3\u003c/span\u003ef shows that the content ratios varied from 0.4 to 5. In comparison to earlier trials, Fig. \u003cspan class=\"InternalRef\"\u003e5\u003c/span\u003eg illustrates the decrease in Ba accumulation spots. As was previously mentioned, the formic acid additive reduces the number of Ba accumulation spots in the PCPSS apparatus, demonstrating the treatment efficacy.\u003c/p\u003e\n\u003c/div\u003e\n\u003cdiv id=\"Sec11\" class=\"Section3\"\u003e\n \u003cdiv class=\"Heading\"\u003e3.1.4. Behavior of Na\u003c/div\u003e\n \u003cp\u003eIn Fig. \u003cspan class=\"InternalRef\"\u003e6\u003c/span\u003e, the response of Na to an electric field is shown using the enhanced PCPSS. When exposed to an electric field without any additional treatment, Na was not routinely removed. As seen in Fig. \u003cspan class=\"InternalRef\"\u003e6\u003c/span\u003ea, the Na content ratios varied from 0.6 to 1.55. The addition of nitric acid (pH 2) resulted in the regular removal of Na. When compared to the ideal PCPSS without treatment, the content ratios, which varied from 0.14 to 0.215, showed high removal percentages. With the other treatments, large percentages of Na removal were also noted. The content ratios of the removed Na were (0.14 to 0.3), (0.175 to 0.315), (0.205 to 0.275), (0.19 to 0.28), and (0.19 to 0.295) for EDTA (0.1 M), the BCBBC (50 ml L\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e), the BCBBC (400 ml L\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e), the PCEB (1 g L\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e), and formic acid (pH 1), respectively. Accumulation of Na in the bottom layers was noticed by applying EDTA (0.1 M), the BCBBC (50 ml L\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e), the BCBBC (400 ml L\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e), and the PCEB (1 g L\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e). When compared to other treatments, the application of nitric acid (pH 2) produced the lowest content ratio values (0.14 to 0.215), despite the fact that other treatments significantly removed Na from the actual contaminated soil.\u003c/p\u003e\n\u003c/div\u003e\n\u003cdiv id=\"Sec12\" class=\"Section3\"\u003e\n \u003cdiv class=\"Heading\"\u003e3.1.5. Behavior of Li\u003c/div\u003e\n \u003cp\u003eFigure \u003cspan class=\"InternalRef\"\u003e7\u003c/span\u003e illustrates the distribution of Li in actual polluted soils following the application of an electric field, both with and without treatments. Li that exists in the surface layers was irregularly removed when the PCPSS was applied without any treatments. Li accumulated in the middle of the PCPSS apparatus. As shown in Fig. \u003cspan class=\"InternalRef\"\u003e7\u003c/span\u003ea, the Li content ratios varied from 0.84 to 1.36. When compared to the optimal PCPSS without treatment, the content ratio values improved with the addition of nitric acid (pH 2) (0.66 to 1.16). Additionally, the addition of nitric acid (pH 2) increased the removal of Li from the surface layers, and the accumulation volume from the center of the PCPSS apparatus was decreased (Fig. \u003cspan class=\"InternalRef\"\u003e7\u003c/span\u003eb). Compared to the ideal PCPSS without treatment and nitric acid treatment, EDTA additions were able to decrease the amount of Li accumulation. When compared to nitric acid treatment, EDTA additives marginally decreased the amount of Li that was removed from the surface layers. As seen in Fig. \u003cspan class=\"InternalRef\"\u003e7\u003c/span\u003ec, the content ratios varied from 0.6 to 1.45. The application of BCBBC (50 ml L\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e) exhibited behavior similar to that of the EDTA treatment, and as seen in Fig. \u003cspan class=\"InternalRef\"\u003e7\u003c/span\u003ed, the content ratios of Li varied from 0.6 to 1.5. Nevertheless, the degree of symmetry of Li removal improved horizontally when the BCBBC concentrations were increased from 50 to 400 ml L\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e, with content ratios ranging from 0.78 to 1.38 (Fig. \u003cspan class=\"InternalRef\"\u003e7\u003c/span\u003ee). Li was removed irregularly with content ratios ranging from 0.64 to 1.12 after the PCEB (1 g L\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e) was applied (Fig. \u003cspan class=\"InternalRef\"\u003e7\u003c/span\u003ef). In comparison to the earlier treatments, applying formic acid (pH 1) enhanced the volume of Li removed from the surface layers and decreased the accumulation percentages around the cathode pipes (bottom layers). According to the explanation above, the formic acid treatment had the greatest outcomes for removing Li from real polluted soils.\u003c/p\u003e\n\u003c/div\u003e\n\u003cdiv id=\"Sec13\" class=\"Section3\"\u003e\n \u003cdiv class=\"Heading\"\u003e3.1.6. Behavior of K\u003c/div\u003e\n \u003cp\u003eFigure \u003cspan class=\"InternalRef\"\u003e8\u003c/span\u003e shows the distribution of K inside the PCPSS apparatus following the assessment of the PCPSS with and without treatments. The PCPSS was applied without treatment (Fig. \u003cspan class=\"InternalRef\"\u003e8\u003c/span\u003ea), which led to the accumulation of K around the cathode pipes and the irregular removal of K from the PCPSS surface layers. As shown in Fig. \u003cspan class=\"InternalRef\"\u003e8\u003c/span\u003ea, the content ratios ranged from 0.84 to 1.12. Applying nitric acid (pH 2) enhanced the K that was removed from the PCPSS surface layers. When nitric acid (pH 2) was used instead of PCPSS without treatments, the total removal of K was enhanced, with content ratios ranging from 0.52 to 0.9 (Fig. \u003cspan class=\"InternalRef\"\u003e8\u003c/span\u003eb). Additionally, as compared to the ideal PCPSS without treatment, the addition of EDTA (0.1 M) enhanced the removal of K from the PCPSS\u0026apos;s surface layers. The range of content ratios was 0.54 to 1.04. When compared to the whole apparatus, the addition of EDTA (0.1 M) enhanced the accumulation of K in the bottom layers (Fig. \u003cspan class=\"InternalRef\"\u003e8\u003c/span\u003ec). In comparison to the ideal PCPSS without treatment, the addition of BCBBC (50 ml L\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e) increased the amount of K that was removed from the surface layers. Furthermore, the space between the cathode pipes was where K was most concentrated (Fig. \u003cspan class=\"InternalRef\"\u003e8\u003c/span\u003ed). In comparison to the ideal PCPSS without treatment, the removed K from the entire PCPSS apparatus improved when the BCBBC concentration was increased from 50 to 400 ml L\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e. According to Fig. \u003cspan class=\"InternalRef\"\u003e8\u003c/span\u003ee, the content ratios varied from 0.68 to 1.06. Although the removal of K from the surface layers was enhanced by the PCEP (1 g L\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e) additions, this removal was not regular. Additionally, as seen in Fig. \u003cspan class=\"InternalRef\"\u003e8\u003c/span\u003ef, the amount of accumulated K in the bottom layers decreased after the application of PCEP (1 g L\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e). The range of the accumulation ratios was 0.58 to 1.14. Although the application of formic acid (pH 1) resulted in an uneven removal of K from the surface layers, the content ratios were lower than those of the other treatments. Figure \u003cspan class=\"InternalRef\"\u003e8\u003c/span\u003eg shows that the content ratios ranged from 0.6 to 0.94. Nitric acid (pH 2) and formic acid (pH 1) are the most effective treatments for the K that has been removed from the actual contaminated soil, according to the content ratio data.\u003c/p\u003e\n\u003c/div\u003e\n\u003cdiv id=\"Sec14\" class=\"Section2\"\u003e\n \u003ch2\u003e3.2. Behavior of cations in the presence of an electric field utilizing the solar-powered pilot-scale PCPSS\u003c/h2\u003e\n \u003cp\u003eBoth the center and the area behind the center (11 cm) of the pilot scale PCPSS device were used to assess the vertical distribution of cations (Figs. \u003cspan class=\"InternalRef\"\u003e9\u003c/span\u003e and \u003cspan class=\"InternalRef\"\u003e10\u003c/span\u003e). Formic acid with a pH of 1.5 and applied voltages of 48\u0026thinsp;\u0026plusmn;\u0026thinsp;1 V were used in the pilot scale experiment [\u003cspan class=\"CitationRef\"\u003e1\u003c/span\u003e]. The distribution of Mg, Ca, Ba, Na, Li, and K inside the PCPSS pilot scale, where samples were taken vertically from the center, is shown in Fig. \u003cspan class=\"InternalRef\"\u003e9\u003c/span\u003e. Among the cations under study, Na had the greatest removal ratios, while Ba had the lowest. The average removal of cations in the first 20 centimeters of the vertical distance from the PCPSS center was arranged as follows: Na (73%)\u0026thinsp;\u0026gt;\u0026thinsp;Ca (52.8%)\u0026thinsp;\u0026gt;\u0026thinsp;K (41.6%)\u0026thinsp;\u0026gt;\u0026thinsp;Mg (36.6%)\u0026thinsp;\u0026gt;\u0026thinsp;Li (25.1%)\u0026thinsp;\u0026gt;\u0026thinsp;Ba (2.3%). In the first 20 cm of the PCPSS pilot unit, the vertical oscillation removal of K and Mg was observed. The average cation removal from the vertical distance from the PCPSS pilot unit\u0026apos;s center (20\u0026ndash;40 cm) decreased as follows: Na (54.7%)\u0026thinsp;\u0026gt;\u0026thinsp;K (29.8%)\u0026thinsp;\u0026gt;\u0026thinsp;Mg (29.5%)\u0026thinsp;\u0026gt;\u0026thinsp;Li (28.9%)\u0026thinsp;\u0026gt;\u0026thinsp;Ca (22.7%)\u0026thinsp;\u0026gt;\u0026thinsp;Ba (16.2%). Cations that were vertically removed from 0\u0026ndash;20 cm had higher removal efficiency than those that were found within 20\u0026ndash;40 cm. The nearby anode may be the cause of the comparatively high ion removal ratios in the surface layers. The total average removal of cations (0\u0026ndash;40 cm) from the PCPSS pilot unit\u0026apos;s center was arranged in the following descending order: Na (63.9%)\u0026thinsp;\u0026gt;\u0026thinsp;Ca (37.8%)\u0026thinsp;\u0026gt;\u0026thinsp;K (35.7%)\u0026thinsp;\u0026gt;\u0026thinsp;Mg (33%)\u0026thinsp;\u0026gt;\u0026thinsp;Li (27%)\u0026thinsp;\u0026gt;\u0026thinsp;Ba (9.2%). The average vertical removal of cations from the second area, which was 11 cm behind the center and within the range of 0\u0026ndash;20 cm, was arranged as follows: Na (74%)\u0026thinsp;\u0026gt;\u0026thinsp;Ca (56.4%)\u0026thinsp;\u0026gt;\u0026thinsp;K (42.7%)\u0026thinsp;\u0026gt;\u0026thinsp;Mg (33.8%)\u0026thinsp;\u0026gt;\u0026thinsp;Li (26.7%)\u0026thinsp;\u0026gt;\u0026thinsp;Ba (24.6%) as presented in Fig. \u003cspan class=\"InternalRef\"\u003e10\u003c/span\u003e. Among the cations under study, Na had the greatest removal ratios, while Ba had the lowest. The average vertical cation removal from 0\u0026ndash;20 cm (11 cm behind the center) was marginally superior to samples taken from the PCPSS pilot unit\u0026apos;s center, with the exception of Ba, where the average removal percentage increased significantly from 2.3% to 24.6%. Within 20\u0026ndash;40 cm, the average vertical cation removal from the region 11 cm behind the center was as follows: Na (70.7%)\u0026thinsp;\u0026gt;\u0026thinsp;Ca (35.9%)\u0026thinsp;\u0026gt;\u0026thinsp;K (32.8%)\u0026thinsp;\u0026gt;\u0026thinsp;Li (27.4%)\u0026thinsp;\u0026gt;\u0026thinsp;Mg (19.8%)\u0026thinsp;\u0026gt;\u0026thinsp;Ba (5.4%). For the whole PCPSS pilot unit, the average vertical cation removal from the area 11 cm behind the center was as follows: Na (72.3 %)\u0026thinsp;\u0026gt;\u0026thinsp;Ca (46.1 %)\u0026thinsp;\u0026gt;\u0026thinsp;K (37.7 %)\u0026thinsp;\u0026gt;\u0026thinsp;Li (27 %)\u0026thinsp;\u0026gt;\u0026thinsp;Mg (26.8 %)\u0026thinsp;\u0026gt;\u0026thinsp;Ba (15 %) Except for Mg and Li, the average removal of cations from the whole unit of the PCPSS pilot scale was much better in the area located 11 cm behind the center compared to samples collected from the center. Na, which is regarded as the primary challenge for recovering salt-affected soil, has the highest removal efficiency. Therefore, it is strongly advised to use the PCPSS pilot scale unit to concurrently remediate inorganic contaminants and restore salt-affected soil.\u003c/p\u003e\n\u003c/div\u003e"},{"header":"4. Soil rehabilitation after the application of soil electrokinetic remediation","content":"\u003cp\u003eAfter the application of soil electrokinetic remediation, the treated soil will be subject to several modifications, particularly in the pH and ion concentrations [\u003cspan citationid=\"CR28\" class=\"CitationRef\"\u003e28\u003c/span\u003e]. Most of the investigations were focused on optimizing the performance, including modifying the current design [\u003cspan citationid=\"CR30\" class=\"CitationRef\"\u003e30\u003c/span\u003e], application of pulsed electric field technique [\u003cspan citationid=\"CR47\" class=\"CitationRef\"\u003e47\u003c/span\u003e], utilizing reverse polarity mode [\u003cspan citationid=\"CR48\" class=\"CitationRef\"\u003e48\u003c/span\u003e], incorporating nozzles and pipes [\u003cspan citationid=\"CR46\" class=\"CitationRef\"\u003e46\u003c/span\u003e], applying electrode approaching system [\u003cspan citationid=\"CR49\" class=\"CitationRef\"\u003e49\u003c/span\u003e], controlling the pH of soil, catholyte, and anolyte [\u003cspan citationid=\"CR28\" class=\"CitationRef\"\u003e28\u003c/span\u003e], integrated soil electrokinetic/electroosmosis-vacuum [\u003cspan citationid=\"CR30\" class=\"CitationRef\"\u003e30\u003c/span\u003e], avoiding soil cracking [\u003cspan citationid=\"CR50\" class=\"CitationRef\"\u003e50\u003c/span\u003e], utilizing permeable reactive barriers [\u003cspan citationid=\"CR51\" class=\"CitationRef\"\u003e51\u003c/span\u003e], [\u003cspan citationid=\"CR52\" class=\"CitationRef\"\u003e52\u003c/span\u003e], investigate the impact of electrode materials [\u003cspan citationid=\"CR53\" class=\"CitationRef\"\u003e53\u003c/span\u003e], etc.\u003c/p\u003e \u003cp\u003eThe rehabilitation program could be carried out through the operation of soil electrokinetics in which the fluctuation of pH could be controlled via several methods [\u003cspan citationid=\"CR28\" class=\"CitationRef\"\u003e28\u003c/span\u003e]. Some electrokinetic studies require the addition of a chemical (acid or base) to the polluted soil to increase the solubility of pollutants (inorganic or organic) inside the soil pores to make them subject to eventually change the soil pH. In this case, soil rehabilitation is required to return soil to its initial status, such as applying reverse polarity mode for the same period that was applied before, excavating the soil adjacent to the anode and cathode and mixing them, and mixing the pH-value-opposing solution with the treated soil (adding acid to soil that has been treated with base, and vice versa). All these challenges will be taken into consideration in our future research.\u003c/p\u003e"},{"header":"5. Conclusions","content":"\u003cp\u003eOne of the numerous applications for the soil electrokinetic is the remediation of contaminated soils with inorganic contaminants. Despite being regarded as a physicochemical separation technique, soil electrokinetic remediation is unable to distinguish between various ions during removal. We previously investigated the possibility of improving the soil electrokinetic remediation of inorganic pollutants using real contaminated soils at lab/bench and pilot levels by adding different enhancement chemical before scaling up. The behavior of soil cations, such as Mg, Ca, Ba, Na, Li, and K, is being investigated in the current study. The findings may be summed up as follows:\u003c/p\u003e \u003cp\u003e \u003cul\u003e \u003cli\u003e \u003cp\u003eUsing the PCPSS, the results showed that acidity effectively improved the removed Mg when exposed to an electric field. The similar pattern was also seen in the way that Ca responded to the electric field, with formic acid (pH 1) being the most effective method of removing calcium.\u003c/p\u003e \u003c/li\u003e \u003cli\u003e \u003cp\u003eIn addition to decreasing the accumulation percentages around the cathode pipes (bottom layers), applying formic acid (pH 1) increased the contents of Li removed from the surface layers as compared to the other treatments. The removed Mg was found to be less than the Ca.\u003c/p\u003e \u003c/li\u003e \u003cli\u003e \u003cp\u003eApplying formic acid (pH 1) decreased the quantity of Ba accumulation spots inside the PCPSS apparatus, however Ba accumulation spots were seen to emerge with various treatments.\u003c/p\u003e \u003c/li\u003e \u003cli\u003e \u003cp\u003eNa showed the lowest content ratio values (higher removal percentages) during the lab/bench scale enhancement experiments, while the other cations had the highest content ratios. Since Na is thought to be the primary obstacle to recovering salt-affected soil, the pilot PCPSS unit is a suggested method for doing so concurrently with contaminated soil remediation.\u003c/p\u003e \u003c/li\u003e \u003c/ul\u003e \u003c/p\u003e"},{"header":"Statements and Declarations","content":"\u003cp\u003e\u003cstrong\u003e\u003cu\u003eFunding\u003c/u\u003e\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThis work was supported by Science and Technology \u0026amp; Innovation Funding Authority (STIFA), previously known also as Science and Technology \u0026amp; Development Fund (STDF), Grant No. 39369.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003e\u003cu\u003eCompeting Interests\u003c/u\u003e\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this review.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003e\u003cu\u003eAuthor contribution\u003c/u\u003e\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eA.A.-S suggested the article topic, analyzed the results, prepared the figures and tables, and wrote the manuscript; and A.H., A.S., and M.A.O. improved the content, and revised the manuscript.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003e\u003cu\u003eData Availability\u003c/u\u003e\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eData will be made available on request\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003e\u003cu\u003eEthics approval and consent to participate\u003c/u\u003e\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThere is no human or animal study included in this work.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003e\u003cu\u003eConsent for publication\u003c/u\u003e\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eNo personal information of any kind is included in the work.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003e\u003cu\u003eClinical trial\u003c/u\u003e\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eClinical trial number: not applicable.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\n \u003cli\u003eA. 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Syst.\u003c/em\u003e, vol. 9, no. 8, p. 2500197, Aug. 2025, doi: https://doi.org/10.1002/adsu.202500197.\u003c/li\u003e\n\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[{"identity":"0d181adb-0ca1-4a8b-ab52-642328cfc1b8","identifier":"10.13039/501100003009","name":"Science and Technology Development Fund","awardNumber":"39369","order_by":0}],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":true,"hideJournal":true,"highlight":"","institution":"Desert Research Center","isAcceptedByJournal":false,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true},"keywords":"Soil electrokinetics, Process optimization/intensification, The PCPSS, Upscaling approach, Cations removal, Enhancement regents","lastPublishedDoi":"10.21203/rs.3.rs-8891372/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-8891372/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eSoil electrokinetics (SEK) has a variety of applications, one of which is remediating contaminated soils that contain inorganic contaminants. The SEK remediation (SEKR), which is regarded as a physicochemical separation technique, is unable to distinguish between various ions in removal. In continuation with our recent publication in IJEST titled \"\u003cem\u003eScaling up soil electrokinetic removal of inorganic contaminants based on lab chemical and biological optimizations\u003c/em\u003e\" [\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e], which focused on the enhancement of SEKR of inorganic pollutants in real soils, these results are expanded upon in this article to show how cations linked to inorganic contaminants are removed. In the present investigation, the behavior/migration of six cations\u003cb\u003e\u0026mdash;\u003c/b\u003eMg, Ca, Ba, Na, Li, and K\u003cb\u003e\u0026mdash;\u003c/b\u003ewas illustrated. The findings demonstrated that the amount of Mg removed using the perforated cathode pipe SEKR system (PCPSS) under the influence of an electric field was proportionate to the rise in soil acidity. It was found that the best chemical to combine with soil to improve the removal of calcium was formic acid (pH 1). Compared to Mg, the amount of Ca removed was greater. The application of formic acid (pH 1) decreased the quantity of Ba accumulation spots/areas within the PCPSS apparatus. Using the recommended enhancing reagents, the content ratios with the removed Na had the lowest values, which exhibit the best rates of removal. In addition to decreasing the accumulation percentages around the cathode pipes (bottom layers), applying formic acid (pH 1) enhanced the amounts of Li removed from the surface layers as compared to the other treatments. After the pilot scale unit of the PCPSS was terminated, the removal percentages of the investigated cations were greatest for Na (lowest content ratios). Since Na is thought to be the primary obstacle to reclaiming salt-affected soil, it is highly recommended to recover salt-affected soil and remove inorganic pollutants simultaneously using the PCPSS pilot scale unit.\u003c/p\u003e","manuscriptTitle":"Laboratory and pilot-scale investigation of soil cations behavior in conjunction with electrokinetic remediation of inorganic pollutants","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2026-02-18 08:20:44","doi":"10.21203/rs.3.rs-8891372/v1","editorialEvents":[{"type":"communityComments","content":0}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true}}],"origin":"","ownerIdentity":"980f1536-4465-4d9a-a899-a4de6ebc7c11","owner":[],"postedDate":"February 18th, 2026","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"posted","subjectAreas":[{"id":62991141,"name":"Environmental Engineering"}],"tags":[],"updatedAt":"2026-02-18T08:20:44+00:00","versionOfRecord":[],"versionCreatedAt":"2026-02-18 08:20:44","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-8891372","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-8891372","identity":"rs-8891372","version":["v1"]},"buildId":"XKTyCvWXoU3ODBz1xrDgd","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}