Time-Dependent Dissolution of Potassium from K-Bearing Mineral Residues in Organic Acids

Time-Dependent Dissolution of Potassium from K-Bearing Mineral Residues in Organic Acids | Research Square window.SnipcartSettings = { analytics: { enabled: false } }; (function() { var accessVector = localStorage.getItem('access_vector') || ''; window.dataLayer = window.dataLayer || []; if (accessVector) { window.dataLayer.push({ user: { profile: { profileInfo: { snid: accessVector } } } }); } })(); (function(w,d,s,l,i){w[l]=w[l]||[];w[l].push({'gtm.start':new Date().getTime(),event:'gtm.js'});var f=d.getElementsByTagName(s)[0],j=d.createElement(s),dl=l!='dataLayer'?'&l='+l:'';j.async=true;j.src='https://www.googletagmanager.com/gtm.js?id='+i+dl;f.parentNode.insertBefore(j,f);})(window,document,'script','dataLayer','GTM-K279D39R'); Browse Preprints In Review Journals COVID-19 Preprints AJE Video Bytes Research Tools Research Promotion AJE Professional Editing AJE Rubriq About Preprint Platform In Review Editorial Policies Our Team Advisory Board Help Center Sign In Submit a Preprint Cite Share Download PDF Research Article Time-Dependent Dissolution of Potassium from K-Bearing Mineral Residues in Organic Acids Ayodeji Sunday Awoniyi, Adebayo Jonathan Adeyemo, John Okhienaiye Agbenin, and 3 more This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-5987694/v1 This work is licensed under a CC BY 4.0 License Status: Under Review Version 1 posted 4 You are reading this latest preprint version Abstract Background and Aims: Potassium (K)- bearing minerals are vital for soil fertility and act as slow-release reservoirs for crop productivity. Organic acids, such as oxalic and citric acids, enhance K dissolution. Methods Time-dependent experiments measured K dissolution from minerals in oxalic and citric acids. Mehlich-1 extraction and atomic absorption spectrophotometry quantified K release over intervals under controlled conditions. Results Oxalic acid enhanced K release by 25% more than citric acid. For biotite-mica, increasing oxalic acid concentration from 0.5 to 5.0 mmol L⁻¹ raised K release from 800 to 1600 mg kg⁻¹. During a further increase to 10 mmol L⁻¹, slightly improved dissolution was recorded. Percentage K release varied by mineral, biotite-mica, muscovite-mica, and K-feldspar recorded 5–11%, 3–7%, and 2–6% respectively. Citric acid caused significant K release between 0.5 and 1.0 mmol L⁻¹, with increases up to 10 mmol L⁻¹. Above 5 mmol L⁻¹, muscovite-mica dissolved more K than biotite-mica and K-feldspar, with K-feldspar showing higher dissolution percentages of 3.1–7.5% in citric acid than oxalic acid that recorded 2.4–6.2%. Conclusion Organic acids enhance K release via chelation, destabilization of mineral surfaces, and solubility increases. Oxalic acid’s superior performance highlights its role in improving soil fertility. Also, oxalic acid outperformed citric acid in dissolving K from minerals, underscoring the importance of targeted nutrient management strategies. K-dissolution Organic acids Soil fertility K-bearing minerals Mineral solubility Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 1.0 Introduction Potassium (K) is an essential macronutrient for plant growth, playing a crucial role in various physiological and biochemical processes. It is involved in enzyme activation, photosynthesis, osmoregulation, and nutrient transport, all of which are critical for maintaining plant health and productivity [ 1 ]. Unlike nitrogen and phosphorus, potassium does not form part of the structural components of plants. However, it is pivotal in regulating water usage efficiency and enhancing resistance to abiotic stress, such as drought and salinity [ 2 , 3 , 4 ]. In soils, potassium exists in various forms, including soluble, exchangeable, and fixed or non-exchangeable forms, the latter of which is mainly associated with K-bearing minerals such as feldspars and micas [ 5 , 6 ]). The release of potassium from these minerals through weathering processes is often insufficient to meet the demands of intensive cropping systems, especially in tropical and subtropical regions, where rapid weathering and leaching can deplete available K [ 7 , 8 ]. The increasing reliance on synthetic K fertilizers poses economic and environmental challenges. Thus, alternative strategies, such as utilizing natural K-bearing minerals and enhancing their dissolution using organic acids, are being explored to improve soil fertility sustainably [ 9 , 10 , 11 ]. Organic acids, such as oxalic and citric acids, produced by plant roots and soil microbes, play a significant role in solubilizing potassium by chelating metal cations and disrupting mineral lattices, thereby increasing K availability in the soil solution [ 12 , 11 , 13 ]. K-bearing minerals, such as feldspars, biotite, muscovite, and K-feldspar, play a significant role as natural K sources in soils. These minerals account for most of the non-exchangeable K pool, which serves as a long-term nutrient reservoir, especially in tropical and subtropical regions where soils are highly weathered. The slow-release nature of K from these minerals is essential for maintaining soil fertility and crop productivity over time [ 14 , 15 , 8 ]. Chemically, K-bearing minerals consist of K incorporated into their crystalline structures. Micas, for instance, have K in interlayer spaces, which makes them relatively more accessible during weathering [ 16 , 17 , 18 ]. In contrast, feldspars hold K within their tetrahedral frameworks, requiring more intensive weathering processes to release the nutrient [ 19 , 20 ]. The release of K from these minerals occurs through chemical, biological, and physical weathering processes. Chemical weathering involves the breakdown of the mineral structure by interactions with water, carbon dioxide, and organic acids, leading to the release of K into the soil solution. Biological weathering is driven by organic acids produced by plant roots and microorganisms, which chelate metal ions, destabilize mineral surfaces, and enhance the hydrolysis of K-bearing minerals. On the other hand, physical weathering involves the mechanical breakdown of minerals into smaller particles, increasing their surface area and facilitating chemical interactions [ 21 , 22 ]. In agriculture, K-bearing minerals serve as sustainable alternatives to synthetic K fertilizers. They provide a natural, slow-release source of K, which is particularly valuable in low-input farming systems. By enhancing the dissolution of these minerals through organic acid amendments or promoting microbial activity, farmers can improve the bioavailability of K, ensuring long-term soil fertility and reducing reliance on chemical fertilizers [ 23 , 24 ]. Organic acids, such as oxalic and citric acids, are crucial in enhancing nutrient dissolution from soil minerals, particularly K and other essential nutrients bound within mineral matrices. These low-molecular-weight organic acids, commonly exuded by plant roots and soil microorganisms, act as natural chelating agents and significantly influence the chemical processes that release nutrients into the soil solution [ 25 ]. Oxalic and citric acids enhance nutrient dissolution through multiple mechanisms. One of the primary mechanisms is their ability to lower the pH of the soil microenvironment. This acidification destabilizes mineral surfaces, releasing cations like K, Ca, Mg, and Fe from mineral structures [ 26 , 27 ]. Additionally, these acids form soluble complexes with metal ions, a process known as chelation, which further drives the dissolution of minerals by removing reaction products from the surface and enhancing the solubility of otherwise insoluble compounds [ 28 ]. Oxalic acid, due to its strong chelating ability and high acidity, is particularly effective in breaking down silicate minerals such as feldspars and micas. It promotes K release by displacing it from interlayer and framework positions within the mineral structure. Similarly, citric acid enhances nutrient dissolution with slightly different dynamics, often showing a more gradual but sustained effect than oxalic acid. The carboxyl groups in citric acid interact with mineral surfaces, facilitating the desorption and release of nutrients into the soil solution [ 29 , 30 ]. The effectiveness of these organic acids is influenced by their concentration, the nature of the minerals involved, and the duration of their interaction. For instance, higher concentrations of oxalic and citric acids result in greater dissolution rates, although diminishing returns may occur at very high concentrations [ 31 , 32 ]. These acids also exhibit differential effects on various minerals, with oxalic acid generally outperforming citric acid in dissolving K from silicate minerals. Therefore, evaluating the time-dependent dissolution of K in the presence of these organic acids provides valuable insights into their effectiveness and mechanisms in nutrient cycling, which is critical for developing sustainable soil management strategies. 2.0 Materials and Methods 2.1 Collection and preparation of K-bearing mineral residues for X-ray diffraction analysis The K-bearing mineral residues for this study were collected at the Ola-Ebimi quarry site at Oye-Ekiti (7°48'55.01"N, 5°20'40.70"E) and Ijero-Ekiti (7°48'55.12"N, 5°04'56.53"E) in Ekiti State. The places were chosen because of the large volume of rocks extracted and processed, producing considerable residues. These residues have created an environmental problem of high magnitude, with areas of significant size that raise questions about their storage, management, and destination. In this sense, rock residue for agricultural purposes has been studied for possible recycling since it does not provide potential contamination to soil, water, and plants [ 8 , 33 ]. For this research, three representative samples of each K-bearing mineral residue were collected with a hammer and a chisel. The K-bearing residues were identified and labelled using the observable physical features. The K-bearing mineral residues were pulverized using a ballpoint mill into very fine powdery form. The pulverized samples were characterized with X-ray diffraction (Angstrom ADX2700, USA). The samples were filled inside the sample handler and placed in the diffraction chamber. The following XRD analysis parameters were employed: a graphite-monochromatic Cu radiation source at 40 kV and 30 mA was used with a step size of 0.2 and a scan speed of 1.0 sec. The diffraction intensities were noted in the 2θ = 5 o —70 o range. The experiment was carried out in the Chemical Analysis Laboratory, Department of Soil Science, Faculty of Agricultural Sciences, Federal University Oye Ekiti, Ekiti State, while the x-ray was carried out at the Central Laboratory, the Federal University of Agriculture, Abeokuta, Ogun State, Nigeria. It was a randomized block design in 2 × 3 × 4 factorial experiments consisting of 24 treatments and three replications. The studied factors were two organic acids-oxalic acid (C 2 H 2 O 4 ) and citric acid (C 6 H 8 O 7 ), both P.A. reagents, three K-bearing mineral residues: biotite-mica, muscovite-mica and K-feldspar; and four rates of organic acids: 0.5, 1.0, 5.0 and 10 mmol L-1, established based on the values found in the literature [ 34 , 35 , 36 ]. 2.2 Determination of total K concentration in the K-bearing mineral residues The total K concentrations in the K-bearing residues for this study were determined by the mixed acid digestion method described by Agbenin [ 37 ]. Briefly, 0.5 g of the pulverized mineral was weighed into a digestion tube, to which 1 mL of concentrated HClO 4 , 5 mL of concentrated HNO 3 acid, and 0.5 mL of concentrated H 2 SO 4 were added and slowly digested. Moderate heat was gradually increased for 10–15 minutes until white fumes appeared. The tube was then set aside to cool down and diluted to 40 ml. This was filtered through a Whatman No. 44 filter paper into a 50-ml flask and then made up to the 50-ml mark. The total K concentration in the filtrate was determined using a Flame Photometer (Model FP640, China). 2.3 Dissolution of K-bearing minerals and their residues in oxalic and citric acids The release of K from the K-bearing minerals was determined in two organic acids, namely oxalic and citric acids. The organic acids' equivalent concentrations ranged from 5 x 10 − 4 to 1 x 10 − 2 mol of the two prepared acids. The pH of the different acid concentrations was determined using a portable pH meter (Phoenix pH instrument EC-26, Italy). The measurements of the pH of the various concentrations of the organic acids were performed to determine the H + ion concentration, and the oxalate and citrate concentrations in the solution, assuming the first ionization of the two organic acids occurred according to the following reactions: Given the pH of the solutions and the respective k a1 of the oxalic and citric acid solutions, the (HC2O − ) and (H7C6O − ) were calculated for the varying concentrations of the two acids. For the mineral residues, Approximately 0.5 g of the pulverized K-bearing mineral was measured into a 100-mL volumetric flask and 20 mL of oxalic acid with varying concentrations ranging from 5 x 10 − 4 to 1 x 10 − 2 mol L -1 was added and replicated three times. The flask was placed in a mechanical shaker. The suspension was shaken for between 30 minutes and four hours. The suspension was filtered into a sample bottle through a Whatman No. 1 filter paper. The above procedure was also repeated for citric acid with varying concentrations. The concentrations of K in the filtrates were determined using a Flame Photometer (Model FP640, China). 2.4 Statistical analysis Data collected were analyzed using the general linear model of Minitab 17.0 edition. The obtained data were tested for the significance of differences in K release by the two acids among the three k-bearing minerals. The results were summarized in tables and graphs. Tukey HSD is the statistical post hoc method used to confirm the significance of the means obtained at a 5% probability or confidence level. All the treatment means, and standard errors were computed before putting up the graphs and were made via Microsoft Excel 2007. 3.0 Results 3.1 Hydrogen ion and ligand concentrations in the organic acid solutions Based on the first ionization constants of the two organic acids, the hydrogen ion, H + , activities in the two organic acid solutions increased with the increasing concentrations of the two organic acid solutions (Fig. 1 ). In the oxalic acid solution, H + activities increased linearly with increasing concentration in contrast to the citric acid solution with a fairly gentle increase in H + activities. The H + activities were consistently more significant in the oxalic acid solution than in a citric acid solution at the different concentrations following the measured pH of the two organic acid solutions. The pH decreased from 3.4 at 0.5 mmol to 2.4 at 10 mmol of the oxalic solution, whereas pH decreased from 3.6 at 0.5 mmol to 2.9 at 10 mmol of the citric acid solution. Similarly, the activities of the two ligands, namely the oxalate, HC2O − , and citrate, C6H7O − , increased with increasing concentrations of the two organic acid solutions (Fig. 1 ). The activities of HC2O − increased exponentially by increasing the oxalic acid concentration from 1.0 mmol L -1 to 5 mmol L -1 but flattened out when the concentration of the oxalic acid solution was raised from 5 to 10 mmol L -1 (Fig. 1 ), probably attaining its buffer range at this concentration. Consistent with the H + activities with the increasing concentration of the citric acid solution, the C6H7O − activities increased gently with increasing concentration of the citric acid. At any given concentration of the two organic acid solutions, HC2O − activities were more significant than the C6H7O − activities, consistent with the dissociation constants of oxalic acid ( k a1 = 6.5 x10 −2 ) and citric acid ( k a1 = 8.4 x 10 −4 ). 3.2 Characterization of the K-bearing residues by X-ray Diffraction Powder x-ray diffraction indicated characteristic first-order diffraction peaks at 1.01 nm and third-order between 0.331 and 0.335 nm, indicative of micaceous minerals in the K-bearing mineral residues (Figs. 2 and 3 ). Physical characteristics of the mineral residues from the quarry sites, assessed visually, suggest the presence of biotite-mica and muscovite-mica contained in the K-rich mineral residues from one quarry site, while the other K-rich mineral residue from the second quarry site contained K-feldspar. 3.3 Total K concentration and dissolution in organic acids of varying concentrations The total K concentration of the three K-bearing minerals ranged from 1.6 to 1.8% K or 1.93 to 2.16% K2O. The muscovite-mica had the highest K concentration of 2.16% K2O, followed by K- feldspar at 2.04% K2O, while the biotite-mica contained 1.93% K2O. The dissolution of K-bearing minerals (biotite-mica, muscovite-mica and K-feldspar) in oxalic acid showed significant differences in the amount of K released upon dissolution with varying concentrations of oxalic acid. As the concentrations of oxalic acid increased, there was an increasing amount of K released from the K-bearing minerals with a tendency toward equilibrium attainment at 5 mmol L -1 of the acid solution (Fig. 4 ). The differences in the amounts of K released by the biotite-mica were generally significant between the concentrations. For instance, increasing the concentration of the oxalic acid from 0.5 mmol 1 –1 to 5.0 mmol l -1 increased K released by biotite-mica from 800 mg kg -1 to 1600 mg kg -1 , whereas increasing the acid concentration from 5 to 10 mmol l -1 only gently or slightly increased the amounts released by the minerals. A distinctive feature of the dissolution of K from the biotite-mica, muscovite-mica and K-feldspar is that biotite-mica released more significant amounts of K than muscovite-mica and K-feldspar (Fig. 4 ). The order of K dissolution in the oxalic acid of varying concentration was biotite-mica > muscovite-mica > K-feldspar (Fig. 4 ). The percentage of K release from the total K concentration in the biotite-mica ranged from 5.0% at 0.5 mmol to 10% at 10 mmol concentration of oxalic acid, muscovite mica from 3–7% and K- feldspar from 2–6% of the total K composition of the minerals (Table 1 ). Among the three minerals dissolved in oxalic acid in this study, biotite-mica had the highest percentage of K dissolution. The dissolution of K in biotite-mica, muscovite-mica and K-feldspar by citric acid showed increasing amounts of K released with increasing concentrations of the acid (Fig. 5 ). There was a steep increase in the amounts of K released into the citric acid solution by the K-bearing minerals from 0.5 to 1.0 mmol concentration of the acid. However, from 1.0 to 10 mmol of the acid concentration, the amounts of K released increased linearly with increasing concentration but with a much gentler slope than the K dissolution at 0.5 and 1.0 mmol L -1 of the acid concentration. In contrast to the dissolution of the K-bearing minerals in oxalic acid, there were no distinct and significant differences in the amounts of K released between the K-bearing minerals in the citric acid solution concentration ≤ 5.0 mmol. However, at concentrations > 5.0 mmol, more K was dissolved in muscovite mica than in biotite-mica and K-feldspar. The K-dissolution pattern in the citric acid at a concentration greater than 5.0 mmol L -1 was biotite-mica > muscovite-mica > K-feldspar (Table 1 ). A higher percentage of total K was dissolved from K-feldspar in all the concentrations of citric acids (3.1–7.5%) than in oxalic acid (2.4–6.2%) (Table 1 ). However, the biotite-mica appeared more soluble in citric acid than muscovite-mica and K-feldspar, consistent with the dissolution in oxalic acid. The percentage of total K dissolved from biotite-mica in the citric acid solutions ranged from 4.9% at 0.5 mmol to 7.6% at 10 mmol, almost similar to the trend of dissolution in oxalic acid. Table 1 The total K concentrations, range, and mean of soluble K, including the percentages of soluble to total K concentration in the K-bearing minerals in two organic acids of varying concentrations. K-bearing Organic Total K conc. Dissolved K Range Mean Percent solubility Rangemean mineral acid 1 ---------------- mg kg -1 ------------------ --------- % --------- Biotite-mica Oxalic 16.1 b 0.8–1.7 1.3 a 5–10 7.9 a Muscovite-mica 17.6 a 0.6–1.3 0.9 a 3.1–7.4 5.0 b K-feldspar 17.2 a 0.4–1.1 0.7 a 2.4–6.2 4.1 b Biotite-mica Citric 16.1 b 0.8–1.2 1.0 a 4.9–7.6 6.0 a Muscovite-mica 17.6 a 0.5–1.4 0.8 b 2.6–7.7 4.7 b K-feldspar 17.2 a 0.5–1.3 1.0 a 3.1–7.5 5.8 a 1 The concentration range of the oxalic and citric acid solutions is 0.5 – 10 mmol. According to Tukey's test, the same letters in superscript on a column for the same parameter are not different from one another (P < 0.05). 4.0 Discussion 4.1 Characterization and K concentration of the K-bearing mineral residues The K-bearing residues used for this study contained less than 3% K2O, but the concentration is sufficient to meet crop nutrition if the residues could release K at a rate that meets crop requirements. X-ray diffraction of the K-bearing residues showed diffraction peaks at 1.01 nm (Figs. 2 and 3 ), characteristic of micaceous minerals [ 38 ], confirming visual observations of muscovite and biotite minerals in the mineral residues. However, the total concentrations of K in the mineral residues were almost five times lower than the concentration of K2O in a pure specimen of muscovite or biotite, which ranges from 10 to 12% [ 39 ]. 4.2 Dissolution of K-bearing mineral residues in oxalic and citric acids Organic acids facilitate the weathering of minerals and rocks by forming metal-organic complexes. Potassium-bearing minerals exposed to varying concentrations of organic acids release different concentrations of K that vary with concentrations of the organic acids. The varying amount of K released from the three K-bearing minerals examined in this study conformed to this prediction and further substantiated the report of Bilias & Barbayiannis [ 40 ], who observed increasing dissolution of K with increasing concentration of oxalic acid from 0 to 400 mmol L − 1 from K- bearing minerals. The highest K concentration was dissolved in the 0.01N organic acid concentration. Higher K release continued to increase with time, even after 4 hours of continuous agitation, suggesting that the K-bearing mineral wastes collected at these quarry sites can release K for some time to satisfy the nutrition of crop plants. Long-term K release is generally observed with specimen K-bearing minerals [ 41 ]. Among the principal K-bearing minerals, K-feldspars or microcline released less K in the two organic acids, probably because of the initially low K concentration in the residue. The sequence of K dissolved in oxalic acid was mica-biotite > mica-muscovite > K feldspar, which agrees with the report by Richardson et al. [ 42 ]. However, the sequence of K release into the citric acid solution followed the order mica-muscovite > K feldspar > mica-biotite in citric acid. The comparison between K released by the organic acids shows that oxalic acid dissolved more K from mica-biotite than from citric acid, regardless of the organic acid concentrations, consistent with the report by Duarte et al . [ 9 ]. Citric acid dissolved more K from the mica-muscovite and K- feldspar than oxalic acid. Two mechanisms are operational in the dissolution of K from K-bearing minerals by polyfunctional organic acids such as oxalic and citric acids, examined in this study by Lin et al. [ 31 ]. One mechanism involved the proton attack or exchange with K in the mineral structure; this proton promoted the dissolution of K from the K-bearing minerals. Figure 1 shows that the concentration of H + dissociated from the oxalic acid far exceeded the H + elaborated from the citric acid, hence the tendency for more outstanding K release from the K-bearing minerals in oxalic than citric acid. Proton attack of minerals via cation exchange in soil minerals remains a potent mechanism of weathering rocks and minerals in soils [ 43 , 44 ]. The second mechanism of K dissolution from K-bearing minerals in polyfunctional organic acids is the ligand-promoted dissolution of minerals, especially when pH increases or acidity decreases [ 45 ]. This mechanism may be more important than the proton or H+-promoted dissolution of minerals in soils. For instance, ligand-promoted dissolution was reportedly more effective than proton-promoted dissolution of plagioclase or Ca-feldspar [ 46 ]. The oxalic acid dissolving more K from the mica-biotite than citric acid would imply that proton-promoted dissolution of K was the predominant mechanism of K release compared to ligand-promoted K-dissolution. On the other hand, citric acid dissolved more K in K- feldspar or microcline than oxalic acid, probably indicating the dominance of ligand-promoted dissolution of K from K-feldspar over proton-promoted dissolution. However, there was no apparent difference in K dissolved from mica-muscovite in the oxalic acid (5% of total K) and citric acid (4.7% of total K). The average total K solubilized by citric acid as a percent of total K in the K-bearing minerals, which is 4.7%, agrees fairly well with 4.3% of the total K dissolved from a K-bearing rock residue studied by Machado et al . [ 39 ]. in Brazil. The slight difference can be attributed to the stoichiometric differences in the K-bearing residue and the complexing ability of oxalate and citrate for K and the release of other cations such as Al, Fe, Mg and Si from the K-feldspar [ 46 ]. The effect of oxalic and citric acids on the release of mineral K in K-bearing minerals is because of the dissociated H + ions and complexing organic ligands, oxalate and citrate, respectively, in the organic acid solution [ 47 ]. The varying amounts of K dissociated from the K-bearing minerals are a consequence of the differences in the amounts of ligands and hydrogen ions concentrations generated by the two polyfunctional organic acids [ 48 ] and in the complexation capacity of the ligands (Figs. 2 and 3 ). The marginally higher amount of K + released into oxalic acid at different intervals than citric acid accords with the reports by Lin et al. [ 31 ]. 5.0 Conclusion Potassium is a key nutrient element that several staple food crops, especially roots and tubers, require in significant quantities. The K requirements of roots and tuber crops, Dioscorea spp , are enormous, thus necessitating the assessment of the solubility of K from some K-bearing mineral residues, available in many quarry sites, to recapitalize soil K stocks without recourse to expensive inorganic fertilizers priced beyond the reach of poor-resourced farmers. Organic acids primarily elaborate into the soil and rhizosphere from root exudation, microbial metabolites and organic matter decomposition facilitate mineral dissolution by forming metal-organic complexes. Potassium-bearing minerals exposed to organic acids often release different concentrations of K that vary with the concentrations of the organic acids. In this study, we examined the time-dependent dissolution of K from three K-bearing mineral residues in oxalic and citric of varying concentrations ranging from 0.5 to 10 mmol. X-ray diffraction indicated that the K-minerals occurring in the K-rich residues were biotite-mica and muscovite-mica, identified by the characteristic x-ray peak between 1.0 and 1.01 nm from one quarry site at Oye-Ekiti. The third K-mineral in another K-rich residue, taken from another quarry site, was K-feldspar. The total K concentration of the three K-bearing mineral residues ranged from 1.6 to 1.8% K or 1.93 to 2.16% K2O. The muscovite-mica mineral residue had the highest K2O concentration (2.16%), followed by the K-feldspar mineral residue (2.04%) and the biotite-mica mineral residue containing 1.93% K2O. The time-dependent K dissolution trends from the K-bearing mineral residues increased with time and the increasing concentration of oxalic and citric acids, attaining a steady state at about 2–3 hours with continuous agitation of the K-mineral residue suspension in the organic acids. Generally, oxalic acid dissolved a greater concentration of K than citric acid, especially for the mineral residue containing mica-biotite. The solubility of K as a percentage of the total K contained in the K-bearing mineral residues ranged from 4.1% for the K-feldspar residue to 7.9% for the mica-biotite residue in oxalic acid, whereas, in citric acid, the solubility of K ranged from 4.7% for mica-muscovite to 6% for mica-biotite. In the oxalic acid solution, the order of solubility of the K-bearing mineral residues was mica-biotite > mica-muscovite > K-feldspar. In contrast, the K- K-solubility order in the citric acid solution was mica-biotite > K-feldspar > mica-muscovite. Pot experiments and field trials involving the direct applications of these K-bearing mineral wastes to soils to determine their K-supplying capacities and rates to meet the K nutrition of crops are required to validate this laboratory study. Hence, this study provides the baseline information on K solubility in the K-bearing mineral residues that could have potential direct field applications to satisfy the K nutrition of field crops with high K requirements, such as yams ( Dioscorea spp .) Declarations Data Availability The data that support the findings of this study are available from Dr. Adebayo Jonathan ADEYEMO but restrictions apply to the availability of these data, which were used under license for the current study, and so are not publicly available. Data are however available from the authors upon reasonable request and with permission of Dr. Adebayo Jonathan Adeyemo. Acknowledgements The author appreciates the technical assistance from the Department of Soil Science and Land Resources Management, Federal University Oye Ekiti; access provided by the two communities in Oye and Ijero in Ekiti State, Nigeria, which was fundamental to this research work; and financial support from the TETFUND/FARA/ARIFA Postdoctoral Research Fellowship tenable in Brazil. This acknowledgement will ensure that all contributors and supporters are duly recognised. Conflict of Interest The authors declare no conflicts of interest. Funding information This research was supported by funds received by a fellowship from the Nigeria Tertiary Education Trust Fund and Forum for Agricultural Research in Africa (TETFUND/FARA) given to the second author for his postdoctoral research in Brazil. Authors´ Contribution Many people participated in this scientific report. The responsibilities were as follows: conceptualisation, JOA, AJA, ASA, and AOI; methodology, JOA and AJA and ASA; validation and formal analysis, JOA and AJA; resources, JOA and AJA; data curation, AJA, DAFF and DMSO; writing-original draft preparation, AJA and ASA; writing-review and correction, AJA and AOI; project administration, JOA and AJA; and funding acquisition, JOA AJA and ASA. All the authors have read and agreed to the published version of the manuscript. Ethics declarations This work mainly concerns time–dependent K-dissolution in the laboratory and does not involve any information on humans or animals; thus, an ethical statement does not apply to the manuscript's context. Clinical trial number Not applicable. Consent to Publish declaration Not applicable Consent to Participate declaration Not applicable References Johnson R, Vishwakarma K, Hossen MS, Kumar V, Shackira AM, Puthur JT, Abdi G, Sarraf M, Hasanuzzaman M. 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DOI: 10.3390/agronomy14030609 . Ribeiro IDA, Volpiano CG, Vargas LK, Granada CE, Lisboa BB, Passaglia LMP. Use of mineral weathering bacteria to enhance nutrient availability in crops: A review. Front Plant Sci 2020;11:590774. DOI: 10.3389/fpls.2020.590774 . Kong M, Huang L, Li L, Zhang Z, Zheng S, Wang MK. Effects of oxalic and citric acids on three clay minerals after incubation. Appl Clay Sci 2014;99:207–214. DOI: 10.1016/j.clay.2014.06.035 . Clarholm M, Skyllberg U, Rosling A. Organic acid induced release of nutrients from metal-stabilized soil organic matter – The unbutton model. Soil Biol Biochem 2015;84:168–176. DOI: 10.1016/j.soilbio.2015.02.019 . Krahl LL, Valadares LF, SousaSilva JC, Marchi G, Martins É de S. Dissolution of silicate minerals and nutrient availability for corn grown successively. Pesq Agropec Bras 2022;57:e01467. DOI: 10.1590/S1678-3921.pab2022.v57.01467 . Reichard PU, Kretzschmar R, Kraemer SM. Dissolution mechanisms of goethite in the presence of siderophores and organic acids. Geochim Cosmochim Acta 2007;71(23):0–5650. DOI: 10.1016/j.gca.2006.12.022 . Oburger E, Leitner D, Jones DL, Zygalakis KC, Schnepf A, Roose T. Adsorption and desorption dynamics of citric acid anions in soil. Eur J Soil Sci 2011;62(5):733–742. DOI: 10.1111/j.1365-2389.2011.01384.x . Shabtai IA, Hafner BD, Schweizer SA, Höschen C, Possinger A, Lehmann J, Bauerle T. Root exudates simultaneously form and disrupt soil organo-mineral associations. Commun Earth Environ 2024;5:699. DOI: 10.1038/s43247-024-01879-6 . Lin S, Wang W, Wu L, Zhong M, Zhang C, Yu Y, Zhang Z, Wu Y. The effect of oxalic acid and citric acid on the modification of wollastonite surface. Materials 2023;16(24):7704. DOI: 10.3390/ma16247704 . Jalali M, Jalali M, Antoniadis V. The release of Cd, Cu, Fe, Mn, Ni, Pb, and Zn from clay loam and sandy loam soils under the influence of various organic amendments and low-molecular-weight organic acids. J Hazard Mater 2023;459:132111. DOI: 10.1016/j.jhazmat.2023.132111 . Guarçoni A, Fanton CJ. Resíduo de beneficiamento do granito como fertilizante alternativo na cultura do café. Rev Cienc Agron 2011;42:16–26. DOI: 10.1590/S1806-66902011000100003 . Andrade FV, Mendonça ES, Alvarez VVH, Novais RF. Adição de ácidos orgânicos e húmicos em Latossolos e adsorção de fosfato. Rev Bras Cienc Solo 2003;27:1003–1011. DOI: 10.1590/S0100-06832003000600004 . Corrêa MM, Andrade FV, Mendonça ES, Schaefer CEGR, Pereira TTC, Almeida CC. Ácidos orgânicos de baixo peso molecular, ácidos húmicos e alterações em algumas propriedades físicas e químicas de Latossolos, Plintossolo e Neossolo Quartzarênico. Rev Bras Cienc Solo 2008;32:121–131. DOI: 10.1590/S0100-06832008000100012 . Pires AMM, Mattiazzo ME. Kinetics of heavy metal solubilization by organic acids in sludge-treated soils. Rev Bras Cienc Solo 2007;31:143–151. DOI: 10.1590/S0100-06832007000100015 . Agbenin JO. Laboratory Manual for Soil and Plant Analysis. Department of Soil Science, Ahmadu Bello University, Zaria 1995; 140 pp. Srinivasarao Ch, et al. Farming with rocks and minerals: challenges and opportunities. Anais da Academia Brasileira de Ciências 2006;78(4):731–747. DOI: 10.1590/S0001-37652006000400009 . Machado RV, Andrade FV, Passos RR, Ribeiro RCC, Mendonça ES, Mesquita LF. Characterization of ornamental rock residue and potassium liberation via organic acid application. Rev Bras Cienc Solo 2016;v40:e0150153. DOI: 10.1590/18069657rbcs20150153 . Bilias F, Barbayiannis N. Potassium availability: An approach using thermodynamic parameters derived from quantity-intensity relationships. Geoderma 2019;338:355–364. DOI: 10.1016/j.geoderma.2018.12.02 . Han GZ, Huang LM, Tang XG. Potassium supply capacity response to K-bearing mineral changes in Chinese purple paddy soil chronosequences. J Soils Sediments 2018. DOI: 10.1007/s11368-018-2124-y . Richardson JA, Anderton CR, Bhattacharjee A. Saprotrophic fungus induces microscale mineral weathering to source potassium in a carbon-limited environment. Minerals 2023;13(5):641. DOI: 10.3390/min13050641 . Agbenin JO. The Environmental Chemistry of Soils: Principles and Applications. University Press, Ibadan 2020. Krahl LL, Valadares LF, SousaSilva JC, Marchi G, Martins É de S. Increase in cation exchange capacity by the action of maize rhizosphere on Mg or Fe biotite-rich rocks. Pesq Agropec Trop Goiânia 2022;52. DOI: 10.1590/1983-40632022v5272376 . Song M, Pedruzzi I, Peng Y, Li P, Liu J, Yu J. K-Extraction from muscovite by the isolated fungi. Geomicrobiol J 2015;1–9. DOI: 10.1080/01490451.2014.985409 . Bartz M, Peña J, Grand S, King GE. Potential impacts of chemical weathering on feldspar luminescence dating properties. Geochronology 2023;5:51–64. DOI: 10.5194/gchron-5-51-2023 . Pokrovsky OS, Golubev SV, Jordan G. Effect of organic and inorganic ligands on calcite and magnesite dissolution rates at 60°C and 30 atm pCO2. Chem Geol 2009;265(1–2):0–43. DOI: 10.1016/j.chemgeo.2008.11.011 . Huang, P.M. Chemistry of Soil Potassium. In Chemical Processes in Soils. Book Series No. 8, Soil Science Society of America, Madison, Wisconsin 2005; pp 227–292. Additional Declarations No competing interests reported. Cite Share Download PDF Status: Under Review Version 1 posted Editorial decision: Revision requested 13 Mar, 2025 Editor assigned by journal 13 Mar, 2025 Submission checks completed at journal 04 Mar, 2025 First submitted to journal 08 Feb, 2025 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. Our growing team is made up of researchers and industry professionals working together to solve the most critical problems facing scientific publishing. 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-5987694","acceptedTermsAndConditions":true,"allowDirectSubmit":false,"archivedVersions":[],"articleType":"Research Article","associatedPublications":[],"authors":[{"id":423903109,"identity":"d4db9908-ab66-4f0f-9a47-3b1a63e5d425","order_by":0,"name":"Ayodeji Sunday Awoniyi","email":"","orcid":"","institution":"Federal University Oye Ekiti","correspondingAuthor":false,"prefix":"","firstName":"Ayodeji","middleName":"Sunday","lastName":"Awoniyi","suffix":""},{"id":423903110,"identity":"51990603-38f6-4be9-ba2b-c6c9dc521d9a","order_by":1,"name":"Adebayo Jonathan Adeyemo","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAAA/klEQVRIiWNgGAWjYFCCAwwSYJq98QFMgFgtPIcNIKoJa2GAapFIJlILf+Phhzc+ttlE80s+ZpP+UMMgx3cjge3hF3w2HDhmbDmzLS135uxkNiCHwVjyRgK7sQxerxwwk+ZtO5y74Xb+MYkDbAyJG4C2SEvg0SF/4Pg36b9t/3M33DwMtOUfQz1BLQYHzphJM7YdyN1wg5lN4mAbQ4IBUIvkBzxaDA+cKbbsOZecO7MnmdnibJ+E4cwzD9uk8XlF7sbxjTd+lNnl9rMfZrxR8c1Gnu948jHJH/j0SBxgYGBkQ3CBmLGBmQefFv4GIPEHTZARry2jYBSMglEw0gAAOzFXnCXGW7EAAAAASUVORK5CYII=","orcid":"","institution":"Federal University of Technology","correspondingAuthor":true,"prefix":"","firstName":"Adebayo","middleName":"Jonathan","lastName":"Adeyemo","suffix":""},{"id":423903111,"identity":"e8d7feb3-d90c-4b41-a076-5da224bd1850","order_by":2,"name":"John Okhienaiye Agbenin","email":"","orcid":"","institution":"Federal University Oye Ekiti","correspondingAuthor":false,"prefix":"","firstName":"John","middleName":"Okhienaiye","lastName":"Agbenin","suffix":""},{"id":423903112,"identity":"081bb2fb-ee7c-42ba-a573-547cff3961ac","order_by":3,"name":"Augustus Oludotun Ilori","email":"","orcid":"","institution":"Federal University Oye Ekiti","correspondingAuthor":false,"prefix":"","firstName":"Augustus","middleName":"Oludotun","lastName":"Ilori","suffix":""},{"id":423903113,"identity":"7ab92e50-36fc-4f91-bb50-79f198fe9928","order_by":4,"name":"Dener Márcio da Silva Oliveira","email":"","orcid":"","institution":"Federal University of Vicosa, Minas Gerais","correspondingAuthor":false,"prefix":"","firstName":"Dener","middleName":"Márcio da Silva","lastName":"Oliveira","suffix":""},{"id":423903114,"identity":"2f0d70a7-882b-4698-955b-59c90643e2c9","order_by":5,"name":"Diego Antonio França de Freitas","email":"","orcid":"","institution":"Federal University of Vicosa, Minas Gerais","correspondingAuthor":false,"prefix":"","firstName":"Diego","middleName":"Antonio França","lastName":"de Freitas","suffix":""}],"badges":[],"createdAt":"2025-02-08 12:23:15","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-5987694/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-5987694/v1","draftVersion":[],"editorialEvents":[],"editorialNote":"","failedWorkflow":false,"files":[{"id":77912911,"identity":"e2931508-ac28-43f0-be28-d481317a6a03","added_by":"auto","created_at":"2025-03-06 18:24:36","extension":"jpg","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":189774,"visible":true,"origin":"","legend":"\u003cp\u003eThe Hydrogen ion, H\u003csup\u003e+ \u003c/sup\u003eactivities and the two ligands, oxalate, HC\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e\u003csup\u003e-\u003c/sup\u003e and citrate, H\u003csub\u003e7\u003c/sub\u003eC\u003csub\u003e6\u003c/sub\u003eO\u003csub\u003e7\u003c/sub\u003e\u003csup\u003e-\u003c/sup\u003e determined from the first dissociation constants of oxalic and citric acids at varying acid concentrations.\u003c/p\u003e","description":"","filename":"Picture1.jpg","url":"https://assets-eu.researchsquare.com/files/rs-5987694/v1/b2c81991d4b414d5eeaba5e9.jpg"},{"id":77912938,"identity":"c006d4d3-a658-45e2-9a48-622b42428a96","added_by":"auto","created_at":"2025-03-06 18:24:53","extension":"jpg","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":128279,"visible":true,"origin":"","legend":"\u003cp\u003eThe X-ray diffractogram of the mica-biotite-bearing mineral residues from a quarry site in Oye –Ekiti, Nigeria.\u003c/p\u003e","description":"","filename":"Picture2.jpg","url":"https://assets-eu.researchsquare.com/files/rs-5987694/v1/6dd9f601b241077ad169b622.jpg"},{"id":77913084,"identity":"e09aa277-e5e2-40b1-b7bc-bf28cdfbfd88","added_by":"auto","created_at":"2025-03-06 18:32:36","extension":"jpg","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":100148,"visible":true,"origin":"","legend":"\u003cp\u003eThe X-ray diffractogram of the mica-muscovite-bearing mineral residues from a quarry site in Oye Ekiti, Nigeria\u003c/p\u003e","description":"","filename":"Picture3.jpg","url":"https://assets-eu.researchsquare.com/files/rs-5987694/v1/aa293350b13d794b702509e6.jpg"},{"id":77912914,"identity":"b156c648-9a3f-467a-a0b7-78dbd64f6203","added_by":"auto","created_at":"2025-03-06 18:24:36","extension":"jpg","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":131088,"visible":true,"origin":"","legend":"\u003cp\u003eThe concentration of K dissolved from K-bearing minerals in oxalic acid, H\u003csub\u003e2\u003c/sub\u003eC\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e, of varying concentrations.\u003c/p\u003e","description":"","filename":"Picture4.jpg","url":"https://assets-eu.researchsquare.com/files/rs-5987694/v1/79c0c636517a50458ab0580b.jpg"},{"id":77913086,"identity":"53a611aa-9aa9-4c9c-af38-425c66b092a2","added_by":"auto","created_at":"2025-03-06 18:32:36","extension":"jpg","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":135646,"visible":true,"origin":"","legend":"\u003cp\u003eThe concentration of K dissolved from three K-bearing minerals in citric acid, H\u003csub\u003e8\u003c/sub\u003eC\u003csub\u003e6\u003c/sub\u003eO\u003csub\u003e7\u003c/sub\u003e, of varying concentrations.\u003c/p\u003e","description":"","filename":"Picture5.jpg","url":"https://assets-eu.researchsquare.com/files/rs-5987694/v1/734333a258fec4ac4cb49187.jpg"},{"id":77913658,"identity":"d89c8941-a398-4b2c-9a03-df33cf3e2f6e","added_by":"auto","created_at":"2025-03-06 18:40:36","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":1620297,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-5987694/v1/f4d2dbfc-64f9-4ca3-b4f4-b11d5ff0e36f.pdf"}],"financialInterests":"No competing interests reported.","formattedTitle":"Time-Dependent Dissolution of Potassium from K-Bearing Mineral Residues in Organic Acids","fulltext":[{"header":"1.0 Introduction","content":"\u003cp\u003ePotassium (K) is an essential macronutrient for plant growth, playing a crucial role in various physiological and biochemical processes. It is involved in enzyme activation, photosynthesis, osmoregulation, and nutrient transport, all of which are critical for maintaining plant health and productivity [\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e]. Unlike nitrogen and phosphorus, potassium does not form part of the structural components of plants. However, it is pivotal in regulating water usage efficiency and enhancing resistance to abiotic stress, such as drought and salinity [\u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e, \u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e, \u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e4\u003c/span\u003e]. In soils, potassium exists in various forms, including soluble, exchangeable, and fixed or non-exchangeable forms, the latter of which is mainly associated with K-bearing minerals such as feldspars and micas [\u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e, \u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e]). The release of potassium from these minerals through weathering processes is often insufficient to meet the demands of intensive cropping systems, especially in tropical and subtropical regions, where rapid weathering and leaching can deplete available K [\u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e7\u003c/span\u003e, \u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eThe increasing reliance on synthetic K fertilizers poses economic and environmental challenges. Thus, alternative strategies, such as utilizing natural K-bearing minerals and enhancing their dissolution using organic acids, are being explored to improve soil fertility sustainably [\u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e, \u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e, \u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e]. Organic acids, such as oxalic and citric acids, produced by plant roots and soil microbes, play a significant role in solubilizing potassium by chelating metal cations and disrupting mineral lattices, thereby increasing K availability in the soil solution [\u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e12\u003c/span\u003e, \u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e, \u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eK-bearing minerals, such as feldspars, biotite, muscovite, and K-feldspar, play a significant role as natural K sources in soils. These minerals account for most of the non-exchangeable K pool, which serves as a long-term nutrient reservoir, especially in tropical and subtropical regions where soils are highly weathered. The slow-release nature of K from these minerals is essential for maintaining soil fertility and crop productivity over time [\u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e14\u003c/span\u003e, \u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e15\u003c/span\u003e, \u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e]. Chemically, K-bearing minerals consist of K incorporated into their crystalline structures. Micas, for instance, have K in interlayer spaces, which makes them relatively more accessible during weathering [\u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e16\u003c/span\u003e, \u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e17\u003c/span\u003e, \u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e18\u003c/span\u003e]. In contrast, feldspars hold K within their tetrahedral frameworks, requiring more intensive weathering processes to release the nutrient [\u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e19\u003c/span\u003e, \u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e20\u003c/span\u003e]. The release of K from these minerals occurs through chemical, biological, and physical weathering processes. Chemical weathering involves the breakdown of the mineral structure by interactions with water, carbon dioxide, and organic acids, leading to the release of K into the soil solution. Biological weathering is driven by organic acids produced by plant roots and microorganisms, which chelate metal ions, destabilize mineral surfaces, and enhance the hydrolysis of K-bearing minerals. On the other hand, physical weathering involves the mechanical breakdown of minerals into smaller particles, increasing their surface area and facilitating chemical interactions [\u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e21\u003c/span\u003e, \u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e22\u003c/span\u003e]. In agriculture, K-bearing minerals serve as sustainable alternatives to synthetic K fertilizers. They provide a natural, slow-release source of K, which is particularly valuable in low-input farming systems. By enhancing the dissolution of these minerals through organic acid amendments or promoting microbial activity, farmers can improve the bioavailability of K, ensuring long-term soil fertility and reducing reliance on chemical fertilizers [\u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e23\u003c/span\u003e, \u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e24\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eOrganic acids, such as oxalic and citric acids, are crucial in enhancing nutrient dissolution from soil minerals, particularly K and other essential nutrients bound within mineral matrices. These low-molecular-weight organic acids, commonly exuded by plant roots and soil microorganisms, act as natural chelating agents and significantly influence the chemical processes that release nutrients into the soil solution [\u003cspan citationid=\"CR25\" class=\"CitationRef\"\u003e25\u003c/span\u003e]. Oxalic and citric acids enhance nutrient dissolution through multiple mechanisms. One of the primary mechanisms is their ability to lower the pH of the soil microenvironment. This acidification destabilizes mineral surfaces, releasing cations like K, Ca, Mg, and Fe from mineral structures [\u003cspan citationid=\"CR26\" class=\"CitationRef\"\u003e26\u003c/span\u003e, \u003cspan citationid=\"CR27\" class=\"CitationRef\"\u003e27\u003c/span\u003e]. Additionally, these acids form soluble complexes with metal ions, a process known as chelation, which further drives the dissolution of minerals by removing reaction products from the surface and enhancing the solubility of otherwise insoluble compounds [\u003cspan citationid=\"CR28\" class=\"CitationRef\"\u003e28\u003c/span\u003e]. Oxalic acid, due to its strong chelating ability and high acidity, is particularly effective in breaking down silicate minerals such as feldspars and micas. It promotes K release by displacing it from interlayer and framework positions within the mineral structure. Similarly, citric acid enhances nutrient dissolution with slightly different dynamics, often showing a more gradual but sustained effect than oxalic acid. The carboxyl groups in citric acid interact with mineral surfaces, facilitating the desorption and release of nutrients into the soil solution [\u003cspan citationid=\"CR29\" class=\"CitationRef\"\u003e29\u003c/span\u003e, \u003cspan citationid=\"CR30\" class=\"CitationRef\"\u003e30\u003c/span\u003e]. The effectiveness of these organic acids is influenced by their concentration, the nature of the minerals involved, and the duration of their interaction. For instance, higher concentrations of oxalic and citric acids result in greater dissolution rates, although diminishing returns may occur at very high concentrations [\u003cspan citationid=\"CR31\" class=\"CitationRef\"\u003e31\u003c/span\u003e, \u003cspan citationid=\"CR32\" class=\"CitationRef\"\u003e32\u003c/span\u003e]. These acids also exhibit differential effects on various minerals, with oxalic acid generally outperforming citric acid in dissolving K from silicate minerals. Therefore, evaluating the time-dependent dissolution of K in the presence of these organic acids provides valuable insights into their effectiveness and mechanisms in nutrient cycling, which is critical for developing sustainable soil management strategies.\u003c/p\u003e"},{"header":"2.0 Materials and Methods","content":"\u003cdiv id=\"Sec3\" class=\"Section2\"\u003e\n \u003ch2\u003e2.1 Collection and preparation of K-bearing mineral residues for X-ray diffraction analysis\u003c/h2\u003e\n \u003cp\u003eThe K-bearing mineral residues for this study were collected at the Ola-Ebimi quarry site at Oye-Ekiti (7\u0026deg;48\u0026apos;55.01\u0026quot;N, 5\u0026deg;20\u0026apos;40.70\u0026quot;E) and Ijero-Ekiti (7\u0026deg;48\u0026apos;55.12\u0026quot;N, 5\u0026deg;04\u0026apos;56.53\u0026quot;E) in Ekiti State. The places were chosen because of the large volume of rocks extracted and processed, producing considerable residues. These residues have created an environmental problem of high magnitude, with areas of significant size that raise questions about their storage, management, and destination. In this sense, rock residue for agricultural purposes has been studied for possible recycling since it does not provide potential contamination to soil, water, and plants [\u003cspan class=\"CitationRef\"\u003e8\u003c/span\u003e, \u003cspan class=\"CitationRef\"\u003e33\u003c/span\u003e]. For this research, three representative samples of each K-bearing mineral residue were collected with a hammer and a chisel. The K-bearing residues were identified and labelled using the observable physical features. The K-bearing mineral residues were pulverized using a ballpoint mill into very fine powdery form. The pulverized samples were characterized with X-ray diffraction (Angstrom ADX2700, USA). The samples were filled inside the sample handler and placed in the diffraction chamber. The following XRD analysis parameters were employed: a graphite-monochromatic Cu radiation source at 40 kV and 30 mA was used with a step size of 0.2 and a scan speed of 1.0 sec. The diffraction intensities were noted in the 2\u0026theta;\u0026thinsp;=\u0026thinsp;5 \u003csup\u003eo\u003c/sup\u003e \u0026mdash;70 \u003csup\u003eo\u003c/sup\u003e range. The experiment was carried out in the Chemical Analysis Laboratory, Department of Soil Science, Faculty of Agricultural Sciences, Federal University Oye Ekiti, Ekiti State, while the x-ray was carried out at the Central Laboratory, the Federal University of Agriculture, Abeokuta, Ogun State, Nigeria. It was a randomized block design in 2 \u0026times; 3 \u0026times; 4 factorial experiments consisting of 24 treatments and three replications. The studied factors were two organic acids-oxalic acid (C\u003csub\u003e2\u003c/sub\u003eH\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e) and citric acid (C\u003csub\u003e6\u003c/sub\u003eH\u003csub\u003e8\u003c/sub\u003eO\u003csub\u003e7\u003c/sub\u003e), both P.A. reagents, three K-bearing mineral residues: biotite-mica, muscovite-mica and K-feldspar; and four rates of organic acids: 0.5, 1.0, 5.0 and 10 mmol L-1, established based on the values found in the literature [\u003cspan class=\"CitationRef\"\u003e34\u003c/span\u003e, \u003cspan class=\"CitationRef\"\u003e35\u003c/span\u003e, \u003cspan class=\"CitationRef\"\u003e36\u003c/span\u003e].\u003c/p\u003e\n\u003c/div\u003e\n\u003cdiv id=\"Sec4\" class=\"Section2\"\u003e\n \u003ch2\u003e2.2 Determination of total K concentration in the K-bearing mineral residues\u003c/h2\u003e\n \u003cp\u003eThe total K concentrations in the K-bearing residues for this study were determined by the mixed acid digestion method described by Agbenin [\u003cspan class=\"CitationRef\"\u003e37\u003c/span\u003e]. Briefly, 0.5 g of the pulverized mineral was weighed into a digestion tube, to which 1 mL of concentrated HClO\u003csub\u003e4\u003c/sub\u003e, 5 mL of concentrated HNO\u003csub\u003e3\u003c/sub\u003e acid, and 0.5 mL of concentrated H\u003csub\u003e2\u003c/sub\u003eSO\u003csub\u003e4\u003c/sub\u003e were added and slowly digested. Moderate heat was gradually increased for 10\u0026ndash;15 minutes until white fumes appeared. The tube was then set aside to cool down and diluted to 40 ml. This was filtered through a Whatman No. 44 filter paper into a 50-ml flask and then made up to the 50-ml mark. The total K concentration in the filtrate was determined using a Flame Photometer (Model FP640, China).\u003c/p\u003e\n\u003c/div\u003e\n\u003cdiv id=\"Sec5\" class=\"Section2\"\u003e\n \u003ch2\u003e2.3 Dissolution of K-bearing minerals and their residues in oxalic and citric acids\u003c/h2\u003e\n \u003cp\u003eThe release of K from the K-bearing minerals was determined in two organic acids, namely oxalic and citric acids. The organic acids\u0026apos; equivalent concentrations ranged from 5 x 10\u003csup\u003e\u0026minus;\u0026thinsp;4\u003c/sup\u003e to 1 x 10\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e mol of the two prepared acids. The pH of the different acid concentrations was determined using a portable pH meter (Phoenix pH instrument EC-26, Italy). The measurements of the pH of the various concentrations of the organic acids were performed to determine the H\u003csup\u003e+\u003c/sup\u003e ion concentration, and the oxalate and citrate concentrations in the solution, assuming the first ionization of the two organic acids occurred according to the following reactions:\u003c/p\u003e\n \u003cp\u003e\u003cimg 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\"\u003e\u003c/p\u003e\n \u003cp\u003eGiven the pH of the solutions and the respective \u003cem\u003ek\u003c/em\u003ea1 of the oxalic and citric acid solutions, the (HC2O\u003csup\u003e\u0026minus;\u003c/sup\u003e) and (H7C6O\u003csup\u003e\u0026minus;\u003c/sup\u003e) were calculated for the varying concentrations of the two acids. For the mineral residues, Approximately 0.5 g of the pulverized K-bearing mineral was measured into a 100-mL volumetric flask and 20 mL of oxalic acid with varying concentrations ranging from 5 x 10\u003csup\u003e\u0026minus;\u0026thinsp;4\u003c/sup\u003e to 1 x 10\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e mol L\u003csup\u003e-1\u003c/sup\u003e was added and replicated three times. The flask was placed in a mechanical shaker. The suspension was shaken for between 30 minutes and four hours. The suspension was filtered into a sample bottle through a Whatman No. 1 filter paper. The above procedure was also repeated for citric acid with varying concentrations. The concentrations of K in the filtrates were determined using a Flame Photometer (Model FP640, China).\u003c/p\u003e\n\u003c/div\u003e\n\u003cdiv id=\"Sec6\" class=\"Section2\"\u003e\n \u003ch2\u003e2.4 Statistical analysis\u003c/h2\u003e\n \u003cp\u003eData collected were analyzed using the general linear model of Minitab 17.0 edition. The obtained data were tested for the significance of differences in K release by the two acids among the three k-bearing minerals. The results were summarized in tables and graphs. Tukey HSD is the statistical post hoc method used to confirm the significance of the means obtained at a 5% probability or confidence level. All the treatment means, and standard errors were computed before putting up the graphs and were made via Microsoft Excel 2007.\u003c/p\u003e\n\u003c/div\u003e"},{"header":"3.0 Results","content":"\u003cdiv id=\"Sec8\" class=\"Section2\"\u003e \u003ch2\u003e3.1 Hydrogen ion and ligand concentrations in the organic acid solutions\u003c/h2\u003e \u003cp\u003eBased on the first ionization constants of the two organic acids, the hydrogen ion, H\u003csup\u003e+\u003c/sup\u003e, activities in the two organic acid solutions increased with the increasing concentrations of the two organic acid solutions (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e). In the oxalic acid solution, H\u003csup\u003e+\u003c/sup\u003e activities increased linearly with increasing concentration in contrast to the citric acid solution with a fairly gentle increase in H\u003csup\u003e+\u003c/sup\u003e activities. The H\u003csup\u003e+\u003c/sup\u003e activities were consistently more significant in the oxalic acid solution than in a citric acid solution at the different concentrations following the measured pH of the two organic acid solutions. The pH decreased from 3.4 at 0.5 mmol to 2.4 at 10 mmol of the oxalic solution, whereas pH decreased from 3.6 at 0.5 mmol to 2.9 at 10 mmol of the citric acid solution. Similarly, the activities of the two ligands, namely the oxalate, HC2O\u003csup\u003e\u0026minus;\u003c/sup\u003e, and citrate, C6H7O\u003csup\u003e\u0026minus;\u003c/sup\u003e, increased with increasing concentrations of the two organic acid solutions (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e). The activities of HC2O\u003csup\u003e\u0026minus;\u003c/sup\u003e increased exponentially by increasing the oxalic acid concentration from 1.0 mmol L\u003csup\u003e-1\u003c/sup\u003e to 5 mmol L\u003csup\u003e-1\u003c/sup\u003e but flattened out when the concentration of the oxalic acid solution was raised from 5 to 10 mmol L\u003csup\u003e-1\u003c/sup\u003e (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e), probably attaining its buffer range at this concentration. Consistent with the H\u003csup\u003e+\u003c/sup\u003e activities with the increasing concentration of the citric acid solution, the C6H7O\u003csup\u003e\u0026minus;\u003c/sup\u003e activities increased gently with increasing concentration of the citric acid. At any given concentration of the two organic acid solutions, HC2O\u003csup\u003e\u0026minus;\u003c/sup\u003e activities were more significant than the C6H7O\u003csup\u003e\u0026minus;\u003c/sup\u003e activities, consistent with the dissociation constants of oxalic acid (\u003cem\u003ek\u003c/em\u003ea1\u0026thinsp;=\u0026thinsp;6.5 x10\u003csup\u003e\u0026minus;2\u003c/sup\u003e) and citric acid (\u003cem\u003ek\u003c/em\u003ea1\u0026thinsp;=\u0026thinsp;8.4 x 10\u003csup\u003e\u0026minus;4\u003c/sup\u003e).\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec9\" class=\"Section2\"\u003e \u003ch2\u003e3.2 Characterization of the K-bearing residues by X-ray Diffraction\u003c/h2\u003e \u003cp\u003ePowder x-ray diffraction indicated characteristic first-order diffraction peaks at 1.01 nm and third-order between 0.331 and 0.335 nm, indicative of micaceous minerals in the K-bearing mineral residues (Figs.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e and \u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e). Physical characteristics of the mineral residues from the quarry sites, assessed visually, suggest the presence of biotite-mica and muscovite-mica contained in the K-rich mineral residues from one quarry site, while the other K-rich mineral residue from the second quarry site contained K-feldspar.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec10\" class=\"Section2\"\u003e \u003ch2\u003e3.3 Total K concentration and dissolution in organic acids of varying concentrations\u003c/h2\u003e \u003cp\u003eThe total K concentration of the three K-bearing minerals ranged from 1.6 to 1.8% K or 1.93 to 2.16% K2O. The muscovite-mica had the highest K concentration of 2.16% K2O, followed by K- feldspar at 2.04% K2O, while the biotite-mica contained 1.93% K2O. The dissolution of K-bearing minerals (biotite-mica, muscovite-mica and K-feldspar) in oxalic acid showed significant differences in the amount of K released upon dissolution with varying concentrations of oxalic acid. As the concentrations of oxalic acid increased, there was an increasing amount of K released from the K-bearing minerals with a tendency toward equilibrium attainment at 5 mmol L\u003csup\u003e-1\u003c/sup\u003e of the acid solution (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003e). The differences in the amounts of K released by the biotite-mica were generally significant between the concentrations. For instance, increasing the concentration of the oxalic acid from 0.5 mmol 1\u003csup\u003e\u0026ndash;1\u003c/sup\u003e to 5.0 mmol l\u003csup\u003e-1\u003c/sup\u003e increased K released by biotite-mica from 800 mg kg\u003csup\u003e-1\u003c/sup\u003e to 1600 mg kg\u003csup\u003e-1\u003c/sup\u003e, whereas increasing the acid concentration from 5 to 10 mmol l\u003csup\u003e-1\u003c/sup\u003e only gently or slightly increased the amounts released by the minerals. A distinctive feature of the dissolution of K from the biotite-mica, muscovite-mica and K-feldspar is that biotite-mica released more significant amounts of K than muscovite-mica and K-feldspar (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003e). The order of K dissolution in the oxalic acid of varying concentration was biotite-mica\u0026thinsp;\u0026gt;\u0026thinsp;muscovite-mica\u0026thinsp;\u0026gt;\u0026thinsp;K-feldspar (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003e). The percentage of K release from the total K concentration in the biotite-mica ranged from 5.0% at 0.5 mmol to 10% at 10 mmol concentration of oxalic acid, muscovite mica from 3\u0026ndash;7% and K- feldspar from 2\u0026ndash;6% of the total K composition of the minerals (Table\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e). Among the three minerals dissolved in oxalic acid in this study, biotite-mica had the highest percentage of K dissolution. The dissolution of K in biotite-mica, muscovite-mica and K-feldspar by citric acid showed increasing amounts of K released with increasing concentrations of the acid (Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003e). There was a steep increase in the amounts of K released into the citric acid solution by the K-bearing minerals from 0.5 to 1.0 mmol concentration of the acid. However, from 1.0 to 10 mmol of the acid concentration, the amounts of K released increased linearly with increasing concentration but with a much gentler slope than the K dissolution at 0.5 and 1.0 mmol L\u003csup\u003e-1\u003c/sup\u003e of the acid concentration. In contrast to the dissolution of the K-bearing minerals in oxalic acid, there were no distinct and significant differences in the amounts of K released between the K-bearing minerals in the citric acid solution concentration\u0026thinsp;\u0026le;\u0026thinsp;5.0 mmol. However, at concentrations\u0026thinsp;\u0026gt;\u0026thinsp;5.0 mmol, more K was dissolved in muscovite mica than in biotite-mica and K-feldspar. The K-dissolution pattern in the citric acid at a concentration greater than 5.0 mmol L\u003csup\u003e-1\u003c/sup\u003e was biotite-mica\u0026thinsp;\u0026gt;\u0026thinsp;muscovite-mica\u0026thinsp;\u0026gt;\u0026thinsp;K-feldspar (Table\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e). A higher percentage of total K was dissolved from K-feldspar in all the concentrations of citric acids (3.1\u0026ndash;7.5%) than in oxalic acid (2.4\u0026ndash;6.2%) (Table\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e). However, the biotite-mica appeared more soluble in citric acid than muscovite-mica and K-feldspar, consistent with the dissolution in oxalic acid. The percentage of total K dissolved from biotite-mica in the citric acid solutions ranged from 4.9% at 0.5 mmol to 7.6% at 10 mmol, almost similar to the trend of dissolution in oxalic acid.\u003c/p\u003e \u003cp\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\u003eThe total K concentrations, range, and mean of soluble K, including the percentages of soluble to total K concentration in the K-bearing minerals in two organic acids of varying concentrations.\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"7\"\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 \u003cdiv align=\"left\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c5\" colnum=\"5\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c6\" colnum=\"6\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c7\" colnum=\"7\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e \u003cp\u003eK-bearing\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003eOrganic\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003eTotal K conc.\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c4\"\u003e \u003cp\u003eDissolved K Range\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c5\"\u003e \u003cp\u003eMean\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colspan=\"2\" nameend=\"c7\" namest=\"c6\"\u003e \u003cp\u003ePercent solubility Rangemean\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003emineral\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eacid\u003csup\u003e1\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colspan=\"3\" nameend=\"c5\" namest=\"c3\"\u003e \u003cp\u003e---------------- mg kg\u003csup\u003e-1\u003c/sup\u003e------------------\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colspan=\"2\" nameend=\"c7\" namest=\"c6\"\u003e \u003cp\u003e--------- % ---------\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eBiotite-mica\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e\u003cb\u003eOxalic\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e16.1\u003csup\u003eb\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e0.8\u0026ndash;1.7\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e1.3\u003csup\u003ea\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e5\u0026ndash;10\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e7.9\u003csup\u003ea\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eMuscovite-mica\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e17.6\u003csup\u003ea\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e0.6\u0026ndash;1.3\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e0.9\u003csup\u003ea\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e3.1\u0026ndash;7.4\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e5.0\u003csup\u003eb\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eK-feldspar\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e17.2\u003csup\u003ea\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e0.4\u0026ndash;1.1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e0.7\u003csup\u003ea\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e2.4\u0026ndash;6.2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e4.1\u003csup\u003eb\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eBiotite-mica\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e\u003cb\u003eCitric\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e16.1\u003csup\u003eb\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e0.8\u0026ndash;1.2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e1.0\u003csup\u003ea\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e4.9\u0026ndash;7.6\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e6.0\u003csup\u003ea\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eMuscovite-mica\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e17.6\u003csup\u003ea\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e0.5\u0026ndash;1.4\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e0.8\u003csup\u003eb\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e2.6\u0026ndash;7.7\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e4.7\u003csup\u003eb\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eK-feldspar\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e17.2\u003csup\u003ea\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e0.5\u0026ndash;1.3\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e1.0\u003csup\u003ea\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e3.1\u0026ndash;7.5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e5.8\u003csup\u003ea\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\u003cp\u003e\u003csup\u003e1\u003c/sup\u003eThe\u0026nbsp;concentration\u0026nbsp;range\u0026nbsp;of\u0026nbsp;the\u0026nbsp;oxalic\u0026nbsp;and\u0026nbsp;citric\u0026nbsp;acid\u0026nbsp;solutions\u0026nbsp;is\u0026nbsp;0.5\u0026nbsp;\u0026ndash;\u0026nbsp;10 mmol.\u003c/p\u003e\n\u003cp\u003eAccording to Tukey\u0026apos;s test, the same letters in superscript on a column for the same parameter are not different from one another (P \u0026lt; 0.05).\u003c/p\u003e \u003c/div\u003e"},{"header":"4.0 Discussion","content":"\u003cdiv id=\"Sec12\" class=\"Section2\"\u003e \u003ch2\u003e4.1 Characterization and K concentration of the K-bearing mineral residues\u003c/h2\u003e \u003cp\u003eThe K-bearing residues used for this study contained less than 3% K2O, but the concentration is sufficient to meet crop nutrition if the residues could release K at a rate that meets crop requirements. X-ray diffraction of the K-bearing residues showed diffraction peaks at 1.01 nm (Figs.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e and \u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e), characteristic of micaceous minerals [\u003cspan citationid=\"CR38\" class=\"CitationRef\"\u003e38\u003c/span\u003e], confirming visual observations of muscovite and biotite minerals in the mineral residues. However, the total concentrations of K in the mineral residues were almost five times lower than the concentration of K2O in a pure specimen of muscovite or biotite, which ranges from 10 to 12% [\u003cspan citationid=\"CR39\" class=\"CitationRef\"\u003e39\u003c/span\u003e].\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec13\" class=\"Section2\"\u003e \u003ch2\u003e4.2 Dissolution of K-bearing mineral residues in oxalic and citric acids\u003c/h2\u003e \u003cp\u003eOrganic acids facilitate the weathering of minerals and rocks by forming metal-organic complexes. Potassium-bearing minerals exposed to varying concentrations of organic acids release different concentrations of K that vary with concentrations of the organic acids. The varying amount of K released from the three K-bearing minerals examined in this study conformed to this prediction and further substantiated the report of Bilias \u0026amp; Barbayiannis [\u003cspan citationid=\"CR40\" class=\"CitationRef\"\u003e40\u003c/span\u003e], who observed increasing dissolution of K with increasing concentration of oxalic acid from 0 to 400 mmol L\u003csup\u003e\u003cem\u003e\u0026minus;\u003c/em\u003e\u0026thinsp;1\u003c/sup\u003e from K- bearing minerals. The highest K concentration was dissolved in the 0.01N organic acid concentration. Higher K release continued to increase with time, even after 4 hours of continuous agitation, suggesting that the K-bearing mineral wastes collected at these quarry sites can release K for some time to satisfy the nutrition of crop plants. Long-term K release is generally observed with specimen K-bearing minerals [\u003cspan citationid=\"CR41\" class=\"CitationRef\"\u003e41\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eAmong the principal K-bearing minerals, K-feldspars or microcline released less K in the two organic acids, probably because of the initially low K concentration in the residue. The sequence of K dissolved in oxalic acid was mica-biotite\u0026thinsp;\u0026gt;\u0026thinsp;mica-muscovite\u0026thinsp;\u0026gt;\u0026thinsp;K feldspar, which agrees with the report by Richardson et al. [\u003cspan citationid=\"CR42\" class=\"CitationRef\"\u003e42\u003c/span\u003e]. However, the sequence of K release into the citric acid solution followed the order mica-muscovite\u0026thinsp;\u0026gt;\u0026thinsp;K feldspar\u0026thinsp;\u0026gt;\u0026thinsp;mica-biotite in citric acid. The comparison between K released by the organic acids shows that oxalic acid dissolved more K from mica-biotite than from citric acid, regardless of the organic acid concentrations, consistent with the report by Duarte \u003cem\u003eet al\u003c/em\u003e. [\u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e]. Citric acid dissolved more K from the mica-muscovite and K- feldspar than oxalic acid.\u003c/p\u003e \u003cp\u003eTwo mechanisms are operational in the dissolution of K from K-bearing minerals by polyfunctional organic acids such as oxalic and citric acids, examined in this study by Lin et al. [\u003cspan citationid=\"CR31\" class=\"CitationRef\"\u003e31\u003c/span\u003e]. One mechanism involved the proton attack or exchange with K in the mineral structure; this proton promoted the dissolution of K from the K-bearing minerals. Figure\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e shows that the concentration of H\u003csup\u003e+\u003c/sup\u003e dissociated from the oxalic acid far exceeded the H\u003csup\u003e+\u003c/sup\u003e elaborated from the citric acid, hence the tendency for more outstanding K release from the K-bearing minerals in oxalic than citric acid. Proton attack of minerals via cation exchange in soil minerals remains a potent mechanism of weathering rocks and minerals in soils [\u003cspan citationid=\"CR43\" class=\"CitationRef\"\u003e43\u003c/span\u003e, \u003cspan citationid=\"CR44\" class=\"CitationRef\"\u003e44\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eThe second mechanism of K dissolution from K-bearing minerals in polyfunctional organic acids is the ligand-promoted dissolution of minerals, especially when pH increases or acidity decreases [\u003cspan citationid=\"CR45\" class=\"CitationRef\"\u003e45\u003c/span\u003e]. This mechanism may be more important than the proton or H+-promoted dissolution of minerals in soils. For instance, ligand-promoted dissolution was reportedly more effective than proton-promoted dissolution of plagioclase or Ca-feldspar [\u003cspan citationid=\"CR46\" class=\"CitationRef\"\u003e46\u003c/span\u003e]. The oxalic acid dissolving more K from the mica-biotite than citric acid would imply that proton-promoted dissolution of K was the predominant mechanism of K release compared to ligand-promoted K-dissolution. On the other hand, citric acid dissolved more K in K- feldspar or microcline than oxalic acid, probably indicating the dominance of ligand-promoted dissolution of K from K-feldspar over proton-promoted dissolution. However, there was no apparent difference in K dissolved from mica-muscovite in the oxalic acid (5% of total K) and citric acid (4.7% of total K). The average total K solubilized by citric acid as a percent of total K in the K-bearing minerals, which is 4.7%, agrees fairly well with 4.3% of the total K dissolved from a K-bearing rock residue studied by Machado \u003cem\u003eet al\u003c/em\u003e. [\u003cspan citationid=\"CR39\" class=\"CitationRef\"\u003e39\u003c/span\u003e]. in Brazil. The slight difference can be attributed to the stoichiometric differences in the K-bearing residue and the complexing ability of oxalate and citrate for K and the release of other cations such as Al, Fe, Mg and Si from the K-feldspar [\u003cspan citationid=\"CR46\" class=\"CitationRef\"\u003e46\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eThe effect of oxalic and citric acids on the release of mineral K in K-bearing minerals is because of the dissociated H\u003csup\u003e+\u003c/sup\u003e ions and complexing organic ligands, oxalate and citrate, respectively, in the organic acid solution [\u003cspan citationid=\"CR47\" class=\"CitationRef\"\u003e47\u003c/span\u003e]. The varying amounts of K dissociated from the K-bearing minerals are a consequence of the differences in the amounts of ligands and hydrogen ions concentrations generated by the two polyfunctional organic acids [\u003cspan citationid=\"CR48\" class=\"CitationRef\"\u003e48\u003c/span\u003e] and in the complexation capacity of the ligands (Figs.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e and \u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e). The marginally higher amount of K\u003csup\u003e+\u003c/sup\u003e released into oxalic acid at different intervals than citric acid accords with the reports by Lin et al. [\u003cspan citationid=\"CR31\" class=\"CitationRef\"\u003e31\u003c/span\u003e].\u003c/p\u003e \u003c/div\u003e"},{"header":"5.0 Conclusion","content":"\u003cp\u003ePotassium is a key nutrient element that several staple food crops, especially roots and tubers, require in significant quantities. The K requirements of roots and tuber crops, \u003cem\u003eDioscorea spp\u003c/em\u003e, are enormous, thus necessitating the assessment of the solubility of K from some K-bearing mineral residues, available in many quarry sites, to recapitalize soil K stocks without recourse to expensive inorganic fertilizers priced beyond the reach of poor-resourced farmers.\u003c/p\u003e \u003cp\u003eOrganic acids primarily elaborate into the soil and rhizosphere from root exudation, microbial metabolites and organic matter decomposition facilitate mineral dissolution by forming metal-organic complexes. Potassium-bearing minerals exposed to organic acids often release different concentrations of K that vary with the concentrations of the organic acids. In this study, we examined the time-dependent dissolution of K from three K-bearing mineral residues in oxalic and citric of varying concentrations ranging from 0.5 to 10 mmol. X-ray diffraction indicated that the K-minerals occurring in the K-rich residues were biotite-mica and muscovite-mica, identified by the characteristic x-ray peak between 1.0 and 1.01 nm from one quarry site at Oye-Ekiti. The third K-mineral in another K-rich residue, taken from another quarry site, was K-feldspar. The total K concentration of the three K-bearing mineral residues ranged from 1.6 to 1.8% K or 1.93 to 2.16% K2O. The muscovite-mica mineral residue had the highest K2O concentration (2.16%), followed by the K-feldspar mineral residue (2.04%) and the biotite-mica mineral residue containing 1.93% K2O.\u003c/p\u003e \u003cp\u003eThe time-dependent K dissolution trends from the K-bearing mineral residues increased with time and the increasing concentration of oxalic and citric acids, attaining a steady state at about 2\u0026ndash;3 hours with continuous agitation of the K-mineral residue suspension in the organic acids. Generally, oxalic acid dissolved a greater concentration of K than citric acid, especially for the mineral residue containing mica-biotite. The solubility of K as a percentage of the total K contained in the K-bearing mineral residues ranged from 4.1% for the K-feldspar residue to 7.9% for the mica-biotite residue in oxalic acid, whereas, in citric acid, the solubility of K ranged from 4.7% for mica-muscovite to 6% for mica-biotite. In the oxalic acid solution, the order of solubility of the K-bearing mineral residues was mica-biotite\u0026thinsp;\u0026gt;\u0026thinsp;mica-muscovite\u0026thinsp;\u0026gt;\u0026thinsp;K-feldspar. In contrast, the K- K-solubility order in the citric acid solution was mica-biotite\u0026thinsp;\u0026gt;\u0026thinsp;K-feldspar\u0026thinsp;\u0026gt;\u0026thinsp;mica-muscovite.\u003c/p\u003e \u003cp\u003ePot experiments and field trials involving the direct applications of these K-bearing mineral wastes to soils to determine their K-supplying capacities and rates to meet the K nutrition of crops are required to validate this laboratory study. Hence, this study provides the baseline information on K solubility in the K-bearing mineral residues that could have potential direct field applications to satisfy the K nutrition of field crops with high K requirements, such as yams (\u003cem\u003eDioscorea spp\u003c/em\u003e.)\u003c/p\u003e"},{"header":"Declarations","content":"\u003cp\u003e\u003cstrong\u003eData Availability\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe data that support the findings of this study are available from Dr. Adebayo Jonathan ADEYEMO but restrictions apply to the availability of these data, which were used under license for the current study, and so are not publicly available. Data are however available from the authors upon reasonable request and with permission of Dr. Adebayo Jonathan Adeyemo.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eAcknowledgements\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe author appreciates the technical assistance from the Department of Soil Science and Land Resources Management, Federal University Oye Ekiti; access provided by the two communities in Oye and Ijero in Ekiti State, Nigeria, which was fundamental to this research work; and financial support from the TETFUND/FARA/ARIFA Postdoctoral Research Fellowship tenable in Brazil. This acknowledgement\u0026nbsp;will\u0026nbsp;ensure that\u0026nbsp;all contributors and supporters are duly recognised.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eConflict of Interest\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe authors declare no conflicts of interest.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eFunding information\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThis research was supported by funds received by a fellowship from the Nigeria Tertiary Education Trust Fund and Forum for Agricultural Research in Africa (TETFUND/FARA) given to the second author for his postdoctoral research in Brazil.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eAuthors´ Contribution\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eMany people participated in this scientific report. The responsibilities were as follows: conceptualisation, JOA, AJA, ASA, and AOI; methodology, JOA and AJA and ASA; validation and formal analysis, JOA and AJA; resources, JOA and AJA; data curation, AJA, DAFF and DMSO; writing-original draft preparation, AJA and ASA; writing-review and correction, AJA and AOI; project administration, JOA and AJA; and funding acquisition, JOA AJA and ASA. All the authors have read and agreed to the published version of the manuscript.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eEthics declarations\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThis work mainly concerns time–dependent K-dissolution in the laboratory and does not involve any information on humans or animals; thus, an ethical statement does not apply to the manuscript's context.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eClinical trial number\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eNot applicable.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eConsent to Publish declaration\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eNot applicable\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eConsent to Participate declaration\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eNot applicable\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\u003cli\u003e\u003cspan\u003eJohnson R, Vishwakarma K, Hossen MS, Kumar V, Shackira AM, Puthur JT, Abdi G, Sarraf M, Hasanuzzaman M. 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Book Series No. 8, Soil Science Society of America, Madison, Wisconsin 2005; pp 227\u0026ndash;292.\u003c/span\u003e\u003c/li\u003e\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":false,"highlight":"","institution":"","isAcceptedByJournal":true,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"discover-soil","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"","sideBox":"Learn more about [Discover Soil](https://link.springer.com/journal/44378)","snPcode":"44378","submissionUrl":"https://submission.nature.com/new-submission/44378/3","title":"Discover Soil","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"stoa","reportingPortfolio":"Discover Series","inReviewEnabled":true,"inReviewRevisionsEnabled":true},"keywords":"K-dissolution, Organic acids, Soil fertility, K-bearing minerals, Mineral solubility","lastPublishedDoi":"10.21203/rs.3.rs-5987694/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-5987694/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003ch2\u003eBackground and Aims:\u003c/h2\u003e \u003cp\u003ePotassium (K)- bearing minerals are vital for soil fertility and act as slow-release reservoirs for crop productivity. Organic acids, such as oxalic and citric acids, enhance K dissolution.\u003c/p\u003e\u003ch2\u003eMethods\u003c/h2\u003e \u003cp\u003eTime-dependent experiments measured K dissolution from minerals in oxalic and citric acids. Mehlich-1 extraction and atomic absorption spectrophotometry quantified K release over intervals under controlled conditions.\u003c/p\u003e\u003ch2\u003eResults\u003c/h2\u003e \u003cp\u003eOxalic acid enhanced K release by 25% more than citric acid. For biotite-mica, increasing oxalic acid concentration from 0.5 to 5.0 mmol L⁻\u0026sup1; raised K release from 800 to 1600 mg kg⁻\u0026sup1;. During a further increase to 10 mmol L⁻\u0026sup1;, slightly improved dissolution was recorded. Percentage K release varied by mineral, biotite-mica, muscovite-mica, and K-feldspar recorded 5\u0026ndash;11%, 3\u0026ndash;7%, and 2\u0026ndash;6% respectively. Citric acid caused significant K release between 0.5 and 1.0 mmol L⁻\u0026sup1;, with increases up to 10 mmol L⁻\u0026sup1;. Above 5 mmol L⁻\u0026sup1;, muscovite-mica dissolved more K than biotite-mica and K-feldspar, with K-feldspar showing higher dissolution percentages of 3.1\u0026ndash;7.5% in citric acid than oxalic acid that recorded 2.4\u0026ndash;6.2%.\u003c/p\u003e\u003ch2\u003eConclusion\u003c/h2\u003e \u003cp\u003eOrganic acids enhance K release via chelation, destabilization of mineral surfaces, and solubility increases. Oxalic acid\u0026rsquo;s superior performance highlights its role in improving soil fertility. Also, oxalic acid outperformed citric acid in dissolving K from minerals, underscoring the importance of targeted nutrient management strategies.\u003c/p\u003e","manuscriptTitle":"Time-Dependent Dissolution of Potassium from K-Bearing Mineral Residues in Organic Acids","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2025-03-06 18:24:31","doi":"10.21203/rs.3.rs-5987694/v1","editorialEvents":[{"type":"communityComments","content":0},{"type":"decision","content":"Revision requested","date":"2025-03-13T13:08:45+00:00","index":"","fulltext":""},{"type":"editorAssigned","content":"","date":"2025-03-13T12:50:32+00:00","index":"","fulltext":""},{"type":"checksComplete","content":"","date":"2025-03-04T10:18:10+00:00","index":"","fulltext":""},{"type":"submitted","content":"Discover Soil","date":"2025-02-08T12:15:04+00:00","index":"","fulltext":""}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"discover-soil","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"","sideBox":"Learn more about [Discover Soil](https://link.springer.com/journal/44378)","snPcode":"44378","submissionUrl":"https://submission.nature.com/new-submission/44378/3","title":"Discover Soil","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"stoa","reportingPortfolio":"Discover Series","inReviewEnabled":true,"inReviewRevisionsEnabled":true}}],"origin":"","ownerIdentity":"14721a48-9d91-4181-bd0a-b71c46c12b94","owner":[],"postedDate":"March 6th, 2025","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"under-review","subjectAreas":[],"tags":[],"updatedAt":"2025-07-24T08:21:16+00:00","versionOfRecord":[],"versionCreatedAt":"2025-03-06 18:24:31","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-5987694","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-5987694","identity":"rs-5987694","version":["v1"]},"buildId":"8U1c8b4HqxoKbykW_rLl7","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}