Kaolinite suspension treatment using cellulose dissolved in sodium hydroxide as flocculant

Kaolinite suspension treatment using cellulose dissolved in sodium hydroxide as flocculant | 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 Kaolinite suspension treatment using cellulose dissolved in sodium hydroxide as flocculant Tomi Eilamo, Olli Dahl This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-6697938/v1 This work is licensed under a CC BY 4.0 License Status: Published Journal Publication published 27 Feb, 2026 Read the published version in Cellulose → Version 1 posted 4 You are reading this latest preprint version Abstract Kaolinite is clay used in various industries that forms turbid dispersions and disrupts aquatic ecosystems if not separated from process waters before discharge. Conventional coagulation chemicals, such as alum and polyacrylamides could be used to improve separation, but they contain long-term risks to human health and the environment. In this study, we show that cellulose dissolved in aqueous sodium hydroxide can be used to increase the particle size and the settling rate of kaolinite suspension. The effect is further enhanced when the cellulose solution is used together with magnesium chloride. A response surface models were made to evaluate the effect of cellulose and magnesium chloride doses on kaolin suspension turbidity after 10 minutes and after 20 hours of settling. An effective dose was determined and a 0.5 wt.% kaolinite suspension with initial turbidity of 3200 NTU was treated with 20 ppm of dissolved cellulose and 0.5 mM of magnesium chloride to achieve turbidity of 7.3 NTU after 2 minutes of settling and 4.7 NTU after 10 minutes of settling. Additionally, it was shown that the cellulose solution largely retains its ability to flocculate the kaolin suspension in saline waters at least up to 0.5 M of sodium chloride content. These results could have applications especially in industries where both kaolinite and cellulose are present, such as pulp and paper industry. kaolin coagulation/flocculation cellulose solutions sodium hydroxide Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Introduction Kaolinite is a naturally occurring inorganic clay with the chemical formula Al 2 Si 2 O 5 (OH) 4 (Bergaya and Lagaly 2006 ; Selkälä et al. 2019 ). It has a wide variety of industrial applications including coating material for paper, functional filler in paint, plastic, rubber and ink, white ceramics, and raw material in the production of fiber glass (Murray 2000 ). Kaolinite among many other clays is also found in most mine tailings. It is harmful and disruptive to aquatic ecosystems via sunlight and visibility blocking turbidity as well as smothering sedimentation (Shaikh et al. 2017 ; Wang et al. 2019 ). Kaolinite can also cause operational problems, such as transportation problems for mine tailings, and release and capture of contaminants in tailings slurry (D. Liu, Edraki, and Berry 2018a ). To mitigate the environmental and operational issues related to kaolinite use, effective solid-liquid separation should be applied to kaolinite suspensions before discharge or reuse of affected water. Coagulation and/or flocculation are common methods for removal of solids based on preventing the repulsion between suspended particles and increasing the particle size (Sahu and Chaudhari 2013 ; Lee et al. 2014 ; Dahl 2025 ). Flocculation is considered an effective method for solid-liquid separation of colloidal solutions, with additional benefits of low cost, low energy consumption and easy operation relative to alternatives (Wang et al. 2019 ). Effective flocculation leads to easier and faster separation from the liquid medium, i.e.. via settling, flotation or filtration (Lee et al. 2014 ). The most common coagulants used in removal of clay particles such as kaolinite from water are aluminum salts (Divakaran and Sivasankara Pillai 2001 ; Igwegbe et al. 2021a ). Aluminum salts are also the most common coagulants in pulp and paper industry (Sahu and Chaudhari 2013 ), which is a major source of colloidal kaolinite suspensions (Shaikh et al. 2017 ). However, they have their own challenges: aluminum forms hydroxide sludge with high metallic content and the sludge can cause contamination of soil and groundwater from landfill leachates (Reyes-López et al. 2008 ; Shaikh et al. 2018 ; Igwegbe et al. 2021b , a ; Kurusu et al. 2022 ), which in turn has a risk of detrimental effects on human health including correlation with increased risk for Alzheimer’s disease (Crapper et al. 1973 ; Chatterjee et al. 2009 ; Menkiti et al. 2011 ; Kumar et al. 2017 ; Niu 2018 ; Igwegbe et al. 2021a ). Additionally, the flocs metal salt coagulants form are often fragile, small and slow to settle (McCurdy et al. 2004 ; Shaikh et al. 2018 ; Kurusu et al. 2022 ). Because of this, polymeric flocculant is often added to facilitate floc growth and to improve the settling rate (Lee et al. 2014 ; Kurusu et al. 2022 ). The contemporary commercial flocculants are synthetic organic polymers, most commonly polyacrylamides (PAM) (Li et al. 2003 ; Yan et al. 2004 ; Amuda and Alade 2006 ; Zhu et al. 2009 ; Sahu and Chaudhari 2013 ; Shaikh et al. 2017 , 2018 ; Xiong et al. 2018 ; Abbasi Moud 2022 ). In addition to charge neutralization, they are also capable of physically bridging colloidal particles together to form larger and stronger flocs (Sahu and Chaudhari 2013 ; Lee et al. 2014 ; Xiong et al. 2018 ; Abbasi Moud 2022 ). They are used widely to improve and enable various solid-liquid separation processes, such as thickening operations in mineral processing, industrial tailings dewatering, papermaking and water treatment (Yan et al. 2004 ; Zhu et al. 2009 ). These synthetic molecules have sustainability issues, such as high recalcitrance to biodegradation (Lee et al. 2014 ; Joshi and Abed 2017 ) and potential for releasing harmful substances as they degrade by chemical, mechanical, thermal, photolytic, and biological processes (Luo et al. 2011 ; Lee et al. 2014 ; Guezennec et al. 2015 ; Xiong et al. 2018 ). Their release in nature can have a negative impact on environment and human health (Lee et al. 2014 ; Joshi and Abed 2017 ). This means that much like the use of metal salt coagulants, flocculation with contemporary commercial flocculants also leads to generation of hazardous sludge. To address the issue of coagulants and synthetic polymer flocculants contaminating the sludge, natural polymers have been studied as replacements. Especially cellulose as the most common polymer on Earth has been of great interest as a starting point for a natural polymer flocculant. So far, the use of pure cellulose flocculants has been limited by the insolubility of native cellulose and research has been done on various water-soluble cellulose derivatives. Cationized cellulose suitable for flocculation of kaolinite has been prepared from cellulose with (3-chloro-2-hydroxypropyl) trimethylammonium chloride cationization (Aguado et al. 2017 ). Carboxymethyl cellulose has been used as a base for cellulose flocculants due to its water solubility and enhanced reactivity compared to native cellulose (Cai et al. 2015 ). Even acryl amide has been grafted on hydroxyethyl cellulose to improve it as a flocculant (Chaouf et al. 2019 ). Potential issues with cellulose derivatives are lowered biodegradability compared to native cellulose, and potentially toxic or hazardous raw materials and degradation products, i.e. when grafted with acryl compounds. A different approach for using cellulose as a flocculant is to dissolve it directly with a suitable solvent. This leaves the cellulose chemically unaltered, and it remains highly biodegradable and non-toxic. The simplest aqueous solution system is based on sodium hydroxide (NaOH), but it requires the degree of polymerization (DP) of cellulose to be lowered significantly, or only a very low concentration of cellulose can be achieved (Isogai and Atalla 1998 ). The cellulose solution will start regenerating as it enters the target water, but depending on the target water pH, temperature and ion content the regeneration rate varies significantly. Ideally, the rate would be slow enough for the flocculation to happen while the cellulose is still at least partially dissolved and has high surface area, but fast enough that the cellulose can be removed as a solid at the end of the flocculation process. In the context of a paper and chemical pulp mill, a cellulose-based flocculant is especially interesting. The main raw material of paper mills is most commonly kraft pulp, which is generally 75–90% cellulose varying depending on wood species and the exact pulping and bleaching sequence (Molin and Teder 2002 ; Sixta 2006 ; Spence et al. 2010 ). Separation of coating and filler materials such as kaolinite from process waters is one of many goals of water treatment processes in paper mill. If the mill could manufacture water treatment chemicals from kraft pulp with minimal additional chemicals and processes, it could decrease its dependency on external suppliers and gain a secondary product to sell to other industries where clay suspensions need to be treated. The objective of this research was to show that cellulose dissolved in NaOH can function as a flocculant. We showcase the flocculation effect using kaolinite suspension as a model water and monitoring the reduction in turbidity over time as the cellulose solution is added. We also show that the effectiveness of this cellulose-based flocculant is not hindered by high water salinity. Experimental Materials Dry cotton linter MCC powder was purchased from Sigma-Aldrich. Cotton linter MCC was used as it was commercially easily available, although lower-grade MCC, i.e. from recycled cellulosic materials, could be more economically feasible. Two batches of kaolinite are referred to as kaolinite 1 and kaolinite 2. Both batches were purchased from Sigma-Aldrich at different times. They are separated in this manner because they had slightly different initial turbidities at 0.5 wt.% in water. Other materials included NaOH pellets (VWR, GPR RECTAPUR), potassium nitrate (KNO 3 ) (Supelco, EMSURE, ISO, Reag. Ph Eur), magnesium chloride (MgCl 2 ) hexahydrate (VWR, AnalaR NORMAPUR, ACS/Reag. Ph.Eur.), sodium chloride (NaCl) (Sigma Aldrich), and cupriethylenediamine (CED) solution (Oy FF-Chemicals Ab, SCAN 16:62). Flocculant MCC was dissolved in NaOH with the freeze-thaw method (Isogai and Atalla 1998 ). In short, 2 g oven-dry (OD) of cellulose was dispersed in 53.8 ml of water with Ultra-Turrax at 10,000 RPM for 3 minutes. 5 g of sodium hydroxide as pellets was added and the mixture was shaken for 5 minutes at room temperature to dissolve the pellets. The mixture was then frozen at -20°C for at least 18 hours to dissolve cellulose. 41.2 ml of water was added and then the solution was thawed at room temperature while shaking, and stored at 4°C. The final concentrations were 5% NaOH and 2% MCC. The chain length of the MCC was assessed by measuring limiting viscosity in CED solution according to SCAN CM 15:99 (Scandinavian pulp 1999). Limiting viscosity was converted to DP using Mark-Houwink equation $$\:\eta\:={k}^{{\prime\:}}\bullet\:{DP}^{\alpha\:}$$ 1 where η is the limiting viscosity, DP is the degree of polymerization, and the Mark-Houwink interaction parameters k’ and α are 1.33 and 0.905, respectively. Flocculation Dose optimization and response surface model Flocculation tests were done with Kemira Flocculator 2000 in 1 L containers. 5 g of kaolinite 1 was mixed with 1 L of 1 mM KNO 3 solution to avoid surface conductance anomalies kaolinite particles may have at low electrolyte concentration (Rowlands and O’Brien 1995 ; Mpofu et al. 2003 ), and mixed for approximately 10 minutes in the flocculator (30 s rapid, 4 min slow, 30 s rapid, 4 min slow, 30 s rapid) to disperse the kaolinite and assure constant initial turbidity across all test points. Initial turbidity and pH were recorded after this mixing. The purpose of mixing was to achieve consistent initial turbidity of 2300 ± 100 NTU. 2200 NTU was used as the initial turbidity value and 7.5 as the initial pH for all samples due to continuous settling and fluctuations in the turbidity measurement at over 2000 NTU range. MgCl 2 was added as a 0.2 g/ml solution. MgCl 2 was chosen as an electrolyte flocculation aid based on its ability to enhance turbidity reduction with PAM at low concentration when applied to a bentonite suspension (Shaikh et al. 2018 ). Flocculation procedure was (1) MgCl 2 addition, (2) 30 s of rapid mixing, (3) flocculant addition, (4) 10 min of slow agitation followed by immediate removal of mixer from the container, (5) 10-minute settling followed by immediate turbidity measurement with YSI ProDSS at 7 cm below the surface and pH measurement with Thermo Scientific Orion 2 Star. Suspensions were then left to settle overnight and measured again the next day. The combined effect of MgCl 2 and MCC was studied with a central composite full factorial (CCF) statistical model and response surface models (RSM) were fit to the measurement data with multiple linear regression (MLR) using Sartorius MODDE 13 for turbidity after 10 minutes and after 20 hours of settling as the functions of magnesium chloride concentration and MCC concentration (Table 1 ). Water salinity effect To assess the effect of water salinity on flocculant performance in direct flocculation, NaCl was mixed with deionized water at 0.5, 5, 50, and 500 mM concentration. No KNO 3 or MgCl 2 was added. Kaolinite 2 was added, and the initial turbidity was measured to be 3200 NTU from a control sample with no NaCl and 1 mM KNO 3 . Flocculation procedure was then performed as above. Scanning electron microscopy (SEM) Flocs were collected by decanting, frozen, and then dried in Labconco Freezone 2.5. 20 ppm of MCC solution was also regenerated as a reference sample without the presence of kaolinite, but in otherwise identical procedure. The samples were coated with 80/20 gold/palladium in Quorum Technologies Q 150 R sputter coater at 20 mV for 30 seconds. Imaging was done using Zeiss Sigma VP SEM with SE2 detector at 2.00 kV accelerating voltage. Results and discussion Flocculant Degree of polymerization The limiting viscosity of MCC was 130 ml/g. The corresponding average DP was 158 anhydroglucose units and the average molar mass is 2.56 x 10 4 g/mol. PAM flocculants typically have higher molar mass from 10 5 g/mol to over 10 7 g/mol and they tend to perform better the higher the molecular weight at least up to 1.8 x 10 7 g/mol where their internal tangling can start to reduce the interaction with small particles (Xiong et al. 2018 ). Solution stability Low shelf life can be a concern with biopolymer flocculants. MCC flocculant solution for this study was stored at 4°C in a refrigerator over the course of the experiments. The first signs of regenerated cellulose were noticed four weeks after the preparation. No signs of deterioration in flocculation performance were detected over several weeks of trials. Flocculation Dose optimization The initial pH of the kaolinite suspension was 7.5 and the initial turbidity was 2200 NTU. The suspension was slowly settling without chemical additions, but only partially at up to 63.6% turbidity reduction to 800 NTU over 10 minutes and 94.8% to 115 NTU in 20 hours. Adding 1 mM of magnesium chloride had a significant effect on settling, as it improved the turbidity after 10 minutes of settling to 170 NTU and after 20 hours to almost complete clarity at 99.7% reduction at final turbidity of 7.0 NTU. MCC on its own had a slightly better result than MgCl 2 at 93.0% reduction and 155 NTU turbidity after 10 minutes, as well as 99.8% reduction all the way to 4.1 NTU turbidity after 20 hours. A comprehensive list of test points and results are presented in Table 1 . To confirm the effect of MCC solution in turbidity reduction as opposed to only pH increase being the driver of flocculation, 500 µL of 5% NaOH was tested as a “flocculant” in place of the MCC solution with 0.5 mM of MgCl 2 . The increase of floc size was visibly less than with MCC solutions. After 10 minutes of settling, the turbidity was 29.4 NTU. The addition of NaOH therefore improved the settling compared to no flocculant at the same MgCl 2 dose (155 NTU) but was not as good as MCC flocculant (12.8–14 NTU). Table 1 The main CCF test matrix for flocculation experiments with MgCl 2 electrolyte and 5% NaOH / 2% MCC solution flocculant electrolyte concentration (mM) flocculant (ppm) pH Turbidity 10 min (NTU) Turbidity reduction 10 min Turbidity 20 h (NTU) Turbidity reduction 20 h 0 0 7.7 800 63.6% 115 94.8% 1 0 7.6 170 92.3% 7.0 99.7% 0 20 11.0 112 94.9% 18.1 99.2% 1 20 10.6 8.1 99.6% 1.5 99.9% 0 10 10.6 307 86.1% 53.7 97.6% 1 10 10.4 10.6 99.5% 2.5 99.9% 0.5 0 7.3 155 93.0% 4.1 99.8% 0.5 20 10.8 7.9 99.6% 2.0 99.9% 0.5 10 10.5 14.0 99.4% 3.4 99.9% 0.5 10 10.5 14.0 99.4% 3.1 99.9% 0.5 10 10.5 12.8 99.4% 2.5 99.9% With the combination of MgCl 2 and MCC it was already visible during the agitation phase, that the floc size was significantly larger, and water clarity better compared to single chemical treatments. In Fig. 1 the visible difference during agitation phase exemplifies how much faster the water clarification can happen when the chemical combination and dosage is appropriate for the target water when comparing 1 mM MgCl2 and 20 ppm of MCC to 0.5 mM MgCl2 only. Notably, despite the dramatic difference in initial rate of settling and clarification, after 20 hours of settling both test points end up clarifying almost completely at 1.5 and 4.1 NTU, respectively. It should be noted that the addition of electrolytes, such as MgCl 2 in this study, to enhance the floc formation may not be necessary to the same degree depending on the electrolytes already present in the industrial process and waste waters. It has been shown that in flocculation of bentonite clay with PAM, chloride salts of sodium, potassium, magnesium and calcium can all improve the flocculation process (Shaikh et al. 2018 ). One or several of these common elements are likely to be present in industrial process waters already, reducing the need of addition for the sake of water treatment. In mining industry water treatment, the increasing use of saline water has been considered a complication for the management of fine clays in tailings as it may make commonly used flocculants less effective (Liu et al. 2018b ). In the context of MCC flocculant application the use of saline water could be a beneficial development instead. The major downside of using NaOH solution of cellulose is that any increase in cellulose dosage comes with an increase in pH due to NaOH being a strong base. To lessen the effect, the concentration of cellulose in the solution could be increased or the concentration of NaOH decreased. However, this is highly non-trivial as cellulose alkali dissolution can be a fickle process. Increasing the cellulose content tends to lead to increased viscosity, decreased stability during storage and even a risk of gelation immediately after dissolution. The solubility of cellulose can be improved by lowering the degree of DP. However, when using MCC as was done in this research, we are already working close to the leveling-off degree of polymerization (LODP) for cellulose. Decreasing the DP further when nearing the LODP becomes slow or requires extreme hydrolysis conditions as only highly recalcitrant crystalline cellulose segments are left in the polymer chains. Additionally, for the flocculant bridging effect to occur in kaolinite suspension it is generally beneficial for the DP of the flocculant polymer to be high (Aguado et al. 2017 ; Xiong et al. 2018 ). Another approach to improving cellulose solubility is the use of cosolvents or solvent aids with NaOH, such as zinc oxide (Kihlman 2012 ; Budtova and Navard 2016 ; Koistinen et al. 2023 ), urea (Zhou and Zhang 2000 ; Egal et al. 2008 ; Kihlman 2012 ; Budtova and Navard 2016 ) or thiourea (Kihlman 2012 ; Budtova and Navard 2016 ; Yang et al. 2017 ), or even replacing NaOH with lithium hydroxide completely or partially (Cai and Zhang 2005 ; Qiu et al. 2018 ; Zhu et al. 2018 ; Liu et al. 2019 ). All these approaches have significant downsides in the context of water treatment. These water-soluble chemicals may cause problems in subsequent treatment processes, especially biological processes, they may be difficult to separate from the process waters before discharging, and they may contaminate the sludge. Response surface model (RSM) The coefficients for the models were chosen to maximize the coefficient of determination (R 2 ) and the predictive relevance (Q 2 ) of the model by omitting the most statistically insignificant coefficients whenever beneficial. For 10-minute turbidity model all coefficients, squares and the interaction coefficient were included as it gave the best fit and predictive value for the model even though the P-value for square of MCC ppm was 0.111. For 20-hour turbidity model the square of MCC ppm was omitted to increase Q 2 . Histogram analysis showed that the response data for both 10-minute and 20-hour turbidity was skewed. This happened because almost all test points with either MCC or MgCl 2 reduced the turbidity significantly compared to the untreated suspension. The RSM was improved by logarithmic transformation of the results to improve the normality of the distribution and increase Q 2 . The final RSM for 10-minute turbidity had R 2 of 0.976 and Q 2 of 0.753. The final RSM for 20-hour turbidity had R 2 of 0.979 and Q 2 of 0.865. These values indicate that the models not only fit the experimental data superbly but also have high ability to predict outcomes of other chemical doses within the model area. Contour plots were drawn from the models for turbidities after 10 minutes and 20 hours of settling. In Fig. 2 , after 10 minutes of settling the lowest turbidity is expected between the center point and the upper right corner where both MgCl 2 and MCC doses are high. Based on the contour plot, it is expected that MgCl 2 concentration of 0.6–1.0 mM and MCC dose of 12 to 20 ppm should provide turbidity of 5–10 NTU in 10-minute settling. In Fig. 3 after 20 hours of settling the best results are spread more evenly on the vertical axis. This means that even without MCC it is possible to get low turbidity. However, MCC can be used to reduce the amount of MgCl 2 while still reaching good results, and for the absolute best results of < 2 NTU both flocculation chemicals should be used. Overall, the difference between the contour plots highlights the importance of polymeric flocculant aid in short time scales, while in a longer settling period a simple electrolyte that disturbs the charges in kaolinite particles can be enough to facilitate settling. Settling rate The turbidities of samples with 0.5% of kaolinite 2 were measured from the start of settling for 10 minutes to investigate the rate of turbidity reduction with short settling times. The initial turbidity before any chemical additions was 3200 NTU. All samples had 0.5 mM of MgCl 2 , and varying dose of flocculant. MCC was used in 10 and 20 ppm doses, and 5% NaOH solution without cellulose was added to one sample at an amount equal to the NaOH in 20 ppm dose of MCC solution to rule out the effect of pH change from the solvent being the sheer driving force in turbidity reduction. The turbidity was recorded every minute, and the result is presented in Fig. 4 . When there is MCC as flocculant, the settling almost entirely during the agitation and the first minute of settling. The most effective dose in this comparison was 20 ppm of MCC with 0.5 mM MgCl 2 and it resulted in turbidity of 21.7 NTU after only one minute of settling, 7.3 NTU after two minutes of settling and 4.7 NTU after 10 minutes of settling. Because the turbidity reduction and settling happen so fast, it is difficult to emphasize the difference between test points with this test setup. However, the MCC has a significant effect on turbidity reduction and the rate of settling, and the effect is most pronounced during the agitation and the first minutes of settling. Water salinity effect Effect of water salinity of 0.5–500 mM of NaCl on settling of kaolinite over 10 minutes is presented in Fig. 5 . Without the addition of MCC solution, the turbidity is affected by NaCl very little as all samples are between 100 and 180 NTU. 20 ppm of MCC changes the results radically, as the least saline sample settles far worse at 1500 NTU, but at all other salinity levels the settling is improved. The best result is achieved at 50 mM of NaCl, where the turbidity after 10 minutes is 21.3 NTU representing a 99.3% reduction from the initial turbidity of 3200 NTU. The salinity of ocean water is 3.5 wt.%, corresponding to around 600 mM of NaCl. Based on the results, MCC solution can improve the settling rate of kaolinite suspension in most saline waters at least up to salinity levels of ocean water but is at its best at around 10% of ocean water salinity. In mining tailings this is a good property, as the water salinity depends on the mineral content of the soil and the performance of conventional flocculants can be reduced by the salinity (Liu et al. 2018a ; Xiong et al. 2018 ). Scanning electron microscopy (SEM) As seen in Fig. 6ab , SEM images of samples from kaolinite suspensions show almost exclusively particles with kaolinite coated surfaces in the scale of < 100 µm. When regenerated without kaolinite, the MCC solution produces significantly larger particles beyond the 100 µm scale ( Fig. 6cd ). These particles also have distinctly different porous and rough surface textures from flaky and smooth kaolinite. A glimpse of a structure like the regenerated cellulose surface can be seen in the center of Fig. 6 b among the kaolinite flakes. Based on these findings it is likely that when the MCC solution is regenerated in kaolinite suspension, it produces smaller particles than in water, and the regenerated cellulose particles are almost entirely coated with kaolinite. Conclusion Cellulose directly dissolved in aqueous NaOH can significantly increase the particle size and the settling rate of a kaolinite suspension when applied as a flocculant. This effect is improved when the cellulose solution is used together with an electrolyte, such as magnesium chloride. Because the flocs that are formed using this type of flocculant are absent from conventional hazardous water treatment chemicals, they have more potential to be recycled, biodegraded, or repurposed safely. This is a major leap towards circular economy in water treatment sludge quality. In a chemical pulp and paper mill cellulose and NaOH are abundantly available. With suitable processes for converting them to a cellulose solution, the mill could manufacture flocculant for treating the mill waste waters instead of buying synthetic flocculant. With a shelf life of approximately four weeks, the manufactured chemical could also be sold out and used for other industrial water treatment, such as improving the settling of mining industry tailings. Alternatively, to increase shelf life the cellulose and NaOH could be stored as dry powders or pellets, and then dispersed, mixed and dissolved at site as needed since only freezing and mixing are required for a batch production process. A major drawback with this type of flocculant is that NaOH solution of cellulose raises the pH of the targeted water stream. This limits the use to cases where (1) the target water is initially acidic and needs to be neutralized, (2) the target water has high pH buffering ability and the pH change is minor, (3) the resulting floc is significantly more valuable when it is not contaminated with metal salts, hydroxides, or synthetic polymers, and thus worth the extra expense of neutralizing the water afterwards, or (4) the heightened pH is not an issue, for example if the treated water is recycled into a process where high pH is desirable. Cellulose flocculant retains its ability to improve the rate of settling even at high salinity. This makes it potentially useful in settling fine clay in mining industry tailings, where salinity of the water can cause issues with conventional flocculants. It also means that the flocculant is relatively robust to industrial processing plant conditions, where the exact composition of process waters may change day-to-day. Abbreviations CCF, central composite full factorial; CED, cupriethylenediamine; DP, degree of polymerization; KNO 3 , potassium nitrate; LODP, leveling-off degree of polymerization; MgCl 2 , magnesium chloride; MCC, microcrystalline cellulose; MLR, multiple linear regression; NaCl, sodium chloride; NaOH, sodium hydroxide; OD, oven-dry; PAM, polyacrylamide; Q 2 , predictive relevance; R 2 , coefficient of determination; RSM, response surface model; SEM, scanning electron microscopy Declarations Competing interests The authors have no relevant financial or non-financial interests to disclose. Funding This work was completed with funding from Maa- ja vesitekniikan tuki ry. (grant #4799) and initiated as a part of ETSIVÄT project funded by Suomen Kulttuurirahasto. Author Contribution Both authors contributed to the study conception and design. Material preparation, data collection and analysis were performed by Tomi Eilamo. 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Nord Pulp Paper Res J 17:14–28. https://doi.org/10.3183/npprj-2002-17-01-p014-019 Mpofu P, Addai-Mensah J, Ralston J (2003) Investigation of the effect of polymer structure type on flocculation, rheology and dewatering behaviour of kaolinite dispersions. Int J Miner Process 71:247–268. https://doi.org/10.1016/S0301-7516(03)00062-0 Murray HH (2000) Traditional and new applications for kaolin, smectite, and palygorskite: a general overview. Appl Clay Sci 17:207–221. https://doi.org/10.1016/S0169-1317(00)00016-8 Niu Q (2018) Overview of the Relationship Between Aluminum Exposure and Health of Human Being. In: Advances in Experimental Medicine and Biology. Springer New York LLC, pp 1–31 Qiu C, Zhu K, Zhou X, et al (2018) Influences of Coagulation Conditions on the Structure and Properties of Regenerated Cellulose Filaments via Wet-Spinning in LiOH/Urea Solvent. ACS Sustain Chem Eng 6:4056–4067. https://doi.org/10.1021/acssuschemeng.7b04429 Reyes-López JA, Ramírez-Hernández J, Lázaro-Mancilla O, et al (2008) Assessment of groundwater contamination by landfill leachate: A case in México. Waste Manag 28:S33–S39. https://doi.org/10.1016/j.wasman.2008.03.024 Rowlands WN, O’Brien RW (1995) The dynamic mobility and dielectric response of kaolinite particles. J Colloid Interface Sci 175:190–200. https://doi.org/10.1006/jcis.1995.1445 Sahu O, Chaudhari P (2013) Review on Chemical treatment of Industrial Waste Water. J Appl Sci Environ Manag 17:241–257. https://doi.org/10.4314/jasem.v17i2.8 Scandinavian pulp paper and board testing committee (1999) SCAN CM 15:99 Viscosity in cupriethylenediamine solution Selkälä T, Suopajärvi T, Sirviö JA, et al (2019) Efficient entrapment and separation of anionic pollutants from aqueous solutions by sequential combination of cellulose nanofibrils and halloysite nanotubes. Chem Eng J 374:1013–1024. https://doi.org/10.1016/j.cej.2019.06.008 Shaikh SMR, Nasser MS, Hussein I, et al (2017) Influence of polyelectrolytes and other polymer complexes on the flocculation and rheological behaviors of clay minerals: A comprehensive review. Sep Purif Technol 187:137–161 Shaikh SMR, Nasser MS, Magzoub M, et al (2018) Effect of electrolytes on electrokinetics and flocculation behavior of bentonite-polyacrylamide dispersions. Appl Clay Sci 158:46–54. https://doi.org/10.1016/j.clay.2018.03.017 Sixta H (2006) Part I Chemical Pulping, 11 Pulp Properties and Applications. In: Sixta H (ed) Handbook of Pulp. WILEY-VCH Verlag GmbH &Co. KGaA, Weinheim, pp 1009–1067 Spence K, Venditti R, Habibi Y, et al (2010) The effect of chemical composition on microfibrillar cellulose films from wood pulps: Mechanical processing and physical properties. Bioresour Tech 101:5961–5968. https://10.1016/j.biortech.2010.02.104 Wang Z, Huang W, Yang G, et al (2019) Preparation of cellulose-base amphoteric flocculant and its application in the treatment of wastewater. Carbohydr Polym 215:179–188. https://doi.org/10.1016/j.carbpol.2019.03.097 Xiong B, Loss RD, Shields D, et al (2018) Polyacrylamide degradation and its implications in environmental systems. NPJ Clean Water 1:17. https://doi.org/10.1038/s41545-018-0016-8 Yan YD, Glover SM, Jameson GJ, Biggs S (2004) The flocculation efficiency of polydisperse polymer flocculants. Int J Miner Process 73:161–175. https://doi.org/10.1016/S0301-7516(03)00071-1 Yang Y, Zhang Y, Dawelbeit A, et al (2017) Structure and properties of regenerated cellulose fibers from aqueous NaOH/thiourea/urea solution. Cellulose 24:4123–4137. https://doi.org/10.1007/s10570-017-1418-3 Zhou J, Zhang L (2000) Solubility of Cellulose in NaOH/Urea Aqueous Solution. Polym J 32:866–870. https://doi.org/10.1295/polymj.32.866 Zhu K, Qiu C, Lu A, et al (2018) Mechanically Strong Multifilament Fibers Spun from Cellulose Solution via Inducing Formation of Nanofibers. ACS Sustain Chem Eng 6:5314–5321. https://doi.org/10.1021/acssuschemeng.8b00039 Zhu Z, Li T, Lu J, et al (2009) Characterization of kaolin flocs formed by polyacrylamide as flocculation aids. Int J Miner Process 91:94–99. https://doi.org/10.1016/j.minpro.2009.01.003 Additional Declarations No competing interests reported. Cite Share Download PDF Status: Published Journal Publication published 27 Feb, 2026 Read the published version in Cellulose → Version 1 posted Editorial decision: Revision requested 07 Jun, 2025 Editor assigned by journal 07 Jun, 2025 Submission checks completed at journal 20 May, 2025 First submitted to journal 19 May, 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-6697938","acceptedTermsAndConditions":true,"allowDirectSubmit":false,"archivedVersions":[],"articleType":"Research Article","associatedPublications":[],"authors":[{"id":468005346,"identity":"204d8dc5-2c6b-4f28-bca7-e4eac5d2fd54","order_by":0,"name":"Tomi Eilamo","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAAA2ElEQVRIiWNgGAWjYJCCAwwMEjJAmvEBA4MFmD6ATzkPVAuIZjYAMiRANEEtMJpNAqYFr6Ps2bsTDzBUWPDwTzt8rOJHjUQdPwMzI35beM5uOMBwRoJH4nZa2s2eYxISkg3MDPi1SORuOMDYBvTL7RyzGzxsEhIGB/gPEKHlnwSPPFBL4Z9/IC1E2dIgwWMA1MLM20aMljNAvyQck+AxvJ2WLC3bJyE5s5mAFvb23s0fPtTUycndTj748c03G35+9mbmD/i0gEECCo+ZoPpRMApGwSgYBYQAAOGeRBDBZTu/AAAAAElFTkSuQmCC","orcid":"","institution":"Aalto University","correspondingAuthor":true,"prefix":"","firstName":"Tomi","middleName":"","lastName":"Eilamo","suffix":""},{"id":468005347,"identity":"3999633a-b445-42f3-b872-57c42c00cc20","order_by":1,"name":"Olli Dahl","email":"","orcid":"","institution":"Aalto University","correspondingAuthor":false,"prefix":"","firstName":"Olli","middleName":"","lastName":"Dahl","suffix":""}],"badges":[],"createdAt":"2025-05-19 10:23:27","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-6697938/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-6697938/v1","draftVersion":[],"editorialEvents":[{"content":"https://doi.org/10.1007/s10570-026-06991-8","type":"published","date":"2026-02-27T15:58:17+00:00"}],"editorialNote":"","failedWorkflow":false,"files":[{"id":84910829,"identity":"ebcd5263-b1aa-4e69-9347-aea6076d9b49","added_by":"auto","created_at":"2025-06-18 16:56:15","extension":"png","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":370137,"visible":true,"origin":"","legend":"\u003cp\u003eKaolinite flocculation in 1 L test jars – a comparison that highlights the visibly larger particle size 5 minutes into agitation phase when the suspension is treated with 1 mM MgCl\u003csub\u003e2\u003c/sub\u003e and 20 ppm of MCC (left) compared to 0.5 mM MgCl\u003csub\u003e2\u003c/sub\u003e (right)\u003c/p\u003e","description":"","filename":"1.png","url":"https://assets-eu.researchsquare.com/files/rs-6697938/v1/0875574b7fe374dbca9aaab4.png"},{"id":84909989,"identity":"27980cf8-84f1-4a58-bf3d-89dfccd8e33c","added_by":"auto","created_at":"2025-06-18 16:48:15","extension":"png","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":85863,"visible":true,"origin":"","legend":"\u003cp\u003eResponse contour plot for kaolinite suspension turbidity after 10 minutes of settling\u003c/p\u003e","description":"","filename":"2.png","url":"https://assets-eu.researchsquare.com/files/rs-6697938/v1/f5029e0800713c0d62d987a8.png"},{"id":84909994,"identity":"f5f7ea54-b870-4159-b10f-8c185e129e8b","added_by":"auto","created_at":"2025-06-18 16:48:15","extension":"png","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":71162,"visible":true,"origin":"","legend":"\u003cp\u003eResponse contour plot for kaolinite suspension turbidity after 20 hours of settling\u003c/p\u003e","description":"","filename":"3.png","url":"https://assets-eu.researchsquare.com/files/rs-6697938/v1/2f78093d56260ae8ab8b0869.png"},{"id":84909991,"identity":"76db1a10-aa43-488a-8d0b-240f1a939dc5","added_by":"auto","created_at":"2025-06-18 16:48:15","extension":"png","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":22626,"visible":true,"origin":"","legend":"\u003cp\u003eTurbidity of kaolinite suspension during the first 10 minutes of settling when treated with with 0.5 mM MgCl\u003csub\u003e2\u003c/sub\u003e combined with 5 % NaOH dose equal to NaOH in 20 ppm of the MCC solution (circle), 10 ppm of MCC solution (square), and 20 ppm of MCC solution (triangle)\u003c/p\u003e","description":"","filename":"4.png","url":"https://assets-eu.researchsquare.com/files/rs-6697938/v1/8d60e7f96bc278db37c1b984.png"},{"id":84910828,"identity":"2519545b-448e-4706-bcc5-0f4a9072936e","added_by":"auto","created_at":"2025-06-18 16:56:15","extension":"png","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":12406,"visible":true,"origin":"","legend":"\u003cp\u003eThe effect of salinity in mM of NaCl on kaolinite suspension turbidity without flocculant and with 20 ppm of MCC after 10 minutes of settling\u003c/p\u003e","description":"","filename":"5.png","url":"https://assets-eu.researchsquare.com/files/rs-6697938/v1/556011327f4ba217a1c7d2b1.png"},{"id":84909993,"identity":"5b01b569-5fd0-429f-a516-89e13356f88a","added_by":"auto","created_at":"2025-06-18 16:48:15","extension":"png","order_by":6,"title":"Figure 6","display":"","copyAsset":false,"role":"figure","size":371592,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eab \u003c/strong\u003eMCC regenerated in kaolinite suspension compared to \u003cstrong\u003ecd \u003c/strong\u003eMCC regenerated in water in otherwise identical conditions at 1000x magnification on the left and 10,000x magnification on the right\u003c/p\u003e","description":"","filename":"6.png","url":"https://assets-eu.researchsquare.com/files/rs-6697938/v1/7e755183886f8656f296a533.png"},{"id":103766716,"identity":"f454405c-d322-4897-99d9-eab94d970e8a","added_by":"auto","created_at":"2026-03-02 16:15:32","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":1781779,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-6697938/v1/147cd870-9b48-4560-814d-d20dc7a02ec8.pdf"}],"financialInterests":"No competing interests reported.","formattedTitle":"Kaolinite suspension treatment using cellulose dissolved in sodium hydroxide as flocculant","fulltext":[{"header":"Introduction","content":"\u003cp\u003eKaolinite is a naturally occurring inorganic clay with the chemical formula Al\u003csub\u003e2\u003c/sub\u003eSi\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e5\u003c/sub\u003e(OH)\u003csub\u003e4\u003c/sub\u003e (Bergaya and Lagaly \u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e2006\u003c/span\u003e; Selk\u0026auml;l\u0026auml; et al. \u003cspan citationid=\"CR40\" class=\"CitationRef\"\u003e2019\u003c/span\u003e). It has a wide variety of industrial applications including coating material for paper, functional filler in paint, plastic, rubber and ink, white ceramics, and raw material in the production of fiber glass (Murray \u003cspan citationid=\"CR33\" class=\"CitationRef\"\u003e2000\u003c/span\u003e). Kaolinite among many other clays is also found in most mine tailings. It is harmful and disruptive to aquatic ecosystems via sunlight and visibility blocking turbidity as well as smothering sedimentation (Shaikh et al. \u003cspan citationid=\"CR41\" class=\"CitationRef\"\u003e2017\u003c/span\u003e; Wang et al. \u003cspan citationid=\"CR45\" class=\"CitationRef\"\u003e2019\u003c/span\u003e). Kaolinite can also cause operational problems, such as transportation problems for mine tailings, and release and capture of contaminants in tailings slurry (D. Liu, Edraki, and Berry \u003cspan citationid=\"CR25\" class=\"CitationRef\"\u003e2018a\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eTo mitigate the environmental and operational issues related to kaolinite use, effective solid-liquid separation should be applied to kaolinite suspensions before discharge or reuse of affected water. Coagulation and/or flocculation are common methods for removal of solids based on preventing the repulsion between suspended particles and increasing the particle size (Sahu and Chaudhari \u003cspan citationid=\"CR38\" class=\"CitationRef\"\u003e2013\u003c/span\u003e; Lee et al. \u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e2014\u003c/span\u003e; Dahl \u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e2025\u003c/span\u003e). Flocculation is considered an effective method for solid-liquid separation of colloidal solutions, with additional benefits of low cost, low energy consumption and easy operation relative to alternatives (Wang et al. \u003cspan citationid=\"CR45\" class=\"CitationRef\"\u003e2019\u003c/span\u003e). Effective flocculation leads to easier and faster separation from the liquid medium, i.e.. via settling, flotation or filtration (Lee et al. \u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e2014\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eThe most common coagulants used in removal of clay particles such as kaolinite from water are aluminum salts (Divakaran and Sivasankara Pillai \u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e2001\u003c/span\u003e; Igwegbe et al. \u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e2021a\u003c/span\u003e). Aluminum salts are also the most common coagulants in pulp and paper industry (Sahu and Chaudhari \u003cspan citationid=\"CR38\" class=\"CitationRef\"\u003e2013\u003c/span\u003e), which is a major source of colloidal kaolinite suspensions (Shaikh et al. \u003cspan citationid=\"CR41\" class=\"CitationRef\"\u003e2017\u003c/span\u003e). However, they have their own challenges: aluminum forms hydroxide sludge with high metallic content and the sludge can cause contamination of soil and groundwater from landfill leachates (Reyes-L\u0026oacute;pez et al. \u003cspan citationid=\"CR36\" class=\"CitationRef\"\u003e2008\u003c/span\u003e; Shaikh et al. \u003cspan citationid=\"CR42\" class=\"CitationRef\"\u003e2018\u003c/span\u003e; Igwegbe et al. \u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e2021b\u003c/span\u003e, \u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003ea\u003c/span\u003e; Kurusu et al. \u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e2022\u003c/span\u003e), which in turn has a risk of detrimental effects on human health including correlation with increased risk for Alzheimer\u0026rsquo;s disease (Crapper et al. \u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e1973\u003c/span\u003e; Chatterjee et al. \u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e2009\u003c/span\u003e; Menkiti et al. \u003cspan citationid=\"CR30\" class=\"CitationRef\"\u003e2011\u003c/span\u003e; Kumar et al. \u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e2017\u003c/span\u003e; Niu \u003cspan citationid=\"CR34\" class=\"CitationRef\"\u003e2018\u003c/span\u003e; Igwegbe et al. \u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e2021a\u003c/span\u003e). Additionally, the flocs metal salt coagulants form are often fragile, small and slow to settle (McCurdy et al. \u003cspan citationid=\"CR29\" class=\"CitationRef\"\u003e2004\u003c/span\u003e; Shaikh et al. \u003cspan citationid=\"CR42\" class=\"CitationRef\"\u003e2018\u003c/span\u003e; Kurusu et al. \u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e2022\u003c/span\u003e). Because of this, polymeric flocculant is often added to facilitate floc growth and to improve the settling rate (Lee et al. \u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e2014\u003c/span\u003e; Kurusu et al. \u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e2022\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eThe contemporary commercial flocculants are synthetic organic polymers, most commonly polyacrylamides (PAM) (Li et al. \u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e2003\u003c/span\u003e; Yan et al. \u003cspan citationid=\"CR47\" class=\"CitationRef\"\u003e2004\u003c/span\u003e; Amuda and Alade \u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e2006\u003c/span\u003e; Zhu et al. \u003cspan citationid=\"CR51\" class=\"CitationRef\"\u003e2009\u003c/span\u003e; Sahu and Chaudhari \u003cspan citationid=\"CR38\" class=\"CitationRef\"\u003e2013\u003c/span\u003e; Shaikh et al. \u003cspan citationid=\"CR41\" class=\"CitationRef\"\u003e2017\u003c/span\u003e, \u003cspan citationid=\"CR42\" class=\"CitationRef\"\u003e2018\u003c/span\u003e; Xiong et al. \u003cspan citationid=\"CR46\" class=\"CitationRef\"\u003e2018\u003c/span\u003e; Abbasi Moud \u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e2022\u003c/span\u003e). In addition to charge neutralization, they are also capable of physically bridging colloidal particles together to form larger and stronger flocs (Sahu and Chaudhari \u003cspan citationid=\"CR38\" class=\"CitationRef\"\u003e2013\u003c/span\u003e; Lee et al. \u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e2014\u003c/span\u003e; Xiong et al. \u003cspan citationid=\"CR46\" class=\"CitationRef\"\u003e2018\u003c/span\u003e; Abbasi Moud \u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e2022\u003c/span\u003e). They are used widely to improve and enable various solid-liquid separation processes, such as thickening operations in mineral processing, industrial tailings dewatering, papermaking and water treatment (Yan et al. \u003cspan citationid=\"CR47\" class=\"CitationRef\"\u003e2004\u003c/span\u003e; Zhu et al. \u003cspan citationid=\"CR51\" class=\"CitationRef\"\u003e2009\u003c/span\u003e). These synthetic molecules have sustainability issues, such as high recalcitrance to biodegradation (Lee et al. \u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e2014\u003c/span\u003e; Joshi and Abed \u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e2017\u003c/span\u003e) and potential for releasing harmful substances as they degrade by chemical, mechanical, thermal, photolytic, and biological processes (Luo et al. \u003cspan citationid=\"CR28\" class=\"CitationRef\"\u003e2011\u003c/span\u003e; Lee et al. \u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e2014\u003c/span\u003e; Guezennec et al. \u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e2015\u003c/span\u003e; Xiong et al. \u003cspan citationid=\"CR46\" class=\"CitationRef\"\u003e2018\u003c/span\u003e). Their release in nature can have a negative impact on environment and human health (Lee et al. \u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e2014\u003c/span\u003e; Joshi and Abed \u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e2017\u003c/span\u003e). This means that much like the use of metal salt coagulants, flocculation with contemporary commercial flocculants also leads to generation of hazardous sludge.\u003c/p\u003e \u003cp\u003eTo address the issue of coagulants and synthetic polymer flocculants contaminating the sludge, natural polymers have been studied as replacements. Especially cellulose as the most common polymer on Earth has been of great interest as a starting point for a natural polymer flocculant. So far, the use of pure cellulose flocculants has been limited by the insolubility of native cellulose and research has been done on various water-soluble cellulose derivatives. Cationized cellulose suitable for flocculation of kaolinite has been prepared from cellulose with (3-chloro-2-hydroxypropyl) trimethylammonium chloride cationization (Aguado et al. \u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2017\u003c/span\u003e). Carboxymethyl cellulose has been used as a base for cellulose flocculants due to its water solubility and enhanced reactivity compared to native cellulose (Cai et al. \u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e2015\u003c/span\u003e). Even acryl amide has been grafted on hydroxyethyl cellulose to improve it as a flocculant (Chaouf et al. \u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e2019\u003c/span\u003e). Potential issues with cellulose derivatives are lowered biodegradability compared to native cellulose, and potentially toxic or hazardous raw materials and degradation products, i.e. when grafted with acryl compounds.\u003c/p\u003e \u003cp\u003eA different approach for using cellulose as a flocculant is to dissolve it directly with a suitable solvent. This leaves the cellulose chemically unaltered, and it remains highly biodegradable and non-toxic. The simplest aqueous solution system is based on sodium hydroxide (NaOH), but it requires the degree of polymerization (DP) of cellulose to be lowered significantly, or only a very low concentration of cellulose can be achieved (Isogai and Atalla \u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e1998\u003c/span\u003e). The cellulose solution will start regenerating as it enters the target water, but depending on the target water pH, temperature and ion content the regeneration rate varies significantly. Ideally, the rate would be slow enough for the flocculation to happen while the cellulose is still at least partially dissolved and has high surface area, but fast enough that the cellulose can be removed as a solid at the end of the flocculation process.\u003c/p\u003e \u003cp\u003eIn the context of a paper and chemical pulp mill, a cellulose-based flocculant is especially interesting. The main raw material of paper mills is most commonly kraft pulp, which is generally 75\u0026ndash;90% cellulose varying depending on wood species and the exact pulping and bleaching sequence (Molin and Teder \u003cspan citationid=\"CR31\" class=\"CitationRef\"\u003e2002\u003c/span\u003e; Sixta \u003cspan citationid=\"CR43\" class=\"CitationRef\"\u003e2006\u003c/span\u003e; Spence et al. \u003cspan citationid=\"CR44\" class=\"CitationRef\"\u003e2010\u003c/span\u003e). Separation of coating and filler materials such as kaolinite from process waters is one of many goals of water treatment processes in paper mill. If the mill could manufacture water treatment chemicals from kraft pulp with minimal additional chemicals and processes, it could decrease its dependency on external suppliers and gain a secondary product to sell to other industries where clay suspensions need to be treated.\u003c/p\u003e \u003cp\u003eThe objective of this research was to show that cellulose dissolved in NaOH can function as a flocculant. We showcase the flocculation effect using kaolinite suspension as a model water and monitoring the reduction in turbidity over time as the cellulose solution is added. We also show that the effectiveness of this cellulose-based flocculant is not hindered by high water salinity.\u003c/p\u003e"},{"header":"Experimental","content":"\u003cdiv id=\"Sec3\" class=\"Section2\"\u003e \u003ch2\u003eMaterials\u003c/h2\u003e \u003cp\u003eDry cotton linter MCC powder was purchased from Sigma-Aldrich. Cotton linter MCC was used as it was commercially easily available, although lower-grade MCC, i.e. from recycled cellulosic materials, could be more economically feasible. Two batches of kaolinite are referred to as kaolinite 1 and kaolinite 2. Both batches were purchased from Sigma-Aldrich at different times. They are separated in this manner because they had slightly different initial turbidities at 0.5 wt.% in water. Other materials included NaOH pellets (VWR, GPR RECTAPUR), potassium nitrate (KNO\u003csub\u003e3\u003c/sub\u003e) (Supelco, EMSURE, ISO, Reag. Ph Eur), magnesium chloride (MgCl\u003csub\u003e2\u003c/sub\u003e) hexahydrate (VWR, AnalaR NORMAPUR, ACS/Reag. Ph.Eur.), sodium chloride (NaCl) (Sigma Aldrich), and cupriethylenediamine (CED) solution (Oy FF-Chemicals Ab, SCAN 16:62).\u003c/p\u003e \u003c/div\u003e\n\u003ch3\u003eFlocculant\u003c/h3\u003e\n\u003cp\u003eMCC was dissolved in NaOH with the freeze-thaw method (Isogai and Atalla \u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e1998\u003c/span\u003e). In short, 2 g oven-dry (OD) of cellulose was dispersed in 53.8 ml of water with Ultra-Turrax at 10,000 RPM for 3 minutes. 5 g of sodium hydroxide as pellets was added and the mixture was shaken for 5 minutes at room temperature to dissolve the pellets. The mixture was then frozen at -20\u0026deg;C for at least 18 hours to dissolve cellulose. 41.2 ml of water was added and then the solution was thawed at room temperature while shaking, and stored at 4\u0026deg;C. The final concentrations were 5% NaOH and 2% MCC.\u003c/p\u003e \u003cp\u003eThe chain length of the MCC was assessed by measuring limiting viscosity in CED solution according to SCAN CM 15:99 (Scandinavian pulp 1999). Limiting viscosity was converted to DP using Mark-Houwink equation\u003cdiv id=\"Equ1\" class=\"Equation\"\u003e\u003cdiv format=\"TEX\" class=\"mathdisplay\" id=\"FileID_Equ1\" name=\"EquationSource\"\u003e\n$$\\:\\eta\\:={k}^{{\\prime\\:}}\\bullet\\:{DP}^{\\alpha\\:}$$\u003c/div\u003e\u003cdiv class=\"EquationNumber\"\u003e1\u003c/div\u003e\u003c/div\u003e\u003c/p\u003e \u003cp\u003ewhere η is the limiting viscosity, DP is the degree of polymerization, and the Mark-Houwink interaction parameters k\u0026rsquo; and α are 1.33 and 0.905, respectively.\u003c/p\u003e\n\u003ch3\u003eFlocculation\u003c/h3\u003e\n\u003cdiv id=\"Sec6\" class=\"Section2\"\u003e \u003ch2\u003eDose optimization and response surface model\u003c/h2\u003e \u003cp\u003eFlocculation tests were done with Kemira Flocculator 2000 in 1 L containers. 5 g of kaolinite 1 was mixed with 1 L of 1 mM KNO\u003csub\u003e3\u003c/sub\u003e solution to avoid surface conductance anomalies kaolinite particles may have at low electrolyte concentration (Rowlands and O\u0026rsquo;Brien \u003cspan citationid=\"CR37\" class=\"CitationRef\"\u003e1995\u003c/span\u003e; Mpofu et al. \u003cspan citationid=\"CR32\" class=\"CitationRef\"\u003e2003\u003c/span\u003e), and mixed for approximately 10 minutes in the flocculator (30 s rapid, 4 min slow, 30 s rapid, 4 min slow, 30 s rapid) to disperse the kaolinite and assure constant initial turbidity across all test points. Initial turbidity and pH were recorded after this mixing. The purpose of mixing was to achieve consistent initial turbidity of 2300\u0026thinsp;\u0026plusmn;\u0026thinsp;100 NTU. 2200 NTU was used as the initial turbidity value and 7.5 as the initial pH for all samples due to continuous settling and fluctuations in the turbidity measurement at over 2000 NTU range. MgCl\u003csub\u003e2\u003c/sub\u003e was added as a 0.2 g/ml solution. MgCl\u003csub\u003e2\u003c/sub\u003e was chosen as an electrolyte flocculation aid based on its ability to enhance turbidity reduction with PAM at low concentration when applied to a bentonite suspension (Shaikh et al. \u003cspan citationid=\"CR42\" class=\"CitationRef\"\u003e2018\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eFlocculation procedure was (1) MgCl\u003csub\u003e2\u003c/sub\u003e addition, (2) 30 s of rapid mixing, (3) flocculant addition, (4) 10 min of slow agitation followed by immediate removal of mixer from the container, (5) 10-minute settling followed by immediate turbidity measurement with YSI ProDSS at 7 cm below the surface and pH measurement with Thermo Scientific Orion 2 Star. Suspensions were then left to settle overnight and measured again the next day.\u003c/p\u003e \u003cp\u003eThe combined effect of MgCl\u003csub\u003e2\u003c/sub\u003e and MCC was studied with a central composite full factorial (CCF) statistical model and response surface models (RSM) were fit to the measurement data with multiple linear regression (MLR) using Sartorius MODDE 13 for turbidity after 10 minutes and after 20 hours of settling as the functions of magnesium chloride concentration and MCC concentration (Table\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e).\u003c/p\u003e \u003c/div\u003e\n\u003ch3\u003eWater salinity effect\u003c/h3\u003e\n\u003cp\u003eTo assess the effect of water salinity on flocculant performance in direct flocculation, NaCl was mixed with deionized water at 0.5, 5, 50, and 500 mM concentration. No KNO\u003csub\u003e3\u003c/sub\u003e or MgCl\u003csub\u003e2\u003c/sub\u003e was added. Kaolinite 2 was added, and the initial turbidity was measured to be 3200 NTU from a control sample with no NaCl and 1 mM KNO\u003csub\u003e3\u003c/sub\u003e. Flocculation procedure was then performed as above.\u003c/p\u003e \u003cdiv id=\"Sec8\" class=\"Section2\"\u003e \u003ch2\u003eScanning electron microscopy (SEM)\u003c/h2\u003e \u003cp\u003eFlocs were collected by decanting, frozen, and then dried in Labconco Freezone 2.5. 20 ppm of MCC solution was also regenerated as a reference sample without the presence of kaolinite, but in otherwise identical procedure. The samples were coated with 80/20 gold/palladium in Quorum Technologies Q 150 R sputter coater at 20 mV for 30 seconds. Imaging was done using Zeiss Sigma VP SEM with SE2 detector at 2.00 kV accelerating voltage.\u003c/p\u003e \u003c/div\u003e"},{"header":"Results and discussion","content":"\u003cdiv id=\"Sec10\" class=\"Section2\"\u003e \u003ch2\u003eFlocculant\u003c/h2\u003e \u003cdiv id=\"Sec11\" class=\"Section3\"\u003e \u003ch2\u003eDegree of polymerization\u003c/h2\u003e \u003cp\u003eThe limiting viscosity of MCC was 130 ml/g. The corresponding average DP was 158 anhydroglucose units and the average molar mass is 2.56 x 10\u003csup\u003e4\u003c/sup\u003e g/mol. PAM flocculants typically have higher molar mass from 10\u003csup\u003e5\u003c/sup\u003e g/mol to over 10\u003csup\u003e7\u003c/sup\u003e g/mol and they tend to perform better the higher the molecular weight at least up to 1.8 x 10\u003csup\u003e7\u003c/sup\u003e g/mol where their internal tangling can start to reduce the interaction with small particles (Xiong et al. \u003cspan citationid=\"CR46\" class=\"CitationRef\"\u003e2018\u003c/span\u003e).\u003c/p\u003e \u003c/div\u003e \u003c/div\u003e \u003cdiv id=\"Sec12\" class=\"Section2\"\u003e \u003ch2\u003eSolution stability\u003c/h2\u003e \u003cp\u003eLow shelf life can be a concern with biopolymer flocculants. MCC flocculant solution for this study was stored at 4\u0026deg;C in a refrigerator over the course of the experiments. The first signs of regenerated cellulose were noticed four weeks after the preparation. No signs of deterioration in flocculation performance were detected over several weeks of trials.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec13\" class=\"Section2\"\u003e \u003ch2\u003eFlocculation\u003c/h2\u003e \u003cdiv id=\"Sec14\" class=\"Section3\"\u003e \u003ch2\u003eDose optimization\u003c/h2\u003e \u003cp\u003eThe initial pH of the kaolinite suspension was 7.5 and the initial turbidity was 2200 NTU. The suspension was slowly settling without chemical additions, but only partially at up to 63.6% turbidity reduction to 800 NTU over 10 minutes and 94.8% to 115 NTU in 20 hours. Adding 1 mM of magnesium chloride had a significant effect on settling, as it improved the turbidity after 10 minutes of settling to 170 NTU and after 20 hours to almost complete clarity at 99.7% reduction at final turbidity of 7.0 NTU. MCC on its own had a slightly better result than MgCl\u003csub\u003e2\u003c/sub\u003e at 93.0% reduction and 155 NTU turbidity after 10 minutes, as well as 99.8% reduction all the way to 4.1 NTU turbidity after 20 hours. A comprehensive list of test points and results are presented in Table\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e.\u003c/p\u003e \u003cp\u003eTo confirm the effect of MCC solution in turbidity reduction as opposed to only pH increase being the driver of flocculation, 500 \u0026micro;L of 5% NaOH was tested as a \u0026ldquo;flocculant\u0026rdquo; in place of the MCC solution with 0.5 mM of MgCl\u003csub\u003e2\u003c/sub\u003e. The increase of floc size was visibly less than with MCC solutions. After 10 minutes of settling, the turbidity was 29.4 NTU. The addition of NaOH therefore improved the settling compared to no flocculant at the same MgCl\u003csub\u003e2\u003c/sub\u003e dose (155 NTU) but was not as good as MCC flocculant (12.8\u0026ndash;14 NTU).\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 main CCF test matrix for flocculation experiments with MgCl\u003csub\u003e2\u003c/sub\u003e electrolyte and 5% NaOH / 2% MCC solution flocculant\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=\"char\" char=\".\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" 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=\"char\" char=\".\" 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=\"char\" char=\".\" class=\"colspec\" colname=\"c7\" colnum=\"7\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e \u003cp\u003eelectrolyte concentration (mM)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003eflocculant (ppm)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003epH\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c4\"\u003e \u003cp\u003eTurbidity 10 min (NTU)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c5\"\u003e \u003cp\u003eTurbidity reduction 10 min\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c6\"\u003e \u003cp\u003eTurbidity 20 h (NTU)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c7\"\u003e \u003cp\u003eTurbidity reduction 20 h\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e0\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e0\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e7.7\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e800\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e63.6%\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e115\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e \u003cp\u003e94.8%\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e0\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e7.6\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e170\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e92.3%\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e7.0\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e \u003cp\u003e99.7%\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e0\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e20\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e11.0\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e112\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e94.9%\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e18.1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e \u003cp\u003e99.2%\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e20\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e10.6\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e8.1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e99.6%\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e1.5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e \u003cp\u003e99.9%\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e0\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e10\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e10.6\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e307\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e86.1%\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e53.7\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e \u003cp\u003e97.6%\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e10\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e10.4\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e10.6\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e99.5%\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e2.5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e \u003cp\u003e99.9%\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e0.5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e0\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e7.3\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e155\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e93.0%\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e4.1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e \u003cp\u003e99.8%\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e0.5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e20\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e10.8\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e7.9\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e99.6%\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e2.0\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e \u003cp\u003e99.9%\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e0.5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e10\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e10.5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e14.0\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e99.4%\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e3.4\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e \u003cp\u003e99.9%\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e0.5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e10\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e10.5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e14.0\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e99.4%\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e3.1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e \u003cp\u003e99.9%\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e0.5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e10\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e10.5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e12.8\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e99.4%\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e2.5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e \u003cp\u003e99.9%\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\u003eWith the combination of MgCl\u003csub\u003e2\u003c/sub\u003e and MCC it was already visible during the agitation phase, that the floc size was significantly larger, and water clarity better compared to single chemical treatments. In Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e the visible difference during agitation phase exemplifies how much faster the water clarification can happen when the chemical combination and dosage is appropriate for the target water when comparing 1 mM MgCl2 and 20 ppm of MCC to 0.5 mM MgCl2 only. Notably, despite the dramatic difference in initial rate of settling and clarification, after 20 hours of settling both test points end up clarifying almost completely at 1.5 and 4.1 NTU, respectively.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eIt should be noted that the addition of electrolytes, such as MgCl\u003csub\u003e2\u003c/sub\u003e in this study, to enhance the floc formation may not be necessary to the same degree depending on the electrolytes already present in the industrial process and waste waters. It has been shown that in flocculation of bentonite clay with PAM, chloride salts of sodium, potassium, magnesium and calcium can all improve the flocculation process (Shaikh et al. \u003cspan citationid=\"CR42\" class=\"CitationRef\"\u003e2018\u003c/span\u003e). One or several of these common elements are likely to be present in industrial process waters already, reducing the need of addition for the sake of water treatment. In mining industry water treatment, the increasing use of saline water has been considered a complication for the management of fine clays in tailings as it may make commonly used flocculants less effective (Liu et al. \u003cspan citationid=\"CR26\" class=\"CitationRef\"\u003e2018b\u003c/span\u003e). In the context of MCC flocculant application the use of saline water could be a beneficial development instead.\u003c/p\u003e \u003cp\u003eThe major downside of using NaOH solution of cellulose is that any increase in cellulose dosage comes with an increase in pH due to NaOH being a strong base. To lessen the effect, the concentration of cellulose in the solution could be increased or the concentration of NaOH decreased. However, this is highly non-trivial as cellulose alkali dissolution can be a fickle process. Increasing the cellulose content tends to lead to increased viscosity, decreased stability during storage and even a risk of gelation immediately after dissolution.\u003c/p\u003e \u003cp\u003eThe solubility of cellulose can be improved by lowering the degree of DP. However, when using MCC as was done in this research, we are already working close to the leveling-off degree of polymerization (LODP) for cellulose. Decreasing the DP further when nearing the LODP becomes slow or requires extreme hydrolysis conditions as only highly recalcitrant crystalline cellulose segments are left in the polymer chains. Additionally, for the flocculant bridging effect to occur in kaolinite suspension it is generally beneficial for the DP of the flocculant polymer to be high (Aguado et al. \u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2017\u003c/span\u003e; Xiong et al. \u003cspan citationid=\"CR46\" class=\"CitationRef\"\u003e2018\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eAnother approach to improving cellulose solubility is the use of cosolvents or solvent aids with NaOH, such as zinc oxide (Kihlman \u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e2012\u003c/span\u003e; Budtova and Navard \u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e2016\u003c/span\u003e; Koistinen et al. \u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e2023\u003c/span\u003e), urea (Zhou and Zhang \u003cspan citationid=\"CR49\" class=\"CitationRef\"\u003e2000\u003c/span\u003e; Egal et al. \u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e2008\u003c/span\u003e; Kihlman \u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e2012\u003c/span\u003e; Budtova and Navard \u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e2016\u003c/span\u003e) or thiourea (Kihlman \u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e2012\u003c/span\u003e; Budtova and Navard \u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e2016\u003c/span\u003e; Yang et al. \u003cspan citationid=\"CR48\" class=\"CitationRef\"\u003e2017\u003c/span\u003e), or even replacing NaOH with lithium hydroxide completely or partially (Cai and Zhang \u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e2005\u003c/span\u003e; Qiu et al. \u003cspan citationid=\"CR35\" class=\"CitationRef\"\u003e2018\u003c/span\u003e; Zhu et al. \u003cspan citationid=\"CR50\" class=\"CitationRef\"\u003e2018\u003c/span\u003e; Liu et al. \u003cspan citationid=\"CR27\" class=\"CitationRef\"\u003e2019\u003c/span\u003e). All these approaches have significant downsides in the context of water treatment. These water-soluble chemicals may cause problems in subsequent treatment processes, especially biological processes, they may be difficult to separate from the process waters before discharging, and they may contaminate the sludge.\u003c/p\u003e \u003c/div\u003e \u003c/div\u003e \u003cdiv id=\"Sec15\" class=\"Section2\"\u003e \u003ch2\u003eResponse surface model (RSM)\u003c/h2\u003e \u003cp\u003eThe coefficients for the models were chosen to maximize the coefficient of determination (R\u003csup\u003e2\u003c/sup\u003e) and the predictive relevance (Q\u003csup\u003e2\u003c/sup\u003e) of the model by omitting the most statistically insignificant coefficients whenever beneficial. For 10-minute turbidity model all coefficients, squares and the interaction coefficient were included as it gave the best fit and predictive value for the model even though the P-value for square of MCC ppm was 0.111. For 20-hour turbidity model the square of MCC ppm was omitted to increase Q\u003csup\u003e2\u003c/sup\u003e.\u003c/p\u003e \u003cp\u003eHistogram analysis showed that the response data for both 10-minute and 20-hour turbidity was skewed. This happened because almost all test points with either MCC or MgCl\u003csub\u003e2\u003c/sub\u003e reduced the turbidity significantly compared to the untreated suspension. The RSM was improved by logarithmic transformation of the results to improve the normality of the distribution and increase Q\u003csup\u003e2\u003c/sup\u003e.\u003c/p\u003e \u003cp\u003eThe final RSM for 10-minute turbidity had R\u003csup\u003e2\u003c/sup\u003e of 0.976 and Q\u003csup\u003e2\u003c/sup\u003e of 0.753. The final RSM for 20-hour turbidity had R\u003csup\u003e2\u003c/sup\u003e of 0.979 and Q\u003csup\u003e2\u003c/sup\u003e of 0.865. These values indicate that the models not only fit the experimental data superbly but also have high ability to predict outcomes of other chemical doses within the model area.\u003c/p\u003e \u003cp\u003eContour plots were drawn from the models for turbidities after 10 minutes and 20 hours of settling. In Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e, after 10 minutes of settling the lowest turbidity is expected between the center point and the upper right corner where both MgCl\u003csub\u003e2\u003c/sub\u003e and MCC doses are high. Based on the contour plot, it is expected that MgCl\u003csub\u003e2\u003c/sub\u003e concentration of 0.6\u0026ndash;1.0 mM and MCC dose of 12 to 20 ppm should provide turbidity of 5\u0026ndash;10 NTU in 10-minute settling.\u003c/p\u003e \u003cp\u003eIn Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e after 20 hours of settling the best results are spread more evenly on the vertical axis. This means that even without MCC it is possible to get low turbidity. However, MCC can be used to reduce the amount of MgCl\u003csub\u003e2\u003c/sub\u003e while still reaching good results, and for the absolute best results of \u0026lt;\u0026thinsp;2 NTU both flocculation chemicals should be used. Overall, the difference between the contour plots highlights the importance of polymeric flocculant aid in short time scales, while in a longer settling period a simple electrolyte that disturbs the charges in kaolinite particles can be enough to facilitate settling.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec16\" class=\"Section2\"\u003e \u003ch2\u003eSettling rate\u003c/h2\u003e \u003cp\u003eThe turbidities of samples with 0.5% of kaolinite 2 were measured from the start of settling for 10 minutes to investigate the rate of turbidity reduction with short settling times. The initial turbidity before any chemical additions was 3200 NTU. All samples had 0.5 mM of MgCl\u003csub\u003e2\u003c/sub\u003e, and varying dose of flocculant. MCC was used in 10 and 20 ppm doses, and 5% NaOH solution without cellulose was added to one sample at an amount equal to the NaOH in 20 ppm dose of MCC solution to rule out the effect of pH change from the solvent being the sheer driving force in turbidity reduction. The turbidity was recorded every minute, and the result is presented in Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003e.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eWhen there is MCC as flocculant, the settling almost entirely during the agitation and the first minute of settling. The most effective dose in this comparison was 20 ppm of MCC with 0.5 mM MgCl\u003csub\u003e2\u003c/sub\u003e and it resulted in turbidity of 21.7 NTU after only one minute of settling, 7.3 NTU after two minutes of settling and 4.7 NTU after 10 minutes of settling. Because the turbidity reduction and settling happen so fast, it is difficult to emphasize the difference between test points with this test setup. However, the MCC has a significant effect on turbidity reduction and the rate of settling, and the effect is most pronounced during the agitation and the first minutes of settling.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec17\" class=\"Section2\"\u003e \u003ch2\u003eWater salinity effect\u003c/h2\u003e \u003cp\u003eEffect of water salinity of 0.5\u0026ndash;500 mM of NaCl on settling of kaolinite over 10 minutes is presented in Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003e. Without the addition of MCC solution, the turbidity is affected by NaCl very little as all samples are between 100 and 180 NTU. 20 ppm of MCC changes the results radically, as the least saline sample settles far worse at 1500 NTU, but at all other salinity levels the settling is improved. The best result is achieved at 50 mM of NaCl, where the turbidity after 10 minutes is 21.3 NTU representing a 99.3% reduction from the initial turbidity of 3200 NTU.\u003c/p\u003e \u003cp\u003eThe salinity of ocean water is 3.5 wt.%, corresponding to around 600 mM of NaCl. Based on the results, MCC solution can improve the settling rate of kaolinite suspension in most saline waters at least up to salinity levels of ocean water but is at its best at around 10% of ocean water salinity. In mining tailings this is a good property, as the water salinity depends on the mineral content of the soil and the performance of conventional flocculants can be reduced by the salinity (Liu et al. \u003cspan citationid=\"CR25\" class=\"CitationRef\"\u003e2018a\u003c/span\u003e; Xiong et al. \u003cspan citationid=\"CR46\" class=\"CitationRef\"\u003e2018\u003c/span\u003e).\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec18\" class=\"Section2\"\u003e \u003ch2\u003eScanning electron microscopy (SEM)\u003c/h2\u003e \u003cp\u003eAs seen in \u003cb\u003eFig.\u0026nbsp;6ab\u003c/b\u003e, SEM images of samples from kaolinite suspensions show almost exclusively particles with kaolinite coated surfaces in the scale of \u0026lt;\u0026thinsp;100 \u0026micro;m. When regenerated without kaolinite, the MCC solution produces significantly larger particles beyond the 100 \u0026micro;m scale (\u003cb\u003eFig.\u0026nbsp;6cd\u003c/b\u003e). These particles also have distinctly different porous and rough surface textures from flaky and smooth kaolinite. A glimpse of a structure like the regenerated cellulose surface can be seen in the center of Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003eb among the kaolinite flakes. Based on these findings it is likely that when the MCC solution is regenerated in kaolinite suspension, it produces smaller particles than in water, and the regenerated cellulose particles are almost entirely coated with kaolinite.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e"},{"header":"Conclusion","content":"\u003cp\u003eCellulose directly dissolved in aqueous NaOH can significantly increase the particle size and the settling rate of a kaolinite suspension when applied as a flocculant. This effect is improved when the cellulose solution is used together with an electrolyte, such as magnesium chloride. Because the flocs that are formed using this type of flocculant are absent from conventional hazardous water treatment chemicals, they have more potential to be recycled, biodegraded, or repurposed safely. This is a major leap towards circular economy in water treatment sludge quality.\u003c/p\u003e \u003cp\u003eIn a chemical pulp and paper mill cellulose and NaOH are abundantly available. With suitable processes for converting them to a cellulose solution, the mill could manufacture flocculant for treating the mill waste waters instead of buying synthetic flocculant. With a shelf life of approximately four weeks, the manufactured chemical could also be sold out and used for other industrial water treatment, such as improving the settling of mining industry tailings. Alternatively, to increase shelf life the cellulose and NaOH could be stored as dry powders or pellets, and then dispersed, mixed and dissolved at site as needed since only freezing and mixing are required for a batch production process.\u003c/p\u003e \u003cp\u003eA major drawback with this type of flocculant is that NaOH solution of cellulose raises the pH of the targeted water stream. This limits the use to cases where (1) the target water is initially acidic and needs to be neutralized, (2) the target water has high pH buffering ability and the pH change is minor, (3) the resulting floc is significantly more valuable when it is not contaminated with metal salts, hydroxides, or synthetic polymers, and thus worth the extra expense of neutralizing the water afterwards, or (4) the heightened pH is not an issue, for example if the treated water is recycled into a process where high pH is desirable.\u003c/p\u003e \u003cp\u003eCellulose flocculant retains its ability to improve the rate of settling even at high salinity. This makes it potentially useful in settling fine clay in mining industry tailings, where salinity of the water can cause issues with conventional flocculants. It also means that the flocculant is relatively robust to industrial processing plant conditions, where the exact composition of process waters may change day-to-day.\u003c/p\u003e"},{"header":"Abbreviations","content":"\u003cp\u003eCCF,\u0026nbsp;central composite full factorial; CED, cupriethylenediamine; DP,\u0026nbsp;degree of polymerization;\u0026nbsp;KNO\u003csub\u003e3\u003c/sub\u003e, potassium nitrate; LODP,\u0026nbsp;leveling-off degree of polymerization;\u0026nbsp;MgCl\u003csub\u003e2\u003c/sub\u003e, magnesium chloride;\u0026nbsp;MCC, microcrystalline cellulose; MLR, multiple linear regression; NaCl, sodium chloride; NaOH, sodium hydroxide; OD, oven-dry; PAM, polyacrylamide; Q\u003csup\u003e2\u003c/sup\u003e, predictive relevance; R\u003csup\u003e2\u003c/sup\u003e, coefficient of determination; RSM, response surface model; SEM, scanning electron microscopy\u003c/p\u003e"},{"header":"Declarations","content":"\u003ch2\u003eCompeting interests\u003c/h2\u003e \u003cp\u003eThe authors have no relevant financial or non-financial interests to disclose.\u003c/p\u003e \u003ch2\u003eFunding\u003c/h2\u003e \u003cp\u003eThis work was completed with funding from Maa- ja vesitekniikan tuki ry. (grant #4799) and initiated as a part of ETSIV\u0026Auml;T project funded by Suomen Kulttuurirahasto.\u003c/p\u003e\u003ch2\u003eAuthor Contribution\u003c/h2\u003e\u003cp\u003eBoth authors contributed to the study conception and design. Material preparation, data collection and analysis were performed by Tomi Eilamo. The first draft of the manuscript was written by Tomi Eilamo and finalized by Tomi Eilamo with the support and comments of Olli Dahl. Both authors read and approved the final manuscript.\u003c/p\u003e\u003ch2\u003eData Availability\u003c/h2\u003e\u003cp\u003eData is provided within the manuscript or supplementary information files\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\u003cli\u003e\u003cspan\u003eAbbasi Moud A (2022) Polymer based flocculants: Review of water purification applications. 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Int J Miner Process 91:94\u0026ndash;99. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1016/j.minpro.2009.01.003\u003c/span\u003e\u003cspan address=\"10.1016/j.minpro.2009.01.003\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\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":"cellulose","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"cels","sideBox":"Learn more about [Cellulose](https://www.springer.com/journal/10570)","snPcode":"10570","submissionUrl":"https://submission.nature.com/new-submission/10570/3","title":"Cellulose","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"em","reportingPortfolio":"Springer Hybrid","inReviewEnabled":true,"inReviewRevisionsEnabled":false},"keywords":"kaolin, coagulation/flocculation, cellulose, solutions, sodium hydroxide","lastPublishedDoi":"10.21203/rs.3.rs-6697938/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-6697938/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eKaolinite is clay used in various industries that forms turbid dispersions and disrupts aquatic ecosystems if not separated from process waters before discharge. Conventional coagulation chemicals, such as alum and polyacrylamides could be used to improve separation, but they contain long-term risks to human health and the environment. In this study, we show that cellulose dissolved in aqueous sodium hydroxide can be used to increase the particle size and the settling rate of kaolinite suspension. The effect is further enhanced when the cellulose solution is used together with magnesium chloride. A response surface models were made to evaluate the effect of cellulose and magnesium chloride doses on kaolin suspension turbidity after 10 minutes and after 20 hours of settling. An effective dose was determined and a 0.5 wt.% kaolinite suspension with initial turbidity of 3200 NTU was treated with 20 ppm of dissolved cellulose and 0.5 mM of magnesium chloride to achieve turbidity of 7.3 NTU after 2 minutes of settling and 4.7 NTU after 10 minutes of settling. Additionally, it was shown that the cellulose solution largely retains its ability to flocculate the kaolin suspension in saline waters at least up to 0.5 M of sodium chloride content. These results could have applications especially in industries where both kaolinite and cellulose are present, such as pulp and paper industry.\u003c/p\u003e","manuscriptTitle":"Kaolinite suspension treatment using cellulose dissolved in sodium hydroxide as flocculant","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2025-06-18 16:48:10","doi":"10.21203/rs.3.rs-6697938/v1","editorialEvents":[{"type":"communityComments","content":0},{"type":"decision","content":"Revision requested","date":"2025-06-07T20:09:53+00:00","index":"","fulltext":""},{"type":"editorAssigned","content":"","date":"2025-06-07T20:06:51+00:00","index":"","fulltext":""},{"type":"checksComplete","content":"","date":"2025-05-20T07:38:29+00:00","index":"","fulltext":""},{"type":"submitted","content":"Cellulose","date":"2025-05-19T10:21:38+00:00","index":"","fulltext":""}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"cellulose","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"cels","sideBox":"Learn more about [Cellulose](https://www.springer.com/journal/10570)","snPcode":"10570","submissionUrl":"https://submission.nature.com/new-submission/10570/3","title":"Cellulose","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"em","reportingPortfolio":"Springer Hybrid","inReviewEnabled":true,"inReviewRevisionsEnabled":false}}],"origin":"","ownerIdentity":"70ecb183-92c1-4f85-8793-02750f0b342c","owner":[],"postedDate":"June 18th, 2025","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"published-in-journal","subjectAreas":[],"tags":[],"updatedAt":"2026-03-02T16:12:26+00:00","versionOfRecord":{"articleIdentity":"rs-6697938","link":"https://doi.org/10.1007/s10570-026-06991-8","journal":{"identity":"cellulose","isVorOnly":false,"title":"Cellulose"},"publishedOn":"2026-02-27 15:58:17","publishedOnDateReadable":"February 27th, 2026"},"versionCreatedAt":"2025-06-18 16:48:10","video":"","vorDoi":"10.1007/s10570-026-06991-8","vorDoiUrl":"https://doi.org/10.1007/s10570-026-06991-8","workflowStages":[]},"version":"v1","identity":"rs-6697938","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-6697938","identity":"rs-6697938","version":["v1"]},"buildId":"8U1c8b4HqxoKbykW_rLl7","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}