• Advances in environmental research
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• v.12 no.2
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• pp.77-93
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• 2023

The water can be contaminated by natural sources or by industrial effluents. One such contaminant is fluoride. Fluoride contamination in the water environment due to natural and artificial activities has been recognized as one of the major problems worldwide. Among the commonly used treatment technologies applied for fluoride removal, the adsorption technique has been explored widely and offers a highly efficient simple and low-cost process for fluoride removal from water. This review paper the recent developments in fluoride removal from surface water by adsorption methods. Studies on fluoride removal from aqueous solutions using various carbon materials are reviewed. Various adsorbents with high fluoride removal capacity have been developed, however, there is still an urgent need to transfer the removal process to an industrial scale. Regeneration studies need to be performed to more extent to recover the adsorbent in field conditions, enhancing the economic feasibility of the process. Based on the review, technical strategies of the adsorption method including the Nano-surface effect, structural memory effect, anti-competitive adsorption and ionic sieve effect can be proposed. The design of adsorbents through these strategies can greatly improve the removal efficiency of fluoride in water and guide the development of new efficient methods for fluoride removal in the future. This paper describes brief discussions on various low-cost adsorbents used for the effective removal of fluoride from water.

• Journal of Korean Society on Water Environment
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• v.25 no.6
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• pp.916-921
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• 2009

This study was aimed to both enhance the fluoride removal and to reduce the phosphorus removal in treating semiconductor wastewater using $Ca(OH)_2$ at low pH so as to facilitate struvite crystallization reaction. The struvite crystallization could be introduced after fluoride removal by retaining the phosphorus source. As the results, the method applied in this study achieved high fluoride removal efficiency (about 91%) with retardation of phosphorus removal at pH 4, compared to conventional methods where the removal of fluoride and phosphorus were done at pH 11. Therefore, the fluoride removal at low pH would contribute to the enhancement of nitrogen and phosphorus removals in a consecutive struvite crystallization reactor. Treatment of semiconductor wastewater at low pH using $Ca(OH)_2$ also had lower (about 20%) water content of precipitated sludge compared to conventional method. As the molar ratio of Ca to F increased the removal efficiencies of fluoride and phosphorus increased. Although the amount of seed dosage didn't affect the removal of fluoride and phosphorus, its increase reduced the water content of precipitated matter. Finally, considering consecutive struvite reaction, the optimum condition for the removal of fluoride and phosphorus was as follow: pH: 4, the molar ratio of Ca:F: 1:1.

• Advances in environmental research
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• v.2 no.1
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• pp.35-49
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• 2013

Research work on removal of fluoride from water, referred to as water defluoridation, has resulted into the development of a number of technologies over the years but they suffer from either cost or efficiency drawbacks. In this work, enhancement effects of phosphate and silicate on defluoridation of water by low-cost Plaster of Paris (calcined gypsum) were studied. To our knowledge, the influence of silicate on defluoridation was not reported. It was claimed, that the presence of some ions in the treated water samples, was decreasing the fluoride removal since these ions compete the fluoride ions on occupying the available adsorption sites, however, phosphate and silicate ions, from its sodium slats, have enhanced the fluoride % removal, hence, precipitation of calcium-fluoro compounds of these ions can be suggested. Percentage removal of $F^-$ by neat Plaster is 48%, the electrical conductance (EC) curve shows the typical curve of Plaster setting which begins at 20 min and finished at 30 min. The addition of phosphate and silicate ions enhances the removal of fluoride to high extent > 90%. Thermodynamics parameters showed spontaneous fluoride removal by neat Plaster and Plaster-silicate system. The percentage removal with time showed second-order reaction kinetics.

• Journal of The Korean Society of Agricultural Engineers
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• v.55 no.3
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• pp.35-40
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• 2013

The present study was conducted to investigate the adsorption potential of red mud for fluoride removal. Different operation parameters such as the effect of contact time, initial concentration, pH, competing anions, seawater, adsorbent dose amount, and adsorbent mixture were studied. Nearly 3 hr was required to reach sorption equilibrium. Equilibrium sorption data were described well by Langmuir model and the maximum adsorption capacity of red mud was 5.28 mg/g. The fluoride adsorption at pH 3 was higher than in the pH range 5-9. The presence of anions such as sulfate, nitrate, phosphate, and bicarbonate had no significant effect on fluoride adsorption onto red mud. The fluoride removal by red mud was greater in seawater than deionized water, resulting from the presence of calcium and magnesium ion in seawater. The use of red mud alone was more effective for the removal of fluoride than mixing red mud with other industrial waste such as oyster shells, lime stone, and steel slag. This study showed that red mud has a potential application in the remediation of fluoride contaminated soil and groundwater.

• Journal of Korean Society of Water and Wastewater
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• v.25 no.5
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• pp.767-775
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• 2011

In this study we verified if the electro-coagulation process can treat properly the nitrate and fluoride that are not removed well in the conventional small water treatment plants which usually employ chlorination and filtration only. As we gave a change of electrode material and gap-distance between electrodes, removal efficiency of the nitrate and fluoride was determined by electro-coagulation process which were equipped with aluminum and stainless steel (SUS304) electrodes. In addition, electrode durability was investigated by determination of electrodes mass change during the repetitive experiments. Removal efficiency was great when aluminum was used as an anode material. Nitrate removals increased as electric density and number of electrodes increased, but fluoride removal was less sensitive to both parameters than nitrate. After 10 minutes of contact time with the current density from $1{\times}10^{-3}$ to $3{\times}10^{-3}A/cm^{2}$, nitrate and fluoride concentration ranged from 9.2 to 1.2mg/L and from 0.02 to 0.01mg/L, which satisfied the regulation limits. Regardless of the repeating number of experiments, removal efficiency of both ions were almost similar and the change of electrode mass ranged within ${\pm}$0.5%, indicating that the loss of the electrode mass is not so much great under the limited circumstances.

• Journal of Korean Society of Environmental Engineers
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• v.32 no.5
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• pp.437-442
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• 2010

This work was initiated both to maximize purity of calcium fluoride sludge and to minimize water content in the settled sludge. The sludge was produced in the process of fluoride removal of semiconductor wastewater by the addition of $Ca^{2+}$ ion. Fludized bed reactor(FBR) using calcium fluoride as a seed was adapted. Optimum pH and molar ratio of $Ca^{2+}/F^-$ were determined in lab-scale study. The experimental results showed that fluoride removal was increased as pH and molar ratio of $Ca^{2+}/F^-$ increased, with the best removal of 79.8% in an optimum condition. In the optimum point of fluoride removal, very low ${PO_4}^{3-}$-P removal of 9.3% was observed. It indicates forming $CaF_2$ crystal of high purity, when side reaction of calcium with phosphate was minimized. In addition, water content of settled sludge was 19.3%, which is relatively low compared to other fluoride removal processes. Consequently, the FBR process proposed in this study was very effective in fluoride removal, producing good sludge of high purity and less water content.

• Clean Technology
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• v.20 no.1
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• pp.51-56
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• 2014

In this study, PSf-$Al(OH)_3$ beads were prepared by immobilizating aluminum hydroxide $Al(OH)_3$ with polysulfone (PSf). The removal experiments of the fluoride ions by PSf-$Al(OH)_3$ beads were conducted batchwise and the parameters such as pH, initial fluoride concentration, and coexisting ions were investigated. The maximum removal capacity obtained from Langmuir isotherm was 52.4 mg/g and the optimum pH region of fluoride ions was in the range of 4 to 10. The removal process of fluoride ions by PSf-$Al(OH)_3$ beads was found to be controlled by both external mass transfer at the earlier stage followed by internal diffusion at the later stage. The presence of coexisting anions such as $HCO_3{^-}$, $SO{_4}^{2-}$, $NO_3{^-}$, and $Cl^-$ had a negative effect on removal of fluoride ions by PSf-$Al(OH)_3$ beads.

• Journal of Korean Society of Environmental Engineers
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• v.32 no.6
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• pp.593-598
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• 2010

The optimum condition for fluoride removal, water content reduction, and $CaF_2$ purity was determined in treating semiconductor waste water in which ammonia nitrogen, phosphorus, and fluoride are existed simultaneously using a fluidized bed reactor. Effects of pH, seed dosage, and recirculation of treated water were investigated through lab-scale experiments. Considering fluoride removal, sludge purity, and water content, that pH 5 and seed dose of 150 g were found to be optimum. Correspondingly, removal of fluoride and phosphate (${PO_4}^{3-}$-P) was 94.24% and 8.97%, respectively, with water content ratio of 12.94%. Increase in an amount of seed dosage not only enhance fluoride removal efficiency, but also buffer fluoride removal-reducing effect due to the variation of recirculation ratio of treated water and pH.

• Journal of Korean Society on Water Environment
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• v.28 no.5
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• pp.717-722
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• 2012

Fluoride can be easily found in semiconductor and display industry. However, there is a lack of research for its effects on the related wastewater treatment. The objective of this study is to evaluate the microbial inhibitory effect by fluoride injection. The research entailed the assessment of removal efficiency of $TCOD_{Cr}$ according to the fluoride concentration and also the Specific Oxygen Uptake Rate (SOUR) was measured. The laboratory scale reactor was prepared and operated with the fluoride concentrations of 0, 10, 50, 100, and 200 mg/L based on concentrations frequently occurring in the wastewater. The results from this study showed that, as the fluoride concentration increase, the Specific Substrate Utilization Rate (SSUR) tend to decrease as expected. Also, the increase in fluoride concentrations resulted in the decrease in SOUR. It is determined that fluoride injection affects the microbial activity. Especially, The addition of above 200 mg/L fluoride into reactor caused rapidly decreased SSUR and SOUR due to the inhibitory effects of fluoride.

• Journal of Korean Society of Water and Wastewater
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• v.19 no.2
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• pp.125-134
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• 2005

Waste concrete powder was used to remove fluoride ions in highly concentrated fluoride wastewater. 92.6% of fluoride in 100 mg F/L wastewater was removed by 1% dose of the cement paste powder that represents characteristics of waste concrete powder, whereas the removal efficiencies of raw cement and lime were 47.3% and 96.4%, respectively. The cement paste powder was competitive to lime, common fluoride removal agent. Various Ca-bearing hydrates such as portlandite, calcium silicate hydrate, and ettringite in cement paste slurry can remove fluoride by precipitating $CaF_2$ and absorbing $F^-$ ions. In the experiments using both cement paste and lime, 50~67% of lime can be substituted by cement paste to satisfy fluoride effluent limitation of 15 mg/L. Since cement paste has higher acid neutralization capacity than lime, it can be recycled to neutralize more acid and to remove more fluoride. Therefore waste concrete powder can be more economical and viable alternative for lime in fluoride wastewater treatment.