• Journal of Korean Society of Environmental Engineers
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• v.22 no.6
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• pp.1127-1137
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• 2000

Applications of lanthanum ion and crude rare earth chloride to the phosphate wastewater and fluorine wastewater, respectively, as treatment agents were studied. For the investigation of phosphate removal characteristics according to the amount of lanthanum ion, initial phosphate content was decreased by about 50% when molar ratio of [$La^{3+}$]:[$PO_4{^{3-}}-P$] was 0.25 and nearly all of phosphate was removed when the molar ratio of [$La^{3+}$]:[$PO_4{^{3-}}-P$] to be doubled. The removal of phosphate by $La^{3+}$ appeared to reach equilibrium state rapidly, and it was exothermic reaction since the removed amount of phosphate was diminished somewhat when the reaction temperature was increased. The zeta potential of combined particulate compound of lanthanum ion and phosphate was located for its isoelectric point at pH 5.5 and the turbidity of treated wastewater was found to vary according to the pH in a similar manner as the absolute value of zeta potential of the combined particulate compound did. For the treatment of fluorine wastewater by crude rare earth chloride, the remaining fluorine content after treatment decreased as the dosage of crude rare earth chloride increased. Whereas, the turbidity of treated wastewater and the amount of sludge generated were shown to increase as more crude rare earth chloride was added. The remaining fluorine content and the turbidity of treated wastewater were decreased and the amount of sludge generated was observed to increase according the increase of coagulant dosage under the condition of constant input of crude rare earth chloride.

• Resources Recycling
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• v.16 no.4
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• pp.27-32
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• 2007

The characteristics of fluorine removal from wastewater have been investigated by precipitation method using calcium as a precipitant for the purpose of the reuse of treated wastewater. In the conditions of 10 mM of the initial concentration of fluorine and pH 4, the precipitation of fluorine was rapidly progressed within a few minutes after the precipitant was added and the precipitation of fluorine was observed to follow a second order reaction. Also, as the addition of precipitant was increased, the reaction rate constant of fluorine precipitation was found to rise. Postulating that the maximum fluorine removal was attained at pH 4, about 70% of fluorine was precipitated compared with the maximum removal when 10 times of equivalent amount of calcium was employed at pH 2 and the fluorine removal was about 96% compared with its maximum value at pH 3 under the same addition of precipitant. The fluorine precipitation reaction was found to be endothermic and the coexistence of $SiF_6{^{2-}}$ with fluorine resulted in its less removal. Finally, the isoelectric point of the precipitate was examined to be ca. pH 5.

• Journal of Korean Society of Environmental Engineers
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• v.29 no.8
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• pp.909-914
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• 2007

Fluorine compounds are the essential chemicals for wet processes of semiconductor and LCD production line. Problems of conventional treatments for fluoride wastewater are their high operation costs and low fluoride removal capacity. In this study, cement paste containing various Ca-bearing hydrates such as portlandite, calcium silicate hydrate(CSH), and ettringite was investigated for fluoride removal. The objectives of this study are to assess the feasibility of using cement paste cured mixture of cement and water as an alternative agent for treatment of fluoride wastewater and to investigate fluoride removal capacity of the cement paste. The performance of cement paste was comparable to that of lime in the kinetic test. In column experiment where the effluent fluoride concentrations were below 0.5 mg/L. Then the leached calcium reached the maximum level of 800 mg/L. The nitrate reduced to the level of less than 10 mg/L. Nitrate in the wastewater was exchanged with interlayer sulfate of these cement hydrate LDHs. Phosphate concentration could be reduced to 10 mg/L by forming calcium phosphate. These results indicate that the cement paste generally has advantageous characteristics as an economical and viable substitute for lime to remove fluoride.

• Proceedings of the KSEEG Conference
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• 2000.04a
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• pp.73-76
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• 2000

• Journal of Korean Society of Environmental Engineers
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• v.32 no.7
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• pp.730-737
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• 2010

It is very important to remove fluoride ion before treating semiconductor wastewater containing high concentration of ammonia, phosphates, and fluoride ions by struvite formation. Calcium ion was generally added for the removal of fluoride ion. However, calcium ions remained after removal of fluoride ion can deteriorate the performance of struvite crystalization. It should be removed completely before struvite formation. In this study, the effect of fluoride and calcium ion concentration on the struvite crystalization was investigated. Removal efficiencies of ortho-phosphate with struvite formation were more abruptly decreased than those of ammonium nitrogen, as increase of fluoride ion concentration in synthetic wastewater. The structures of struvite formed in synthetic wastewater containing calcium ion of up to 500 mg/L were identical. Purity of struvite was deteriorated as increase of calcium ion over 500 mg/L. Removal efficiencies of ammonium nitrogen were more decreased than those of phosphate ions as increase of cacium ion in synthetic wastewater.

• Journal of Korean Society of Environmental Engineers
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• v.35 no.4
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• pp.257-262
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• 2013

The fluorine-containing waste water tends to show a higher removal efficiency through the coagulative precipitation process with calcium. However the tetrafluoroborate produced from the etching process is difficult to remaval due to it's low reactivity with calcium. The objective of this study is improving the efficiency of fluoride ion removal in tetrafluoroborate through decomposing. Research on tetrafluoroborate decomposition depending on reaction pH, temperature, and aluminum dosage were conducted, using a laboratory-scale reactor. The result shows that the reaction of tetrafluoroborate with aluminum is faster with lower pH, higher water temperature, and higher Al/T-F (Aluminum/Total Fluoride) mole ratio. It is found that there was no big change in concentration after over 120 minutes of reaction. This study is to be able to improve the efficiency of tetrafluoroborate and fluoride wastewater treatment by using aluminum.

• Journal of Korean Society of Environmental Engineers
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• v.33 no.10
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• pp.774-781
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• 2011

Nitric acid and hydrofluoric acid are used for acid pickling in zirconium alloy tubing manufacturing process. Nitrate and fluoride in the wastewater were treated by chemical coagulation and SOD (Sulfur Oxidation Denitrification) process. This study is investigated the effect of fluoride concentration and the optimal condition for SOD process. The limited fluoride concentration for SOD process was below 20 mg F-/L. The adjusted pH and alkalinity by NaOH and $NaHCO_3$ was shown to be more effective for removal of nitrate compared with using NaOH. Furthermore, the microbial activator mixed trace elements and ingredient for alkalinity did not only supplement with alkalinity but also enhance the growth and proliferation for sulfur-oxidizing bacteria. As a result, the inorganic industrial wastewater was successfully treated by the microbial activator in SOD process without continuous addition of seed sludge. Finally, SOD process was shown to remove nitrate in industrial wastewater and to contribute the microbial activator for activation of sulfur-oxidizing bacteria.

• 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.

• Applied Chemistry for Engineering
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• v.29 no.4
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• pp.479-483
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• 2018

Our group reported the thermal decomposition of R-22 ($CHClF_2$) refrigerants by nitrogen thermal plasma in previous studies. However, it was proposed that the wastewater generated from the end part of the process contains high concentration of fluoride ion which is a component of R-22. The additional post-treatment process to neutralize the $F^-$ ions in the wastewater was investigated in this study. The wastewater generated through the decomposition of R-22 with the same procedure in the previous work was treated using the neutralizer, $Ca(OH)_2$, and the atmospheric pressure plasma jet (APPJ) independently as a post-treatment process. Wastewater samples were collected directly after the treatment for ion-chromatography analysis to trace the change of the concentration of $F^-$ ion in the wastewater. The fluoride concentration in the wastewater showed the highest value when the single water was used as a neutralizer, and the concentration of fluoride in the wastewater was dramatically reduced when the post-treatments were performed.

• Journal of Korean Society of Environmental Engineers
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• v.33 no.11
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• pp.855-859
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• 2011

The main pollutants from zirconium alloy tubing manufacturing process in nuclear industry are nitrate ($NO_3-N$) and fluoride (F-)Nitric acid, and hydrofluoric acid is used for acid pickling. The process for the removal of nitrate and fluoride is composed of 1st chemical coagulation, SOD (Sulfur Oxidation Denitrification) process using sulfur-oxidizing denitrification, and 2nd chemical coagulation. The characteristic of the wastewater treatment is an application of SOD process. The SOD Process is highly received attention because it is significantly different from existing processes for sulfur denitrification. A JSC (JeonTech-Sulfur- Calcium) Pellet is unification of sulfur and alkalinity material. According to result of SOD process in wastewater treatment plant, the removal efficiency of T-N was over 91% and the average concentration of T-N from influent was 147.55 mg T-N/L and that from effluent was 12.72 mg T-N/L. Therefore, SOD process is a useful to remove nitrogen from inorganic industrial wastewater and a new development of microbial activator was shown to be stable for activation of autotrophic bacteria.