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시멘트 페이스트를 이용한 불산폐수 처리에 관한 연구

Title
시멘트 페이스트를 이용한 불산폐수 처리에 관한 연구
Other Titles
Treatment of Fluoride Wastewater Using Cement Paste
Author
변혜정
Alternative Author(s)
Byun, Hye-Jung
Advisor(s)
박주양
Issue Date
2007-02
Publisher
한양대학교
Degree
Master
Abstract
불산폐수 처리를 위해 일반적으로 사용하는 lime을 이용한 침전법은 lime의 용해도가 낮아 약품을 과량 주입하여야 하며, fluorite(CaF₂) 결정이 매우 작아 결정형성을 돕기 위한 무기응고제의 과량 주입으로 다량의 슬러지가 발생하는 문제점을 가지고 있다. 그리고 실제 불산폐수 내에는 불소 외에 nitrate와 phosphate 등의 오염물질을 함유하고 있어, 불소제거를 방해할 뿐만 아니라 후속처리공정이 필요하여 그로인한 많은 비용이 소요되고 있다. 따라서 본 연구에서는 시멘트 수화반응 동안 생성된 다량의 시멘트 수화물을 함유하고 있는 시멘트 페이스트를 이용하여 불산폐수를 처리함으로써, 실제 폐수처리 가능성을 파악하고 불산폐수 처리효율은 평가하고자 하였다. 실험에 의해 최적 입도로 결정된 150 ㎛ 이하의 시멘트 페이스트를 이용해 불산폐수를 처리한 결과, 기존 처리제인 lime에 상응하는 불소 및 phosphate 제거율을 확인할 수 있었다. 또한 시멘트 페이스트 주입량별 불소 농도 및 음이온의 농도를 modeling을 통한 예측치와 실측치를 비교하였을 때, 경향이 동일하게 나오는 것을 알 수 있었다. 연속식 불산폐수 처리에서는 Ca^(2+)와의 반응으로 불소를 포함한 phosphate, sulfate가 안정적으로 처리되었으며, nitrate는 LDHs 계열 물질인 시멘트 수화물의 이온교환 반응에 의하여 제거되었다. 따라서 시멘트 페이스트를 이용한 불산폐수 처리 시스템은 불소 외에 오염물질을 동시에 처리함으로써 보다 효과적인 시스템으로 활용 가능할 것으로 사료된다.
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 kinetic experiments were performed to investigate the behavior of fluoride removal by cement paste and lime. The fluoride removal efficiency of cement paste was 94%, which were comparable to that of lime 95%. Various Ca-bearing hydrates such as portlandite, calcium silicate hydrate(C-S-H) and ettringite in cement paste were identified to remove fluoride by precipitating fluorite(CaF₂) and adsorbing F^(-) ions. The removal efficiencies of phosphate in cement paste and lime amounted to 85% and 80%, respectively. Phosphate was removed from the wastewater by forming calcium compounds : CaHPO₄2H₂O, CaHPO₄, Ca4H(PO₄)₃2.5H₂O, Ca₃(PO₄)₂, Ca_(5)(PO₄)₃OH and Ca₃(PO₄)₂. To evaluate the successive fluoride removal capacity of cement paste, a column experiment was performed. In column experiment where the input fluoride concentration was 408 mg/L and the residence time of the porewater was 6 hr, the effluent concentrations were below 0.5 mg/L. As calcium gradually leached out from cement paste, fluoride concentration was decreased until 120 pore volume. Then the leached calcium reached the maximum level of 800 mg/L, which was maintained until the breakthrough point. After the calcium leached out from cement hydrates such as portlandite, calcium silicate hydrate, and ettringite was completely used up, CaF₂ particles were not precipitated anymore. The nitrate concentration of 331mg/L immediately reduced to the level of less than 10 mg/L. Nitrate was believed to be adsorbed onto ca-bearing hydrates in cement paste which belongs toa family of layered double hydroxide(LDH) materials which multifunctional immoblilization capabilities such as ion exchange, intercalation and adsorption of anion. Nitrate in the wastewater was exchanged with interlayer sulfate of these cement hydrate LDHs. The initial sulfate concentration of 520 mg/L reduced to below 10 mg/L until 30 pore volume. Sulfate removal was by precipitation CaSO4. After 30 pore volume, effluent sulfate concentration was gradually increased by ion exchange until the breakthrough point. Phosphate concentrations up to 1151 mg/L could be reduced to 10 mg/L. The phosphate removal mechanism was described by forming calcium phosphate. On the basis of the above experimental findings, cement paste reactor has been shown to reduce the fluoride concentration of the wastewater to below 0.5 mg/L and it removes other pollutants such as nitrate, sulfate and phosphate in the wastewater. These results indicate that the cement paste generally has advantageous characteristics as an economical and viable substitute for lime to remove fluoride.
URI
https://repository.hanyang.ac.kr/handle/20.500.11754/149524http://hanyang.dcollection.net/common/orgView/200000406150
Appears in Collections:
GRADUATE SCHOOL[S](대학원) > DEPARTMENT OF CIVIL ENGINEERING(토목공학과) > Theses (Master)
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