Effect of hydrated lime particle size on fluoride removal in wastewater treatment

국문 초록 (Abstract)

수산화칼슘(Ca(OH)2)은 반도체 제조공정 등에서 발생하는 불소 함유 폐수의 처리에 널리 사용되며, 일반적으로 응집-침전 방식으로 CaF2를 형성하여 불소를 제거한다. 그러나 기존의 거대입자형 Ca(OH)2는 반응성이 낮아 과도한 약품 투입이 필요하고, 그에 따라 슬러지 발생량이 증가하여 처리 비용 및 환경 부담이 커진다는 문제가 있다.
본 연구에서는 미세입자형 Ca(OH)2(HL-2500)를 적용하여 반응성을 개선하고, 불소 제거 효율, 슬러지 특성, 공정 지속가능성을 기존 Ca(OH)2(HL-500)와 비교 분석하였다. 500 mg/L의 불소를 함유한 합성 폐수를 대상으로 교반 실험을 수행하였으며, 불소 및 칼슘 잔류 농도, 슬러지 부피 및 수분 함량, 표면 형태와 성분 분석 등을 통해 성능을 종합적으로 평가하였다.
그 결과, HL-2500은 30분 내에 97%의 불소 제거율을 달성하여 방류기준을 충족시켰고, 슬러지 부피와 수분 함량은 각각 32%, 60% 감소하였다. 또한 F:Ca 원자비가 2.33으로 고순도 CaF2 침전이 확인되었으며, SEM 분석 결과 조밀하고 구형의 응집체가 관찰되었다. 이는 미세입자의 빠른 Ca2+ 방출이 CaF2 과포화를 유도하고, 균일한 핵생성과 성장으로 반응 효율을 높였기 때문이다.
또한 HL-2500 적용 시 약품 사용량 절감, 슬러지 감소, 공정 운영비 절감 등의 이점이 있으며, 형석 대체 소재로 활용 가능한 CaF2 슬러지를 생성하여 자원화 가능성도 확인되었다. 본 연구는 HL-2500이 보다 경제적이고 환경친화적인 불소 폐수 처리 대안이 될 수 있음을 제시하며, 향후 산업 현장 적용 확대를 위한 기초 자료를 제공한다.

다국어 초록 (Multilingual Abstract)

Calcium hydroxide (Ca(OH)2) is widely used for the treatment of fluoride-containing wastewater generated from semiconductor manufacturing and similar industrial processes. Typically, it removes fluoride through coagulation–precipitation by forming calcium fluoride (CaF2). However, conventional coarse-particle Ca(OH)2 exhibits low reactivity, requiring excessive chemical dosing, which increases sludge generation, treatment costs, and environmental burden.
In this study, fine-particle Ca(OH)2 (HL-2500) was applied to enhance reactivity, and its fluoride removal efficiency, sludge characteristics, and process sustainability were comparatively analyzed against conventional Ca(OH)2 (HL-500). Jar tests were conducted using synthetic wastewater containing 500 mg/L of fluoride, and performance was comprehensively evaluated through measurements of residual fluoride and calcium concentrations, sludge volume and moisture content, and surface morphology and composition analyses.
As a result, HL-2500 achieved a 97% fluoride removal rate within 30 minutes, meeting the discharge standard, while sludge volume and moisture content were reduced by 32% and 60%, respectively. The F:Ca atomic ratio of 2.33 indicated the formation of high-purity CaF2 precipitates, and SEM analysis revealed dense, spherical agglomerates. This was attributed to the rapid release of Ca2+ ions from fine particles, which promoted CaF2 supersaturation and enhanced uniform nucleation and crystal growth, thereby improving reaction efficiency.
Moreover, the application of HL-2500 offered advantages such as reduced chemical consumption, decreased sludge production, and lower operational costs. The resulting CaF2 sludge, with high purity, demonstrated potential for resource recovery as a substitute for natural fluorspar. This study suggests that HL-2500 can serve as a more economical and environmentally friendly alternative for fluoride wastewater treatment and provides a technical basis for future industrial applications.

목차 (Table of Contents)

• 1. Introduction 1
• 1.1 Background 1
• 1.2 Objectives and Scope 4
• 1.3 Environmental and Industrial Significance 6
• 2. Literature Review 7
• 2.1 Fluoride Contamination 7
• 2.2 Ca(OH)2-Based Fluoride Removal 9
• 2.3 Sludge Management in Fluoride Treatment 12
• 2.4 Research Gaps and Novel Contributions 13
• 3. Materials and Methods 14
• 3.1 Materials and Reagents 14
• 3.2 Experimental Procedure 17
• 3.3 Analytical Methods 19
• 4. Results and Discussion 21
• 4.1 Fluoride Removal Performance 21
• 4.2 Sludge Characteristics 31
• 5. Conclusion 40
• 5.1 Reaction Mechanism 40
• 5.2 Practical Implementation Scenario 41
• 5.3 Resource Recovery Potential of Sludge 43
• 5.4 Limitations and Future Recommendations 44