As a low-cost and commonly used technology, coagulation usually encounters two difficulties in disposing arsenite (As(III)): (1) the removal efficiency is much lower than that of arsenate (As(V)), and (2) acidic conditions are quite detrimental to As(III) removal. Calcium peroxide (CaO₂) possesses dual functions of oxidizing pollutant and elevating solution pH. A CaO₂-enhanced coagulation method was thus constructed in this study, aiming to develop a versatile coagulation strategy to treat As(III) pollution. Results showed that low-dose CaO₂ (20 mg/L) significantly improved As(III) coagulation, and cocoagulation with Ti(SO₄)₂ (10 mg Ti/L) achieved above 90% removal (initial As(III) was 1.0 mg/L) at pH 4.0–7.0. The oxidation function of CaO₂ played the dominant role, whereas the pH-elevation mechanism worked a more prominent role with the increase of the CaO₂ dose. The CaO₂ with long-lasting oxidizing ability persistently converted As(III) into As(V), thus prompting the quick sequestration of resultant As(V) by coagulation reaction. The dried flocs could be further reused as As(III) adsorbent and reached a maximum adsorption capacity of 345.3 mg/g Ti (pH 5.0). CaO₂-enhanced coagulation was a universal As(III) pollution control method with high efficiency and operational simplicity. For practical wastewater treatment, the dose of coagulant and CaO₂ should be further optimized according to As(III) concentration, coagulant type, and water quality parameters.

中文翻译：

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低剂量 CaO2 通过提高溶液 pH 值和持续将 As(III) 氧化成 As(V) 来增强亚砷酸盐的凝聚

混凝作为一种成本低廉、常用的技术，在处理亚砷酸盐（As（III））时通常会遇到两个困难：（1）去除效率远低于砷酸盐（As（V）），（2）酸性条件对 As(III) 的去除非常不利。过氧化钙 (CaO ₂ ) 具有氧化污染物和提高溶液 pH 值的双重功能。因此，本研究构建了一种 CaO ₂增强的混凝方法，旨在开发一种通用的混凝策略来处理 As(III) 污染。结果表明，低剂量 CaO ₂ (20 mg/L) 可显着改善 As(III) 的凝聚，以及与 Ti(SO ₄ ) _{2 的}凝聚(10 mg Ti/L) 在 pH 4.0–7.0 下达到 90% 以上的去除率（初始 As(III) 为 1.0 mg/L）。CaO ₂的氧化作用起主导作用，而随着CaO ₂剂量的增加，pH升高机制的作用更加突出。具有持久氧化能力的 CaO ₂持续将 As(III) 转化为 As(V)，从而促使通过凝结反应快速螯合生成的 As(V)。干燥后的絮状物可进一步作为 As(III) 吸附剂重复使用，并达到 345.3 mg/g Ti（pH 5.0）的最大吸附容量。CaO ₂增强混凝是一种通用的 As(III) 污染控制方法，具有高效和操作简单的特点。对于实际废水处理，混凝剂和 CaO 的剂量₂应根据 As(III) 浓度、混凝剂类型和水质参数进一步优化。