Abstract

A low-cost arsenic removal method based on oxidation-coagulation at optimized pH (OCOP), which is popular as Arsiron-Nilogon in Assam, India, uses KMnO₄ to remove arsenic and oxidation of As(III) to As(V) before coagulation using FeCl₃. In this method KMnO₄ shows a major role in oxidation and removal of arsenic from the water. However, the relative efficacy of other oxidants, viz., Fenton’s reagent, NaOCl and H₂O₂, vis a vis KMnO₄, in OCOP method has not yet been studied systematically. Here we report a comparative study of the removal of arsenic by OCOP with different oxidising agents, viz., KMnO₄, Fenton’s reagent, NaOCl and H₂O₂ keeping the doses of NaHCO₃ and FeCl₃ constant at 100 and 25 mg/L, respectively. A set of OCOP experiments performed with varying KMnO₄ dose from 0.2 to 2 mg/L at an interval of 0.2 was examined. This set of OCOP experiments also verified the other oxidants taken in equivalent of the dose of KMnO₄. Filtered water taken after 2 h gives result of arsenic removal and oxidation extent of each oxidant. In the OCOP method of arsenic removal, the performance of the four chosen oxidants increases in the order H₂O₂ < NaOCl \( \ll \) Fenton’s reagent < KMnO₄. With other conditions remaining the same, 2 mg/L KMnO₄ and equivalent quantities of Fenton’s reagent, NaOCl and H₂O₂ could remove As³⁺ from initial concentration 200 μg/L in water to maximum 100, 98.8, 89.0 and 88.0%, respectively. The much better performance of KMnO₄ and Fenton’s reagent as compared to that of H₂O₂ and NaOCl is due to additional adsorption of arsenic by MnO₂ and FeOOH formed from KMnO₄ and ferrous iron of Fenton’s reagent. The results also suggest a role of MnO₂ in previously reported catalysis of oxidation of As³⁺ to As⁵⁺. The adsorption isotherms suggest that arsenic is adsorbed on the surface as well as inside coagulates/precipitates mixtures of FeOOH and MnO₂ produced during the OCOP process.

中文翻译：

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不同氧化剂的氧化-混凝处理去除水中亚砷酸盐

摘要

一种基于优化 pH 值氧化凝结 (OCOP) 的低成本除砷方法，在印度阿萨姆邦流行为Arsiron-Nilogon，使用 KMnO ₄去除砷并将 As(III) 氧化为 As(V) 之前使用 FeCl _{3 进行}混凝。在该方法中，KMnO ₄在氧化和去除水中的砷方面发挥着重要作用。然而，其他氧化剂的相对效能，即，芬顿试剂，次氯酸钠和H ₂ ö ₂，可见 一个可见的KMnO ₄，在OCOP方法尚未得到系统的研究。在这里，我们报告了使用不同氧化剂（即 KMnO _4）通过 OCOP 去除砷的比较研究、芬顿试剂、NaOCl 和 H ₂ O ₂将 NaHCO ₃和 FeCl ₃的剂量分别保持在 100 和 25 mg/L 不变。检查了以0.2 至 2 mg/L 的不同 KMnO ₄剂量以 0.2 的间隔进行的一组 OCOP 实验。这组OCOP实验还验证了以KMnO ₄剂量等效的其他氧化剂。2 h 后滤出的水给出了每种氧化剂的除砷和氧化程度的结果。在除砷的 OCOP 方法中，四种所选氧化剂的性能按 H ₂ O ₂ < NaOCl \( \ll \) Fenton's 试剂 < KMnO ₄的顺序增加. 在其他条件保持不变的情况下，2 mg/L KMnO ₄和等量的 Fenton 试剂、NaOCl 和 H ₂ O ₂可以将 As ³⁺从水中的初始浓度 200 μg/L去除到最大 100、98.8、89.0 和 88.0% ， 分别。与H ₂ O ₂和NaOCl相比，KMnO ₄和Fenton 试剂的性能要好得多，这是由于MnO ₂和FeOOH对砷的额外吸附，这些MnO ₂和FeOOH 由KMnO ₄和Fenton 试剂的亚铁形成。结果还表明 MnO ₂在先前报道的 As ³⁺氧化为 As ^{5+ 的}催化中的作用. 吸附等温线表明砷被吸附在表面以及内部凝聚物/沉淀物在 OCOP 过程中产生的 FeOOH 和 MnO _{2 的}混合物。