State Key Lab of Urban Water Resource and Environment (HIT), Harbin Institute of Technology, Harbin, PR China.
Water Res. 2009 Dec;43(20):5119-28. doi: 10.1016/j.watres.2008.12.054. Epub 2009 Jan 20.
A novel KMnO(4)-Fe(II) process was developed in this study for As(III) removal. The optimum As(III) removal was achieved at a permanganate dosage of 18.6muM. At the optimum dosage of permanganate, the KMnO(4)-Fe(II) process was much more efficient than the KMnO(4)-Fe(III) process for As(III) removal by 15-38% at pH 5-9. The great difference in As(III) removal in these two processes was not ascribed to the uptake of arsenic by the MnO(2) formed in situ but to the different properties of conventional Fe(III) and the Fe(III) formed in situ. It was found that the presence of Ca(2+) had limited effects on As(III) removal under acidic conditions but resulted in a significant increase in As(III) removal under neutral and alkaline conditions in the KMnO(4)-Fe(II) process. Moreover, the effects of Ca(2+) on As(III) removal in the KMnO(4)-Fe(II) process were greater at lower permanganate dosage when Fe(II) was not completely oxidized by permanganate. This study revealed that the improvement of As(III) removal at pH 7-9 in the KMnO(4)-Fe(II) process by Ca(2+) was associated with three reasons: (1) the specific adsorption of Ca(2+) increased the surface charge; (2) the formation of amorphous calcium carbonate and calcite precipitate that could co-precipitate arsenate; (3) the introduction of calcium resulted in more precipitated ferrous hydroxide or ferric hydroxide. On the other hand, the enhancement of arsenic removal by Ca(2+) under acidic conditions was ascribed to the increase of Fe retained in the precipitate. FTIR tests demonstrated that As(III) was removed as arsenate by forming monodentate complex with Fe(III) formed in situ in the KMnO(4)-Fe(II) process when KMnO(4) was applied at 18.6muM. The strength of the "non-surface complexed" As-O bonds of the precipitated arsenate species was enhanced by the presence of Ca(2+) and the complexation reactions of arsenate with Fe(III) formed in situ in the presence or absence of Ca(2+) were proposed.
本研究开发了一种用于去除砷（III）的新型 KMnO(4)-Fe(II)工艺。在高锰酸盐剂量为 18.6μM 时，砷（III）的去除效果最佳。在最佳的高锰酸盐剂量下，KMnO(4)-Fe(II)工艺比 KMnO(4)-Fe(III)工艺更有效，在 pH 5-9 下，砷（III）的去除率提高了 15-38%。这两种工艺中砷（III）去除效果的巨大差异并不是由于原位形成的 MnO(2)对砷的吸收，而是由于常规 Fe(III)和原位形成的 Fe(III)的不同性质。研究发现，在酸性条件下，Ca(2+)的存在对砷（III）的去除影响有限，但在中性和碱性条件下，KMnO(4)-Fe(II)工艺中 Ca(2+)的存在会显著增加砷（III）的去除。此外，当高锰酸盐不能完全氧化 Fe(II)时，较低的高锰酸盐剂量下，Ca(2+)对 KMnO(4)-Fe(II)工艺中砷（III）去除的影响更大。本研究表明，KMnO(4)-Fe(II)工艺中 Ca(2+)在 pH 7-9 时提高砷（III）去除率与以下三个原因有关：（1）Ca(2+)的特殊吸附增加了表面电荷；（2）形成无定形碳酸钙和方解石沉淀，可共沉淀砷酸盐；（3）引入钙导致更多沉淀的二价和三价氢氧化铁。另一方面，在酸性条件下，Ca(2+)增强砷去除归因于沉淀中保留的 Fe 增加。FTIR 测试表明，当 KMnO(4)的用量为 18.6μM 时，KMnO(4)-Fe(II)工艺中形成的原位 Fe(III)与砷（III）形成单齿配合物，将砷（III）去除为砷酸盐。在有或没有 Ca(2+)的情况下，沉淀中砷酸盐与原位形成的 Fe(III)的配合反应被提出，这增强了沉淀中“非表面络合”As-O 键的强度。
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