School of Environmental Science and Engineering, Southern University of Science and Technology , Shenzhen Shi, Guangdong Sheng 518055, P. R. China.
Environ Sci Technol. 2017 Jun 6;51(11):6308-6318. doi: 10.1021/acs.est.7b00371. Epub 2017 May 22.
Iron-based electrocoagulation can be highly effective for Cr(VI) removal from water supplies. However, the presence of humic acid (HA) inhibited the rate of Cr(VI) removal in electrocoagulation, with the greatest decreases in Cr(VI) removal rate at higher pH. This inhibition was probably due to the formation of Fe(II) complexes with HA that are more rapidly oxidized than uncomplexed Fe(II) by dissolved oxygen, making less Fe(II) available for reduction of Cr(VI). Close association of Fe(III), Cr(III), and HA in the solid products formed during electrocoagulation influenced the fate of both Cr(III) and HA. At pH 8, the solid products were colloids (1-200 nm) with Cr(III) and HA concentrations in the filtered fraction being quite high, while at pH 6 these concentrations were low due to aggregation of small particles. X-ray diffraction and X-ray absorption fine structure spectroscopy indicated that the iron oxides produced were a mixture of lepidocrocite and ferrihydrite, with the proportion of ferrihydrite increasing in the presence of HA. Cr(VI) was completely reduced to Cr(III) in electrocoagulation, and the coordination environment of the Cr(III) in the solids was similar regardless of the humic acid loading, pH, and dissolved oxygen level.
铁基电化学混凝法对于从供水中去除六价铬非常有效。然而，腐殖酸（HA）的存在会抑制电化学混凝法中六价铬的去除速率，在较高 pH 值下，六价铬去除率的下降幅度最大。这种抑制可能是由于 HA 与 Fe(II)形成了更易被溶解氧氧化的 Fe(II)络合物，使得用于还原六价铬的 Fe(II)减少。在电化学混凝过程中形成的固体产物中 Fe(III)、Cr(III)和 HA 的紧密结合影响了 Cr(III)和 HA 的命运。在 pH 值为 8 时，固体产物为胶体（1-200nm），过滤部分的 Cr(III)和 HA 浓度相当高，而在 pH 值为 6 时，由于小颗粒的聚集，这些浓度较低。X 射线衍射和 X 射线吸收精细结构光谱表明，所生成的氧化铁是针铁矿和水铁矿的混合物，在 HA 的存在下，水铁矿的比例增加。六价铬在电化学混凝中被完全还原为三价铬，并且无论腐殖酸负载、pH 值和溶解氧水平如何，固体中 Cr(III)的配位环境都相似。
