School of Chemistry and Chemical Engineering, Beijing Institute of Technology, Beijing 100081, China; State Key Laboratory of Environmental Aquatic Chemistry, Key Laboratory of Drinking Water Science and Technology, Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences, Beijing 100085, China.
Department of Civil and Environmental Engineering, Imperial College London, South Kensington Campus, London SW7 2AZ, United Kingdom.
Water Res. 2020 Oct 15;185:116250. doi: 10.1016/j.watres.2020.116250. Epub 2020 Jul 28.
Although Fe(II) salts have been widely used as coagulants in water treatment for many years, the underlying mechanisms of their performance remain unclear. Here, we present a detailed study of the coagulation behavior of Fe(II) salts and crystallization of flocs, and investigate the effect of humic acid (HA) under different DO concentrations and pH conditions. The behavior of Fe(II) and Fe(III) coagulants was found to be markedly different with the flocs from Fe(II) consisting of planar-like crystalline γ-FeOOH in contrast to the small amorphous spherical-like flocs from Fe(III) dosing. The effect of HA on Fe(II) coagulation was different under different DO concentrations and pH, where by the growth of γ-FeOOH was inhibited by the presence of HA, but independent of DO concentration and pH. It was found that Fe(II) was present within the internal structure of γ-FeOOH, and a plausible formation mechanism is proposed. Firstly, planar nanoparticles of Fe(OH) were formed via Fe(II) ion hydrolysis which then servedas the nucleus for subsequent crystal growth. With oxidation, Fe(II) on the surface of nanoparticles transformed to Fe(III). Finally, the formation of γ-FeOOH in Fe(II) coagulation was accompanied by a change in solution colour to yellow.
尽管 Fe(II)盐多年来一直被广泛用作水处理中的混凝剂，但它们的作用机制仍不清楚。在这里，我们对 Fe(II)盐的混凝行为和絮体的结晶进行了详细研究，并研究了不同 DO 浓度和 pH 条件下腐殖酸 (HA)的影响。研究发现，Fe(II)和 Fe(III)混凝剂的行为明显不同，Fe(II)形成的絮体由平面状结晶 γ-FeOOH 组成，而 Fe(III)形成的絮体则由小的无定形球形絮体组成。HA 对 Fe(II)混凝的影响因 DO 浓度和 pH 而异，HA 抑制了 γ-FeOOH 的生长，但与 DO 浓度和 pH 无关。研究还发现 Fe(II)存在于 γ-FeOOH 的内部结构中，并提出了一种可能的形成机制。首先，通过 Fe(II)离子水解形成 Fe(OH)平面纳米粒子，然后这些纳米粒子作为后续晶体生长的核。随着氧化，纳米粒子表面的 Fe(II)转化为 Fe(III)。最后，在 Fe(II)混凝过程中形成 γ-FeOOH 的同时，溶液颜色也会变为黄色。
