Development of a novel process for arsenic(Ⅴ) removal from water using Fe-ettringite

摘要

The Fe-ettringite formation and its arsenic removal capacity were investigated. The syner-getic effect of initially injected ferric iron and formation of ettringite crystal in later stages contributed to improved removal capacity. The As(Ⅴ) removal capacity by the formation of As(Ⅴ)-containing Fe-ettringite (As/Fe-ettringite) was estimated through kinetic and equilibrium batch experiments. The As/Fe-ettringite formation was induced by injecting CaO and FeCl_3 into synthetic As(Ⅴ) wastewater (1.33 mM). Different molar ratios of As(Ⅴ)/Ca/Fe (1:2:1, 1:4:2, 1:6:3, 1:8:4, and 1:10:5) were experimented in batches, the ratio of 1:6:3 showed the best removal efficiency (≈95%) among them. The control experiments in which CaO (8.008 mM) and FeCl_3 (4.004 mM) were used individually showed much lower arsenic removal capacities (2.5% for CaO and 32.5% for FeCl_3) compared with the combined system of CaO and FeCl_3 which led to As/Fe-ettringite formation. Equilibrium experiments were conducted in the pH range from 3 to 13, and the result showed As(Ⅴ) removal by As/Fe-ettringite formation was significant in the pH range from 10.9 to 11.8, which was favorable for the formation of ettringite phases. Well-crystalized As/Fe-ettringite was observed in the FE-SEM micrographs of samples, and the needle-like crystals were most abundant and clear in the sample taken at pH of 12.