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

The Fe-ettringite formation and its arsenic removal capacity were investigated. The synergetic 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 FeCl3 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 FeCl3 (4.004 mM) were used individually showed much lower arsenic removal capacities (2.5% for CaO and 32.5% for FeCl3) compared with the combined system of CaO and FeCl3 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.