The pollution of groundwater by high-concentration iron ions is a critical global problem requiring urgent solutions. However, studies on iron removal from groundwater via induced crystallization are limited, particularly for high iron concentrations. Therefore, we performed a pilot study on high-concentration iron removal from groundwater in Northeast China with a two-stage circulating pellet fluidized bed (CPFB). Under conditions of 5–16 mg/L Fe2+ in groundwater, in the first-stage CPFB, with control of the dissolved oxygen (DO) at 9.1–9.4 mg/L and pH at 7.3–7.5, the total iron (TFe), soluble iron (SFe), and oxidized iron (OFe) could be removed to 1–3 mg/L through oxidation-chemical crystallization, with the maximum removal rates reaching 78%, 47%, and 87%, respectively. In the second-stage CPFB, adding 200 mg/L sodium hydroxide further reduced the residual iron to 0.25 mg/L via iron–manganese-calcium cocrystallization. Meanwhile, manganese was synergistically reduced to 0.08 mg/L, with a removal rate of 82%. The effluent turbidity was 8–10 NTU, and the iron and manganese concentrations in the effluent met the World Health Organization drinking water standards. Density functional theory (DFT) was used to simulate the induced crystallization removal mechanism and pathway of SFe and OFe. Additionally, using physical characterization, we found that the final iron product was γ-Fe2O3 and that the products of calcium and manganese were CaCO3, MnO2, and MnOOH. This study presents a novel process that enables efficient removal of high-concentration iron from groundwater and synergistic cocrystallization of iron, manganese, and calcium.
Hu et al. (Fri,) studied this question.