Hematite-Based Scorodite Synthesis Process with Recirculation of Fe2+-Containing Solutions for Arsenic Stabilization

Various scorodite synthesis processes have attracted attention as stable arsenic immobilization methods for non-ferrous smelting plants. The hematite method, which uses hematite as the iron source, produces scorodite from As(V), Fe2O3, and Fe2+ in solution. Compared with other scorodite synthesis routes, this method does not involve large changes in the solution pH and/or the Fe2+ concentration. In this study, we developed a recirculating process to reuse the post-reaction solution, and its feasibility was experimentally verified. Storage and reuse of the post-reaction solution will allow for an industrially favorable operation with simplified solution management and reduced wastewater generation. A laboratory-scale apparatus was constructed consisting of a reactor, filtration unit, and post-reaction solution reservoir. Scorodite formation behavior and changes in solution composition were compared between fresh reagent-based solutions and repeatedly recirculated solutions. Under recirculation conditions, slight differences in particle growth behavior were observed; however, scorodite formation proceeded stably. Without adjustment of the pH and Fe2+ concentration, arsenic was successfully immobilized as scorodite through repeated batch operations by simply adding stoichiometric amounts of hematite relative to the supplied arsenic. By combining this hematite-based recirculation process with downstream low-concentration arsenic removal technologies, an efficient and flexible arsenic treatment flow can be constructed while minimizing reagent consumption and wastewater generation.