The design of scorodite@FeOOH core-shell materials and its stability treatment for arsenide

Arsenic as a highly toxic substance must be stabilized and immobilized to avoid environmental pollution. The natural scorodite ore (FeAsO₄·2H₂O) is stable that originated from the arsenic oxide are encapsulated by iron oxide layer in the crystal structure of scorodite, form the similar core-shell structure. The special core-shell structure can successfully improve the stability of arsenide. In this study, the scorodite@FeOOH materials with core-shell structure were designed and synthesized by soaking the scorodite in alkaline solution. The core-shell structure was formed in 6 h with the pH range of 10.00–13.00. By analyzing the formation pathway, the arsenical ferrihydrite was formed in soaking process, meanwhile the Fe(OH)₃ particles were produced, then both of them continue to grow, thus form the core-shell structure. After ageing treatment, the scorodite@FeOOH core-shell structures were formed. Toxicity Characteristic Leaching Procedure measurements were performed to evaluate the safety of this scorodite@FeOOH material in acid or alkaline solutions. The results indicated that the scorodite@FeOOH material had high stability under acid and alkaline condition. Within 10 days, the concentrations of arsenic in leaching liquid were below 0.01 mg·L⁻¹. This stabilization result indicates the treatment way from arsenide to the stable core-shell structure is an effective strategy for arsenic immobilization.