A novel process of immobilizing sodium arsenate crystals as scorodite using Fe(OH)3 as an iron source

Abstract

Sodium arsenate crystals are a hazardous waste produced from the utilization of arsenic–alkali residue in antimony metallurgy that pose a serious threat to the environment. In this article, to eradicate the damage caused by sodium arsenate and enhance the sustainable development of nonferrous metallurgy, a novel process was proposed to immobilize arsenic as flaky scorodite using Fe(OH)3 as an iron source. Various methods, such as X-ray diffraction (XRD), scanning electron microscopy (SEM), and inductively coupled plasma atomic emission spectrometry (ICPAES), were applied to characterize these synthesized products. The whole process is divided into three parts. In the thermodynamic analysis, the stable area of scorodite in the Pourbaix diagram significantly expands at high ionic activity and temperature, which favors the decrease in △rG for scorodite synthesis, and Fe–As coprecipitation is feasible in solution at 0.18 ≤pH≤ 5.30. In the scorodite synthesis, 99.88% of the arsenic was converted to a flaky scorodite with a size of 2–5 µm by optimizing the parameters. In the removal of arsenic, residual arsenic and iron were completely coprecipitated into an iron salt by dropping NaOH solution to a final pH of 5.0. The final products include scorodite and sodium sulfate in this process. Overall, this new approach successfully eliminates the potential arsenic pollution from the utilization of arsenic–alkali residue in antimony metallurgy and can potentially be applied to dispose of other high arsenic-bearing wastes.