Abstract:To improve stability of scorodite, a method of simultaneous synthesis and in-situ coating of scorodite was proposed. Scorodite particles with polyhedral and raspberry-like morphologies were synthesized in an Fe(II)-As(V)-H₂O system at 90 °C and pH 1.5 by blowing oxygen gas into the system. When the initial Fe/As molar ratio exceeded 1:1, a coating of sulfate-containing iron (hydr)oxides formed on the surfaces of scorodite particles during synthesis. To evaluate the leaching stability of synthesized scorodite samples, toxicity characteristic leaching procedure (TCLP) tests were conducted at pH 4.93 for 60 h, and long-term leaching tests were conducted for 30-40 d within a pH range of 5.40-10.88. The leaching results indicated that the release of arsenic from scorodite was noticeably postponed by the coating, and the average arsenic concentrations in the leaching solutions were as low as 0.12 mg/L in the TCLP tests and lower than 0.5 mg/L in the long-term leaching tests.

Key words: scorodite; arsenic immobilization; nucleation; in-situ coating; stability