Arsenic Reduction in Chloride Solutions at 25-75°C

Abstract

Arsenic (III) is reduced to its elementary state in concentrated hydrochloric acid solutions of tin dichloride. In solutions with an acid concentration below 5 mol/l and Sn:As ratio of less than 100, the rate of arsenic reduction is negligible. Catalytic methods of increasing the reaction rate are based on precipitating the arsenic in the presence of Au, Pt, Pd, or Hg compounds. The results of multicomponent heterogeneous systems AsCl3-SnCl2-CaCl2(NaCl)-HCl-H2O showed that the rate can be increased without the catalysts by raising the concentrations of CaCl2 or NaCl in hydrochloric acid solutions. The physico-chemical simulation of reduction-oxidation processes showed that from the thermodynamic point of view arsenic can be precipitated quantitatively at any concentrations of the acid and chloride ions; the equilibrium As concentrations do not exceed 10-7 mol/kg H2O for both concentrated and dilute chloride solutions. The influence of CaCl2 and NaCl is similar to that of hydrochloric acid. The experimenta...