Ferric chloride leaching of antimony from stibnite

Abstract

A circulatory hydrometallurgical process: ferric trichloride (FeCl3) leaching of antimony sulfide (Sb2S3) (production of Sb by replacing it with iron) followed by membrane electrowinning of ferrous chloride (FeCl2), was developed to cleanly extract Sb from stibnite. First, Sb was leached (leaching efficiency >98%), using FeCl3 as leaching reagent, under the following optimum conditions: temperature of 50 °C, liquid-to-solid ratio of 8:1, α(FeCl3) of 1.2 (where α represents the excess coefficient), and time of 1 h. Then, an Fe plate was used to replace Sb from the leaching solution using a two-step process. Approximately 96.86% of the Sb in the leaching solution was extracted, and pure FeCl2 was obtained. Finally, the FeCl2 solution was subjected to membrane electrowinning to regenerate the FeCl3 solution used as leaching solution at the anode and the Fe plate used as cathode. The optimal membrane electrowinning conditions were as follows: current density of 300 A/m2, temperature of 40 °C, and pH = 2.0. Both the anode and cathode current efficiencies were higher than 99%. The FeCl3 solution and Fe plate were reused for the leaching process and Sb replacement, respectively, while superfluous metallic Fe was open circuited. This novel process presents several advantages, including recirculating all solutions, high current efficiency, and low reagent consumption.