Process Mechanism for Production of Green Lixiviant Thiosulfate at Atmospheric Pressure

Abstract

The serious environmental pollution and human health risks caused by highly toxic cyanide have necessitated the search for a nontoxic and alternative lixiviant. However, conventional chemical thiosulfate suffers from high consumption, which makes the commercialization of non-cyanide green extraction of precious metals difficult. Therefore, the development of green and low-energy technology for producing thiosulfate from sulfur-containing materials is of high academic and industrial interest. Herein, the process mechanism of producing thiosulfate at atmospheric pressure was first elucidated to facilitate the production of sufficient thiosulfate. By precisely regulating significant parameters, the concentration of thiosulfate can be increased to up to 0.32 M under optimal conditions. Furthermore, the conversion characteristics of sulfur and iron in this process are as follows: S22– → S2– → S2O32– → Sn2– (n > 2)/(S4O62– → S3O62–) → SO32– → SO42–, and Fe(II)–S2 → Fe(II)–S → Fe(II)–O/Sn → Fe(III)–O/OH and Fe(III)–SO3/SO4. Importantly, the sustainable existence of metastable thiosulfate is achieved under the oxidation system designed, preventing the peroxidation of S2O32– into S4O62– and S3O62–. This fruitful research provides valuable scientific insights for promoting the commercial application of thiosulfate with lower cost and environmental impact in the precious metal extraction industry.