Formation characteristics of dithionate and sulfate ions in the pyrolusite leaching process with SO2

Abstract

As a byproduct in the pyrolusite leaching process with SO2, the existence of MnS2O6 will decrease the purity of MnSO4 produced by leaching. For obtaining MnSO4 with satisfactory quality, it is beneficial to decrease the formation of MnS2O6 during the leaching process. A study on the formation characteristics of dithionate and sulfate formed in pyrolusite leaching process with SO2 was carried out. The results indicated that $${\text{S}}_{ 2} {\text{O}}_{ 6}^{ 2- }$$ formation and mole ratio of $${{{\text{S}}_{ 2} {\text{O}}_{ 6}^{ 2- } } \mathord{\left/ {\vphantom {{{\text{S}}_{ 2} {\text{O}}_{ 6}^{ 2- } } {{\text{SO}}_{ 4}^{ 2- } }}} \right. \kern-0pt} {{\text{SO}}_{ 4}^{ 2- } }}$$ increased with increasing initial pH, liquid–solid ratio and SO2 concentration, but was independent of particle size and stirring speed when particle size was less than 200 μm and stirring speed exceeded 400 rpm. The suitable conditions for obtaining MnSO4 product was 45 C and 0.4 mol L−1 H+ concentration with $${\text{S}}_{ 2} {\text{O}}_{ 6}^{ 2- }$$ concentration and $${\text{S}}_{ 2} {\text{O}}_{ 6}^{ 2- } /{\text{SO}}_{ 4}^{ 2- }$$ ratio were lower than 0.7 g L−1 and 0.02. Besides, the molar ratio of $${\text{S}}_{ 2} {\text{O}}_{ 6}^{ 2- }$$ to $${\text{SO}}_{ 4}^{ 2- }$$ (R) was put forward as a correlated parameter to evaluate the formation of reaction products, whose kinetics was analyzed in depth. The kinetic equation was related to reaction temperature, H+ and SO2 concentration, and the calculated reaction orders for SO2 concentration and initial H+ were 0.27 and − 0.17, the activation energy was 9696 J mol−1.