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

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 S2O62-<inline-graphic></inline-graphic> formation and mole ratio of S2O62-/SO42-<inline-graphic></inline-graphic> 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 S2O62-<inline-graphic></inline-graphic> concentration and S2O62-/SO42-<inline-graphic></inline-graphic> ratio were lower than 0.7 g L⁻¹ and 0.02. Besides, the molar ratio of S2O62-<inline-graphic></inline-graphic> to SO42-<inline-graphic></inline-graphic> (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. [ABSTRACT FROM AUTHOR]