Enhancement effects of distiller's dried grains as reducing agents on the kinetics and leaching of pyrolusite from manganese ore

Abstract To solve the problem of environmental pollution, Distiller’s dried grains (DDGS), a biomass, is used as a clean reducing agent for the leaching process of pyrolusite. Experimental results have shown that the leaching rate of manganese can reach 92.1% with the optimized conditions including a sulfuric acid concentration of 3.5 mol/L, a DDGS to pyrolusite ratio of 0.4, a liquid–solid ratio of 3 mL/g, a temperature of 363K, a time of 3 h, and a rotation speed of 400 rpm. This article explored the mechanism of the entire leaching process: the crude fiber in DDGS is hydrolyzed into reducing sugars, and the MnO₂ in pyrolusite undergoes an oxidation–reduction reaction to generate Mn²⁺ and studied the kinetics of the leaching process following the unreacted shrinkage nuclear reaction model controlled by the surface chemical reaction (\(1-(1-X)^{1/3}=\text{kt}\)). The equation of leaching kinetics is \(1−1-\text{X}^{\frac{1}{3}} = 3738.06 \cdot [\text{H}_{2}\text{SO}_{4}]^{0.57} \cdot \left[\frac{L}{S}\right]^{0.78} \cdot \left[\frac{DDGS}{\text{pyrolusite}}\right]^{0.25} \cdot [rpm]^{0.09} \cdot \exp(-48.448/(RT)\) This work provides a green and effective leaching process for the leaching of pyrolusite