Recovery of manganese from low-grade pyrolusite ore by reductively acid leaching process using lignin as a low cost reductant

Recovery of manganese from low-grade pyrolusite was investigated by reductive leaching method using lignin as a reductant in the sulfuric acid medium. Lignin is a very abundant biopolymer available from the pulping wastewater in the pulp and textile industry. Effects of lignin amount, temperature, H2SO4 concentration and the leaching time on the leaching efficiency of Mn and main impurities (Fe, Al) were examined. The leaching temperature and H2SO4 concentration have a major effect on the extraction of Mn, Fe and Al. The maximum leaching efficiency of manganese can reach above 91% under the optimal experimental conditions. The experimental results demonstrated that lignin is a low cost, renewable and environmentally benign reductant for leaching low-grade manganese ore. The kinetic analysis further indicated that the behavior of reductively acid leaching Mn from pyrolusite in sulfuric acid solution follows Avrami equation well. The degradation mechanism of reductively acid leaching pyrolusite by lignin was also investigated by the gas chromatography-mass spectrometry, focusing on the cleavage of dimers into monolignols.