Study On Reductive Leaching Of Low-grade Pyrolusite Ores And Leaching Kinetics

Extraction of manganese from low-grade pyrolusite ore was investigated using oat straw as a reducing agent compared with oxalic acid as a reference reducing agent. Selective leaching of manganese and control of impurities contents were studied systematically in this thesis.The reductive leaching experiment on low-grade pyrolusite ore was carried out using oxalic acid as a reducing agent in dilute sulfuric acid medium. The results show that the successive order of factors affecting the leaching rate of manganese is the dosage of oxalic acid, sulfuric acid concentration, liquid-solid ratio, temperature and leaching time. The optimal parameters are as follows: agitation speed400r/min, liquid-to-solid ratio10mL/g, H2SO4150g/L,0.4g H2C2O4·H2O/g,60min,40℃. Under above optimal conditions, the leaching rate of manganese reached94.4%while iron dissolved was20.9%and selectivity of reaction was72.2%. The dissolution of silicon and conversion rate of oxalic acid were also studied.Sulfuric acid leaching of low-grade pyrolusite ore using oat straw as a reducing agent was studied and the content of organic impurities from leaching solution was measured by COD. The leaching rate of manganese reached96.1%while iron dissolved was46.8%and COD was6.2g/L under the optimal condition which was determined for lOg of pyrolusite ore as oat straw amount of3g,150g/L H2SO4, using liquid-to-solid ratio of9mL/g for60min at90℃. Extraction of manganese from low-grade pyrolusite ore through slow reaction process is proposed to reduce the content of organic impurities. The results show that the leaching rate of manganese was91.8%, COD was0.67g/L and the hydrolysis efficiency of cellulose and hemicellulose was82.3%and40.1%respectively when leaching time reached5h.The kinetics of leaching pyrolusite ore using oat straw as a reducing agent was researched and it indicates that the leaching process follows the Shrinking core model and the leaching rate of manganese is controlled by the interface chemical reaction. The apparent activation energy were calculated to be69.4kJ/mol, the reaction order are1.66and0.90for sulfuric acid and oat straw, respectively. Finally, the macro-kinetic equations were as follows. According to the present experimental results, it was also concluded that the leaching rate of manganese from pyrolusite ore is limited by the acid hydrolysis rate of oat straw. Because of different acid hydrolysis property between cellulose and hemicellulose, cellulose and hemicellulose in oat straw could be reacted with pyrolusite ore in different conditions respectively.1-(1-x)1/3=224.9/rnc11.66c20.90exp(69431/RT)t...