Study On The Process Of Reducing Leaching Of Pyrolusite By Sodium Sulfite

At present,the low-grade pyrolusite ores are usually treated via reduction roasting-acid leaching in China,but there are many disadvantages such as requiring a large energy consumption,poor operation conditions as well as polluting environment.In this thesis,low-grade pyrolusite was leached by using sodium sulfite as a reductant and sulfuric acid(H2SO4)as leaching agent,a process for reductive leaching manganese from low-grade pyrolusite was experimentally investigated,which realized the selectivity and highly effective dissolution of manganese.The optimum parameters were obtained in this study,which can provide a new technique for the industrial leaching of pyrolusite.The effects of ratio of acid to ore,reaction temperature,sodium sulfite mass,reaction time,liquid-solid ratio,agitation rate on manganese,iron leaching ratio were investigated,the optimum experimental conditions were gained as follows,ratio of acid to ore is 0.36,reaction temperature is 60?,sodium sulfite mass are 1.24 times of the theoretical amount,reaction time is 120 min,liquid-solid ratio is 6:1,agitation rate is 400r·min-1,under the conditions above,the leaching ratio of manganese is 96.26%,and the leaching ratio of iron is 2.21%.The reductive leaching process of low-grade pyrolusite using sodium sulfite as a reductant was optimized by response surface methodology,the X,(ratio of acid to ore),X2(temperature,?)and X3(sodium sulfite mass)were confirmed as process variables,Y1(leaching ratio of manganese,%)and Y2(leaching ratio of iron,%)as response indicators were investigated,two order polynomial equations of model on leaching ratio of manganese and leaching ratio of iron were obtained as follows:Y1=96.46+7.10X1+1.70X2+1.42X3+0.59X1X2+2.74X1X3-1.79X2X3-4.69X12-1.22X22-1.45X32Y2=2.19+6.81X1+0.34X2-0.98X3-0.31X1X2+0.17X1X3-0.47X2X3+3.49X12+0.26X22+0.80X32The optimal technological conditions obtained by reponse surface methodology were determined to be ratio of acid to ore of 0.36,temperature of 61.93?,sodium sulfite mass of 1.24 times of the theoretical amount,under the optimized conditions,the leaching ratio of manganese is 96.34%and the leaching ratio of iron is 1.84%.In order to verify the validity of the model,three tests were conducted under the ratio of acid to ore of 0.36?temperature of 61.93? and sodium sulfite mass of 1.24 times of the theoretical amount.The results showed that the average leaching ratio of manganese can reach to 96.61%and the average leaching ratio of manganese can reach to 2.01%.The kinetics of process of reductive leaching manganese from low-grade pyrolusite using sodium sulfite as a reductant was studied,and it indicated that the leaching process of manganese is controlled by both chemical reaction on particle surface and diffusion across the product layer,the apparent activation energy is found to be 22.36kJ/mol,and the kinetics equation of leaching process can be expressed as:...