Reduction Of Lom-grade Pyrolusite With Less C Organic Matters

In face of the continuous growth of imports on manganese and the short supply of Mn-chemical products in recent years,reductive leaching of low-grade pyrolusite in Guangxi Xialei area with less C organic matters was investigated.The selected reductions were formic acid,formaldehyde and the compound of formaldehyde and iron powder.The optimum technology was obtained by the single-factor experiments and response surface methodology,thermodynamics and kinetics of the leaching process by formaldehyde was also discussed.The influences of concentrations of suifuric acid,reaction time,reaction temperature as well as liquid-solid ratio on the leaching rate were discussed when formic acid and sulfuric acid were employed to reacted.Multivariate regression was conducted under the basis of analysis by Design-export,the two polynomial equation between leaching rate and reaction parameter can be described:yield%=82.46+4.96A+2.34B+1.67C+1.66D-0.27AB+0.045AC-0.68AD+0.81BC+0.074BD+0.075CD-3.3A2-0.4B2+0.091C2+0.54D2.The leaching efficiency of manganese reached 90.05%together with 80.07%iron and 31.55%Aluminum under the optical conditions:2.76mol/L H2SO4,4ml formic acid,120min and 363K.The leaching rate was good and the more dosage of formic acid was used in the process.The single-factor experiments and response surface methodology were employed to optimize the leaching process with formaldehyde as reductant.Multivariate regression was conducted and the two polynomial equation between leaching rate and reaction parameter can be described:y(Mn)%=84.64+3.45A+4.42B+3.6C+0.088AB+0.16AC-2.09AD-1.06BC-0.071BD-1.75CD+0.92A2+0.19B2-0.53C2-1.47D2.The extraction rate of Mn reached 94%together with 77.78%Fe and 18.57%Al under of the conditions of 2.75mol/L H2SO4 and 2.4ml formaldehyde solution at 359K for 133min while liquid-solid ratio of 8 and stir speed of 200r/min.Leaching process with formaldehyde showed low cost and better leaching efficiency from the point of technology.The thermodynamic data of leaching process showed it favorably shift equilibrium in nonstandard state.The kinetics showed reaction control process was a diffusion-chemical hybrid control.The apparent activation energy of the two stage were 34.81KJ/mol and 30.1KJ/mol.After calculation of sulfuric acid and formaldehyde reaction's series the kinetics equations of the two stage were established as:1/3ln(1-X)+(1-X)-1/3-1=6.75 × 104 ×c(H2SO4)1.37c(CH2O)0.98 e-3.4810/RT(1)1/3ln(1-X)+(1-X)-1/3-1=5.94 ×103×c(H2SO4)1.67c(CH2O)2.22-30100/RT(2)The compound of formaldehyde and iron powder were used to optimize the reductive process with formaldehyde.Multivariate regression was conducted based on the relative data and the two polynomial equation between leaching rate and reaction parameter can be described:yield%=85.52+0.9A+1.34B+2.42C-7.7D-0.098AB-0.27AC+0.57AD-0.49BC-0.18BD+0.53CD-0.8A20.77B2-1.01 C2+4.14D2?The leaching efficiency was up to 98.04%and the concentration of formic acid the leaching solution was reduced from 2.24g/L to 1.4g/L when the reaction parameters were under the optimum.