Study On Hydrometallurgical Leaching Of Pyrolusite And Element Migration Enhanced By Microwave

Manganese sulfate solution prepared by rhodrosite can be used to produce electrolytic manganese(EM)and electrolytic manganese dioxide(EMD)after removing impurities.However,in recent years,the grade of rhodrosite manganese is declining,and the cost of industrial utilization is also rising.Therefore,the use of pyrolusite to produce EM and EMD has also become an industry trend.In view of the problems of low manganese leaching rate and difficult sulfur conversion in the hydrometallurgical reduction leaching reaction of pyrolusite-pyrite,many researchers proposed to use chemical process intensification technology to promote manganese leaching and sulfur conversion.Based on above idea,in this thesis,pyrolusite and pyrite produced from Guangxi were taken as research samples,and microwave was used as process intensification means to study the hydrometallurgical reduction leaching behavior and kinetic mechanism of pyrolusite.Through the description of leaching kinetic behavior and analysis of element migration law,the enhancing effect of microwave in acid leaching of pyrolusite and pyrite was proved,and the conclusions obtained are as follows:①Based on the characteristics of microwave unconventional heating,volumetric heating and selective heating,the microwave-enhanced hydrometallurgical reduction leaching behavior of pyrolusite was studied,and the optimal reaction parameters were obtained.Under the conditions of reaction temperature of 363 K,initial sulfuric acid concentration of 1.6 mol/L,mass ratio of pyrite to pyrolusite of 0.25,liquid-solid ratio of 10,microwave power of 540 W,leaching time of 3 h,95.73%leaching rate of manganese was obtained.Under the same conditions,the leaching rate of Mn by conventional heating was 80.52%,and the leaching rate of Mn by microwave heating was 15.21%higher than that by conventional heating.Through response surface analysis,the influencing order of each factor on manganese leaching rate was determined as follows:leaching time>reaction temperature>microwave power mass>mass ratio of pyrite and pyrolusite initial>sulfuric acid concentration>liquid-solid ratio.②The kinetic study shows that the microwave-enhanced hydrometallurgical leaching reaction of pyrolusite was determined by two rate control steps.In the first stage of leaching(t = 0～100 min),it was controlled by chemical reaction,and the apparent activation energy was 30.95 kJ/mol,the apparent rate equation was:1-(1-r)1/3=46.71[H2SO4]0.3402[mFeS2/mMnO2]0.7154[VL/MS]0.7821exp(-30950/RT)·t In the second stage of leaching(t = 100～180 min),it was controlled by diffusion through product layer,and the apparent activation energy was 21.59 kJ/mol,the apparent rate equation was:1-3(1-r/1-r1)2/3+2(1-(1-r1)(r-r1)1/3)=387000[H2SO4]0.6093[mFeS2/mMnO2]1.4498[VL/MS]1.2043exp(-21590/RT)·t The conventional heating leaching of pyrolusite was controlled by surface chemical reaction,and the apparent activation energy was 39.93 kJ/mol.The apparent activation energy of microwave leaching was 8.98～18.34 kJ/mol lower than that of conventional heating leaching.③ The total dielectric constant ε’ and dielectric loss factor ε’ of the solid-liquid mixture system of leaching reaction were measured by cylindrical cavity perturbation method.The ε’ was kept at about 35 F/M and the ε’ was kept at about 2.8 F/M,which indicated that the reaction system had strong wave-absorbing performance and high ability of converting microwave energy into heat energy.Microwave promotes the migration and transformation of elements sulfur,iron,manganese and so on.The elemental sulfur in the microwave leaching residue almost exists in the form of SO42-and SO32-;element iron acts as an electronic bridge in the acid leaching process of pyrolusite and pyrite;The migration path of manganese was MnO2→Mn2O3→Mn3O4→Mn2+;The surface of microwave leaching slag was smooth,while the surface of conventional heating leaching slag had obvious micro-particle attachment.④ The mechanism analysis showed that the microwave increased the leaching rate of manganese by forming cracks on the surface of mineral particles and increasing the contact area between leaching agent and mineral interior material.The calculation results show that in the sulfuric acid leaching system with a concentration of 1.6mol/L,φ(?)(Fe3+/Fe2+)-0.771V,φ(?)Fe(MnO2/Mn2+)=1.248V,MnO2 has stronger oxidation than Fe3+,and is more capable of achieving the oxidation of sulfur into the high-value form.