| Manganese is one of the most important strategic resources,which were widely used in steel,alloys,batteries,dyes,medicine and other fields.In recent years,the“two-ore plus acid method”(pyrolusite and pyrite with sulfuric acid)becomes the main method for industrial leaching of manganese.However,the process of leaching manganese ore by the“two-ore plus acid method”generally has disadvantages of high leaching temperature,low leaching rate and electrolysis efficiency,resulting in high electrolysis energy consumption.The experimental parameters were poor matched with process amplification.The subsequent pollution of manganese slag had harmed to sustainable development of electrolytic manganese dioxide industry.Therefore,based on the acid leaching and electrolysis process of“two-ore plus acid method”,the process strengthening and amplification of electrolytic manganese dioxide(EMD)production process were carried out in this dissertation.The main research contents and results were as follows:(1)The strengthening of leaching process of"two-ore acid adding method"was studied by using rigid and rigid flexible combined impeller,and the effects of impeller type,temperature,liquid-solid ratio and leaching time on the leaching rate of manganese ore were investigated.At the same time,the impurity removal behavior and leaching kinetics were studied with different impeller types and dosage of vulcanizing agent.The results showed that the rigid-flexible combined impeller can effectively shorten the leaching time of"two-ore acid adding method".The optimal leaching conditions were as follow:at 363 K,liquid-solid ratio 10:1,sulfuric acid concentration 1.5 mol?L-1,mass ratio of pyrite to pyrolusite 0.2,leaching time 240 min.Under these conditions,the leaching rate of manganese reaches 95.39%.Rigid-flexible combined impeller makes the fluid and solid particles in the tank chaotic coupling to the maximum extent,which can speed up the impurity removal process.The curing agent SDD has obvious removal effect on nickel,cobalt and cadmium impurities,but poor removal effect on zinc.Through the studied on the selection of leaching kinetics model,it was determined that the leaching process of"two-ore acid adding method"in the stirred tank with rigid and flexible combined impeller could be described by the kernel reduction model.The control step was interface chemical reaction,the apparent activation energy was 26.97 k J?mol-1,and the macro kinetics equation was:1-(1-X)3/1=0.90528[FeS2]0.9631[H2SO4]1.6442(r)2.4759(s)1.1618exp(-26969/RT)t(2)The flow field characteristics and the solid-liquid suspension characteristics were investigated with the fluent numerical simulation software in the double rigid-flexible pitched(DRF-P)impeller system and double rigid pitched(DR-P)impeller system.Meanwhile the effects of impeller structure,the impeller speeds,flexible sheet length and flexible sheet width on the axial local solid holdup.The results showed that the DRF-P impeller can effectively destroy the symmetry structure of the flow field when compared with the DR-P impeller.The maximum turbulent energy value of the liquid phase(0.037)was increased by 41.02%,the maximum tangential velocity value of the liquid phase(0.13)was increased by 60.22%,and the maximum axial velocity value of the liquid phase(0.14)was increased by 28.57%,which made the fluid structure in the mesostatic state in the stirred tank gradually evolve to the chaotic zone.The fluid structure in the stirred tank gradually evolves to the chaotic zone,which increases the axial and tangential velocities of solid particles and increases the local solid content and the degree of suspension of solid particles.(3)The frequency-conversion rigid-flexible stirring reactor was used to enhance the leaching process of manganese ore,comparative analysis of the influence of different blade types,mixing blade operation mode and frequency conversion time on manganese ore leaching effect and mixing power consumption.And the distribution of acid liquid,pyrolusite and pyrite in the manganese ore leaching and amplifying device was calculated through computational fluid dynamics.The results showed that the variable-frequency rigid-flexible impellers increased the axial movement speed of the fluid through the flexible steel wire rope,thereby increasing the suspension effect of the mineral powder,reducing the mineral powder deposition at the bottom of the device,shortening the leaching time of manganese ore and increasing the Mn2+content in the leaching solution.When the frequency conversion time was 30 min,the Mn2+content of the frequency-converted rigid-flexible impeller system was increased by 8.9%and decreased by 2.7%compared to the rigid and rigid-flexible impeller systems,and the stirring power consumption was reduced by 7%and 28%,respectively.And the rigid-flexible impeller could enhance the suspension degree of solid particles more than the rigid impeller,which was beneficial to the efficient leaching of manganese ore.(4)Electrochemical tests were performed on the anode of the EMD electrolysis process,including potentiostatic current-time test and cyclic scanning voltammetry test.At the same time,Ce(SO4)2 was added to explore the effect on electrode reaction,and the electrolysis product was analyzed.The results showed that the anode periodic potential-time electrochemical oscillation phenomenon was discovered in the EMD electrolysis process.This oscillation caused an additional power consumption of>5.2%,and the electrochemical oscillation was rooted in the catalytic oxidation of water by?-Mn O2 produced.In addition,a small dosage of Ce(SO4)2 to the electrolyte could adjust the oscillation,and the electrochemical performance of EMD was significantly improved.This result provided a new way of thinking about the correlation between macroscopic non-equilibrium phenomena and microchemical mechanisms.In a summary,nonlinear kinetics exist in the leaching and electrolysis process of EMD manufacturing.Leaching ratio and current efficiency can be elevated by controlling chaotic mixing and electrochemical oscillation performance. |
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