Experimental Study On Controlling Parameters And Mechanism Of Manganese In Wastewater By Membrane Electrolytic

With the development of the steel industry,China’s demand for manganese resources has increased year by year.In the process of manganese ore mining and electrolytic preparation,a large amount of high-concentration manganese-containing waste liquid is often produced due to the constraints of existing processes.At present,most of the electrolytic manganese enterprises in China treat the manganese ions in the electrolytic waste liquid in the form of manganese slag,which not only easily causes secondary pollution but also seriously wastes manganese resources.Therefore,the treatment and recycling of high-concentration electrolytic waste liquid have become urgent problems to be solved in the manganese production industry.Based on the characteristics of high efficiency,low energy consumption,economy and environmental protection of the ion membrane electrolysis method,this study improved the existing single membrane electrolysis method,and proposed a double-membrane three-chamber same tank electrolysis process.This process recovers metal manganese and particulate electrolytic manganese dioxide while processing high-concentration manganese-containing waste liquid,and achieves efficient recycling of manganese resources.At the same time,the sulfuric acid is recovered through the selective permeability of the ion exchange membranes on both sides of the compartment.The recovered sulfuric acid is used in the acid leaching process of manganese ore before,which reduces the environmental pollution caused by waste acid.The experiment is divided into three parts.In the first part,a homogeneous ion exchange membrane（TRJM-10W）and a titanium-based lead dioxide coating anode were selected as the best experimental materials through single-factor control experiments.Then determine the effects of Mn²⁺concentration,current density,temperature,pole spacing,（NH₄）₂SO₄concentration in catholyte,H2SO4 concentration in anolyte,and initial H2SO4 concentration in the compartment.We combined multi-factor orthogonal experiments to explore the degree of influence of each factor on current density and acid recovery rate,and combined the current efficiency,energy consumption,acid recovery rate and product quality to determine the optimal process parameters.The experimental results show that current density and Mn²⁺concentration are the two factors that have the most significant effect on current efficiency.Since the temperature change has a greater impact on the anode current efficiency than the cathode,the electrolytic temperature in the double-membrane three-chamber same tank electrolysis process should meet the anode electrolytic conditions as much as possible.The concentration of H2SO4 in the anolyte and the concentration of catholyte（NH₄）₂SO₄ are the main factors affecting the sulfuric acid enrichment in the compartment.Reasonably controlling the concentration of H+in the anolyte can effectively improve the acid recovery.Based on experimental analysis,the optimal process conditions for the simultaneous electrolysis of metal manganese and manganese dioxide in the double-membrane three-chamber are determined as follows:the concentration of Mn²⁺in the catholyte is 40g/L,the concentration of（NH₄）₂SO₄ is 110g/L,and the cathode current density is 400A/m²;Mn²⁺concentration in the anode solution is 40g/L,H2SO4 concentration is 2.5mol/L,anode current density is 800A/m²;initial sulfuric acid concentration in the intermediate solution is0.5%;electrode spacing is 90mm;electrolysis temperature is 45℃.With the optimal electrolysis conditions,the cathode current efficiency can reach 77.53%,the anode current efficiency can reach 84.87%,the acid recovery rate can reach 63.2%,the cathode energy consumption is 6725.28kW·h/t,the anode energy consumption is 3889.91kW·h/t,and the tank voltage is 5.35V.The macroscopic surface of the cathode product is smooth and flat,with a bright silver-white metallic luster,and less dendrites at the edges;the microscopic surface deposits are dense,the grains are tightly connected,and they pile up in layers.The anode product particle electrolytic manganese dioxide crystal type is alpha type,which has higher purity,fine particles,uniform particle size distribution,and more regular crystal morphology.The second part of the experiment explores the ion migration process and reaction mechanism in the electrolysis process by monitoring the changes in the ion concentration of each compartment in the double-membrane three-chamber electrolytic cell.It was found through experiments that during the double-membrane three-chamber electrolysis process,the cathode compartment and the compartment mainly rely on SO₄^2-migration to conduct electricity,and the anode compartment and the compartment rely on H⁺migration to conduct electricity.The decrease in Mn²⁺concentration in the cathode chamber is mainly due to the electrochemical reduction reaction.A small amount of Mn²⁺leaks into the compartment under the pressure of concentration difference.At the same time,the water electrolysis reaction occurs in the cathode,and the pH of the catholyte will increase due to the OH^-produced by the water electrolysis.With the H⁺diffusion effect between the cathode compartment and the compartment gradually becoming obvious,the pH of the catholyte tends to stabilize in the later stage of electrolysis,and SO₄^2-migrated to the compartment under the action of electric field force.The Mn²⁺in the compartment comes from the Mn²⁺in the cathode and anode compartments,which leaks under the effect of concentration diffusion and electric field force.The concentration gradually increases with the extension of the electrolysis time,but the increase is small and within an acceptable range.The H⁺in the compartment migrates from the anode compartment,and the source includes the H⁺in the initial anolyte and the H⁺produced by water electrolysis.Then the H⁺entering the compartment and the SO₄^2-migrated from the cathode compartment combine to form H2SO4 to achieve the enrichment of sulfuric acid.The sharp decrease of the Mn²⁺concentration in the anolyte is mainly due to the electrochemical oxidation reaction.The deposition of particulate electrolytic manganese dioxide is divided into two steps:anode reaction and particle formation.First,Mn²⁺is oxidized on the electrode surface to Mn³⁺,and then Mn³⁺is disproportionated in the acidic anolyte to generate particulate electrolytic manganese dioxide.As the electrolytic reaction proceeds,The reason why the H⁺concentration in the anode chamber gradually decreases is that H⁺migrates to the compartment.In the third part,the energy consumption and product efficiency of the double-membrane three-chamber same tank electrolysis process are compared with the traditional non-membrane electrolysis process,and we preliminary analyzed the economic benefits of the double-membrane three-chamber electrolysis process.Compared with the traditional non-membrane electrolysis process,the double-membrane three-chamber electrolysis process consumes more electrical energy of per ton manganese products and increases the cost of electrolysis due to the effects of membrane resistance and pole spacing.But combined with the analysis of product benefits,the increased product benefits far outweigh the cost increase.Overall,the double-film three-chamber electrolysis process has well economic benefits,and has good economics and practicability.By analyzing and demonstrating a large number of experimental data,the paper verifies the feasibility of the efficient recovery of manganese resources by the double-membrane three-chamber electrolysis process.Compared with single-membrane electrolysis,the double-membrane three-chamber electrolysis process can effectively improve production efficiency and reduce energy consumption.At the same time,the recovered sulfuric acid reduces acid pollution caused by waste acid and relieves environmental pressure.This is an electrolytic process that integrates the three benefits of energy saving,environmental protection and economy.At present,the research on the recovery of manganese by the double-membrane three-chamber electrolytic process is still in the preliminary exploration stage.In the future,we can develop new materials and improve the structure of the device,so that the process can be applied on a large scale in the manganese production industry and promote the technological innovation of the membrane electrolytic process.