Research On Critical Technique Of Cleaner Production Of Electrolytic Manganese

Electrolytic manganese industry is the second largeast industry in the field of ferrous metallurgy in China and it belongs to the industry of high pollution and high energy consumption.In order to promote the current efficiency in the electrolysis,SeO2 is generally used as electrolytic additive in our country by electrolytic manganese enterprises.However,there are three problems by introducing SeO2:1,SeO2 would participate the reduction of Mn2+ and thus lower the purity of product;2,the increasing price of Se02 had brought serious economic burden to enterprise;3,the toxicity of SeO2 poses potential threat to worker and ambient environment.Therefore,it is urgent to develop non-selenium electrolytic additives to replace SeO2 additives.In addition,to ensure the continuous electrolysis,lead-silver alloy is used as anode,but the cell voltage is high and the anode slime is vast and toxic.With the introduction of the environmental tax,the treatment of lead-contained anode slime will severely restrict the development of enterprise.The method of using canvas diaphragm in electrolyzer to separate the anode compartment from the cathode compartment could enjoy the benefit of sharing electrolyte,but it could make the Mn2+,which existed in cathode area,overflow to the anode area to form large quantity of anode slime,as a result,frequently cleaning work are needed to maintain the normal operation.(1)Optimization of the electrodeposited manganese parametersThe main electrolytic parameters:current density(i0),Mn2+ concentration,SO2 concentration and pH value were investigated by using the single factor experiment.The results showed that the current density has significant effects on the current efficiency,and can significantly affect the grain size,the optimal current density was 50mA/cm2;when fixed this parameter,it was found that the increasing of Mn2+concentration was conducive to increase the current efficiency,considering the manganese's morphplogy and the current efficiency,the optimal Mn2+ contentration was 25g/L,at this time,the optimal pH value was 7.8 and the optimal concentration of SO2 was 0.2g/L;(2)Screening and performance research on electrolytic additivesUsed 0.2g/L SO2 as the main additive,chosen Zn2+,polyacrylamide(PAM)as auxiliary additive.The mechanism of these two additives and the effect on the morphology of deposited metal were detected by using cyclic voltammograms and constant current deposition experimental.The results showed that Zn2+ could be reduced to Zn in the electrolysis,and thus inhits the hydrogen evolution reaction and promote the current efficiency;while PAM has strong leveling effect and it could make the deposit more compact.The higher current efficiency and good morphology were obtained in the presence of 1.0 mg/L Zn2+ and 5.0 mg/L PAM after electrolysis at 50 mA/cm2 for 2.5h,the metal deposited at the cathode was compact,light,moreover,the purity of deposit could reach up to 99.90%.(3)Research on novel titanium coating anode and Pilot testTitanium coating anodes have low oxidation overpotential,good electrocatalytic activity,lower the content of side reaction,thus greatly reduce the quantity of anode slime and significantly lower the cell voltage.Pilot tests showed that A series(tabular-fine particles)coating anode was of the best,and there were no difference between traditional industrial lead-silver alloy anode and the novel titanium-based Ir-Ta oxide coated anode with regarding to the anode current,the corresponding cathode's current,the cathode 24h-electrolysis output,hence,it conforms to the industrial electrolytic production requirements.(4)Design and research on anion exchange membrane electrolyzer.Two types of exchange membranes were screened from the five sold anion-exchange membranes through static experiments and dynamic experiments,which were classified as membrane Ml and membrane M2.The highest space time yield is obtained when the area ratio of the membrane area to the cathode plate is 1:0.7;When using membrane M1,the optimum concentration of H2SO4 in anolyte is 0.8 mol/L,while using membrane M2,the optimum concentration of H2SO4 in anolyte is 1.0 mol/L;When the feed solution in anode chamber was NH3·H2O,the anode product is NH4HSO4,the volume of anolyte is greatly reduced,therefore,the industrial water balance could be realized.