Resource Utilization Of Manganiferous Wastewater For Preparation Of Manganese Carbonate

Manganese carbonate,which is an important raw material for the manufacture of soft ferrites,has been widely used in modern fields such as coatings,medicines,and dyes.At present,manganese carbonate is mainly prepared by raw material of manganese ore.However,there are shortage of manganese ore resources and low additional value of manganese-containing wastewater in China.Therefore,the method of obtaining manganese carbonate from raw material of manganese ore has great limitations in the process of industrialization.The wastewater,which produced during the production of titanium dioxide by sulfuric acid method,has a high content of manganese.Traditionally,the manganese-containing wastewater is often treated by traditional calcium oxide neutralization process,it will not only cause secondary pollution of waste residue,but also waste manganese resources of wastewater.Therefore,the recovery of manganese in the manganese-containing wastewater to produce manganese carbonate not only relieves the shortage of manganese ore resources,but also avoids environmental pollution problems.Based on above,optimization of critical conditions were conducted on the process of pretreatment and manganese precipitation from wastewaters produced from sulfate titanium dioxide preparation wastewater,and the products were characterized by XRD,SEM,TGA and ICP-AES.The concrete contents are as follows:?1?The fractional precipitation was applied to remove impurity of metal ions in the pretreatment process of titanium dioxide wastewater.Firstly,iron and aluminium were removed by hydrolysis precipitation method with hydrogen peroxide?30%,in mass fraction?as oxidant.Results showed that the precipitation rate of iron reaches99.54%at temperature of 90?,solution pH of 5.0 and add 2.5 times theoretical dosage of hydrogen peroxide.Secondly,heavy metals were removed by sulphide precipitation method.The concentrations of Ni²⁺,Ba²⁺and Cu²⁺that both less than 0.01g·L^-1 could be achieved with pH value kept 5.5 for 2 h at temperature of 60?.Finally,the removal rate of Ca²⁺,Mg²⁺were 80.24%and 73.52%by frozen-heat concentration method until flocculent substances appear,respectively.The removal rate of Ca²⁺,Mg²⁺of solution after concentration were 99.01%and 98.44%,respectively,at temperature of 90?,solution pH of 5.5,time of 1 h and add 2.0 times theoretical dosage of ammonium fluoride.?2?The method of carbonate precipitation with ammonium bicarbonate solution as precipitant and sodium dodecyl sulfate as an additive was used to recover manganese from wastewaters.Firstly,process conditions of carbonate precipitation of simulated wastewater were optimized by single factor tests.Based on results of single factor tests,the process conditions were further optimized by response surface methodology.A combination of single factor and response surface experiments was used to investigate the effects of reaction temperature,excess coefficient of ammonium bicarbonate?NH₄HCO₃?,pH of the solution,aging time,concentration of NH₄HCO₃ and feeding methods on the precipitation of manganese precipitation rate.Based on the regression analysis,regression equations related to response values and factors were established.The optimal process conditions were determined as follows:reaction temperature of30?,excess coefficient of 1.11,solution pH of 7.1,and aging time of 2 h.The predicted and experimental values of precipitation rate of manganese were 99.83%and99.89%,respectively,and the relative errors was merely 0.06%,which indicated that established models were accurate and reliable for the analysis and prediction of the process of the manganese precipitation rate.?3?Based on the simulated results,when the NH₄HCO₃ concentration of 1.0mol/L and the feeding method of adding NH₄HCO₃ solution to MnSO₄ solution were constant,process conditions of carbonate precipitation of titanium dioxide wastewater were optimized by single factor method and response surface method,respectively.The effects of reaction temperature,excess coefficient of NH4HCO3,pH of the solution and aging time on the precipitation of manganese precipitation rate were investigated.Based on the regression analysis,regression equations related to response values and factors were established.The optimal process conditions were determined as follows:reaction temperature of 33?,excess coefficient of 1.06,solution pH of 7.2,and aging time of 2 h.The predicted and experimental values of precipitation rate of manganese were 99.30%and 98.90%,respectively,and the relative errors were merely 0.40%.The manganese content in the product was 43.53%determined by ICP-AES analysis method,which reached the standard of industrial grade product?HG/T 4203-2011?.The results not only can realize the recovery of manganese from titanium dioxide wastewater by sulfuric acid method,but also provide a new idea for the resource reclamation of manganese-containing wastewater.