Study On The Fractional Crystallization Of Sulphate Mixtures From Wet Manganese Refining

The smelting methods of manganese are mainly divided into pyrometallurgical and hydrometallurgical process.Due to the high purity and good quality of manganese produced by hydrometallurgical process,hydrometallurgy accounts for 90%of global manganese production.However,,a large amount of sulphate mixture waste residue will be generated through hydrometallurgical method.Direct discharge of these wastes will not only destroy the ecological environment,but also cause a great waste of manganese resources.Therefore,this research systematically studied the crystallization thermodynamics of manganese sulfate and ammonium sulfate in the sulfate mixture.On this basis,a new qualitative crystallization process of sulfate mixture was developed,and finally realized esource utilization of sulfate.First,the gravimetric method and isothermal solubility method were used to measurethe solution phase equilibrium data of binary system(NH₄)₂SO₄-H₂O,MnSO₄-H₂O and ternary system(NH₄)₂SO₄-MnSO₄-H₂O at different temperatures.The different crystalline regions of phase diagram were analyzed.The results showed that,compared to the ternary phase diagram at 25?with seven crystalline regions,the phase diagram at other temperatures has only six crystalline regions,and the equilibrium complex salt is converted from(NH₄)₂SO₄·MnSO₄·6H₂O to(NH₄)₂SO₄·2MnSO₄.In addition,the phase equilibrium data of the ternary system(NH₄)₂SO₄-MnSO₄-H₂O was simulated and calculated using the Pitzer model theory,and the simulated solubility calculation results were compared with the experimentally measured data.The results showed that there are good agreements betwwen the calculation results and experimental data.Especially,compared with other temperatures,the data at 25?has the highest agreement,which further demonstrated the accuracy and reliability of the experimentally data.Finally,on the basis of thermodynamic research,the crystallization process of sulfate mixture was explored.Fluorine precipitation method was used to study the separation process of magnesium sulfate in the sulfate mixture,and the effects of different NH₄F addition amount,reaction temperature,addition of seed crystals and reaction time on the separation rate of magnesium sulfate were investigated.In addition,ammonia water was used as a precipitant during the manganese sulfate separation process in the sulfate mixture.The effects of reaction temperature,solution pH and reaction time on the separation rate of manganese and the content of manganese in trimanganese tetraoxide were investigated.The ammonium sulfate product was prepared by evaporating crystallization.And the effects of different reaction temperature,solution pH and rotation rate on the particle size of ammonium sulfate were investigated.In the end,the best technological conditions were determined and the quality crystalline product was prepared.The separation efficiency of magnesium sulfate and manganese sulfate through these processes can reach more than 99%,which reaches the national industrial standard.Through this process,the resource reuse of sulfate mixture was successfully achieved.