Research On The Solubility Of Magnesium And Ammonium In MnSO₄ Solution And The Crystallization Kinetics Of The Double Salt

Nowadays,the electrolytic manganese industry is in stable development,but at the same time,there are many problems that have not been solved.The phenomenon of high Mg²⁺concentration in manganese electrolyte has become an obstacle to the development of the electrolytic manganese industry and is a common problem in the manganese industry.By referring to the literature and on-site investigation,it is found that there are few studies on the harm of Mg²⁺in the manganese sulfate solution system.The research team put forward the idea of double salt crystallization to remove magnesium.In order to improve the technology,the thesis intends to carry out the study of the solubility of ammonium and magnesium in Mn SO₄ solution and the kinetics of the double salt crystallization process of Mn SO₄ solution system.In this paper,the thermodynamics and kinetics of the crystallization of double salts in the mixed system of Mn SO₄,Mg SO₄,and?NH₄?₂SO₄ were studied.Through in-depth experimental discussion and mechanism analysis of the crystallization process,the crystallization process mechanism of ammonium,magnesium and manganese double salt was revealed,and the crystallization kinetic model was established.The effects of factors such as solution concentration,temperature,rotation speed,holding time,and seed crystal on the crystallization of double salt were studied,and more suitable crystallization operating conditions were determined.This laid the foundation for the follow-up control of magnesium removal technology with double salt crystallization method,and provided a supplement to the improvement of magnesium removal technology by hydrometallurgy purification.?1?At a temperature of 298K?358K,the solubility of Mg SO₄ and?NH₄?₂SO₄in Mn SO₄ solutions of different concentrations(18?38g/L Mn²⁺)was determined by static equilibrium method.And use Apelblat semi-empirical formula for fitting correlation to get the solubility empirical equations and the fitting results are ideal.By further fitting,the Regression equations between the solubility of Mg SO₄ or?NH₄?₂SO₄,temperature and Mn²⁺concentration is obtained.The solubility method was used to estimate the resolving heat of Mg SO₄ in Mn SO₄ solutions with different concentrations and temperatures,and the fitting results are ideal.The results show that as the concentration of manganese sulfate increases,the heat of dissolution of the system increases slightly from 8.94 k J/mol to 9.927 k J/mol.?2?The optimized?L law model was used to study the evaporation crystallization kinetics of the double salt.Through curve fitting,the growth and nucleation kinetic equations for the evaporation and crystallization of ammonium,magnesium and manganese complex salts at 30rpm were obtained.And the fitting index R² of the crystal nucleation and growth kinetic equations were all above 0.98,and the fitting results were satisfactory.Under these conditions,the nucleation and growth kinetic equation of ammonium,magnesium and manganese composite salt crystals are:298K:B=4.4824×10¹⁷?^-1.62828,R²=0.99759;G=2.6211×10^-7?^-1.16546,R²=0.99236308K:B=1.0819×10¹⁶?^-1.31523,R²=0.99689;G=7.1686×10^-8?^-0.97708,R²=0.99826318K:B=6.8315×10¹⁶?^-1.47054,R²=0.98382;G=2.6995×10^-8?^-0.85193,R²=0.98563328K:B=4.6793×10¹⁵?^-1.31112,R²=0.98719;G=4.9448×10^-8?^-0.92185,R²=0.98878?3?Based on the crystallization thermodynamics and kinetics studies of ammonium magnesium manganese composite salt.The effects of various factors?solution concentration and crystallization temperature,stirring speed,holding time and presence or absence of seed crystals?on the crystallization process and the particle size and quality of crystalline products were studied,obtaining more suitable crystallization operating conditions under the manganese,magnesium and ammonium content of the evaporated solution.The crystallization operating conditions are:28g/L Mn²⁺,20g/L Mg²⁺,100g/L?NH₄?₂SO₄,crystallization temperature of 328K,rotation speed of 90rpm,crystallization time of 3600s and addition of 8%seed crystals.Under these conditions,the crystallization ratios of manganese,magnesium,and ammonium were 68.05%,97.59%,and 94.81%,respectively.