Study On The Preparation Of Magnesium Hydrogen Phosphate From Wet-process Phosphoric Acid

Magnesium hydrogen phosphate is widely used in sewage treatment,food,medicine,etc.It is often used as a chemical precipitation agent in urban and industrial sewage treatment,and reacts with NH₄⁺to generate MAP?magnesium ammonium phosphate?,which can remove the eutrophication pollution source of water-ammonia nitrogen.At present,the method of preparing magnesium hydrogen phosphate at home and abroad is mainly prepared by the reaction of thermal acid and magnesium oxide?or magnesium hydroxide?.Neither dynamic nor dynamic data have been systematically studied.First of all,this subject studied the preparation process of magnesium hydrogen phosphate using wet-process phosphoric acid and magnesium oxide as raw materials.In order to improve the product quality,the wet-process phosphoric acid was subjected to impurity pretreatment,and the different magnesium oxide concentration,reaction temperature,stirring speed,reaction The effect of preparation conditions such as p H and reaction time on the purity and particle size of magnesium hydrogen phosphate product.The optimal preparation conditions are:magnesium oxide concentration is 5 g/100 g water,reaction temperature is 65?,stirring speed is 250 r/min,reaction time is 50 min,and the prepared industrial grade MgHPO₄·3H₂O?purity greater than 96%?The average particle size of the product is 93.61?m.From the treatment of raw materials to the preparation of magnesium hydrogen phosphate,the yield of wet-process phosphoric acid is about 80%,and the yield of magnesium oxide is about 88%.Secondly,the thermodynamic data of magnesium hydrogen phosphate crystals were measured.The solid-liquid equilibrium data of 298.15 K and 313.15 K ternary system MgHPO₄-Na₂HPO₄-H₂O?17%H₃PO₄ solution?and two binary subsystems were studied by isothermal dissolution method.Through the determination of the solubility of MgHPO₄·3H₂O in phosphoric acid,it was found that its solubility basically does not change with the change of temperature,but the concentration of phosphoric acid has a great influence on its solubility.The study found that the binary system phase of magnesium hydrogen phosphate-water in 17%phosphoric acid solution is balanced,and the equilibrium solid phases are magnesium hydrogen phosphate heptahydrate and magnesium hydrogen phosphate trihydrate.The binary system phase equilibrium solid phases of disodium hydrogen phosphate-water in 17%phosphoric acid solution in the range of 273.15 K-363.15 K are Na₂HPO₄·12H₂O and Na₂HPO₄·7H₂O,respectively.At 298.15 K MgHPO₄-Na₂HPO₄-H₂O?17%H₃PO₄ solution?ternary system phase equilibrium,the phase diagram has a common saturation point and three crystalline regions,namely MgHPO₄·7H₂O crystalline region,Na₂HPO₄·12H₂O crystalline region and MgHPO₄·7H₂O+Na₂HPO₄·12H₂O co-crystal zone.The crystallization area of Na₂HPO₄·12H₂O is very small,and the other two co-crystallization areas are very large.At 313.15 K,there is a common saturation point and three equilibrium solid phases in the MgHPO₄-Na₂HPO₄-H₂O?17%H₃PO₄ solution?ternary system phase equilibrium system,namely MgHPO₄·3H₂O,Na₂HPO₄·7H₂O and Mg HPO·3H₂O+Na₂HPO₄·7H₂O Co-saturated solid phase.In the ternary phase diagram,the MgHPO₄·3H₂O phase region and the MgHPO₄·3H₂O+Na₂HPO₄·7H₂O co-crystal phase region are large,and the Na₂HPO₄·7H₂O crystal phase region is small.Finally,the continuous steady-state method was used to study the crystallization kinetics of the reaction of MgHPO₄·3H₂O with magnesium oxide and phosphoric acid.Growth,and finally confirmed its crystallization kinetics growth model.By using Matlab software to perform multiple linear regression to fit the growth rate and nucleation rate equations,and by comparing the theoretical value with the experimental value,it is found that the deviation is controlled within 10%,and the growth rate equation has certain practical production guidance significance.The temperature has the most obvious effect on the reaction crystallization process,its growth rate increases significantly,the crystal quality is significantly improved,and the crystal morphology has obviously changed;the second most significant factor that affects the crystallization process is the average residence time;and the least impact factor on the crystallization process is the concentration of phosphoric acid.