Preparation Of Monocalcium Phosphatewith Low Grade Phosphate Rock By Wet-Process Phosphoric Acid

MCP?monocalcium phosphate?has the highest phosphorus content,solubility,and higherbiological value in calcium phosphate salts.Atpresent,MCP is preparedby the method of calcium carbonate reacting with high concentration phosphoric acid which is prepared with thermal-process phosphoric acid and dihydrate phosphogypsum process of wet-process phosphoric acid.However,thermal-process phosphoric acid has much disadvantages:high production cost,much energy consumption,and high phosphate rock grade.Dihydrate phosphogypsum process of WPA has a dependence on sulfur and is failure of utilization of by-products which is a waste of resources.In this study,hydrochloric acid is used to decompose low grade phosphate rock.And the leaching solution obtained is extracted with the mixed extractant to remove impurities such as iron.MCP can be prepared from the purified solution,so that calcium and phosphorus from phosphate rock have been comprehensively utilized,which can improve the utilization rate of phosphate resources.The main work is as follows:The effects of HCl concentration,actual amount of HCl?acid ratio?,reaction time and feed temperature on the leaching rate of phosphorus and other impurity ions in phosphate rock were emphatically researched.Measuring the leaching rate of the target substance phosphorus and impurity ion iron,the optimal leaching conditions were determined by using orthogonal experimental design:the concentration of hydrochloric acid is 20 wt%,the acid ratio is 1.01,the feeding temperature is 25?,and the reaction time is 15 min.Under this condition,the leaching rate of phosphorus is 96.75%and iron is 22.85%,which not only ensures the higher phosphorus leaching rate,but also inhibits the leaching rate of impurity iron.Different solvent such as n-butanol and n-pentanol,1-octanol,isopropyl ether,petroleum ether,MTBE,MIBK,TBP,DEPHA,MIBK+DEPHA,TBP+DEPHA,MIBK+TBP have been used as extractant,remove of iron in leaching solution.It is shows that the best separation efficiency is mixed extractant TBP+MIBK,the separation coefficient _Fe,PO43 is up to 467.47.The effect of extraction factors on extraction efficiency has been investigated with the uniform design test.Regression analysis method has been applied in uniform design experimental data,and the quadratic polynomial stepwise regression model has been obtained to describe of the relationship of separation coefficient _Fe,PO43 with extract parameters of mixed extractant ratio,phase ratio,extraction time,extraction temperature.The regression equation as follows:y=150.8823-35.6023X₁+1.1037X₁ X₂+0.7152X₁ X₄-0.3297X₂ X₃-0.2784X₂ X₄+0.0096X ₃X₄+0.7008X₂²-0.0203X₄²The optimal extraction conditions were obtained from regressive equation:the ratio of mix extractant is 1:1,phase ratio is1:1,the extraction time is 23 min,and extraction temperature is 25?.The extraction equilibrium isotherm was plotted at different phase ratio,and the extraction saturation capacity was 25 g/L.The extraction equilibrium equation was fitted as follows:y=25.54-49.72e^-3.31xPurified leaching solution,adjust pH to 3,and the ratio of calcium to phosphorus in which was 1:?4.7—4.8?,MCP was obtained by drying after crystallization and filtration.