Study On Phase Equilibrium And Phase Separation Of Hydrochloric Acid Leaching Liquid Of Fly Ash

Aluminum extraction from fly ash is the main way to make use of fly ash as a resource.For the process of aluminum extraction from fly ash by hydrochloric acid,there are a lot of impurity ions such as iron and calcium in the acid extract,which seriously affects the quality of the product.According to the theory of phase equilibrium,crystallization separation of mixed salt solution is an effective method,but it lacks the corresponding basic data in the acid system.In this paper,the phase equilibrium and phase diagram of AlCl₃-FeCl₃?-CaCl₂?-H₂O?-HCl?system were studied by means of isothermal solution equilibrium method,aiming at the plasma of aluminum,iron and calcium in the acid leaching solution,and the acid leaching solution was evaporated and crystallized to obtain pure AlCl₃·6H₂O.Finally,a brief analysis and calculation of the process is made,which is of great significance for the extraction of aluminum by the acid process of fly ash.The main research contents and conclusions are as follows:?1?The phase equilibria of AlCl₃-FeCl₃-H₂O?-HCl?system with different H+ concentration?1.3 mol/L,4.0 mol/L and 11.5 mol/L?and H+ concentration of 1.3 mol/L at 25 ? and 30 ? were studied by isothermal dissolution equilibrium method.The result shows that the phase diagram of AlCl₃-FeCl₃-H₂O?-HCl?system belongs to simple co saturation type,and there is no double salt in the system.The solubility curve divides the phase diagram into five regions: AlCl₃·6H₂O crystallization region,FeCl₃·6H₂O crystallization region,unsaturated region,cosaturation region and solid phase region,and the crystallization region of AlCl₃·6H₂O is significantly larger than that of FeCl₃·6H₂O.With the increase of H+ concentration,the solubility of AlCl₃ decreases gradually,and the crystallization region of AlCl₃·6H₂O increases obviously,while the change of H+ concentration has little effect on the solubility of FeCl₃·6H₂O.When the concentration of H+ was 11.5mol/L,the solubility of AlCl₃ increased from 0.51% to 5.25%,until it reaches the co saturation.The higher the temperature is,the higher the solubility of FeCl₃·6H₂O is,and the better the separation of AlCl₃·6H₂O is.?2?In the same way,the phase equilibria of AlCl₃-CaCl₂-H₂O?-HCl?system under different conditions were studied by isothermal solution equilibria method.The result shows that the phase diagram of AlCl₃-CaCl₂-H₂O?-HCl?system belongs to the simple cosaturation type,and the solubility curve divides the phase diagram into five regions: AlCl₃·6H₂O crystal region,CaCl₂·6H₂O crystal region,unsaturated region,cosaturation region and solid phase region.The solubility of AlCl₃ decreased from 30.83% to 0.51%,and the solubility of CaCl₂ decreased from 43.40% to 31.83%.The crystallization region of AlCl₃·6H₂O was significantly larger than that of CaCl₂·6H₂O.The solubility of calcium chloride is greatly affected by temperature,from 38.91% at 20 ? to 49.09% at 30 ?.?3?The phase diagram of AlCl₃-FeCl₃?-CaCl₂?-H₂O?-HCl?system was calculated,to obtain the relationship between the amount of water evaporated pickle liquor and a crystalline product yield and other physical.The application of AlCl₃-FeCl₃?-CaCl₂?-H₂O?-HCl?was analyzed.To test the application of phase diagram theory in the separation of acid leaching solution,the separation of Al-Fe and Al-Ca in acid leaching solution was studied.In the aluminoferric acid leaching solution,the average yield of the product through 10 cycles is over 87%,the average purity is over 95%,the purity of the product after washing is over 99%,and the final average iron removal rate is over 91%.The average yield of the product is more than 89% after 10 cycles,the purity of the product is more than 98% after washing,and the final average calcium removal rate is more than 87%.By acid leaching of Pingshuo CFB fly ash and four cycles of crystallization,the average yield of the product is more than 81%.Finally,the pale yellow AlCl₃·6H₂O powder with purity of more than 98% is obtained.The content of iron and calcium in the product is 0.08% and 0.24%,which is far higher than the qualified requirements of the product.A brief calculation and analysis of the process provided by the fly ash acid method is carried out.The implementation of this process can not only bring certain economic benefits,but also bring huge ecological and environmental benefits.In this paper,the phase equilibrium of AlCl₃-FeCl₃?-CaCl₂?-H₂O?-HCl?system was studied by isothermal solution equilibrium method under different acidity and temperature conditions,and the corresponding phase diagram and density composition diagram were drawn.The crystallization separation process of acid leaching solution was studied by combining the phase diagram.In this paper,the basic data of phase equilibrium of AlCl₃-FeCl₃?-CaCl₂?-H₂O?-HCl?in acid condition are supplemented and perfected,which provides a theoretical basis for the efficient separation of aluminum and iron.