Study On The Solid Solution Of Potassium Chloride And Ammonium Chloride

In industrial production,the mixture of potassium chloride and ammonium chloride is often encountered,which is difficult to be separated as a solid solution of potassium chloride and ammonium chloride formed in the system.There are many researches about the KCl-NH₄Cl-H₂O ternary salt-water system and the solid solution of potassium chloride and ammonium chloride are not sufficient.It is necessary to further study the KCl-NH₄Cl-H₂O ternary salt-water system and the solid solution of potassium chloride and ammonium chloride.First of all,the change rules of solid solution formed in crystallization regions of the phase diagram of KCl-NH₄Cl-H₂O ternary salt-water system at 25?were studied.The solid solution of potassium chloride and ammonium chloride is obtained by isothermal equilibrium method,and its composition and crystal structure are determined by chemical titration and X-ray diffraction?XRD?method respectively.The results show that the crystals formed in mixed crystal region in the phase diagram of KCl-NH₄Cl-H₂O ternary salt-water system at25?are consisted of solid solution based on ammonium chloride and solid solution based on potassium chloride,and potassium chloride and ammonium chloride are saturated in the solid solution based on ammonium chloride and the solid solution based on potassium chloride respectively.By the solid phase composition of the dividing line between mixed crystalline region and solid solution area can get the solid solubility of corresponding solid solution.The variable temperature phase diagram of KCl-NH₄Cl-H₂O ternary salt-water system was determined by isothermal method,and the equilibrium solid phase was identified by the humid residue method combined with XRD.Increasing temperature from 30? to 70?,it is found that unsaturated region of the KCl-NH4Cl-H2O ternary system increases;Range of the saturated liquid line of potassium chloride and ammonium chloride pure salt crystallization region becomes larger;potassium chloride mass content of the co-saturated points is almost the same,but the ammonium chloride content significantly increases;the crystallization area of solid solution based on ammonium chloride becomes smaller.When the temperature increases from 30? to 70?,the solid solubility of potassium chloride in solid solution based on ammonium chloride decreases from 17.35 wt% at 30? to 16.15 wt% at 70?;the solid solubility of ammonium chloride in solid solution based on potassium chloride from19.05 wt% at 30?increases slightly to 19.84 wt% at 70?.The XRD method was applied to the measurement of inorganic salt solid solution,and the solid solubility of potassium chloride in solid solution based on ammonium chloride and the solid solubility of ammonium chloride in solid solution based on potassium chloride at 25?were measured.The results show that there is a good linear relationship between the content of potassium chloride in the solid solution based on ammonium chloride and the crystal cell parameter a of the solid solution,and so is the relationship between the content of ammonium chloride in the solid solution based on potassium chloride and the crystal cell parameter a of the solid solution;the relative errors between the experimental results and the literature values are 4.14% and 0.31%respectively.The experimental results and literature values conform well,which shows that the XRD method for determining the solid solubility of inorganic salt solid solution is feasible.