Study On Quaternary System Phase Equilibrium To Prepare Chloride-Free Potach Fertilizers And Ammonium Carnallite With Carnallite As Raw Material

Qarhan Salt Lake is abundant in inorganic salt resource,but there are many problems in the process of resource exploration.The local enterprises only pay attention to exploiting potassium resources but ignore other resources,resulting in product single and resources wasting.Because potassium chloride is not suitable for saline-alkali soil and chloride-sensitive plants,the production of chloride-free potash fertilizers is paid attention.In order to guide the production of chloride-free potash fertilizers,this paper have studied the phase equilibrium of K+,NH4+//Cl-,SO42--H2O system at 80.0? and design a technology to product chloride-free potash fertilizers according to the phase diagram of K+,NH4+//Cl-,SO42--H2O system.Then,this paper studied the metastable equilibrium of K+,Mg2+//Cl-,SO42--H2O at 25.0? and calculated the solubility data based on the Pitzer model.Besides,to develop and utilize the potassium and magnesium resources in Qarhan Salt Lake comprehensively,this paper studied the phase equilibrium of KCl-MgCl2-NH4Cl-H2O at 25.0? and design the technology of the production of ammonium carnallite.The solubilities of the quaternary system K+,NH4+//Cl-,SO42--H2O and its two ternary subsystems NH4Cl-KCl-H2O,(NH4)2SO4-K2SO4-H2O at 80.0? were measured using the isothermal dissolution method.In the phase diagram of K+,NH4+//Cl-,SO42--H2O system,there are three crystalline zones,which correspond to(K1-t,NH4t)2SO4,(K1-m,NH4m)Cl and(NH4 n,K1-n)Cl,respectively.The crystalline region of(K1-t,NH4 t)2SO4 is the largest,indicating(K1-t,NH4-t)2SO4 crystallize out easily.According to the analysis and the calculation for the phase diagrams of K+,NH4+//Cl-,SO42--H2O system at 80.0? and 50.0?,the paper proposed a technological process.In the process,the(K1-t,NH4 t)2SO4 can be prepared at 80.0? and the(NH4 n,K1-n)Cl can crystallize out at 50.0?.The mass fraction of K2SO4 in product Li(K1-t,NH4 t)2SO4(t=0.1465)is 88.48%.Then theoretical calculations and experimental verification about the process could be accomplished.The phase diagram of KCl-MgCl2-NH4Cl-H2O system at 25.0? consists of seven co-saturated points and eight solid phase crystalline regions.The eight regions are MgCl2·6H2O,KCl,NH4CI,KCl·MgCl2·6H2O,NH4Cl·MgCl2·6H2O,(K1-m,NH4 m)Cl,(NH4 n,K1-n)Cl and(K1-m,NH4 m)Cl·MgCl2·6H2O,respectively.Under the guidance of the quaternary system phase diagram at 25.0?,this paper optimized and designed two technological processes for preparing ammonium carnallite with carnallite as raw material and ammonium chloride as salting-out agent.At last,this paper compared the two processes with those in literature and selected the optimal technological process.The metastable phase diagram of K+,Mg2+//Cl-,SO42--H2O system consists of seven co-saturated points and eight solid phase crystalline regions.The eight regions are KCl,K2SO4,MgCl2·6H2O,MgSO4·5H2O,MgSO4 6H2O,K2SO4·MgSO4·6H2O,KCl·MgC12·6H2O and KCl·MgSO4·3H2O,respectively.Besides,the solubilities of three ternary system were measured and the corresponding phase diagrams were plotted.On the basis of Pitzer electrolyte solution theory,the metastable solubility of K+,Mg2+//Cl-,SO42--H2O system at 25.0? was calculated via building model of the quaternary system.The results showed that the experimental values were well consistent with the calculated values.