Speration Of Inorganic Salts Base On Phase Diagram

Phase diagram of water-salt system describes phase equilibrium of water-salt system with the geometry figure and forms the theory foundation of chemical engineering. According to the phase diagram, one can be informed if a certain crystal will form at a give temperature and component concentration. Besides, one can also be informed the sequence of salt-out of each related salt. Separation method based on phase diagram is usually favorable because of its no need of other raw materials, little comsuption of facility and low energy consuming et al. So it has been applied widely in chemical industry of inorganic salts.To separate lithium salt from salt lake brine containing a lage amount of magnesium and to separate calcium sulphate from copper sulphate aqueous solution, new separation methods based on solubility phase diagram have been proposed in this thesis. The research contents include:1) Pridection of the pase diagram of the ternary LiCl-MgCl2-H2O system: According to the BET model, a series of computer programs have been written to simulate the model parameters and to predict the pase diagram. Using the program, the pase diagram of ternary LiCl-MgCl2-H2O system is pridectded with origin BET model and expanded BET model, which include the salt-salt interaction parameter.2) Separation of lithium salt from salt lake brine containing a large amount of magnesium: At fist, simulated brine which has the same component as the brine after solar pool is prepared. Then the phase diagram of the LiCl-MgCl2-H2O system is analyzed to design a routin line for separating. After twice evaporation and crystallization, the ratio of magnesium and lithium in the simulated brine is decreased successfully and easily from 19.3:1 to 6.3:1. Synchronously, the rate of recovery in each circle of evaporation and crystallization is close to 86%.3) Removing calcium sulphate from copper sulphate aqueous solution: The copper sulphate aqueous solution produced by the JinChuan Company is researched here. From the phase diagram of the binary CaSO4-H2O system, it's found the solubility of anhydrate at 90°C is half of the solubility of gypsum at 25°C. Then, according to the assumption that the rule keep intact in the solution containing copper salphate, a scheme is contrived to separate calcium from copper salphate. As a result, the content of calcium in the solution is decreased from 0.485 g·L-1 to 0.210 g·L-1 after evaporating half of water and boiling about 3 hours with anhydate seed. The calcium exist in copper salphate is only about 0.005% while the rate of crystallization is controlled at 75~78%.The prediction of pase diagram indicated that the BET model is more suitable for the high concentration electrolytical solution whose hydrating ability is also strong. The two series experiments show that ordinary phase separation can provide perfect result in salt lake exploitation; the copper salphate product containing calcium less than 0.02% is achieved through the technology developed by us, while in the present technics, however, three times of recrystalltion must be done to achieved the same purity.