Probe Into The Basic Lixiviation Theory And Development Path For Polyhalite

China is short of potassium-bearing fertilizer, and it is also a big agriculture country in the world.Polyhalite (K2SO4 · MgSO4 · 2CaSO4 · 2H2O) is one of the insoluble potassium mineral in wide distributed sulfate-type potassium-bearing deposit, in which the concentration of potassium sulfate (K2SO4) is about 28% theoretically. Many polyhalite deposits have been founded in China, but, because of its own special geological characteristics, like its insolubility, buried depth more than hundreds or thousands meters under the surface, these deposits have been regarded to be inusable or disable exploitative deposit.This Ph.D thesis has focused on Nong-Le polyhalite deposit of Qu-Xian County, eastern Sichuan Province. Based on a quantity of achievment studying on geological features and mineral characters of polyhalite deposit, the thesis has analysed the general imformations of the polyhalite resources, basic geological characteristics and hydrogeologic condition. It was finally conclued in the thesis that the special geological features including perfect enclosed and high permeability of the deep-buried polyhalite deposits occurred in marine sediemntary basin in China make it possible to minning these deposits by lixiviation technique method. Therefore, it is the key problem of the technique of lixiviation polyhalite to look for the high efficacy lixiviation dissolvent and reasonably to enlarge the resolution limitation to the usable contents from polyhalite in the deposit. Unfortunately, until now any references have not been reported both at home and abroad.It was confirmed that Nong-Le polyhalite has the classic characteristic of polyhalite by the experimental research on the micro-texture and X-ray diffractionfeature. The resolution equilibrium consistencies of liquid-phase K+ of polyhalite in water are tested to be 19.13, 22.30, 36.78 (mg/ml) under the temperature of 298K, 323K, 348K, respectively. Analysing and contrasting the solubilization of polyhalite in several inorganic salt solutions like CaCl2, Ca(OH)2, Na2CO3, (NH^CCh, BaCl2 by experiment tests, CaCl2 solution is finally selected as lixiviation dissolvent which is characterized with nonpoisonous, low cost and little influence to sedimentary stratigraphies. At the temperature of 298K, in the liquor of 5% and 10% CaCl2, the resolution equilibrium consistencies of K+ are 25.65 and 35.24 (mg/ml) respectively. The experimental results have proved that CaCl2 could be a beneficial solubilization to polyhalite. Under testing on impact of temperature and consistency of CaCl2 solution, it has been observed that the potassium resolution equilibrium consistency will increase with the temperature rising and the concentration of CaCl2 increasing.Based on Pitzer theory and HW equation and experimental results, the resolution equilibrium constant (Ksp) of polyhalite in water has been calculated theoretically. The result (1.018E-14 at 298K) is quite similar to the polyhalite Ksp as 1.804E-14 by calculating using standard chemical potential and it is proved that the experimental data is credible. Ksp gained by calculating were 18.85E-14 and 48.29E-14 in 5% and 10% CaCl2 solution at 298K respectively. Companying with consistency CaCl2 increasing, the polyhalite Ksp is enlarging. By using the Ksp of simple-salt CaS(VH2O, CaSO4, MgSO4 and K2SO4 under the temprature of 273K-348K, the resolution equilibrium constant (Ksp) of polyhalite in the same temperature rang has been estimated and approximated to the experimental data. It is concluded that the Ksp of complex-salt can be estimated by using the Ksp of simple-salt when it is lack in experimental data. The enlarging effect of CaCl2 to the solubility of polyhalite is confirmed theoritically through the results of thermodynamics calculation.The influence to polyhalite lixiviation procedure by consistency and temperature of CaCl2 lixiviation dissolvent and grain-size of ore rock has been researched by experiment. The recovery of K+ increases with higher temperature and concentrationof CaCb, but decreases with size of ore. The concentration of CaCl2 was selested as 5% considering the cost of lixiviation and other reasons. The recovery of K+ can be over 80% at experimental conditions.The macroscopic reaction dynamics of lixviation of polyhalite in CaCb solution was studied based on the heterogeneous-phase reaction dynamic principle and the experimental data. The chemical reaction between polyhalite and CaCl2 has been discovered to be the first order respect to CaCb. The types of reaction were relevant to the experiment conditions (temperature, stirring and etc.). Without stirring condition, the surface activation energy (Ea) of the reaction obtained through calculation is 11.52kJ/mol and the velocity constant &=1.267exp(-11523/RT). The lixiviation procedure is controlled by solid products bedding diffusion and suites to "Contraction Non-Action Nuclear Model" controlled by solid products bedding diffusion under the case of variable concentration, its equation is:fl ±1 DMC — ln(l - a) - (1 - a) 3 =--------^-t, in the equation the solid products beddingL3 J pSr0diffusion constant D ' = -0.0969T+27.49(10"8 cm.s"1). The surface activation energy (Ea) and the velocity constant of the reaction were relevant to temperature under stirring condition. The Ea has been calculated decreasing from 48.35kJ/mol to 2.83kJ/mol following with temperature increasing from 288K to 348K. When temperature is changed from 288K to 303K, the lixiviation procedure is controlled by chemical reaction and the dynamic equation can be expressed as-^(1-a)1" =^^-t , Ks ' =-0.3416T +97.07 (10"5 cm.s"1). At the range oftemperature 303K to 348K, the lixiviation procedure is controlled by solid products bedding diffusion and suites to solid products bedding diffusion controlling Contraction Non-Action Nuclear Model. The macroscopic reaction dynamics modelhas been established as:D'MCp8r{-t, D'=-0.0621T+18.05(10'9 cm.s"1). All above research results have suggested that CaCl2 could be the...