Research On The Mixing Brine Method To Produce Low-Sodium Carnallite From West Taijinar Saline Lake Brine

Salt lake brine, abundant with sodium, potassium, magnesium, lithium, boron and other useful elements, is an important liquid mineral resource. Potassium is one of the scarcest resources, and almost 97% of potassium resources stored in the brine in China. West Taijinar salt lake, located in Qinghai province, has the large reserve of potassium, the grade of potassium is high, and the development condition is also superior. Comprehensive development and utilization of the potassium resource in West Taijinar Salt Lake is meaningful for resolving the contradiction between supply and demand of potash, and the local economy will be promoted too. Based on the chemical composition of brine and current situation of development, the mixing brine method to produce low-sodium carnallite from West Taijinar salt lake brine was studied.Through the isothermal evaporation experiment under 15℃、25 ℃ and 35 ℃, the evaporative crystallization law of West Taijinar salt lake brine was ascertained, and the relationship between the brine’s density and chemical composition with the water evaporated rate was obtained. Results show that the crystalline form of potassium ions are chloride and carnallite at 15 ℃and 25℃, kainite at 35 ℃. The sodium chloride precipitate with potassium during the evaporation process, the content of sodium chloride in the brine of potash precipitation stage and carnallite is lowest at 25℃.Research of reducing sodium chloride from the potassium chloride saturated brine by mixing old brine have been done. The connection of ion concentration in liquid phase and crystallization time was obtained. Results show that after 4.5 hours crystallization, the liquid phase reaches the equilibrium, and the solid phase precipitates completely. Through the mixing brine research, the more old brine mixed in the potassium chloride saturated brine, the more sodium chloride will be separated out, and the loss rate of potassium will increase too. The carnallite will be precipitated when the mixing brine ratio (potassium chloride separating brine vs old brine) less than 3.3:1, the loss rate of potassium will sharply increase. So the suitable mixing brine ratio for reducing sodium chloride is determined to 3.3:1.In order to shorten the metallogenic time of carnallite, and reduce the effect of natural factors, the old brine is mixed in the carnallite saturated brine for preparing low-sodium carnallite. Research shows that the best metallogenic time for mixing brine method to produce carnallite is 60 minutes. The mixing brine ratio (carnallite saturated brine vs old brine) influences the amount of carnallite. The yield of carnallite and the content of sodium chloride in the carnallite increases with the increase amount of old brine. When the mixing brine ratio (mC:mF) is 1.4:1, the percentage of carnallite and mother solution reaches the maximum 5.29, the yield of potassium can reach 53.06%, and content of sodium chloride impurity is only 3.53%. The brine mix way effects the crystallization of low-sodium carnallite. At the same crystallization time, the way with two kinds of brine added simultaneously is beneficial to improve the yield of carnallite.Combined with the phase diagram of water-salt system Na+, K+, Mg2+//Cl--H2O at 25 ℃, the production of KCl from carnallite contained with different amount of NaCl was calculated using the secondary hydrolytic decomposition method. If X represents the percentage of sodium chloride in carnallite, H1 represents the amount value of water added at first time, H2 represents the amount value of water added at second time, and they satisfy with the equation Hi=51.70-0.518X, H2=3.434X-7 and H=2.916X+44.4. The mathematical relationship between the recovery of KCl (Y) and the percentage of NaCl (X) is Y= 90.835-2.7123X.According to the research results, the mixing brine process to produce low- sodium carnallite from West Taijinar saline lake brine was established. The process could reduce the effects of natural factors, shorten the metallogenic time of carnallite and reduce the content of sodium chloride in carnallite, it is beneficial to produce quality low-sodium carnallite for preparing potassium chloride. The results can give the guidance to develop the West Taijinar salt lake brine resources, and has reference significance for other magnesium sulfate subtype salt lake resources development.