The Polyhalite Dissolution Behavior And The Primary Technology Process Of Preparing Potassium Sulfate

Potash is one of three major agricultural fertilizer, which plays an importantrole in improving yield and quality of agricultural products. At present, thecontradiction between supply and demand of potash fertilizer industry in China isstill severe. Water soluble potassium mineral are not rich in China, so it becomesmore significant to study the non-water soluble potassium mineral. Polyhalite is awidely distributed in sulfate type potassium deposits of hard dissolved potassiummineral, of which the concentration of potassium sulfate is about28%theoretically.China is rich in polyhalite, which reserves in eastern Sichuan, converted into K₂O,are approximately over ten billion tons. It should be a key source for sylvite industryin China. Therefore, solving the polyhalite chemical hard dissolved problems, findappropriate dissolved system, and the effective ingredient polyhalite, such as Mg²⁺,K⁺, SO₄^2-, dissolved and extraction, is polyhalite quarries to exploitation of the key.The experiment result of has theoretical reference and practical application value.The paper investigated the impact of temperature on the solubility of polyhalitein water, CaC12solution, Ca（OH）₂solution at atmospheric pressure. Theresolution equilibrium consistencies of liquid-phase K⁺of polyhalite in water weretested to be20.29,22.32,23.24and24.72g/L under the temperature of25℃,50℃,60℃and100℃. The accumulated recovery of K⁺were70.09%、77.13%、80.09%、85.15%respectively. While in CaC12solution were tested to be25.29,27.77g/L under the temperature of25℃and50℃. The accumulated recovery ofK⁺were86.35%、90.33%respectively. In Ca（OH）₂solution, compared with waterand CaC12solution, accelerated growth of K⁺concentration changes over time, toreach a higher concentration in a short time. The resolution equilibrium consistenciesof liquid-phase K⁺were tested to be17.15、20.42、23.17g/L under the temperature of25℃,50℃and75℃after reacting for about4hours respectively. Theaccumulated recovery of K⁺were78.80%、85.94、92.05%respectively.The thesis research focused on using Ca（OH）₂as leachant, comparing to theCaCl₂and water medium, optimized the leaching process parameters; and todetermine the technical proposal of preparing potassium product.The thesis took the leaching rate of K⁺as index, investigated each unit cell’seffects on solubility property of polyhalite in Ca（OH）₂and CaCl₂solutions, inaccordance with the infiltration technological conditions of orthogonal experimentoptimization,5%of CaCl₂as leachant, at the ratio of4:1of liquid and solid. Understirring, it reacted for3hours at the temperature of60℃, and the recovery of K⁺canbe90.05%. while using4g Ca（OH）₂as leachant, at the ratio of4:1of liquid andsolid, under stirring, it reacted for3hours at the temperature of60℃, and therecovery of K⁺can be91.65%. Compared with the two kinds of leachant, whenusing CaCl₂as leachant, the leaching solution contained high quality of Cl^-toincrease the difficulty in preparation of potassium sulfate. while using Ca（OH）₂asleachant, the concentration of K⁺and SO₄^2-were far greater than other ions in theleaching solution, which was helpful for preparation of potassium sulfate, but it alsohad shortcomings, the reaction liquid was more stick to increase the the difficulty infilting. But all in all, Ca（OH）₂was more suitable to be the leachant for polyhalitethan CaCl₂.In the multiple use of recycled water experiment, the concentration of K⁺reached25.15g/L after3cycle. Brine which was direactly evaporated afteracidification, produced the K₂SO₄product was90.06%pure, the content of Cl^-was0.661%, reached the agricultural use of K₂SO₄national standard.The evaporation ofthe preparation of feed-grade plan: firstly, evaporated450g of water, filter out theprecipitated solid phase impurities, the filtrate continue to be evaporated, get thepurity of98.76%feed-grade K₂SO₄product, of the recovery of K₂SO₄was88.96%.Other steps, the preparation of the first leaching solution of excellent agriculturalpotassium sulfate product simply evaporate162g of water, potassium sulfateproduct purity of96.35%, of the recovery of K₂SO₄was89.47%, Cl^-content of0.7366%.Tailings and ore X-ray diffraction analysis of the spectra can be seen that thepolyhalite characteristic diffraction peaks had disappeard in tailings, indicated thatCa（OH）₂and polyhalite had basically reacted.