Preparation Of Potassium Sulfate From Potassium-rich Rocks

Potassium fertilizer is one of the three basic fertilizers, which is also necessaryfor crop growth. At present, potassium chloride,potassium sulfate and potassiumnitrate are three kinds of potassium fertilizers mainly used. But for thechloride-sensitive crops, such as tobacco,flax,cotton,watermelon,tea, they need touse the chloride-free potassium fertilizer, not only for their economic benefits, butalso for their growing demands. So, the demand for potassium sulfate is increasing, atthe same time, the price are growing quickly. To a certain extent, potassium sulfateusing crisis are caused.In our country, soluble potassic resources are limited badly, but we are rich ininsoluble potash ore resources. In order to solve the potassium energy crisis, we needto development of insoluble potash ore resources, which is very important.Experiment based on the K⁺,Na⁺//Cl^-,SO₄^2--H₂O quaternary system phasediagram at 25℃, obtaining the best ratio of preparing potassium sulfate by a two-step:first step is: m_KCl=0.776×m_Na2SO4, V_H2O=1.768×m_Na2SO4; second step is:m_KCl=0.685m_G, V_H2O=1.570×m_G. Through these two steps, pure K₃Na(SO₄)₂ andpotassium sulfate can be produced.Sintering flooding filtrate mother liquid, which is from potassium-rich rocks ofLuonan country in Shanxi province, was used to produce potassium sulfate. The keyto the experiment is the purification work and preparing method. During theexperiment, first, CO₂ gas was injected into the liquid to filtrate it, then KMnO₄ wasadded, which can reduce Si plastic impurities of the solution from 500mg/L to lessthan 10mg/L. After that, the liquid became a solution of NaHCO₃-KHCO₃-H₂Osystem. By the solubility differences of NaHCO₃ and KHCO₃ at 70℃, the liquid wasevaporated, removing mostly Na+. The sulfuric acid was added when the densityincreased to 1.589g/cm³, that is m(K₂CO₃)/m(Na₂CO₃) = 8. Potassium sulfate wasobtained by filtrating. The rest of the solution was filtrated and crystallized again.When the density of the solution was between 1.16 g/cm³ and 1.18 g/cm³,precipitation was K₃Na(SO₄)₂. Potassium sulfate was then produced according to the process. The K₂SO₄ prepared is up to the first class requirements of nationalagriculture potassium sulfate.