Preparation Of Potassium Sulfate By Separation Of Potassium And Sodium Salt With Ammonia-alcohol

Potassium sulfate is the main chloride-free potassium fertilizer in agriculture, which can provide potassium and sulfur to crops. In our country, soluble potash resources are limited badly, but we are rich in insoluble potash ore resources, in which potash feldspar is the main form. Therefore, the development of insoluble potash ore resources is vitally important.Take the filtered liquid of the potassium-rich rocks’sinter from Luonan County, Shanxi Province as object of the study. Firstly, after the evaporation of mother liquid, solution LN-Y2 was gained in which the mass ratio of K₂CO₃ and Na₂CO₃ was 0.93. Secondly, by adding CO₂ gas, ammonia and sec-butanol to solution LN-Y2, sodium bicarbonate was removed to obtain solution LN-Y3 where the mass ratio of K₂CO₃ and Na₂CO₃ was 8.55. Thirdly, through controlling the density, potassium bicarbonate was prepared by evaporating solution LN-Y3 to produce agricultural potassium sulfate.The influences of the different concentrations of alcohol to the mass ratio of K₂CO₃ and Na₂CO₃ were investigated, and n-butanol and sec-butanol were determined to be elected. Considering the amount of alcohol, price, the energy consumption of recycling, safety and environmental factors, sec-butanol was suitable for the separation of potassium and sodium.In ammonia and sec-butanol, the process conditions were studied through the single-factor and orthogonal experiments. The results indicated when reaction time was 90min, sec-butanol concentration was 50%, ammonia concentration was 20%, the flow of CO₂ was 140 L/h, reaction temperature was 40℃, the mass ratio of K₂CO₃ and Na₂CO₃ were respectively 4.04, 3.54, 5.92, 4.60, 4.66; that the optimum process conditions were: reaction time 90min, sec-butanol concentration 70%, ammonia concentration 15%, the flow of CO₂ 140 L/h, reaction temperature 35℃. Under these conditions, 92% of the sodium carbonate could be removed and the mass ratio of K₂CO₃ and Na₂CO₃ reached up to 8.55 in solution LN-Y3. Through stewing and simple distillation, sec-butanol and ammonia were recycled, and their recoveries were 88% and 80%.Solution LN-Y3 was evaporated at 90℃until its density increased to 1.45g/cm³. At this time, the mass fraction of potassium bicarbonate separated was up to 95.29%. Sulfuric acid was added to the solution of potassium bicarbonate to prepare potassium sulfate. By X-ray diffraction and chemical analysis, the performance and structure of products were characterized. Analytical results showed the sodium carbonate and sodium bicarbonate could be recycled in the sintering process of potash feldspar; The potassium bicarbonate could be used to prepare potassium sulfate, of which the mass fraction of K₂O was 44.79%; The potassium sulfate prepared reached the first-rate of national agriculture potassium sulfate standard, of which the mass fraction of K₂O was 51.16%.