关键词: 钾长石, 硅凝胶, 醇析, 钾明矾, 热解, 氧化铝

Abstract: Potassium feldspar is the typical insoluble potassium ore with enormous reserves in the whole world, which contains mainly potassium, aluminum and silicon valuable elements. It will be of great strategic significance to produce soluble potassium fertilizer, aluminum potassium sulfate, alumina and silica gel from potassium feldspar. Instead of the traditionally high temperature roasting (more than 700℃), in this work, potassium feldspar from Hebei province was decomposed using KOH sub-molten salt method at low-temperature (less than 240℃) and normal-pressure. The excess unreacted KOH was recovered through extraction of ethanol aqueous solution, and then the decomposed sample was dissolved with 2 mol/L sulfuric acid solution to transfer K, Al, Si in the mineral powder into the liquid phase, called the mother solution for the separation and recovery of K, Al, Si. Here, sol?gel method and stepwise alcohol precipitation method were used to separate and recover Si, Al and K from the mother solution. The preparation conditions of silica gels, aluminum potassium sulfate and K2SO4 from the mother liquor and the conditions to produce Al2O3 from KAl(SO4)2?12H2O pyrolysis were investigated. An efficient and clean technological route for the comprehensive utilization of potassium feldspar resources was developed. The results showed that the main compositions of potassium feldspar were K2O 13.13wt%, Al2O3 16.66wt% and SiO2 58.28wt%. Silica gel was easy to be formed in the mother solution at 95℃ and concentration of H+ 3.800 mol/L, the desilication rate was over 98%, and SiO2 content of silica gel was more than 99.0%. The BET surface area was more than 700 m2/g, pore volume was about 1.0 cm3/g and pore size was 5?6 nm. The separation of potassium and aluminum from the mother solution was enhanced by the stepwise alcohol precipitation. Firstly, aluminum potassium sulfate with high purity was precipitated at 25℃, the volume ratio of ethanol to feed 1.0, stirring speed 200 r/min, time 5 min, the precipitation rate of aluminum reached 98%, and then the temperature in the solution was decreased to 5℃ with the volume ratio of ethanol to feed 2.0, and potassium sulfate was precipitated, the recovery rate of potassium reached 89%. Alumina was prepared by pyrolysis of aluminum potassium sulfate. When the pyrolysis time was 2 h, the decomposition rate of aluminum potassium sulfate reached 99.8% at 1000℃, and the purity of the alumina product could reach 94%.

Key words: potassium feldspar, silicon gels, ethanol precipitation, KAl(SO4)2·12H2O, pyrolysis, Al2O3