Extraction of potassium from K-feldspar via the CaCl2 calcination route

The extraction of potassium from K-feldspar via a calcium chloride calcination route was studied with a focus on the effects of the calcination atmosphere, calcination temperature and time, mass ratio of CaCl2 to K-feldspar ore and particle size of the K-feldspar ore. The results demonstrated that a competing high-temperature hydrolysis reaction of calcium chloride with moisture in a damp atmosphere occurred concurrently with the conversion reaction of K-feldspar with CaCl2, thus reducing the amount of potassium extracted. The conversion reaction started at approximately 600 degrees C and accelerated with increasing temperature. When the temperature rose above 900 degrees C, the extraction of potassium gradually decreased due to the volatilization of the product, KCl. As much as approximately 41% of the potassium was volatilized in 40 min at 1100 degrees C. The mass ratio of CaCl2/K-feldspar ore significantly affected the extraction. At a mass ratio of 1.15 and 900 degrees C, the potassium extraction reached 91% in 40 min, while the extraction was reduced to only 22% at the theoretical mass ratio of 0.2. Optimal process conditions are as follows: ore particle size of 50-75 mu m, tablet forming pressure of 3 MPa, dry nitrogen atmosphere, mass ratio of CaCl2/ore 1.15: 1, calcination temperature of 900 degrees C, and calcination time of 40 min. The XRD analysis revealed that a complex phase transition of the product SiO2 was also accompanied by the conversion reaction of K-feldspar/CaCl2. The SiO2 product formed at the initial stage was in the quartz phase at 900 degrees C and was gradually transformed into cristobalite after 30 min. (C) 2015 The Chemical Industry and Engineering Society of China, and Chemical Industry Press. All rights reserved.