Recovery of Potassium from K-Feldspar by Thermal Decomposition with Flue Gas Desulfurization Gypsum and CaCO₃: Analysis of Mechanism and Kinetics

The thermal decomposition mechanism of K-feldspar with industrial waste of FGD gypsum to produce soluble potassium (K) salt was investigated. Effects of the reaction temperature and the amount of reagents used on the recovery of K were studied. The results showed that increasing the reaction temperature and mass ratio of CaCO3/KAlSi3O8 and CaSO4/KAlSi3O8 was beneficial to the decomposition of K-feldspar. The recovery ratio of K was higher than 90% with the mass ratio of KAlSi3O8:CaSO4:CaCO3 = 1:1:3 at 1373 K for 40 min, and the product K2SO4 with a purity of 91.3% was obtained. A crystal structure disintegration mechanism for KAlSi3O8 was proposed on the basis of the characterization of phase transformation sequences by XRD, FTIR, and SEM/EDS. It was found that two product layers formed successively during the KAlSi3O8 decomposition process. K was enriched in the outer product layer, and the decomposition rate was controlled by Ca diffusion through the inner one. Based on the experimental results, a kinetics model of K-feldspar decomposition was established using the Crank-Ginstling-Brounshtein equation, and the apparent activation energy was determined.