The thermal decomposition mechanism of K-feldspar with industrial waste of FGD gypsum to produce soluble potassium (IC) salt was investigated. Effects of the reaction temperature and the amount of reagents used on the recovery of IC 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 IC2SO4 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 diffusidn 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.