Solution kinetics of gypsum

Two sets of six samples of crushed gypsum and demineralized water were prepared. One set contained crystals of a grain size between 125 and 250 microns, the other set between 500 and 1000 microns. Once a week one sample from each set was dried and weighed. The ion activity product was calculated from the final weight loss of both sets, and found to be 10????? for the larger-grain-sized samples at 25°c., and 10????? for the smaller-grain-sized samples at 25°c. Comparison with the solubility product 10????? suggests that the solutions were very near equilibrium. During the first weeks of the experiment, the samples of smaller grains dissolved at a slightly faster rate than those of larger grains, but the difference was reduced as the solutions approached equilibrium. The rate of solution was not constant for either set of samples, probably due to the presence of very fine particles of gypsum attached to the grains during grinding, whcich dissolved at a faster rate due to a higher surface-area-to-mass ratio.No embarg