Comparison of different models for describing gypsum dissolution kinetics in different aqueous salt solutions

Abstract

Gypsum dissolution as a function of time was measured in solutions having a sodium adsorption ratio (SAR) of 7.5, 14 and 27 (mmol(+) kg-1)1/2 and an electrical conductivity (EC) of 1 5 and 3.1 dS m-1. The amount of gypsum dissolved increased with increases in the SAR and EC values of the different equilibrating solutions. The rate of gypsum dissolution was higher initially but declined with increasing time of equilibration. Of the total amount of gypsum dissolved in 40 h, about 60-70% dissolution occurred during the first 5 min. Comparisons of coefficients of determination (r2) and standard errors of estimate indicated that, in addition to the most widely used linear form of the first-order model, other models such as the power function, empirical (modified from first-order) and the Elovich equation, can also be used to describe the kinetics of gypsum dissolution in aqueous solutions varying in SAR and EC.