The chemical kinetics dissolution of rock salts from Sakon Nakhon Basin is characterized by drill cores and compared to geochemical compositions of natural brines obtained within the study areas in Udon Thani and Sakon Nakhon Province, Thailand. A criterion for rock salt core analysis depends upon the maximum amount of halite, based on X-ray diffractometry. Mass balance relation between brines and rock salt dissolution is conducted by the difference of initial and final weights of the core sample in each experimental batch. To monitor salinity related to its dissolution, the concentrations of total dissolved solids (TDS) are determined for each time period. The dissolution rate of rock salts can be evaluated from chemical compositions of the reactants; sodium-chloride (Na-Cl, halite) and calcium-sulphate (Ca-SO4, anhydrite), corresponding to the TDS content, against the experimental variables of time and temperature. The most important aspect of brine and rock salt interfaces concerns the chemical kinetics developed for the rate of reaction (R) and rate constant (k) as R = k [NaCl](0.7)[CaSO4](0.8). The overall order of the reaction is experimentally 1.5 with respect to concentration of sodium chloride and calcium sulphate. Phase transitions based on the behavior of the thermodynamic free energy as a function of thermodynamic variables are accompanied by the release of heat. The activation energy needs for the dissolution reaction of rock salt is -18.08 kJ/mol. The experimental result indicates the exothermic reaction, similar to the calculation by theoretical thermodynamics. Saturation indexes of brines as a function of anhydrite reveal the supersaturating condition while rock salt dissolution reaches the equilibrium condition.
