Influences of SO4^2- on the solubility of calcite and dolomite

A computer analogue is given to simulate the influences of SO4^2- ion on calcite and dolomite solubility in Na2SO4,CaSO4 and MgSO4 solutions with different Pco2 at 25℃ by means of the software for hydrogeochemical modeling -PHREEQC. The results show that the existence of SO4^2- ion in solution raises calcite and dolomite solubility considerably. For example, the solubility of the calcite and dolomite in Na2SO4 solution with 1 200mmol/L in concentration and Pco2= 0 at 25 ℃ are 9. 544 and 9. 897 times greater respectively than those in pure water. The chemical mechanism for this is as follows： when common ions do not exist in solution, salt effect and ion pairs raise the solubility significantly. As common ions exist in solution, incongruent dissolution will take place, thus helps dolomitization or dedolomitization to occur. It is also concluded that the salt effect in all the cases should not be neglected including even in the cases with common ion especially when SO4^2- concentration is high.