A COMPARATIVE STUDY ON THE DISSOLUTION AND SOLUBILITY OF CALCITE RHODOCHROSITE SMITHSONITE AND OTAVITE AT 25 degrees C

The solubility products for calcite-group minerals are very important to interpretate their behavior in natural water, which have a great influence on the migration and transformation of heavy metals in the environment. But discrepant solubility values for these minerals were reported previously. In the present work, calcite, rhodochrosite, smithsonite and otavite were prepared, and their dissolution processes lasting nine months were then experimentally investigated. After the 5040h dissolution in the airsaturated water, the aqueous concentrations of Ca, Mn, Zn and Cd attained the steady state of 0.511 similar to 0.562 mmol/L for calcite, 0.211 - 0.234 mmol/L for rhodochrosite, 0.277 similar to 0.314 mmol/L for smithsonite and 0.00346 similar to 0.00648 mmol/L for otavite, respectively. For the dissolution in the N-2 -degassed water, the air-saturated water and the CO2-saturated water at 25 degrees C, the solubility product (log K-sp) and the Gibbs free energies of formation (Delta G(f)degrees) were estimated to be -8.38 +/- 0.07 similar to -8.43 +/- 0.04 and -1129.27 +/- 0.40 similar to -1129.57 +/- 0.23 kJ/mol for calcite (CaCO3), -10.18 +/- 0.04 similar to -10.29 +/- 0.12 and -814.00 +/- 0.22 similar to -814.65 +/- 0.66 kJ/mol for rhodochrosite (MnCO3), -10.70 +/- 0.04 similar to -10.50 +/- 0.09 and -735.97 +/- 0.25 similar to -734.84 +/- 0.54 kJ/mol for smithsonite (ZnCO3), -11.55 +/- 0.08 similar to -11.71 +/- 0.11 and -671.40 +/- 0.46 similar to -672.30 +/- 0.64 kJ/mol for otavite (CdCO3), respectively.