Thermodynamic analysis of possibility of using calcium compounds for removal of heavy metal ions from aqueous solutions

Abstract

The aim of this investigation is the thermodynamic simulation of processes, occurring at interaction of calcium compounds (silicates etc.) with water solutions containing heavy metals, as well as the analysis of the obtained results by explanation of the effects observed in the binding and immobilization of heavy metal ions from water solutions. The results of the thermodynamic modelling allowed the authors to make a number of conclusions that are converged with the literature experimental data. In particular, the main components of the cement clinker during the contact with water allow reaching the high pH value of the water medium. This is sufficient to convert most heavy metal ions into insoluble compounds. The processes, occurring during the interaction of calcium compounds with water and dissolved heavy metals, in the case of equilibrium achieving, should lead to a significant decrease in the concentration of heavy metals in water. These processes should be accompanied by the increase in the concentration of calcium ions in the solution. The presence of carbon dioxide in excess in the system leads to the fact that the solution pH will correspond to a neutral or weakly acidic medium. However, even in this case, there will be a decrease in the concentration of heavy metal ions by several orders of magnitude.