Solubility constant and surface energy of copper(II) hydroxocarbonate in water

The equilibrium between crystalline copper(II) hydroxocarbonate (malachite) and itsaqueous solution was studied using the conductometric method. It has been found that one-day exposure is enough to establish equilibrium between the liquid and solid phases of the solution. In the following days, the influence of side effects (interaction with carbon dioxide in the air) causes an increase in the electrical conductivity of the solution. In an aqueous solution, the equilibrium concentration of copper(II) hydroxocarbonateand its solubility constant (solubility product) depend on the size and shape of the particles of the studied crystalline malachite samples. The introduction of an additional operation of centrifugation of the filler liquid leads to an increase in the electrical conductivity of the solution by reducing the size of the ions; therefore, this step should not be included in the sample preparation process. The obtained solubility constants are in good agreement with the available experimental data of other authors. The surface energy of the malachite-aqueous solution interface was estimated. Thus, the optimal conditions for determining the solubility product of a poorly soluble salt by the conductometric method are its dissolution in water in the form of small crystals followed by maintaining the solution for 24 hours to establish equilibrium between the liquid and solid phases and then measuring the electrical conductivity of the supernatant. The obtained results can be used to improve the technologies of copper ion precipitation from spent process solutions.