Influence of Zn(II) on the crystallisation of calcium carbonate application to scaling mechanisms

In order to achieve a better understanding of scaling mechanisms, our team has been working on the modification to the crystallisation of calcium carb onate when other compounds are present in tap water. This paper presents a study on the influence of Zn2+ ions. The concentrations chosen were the sta ndard and 10-fold less than the standard for drinking water in France, i.e. 5 and 0.5 mg/L. Control synthetic water and doped water were submitted to an analytical method to test the crystallisation of calcium carbonate (in t he form of calcite) in the bulk of the solution. After 4 h of crystallisati on, the presence of zinc increased the number of crystals in the bulk of th e solution. Zinc may act as an accelerator of heterogeneous nucleation in t he bulk of the solution instead of on the surface, and may decrease the ris ks of scaling. The greater the concentration, the greater the effect. Compa red with other compounds, the effect of zinc is greater; this may be due to the fact that zinc precipitates mainly in the form of zinc carbonate, whic h is isomorphous to calcite.