The effect of the presence of Zn is solutions supersaturated with respect to calcium carbonate was investigated at 25°C, pH 8.50. The stability domain of the calcium carbonate solutions was measured in the supersaturation ratio (SRcalcite) values between 20.89-32.36. Below the least SRcalcite value the solutions were stable. Above it, precipitation was spontaneous past induction time, inversely proportional to SRcalcite according to the classical nucleation theory (CNT). In the presence of 1.3 ppm of Zn in the supersaturated solutions, the stability domain was shifted to higher SRcalcite values (47.86<SRcalcite<112.2). The presence of Zn stabilized all three calcium carbonate polymorphs. In the absence of Zn only vaterite and calcite were identified in the precipitated. In all cases no Zn oxides were formed. The rate of spontaneous precipitation of calcium carbonate in the presence of Zn, was reduced by as much as 98% at the least SRcalcite values tested. Adsorption of Zn at the active sites of the supercritical nuclei of vaterite is responsible for the reduction of the rates of CaCO3 precipitation and for the delay of conversion of unstable polymorphs. Finally, induction times in the presence of Zn were significantly longer for the same SRcalcite values without Zn, suggesting that Zn is a nucleation inhibitor as well.

Subject
Water, Precipitation (solids), Calcium carbonate, Vaterite, Solids, Nucleation, Sodium chloride, Calcite, Supersaturation, Constants, Sodium chloride solution, Crystal growth, Zinc
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2022
Association for Materials Protection and Performance (AMPP)
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