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Nucleation And Crystal Growth Of Calcium Carbonate In The Presence Of Zn

Picture for Nucleation And Crystal Growth Of Calcium Carbonate In The Presence Of Zn
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Calcium carbonate precipitation in the presence of pollutants is a carrier of importance for their transport to the sediments and for their subsequent release depending on the local microenvironment conditions. Zinc is often present in industrial waters (heat exchangers and boilers) mainly for corrosion protection. Depending on the alkalinity and calcium concentration of waters used in water intensive processes, calcium carbonate fouling is common. Moreover, among other metals, is present in natural waters together with iron and copper, where the concentration of Zn(II) may reach at levels of several ppm.

Product Number: 51322-17700-SG
Author: Peter G. Koutsoukos, Panagiota D. Natsi, Zahid Amjad
Publication Date: 2022
Industries: Corrosion Monitoring and Control , Coatings and Linings , Coatings
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The effect of the presence of Zn is solutions supersaturated with respect to calcium carbonate was investigated at 250C, 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.

The effect of the presence of Zn is solutions supersaturated with respect to calcium carbonate was investigated at 250C, 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.

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