Experimentelle Untersuchungen über den Einfluss einiger Zwei- und Dreiwertiger Metallkationen auf die Bildung und das Wachstum von CaCO3Experimental Study of the Influence of Some Divalent and Trivalent Metal Cations on Nucleation and Growth of CaCO3

Abstract

Abstract The influence of the metal cations Mg 2+ , Mn 2+ , Co 2+ , Zn 2+ , Cu 2+ , Fe 2+ , Fe 3+ and Al 3+ on the precipitation of calcium carbonate from an aqueous solution is reported. The dissolved CO 2 was stripped from a slightly acid solution of Ca(HCO 3 ) 2 by stirring. A critical supersaturation was achieved and calcite was precipitated. It was possible to track the resulting reduction in the concentration of Ca 2+ in relation to time by measuring of the electrolytic conductivity and the pH value. The influence of the metal in concentration between 0.01 and 1.00 mmol/L on precipitation of CaCO 3 was determinated. Because of the metal species present in the solution, two competing processes take place. Charged mononuclear and polynuclear metal hydroxo complexes are adsorbed onto the surfaces of the CaCO 3 nuclear crystal and, thus, any further growth of the crystal is strongly inhibited. At the same time the inhibition of the precipitation of calcite is also dependent on the concentration and the stability of this hydroxo complexes. As a result of nucleation catalysis very small quantities of neutral hydroxide particles cause the accelerated formation of CaCO 3 nuclear crystals, which counteracts the inhibition.