Physics
Scientific paper
Jan 1989
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1989gecoa..53....9z&link_type=abstract
Geochimica et Cosmochimica Acta, vol. 53, Issue 1, pp.9-19
Physics
3
Scientific paper
The Sorption and precipitation of Zn was investigated in equilibrium calcite (CaCO 3(s) ) suspensions at Zn concentrations that approached and exceeded the solubility of known zinc carbonate solids. Surface-enhanced precipitation was not observed and CaCO 3(s) did not nucleate Zn solids when the aqueous ion activity product (IAP) was below the equilibrium IAP of the least soluble, kinetically viable Zn phase. The CaCO 3(s) surface was not requisite for Zn precipitation. When CaCO 3(s) was present the precipitate formed a surface coating or discrete Zn particles bound to the surface. X-ray photoelectron spectroscopy, X-ray diffraction, and energy dispersive X-ray spectrometry of both Zn-treated CaCO 3(s) and isolated Zn particles implied, but did not confirm, that the precipitate was hydrozincite [ Zn 5 ( OH ) 6 ( CO 3 ) 2( S ) ] or its hydrated form. Zinc-treated calcite maintained Zn concentrations that agreed with the solubility of a synthetic hydrozincite measured by Schindler et al. (1969). Direct measurements showed that the equilibrium solubility of the precipitate exceeded that of a natural hydrozincite ( log IAP = a 5 Zn 2+ a 2 CO 2- 3 / a 6 H + = 6.41 ± 0.51) and was less than a natural smithsonite ( log IAP = a Zn 2+ a CO 2- 3 = -10.53 ± 0.10). It is suggested that a poorly ordered form of hydrozincite that regulates Zn activities at higher levels than well-crystallized natural varieties readily precipitates in CaCO 3( aq ) / CaCO 3( s ) systems. The environmental significance of this phase is unknown.
Dake L. S.
Harsh James B.
Kittrick James A.
Zachara John M.
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