Marine chemistry of cadmium: A comparison of theoretical and field observations

Abstract

Abstract Thermodynamic models showed that CdCO3(c) and Cd3(PO4)2(c) were the most stable Cd minerals in oxic and moderately oxic marine environments. A comparison between the published data on dissolved Cd in seawater and the thermodynamic observations, however, supported the formation of Cd phosphate. It was, therefore, proposed that formation/dissolution of Cd phosphate could control dissolved Cd in interstitial waters and seawaters. A mechanism for Cd phosphate formation is also proposed. Chloro‐complexes were the most abundant Cd species in standard seawater with CdCl2° (57 %) as the most important species, followed by CdCl+ (39 %) and CdCl3 − (11 %). Increase in salinity enhanced concentrations of high order Cd‐chloro complexes and vice versa. The concentration of ionic Cd2+ was found to be about 1 % of the total dissolved Cd. In anoxic environment (pe+pH < 4.5), Cd sulfide was the most stable mineral and Cd‐sulfide complexes were the most abundant chemical forms of Cd in seawater. Reports on the ads...