The Chemistry of Lead and Cadmium in Soil: Solid Phase Formation
1975
Santillan-Medrano, Javier | Jurinak, J. J.
Equilibrium batch studies were conducted to obtain solubility data of Pb and Cd in soils. The data were plotted on equilibrium solubility diagrams using pH as the master variable. In the construction of the diagram the hydroxide, carbonate, and phosphate compounds of Pb and Cd were given particular attention. Both Pb and Cd solubility decreased in the soils as pH increased. The lowest values were obtained in the calcareous soil. Under a given set of conditions, however, Cd activity in solution was always notably greater than that of Pb. In noncalcareous soils the solubility of Pb appeared to be regulated by Pb(OH)₂, Pb₃(PO₄)₂, Pb₄O(PO₄)₂, Pb₅(PO₄)₃OH, depending on the pH. In calcareous soils, PbCO₃ also assumed importance. At higher Cd concentrations the precipitation of Cd₃(PO₄)₂ and/or CdCO₃ regulated cadmium solubility. At low Cd concentrations the equilibrium solution was undersaturated with regards to both Cd₃(PO₄)₂ and CdCO₃.
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