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This article in SSSAJ

  1. Vol. 48 No. 5, p. 1040-1044
    Received: Apr 25, 1984
    Accepted: Apr 27, 1984

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Effects of pH and Phosphate on Cadmium Sorption by a Hydrous Ferric Oxide1

  1. S. Kuo and
  2. B. L. McNeal2



Sorption of cadmium by phosphate-free and phosphate-enriched hydrous iron oxides was investigated in 0.1M NaNO3 solution. Significant Cd sorption by the phosphate-free oxide sample occurred at pH levels below the oxide zero point of charge (pHZPC), indicating that the sorption was sufficiently energetic to over come some electrostatic repulsion. Phosphate enrichment of the oxide enhanced its capability to retain Cd, and lowered the average pH of the sorption edge. The Langmuir sorption constant for Cd was increased by such enrichment. Such results could be attributed to reduction of the pHZPC and surface potential with phosphate enrichment, and were described satisfactorily by simplified electrostatic theory. Calculated activities of soluble Cd in the pH range of 4 to 7 were well below those calculated from the solubilities of Cd(OH)2 or Cd3(PO4)2. This suggests that precipitation of these two compounds was not a likely mechanism controlling the concentrations of soluble Cd for these systems.

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