EFFECTS OF PH AND PHOSPHATE ON CADMIUM SORPTION BY A HYDROUS FERRIC-OXIDE

Signficant Cd sorption by the phosphate-free oxide sample occurred at pH levels below the oxide zero point of charge, indicating that the sorption was sufficiently energetic to overcome 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. This suggests that precipitation of these two compounds was not a likely mechanism controlling the concentrations of soluble Cd for these systems.