Cadmium Adsorption by Aerobic Lake Sediments

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Abstract
Factors that influence the adsorption of cadmium on aerobic lake sediments were investigated, including sediment type, pH, and soluble ligand composition. Conditional adsorption constants were experimentally determined for sediments samples in native lake water from Sturgeon Lake, Oregon. Correlation of adsorption constant values with sediment characteristics including mean grain size, iron and manganese content, volatile solids content, and cation exchange capacity indicated significant dependence only on mean grain size. Another approach, using specific geochemical phase adsorption constants from another study to assess that phase's contribution to adsorption, predicted that iron oxides controlled cadmium adsorption. A speciation‐distribution model for cadmium in the water column indicated that the dominant chemical forms were the free cadmium ion and cadmium adsorbed to suspended solids. As pH increased from 5 to 9, the adsorbed fraction increased and the free ionic fraction decreased markedly. Organic ligand complexes were predicted to be the dominant soluble cadmium complex in the neutral pH range, while the cadmium carbonate complex dominated at pH 9.