KINETIC-STUDIES OF CADMIUM AND FERRICYANIDE ADSORPTION ON GOETHITE

Batch and dynamic column methods were used to investigate the sorption rates of ferricyanide ion and cadmium on goethite under consant-pH conditions. Results indicated the rate of adsorption for ferricyanide to be limited by surface mass transfer. Analysis of column data showed mass transfer to be rate limiting during initial adsorption of cadmium and a secondary reaction to be rate limiting overall with a forward conditional rate constant of 3.02×10-3 L mol-1 s-1. Total reactive surface site density for cadmium agreed well with the value obtained from more dilute batch studies. In contrast, the data for ferricyanide showed a single-reaction approach to be sufficient; however, the batch-derived site density was substantially greater than that obtained from the column. These results are discussed in view of the surface-bonding character of these solutes, and implications for laboratory-generated partitioning data are examined.