Different cadmium adsorption behavior of juniper wood and bark sorbents

In acidic aqueous solutions, cadmium (Cd) adsorption on sorbents made from juniper bark was greater than on sorbents made from juniper wood. Increase in Cd adsorption with increase in solution pH in the range 2-5, for both types of sorbents, suggested that surface carboxylic groups (RCOO^-) might be involved in the adsorption of Cd cations. The difference in adsorption behavior of the two types of sorbents appears to be related to the concentration of carboxylic groups available for interaction with Cd cations on the sorbent surface. Diffuse reflectance infrared Fourier transform (DRIFT) spectra showed that the surface concentration carboxyl groups were higher for bark compared to wood. However, metal displacement experiments showed that the calcium (Ca) content of the sorbents might also be important in the Cd adsorption process. The amount of Ca displaced by Cd adsorption was greater for bark compared to wood.