Practical and mechanistic aspects of the removal of cadmium from aqueous systems using peat

A sphagnum peat moss removed Cd from aqueous solutions very efficiently, and its effectiveness in taking up the metal was significantly enhanced by exposure to a 1 N NaOH solution. The capacity of the untreated peat for Cd reached 300 g/kg and that of the NaOH-activated peat was over 400 g/kg. Although saturation was rarely reached, the Cd uptake from concentrated solutions often exceeded 200 g/kg. In column experiments, 1 g of the NaOH-activated peat completely removed the metal from over 0.2 L of a 200-mg/L Cd solution (final Cd concentration < 0.1 mg/L), while 1 g of non-activated peat cleared Cd from less than 25% of that volume. The cation exchange capacity measured for the peat depended on the time of contact with the exchanging solution. After 72 h contact, the value for the NaOH-activated peat was 135 cmol_c/kg. In addition to uptake by exchange, a significant amount of Cd was sorbed by non-exchange mechanisms. FTIR spectroscopy revealed the importance of carboxyl groups in the uptake.