Heavy metals biosorption on cork biomass: effect of the pre-treatment

The effect of the pre-treatment of cork biomass on the biosorption of heavy metals (Cu, Zn and Ni) was studied. The pre-treatment by Fisher reaction confirmed the important role of carboxylic groups in the binding of the heavy metals. The pre-treatment of the cork biomass with a 0.5 M sodium chloride solution led to an increase of 30% of cork sorption capacity for copper, while the pre-treatment with a 0.5 M calcium chloride solution did not improve significantly the performance of the biomass. The sorption capacity of cork biomass did not change after being boiled in deionised water or washed with solutions 0.1 M NaCl and NaOH, while the heating/boiling in alkaline solutions increased the amount of copper adsorbed in the biomass. The use of oxidising agents (NaClO and NalO(3)) in the pre-treatment step allowed an increase of the sorption capacity of the biomass. Actually, an increase of 70-80% of the sorption capacity was obtained when the pre-treatment was carried out for 30 min with a solution containing 7% of active chlorine at room temperature. Finally, the porous carbon produced from cork by direct activation with steam at 700 and 800degreesC presented a sorption capacity four to six times higher than the original cork biomass, when contacting a 200 mg/dm(3) copper solution. (C) 2004 Elsevier B.V. All rights reserved.