Biosorption has many advantages over conventional metal recovery processes such as chemical precipitation and electrowinning. One of these is the rapid rate at which the reaction occurs, resulting in the need for only short contact times for batch processing of aqueous metal-containing wastes. Factors such as metal concentration in Solution, Solution temperature and sorbent concentration all affect the rate at which the sorption reaction takes place. The mechanism of the sorption also influences the kinetics, with the first-order physical sorption mechanisms allowing rapid establishment of equilibrium conditions, while the second-order chemical mechanisms result ill slow kinetics with equilibrium establishment taking as long as 24-48 h to occur. The sorption of platinum by immobilized Saccharomyces cerevisiae biomass was observed to be a chemical sorption mechanism, with rapid initial sorption resulting in removal of approximately 70% of the metal from a 50 mg/l platinum solution in 5 min. The reaction was either endothermic or exothermic, depending on the temperature, and the rate was increased by an increase ill solution temperature up to 37 degrees C. Calculated activation energies were in the region recognized as indicating a chemical sorption mechanism. The results obtained thus indicate that sorption of platinum from aqueous waste solutions is a rapid, and thus cost effective, method for the recovery of platinum from waste streams. (c) 2007 Elsevier Ltd. All rights reserved.