Equilibrium and kinetic aspects of cobalt biosorption onto a new biosorbent, PFB1, were studied. The biosorbent, PFB1, had a specific surface area of 256.8m(2)g(-1) and showed high equilibrium capacities for cobalt uptake, the highest being 190 mg g(-1) in the range of concentrations employed. The equilibrium uptake increased and then decreased with initial pH with the highest uptake at pH 7. The equilibrium uptake also decreased with increasing temperature in the range 30-45 degrees C. The kinetics of cobalt uptake were analysed using mathematical models and the external mass transfer coefficient for cobalt biosorption on PFB1 was 0.075 m s(-1). EDAX and EPR studies indicated involvement of an ion-exchange mechanism and free-radical interaction in the biosorption process. Desorption/readsorption studies for three adsorption-desorption cycles were carried out with acidic, basic and salt desorbents and the highest desorption efficiencies of 92.5% and 70.5% at the end of the first and third cycles, respectively, were obtained with 0.1 N HCl as the desorbent.