Biosorption of cadmium ion by coconut copra meal, an agricultural waste product was investigated as a function of initial solution pH and initial cadmium concentration. Pseudo-second-order kinetic analyses were performed to determine the rate constant of biosorption, the equilibrium capacity, and initial biosorption rate. Cadmium biosorption by copra meal was found to be dependent on the initial solution pH and initial cadmium concentration. Ion exchange occurred in the initial biosorption period. In addition, mathematical relationships were drawn to relate the change in the solution hydrogen ion concentration with equilibrium biosorption capacity, initial cadmium concentration, and equilibrium biosorption capacity. (c) 2006 Elsevier B.V. All rights reserved.