Biosorption thermodynamics of cadmium on coconut copra meal as biosorbent

Coconut copra meal, a waste product of coconut oil production was investigated for its potential use as a biosorbent for cadmium ions from an aqueous solution. A comparison of linear least-squares method and a trial and error non-linear method of three widely used isotherms, Langmuir, Freundlich, and Redlich-Peterson, were examined. Langmuir isotherm parameters obtained from the four Langmuir linear equations by using linear method were not similar, but were the same when non-linear method was used. The best-fitting isotherms were Langmuir and Redlich-Peterson isotherms. Langmuir isotherm is a special case of Redlich-Peterson isotherm when constant g is unity. In addition, various thermodynamic parameters, such as ΔG°, ΔH°, and ΔS°, were calculated. The biosorption process is a spontaneous and exothermic process. © 2006 Elsevier B.V. All rights reserved.