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.