Nonlinear Kinetic and Equilibrium Adsorption Isotherm Study of Cadmium (II) Sorption by Dacryodes edulis Biomass

Abstract

The kinetics and equilibrium adsorption isotherm of cadmium (II) adsorption onto Dacryodes edulis (native peer seed) biomass was studied using a nonlinear approach, which is unpopular but proven in some literature to be more reliable and easier. In optimizing the process, about 98% removal of the cadmium ion was achieved within five minutes at pH 7 by contacting just 30 mg of the Dacryodes edulis seed biomass with the adsorbate solution of a concentration of 100 mg/L. Non-linear investigation of the kinetics and adsorption isotherms of the process was done using the R console statistical and computing software. The results indicated that the Elovich mechanism and the Freundlich adsorption isotherm most suitably described the kinetics and adsorption isotherm, respectively, of the process as provided by their least values of the sum of squared residuals (SSR). This outcome implied a chemical adsorption  (chemisorption) mechanism and a multi-layer coverage by the cadmium ions on heterogeneous active sites of the biomass surface with a Freundlich constant or capacity factor, Kf of 27.83 mg g^-1, heterogeneity factor, 1/n of 0.2614 and Elovich constants, α and β of 7.0 mg g⁻¹ s⁻¹ and 1.0 g mg^-1, respectively. These findings indicate that Dacryodes edulis seed biomass has a good potential for cadmium (II) adsorption.

Keywords: Dacryodes edulis, Elovich kinetic model, Freundlich isotherm, Langmuir isotherm, Nonlinear