Biosorption of Cr (III) from aqueous solution by the leaf biomass of Calotropis procera –‘bom bom’

摘要

The biosorption of Cr (III) onto the leaf biomass of Calotropis procera popularly known as ‘bom bom’ in western Nigeria, over a wide range of reaction conditions were studied. The batch experiments showed that the biosorption of Cr (III) onto Calotropis procera leaf biomass is a rapid process reaching equilibrium within 10 minutes at an optimum pH value of 5. Other reaction conditions such as biomass dosage, initial metal ion concentration and temperature were also found to influence the biosorption process. Both Langmuir and Freundlich isotherms were employed to describe the biosorption process and both proved to be applicable. However, Langmuir gave a better fit with an R-Squared value of 0.967 (closer to unity than that of freundlich), Langmuir constant, KL of 0.0188 and monolayer adsorption capacity, qm of 32.26 whereas the R-squared value for the freundlich plot was 0.948 with adsorption capacity Kf and adsorption intensity, n of 1.156 and 1.146 respectively. The biosorption process followed the pseudo-second order kinetic model evident by an R-squared value of 0.999 and the pseudo second order rate constant, K2 of 0.3668 gmg-1min-1 . Thermodynamic studies revealed negative value of change in free energy, ΔG° (-4.046KJmol-1) as an indicator of feasibility and spontaneity of the Cr (III) biosorption process. A positive value of enthalpy, ΔH° (26.099 KJmol-1) was obtained which indicated the endothermic nature of the biosorption process. FT-IR studies of the biosorbent before and after the biosorption process indicated that carboxylate, amino and nitro functional groups were involved in the sorption of Cr (III) onto Calotropis procera leaf biomass. These findings indicate that the leaf of biomass of Calotropis procera could be employed in the removal of Cr (III) from aqueous solutions and industrial effluents.