Application of activated biomass waste as an adsorbent for the removal of lead (II) ion from wastewater

Abstract

This work focuses on the application of activated biomass as an alternative to conventional adsorbents for the removal of Pb2+ from wastewater. The biomass was carbonized at 800 °C before chemical activation. Scanning Electron Microscope (SEM) and UV/VIS Spectrophotometer were used in characterizing the adsorbents. Batch adsorption studies were carried out to determine the effect of process conditions on the percentage removal. The kinetic studies were carried out using Pseudo-first order, Pseudo-second order, Elovich and Weber morris kinetic models while the thermodynamics studies were carried out using Gibbs free energy equation. SEM characterization revealed that micro porous space on the surface of the adsorbents (biomass wastes) increased significantly after activation. The composites maintained high surface area after chemical activation. pH of point zero charge revealed negative charge predominance on the surface of the adsorbents and adsorption was found to be very fast due to strong electrostatic force between Pb2+ and ion diffusion on the biomass surface. Cassava peel demonstrated highest potential for lead (II) ion removal from solution with 96.83% removal after 80 min with 50 mg/l lead concentration and adsorbent/liquid ratio of 0.3 g/30 ml at 60 °C and pH of 7.6. The highest adsorption capacities recorded with cassava peels, groundnut shell and yam peel at initial concentration of 50 mg/g were 50. 1 mg g, 46.6 mg/g and 38.5 mg/g ΔH, ΔS and R2 values for the adsorption with cassava peels are: 12762 J/mol, 67.2 J/kmol.K and 0.945; for groundnut shell adsorbent, the ΔH, ΔS and R2 values are; 36756 J/mol, 130 J/mol.K and 0.997; while for yam peels adsorbent, the ΔH, ΔS and R2 values are 12163 J/mol, 46 J/mol.K and 0.9278. Thus, the sorption process was feasible, spontaneous and endothermic. Adsorption of Pb2+was rapid and showed high kinetic performance. The experimental data were well fitted with pseudo second order kinetic model. However, the present approach has the advantage of simplicity, less time consuming and most importantly, low cost.