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In this study, the adsorption efficiency of cashew peduncle bagasse (CPB) is reported for the removal of single-(mono-) and multi-metal ions (Cd2+; Cu2+; Ni2+; Pb2+; and Zn2+) from synthetic and natural effluents using fixed-bed columns. The percentage of saturation realised in this study using a mono-elemental system was as follows: Pb2+ > Cd2+ > Zn2+ > Ni2+ > Cu2+. The metal ion recovery rate was determined by column elution; we demonstrated 100% metal ion recovery using 40 mL of HCl or HNO3 (0.1 mol L−1) as the eluent, with the exception of Pb2+. The adsorbent regeneration process decreased the removal efficiencies to 90% (Pb2+), 44% (Cu2+), 99% (Ni2+), 81% (Cd2+) and 74% (Zn2+) after the first cycle. The breakthrough curves and kinetic adsorption factors controlling the adsorption process were also studied. The Thomas model has produced the best fit with the experimental data.

The metal ions removal on cashew bagasse, a low-cost material, has been studied by batch adsorption. The parameters chemical treatment, particle size, biosorbent concentration, and initial pH were studied. In this study the maximum ions removal was obtained on the cashew bagasse treated with 0.1 mol/L NaOH/3 h, at optimum particle size (20-59 mesh), biosorbent concentration (50 g/L) and initial solution pH 5. The kinetic study indicated that the adsorption metal follows pseudo-second order model for a multielementary system and equilibrium time was achieved in 60 min for all metal ions.

Green coconut shells were treated with acid, base and hydrogen peroxide solutions for 3, 6, 12 and 24 h for removing toxic metals from synthetic wastewater. The removal of ions by the adsorbent treated with 0.1 mol L-1 NaOH/ 3h was 99.5% for Pb2+ and 97.9% for Cu2+. The removal of Cd2+, Ni2+, Zn2+, using adsorbent treated with 1.0 mol L-1 NaOH/3 h, was 98.5, 90.3 and 95.4%, respectively. Particle size, adsorbent concentration and adsorption kinetics were also studied. An adsorbent size of 60-99 mesh and a concentration of 30-40 g/L for 5 min exposure were satisfactory for maximum uptake of Pb2+, Ni2+, Cd2+, Zn2+ and Cu2+ and can be considered as promising parameters for treatment the aqueous effluents contaminated with toxic metals.