Single and simultaneous adsorption of heavy metals onto groundnut shell biochar produced under fast and slow pyrolysis

Abstract

Biochars produced from groundnut shells at the condition of slow and fast pyrolysis (GB350 and GB700) were used as adsorbents for removal of cadmium (Cd2+), mercury (Hg2+) and lead (Pb2+) ions from aqueous solution. Adsorption experiments were carried out at different solution pH, constant biochar dosage and particle size of 2 mm, variant metal ion concentrations, constant contact time and temperature to determine the adsorption efficiency. The removal efficiency of groundnut shell biochar was greater than 99.60% for Cd2+ under the three maximum contaminants limits. The GB700 was able to ascertain 100% removal efficiency for Cd2+ and Pb2+ in binary mixtures with concentrations of 0.04:0.10, 0.08:0.20 and 0.20:0.50 mg/l. The removal efficiency of GB350 was 100% for Pb2+ and Hg2+ except Cd2+ that showed 99.05, 99.46 and 99.69% at folds one, two and five of the ternary system, respectively. The maximum Langmuir capacity for mono-component system was 0.14 for Hg2+ and 0.18 mg/g for Pb2+, 0.09–0.56 mg/g for binary mixtures, 0.05–0.10 mg/g for ternary mixtures by GB350 and GB700, respectively. The results showed groundnut shell biochar can be used as a cost-effective and effective adsorbent for the removal of heavy metals from aqueous environment. Based on the results, further experiments should be carried out to examine the adsorption of the heavy metal contaminants at higher concentrations, a reduced biochar dosage and different contact time.