Simultaneous adsorption of toxic metals in binary systems using peanut and sheanut shells biochars

Converting peanut and sheanut shells into biochar is a smart strategy for recycling agricultural waste. Biochar was produced from peanut and sheanut shells at temperatures of 350 ± 5 °C and 700 ± 5 °C. The adsorption capacities for lead (Pb(2+)), cadmium (Cd(2+)) and mercury (Hg(2+)) in the binary systems were evaluated. In the binary systems with concentrations of 5 : 5 mg/L, 10 : 10 mg/L, 25 : 25 mg/L and 50 : 50 mg/L the removal efficiencies of GB350, SB350, GS350, GB700, SB700 and GS700 were 100% for Pb(2+) and 88.70%–99.46% for Cd(2+), 98.20%–100% for Pb(2+) and 100% for Hg(2+), 79.30%–100% for Cd(2+) and 99.96%–100% for Hg(2+). The higher adsorption percentages of Pb(2+), Cd(2+) and Hg(2+) by the biochar in the binary systems indicated that the pH values of the solutions were good and suitable for adsorption. The biochar from peanut and sheanut shells showed excellent capacity to remove Pb, Cd and Hg in the binary systems. The Langmuir model (0.3351 ≤ R(2) ≤ 0.9901) was more suitable than the Freundlich model (0.0014 ≤ R(2) ≤ 0.9994) for the adsorption of toxic metal ions onto the biochar in the binary systems. The interactive effects of the binary mixtures in the aqueous solution of Pb(2+), Cd(2+), and Hg(2+) were found to be either antagonistic or synergistic. Peanut and sheanut shell biochar were rich in calcium, potassium, magnesium, and sodium, and phosphates affected the mechanisms of Pb and Cd adsorption. The high sulphur content might have influenced the mechanism of Hg adsorption in the aqueous solutions on peanut and sheanut shell biochar. These results suggest that peanut and sheanut shell biochar have enormous potential and are suitable for adsorption of Pb(2+), Cd(2+) and Hg(2+) in wastewater and polluted soil. Therefore, their effectiveness should be further tested in an actual water polluted environment.