Effect of Feedstocks and Production Methods on Activated Carbon Performance on the Sorption of Pb and Cd from an Industrial Effluent

This study features the production of activated carbon from hardwood, softwood and their hybrid for the adsorption of Pb and Cd from industrial effluent. The wood wastes (sawdust) were carbonized at 500 °C followed by activation in air atmosphere (physical activation) and H3PO4-impregnation prior to carbonization (chemical activation). The resulting activated carbons (AC) were characterized for surface structural and morphological properties. The activation method impacted the physiochemical properties of the ACs. For instance, the BET surface area was highest for hardwood derived AC obtained by physical activation, while it was the softwood AC for chemical activation pairs. FTIR analysis revealed that both chemically and physically ACs have the requisite functional groups (phenol, aromatics and hydroxyls) for sorption operations; however, H3PO4 creates more oxy-containing functional groups in the chemically ACs, which enhanced their adsorption performance. Hardwood was the feed material controlling the yield and attributes of both physically and chemically produced hybrid AC in the 1:1 mixed feed. All ACs were employed as adsorbents for the uptake of Pb and Cd at different adsorbent dosage levels (50-250 mg/l) and contact time (5-20 mins). The batch adsorption studies showed that Pb and Cd removal rate increased with increasing adsorbent dosages and contact time until equilibrium was reached at 15 mins. Only chemically ACs achieved 100% removal of Pb and Cd from the effluent at optimum dosage amount. The sorption performance of the adsorbents (based on feedstocks) for both metals uptake can be ranked as softwood (C) > hardwood (C) > hybrid (C) > hardwood (P) > softwood (P) > hybrid (P). C and P refer to the chemical and physical activation methods. The experimental data were found to fit into Langmuir adsorption model (R2 = 0.999) and pseudo second-order kinetic model (R2 = 0.999)