Multistage optimizations of slow pyrolysis synthesis of biochar from palm oil sludge for adsorption of lead

This research investigated the removal of lead (Pb2+) by a novel biochar derived from palm oil sludge (POS-char) by slow pyrolysis. Multistage optimizations with central composite design were carried out to firstly optimize pyrolysis parameters to produce the best POS-char for Pb2+ removal and secondly to optimize adsorption conditions for the highest removal of Pb2+. The optimum pyrolysis parameters were nitrogen flowrate of 30 mL min(-1), heating rate of 10 degrees C min(-1), temperature of 500 degrees C and time of 30 min. The optimum Pb2+ adsorption conditions were concentration of 200 mg L-1, time of 60 min, dosage of 0.3 g and pH of 3.02. The various functional groups within POS-char played a vital role in Pb2+ uptake. Regeneration was demonstrated to be feasible using hydrochloric acid. Adsorption equilibrium was best described by Freundlich model. At low concentration range, adsorption kinetic obeyed pseudo-first-order model, but at high concentration range, it followed pseudo-second-order model. Overall, the results highlighted that POS-char is an effective adsorbent for Pb2+ removal.