Remediation of Ni2+, Pb2+ and Cd2+ by nano zero-valent iron decorated biochar produced via asynchronous and synchronous routes of pyrolysis and carbothermal reduction

Abstract

Heavy metals in the environment pose significant ecological and human health concerns worldwide. Nano Zero-valent iron (nZVI) is a promising heavy metal removal agent due to its non-toxicity and low standard reduction potential. Avoiding agglomeration, passivation, and long-term stability requires a carrier. The porousness and heavy metal binding properties of biochar (BC) make it an effective carrier. This study presents a comparative evaluation of the remediation of Pb2+, Cd2+ and Ni2+ by two nZVI-biochar nanocomposites produced via asynchronous (BC-nZVI) and synchronous (BM-nZVI) routes of pyrolysis and carbothermal reduction. A comprehensive evaluation of the effects of pH, contact time, and isotherm pattern studies were carried out with BC serving as the control. The alkalinity of the medium was contributive in the enhanced remediation. The optimal contact times were 50 minutes and 90 minutes for Cd2+ and Ni2+ respectively. For Pb2+, all materials exhibited fast kinetics of adsorption. For Pb2+ and Ni2+, Langmuir model was best fitted while the Cd2+ sorption was best described by Redlich-Peterson isotherm model. BM-nZVI showed the highest Langmuir capacities of 36.403, 15.388 and 4.553 mg g-1 for Pb2+, Cd2+ and Ni2+ respectively. Decreased sorption of BC-nZVI might be due to pore blockage. The present work demonstrates the efficiency of BM-nZVI for heavy metal remediation