Facile fabrication of magnetic bio-derived chars by co-mixing with Fe3O4 nanoparticles for effective Pb2+ adsorption: Properties and mechanism

Abstract This study enlightened a green and novel method to prepare magnetic bio-derived chars by physical co-mixing and the Pb2+ adsorption behavior of these chars was investigated. Three kinds of magnetic chars were fabricated by wheat stalk biochar, rice husk biochar, and commercial coconut husk activated carbon co-mixing with magnetic nano-iron tetroxide (Fe3O4), respectively. The microstructure, magnetism properties, adsorption performance, and mechanism of magnetic chars were systematically investigated with multiple approaches. The experimental results showed that optimized Fe3O4 magnetic chars with the mass ratio of 1:3 (chars to Fe3O4) exhibited excellent Pb2+ adsorption ability and magnetic separation characteristics. The adsorption kinetics was well described by the pseudo-second order model indicating that the Pb2+ adsorption rate and amount of magnetic chars were enhanced. The maximum Pb2+ adsorption capacities of magnetic wheat stalk biochar, wheat stalk biochar, magnetic rice husk biochar, rice husk biochar, magnetic coconut husk activated carbon, and coconut husk activated carbon were 179.85, 160.39, 95.44, 73.34, 43.38, and 39.15 mg/g, respectively. Furthermore, the mechanism analysis indicated that the Pb2+ adsorption on Fe3O4 magnetic bio-derived chars included the co-precipitation reaction, complexation reaction, conjugation adsorption, ion exchange, and Fe–O coordination. This study presents an attractive method for preparing magnetic bio-derived chars for enhancing heavy metal adsorption without chemical processes and mechanical energy.