Engineered Biochar with Anisotropic Layered Double Hydroxide Nanosheets to Simultaneously and Efficiently Capture Pb and CrO from Electroplating Wastewater

Cationic and anionic heavy metal contaminants generally co-exist in practical industrial effluent, and simultaneously removal of these species is a bottleneck for most of the bio-adsorbents because of their contrary charge. In this work, pinewood sawdust derived engineered biochar (BC) was fabricated with MgAl layered double hydroxide (MgAl-LDH) nanosheets, which could efficiently and simultaneously capture heavy metal cations and oxyanions from wastewater. The synergetic effect between loaded MgAl-LDH and BC substantially improves its adsorption performance towards both cationic and anionic contaminants, i.e., Pb and CrO. The adsorption capacity of MgAl-LDH/BC for Pb reached 591.2 mg/g, which is 263% higher than that of BC, and in the case of CrO, the adsorption capacity is 330.8 mg/g, 416% higher than that of BC. The elimination of Pb was mainly attributed to forming complexations with surface functional groups. While for oxyanions removal, CrO can be reduced to Cr by functional groups, and then generated Cr could replace Al via morphic substitution, consequently formed an MgCr-LDH structure. Further, in the continuous fixed-bed column study, 225 bed volume of simulating electroplating wastewater co-existed with Pb and CrO can be efficiently treated. Hence, this study sheds light on the engineered biochar design to efficiently and simultaneously capture heavy metal cations and oxyanions and its feasibility on real wastewater purification.