Adsorption of metals in oil sands process water by a biochar/iron oxide composite: Influence of the composite structure and surface functional groups

In this work, anaerobic sludge from a wastewater treatment plant was used to prepare a sludge-based biochar/iron oxide (B-FeOx) adsorbent. The B-FeOx adsorbent was successfully used to remove metals, including Cr, Cu, Se and Pb from oil sands process water (OSPW) for the first time. Compared with biochar or FeOx alone, a higher removal efficiency of Cr (80.79%±3.44%), Cu (98.21%±0.25%), Se (88.82%±0.31%) and Pb (90.96%±1.86%) was obtained using the B-FeOx composite. The high removal efficiency was attributed to the improved specific surface area and pore volume of the B-FeOx composite, which increased by about 5.9 and 5.7 times, respectively, when compared to biochar. In addition, functional groups in the composite, such as C-O, C = O, O–H, and some iron-bound functional groups, played an important role in the improvement of the removal efficiency of metals. Moreover, the adsorption process was best modelled by the pseudo-second order kinetic model and Langmuir model. Intraparticle diffusion modelling for adsorption of the four metals using B-FeOx composite resulted in two distinct regions: film and pore diffusion. This study provides the details of a low cost, effective, and environmentally friendly adsorbent for the removal of metals from real OSPW.