Investigation on adsorption behaviors of heavy metal ions (Cd2+, Cr3+, Hg2+ and Pb2+) through low-cost/active manganese dioxide-modified magnetic biochar derived from palm kernel cake residue

In this study, the adsorption behaviors of heavy metal cations such as Cd2+, Cr3+, Pb2+ and Hg2+ were systematically investigated using active MnO2-modified magnetic biochar derived from palm kernel cake residue. The Fe3O4 synthesized via co-precipitation at an optimum ratio of FeCl3 to FeCl2 (2 to 1) was easily coated on surface of carbonized biochar powder (CP). The adsorption performance of magnetic biochar (CP-Fe) was efficiently improved by doping with KMnO4 (CP-Fe-Mn). The physicochemical properties of adsorbents were analyzed by VSM, XRD, BET, Boehm titration, FT-IR, pHpzc and SEM-EDS techniques. A saturation magnetization value of CP-Fe-Mn was 20.94 emu/g, indicating to the paramagnetic properties of obtained adsorbent. A facile recovery of CP-Fe-Mn from aqueous solution after finishing adsorption process was found. The adsorption behaviors of each heavy metal ion over CP-Fe-Mn were found to be a monolayer-physisorption process, confirming by Langmuir, Dubinin-Radushkevich, Temkin, Redlich-Peterson and Toth isotherms. The maximum adsorption capacities (qmax) of Cd2+, Cr3+, Pb2+ and Hg2+ were 18.60, 19.92, 49.64 and 13.69 mg/g, respectively. A rapid adsorption with two-step of intra-particle diffusion processes followed the pseudo-second order and the WeberMorris models, respectively. Furthermore, thermodynamic studies suggested that behavior adsorptions of heavy metals over CP-Fe-Mn were found to be spontaneous nature and endothermic process. It was expected that such a novel low-cost CP-Fe-Mn should be further applied for capable removal of several heavy metals in wastewater.