A feasibility study on production, characterisation and application of empty fruit bunch oil palm biochar for Mn²⁺ removal from aqueous solution

Empty fruit bunch oil palm (EFBOP) is one of the byproducts after oil palm fruitlet is removed in oil palm processing and is considered as waste. In this study, EFBOP was converted to biochar (BC-EFBOP) at 350–700 °C, with an overarching aim of determining the feasibility of adsorptive removal of manganese (a second dominant element in acid mine drainage) from water. Results showed that with increasing temperature, the BC-EFBOP yield decreased from 44.34% to 26.74%, along with the H/C (0.89%–0.29%) and O/C ratios (0.38%–0.23%), and the carbon content increased (62.7%–73.93%). As evidenced by Fourier Transform InfraRed spectroscopy (FTIR) and X-ray Photoelectron Spectroscopy (XPS), abundant oxygen-containing surface functional groups such as hydroxyl (-OH), carboxyl (-COOH), and ether (C–O–C) were retained, and aromatic C[dbnd]C groups were largely generated in the biochar. Pyrolysed biochar at 350 °C (BC350), with the least surface area (0.5 m² g⁻¹), exhibited the highest Mn²⁺ adsorption capacity (8.2 mg g⁻¹), whereas for BC700, with the largest surface area (2.19 m² g⁻¹), had the lowest capacity for Mn²⁺ (1.2 mg g⁻¹). Regardless of the temperature, solution pH of 5 was found to be optimal for Mn²⁺ removal from water. The Langmuir isotherm model best described the equilibrium adsorption data with a maximum adsorption capacity of 1.2–8.2 mg g⁻¹ for initial concentrations of 5–250 mg L⁻¹, whereas the adsorption kinetics followed the pseudo-second-order model. There was nearly four-fold increase in Mn²⁺ ions removal with increased biochar dosage (0.05–0.5 g), at initial Mn²⁺ concentration of 100 mg L⁻¹. The study showed that a low-cost, environmentally friendly BC-EFBOP with optimal surface chemistry could potentially remediate Mn²⁺ ions from aqueous media. However, a proper cost-benefit and techno-economic analysis is needed prior to potential pilot scale studies.