Comparative adsorption study of Pb(II), Fe(II), and Zn(II) using non-chemically activated rubber seed shell biochar and commercial activated carbon

Abstract

The widespread contamination of water sources by heavy metals such as Pb(II), Fe(II), and Zn(II) poses serious environmental and health risks. This study investigated the use of non-chemically activated biochar derived from rubber seed shells, an agricultural waste material, as a sustainable adsorbent for heavy metal removal. Biochars were produced by a two-step carbonisation process at temperatures of 850, 900, and 950 °C, and the physicochemical properties were systematically assessed. The sample carbonised at 850 °C (PRC850) exhibited the most favourable properties, including a high BET surface area (795 m²/g), mesoporous structure, and suitable surface functional groups, as confirmed by SEM, BET, XRD, and FTIR analyses. Initial screening was conducted for Pb(II), Fe(II), and Zn(II) adsorption, and PRC850 demonstrated superior performance, removing up to 98.64% of Pb(II), which was significantly higher than the 85.52% removal rate achieved by commercial-grade activated (CGA) carbon. The adsorption behaviour of Pb(II) was best described by the Langmuir isotherm model, and the pseudo-second-order kinetic model fitted the experimental data well, indicating chemisorption. These findings indicated that rubber seed shell biochar had the potential to serve as a cost-effective and ecologically friendly adsorbent, particularly for Pb(II) removal, while also performing effectively for Fe(II) and Zn(II). © 2025, Faculty of Engineering, Khon Kaen University. All rights reserved.