Effect of Rape-Straw-Derived Biochar on the Adsorption Properties of Single and Complex Trace Elements

Abstract

Copyrolysis biochar derived from rape straw (RSBC) was prepared through oxygen-limited pyrolysis at 500 °C and utilized to investigate its adsorption capability for single and complex trace elements (Fe2+, Mn2+, Cu2+, and Zn2+) in contaminated solutions. The microstructures, functional groups, and adsorption behaviors of RSBC were determined through scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), and batch adsorption experiments, respectively. From these, the single/complex adsorption results showed that the adsorption capacity of RSBC for Fe2+, Mn2+, Cu2+, and Zn2+ was 32.21/23.78, 8.95/3.41, 28.12/7.19, and 13.77/4.92 mg/g, respectively. The Langmuir isotherm model fit better than that of Freundlich in the mixed adsorption system, while the pseudo-second-order kinetic model was the most suitable for single adsorption. Thermodynamic adsorption analysis revealed that the removal rate of the four ions by RSBC was 22.14%, 8.95%, 18.75%, and 13.77%, respectively. Moreover, the adsorption mechanism was primarily chemical adsorption, including ion exchange, precipitation, and complexation, because of the binding effects of aromatic structures and polar groups. Additionally, biochar, with its porous structure and high ash content also provided favorable conditions for adsorption of those ions. Through this simple procedure, this work provides a potential strategy to produce biochar with a high adsorption capacity to remediate trace elements in contaminated solutions.