High efficiency adsorption of Cd(II) by KHCO3-activated Fe/Mn co-modified peanut shell biochar: adsorption performance, mechanisms, and life cycle assessment

Abstract

Cadmium (Cd) is a ubiquitous environmental pollutant in aqueous solution worldwide, posing serious risk to human health and ecosystem stability. Adsorption using efficient adsorbents is considered the most promising method to remove Cd(II). To achieve efficient removal of Cd(II), a low-cost, environmental friendly KHCO₃-activated Fe/Mn co-modified peanut shell biochar (K-FM-BC) was synthesized by one-pot method, its Cd(II) adsorption performance and mechanisms and potential environmental impact are elucidated in detail via batch adsorption, multi-spectroscopic characterization, density functional theory calculation (DFT), and Life cycle assessment (LCA). The results showed that K-FM-BC was covered by FeO and MnO particles with uneven and rough surface, its adsorption of Cd(II) was fitted to the Langmuir and pseudo-second-order kinetic models, with the theoretical maximum adsorption capacity (657.89 mg/g) much higher than many previous studies. Fourier-transform infrared spectrometer, X-ray photoelectron spectroscopy, and Zeta potential analysis showed that Cd(II) adsorption mainly involve the mechanisms of complexation, co-precipitation, and electrostatic attraction. DFT analysis showed that oxygen-containing functional groups play a decisive role in Cd(II) adsorption by K-FM-BC. Additionally, Fe- and Mn- based active sites exhibit stronger binding capacity for Cd(II), with the adsorption energies of −64.77 and −69.18 kcal/mol, respectively. LCA analysis revealed that K-FM-BC production generates 6.20 kg CO₂ eq emissions, with KHCO₃ as the primary contributor of the environmental impact (84 %). Cost-benefit analysis revealed that K-FM-BC demonstrates excellent cost-effectiveness among various adsorbents (96.28 g Cd/$). These results indicate that K-FM-BC has great potential in remediating Cd(II)-contaminated wastewater.