Enhanced cadmium sequestration from animal waste using a combined modified corn straw biochar: Unraveling the mechanisms and performance in hazardous metal removal

Abstract

Cadmium (Cd) is a toxic metallic element, and Cd residues in livestock and poultry manure pose a significant risk to agri-environmental sustainability, food safety and human health as it is returned to the field. This study focuses on the remediation of Cd in livestock manure through the development of a novel modified corn straw biochar (MCSB) using magnesium ions (Mg²⁺), sodium sulfamate (SS), and nano zero-valent iron (nZVI).Comprehensive characterization by scanning electron microscopy (SEM), Fourier transform infrared spectrometry (FTIR), Brunauer-Emmett-Teller (BET), and X-ray diffraction (XRD) reveals that MCSB exhibits enhanced hydrophilicity, with a 260 % increase in specific surface area compared to the unmodified biochar. It contains rich oxygen-containing functional groups and has a rough surface with numerous irregular particles and crystalline substances, providing abundant active sites for Cd adsorption. Adsorption experiments showed that the adsorption process of Cd by MCSB was spontaneous monolayer adsorption. Composting experiments indicate that MCSB effectively promotes the transformation of Cd from bioavailable forms to potentially available and residual states, with conversion efficiencies ranging from 36.98 % to 41.61 %. The passivation mechanism mainly involves electrostatic adsorption and reactions of functional groups. Oxygen-containing groups reduce the bioavailability of Cd, the increased pH enhances the negative charge of MCSB for Cd attraction, and water-soluble Cd is adsorbed and precipitated through interactions with surface functional groups.