Interaction between biochar of different particle sizes and clay minerals in changing biochar physicochemical properties and cadmium sorption capacity

Biochar exhibits substantial potential for interaction with clay minerals upon its introduction into the environment. However, the precise impact of this interaction on the surface properties of biochar and its capacity for metal sorption, particularly in relation to varying biochar particle sizes, remains unclear. Therefore, this study focused on biochar particles derived from pig bone, varying in size, and subjected them to treatment with two common clay minerals (kaolinite and montmorillonite). The objective was to scrutinize their influence on the physicochemical properties of biochar and its binding affinity for Cadmium (Cd). The results revealed that post-interaction with kaolinite and montmorillonite, the Cd sorption capacity of large biochar particles (250–425 μm) saw respective increments of 11.6% and 26.6%, whereas the Cd removal capacity of small biochar particles (25–75 μm) experienced reductions of 8.8% and 18.5%, respectively. Additionally, the surface area of the large biochar particles increased by 19.5% and 32.9%, while that of the small biochar particles decreased by 31.3% and 17.7% after interactions with kaolinite and montmorillonite, respectively. Through the analysis of 2D-FTIR-COS, it was determined that regardless of particle size, COO- on the initial pig bone biochar exhibited the highest sensitivity for Cd adsorption. However, after interaction with kaolinite and montmorillonite, Al–O and Si–O–Al groups were identified as the most responsive for the small biochar particles, while -OH and O–P–O groups exhibited heightened sensitivity for the large biochar particles in adsorbing Cd. The results of this study offer valuable insights into how typical clay minerals can impact the surface properties and metal sorption capacity of biochar of varying particle sizes, which is advantageous for optimizing the production and environmental applications of biochar.