Mechanistic insights into the synergetic remediation and amendment effects of zeolite/biochar composite on heavy metal-polluted red soil

Red soil, the most critical soil resource in tropical/subtropical regions worldwide, faces tremendous threats, including nutrient deficiency, acidification, and heavy metal contamination. There is a great demand for multifunctional eco-materials capable of modifying this situation. Herein, we used widely distributed soil and biomass to develop a zeolite/biochar composite for synergistic red soil remediation and amendment. With the composite material, the Pb²⁺ and Cd²⁺ remediation efficiencies reached 92.8% and 92.9%, respectively, in stems under optimal conditions. Moreover, the acidity and nutrient deficiency conditions of red soil significantly improved. The atomic-scale interaction mechanism during the remediation and amendment process was elucidated with complementary characterization methods, which revealed that in the zeolite/biochar composite material, zeolite contributes to long-term heavy metal remediation effects. Simultaneously, biochar is responsible for soil quality amendment and short-term heavy metal remediation. Furthermore, for the first time, single-atom heavy metal ions were observed on biochar during the remediation process, indicating the broad distribution of single atoms in the natural environment.