Comparative Study on the Passivation Effect of Potato Peel and Pig Manure-Based Biochar Prepared by Cyclic Catalytic Pyrolysis on Cd and Pb in Soil: An Experimental Study in a Ring Pipe

This study innovatively combines the cyclic catalytic pyrolysis system (CCPS) with a circular pipe device, using biochar from potato peels (PP) and pig manure (PM) to passivate Cd and Pb in the soil, and explores the influencing mechanisms via multiple methods. Results showed that in aqueous adsorption, biochar from the CCPS performed better, with the potato peel-based biochar produced via the cyclic catalytic pyrolysis system (PPB-2) achieving 100% removal of Cd2+ and Pb2+ within 100–270 min. In the soil remediation experiment using a ring pipe setup, pig manure-based biochar produced via the cyclic catalytic pyrolysis system (PMB-2) exhibited superior performance, reducing Cd concentration from 22.36 mg/kg to 11.21 mg/kg (49.87% removal) and Pb concentration from 718.28 mg/kg to 400.09 mg/kg (44.3% removal) after 40 days. This confirms that the PM-derived biochar prepared by CCPS is more suitable for the remediation of cadmium- and lead-contaminated soils, providing a reference for research on soil heavy metal passivation. Notably, the raw materials (PP and PM) are low-cost, locally abundant agricultural wastes, enabling resource recycling and lowering large-scale application costs. The ring pipe encapsulation further simplifies operational procedures for practical promotion while avoiding direct biochar–soil contact and mitigating secondary pollution risks.