Modelling and Predicting Cadmium Speciation in Soil Mixed with Biochar: From Microscopic Mechanisms to Macroscopic Effects

Summary

Biochar is a type of carbon-rich product of biomass pyrolysis under limited oxygen, is capable for pollutants (e.g., Cd, PFAS) immobilization in contaminated soils. Despite evidence of liming effects, adsorption, redox facilitation, and CdS precipitation, the underlying mechanisms remain poorly understood due to the chemical complexity of biochar-soil systems. This dissertation aims to develop and integrate a three-site NICA-Donnan model for biochar into a multi-surface modelling framework (MSM) to predict Cd partitioning under different conditions. A comprehensive dataset from newly produced and literature-sourced plant-based biochars informed model parameterization. The approach was validated through batch and column experiments with varying soil types and redox states. Results reveals that several mechanisms such as pH effects, CdS formation are the key mechanisms in Cd mobility. This work enables the MSM method deal with soil mixed with biochar, aids in designing tailored remediation strategies by selecting biochars with properties optimized for specific soil conditions.