Predicting cadmium speciation in biochar-amended soils

Background

Soil contamination with cadmium (Cd) is a widespread problem throughout the world. Since the transfer of Cd from soil into food crops like rice can be an important pathway for human exposure to cadmium, human health risks can be a major concern in areas with soils exhibiting high levels of Cd. The solubility of Cd in paddy soils is important with respect to its bioavailability for uptake by rice plants. Amending contaminated paddy soils with biochar is a promising approach to bind Cd when the capacity of the soil to retain Cd is limited. Consequently, biochar amendment will reduce Cd bioavailability and uptake by rice plants. In order to predict the effectiveness and dosing of biochar to Cd contaminated paddy soils, multi-surface modelling can be used, which includes the NICA-Donnan model. For NICA-Donnan model application, Cd binding parameters are needed for biochar. In this project, these parameters will be derived and tested in soils contaminated with Cd. This project will help to predict the effectiveness of biochar application and to develop guidelines for biochar application to Cd contaminated soils.

Description

In this PhD research project, I model the cadmium (Cd) speciation in soils amended with biochar to quantify the impact of biochars on cadmium bioavailability in soil. For this purpose, a multi-surface modelling approach is used, which includes the NICA-Donnan model. To be able to use the NICA-Donnan for predicting Cd binding to biochar, I will first derive the NICA-Donnan model parameters for describing proton and Cd binding to biochar in pure systems using acid-base titration and batch experiments. Next, these binding parameters will be incorporated into a multi-surface modelling approach to predict Cd solubility in biochar-amended soil. Finally, the multi-surface model will be applied to a pot experiment in which the effects of biochar on Cd uptake by rice plants will be quantified.

Results

A set of recommended generic proton binding parameters has been derived for a novel three-site NICA-Donnan model using 20 biochars produced from plant-based materials at different temperatures and 16 plant-based biochars taken from literature. For a set of selected biochars, NICA-Donnan binding parameters have been derived for Cd and Ca. These NICA-Donnan binding parameters will be tested in a multi-surface modelling approach for predicting Cd solubility in biochar-amended soil. When successful, the same modelling approach will be tested in a pot experiment setting where Cd uptake by rice plants will be measured.