Biochar As a Remediation Material for Agricultural Soils Elevated in Cadmium.

Cadmium (Cd) is a heavy metal that can be toxic for living beings at very low concentrations, and thus can pose food safety concerns. Some soils within California’s Salinas Valley,where leafy vegetables are commonly grown, are enriched in geocenic Cd. One solution to reduce plant uptake may be soil amendments of biochar, a carbon rich material produced by thermal converstion, that can adsorb a variety of pollutants, including Cd.However, not enough is known regarding the specific binding mechanisms involved, and how Cd retention will change over time, which are essential information for selecting and optimizingbiochars. This research aims to identify trends between feedstock and pyrolysis temperature and Cd retention, identify main surface characteristics, and evaluate the adsorption and desorption over time. We hypothesize: (i) there is an optimal relationship between surface area and functional groups to obtain maximum adsorption; (ii) the effect of time on adsorption can either be rising with the increasing content of functional groups derived by surface oxidation, and decreasing with reduction of surface area due to physical break down and steric effects which limits the diffusion of Cd into internal pores. A preliminary set of 9 raw biochars and 8 modified biochars (with post-treatments) were exanimated regarding their Cd adsorptive capacities and five were selected for furtherevaluation. Laboratory aging experiments will be evaluated with acid washing treatments. Next, a series of batch sorption experiments will compare retention rates between fresh and aged biochars. If results are promising, data from this study will be used to develop soil management strategies to ensure safe production of leafy green crops in soil with elevated Cd levels.