Transport and Retention of Cadmium in Biochar-Amended Sand Porous Media

Abstract

HighlightsBatch experiment indicated that sorption of Cd on biochar was highly pH-dependant.The main mechanism of Cd-biochar sorption were surface precipitation and ion exchange.Biochar affected the transportation of the attached Cd.At the same ionic strength, the transportation is faster in the presence of Ca2+ than Na+.Abstract. Cadmium (Cd) is toxic to plants and animals, leaching of Cd through soil profiles can affect its accumulation and pollute the ground-water. In this study, we performed batch and column experiments to study the effect of biochar on the retention and transport of Cd in saturated porous media under different solution chemistry. Specific factors were considered including pH, ionic strength, and biochar dosages. The results of batch experiment indicated that sorption of Cd on biochar was highly pH-dependant, but ionic strength had negligible effect on the adsorption of Cd to biochar. The mechanism of the adsorption process of biochar for Cd mainly involves surface precipitation and ion exchange. In the column experiment, the increase in pH and biochar dosages made the Cd more stable, whereas the increase in ionic strength improved the migration of Cd. The increased retention time of Cd was related to the greater retarded coefficient value (R) based on two-site kinetic retention model. The decrease of partitioning coefficient (ß) and fraction of instantaneous sorption sites (f) were in favor of the continuous and dynamic adsorption under column conditions. This study will provide a theoretical and scientific basis for the rational assessment of cadmium-related risks in biochar-modified environments. Keywords: Adsorption, Biochar, Cadmium, Porous media, Transport.