| dc.description.abstract | The objective of this study was to assess the feasibility of using carbon-based adsorbents derived from agricultural wastes including camphor tree leaves and corncobs to immobilize cadmium (Cd) in a contaminated rice paddy. Specifically, (1) three types of carbonaceous sorbents including activated carbons, biochars and hydrothermal chars (or hydrochars) were synthesized from these two feedstocks and characterized with the surface and morphological properties of each one; (2) followed by aqueous Cd-adsorption experiments of individual synthetic sorbent under various conditions in order to not only compare the adsorption capacity but also acquire the adsorption mechanisms; and (3) lastly by soil incubation tests to both validate the predicting power of the linear equilibrium distribution model acquired from aqueous isotherms and ensure the Cd-sequestering effect of sorbents in anaerobic paddy soil. Under a pH condition that was representative of the pore water pH detected in the paddy soil (i.e., pH 6.5), data of sorption kinetic and equilibrium experiments carried out at both high and low levels of Cd were found to be better explained by the pseudo-second-order model and the Langmuir isotherm, respectively. Of the leaf sorbents, activated carbon showed the highest Cd2+ sorption capacity in DI water (Qmax= 13.33 mg g-1), whereas biochar displayed the best effectiveness in porewater (Qmax =8.48 mg g-1); as for the corncob sorbents, activated carbon exhibited the highest capacity of Cd adsorption no matter in the DI or porewater matrix. When combined with the characterization measurements, surface area, pore volume, and oxygen-containing functional groups on the surface were the factors that seemed to play more significant roles in the adsorptive interaction between ionic Cd and the sorbent. Finally, although the prediction of the linear model was not completely validated by the soil incubation results, the immobilization trend observed from the incubations was fully consistent to the model. Together, findings of this work suggest that biochars and hydrochars could be relatively effective, low-cost, and eco-friendly sorbents for many environmental applications, particularly concerning in situ metal immobilization. | en_US |