Iron-modified biochar (FBC) can be used to immobilize metal(loid)s in contaminated soils and thereby reduce the transfer of toxic elements into food crops. However, there is limited knowledge of how different FBC preparation methods and resulting FBC surface properties (e.g., iron content and mineralogy; surface area) influence the effectiveness and longevity of FBCs as adsorbents for trace metal(loid) contaminants in soil. Here, we evaluate the effect of two FBCs (FBC1, the alkali iron solution soaking biochar and FBC2, the acid iron solution soaking biochar with ultrasonic treatment) on the solubility of arsenic (As) and cadmium (Cd), as well as micronutrients (e.g., zinc; copper; molybdenum) in microcosm experiments with soil contaminated with sewage sludge and an As- contaminated rice paddy soil. A ferrihydrite nanoparticle was also applied in the microcosm soils to compare the effect of FBCs and an iron oxyhydroxide amendment. Porewater was monitored for trace element (As, Cd, micronutrient) concentrations as well as dissolved inorganic carbon, sulfide, and As speciation to support geochemical modeling analysis of secondary mineral precipitation as an immobilization mechanism. A variety of characterization techniques including scanning electron microscopy-energy dispersive X-ray spectroscopy (SEM-EDS), X-ray diffraction (XRD), and Brunauer-Emmett-Teller (BET) surface area analysis were used to explain the performance of biochars. In the first flooded phase, ferrihydrite with the same Fe mass as the FBC2 amendment exhibits the best performance for immobilization of both As and Cd in sewage sludge contaminated soil. FBC2 is more effective than FBC1 in As immobilization, while the reverse was found for Cd. After drying the soils, a second flooded phase will be used to assess the capacity for in situ regeneration of the FBCs and their longevity compared to ferrihydrite. Equilibrium geochemical modeling and biochar characterization will be applied to explain the different performance of FBCs and provide guidance for optimal FBC preparation methods.

Effect of iron-modified biochars on in situ immobilization of As and Cd in flooded soils

ACS Spring Meeting 2021

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.