Accumulators for the Capture of Heavy Metals in Thermal Conversion Systems

A clay ceramic with organic additives (biomass and biochar) was investigated for the development of highly porous accumulators to capture heavy metals in thermal conversion systems. The structure was characterized using X-ray pair distribution function analysis, differential scanning calorimetry, and scanning electron microscopy. It was found that the organic additives transformed into porosity during firing. The morphology of the pores also corresponded to the morphology of the organic additives. Hence, the clay ceramic with a 15-wt% addition of biochar had a porosity of 46 vol% with 20-μm interconnected pores after firing. The resulting accumulator was found to capture cadmium (a model for heavy metals with high volatility) via condensation of the cadmium vapor as 2-μm beads in the pores. The cadmium capture efficiency reached up to 57% using a 15-wt% addition of biochar. Furthermore, cadmium was captured at higher temperatures than the condensation temperature in the atmosphere. This means that heavy metals may be captured before they condense in fly ash to promote the recycling of this material.