(589a) Performance of Modified Thief Sorbents On Mercury Removal
In this study, the adsorption performance of elemental mercury onto the commercially produced Thief sorbent, and Thief sorbent modified with ferric chloride and sodium chloride was investigated. Thief Sorbents consist of partially combusted coal extracted from the furnace at a power plant. The results indicated that the modification of these sorbents enhanced considerably their capacity, decreased their surface area and changed the sorption mechanism towards mercury. For the highest surface area Thief sorbent as received, modification with ferric chloride made the surface area decrease from 326 m2/g to 202 m2/g, while with sodium chloride modification decreased it to 98m2/g. Ferric chloride impregnated Thief sorbents presented the highest sorption capacity while sodium chloride impregnated Thief sorbents exhibited the highest cost-effectiveness of all the sorbents tested due to the lower price of sodium chloride compared to ferric chloride. The sorption capacity increased from 21µg/g Hg for the highest capacity Thief sorbent as received, to 206 µg/g Hg after modification with ferric chloride; while the modification with sodium chloride increased its capacity 70.19 µg/g Hg. An analysis of the cost-effectiveness of the sorbents shows that the cost of removing mercury can be decreased from about $10,000 kg/Hg removed to $7,373 kg/Hg removed with sodium chloride modification. It was therefore shown, that this is a viable procedure to produce high capacity sorbents at a very attractive price. The sorption mechanism was studied through SEM scans and XPS spectra analysis. The results showed a change in the mechanism of impregnated sorbents. In this case a combination of physical and chemical adsorption was observed. Physical adsorption occurred for all sorbents as a first step of the mechanism, while chemical adsorption via mercury oxidation was the final step of the mechanism for impregnated sorbents.
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