Review of the Role of Aqueous Chemistry in Mercury Removal by Acid Gas Scrubbers on Incinerator Systems

Incinerators that process mercury-containing feedstocks need to remove mercury from the flue gas with sufficient efficiency to meet regulations for mercury emissions from the stack. Equipment designed to remove other pollutants, such as acid gases and particulate matter, can remove mercury as well, under certain conditions. Acid gas scrubbers, designed to remove compounds such as HCl and SO₂, can remove mercury, when the latter is found in the flue gas in an oxidized form. There is a growing body of evidence that mercury, once absorbed into the scrubbing solution, can be reduced back to the nonsoluble elemental form, resulting in little net capture of mercury. Dissolved sulfur compounds in the scrubbing solution play an important role in the reduction of absorbed mercury. In this paper, the mechanisms for mercury capture and release in scrubbing solutions are presented. Conditions that promote or inhibit retention of mercury in scrubbers are discussed, as well as the use of additives to improve mercury retention in scrubbers.