Intra-particle migration of mercury in granular polysulfide-rubber-coated activated carbon (PSR-AC)

The depth profile of mercuric ion after the reaction with polysulfide-rubber-coated activated carbon (PSR-AC) was investigated using micro-X-ray fluorescence (micro-XRF) imaging techniques and mathematical modeling. The micro-XRF results revealed that mercury was concentrated at 0-100 microm from the exterior of the particle after 3 months of treatment with PSR-AC in 10 ppm HgCl(2) aqueous solution. The micro-X-ray absorption near edge spectroscopic (micro-XANES) analyses indicated HgS as a major mercury species, and suggested that the intra-particle mercury transport involved a chemical reaction with PSR polymer. An intra-particle mass transfer model was developed based on either a Langmuir sorption isotherm with liquid phase diffusion (Langmuir model) or a kinetic sorption with surface diffusion (kinetic sorption model). The Langmuir model predicted the general trend of mercury diffusion, although at a slower rate than observed from the micro-XRF map. A kinetic sorption model suggested faster mercury transport, which overestimated the movement of mercuric ions through an exchange reaction between the fast and slow reaction sites. Both micro-XRF and mathematical modeling results suggest mercury removal occurs not only at the outer surface of the PSR-AC particle but also at some interior regions due to a large PSR surface area within an AC particle.