Methylation of mercury (Hg) to produce bioavailable methylmercury occurs primarily as a result of bacterial sulfate reduction in anaerobic environments. We investigated a new method for treatment of Hg-contaminated sediments by addition of either pyrolusite (MnO2) or potassium birnessite (K endmember of (K, Na, Ca).5(Mn4+, Mn3+)2O4●1.5H2O). In reduced sediments, the Mn-oxide treatment is intended to buffer system redox at a potential higher than that of sulfate reduction and thus slow the rate of Hg methylation. . Batch tests with Hg-contaminated sediments and different Mn-oxides were conducted to compare amendment effectiveness and longevity. Manganese oxide amendments included granular pyrolusite (Axner Pottery Supply, 80% MnO2 and Nagpur Pyrolusite PVT. Ltd. 74.7% MnO2), and synthetic powdered birnessite. Amendment purity was confirmed by by powder X-ray diffraction (XRD) and surface area was determined by BET. Batch incubation experiments consisted of 160 g of wet sediment mixed with 250 mL of water and 50 g of the Mn amendment adjusted for Mn content; no Mn-oxide was added to a sediment control. Experiments were incubated for two weeks. Sediments before and after reaction, and unreacted Mn-oxide amendments, were characterized using bulk and microfocus X-ray absorption spectroscopy (XAS) to examine changes in Mn phases and oxidation state. Analysis of the control sediment showed that Mn in native sediment is Mn2+ as a mixture of Mn carbonate and sorbed or aqueous Mn2+. Reducing conditions in the sediment resulted in the near-complete reaction of the Nagpur MnO2 to manganese carbonate, but did not have any observable effect on the Axner sample. Similarly, XAS analysis showed no observable reduction of Mn in the birnessite-sediment experiment.

Manganese oxide amendments for in situ remediation of mercury contaminated sediments

251st National Meeting (2016)

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