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Abstract
This study investigated the mercury uptake capacity of synthetic mackinawite regarding its surface modification with L-cysteine. Mackinawite (FeS) is an excellent material for mercury uptake from anoxic-contaminated sediments. However, one limitation to its use is the low oxidation stability; it is easily transformed when applied to natural sediments. The modification of mackinawite with L-cysteine improves its oxidation stability, making it a promising material to be used in sediment remediation by in-situ capping. The results showed that L-cysteine does not affect the mercury-uptake capacity of mackinawite (around 490 mg/g for modified and unmodified mackinawite). The Hg (II) uptake decreased as the solution pH changed from acid to alkaline range, especially in solutions with low Hg (II) concentrations. Sorption curves for Hg (II) on modified mackinawite, as a function of initial concentration of Hg (II) and mackinawite, showed the same pattern as that on unmodified mackinawite, indicating no significant difference in the mercury-sorption mechanism. The solids before and after Hg (II) uptake were analyzed by X-ray powder diffraction (XRPD) by noting the composition of both modified and unmodified mackinawite, and the results were in agreement with the sorption experiments.
Acknowledgments
We thank the award of a Marathon Petroleum Post Doctoral Fellowship to MC from the LSU College of Engineering. This work was also supported by the U.S. Department of Interior (USGS) through the Louisiana Water Resources Research Institute (Grant No: 06HQGR0088). The authors are grateful to Ministry of Education of Brazil, PNPD/CAPES/CNPq Project 0267/08-2.