Simultaneous immobilization of mercury and polychlorinated biphynyls from water or sediment using polysulfide-rubber-coated activated carbon
- This research explores a new method of utilizing activated carbon as a multifunctional amendment to treat mercury and polychlorinated biphenyls (PCBs). The multifunctional material, named polysulfide-rubber polymer-coated activated carbon (PSR-AC), was developed by coating a reactive polymer for mercury on activated carbon. The material achieves multiple functions by facilitating two different reaction sites, the PSR polymer surface and the AC surface, for mercury and hydrophobic compounds respectively. This dissertation focuses on several lines of work that includes the development of polysulfide-rubber as a sorbent, the investigation of a favorable interaction between the PSR polymer and mercuric ions, and the study of hydrophobic interactions between AC and hydrophobic compounds. The results are intended to serve as a basis from which to estimate the chemical stabilities of the immobilized contaminants on the PSR-AC surface. This study was started from the simplest clean water system with only mercuric chloride, and was evolved to include natural organic matter and sediment particles. PSR-AC was prepared by synthesizing the polymer and solvent casting of the dissolved PSR polymer with AC. This process resulted in a polymer coating formed by the gradual invasion of the AC by the polysulfide-rubber polymer. High sulfur loading on activated carbon enhanced mercury adsorption, contributing to a three orders of magnitude reduction in mercury concentration. X-ray photoelectron spectroscopy and Fourier transform infra-red spectroscopy results revealed Hg-S bond formation between PSR-AC and mercuric ions. [mu]-X-ray absorption near edge spectroscopic analyses of the immobilized mercury on the PSR-AC surface suggests the chemical bond with mercury on the surface is a combination of Hg-Cl and Hg-S interactions. [mu]-X-ray fluorescence images of the PSR-AC cross-section elucidated that mercuric ions migrate 0~100 [mu]m inward from the exterior of the particle during three months of treatment in HgCl2 aqueous solution. The presence of a surface-mediated chemical reaction was supported by the [mu]-XANES analysis, showing a large fraction of the total mercuric ions within the PSR-AC particle was in the HgS form. Two mathematical models, based on either a Langmuir sorption isotherm or a kinetic sorption approach, were devised to predict the physicochemical processes involved in the intra-particle migration of mercury in a PSR-AC particle. The results indicate that the transport pathways partly include a non-equilibrium state between PSR and mercuric ions that allows a faster transport rate than when a pure equilibrium state was utilized. The PCB sorption efficiencies of PSR-ACs compared to those of ACs were examined to understand the effect of the polymer-coating on the hydrophobicity of the PSR-AC particle. Comparable PCB removals were observed with sulfur loading levels of less than 8 wt.%. The relative significances of the PSR surface and a hydrophobic surface in sorbing dissolved organic matter-bound mercury (Hg-DOM) removal were also tested using PSR-coated polyethylene (PE). The results suggested higher reaction efficiencies of the PSR polymer per unit area. A favorable interaction between PSR and mercuric ions also improved the overall Hg-DOM removal efficiencies by PSR-AC. The AC and PSR-AC achieved effective mercury removal also from sediment porewater with and without the sediment particles in contact with the sorbents. One month of sediment contact with AC and PSR-AC in quiescent conditions decreased the sediment methylmercury concentrations by 76% and > 91%, respectively. These results prompt further research activities regarding the short- and long-term effects of PSR-AC sediment treatments on mercury bioavailability.
|Type of resource
|electronic; electronic resource; remote
|1 online resource.
|Kim, Eun Ah
|Stanford University, Civil & Environmental Engineering Department
|Luthy, Richard G
|Luthy, Richard G
|Leckie, Jim, 1939-
|Leckie, Jim, 1939-
|Statement of responsibility
|Eun Ah Kim.
|Submitted to the Department of Civil and Environmental Engineering.
|Thesis (Ph.D.)--Stanford University, 2012.
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