UMD Theses and Dissertations
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New submissions to the thesis/dissertation collections are added automatically as they are received from the Graduate School. Currently, the Graduate School deposits all theses and dissertations from a given semester after the official graduation date. This means that there may be up to a 4 month delay in the appearance of a given thesis/dissertation in DRUM.
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Item Characterization of Trace Metal Leaching from Maryland Coal Fly Ashes(2011) Ozkok, Enes; Aydilek, Ahmet H; Davis, Allen P; Civil Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Three coal fly ashes with different acid-base characteristics and their mixtures with an embankment soil were analyzed for arsenic, copper, and chromium leaching as function of pH using batch-type water leach tests (pH 4-10). Leach tests results showed that significant Cu release occurred only at pH ~4.3 and dissolved Cr concentrations typically increased with increasing pH. Cr(VI) was determined as the predominant oxidation state in leachates and results from WLTs spiked with Cr(VI) suggest that Cr was strongly sorbed below pH 7. Sorption affinity of fly ashes for Cr(VI) seemed to be to correlated to their oxalate-extractable Fe content, which is presumably a surrogate for amorphous iron (hydr)oxide content. Arsenic release typically followed a similar leaching pattern observed for Cr, with the exception of 100% alkaline fly ash; decreased As release above pH 9 for this sample was attributed to precipitation of Ca-As phases due to its high CaO content.Item Characterization and Mobilization of Arsenic in Various Contaminated Materials(2005-08-03) Peterson, Michael Clayton; Torrents, Alba; Civil Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Arsenic is a potentially toxic contaminant of concern even at relatively low concentrations in the environment. The complex chemistry of arsenic in the environment is influenced by a variety of chemical and physical factors. The presence of iron minerals is believed to be particularly important to arsenic mobility. Extraction methods were used to evaluate arsenic and iron in a variety of contaminated materials including mine tailings and soils. The contaminated materials were also evaluated for arsenic mobilization in batch experiments while pH and redox potential were monitored. A relationship between arsenic and iron was observed to occur in most, but not all, of the arsenic-contaminated samples. The most mobile fractions of arsenic were shown to be highly correlated with a simulated human oral bioavailable extraction method in the samples evaluated. The mobilization of arsenic by the simulated bioavailable extraction method was associated with a negligible mobilization of iron.Item Arsenic(III) Speciation in Sulfidic- and Carbonate-Containing Waters; Thioarsenites as Ligands for Ag(I), Pb(II) and Hg(II)(2004-11-22) Neuberger, Carla Sue; Helz, George R; Chemistry; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)This dissertation has two objectives; the first is to investigate speciation of three d10 metals (Ag(I), Hg(II) and Pb(II)) in sulfidic solutions containing As(III) to determine if thioarsenite could act as a ligand for the metals. Second, a hypothesis that As(III) forms strong complexes with bicarbonate is investigated. The solubility of As in sulfidic solutions (10-4-10-3 M) equilibrated with As2S3+S at near-neutral pH (6.95-7.95) was measured and compared to the solubility of As in binary and ternary assemblages. Three species, AsS(HS)(OH)-, As(OH)3 and H2As3S6-, explain As speciation: 0.5As2S3 + 3H2O  As(OH)3 + 1.5H2S, pK=12.58, 1.5As2S3 + 1.5H2S  H2As3S6- + H+, pK=6.200.77 and 0.5As2S3 + H2O + 0.5H2S AsS(HS)(OH)- + H+ pK=8.740.09. The solubility of As and Ag in sulfidic solutions (10-4-10-3 M) equilibrated with two Ag-As-S assemblages at near-neutral pH (6.89-8.37) was measured. The As species that explained As2S3+S solubility also explained solubilities in the Ag-As-S system. The silver solubility was explained by six species: 0.5Ag2S(s) + 1.5 HS- + 0.5 H+  Ag(HS)2-, pK=0.4060.41; Ag2S (s) + 2 HS-  Ag2S(HS)22-, pK=4.78; 0.5Ag2S (s) + 0.5 HS- + 0.5 H+  Ag(HS) pK=2.110.21; 0.5Ag2S (s) + Cl- + 0.5 HS- + 0.5 H+  Ag(Cl)(HS)-, pK=-1.090.20; 0.5Ag2S (s) + (x-1)S + 0.5 HS-  AgSx- + 0.5 H+, pK=8.510.19 and Ag+ + AsS(HS)(OH)-  AgAsS(HS)(OH)o, pK=-17.17 0.20. As shown by the last equilibrium expressions, dithioarsenite (AsS(HS)(OH)-) is a strong ligand for Ag(I). Two other ternary systems, HgS+As2S3+S and PbS+As2S3+S, were investigated but the solubility of Hg2+ and Pb2+ were not significantly enhanced when arsenic was present. The order of stability of the metal-thioarsenite complexes agrees with predictions by Tossell (2000). The GFo of natural orpiment was calculated to be -80.81.6. The solubility of As2O3 in concentrated bicarbonate solutions at near-neutral pH is enhanced to a small, but statistically significant degree compared to the solubility in chloride solutions of the same ionic strength. This effect is attributed to one complex: As(OH)3 + HCO3-  As(OH)2CO3-, pK=0.570.15. The small constant suggests that As(III)-carbonate complexes will be negligible at carbonate concentrations found in nature.