<p>Natural and constructed clay liners are routinely used to contain waste and wastewater. The impact of acidic solutions on the geochemistry and mineralogy of clays has been widely investigated in relation to acid mine drainage systems at pH > 1.0. The impact of sulfuric acid leachate characterized by pH < 1.0, including potentially negative pH values on the geochemistry and mineralogy of clays is, however, not clear.</p>
<p>To address this deficiency a series of batch and diffusion cell studies, investigating the geochemical and mineralogical impacts of H<sub>2</sub>SO<sub>4</sub> solutions (pH 5.0 to -3.0), were conducted on three mineralogically distinct clays (Kc, Km, and BK). Batch testing was conducted at seven pH treatments (5.0, 3.0, 1.0, 0.0, -1.0, -2.0 and -3.0) using standardized sulfuric acid solutions for four exposure periods (14, 90, 180, and 365 d). Aqueous geochemical, XRD, and Si and Al XANES analyses showed: increased dissolution of aluminosilicates with decreasing pH and increasing exposure period; preferential dissolution of aluminosilicate Al-octahedral layers relative to Si-tetrahedral layers; formation of an amorphous silica-like phase that was confined to the surface layer of the altered clay samples at pH ⤠0.0 and t ⥠90 d; and precipitation of anhydrite and a Al-SO<sub>4</sub>-rich phase (pH ⤠-1.0, t ⥠90 d).</p>
<p>The diffusive transport of H<sub>2</sub>SO<sub>4</sub> (pH =1.0, -1.0, and -3.0) through the Kc and Km clays for 216 d was examined using single reservoir, constant concentration, diffusion cells. The diffusive transport of H<sup>+</sup> within the cells was modeled using 1-D transport models that assumed no absorption, linear absorption, and non-linear absorption of H<sup>+</sup>. The absorption isotherms were calculated from the pH 5.0, 3.0, and 1.0 batch experiment results, which were assumed representative of H<sup>+</sup> absorption at pH < 1.0. However, model results indicated that the batch test results can not account for the observed H<sup>+</sup> consumption in all cells and greatly underestimate the amount of H<sup>+</sup> consumption in the pH -1.0 and -3.0. In the Kc and Km diffusion cells, above-background Ca, Al, Fe, and Si aqueous concentrations were associated with depth intervals characterized by decreased pH values. Respective peak concentrations of 325, 403, 176, 11.7, and 1.38 x 10<sup>3</sup> μmol g<sup>-1</sup> (Kc) and 32.4, 426, 199, 7.2, and 1.22 x 10<sup>3</sup> μmol g<sup>-1</sup> (Km) were measured in the pH -3.0 cells. XRD results showed that the elevated concentrations corresponded to the loss of carbonates and montmorillonite peaks and decreased peak intensities for illite and kaolinite in depth intervals with pH ⤠1.0, in the Kc and Km pH -1.0 and -3.0 cells.</p>
<p>The combined results of these studies indicated that the long-term diffusion of H<sub>2</sub>SO<sub>4</sub> through clays at pH < 1.0 will result in a large amount of primary phase dissolution; however, this will be accompanied by precipitation of soluble Ca and Al sulfate salts and amorphous silica, especially at pH ⤠0.0. Additionally, the presence of even a small amount of carbonate will serve to greatly buffer the diffusive transport of H<sub>2</sub>SO<sub>4</sub> through clays, even at a source pH of -3.0.</p>
| Identifer | oai:union.ndltd.org:USASK/oai:usask.ca:etd-11252008-122801 |
| Date | 26 November 2008 |
| Creators | Shaw, Sean Adam |
| Contributors | Pan, Yuanming, Hendry, M. Jim, Blowes, David, Barbour, S. Lee, Ansdell, Kevin M., Peak, J. Derek |
| Publisher | University of Saskatchewan |
| Source Sets | University of Saskatchewan Library |
| Language | English |
| Detected Language | English |
| Type | text |
| Format | application/pdf |
| Source | http://library.usask.ca/theses/available/etd-11252008-122801/ |
| Rights | unrestricted, I hereby certify that, if appropriate, I have obtained and attached hereto a written permission statement from the owner(s) of each third party copyrighted matter to be included in my thesis, dissertation, or project report, allowing distribution as specified below. I certify that the version I submitted is the same as that approved by my advisory committee. I hereby grant to University of Saskatchewan or its agents the non-exclusive license to archive and make accessible, under the conditions specified below, my thesis, dissertation, or project report in whole or in part in all forms of media, now or hereafter known. I retain all other ownership rights to the copyright of the thesis, dissertation or project report. I also retain the right to use in future works (such as articles or books) all or part of this thesis, dissertation, or project report. |
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