This study was designed to develop an in-situ flushing system for remediating metal-contaminated soils. Specifically, the capabilities of citric acid, an organic acid, to extract metal ions from a metal-contaminated sandy soil, containing 0.42, 0.04, 0.01, and 41.52 mg g-1 of Zn, Cu, Cd, and Pb, respectively, were tested at bench-scale and large-scale levels. Citric acid, at pH 5.5, was used at different levels of concentration and retention time in batch experiments to establish optimum conditions for the maximum removal of heavy metals from the soil. Citric acid exhibited a tremendous potential to extract metal ions from the metal-contaminated soil. The extraction of metal ions increased with an increase in citric acid concentration. A column study (height = 0.6 m; internal diameter = 0.1 m) was conducted to compare metal leaching with surface and subsurface application of citric acid. The results indicated that the subsurface application resulted in a more efficient extraction of metal ions due to uniform distribution of the citric acid. / Finally, a large-scale experiment involving soil columns (height = 1.0 m; internal diameter = 0.2 m) was carried out to develop an in situ soil flushing system to remediate the metal-contaminated soil. Citric acid was supplied into the soil columns through a subsurface irrigation system. This process resulted in an overall extraction of Zn, Cu, Cd, and Pb ions from the soil columns at 83.27%, 1.47%, 16.70%, and 26.55%, respectively. Results obtained in different experimental protocols suggested that continuous flushing of the soil is a suitable method for extracting metal ions from the contaminated soil using citric acid. / The metal-rich leachate was effectively treated with chitosan flakes. Results indicate that for 0.1 M citric acid leachate containing 0.06, 0.02, 0.003, and 5.87 mumoles ml-1 of Zn, Cu, Cd, and Pb, respectively, about 20 g of chitosan would be sufficient to remove about 50% of the contaminants from one liter of leachate in 6 h. Various batch experiments involving pure solutions of metal ions as well as the metal-rich leachate were conducted to establish the metal adsorption properties of chitosan under various physico-chemical conditions. The controlled parameters were the amount of chitosan, reaction time with and without shaking, and the pH of the solution. The sorption of metal ions from pure metal solutions and the leachate was not improved by the agitation, and the maximum adsorption of metal ions onto chitosan flakes occurred at pH 6.0. Sorption equilibrium studies were also conducted with a constant sorbent weight and varying initial concentration of metal ions. The experimental data of adsorption from the solutions, containing metal ions, were found to correlate well with the Langmuir isotherm equation.
| Identifer | oai:union.ndltd.org:LACETR/oai:collectionscanada.gc.ca:QMM.36751 |
| Date | January 2000 |
| Creators | Bassi, Raman. |
| Contributors | Prasher, S. O. (advisor) |
| Publisher | McGill University |
| Source Sets | Library and Archives Canada ETDs Repository / Centre d'archives des thèses électroniques de Bibliothèque et Archives Canada |
| Language | English |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Format | application/pdf |
| Coverage | Doctor of Philosophy (Department of Agricultural and Biosystems Engineering.) |
| Rights | All items in eScholarship@McGill are protected by copyright with all rights reserved unless otherwise indicated. |
| Relation | alephsysno: 001778553, proquestno: NQ69851, Theses scanned by UMI/ProQuest. |
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