Mining treatment effluent pond modeling: a risk-based approach

Abbassi, Rouzbeh (2010) Mining treatment effluent pond modeling: a risk-based approach. Doctoral (PhD) thesis, Memorial University of Newfoundland.

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Acid Mine Drainage (AMD) discharged to the surrounding environment may cause serious environmental problems. Sulphidic mine wastes are oxidized resulting in the consequent release of AMD. Different metals such as cadmium, cobalt, copper, iron, lead, nickel, zinc, etc. are released to the environment when sulfides of these metals are exposed to the air. AMD affects the surface water as well as groundwater nearby and limits the reuse of the mine water for processing purposes. Because of differences in mine sites and ambient conditions, the prediction of AMD water composition is very complicated and remains a great concern for scientists. The determination of the minerals involved in producing AMD, as well as the oxidation reactions and chemical components produced in these reactions, are essential prior to choosing the appropriate treatment technology. The oxidation reactions of the minerals and chemical components produced by these reactions are discussed in this thesis. A methodology for predicting the minerals involved in the production of AMD is presented and may be used in conjunction with analytical techniques to reduce the cost of using sophisticated techniques. -- The determination of the possible chemical components included in AMD may aid in finding a suitable treatment system for treating mine water. Waste Stabilization Pond (WSP) technology is one of the natural treatment methods that use chemical and biological processes for AMD treatment. The design of the WSP is based on many assumptions, one of which is that the pond is well mixed. That is, there are no concentration gradients within the pond or the pond is modeled as a Continuously Stirred Tank Reactor (CSTR). However, in reality due to the heterogeneity of the constituents of the wastewater and influence of controlling parameters (i.e., temperature & concentration), these assumptions are over simplified. The concentration, wind shear, and temperature stratification within the pond significantly impact the flow pattern within the system. Instead of using ideal reactor models, dispersed flow model covers the non-idealities within the pond. This model is highly related to the hydraulic conditions of the pond. This non-ideal model is rarely used for determining the concentration gradient within the pond, because the main parameters of the model (i.e. actual retention time and dispersion coefficient) are not easy to obtain. Computational Fluid Dynamic (CFD) codes are one of the options presented for defining these two parameters. A methodology discussed in this thesis is using CFD as a suitable option for determining the main parameters of the dispersed flow model. A dispersion model is tested and validated for modeling the concentration gradient within the pond, and CFD is used for determining the dispersion coefficient and actual retention time via case studies in this thesis. -- Following the determination of the chemical concentrations in the effluent, assessment of the effect of these concentrations on human health and the ecosystem is required. Environmental risk assessment is a systematic process for describing and quantifying the hazardous effect of chemical contaminants to human health and ecosystems. The USEPA framework is used for identifying and quantifying the risk of chemical contaminants to ecological entities. The four steps of the USEPA framework are hazard identification, exposure assessment, dose-response modeling, and risk characterization. The estimated risk of the effluent of treatment systems may be used to assess the performance of the treatment process. Furthermore, the risk value is associated with different uncertainties and therefore uncertainty assessment may not be neglected in any risk assessment process. The ecological risk assessment methodology and quantification of risk associated with effluent contaminants from the tailing pond to the ecosystem is demonstrated in this thesis via a case study.

Item Type: Thesis (Doctoral (PhD))
Item ID: 9270
Additional Information: Includes bibliographical references (leaves 130-149).
Department(s): Engineering and Applied Science, Faculty of
Date: 2010
Date Type: Submission
Library of Congress Subject Heading: Acid mine drainage--Purification; Mine water--Analysis; Sewage lagoons--Design and construction; Water--Pollution--Risk assessment

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