Civil Engineering ETDs

Publication Date

Winter 11-10-2016

Abstract

From 1950 to the early 1980’s New Mexico played an important role in the production of uranium (U) for the nuclear power industry and the nation’s weapon programs. Though the U mining and milling industry in New Mexico is inactive at present, increased interest in nuclear energy as a CO2 free power source has led to proposals for renewed development of U resources. In particular, U mining projects have been proposed using both underground mining and in situ leach (ISL) mining. When feasible, ISL mining minimizes waste by eliminating; mine waste, mine dewatering, radiation exposure and the recovered U does not require milling with consequent production of milling wastes. However, ISL does not completely avoid environmental impacts and it does produce some wastes which must be managed at the surface. A much greater concern is restoration of groundwater quality following completion of mining operations. This research consisted of 4 phases. Phase 1 involved collection of samples representative of ore materials that might be mined by ISL processes and characterization of their composition and characteristics. Phase 2 consisted of leach studies to determine the leachability of U from the ore materials and to generate an understanding of the expected chemistry after reaction with bicarbonate and dissolved oxygen which are used in ISL lixiviants. Phases 3 and 4 column experiments for the investigation of aquifer stabilization methods that might be used to restore groundwater following the completion of ISL mining. Phase 3 investigated the use of chemical methods while Phase 4 considered application of biological processes. Results from batch experiments suggest that U and co-constituents are released after reaction of ore solids with bicarbonate and dissolved oxygen showing the potential impacts of ISL U mining on groundwater quality. Column leach experiments were conducted to investigate the potential of chemical and biological processes for restoration. The addition of phosphate was used to immobilize U(VI) by chemical precipitation. Sodium lactate was used as an electron donor for the activation of sulfate and metal reducing bacteria, and a control column without a chemical or biological reductant was used to interpret results differences. Given column experiment results, effluent concentrations of U and co-constituents for chemical and biological treatments are similar to those of the control, suggesting limited mixing between the contaminated groundwater and amended restoration fluid. Groundwater restoration should consider hydrodynamics, specifically the mixing that takes place in the interstitial pores within the aquifer.

Keywords

Biological Reductant, Chemical Reductant, Complexation, Hydrodynamics, Immobilization, Lixiviant, Precipitation, Reducing Bacteria, Restoration, Uranium

Document Type

Thesis

Language

English

Degree Name

Civil Engineering

Level of Degree

Masters

Department Name

Civil Engineering

First Committee Member (Chair)

Jose M. Cerrato Corrales

Second Committee Member

Bruce M. Thomson

Third Committee Member

Johanna Blake

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