Pilot Test of the Permeable Reactive Barrier for Removing Uranium from the Flooded Gunnar Pit

Lesley Mcgilp,Dexu Kong,Lee D Wilson,Ian Wilson,Alexey Klyashtorin

doi:10.4236/gep.2020.87009

Abstract

This work reports on applying iron oxide coated sand (IOCS) media in an experimental permeable reactive barrier to remove uranium (U) species from uranium containing water. A field study was conducted at the legacy Gunnar uranium mine & mill site that was abandoned in the 1960s with limited to no decommissioning. The flooded Gunnar mine pit presently contains about 3.2 million m3 of water contaminated by dissolved U (1.2 mg/L), Ra-226 (0.4 Bq/L), and minor concentrations of other contaminants (As, Se, etc.). The water is seeping over the pit rim into Lake Athabasca, posing potential environmental and health concerns. IOCS media can be used to immobilize uranium species through an adsorption process. Herein, the preparation of hydrous ferric oxide sorbents and their supported forms onto silica sands is described. Fourier transform infrared spectroscopy (FTIR) and powder X-ray diffraction (pXRD) were used for structural characterization. The adsorption properties of the IOCS sorbent media were modeled by the Langmuir adsorption isotherm, where a maximum uranium uptake capacity was estimated. Bench-scale adsorption kinetic experiments were also performed before moving to a field trial. Based on these lab results and input on field-scale parameters, a pilot permeable reactive barrier was fabricated and a field test conducted near the Gunnar pit in June 2019. This pilot test provided technical data and information needed for designing a full-scale permeable barrier that employs the IOCS media. This approach can be applied for in-situ water treatment at Gunnar and other legacy uranium sites.

Highlights

The abandoned Gunnar Mine and mill site are located at the northern shore of Lake Athabasca approximately 30 km southwest of Uranium city in northwestern Saskatchewan, Canada
The similar values of pH for the Point of Zero Charge (pHpzc) for the iron oxide coated sand (IOCS) is evidenced by the following comparison, where the pHpzc is 7.8 (Rusch et al, 2010)
A similar observation was noted for the Transmission electron microscopy (TEM) image in Figure 8(e), where a mixture of ferrihydrite and hematite minerals was observed on the silica sand surface

Summary

Introduction

The abandoned Gunnar Mine and mill site are located at the northern shore of Lake Athabasca approximately 30 km southwest of Uranium city in northwestern Saskatchewan, Canada. The flooded pit at the Gunnar site contains a total volume of approximately 3 million m3 of water contaminated by dissolved uranium with a concentration of ~1000 μg/L. This is about two orders magnitude above the regulatory level set by the Saskatchewan Environmental Quality Guideline (SEQG). A preferred mitigation option for the flooded pit is long-term monitoring of the water quality and surface flow. This approved option by the provincial and federal regulators cannot reduce current uranium loadings to Lake Athabasca. Iron oxide coated sands (IOCS) media can be utilized for the purpose

Methods

Results

Conclusion