An investigation into bioleaching of uranium and rare earth elements from quartz-pebble conglomerate ores from Elliot Lake, Ontario

Abstract

Biogeochemical mineral dissolution, the microbial-assisted dissolution of minerals, is an effective method for economically promoting the release of metals of interest from ores and mine waste materials. As the low-grade ores of the Elliot Lake region may be suitable for development of a sustainable heap-leach method for the extraction of U and REEs from the low-grade host mineralization, this thesis is focused on the geochemical and biological process simulation monitoring of the biogeochemical release of elements to the leaching solutions. The response of the retired heap material to a variety of passive closure strategies is also addressed. A series of biogeochemical mineral dissolution experiments have provided a detailed understanding of the biogeochemical mineral dissolution process, with the investigation of passive approaches to prepare for decommissioning to determine suitability to the ore materials from the study site. The chemical analyses of effluents collected throughout the experimentation, coupled with mineralogical and geochemical analyses of the feed and residual mineral material has enabled an understanding of the chemical controls of the overall biogeochemical mineral dissolution process for Fe, U, and Th, together with the preferential leaching release patterns for REEs, to be obtained. A mechanism describing U retention in secondary coatings has been proposed, with a passive approach to closure using inhibition and encapsulation methods being demonstrated, along with a determination of the potential for ongoing radionuclide release from a simulated heap upon decommissioning. The laboratory research in this study has shown that biogeochemical mineral dissolution, followed by waste material encapsulation, can be successfully applied to heap-leach pads potentially, enabling the economic recovery of U, Th, and selected REEs to solution for subsequent metallurgical collection. The studies strongly support the concept of sustainable development for heap-leach operations in the Elliot Lake region.