Cameco Corporation, the world’s leading uranium producer, has investigated the possibility of underground milling of high-grade uranium ore. Brainchild of Chuck Edwards, director, engineering and projects at Cameco, this innovative concept has been elaborated upon and studied. In January 2007, Edwards presented the design as well as technical details at the 39th Annual Canadian Mineral Processors Operators’ Conference in Ottawa.
The idea was conceived in 2000 when milling possibilities for Cigar Lake were being brainstormed. Although it was too late in the project to implement at the Cigar Lake Mine, interest in the proposal was keen. “I am quite confident that the next high-grade underground ore body will use this process,” Edwards said. Given the level of uranium exploration presently underway, there is optimism that such a discovery will be made.
This exploration is due to forecasted increases in future demand for uranium and its current high cost. Globally, there is a trend towards the nuclear option because it is well positioned as an environmentally friendly energy source. Economically developing nations such as China and India are building nuclear reactors and other countries are making plans for future construction. Closer to home, the United States will likely develop new power plants within the next few years. “A nuclear power plant produces virtually no CO2,” said Edwards and the renewed interest in nuclear that this has sparked “is referred to as the nuclear renaissance.”
Cameco predicts that new uranium deposits will need to be brought into production to satisfy the increase in demand. If the right type of ore body were to be found, Cameco would contemplate using underground milling. “You want an underground high-grade mine,” Edwards stated. “To make sense going underground the equipment has to stay fairly small. You want a high-grade mine because the higher the grade, the smaller the equipment for the same production.”
To obtain a high-level understanding of the proposed underground milling method, it can be compared to conventional surface operation. The milling process currently employed at Cameco’s northern Saskatchewan mills includes six basic steps: grinding, leaching, solid/liquid separation, impurity removal, precipitation and drying, and tailings deposition. With underground milling, these steps would be performed below the surface, with the exception of impurity removal and precipitation and drying. These would remain above ground due to the size of required equipment.
As the conceptual process has been ironed out, pre-feasibility studies have identified important benefits underground milling could have versus the standard surface operation. In fact, both the environmental and the cost impact of the proposed method appear favourable.
Environmentally, the treatment of the solid and liquid waste from the underground milling process would offer significant benefits. Edwards explained that overall “there is a much, much smaller environmental impact.” There would be three main areas of improvement. Firstly, visual impact is lessened because of reduced surface operations. Secondly, the tailings would be stored underground, well isolated from water. Currently, tailings are treated and stored on surface. Edwards described the proposed underground disposition as “an extremely safe, environmentally benign method of storing the tailings,” because the underground method would “isolate them more from the water than the ore was to begin with.” Lastly, the liquid waste would be minimized because the equipment used would be relatively small. Effluent could be further reduced if combined with Cameco’s membrane treatment of water. In fact, according to Edwards “we can potentially get to a very, very small amount of effluent discharged, and possibly no effluent discharged, in which case you have zero impact.”
As an added advantage, the financial aspect of such a process has an up side. “You have major environmental benefits and they cost you less than nothing,” emphasized Edwards. This is because cost analysis performed at Cameco revealed that underground milling could offer sizeable capital and operational cost savings. On the capital side, the reduction in cost would result from lower construction expenditures. On the operational side, with the milling taking place right at the site, ore transportation costs would be reduced. Overall, positive attributes of the process could be advantageous for Cameco and further their goal of producing clean energy with the least possible environmental impact.
There are no known obstacles to implementing the underground milling process in a future mine. The technology and equipment required are already available. In addition, the proposed excavations for such an operation would be reasonably small and therefore would not represent any additional concerns with regard to construction and safety.
Should the right ore discovery be made that would suit underground milling, Edwards and his team are ready to swing into action. At such a time, feasibility studies would be conducted and permitting would need to be done. Basically, said Edwards, “the process is 100 per cent ready to go.” Once a site is identified, the exact process would be tailored to the specific characteristics of the discovery. Until then, Edwards and his team are anxiously awaiting exploration developments.