Uranium Symposium Covers State Of The Art

The U2009 uranium symposium held in Keystone, Colo., in May, covered progress on a number of fronts in uranium mining technology, including uranium extraction, exploration and in-situ production.

In the session dealing with uranium extraction, heap leaching, solvent extraction, and ion exchange were all examined.

Heap leaching has a successful track record in gold recovery, but the process is not usually associated with uranium mining. Enter Erik Hunter, a graduate student at the Colorado School of Mines, who spoke about improved methods of uranium leach and recovery, with special emphasis on heap leaching.

Hunter has identified an opportunity in the numerous dumps on old uranium mines on the Colorado Plateau. He suggests locating the heap near an existing disposal cell to reduce environmental impact. A mobile ion exchange unit can be used to recover the uranium from the leach solution.

The most troublesome aspect of uranium recovery was found to be the removal of iron during the uranium precipitation process. The problem was addressed by using various reagents.

Alan Miller of Dutch engineering contractor Bateman-Litwin described two case studies on the development of solvent-extraction processes in uranium recovery in Kazakhstan, as an alternative to using ion exchange. The main lesson that emerged during the tests was the need to use real solutions that came from the mines, since test results were different for each solution.

Furthermore, bench-scale tests in the laboratory were not sufficient, so Miller recommends tests in a pilot plant using real mine solutions.

In one case study, the results from the pilot-scale tests indicated lower capital costs for a solvent-extraction process than for an ion exchange process, and also lower processing costs per pound of uranium.

In a second case study, Miller compared stripping the uranium in a conventional mixer-settler combination, with a process that strips the metal using solvent extraction, concluding that the solvent-extraction process was superior because it makes it easier to avoid uranium precipitation.

Bryn Jones and James Davidson of Australian company Uranium Equities reported on a novel process for recovering uranium from phosphoric acid. According to Uranium 2007, a report prepared by the Nuclear Energy Agency, phosphates contain an estimated 7 to 22 million tonnes of uranium. Phosphates are a raw material for making phosphoric acid, so a process that could recover uranium from the acid could be a potential source of the metal.

Jones and Davidson reviewed the first two generations of processes developed to recover uranium from phosphoric acid. Phos Energy, a subsidiary of Uranium Equities, is now developing a third-generation process together with another company, Urtek.

The company has applied for patents for the new process. While sketchy on details, the speakers said that it is based on a novel pretreatment combined with a robust extraction technology. They reported that the company has been operating a pilot plant since early 2009.

PhosEnergy has completed preliminary engineering for a demonstration plant, which it plans to have in operation later this year. It estimates capital costs at US$100-125 per lb. uranium oxide in annual production, and operating costs of US$20-30 per lb.

The company plans to complete a feasibility study in mid-2010, and have a commercial-scale plant running in 2013.

John Carr of Australian company Clean TeQ described how continuous resin technology can be used to improve uranium recovery from a leaching solution. Carr said the use of elution and sorption technologies could potentially eliminate two stages in the traditional recovery process: the solid/liquid separation process, and the solvent-extraction process.

Carr highlighted two sorption technologies: continuous resin in pulp, used for pulps, and resin in column, used for liquids. Continuous resin in pulp can operate with up to 50% solids, so its use can reduce or eliminate the need for solid/liquid separation.

Carr provided a detailed comparison among various flow sheet configurations. He concluded that continuous resin systems have a high reliability, and that they can both simplify and optimize the uranium recovery process.

Moving from extraction technologies to in-situ production, Ted Way of In-Situ Inc. gave a presentation about well-field mechanics for in-situ uranium mining, which was based on a journal article in the November- December issue of Southwest Hydrology.

“Basic to an in-situ mining operation is a thorough understanding of the site’s hydrogeology, particularly the degree to which fluid movement can be predicted and controlled,” Way said.

The questions that the hydrologist must address include: Is uranium deposited in the saturated zone with sufficient available drawdown? Do the upper and lower confining units of the aquifer provide enough vertical confinement for the leaching solution? Is the formation’s hydraulic conductivity high enough for wells to achieve reasonable productivity and injectivity?

Once a site’s hydrogeology is considered feasible, engineers can use three aspects to enhance the operation’s economy and minimize environmental effects: recovery process design; well-field design; and monitoring programs.

The first aspect, recovery process design, is based on laboratory tests that indicate the distance the leaching solution can travel underground before losing its leaching ability. The results are used to determine the distance between injection wells and production wells.

The second aspect, well-field design, aims to maximize the percentage of the field leached by the solution. Efficiency can be raised by using more wells and by arranging wells in certain optimum geometric configurations.

To ensure containment, the pumping rate is typically 1-3% higher than the injection rate. A groundwater model is usually developed when the field is designed.

The third aspect, a groundwater monitoring program, is essential for protecting areas surrounding the well-field. The program uses monitoring wells around the production field.

Another layer of protection can be added by inner monitoring wells that give an early warning in case of seepage. Monitoring wells overlying and underlying the aquifer are also needed, to protect against vertical leakage.

Innovation in uranium mining is not confined to production and extraction — it also finds its way to exploration. Dale Sutherland of Activation Laboratories spoke about a novel method for exploring for blind uranium deposits by detecting hydrocarbons in soil. It involves collection of near-surface samples, which are analyzed for a group of organic compounds.

The technique is used to identify both the nature of the buried mineral (uranium, gold, copper, etc.) and its location. The organic compounds that it detects are produced by bacteria. Since different bacteria grow on different minerals, an analysis of soil hydrocarbons can give an indication of the subsoil minerals. So far, the technique has been used to explore for gold, kimberlite, uranium and nickel-copper.