Project developer Plateau Uranium aimed to have its Macusani Plateau uranium/lithium project, in Peru, in production by 2020 to be prepared to take advantage of analysts’ forecasts of a uranium supply deficit by then, said president and COO Dr Laurence Stefan at a seminar hosted by the Southern African Institute of Mining and Metallurgy Johannesburg Branch last month.

Historical exploration workings have been carried out on the project to date, at a cost of C$50-million, with the company aiming to raise about $22-million to take the project to the bankable feasibility study phase by mid-2019. The cost of construction and bringing the project on stream is estimated at $300-million. Plateau Uranium is in discussions with an unnamed Chinese investor about securing the required financing.

Stefan told the audience that the company’s uranium exploration properties in the Puno province were considered to be among the largest undeveloped uranium projects in the world as they hosted large measured, indicated and inferred uranium resources.

The company has more than 910 km2 of exploration concessions on the Macusani plateau, where it established a compliant indicated resource estimate of 51.9-million pounds of uranium oxide (U3O8) at 248 parts per million (ppm) U3O8 and 72.1-million pounds of U3O8 at 251 ppm U3O8 in the inferred category when using a 75 ppm uranium cutoff.

At a cutoff of 200 ppm uranium, Plateau has defined higher-grade resources of 32.8-million pounds of U3O8 at 445 ppm U3O8 in the indicated category and 45.9-million pounds of U3O8 at 501 ppm U3O8 in the inferred category.

Plateau has also defined initial lithium and potassium resource estimates in four of its uranium deposits. These comprise 67 000 t of lithium oxide (Li2O) at 0.13% Li2O, 2.34-million tons of potassium oxide (K2O) at 4.47 % K2O and 31-million pounds of U3O8 at 268 ppm U3O8, all in the indicated category. It also holds 109 000 t of Li2O at 0.12% Li2O, 3.93-million tons of K2O at 4.49% K2O and 54.8-million pounds of U3O8 at 283 ppm U3O8, all in the inferred category.

Stefan pointed out that new leach testwork had started in August 2016 using lithium-rich samples with background uranium- and uranium-lithium-rich samples from the Macusani deposit mineralisation.

“The lithium content ranges from 640 ppm to 806 ppm lithium in all samples. The uranium content ranges from background levels of 7 ppm uranium in the uranium-poor samples to between 568 ppm and 629 ppm uranium in the mineralised samples from the various uranium deposits.”

Several parameters were varied during the leach tests, including crushing grind size, acid concentration, leach time and temperature, he added. Leaching was undertaken at atmospheric pressure in stirred tank reactors employing sulphuric acid as the lixiviant. Additionally, he commented that initial scoping testwork entailed roasting, calcining and acid curing.

Stefan said the tests covered temperatures ranging from 50 ºC to 550 ºC. “Although . . . temperatures higher than 180 °C usually guaranteed high lithium recoveries of up to 87% in earlier testwork, the objective of this most recent work was to reach potentially economic lithium recoveries at leaching temperatures below the water boiling point.”

He explained that the initial scoping testwork used “more aggressive conditions”, but did not confirm any significant benefit over the more moderate temperature and atmospheric pressure tank leach processes.

Stefan remarked that more than 150 separate leach test runs had been completed at the project over the past several months and the conclusions of that phase of testwork had resulted in a very simple, straightforward flow sheet without the aggressive processing conditions normally associated with the recovery of lithium from ores.

Consistent lithium recoveries of between 61% and 73% were reported from all samples employing a sulphuric acid leach at a variety of acid concentrations and at temperatures of 65 ºC to 85 ºC, he added.

Samples from the Macusani uranium deposits displayed consistent uranium recoveries of 98% to 99% across all temperatures. Sulphuric acid consumption in the leach varied from 50 kg acid/ton to 140 kg acid/ton of material processed and was sufficient to simultaneously extract uranium and lithium.

Stefan explained that higher acid consumptions were related to finer grind sizes, while coarser grind sizes had much lower acid consumptions with identical lithium and uranium recoveries, thus providing upside for the potential project economics.

“The current and planned test programne is examining the grind versus recovery trade-off with encouraging results. Apart from lithium and uranium, other elements were also leached during the tests, mainly potassium, rubidium and cesium. These will also be evaluated further in the additional leaching-precipitation work planned,” he commented.