Slick Rock Ore Would Go to the Restarted Shootaring Canyon Mill, a 750 t/d SAG, Two-Stage Acid Leach and SX Plant With Added Vanadium Recovery

Anfield Energy's May 2023 preliminary economic assessment for the Shootaring Canyon mill and the Velvet-Wood and Slick Rock uranium projects assumes new equipment in the mill's original building in Utah.

The Shootaring Canyon Mill and Velvet-Wood and Slick Rock Uranium Projects Preliminary Economic Assessment, NI 43-101, was prepared by BRS Inc. and T.P. McNulty and Associates for Anfield Energy Inc. and dated May 6, 2023. Ore from the Velvet-Wood and Slick Rock mines, plus stockpiled material, would be processed at the Shootaring Canyon mill in Ticaboo, Utah. Mountain States Engineers built the mill around 1981 for Plateau Resources, at a design capacity of 750 short tons per day, and it ran only briefly before 1982. It holds a radioactive materials licence, which would need amending before operations could resume. Some equipment, including the CCD thickeners and pumps, has since been salvaged and sold, but the main process building is described as well designed and in generally very good condition.

Critical Data

Overview

The PEA limited its processing costs to the original conventional grinding and agitated leaching circuit, followed by yellowcake precipitation, drying and drum filling. Two options were considered: refurbishing the original equipment with replacements where needed, which would save roughly $4 million, or installing all new equipment in the original building. The PEA uses the second, more expensive option as a conservative measure, because it brings current equipment and best available technology. Both options add vanadium recovery. Leaching would run at a higher free acid concentration, pH 0.8 to 1.2 rather than 1.5 to 2.0, to extract the vanadium, and a vanadium circuit would treat uranium SX raffinate in a small new building next to the mill.

The report notes that the mill was among the last two or three conventional uranium mills built before the industry collapsed, and that its design drew on two decades of improvements. Examples include SAG milling of run-of-mine ore in place of crushing and rod milling, and DSM sieve bends in place of rake or spiral classifiers. Process solutions were heated through the diesel generators' radiators and blocks to speed up leaching. Other features were two-stage leaching to cut acid use, acid-resistant wood-stave leach tanks, high-rate deep CCD thickeners, extensive process instrumentation, and centrifuging of thickened yellowcake before filtering and drying.

Key Process Stages

Ore handling. A front-end loader reclaims run-of-mine ore from a storage area onto a 14 inch grizzly. A surge bin of about 75 t and an apron feeder feed a 3 inch stationary grizzly and a 42 inch mill feed conveyor with a metal detector, belt scale and wet dust scrubber.

Grinding. The SAG mill produces slurry at 65 to 70% solids, which is pumped to four DSM sieve bends with 28 mesh slots. Oversize returns by gravity to the mill, and undersize goes to two wood-stave leach feed holding tanks.

Two-stage leaching. Tetravalent uranium is oxidized with sodium chlorate and dissolved with sulphuric acid. In the first stage, three tanks give two hours at 29% solids, using overflow from the first CCD thickener. A thickener then raises the slurry to about 50% solids for the second stage, four tanks giving 16 hours at 48.8% solids.

CCD washing. Six thickeners wash the residue, with SX raffinate entering at the last one. Five are high-rate units at 50% underflow solids. The last is a high-density unit at up to 60% solids, pumped to the tailings impoundment, from which supernatant is reclaimed.

Clarification. Leach thickener overflow passes a clarifier, at no more than 50 ppm solids, and three automatically backwashed sand filters, at no more than 10 ppm solids, before PLS storage.

Solvent extraction and product. Uranium is concentrated and purified by solvent extraction with Alamine 336, then precipitated as yellowcake, which is thickened, centrifuged, filtered, dried and drummed. The new design would include a fully automated drum filling station that also removes and replaces the drum clamp ring, reducing operator exposure to dust.

Additional Interesting Data and Summary

A 2008 definitive restart estimate by Lyntek proposed full refurbishment with some new CCD thickeners, pumps, instruments and scrubbers. The 2023 PEA instead assumes complete replacement of the equipment, while noting that a new building would cost about $4 to $7 million plus demolition, so the original structure is kept.

In summary, the 2023 PEA would process Slick Rock and Velvet-Wood ore at the restarted Shootaring Canyon mill. It keeps the mill's 1981 SAG, two-stage acid leach, CCD and amine SX flowsheet, re-equipped with modern units, and runs the leach more aggressively so that vanadium can also be recovered.

Key Processes

• Grizzly screening and SAG milling of run-of-mine ore
• DSM sieve bend classification
• Two-stage sulphuric acid and sodium chlorate leaching
• Six-stage countercurrent decantation
• Clarification and sand filtration of pregnant solution
• Amine solvent extraction of uranium
• Yellowcake precipitation, centrifuging, drying and drumming
• Vanadium recovery from SX raffinate (new circuit)

Source: The Shootaring Canyon Mill and Velvet-Wood and Slick Rock Uranium Projects, Preliminary Economic Assessment, National Instrument 43-101, prepared for Anfield Energy Inc., dated May 6, 2023.