Pinyon Plain Uranium Recovery: White Mesa Mill Process

Source: Energy Fuels Inc (2026)
Website: https://www.energyfuels.com/pinyon-plain-mine/

Critical Data

Overview

Energy Fuels Inc. operates the Pinyon Plain Mine in Coconino County, Arizona, with ore processed under a toll milling agreement at the company-owned White Mesa Mill near Blanding, Utah. Built in 1980, the mill has historically processed over five million tons of uranium and vanadium ores from Arizona, Colorado, and Utah. The White Mesa Mill currently operates on a campaign basis, capable of handling 2,000 short tons per day (stpd), and will process ore from the Pinyon Plain Project along with other feed materials. The recovery methods employed at this facility are designed to maximize uranium extraction while maintaining high product purity. The process begins with ore receiving and grinding using a semi-autogenous grinding (SAG) mill, followed by acid leaching with sulfuric acid and sodium chlorate. Counter current decantation (CCD) thickeners wash the uranium-bearing solution from the leach residue, after which solvent extraction (SX) selectively concentrates the uranium using Alamine 336 in a kerosene organic phase. The final stages involve precipitation with ammonia, drying at approximately 1,400°F, and packaging as U3O8 yellowcake. This integrated flowsheet achieves a 95% uranium recovery rate and consistently produces yellowcake in the 98–99% purity range, even from ores containing problematic elements like vanadium, arsenic, or copper. The operation is significant for its ability to efficiently process ore from the Pinyon Plain Mine while utilizing proven, scalable technology. The recovery methods at White Mesa Mill represent a robust and economically viable approach to uranium production in the United States.

Key Process Stages

• Stage 1: Ore Receiving and Grinding: Ore arrives in 24-ton highway haul trucks, weighed, probed, and sampled for dry weight and process control. After scanning for radiation, a front-end loader transfers ore from stockpiles through a 20-inch stationary grizzly into a receiving hopper. A 54-inch conveyor feeds a 6 ft x 18 ft diameter semi-autogenous grinding (SAG) mill operating in closed circuit with vibrating screens. Water is added during grinding, and material passing P80 -28 mesh (approximately 600 µm) is pumped to pulp storage tanks, while coarser material returns for further grinding.
• Stage 2: Leaching: Slurry from the pulp storage tanks (at 50% solids) is metered into leach tanks where sulfuric acid and sodium chlorate are added. The acid leach dissolves uranium from the ore into solution. Typical sulfuric acid consumption is 350 lb per ton of ore. The leach residue slurry is then pumped to the counter current decantation circuit for washing and solid-liquid separation.
• Stage 3: Counter Current Decantation (CCD): The CCD circuit consists of a series of thickeners. Pulp flows in one direction while uranium-bearing solution (overflow) flows counter-currently. Flocculant is added to each thickener to enhance settling. As pulp moves through the circuit, it is progressively washed of uranium content. The barren solids (tailings) leave the last thickener at approximately 50% solids and are pumped to tailings storage facility cells. Solution from tailings cells is recycled as wash water in the CCD circuit.
• Stage 4: Solvent Extraction (SX): The uranium SX circuit separates and concentrates uranium using a four-stage counter-current mixer-settler system. Alamine 336 (a tertiary amine) extracts uranium from the acid solution into a kerosene organic phase. Loaded organic is then stripped with sodium chloride solution in a second four-stage counter-current circuit. A scrubbing mixer-settler removes impurities before stripping, and a regeneration mixer-settler cleans the barren organic. The raffinate (barren leach solution) is sent to tailings cells. The SX circuit is highly selective, achieving 98–99% product purity.
• Stage 5: Precipitation, Drying, and Packaging: The stripped uranium solution is precipitated with ammonia in agitated tanks, forming solid uranium particles. The slurry is then thickened in a two-stage circuit, re-dissolved with wash water, and reprecipitated with ammonia. The final slurry is dewatered in a centrifuge and dried in a multiple hearth dryer at approximately 1,400°F. The resulting uranium oxide (U3O8) concentrate assays +95% (typically 97%) and is stored in a hopper before being packaged in 55-gallon drums, labeled, and readied for shipment.

Additional Interesting Data and Summary

Beyond the core process stages, the White Mesa Mill incorporates several additional technical and operational features critical to the overall uranium recovery campaign. The mill’s solvent extraction circuit is noted for its high selectivity, achieving yellowcake purity of 98–99% even when processing ores containing vanadium, arsenic, selenium, and copper—elements that challenge other recovery methods. A vanadium recovery circuit exists on site but is not anticipated to be used for Pinyon Plain ore due to low vanadium content, ensuring process efficiency. The tailings management system utilizes lined cells where sand solids settle, and solutions are reclaimed and recycled back into the milling process, reducing fresh water demand and minimizing environmental impact. Historical throughput exceeding five million tons of ore demonstrates the mill’s operational maturity. From an economic perspective, the toll milling agreement allows Energy Fuels to leverage existing infrastructure without additional capital for a dedicated mill, improving project economics. The Pinyon Plain Mine operation is expected to supply ore at 500 stpd, with principal design criteria finalized after additional metallurgical testing of the uranium SX process. The 95% recovery rate combined with a product assay of 97% U3O8 supports strong revenue generation given current uranium market conditions. Environmental considerations include radiation scanning of outgoing trucks, contained washing areas, and permanent disposal of tailings in engineered cells. Sustainability initiatives include recycling of tailings pond solutions as wash liquid in the CCD circuit, reducing water consumption. The facility’s campaign-based operation allows flexibility to process alternate feed materials when economically justified. Looking forward, the White Mesa Mill is positioned to continue serving Energy Fuels’ portfolio of uranium mines, including the Pinyon Plain Project, with potential to expand throughput as market conditions warrant. The proven flowsheet and high-purity product output underscore the mill’s role as a strategic asset in domestic uranium production. Further metallurgical test work during the detailed design phase will optimize leach conditions, reagent consumptions, and SX parameters to ensure maximum recovery and cost efficiency over the projected mine life.

Key Processes: SAG Mill

Target Commodities: Uranium