The Nichols Ranch Unit processing plant currently operates only the recovery/extraction circuit, with loaded resin trucked to Cameco Resources' Smith Ranch-Highland facility for elution and yellowcake production under a toll resin processing agreement.
Report context
The Nichols Ranch Unit technical report describes a licensed in situ uranium recovery processing plant designed with three major solution circuits: the recovery/extraction circuit, the elution circuit, and a yellowcake slurry production circuit. At the time of reporting, the plant was constructed and operated with only the first solution circuit installed. Uranerz maintained a "Processing Agreement for Uranium Concentrates" (toll resin processing agreement) with Power Resources Inc., d/b/a Cameco Resources, a wholly owned subsidiary of Cameco Corporation, allowing processing of solutions for the second and third circuits at Cameco Resources' Smith Ranch-Highland facility. The toll resin processing was performed on a fixed unit cost basis, adjusted by inflation as measured using CPI.
Processing route
Recovery/extraction circuit
The recovery/extraction circuit includes the flow of lixiviant from the wellfield to the sand filters, or directly to the ion exchange columns and back to the wellfield. Uranium liberated underground is extracted in the ion exchange system of the process plant. A bleed from the circuit is permanently removed from the lixiviant flow to create a "cone of depression" in the wellfield's static water level and ensure that the lixiviant is contained by the inward movement of groundwater within the designated recovery area. The bleed is disposed of by injection into Class I – Non Hazardous approved deep disposal wells. The volume of the concentrated bleed is approximately 0.5% to 1.5% of the circulating lixiviant flow for the Nichols Ranch Unit and projected to be 2.5% to 3.5% for the Hank Unit.
Toll resin processing
Under the toll resin processing agreement with Cameco Resources, loaded ion exchange resin is removed from the ion exchange columns at the Nichols Ranch Unit processing facility and transferred by truck transport to the Smith Ranch-Highland processing facility. There, the resin is eluted to remove the uranium until it is completely stripped. The barren ion exchange resin is returned to the Nichols Ranch Unit processing facility where it is reused in the ion exchange system. This process is repeated as resin is cycled between the ion exchange system at the Nichols Ranch Unit and the elution circuit at Smith Ranch-Highland.
Elution circuit
At the Smith Ranch-Highland facility, and as planned at the Nichols Ranch Unit, the elution circuit is designed to release uranium from loaded ion exchange resin by applying an aqueous solution of salt and sodium carbonate or sodium bicarbonate. The uranium concentration in the eluate will be built up at a controlled concentration range of between 20 to 40 grams per liter. This uranium-rich eluate is ready for the de-carbonation process that occurs in the uranium precipitation circuit.
The planned elution circuit at the Nichols Ranch Unit would be designed to also accept and elute uranium loaded resin from other satellite operations. A DOT approved trailer would be used to transport resin to and from either Cameco Resources' Smith Ranch-Highland facility or Uranerz's own satellite facilities. The resin would be hydraulically removed from the trailer and screened to remove formation sand and other debris. Once screened, the resin would flow by gravity into a dedicated elution vessel where it would be contacted with eluant.
The elution process reverses the loading reactions for the ion exchange resin and strips the uranium from the resin. The eluant will be an aqueous solution containing salt and sodium carbonate and/or sodium bicarbonate. The chemical reactions are listed as:
R [UO₂(CO₃)₂] = [UO₂(CO₃)₂]²⁻ + R²⁺
R₂[UO₂(CO₃)₃] = [UO₂(CO₃)₃]⁴⁻ + 2R²⁺
Yellowcake production
The yellowcake production circuit starts when the eluate is treated with acid to destroy the carbonate portion of the dissolved uranium complex. In addition to adding the acid slowly, a common defoamer may be used to reduce the foaming activity. The precipitation reagents, hydrogen peroxide and sodium hydroxide, or ammonia are added to the eluate to precipitate uranium yellowcake. The yellowcake slurry is then filtered, washed, dried, and drummed.
The eluate from the elution circuit will be de-carbonated by lowering the pH below 2 with acid. Yellowcake will be precipitated with hydrogen peroxide and a base such as sodium hydroxide or ammonia. The chemical reactions are listed:
De-carbonation: [UO₂(CO₃)₂]²⁻ + 4H⁺ = UO₂²⁺ + 2CO₂ + 2H₂O
[UO₂(CO₃)₃]⁴⁻ + 6H⁺ = UO₂²⁺ + 3CO₂ + 3H₂O
Precipitation: UO₂²⁺ + H₂O₂ + 4H₂O = UO₄·4H₂O + 2H⁺
The precipitated yellowcake slurry will be transferred to a filter where excess liquid will be removed. Following a fresh water wash step that flushes dissolved chlorides, the resulting product cake will be transferred to the yellowcake dryer which further reduces the moisture content, yielding the final dried free flowing product.
The yellowcake dryer will operate under a vacuum. Vacuum conditions lower the temperature at which the yellowcake solids are dried, typically 165 °F to 190 °F. At these temperatures, water soluble uranium oxides and other compounds are not formed. In addition, the vacuum draws solids and water vapor toward the system's interior, preventing unwanted dust releases. This type of dryer is the same design that has been successfully used at Cameco Resources' Smith Ranch-Highland processing facility located in the southern Powder River Basin.
A bleed from the elution and yellowcake precipitation circuits is used to control the concentration of undesirable ions such as sulfates. The chemical strength is refortified during each cycle.
Flow and material balance
The ion exchange system for the Nichols Ranch Unit is designed to accommodate flow rates up to 3,500 GPM. In order to contain the lixiviant within the designated wellfield recovery area, a small portion of the barren solution is withdrawn from the ion exchange circuit. The amount of bleed is estimated to be in the average range of 1% of the overall flow rate or equivalent to about 35 GPM.
As planned, the Hank Unit will be constructed and operated as an adjacent property to the Nichols Ranch Unit and will feed the processing facility directly through a pipeline network. However, as an option and licensed, the ion exchange system for the Hank Unit is designed for flow rates up to 2,500 GPM. The average bleed rate for Hank Unit is estimated to be 3% or equivalent to about 75 GPM.
The bleed solution is to be used to rinse and clean up freshly eluted resin, make-up fresh eluant in the elution circuit, back wash sand filters, and wash yellowcake if necessary. A flow and material balance for the Nichols Ranch Unit processing facility is presented nominally in Figure 17.1. The flow shown is an example capacity for the facilities and does not represent any design or regulatory limits.
Sources of plant liquid effluents and disposal methods
Liquid effluents are expected to be generated from well development water, pumping test water, process bleed, process solutions, wash-down water, and restoration water. The water generated during well development and pumping tests is expected to satisfy WDEQ-WQD Class IV groundwater standards at a minimum and has minimal potential radiological impact on soils or surface water.
The process bleed and wash-down water will be transferred to a deep disposal well. This deep disposal well has been constructed and operated in a manner similar to other operating deep disposal wells at similar in situ uranium recovery sites. Uranerz has permitted four and constructed two deep disposal wells at the Nichols Ranch Unit, and has permitted four disposal wells and constructed none at the Hank Unit. These deep disposal wells have been permitted through the WDEQ and operated according to permit requirements. All of the deep disposal wells have also received an aquifer exemption from the US Environmental Protection Agency (EPA) that is included with the UIC Class I – Non Hazardous permit issued by the WDEQ. The Jane Dough Unit will not require additional disposal wells since it will be operated directly through the CPP at the Nichols Ranch Unit and will be able to use the existing disposal well capacity.
The restoration water will be treated by reverse osmosis or other purification technology. The treated restoration water will be re-injected into the process with the restoration water bleed transferred to the deep disposal well.
Currently, Uranerz operates two Type I – Non Hazardous deep disposal wells. As required, the disposal wells have been completed in approved formations.
Key reported parameters
| Parameter | Value | Basis |
|---|---|---|
| Nichols Ranch ion exchange design flow | up to 3,500 GPM | Design |
| Nichols Ranch average bleed | ~1% of overall flow (~35 GPM) | Estimate |
| Hank Unit ion exchange design flow | up to 2,500 GPM | Licensed option design |
| Hank Unit average bleed | ~3% (~75 GPM) | Estimate |
| Nichols Ranch bleed volume | 0.5% to 1.5% of circulating lixiviant flow | Reported range |
| Hank Unit projected bleed volume | 2.5% to 3.5% of circulating lixiviant flow | Projected range |
| Eluate uranium concentration | 20 to 40 grams per liter | Planned controlled range |
| De-carbonation pH | below 2 | Design |
| Yellowcake dryer temperature | 165 °F to 190 °F | Typical operating range |
| Disposal wells permitted/constructed at Nichols Ranch | 4 permitted, 2 constructed | Reported status |
| Disposal wells permitted/constructed at Hank Unit | 4 permitted, 0 constructed | Reported status |
Project website: https://www.federalregister.gov/documents/2015/07/28/2015-18463/uranerz-energy-corporation-nichols-ranch-isr-project
Technical qualifications
The report describes the Nichols Ranch Unit processing plant as licensed and designed for three major solution circuits, with only the recovery/extraction circuit currently constructed and operated. The elution and yellowcake production circuits at Nichols Ranch are described as planned future construction. The elution process currently occurs at Cameco Resources' Smith Ranch-Highland facility under a toll resin processing agreement on a fixed unit cost basis adjusted by inflation.
Performance data for the elution circuit and yellowcake dryer at the Nichols Ranch Unit are not provided, as those circuits were not yet installed at the time of reporting. The report notes that the vacuum dryer design is "the same design that has been successfully used at Cameco Resource's Smith Ranch-Highland processing facility." The flow and material balance presented in Figure 17.1 is described as an example capacity and "does not represent any design or regulatory limits."
Source: Nichols Ranch Unit , Technical Report, Recovery Methods section (pages 76-81 of 105).
