The sandstone-type roll-front deposits located in the southern part of the Powder River Basin in Wyoming host the Smith Ranch–Highland facility.

The U ore deposits at the Smith Ranch–Highland location were derived from the weathering of granitic source rocks located along the southern margin of the Powder River Basin and from the alteration and leaching of granitic sediments and late Tertiary volcanic ashes deposited within the basin consistent with the origin of the arkosic sandstone host rocks. The absence of mafic minerals within the arkosic sandstone confirms that the sediments were derived primarily from granitic rocks. U was presumably mobilized by oxygenated and carbonated waters and appears to have been immobilized when it encountered reducing conditions within or near carbonaceous matter and pyrite, which are commonly present at variable amounts within the arkosic sandstone. The primary and secondary mineral assemblages suggest that the shallow burial diagenetic processes were not intense, consistent with the insignificant alteration of the detrital minerals and the lack of cementation within the matrix of the host rocks, thus allowing fluids to readily flow during the formation of the roll-front deposits.

In situ recovery (ISR) involves the use of a leaching solution, called a lixiviant, to extract the uranium from the geologic formation in which it occurs, without physically removing the ore-bearing strata. For uranium ISR, the lixiviant typically consists of native groundwater to which an oxidant (typically oxygen or hydrogen peroxide) and a complexing agent (typically sodium bicarbonate and/or carbon dioxide) have been added. ISR is accomplished by injecting the lixiviant through injection wells and circulating it through the ore-bearing strata, where the uranium is mobilized and placed into solution with the lixiviant. The resultant uranium-bearing solution is extracted from the ground via adjacent production wells. The uranium laden groundwater is then routed via underground pipelines to a surface ion exchange (IX) facility.

The most significant aspects of lixiviant compatibility are clay mineralogy and chemical compatibility. The clay mineralogy at Smith Ranch is predominantly kaolinite. This clay mineral is compatible with an ISR operation in that it will not swell and by so doing damage formation permeability, nor is it aggressive in cation exchange processes, which could adversely alter the water chemistry. Chemical compatibility of the formation mineralogy with the ISR process is important. Elevated calcium, sodium and sulfate concentrations, which often occur during ISR can result in the precipitation of calcite or gypsum in the ore sand and reduced formation permeability. Operating experience has shown that the lixiviant in use at Smith Ranch is chemically compatible with the major constituents that could cause formation damage or loss of formation permeability. The amenability of the North Butte orebody to ISR is assured by the similarity of this ore deposit to those located in the surrounding area.

Cameco operates Smith Ranch and Highland as a combined operation. Each has its own processing facility, but the Smith Ranch central plant currently processes all the uranium, including uranium from satellite facilities. The Highland plant is currently idle.

The uranium-bearing solution pumped from a mine unit is piped to the Central Process Plant (CPP) or satellites for extraction of the uranium by use of down flow ion exchange (IX) columns to remove the uranium. As the solution passes through the resin in the IX column, the uranium is preferentially removed from the solution by attachment to the resin.

Once the resin in a column is sufficiently loaded with uranium, the vessel is isolated from the normal process flow and the resin is removed from the column for elution. In the elution process, the resin is contacted with a strong sodium chloride solution, which displaces the uranium and regenerates the resin in a process very similar to regenerating a conventional home water softener. The eluted resin is then placed back in service for additional uranium recovery. The uranium rich fluid (rich eluate) is pumped to the precipitation circuit for further processing.

The barren solution leaving the IX units normally contains less than 2 mg/L (ppm) of uranium. After the barren solution leaves the IX columns, a small bleed, or purge, (averaging 0.5 to 1.5% of the total flow) is removed and sent to the waste water treatment and disposal system. This ensures that there will always be a net cone of depression within the mine unit, thereby reducing the chance of excursions. The remainder of the barren solution is refortified with carbon dioxide and/or carbonate/bicarbonate as necessary to return the carbonate/bicarbonate concentration to the desired operating level. The solution is then pumped back to the mine unit, with the oxidant (02 gas and/or H202) added either as it leaves the CPP or satellite, or just before the solution is re-injected into the production zone.

A chloride brine and soda ash solution is used to remove the uranium from the resin. The rich eluate containing the uranium is pumped to tankage in front of the precipitation circuit for temporary storage. To initiate the precipitation cycle, hydrochloric or sulfuric acid is added to the uranium bearing solution to break down the uranyl carbonate present in the solution. It is then transferred to the precipitation circuit and hydrogen peroxide is then added to the acidified eluate to effect precipitation of the uranium as uranyl peroxide. The addition of hydrogen peroxide reduces the pH of the solution. To optimize crystal growth and settling, a base (e.g., sodium hydroxide or ammonia) is added as a pH adjustment.

The uranium depleted eluate or supernate solution is removed and stored for re-use in future elutions or for disposal. Sodium chloride and sodium carbonate are added to the recycled eluate, as needed, for refortification. Storage tanks and/or lined storage ponds are used to collect and store excess process waters from this circuit, such as the excess spent eluate, prior to disposal via deep well injection.

The resulting slurry from the elution/precipitation circuit is transferred to a thickener allowing the uranium to precipitate for maximum crystal growth and consolidation by gravity. The yellowcake slurry is dewatered as it settles and the eluate is decanted by a weir and transferred back to the elution circuit or sent to the waste water treatment and disposal system. The yellowcake slurry is routed to a filter press for washing to remove soluble contaminates followed by de-watering prior to drying. The yellowcake is dried using a rotary vacuum dryer and packaged in 208 Liters (55 gallons) steel drums for storage and shipment. With this type of dryer, the off-gases generated during drying are filtered to remove entrained particulates. The sealed vacuum system provides ventilation while the dryer is being loaded and unloaded into drums. This type of dryer eliminates airborne effluents. An enclosed, secured storage room adjacent to the yellowcake drying area, is provided for the storage of drummed yellowcake prior to shipment.