|The Smith Ranch Uranium Project|
|R. Mark Stout & Dennis E. Stover|
The Smith Ranch in situ leach (ISL) uranium production facility is located in Converse County, Wyoming, USA. It is slated to become the largest alkaline ISL operation in the world.
Early History of Smith Ranch
The Smith Ranch was founded in 1897 and originally comprised 65 hectares (160 acres). It has grown from its original size to over 30 000 hectares (75 000 acres) today. Thus far there have been five generations of Smiths carrying on the sheep and cattle ranching family business.
It was not until the 1960s that uranium was discovered on the Smith Ranch. In October 1966 a major programme to test for uranium ore was launched by Kerr-McGee Corporation. Over the next three years Kerr-McGee acquired over 200 000 hectares (500 000 acres) of mineral rights. By early 1972 the company had estimated ore reserves in excess of 21 million pounds U3O8 (8080 tU). In September 1972 construction began on the Bill Smith mine shaft. By early 1977 the mine shaft was completed and underground development started at the Bill Smith mine.
In 1976, long term sales agreements with Public Service Electric and Gas of New Jersey (PSE&G) and Philadelphia Electric Company (PECO) were signed. These agreements assured PSE&G and PECO a long term supply of uranium in exchange for funding advance payments for developing the property. The development plan called for three underground mines, at least two surface mines, and a 4000 t/day mill.
Some uranium production, incidental to the development work, occurred in 1977 and early 1978. But in June 1978 the mine was placed on standby for three years and construction of the mill indefinitely deferred. The decision was made after concluding that geologic conditions made underground mining very difficult. The sands were so porous that formation stability was a major concern, as was heaving of the shale zones. Ironically, the same conditions that made underground mining problematic are those which make this area ideally suited to ISL recovery. The underground mine, as it turned out, never recommenced operations.
About this time, Kerr-McGee began to consider Smith Ranch as a possible ISL project, and initiated laboratory scale testing and implementation of two field pilot programmes (see Table 1).
In 1981, an ISL pilot operation began in the "Q sand" area of Section 36 of the site. The Q sand test operated from October 1981 through November 1984. Almost three years after the start of the Q sand pilot a second pilot operation in the "O sand" area of Section 26 began. This test operation ran until January 1991. These two successful pilot programmes, along with laboratory scale tests, demonstrated the amenability of the main Smith Ranch ore deposits to a mild alkaline lixiviate.
The Q sand well pattern size averaged about 30 m by 30 m, and achieved a recovery rate of 58% of in-place reserves. Average ore depth was 152 m. The O sand pilot achieved a recovery rate of 93% of in-place reserves utilising an average well-field pattern size of 36 m by 36 m. Average ore depth was 229 m. The average uranium concentration for the Q test was around 90 mg/l while the O test averaged about 70 mg/l over its life.
Despite the success of these pilot operations, Kerr-McGee made the decision to sell its uranium assets in 1988. In January 1989, Rio Algom Mining Corporation (RAMC) acquired all Kerr-McGees United States uranium holdings, including the Smith Ranch properties. Rio Algoms original plan for Smith Ranch called for a plant designed to produce 2 million pounds of U3O8 (770 tU) per year starting in 1991. However, by late 1989, uranium prices had dropped significantly to around US$9/lb U3O8, forcing RAMC to slow development of the project. Start-up was deferred to 1992. The production rate was to be gradually increased, to reach the 2 million pounds U3O8 design capacity by 1995.
During 1990, emphasis was placed on acquiring key mineral properties around the Smith Ranch area. In 1991 the priorities shifted to delineation drilling of known trends within the existing properties. In late 1992 the development schedule was shifted back again as market conditions remained depressed. Basically, only limited drilling and a continuation of site preparation activities were ongoing in 1993 and 1994.
In late 1994 the outlook began to brighten. In October of that year RAMC participated in the first "matched sale" involving Russian origin uranium under the amendment to the Anti-dumping Suspension Agreement between Russia and the USA. Over the next few months RAMC concluded a number of short term matched sale transactions involving several major US nuclear utilities. During 1995 RAMC was successful in securing two long term matched sale contracts intended to provide a substantial portion of the initial baseload of sales for Smith Ranch.
Several additional long term sales agreements were obtained last year. Included in these contracts were the first matched sale contracts utilising uranium derived from high enriched uranium (HEU) formerly in Russian nuclear weapons. At present about 65% of the forecast Smith Ranch production for its first five years of operation is now committed under long term contracts. A significant portion of these commitments involve matched sales. The matched sales programme was vital to enable RAMC to proceed with development of Smith Ranch.
During January 1996 RAMC received approval from its board of directors for the investment of S$43.8 million in the Smith Ranch project. Pre-construction activities included preparation of a detailed project budget, the development of an initial staffing plan and the associated infrastructure, and bid requests for all major equipment. Actual construction started in April 1996 on the first ion exchange facility (IX-A), and in May 1996 the central processing plant (CPP) construction began. In May 1997 the IX-A facility was completed, and the CPP was completed in June with the exception of the yellowcake dryer. Commercial operations actually began on 20 June 1997, with the injection of oxygen and carbon dioxide into the first well-field. RAMC projects the first yellowcake shipment for 15 September 1997, and the start of the second ion exchange facility (IX-B) operations in March 1998. IX-B is a satellite facility which will increase production capacity from 1 million pounds to the full 2 million pounds U3O8 rate.
Overview of the Smith Ranch Project
and Geological Setting
A substantial portion of RAMCs mineral holdings are on federal lands. Possessory title to federal minerals are obtained through a process called "claim staking", first developed in the USA under the Mining Law of 1872. The basic tenets of the 1872 Mining Law remain in place. Until recently, a mining claim was maintained simply by performing a minimum specified amount of assessment work per claim each year. However, beginning in 1992 the assessment requirement was abandoned in favour of an annual maintenance fee of US$100 per claim (a claim is typically 8.1 hectares or 20 acres in size).
At present, there is no royalty due to the federal government on production from mining claims. There have been several attempts in the past few years in the US Congress to substantially modify mining laws. All of the recently proposed legislation has retained the maintenance fee system and provided for a new federal royalty on mining claims.
RAMC also controls several State of Wyoming uranium leases as well as a number of uranium leases with private parties owning uranium mineral rights in the area, primarily the Smith family. All the state and private leases provide for royalty payments once production commences.
RAMC has arbitrarily named the major sandstone and shale units within the permit area, as shown in Figure 2. Sandstone units from youngest to oldest are E, W, U, S, Q, O, M and K. Actual contact between the Fort Union and Wasatch formations is defined as the base of the School coal seam or the correlatable lignite zone present throughout the permit area. In general, the contact would be at the top of the W sandstone unit when present.
Resources in the permit area are primarily in the Paleocene-Fort Union formation, the O, M and K sandstone units in particular having significant leachable reserves. Lesser resources are contained within the E sandstone of the Eocene-Wasatch formation. Thickness of these sandstone units ranges from 3 to 60 m, with the O sandstone the thickest and most persistent.
The ore occurs as typical Wyoming roll fronts, generally north-facing C-shaped features. The sandstone units, depending upon thickness, interbedded shales and high lime zones, may contain between one and 20 mineral fronts, with the O sandstone unit being the most complex.
In addition, another 6 million pounds U3O8 (2300 tU) of reserves exist within shallow deposits at or slightly below the water table. A portion of these reserves is likely to be amenable to ISL mining. Future efforts will identify the precise size of this leachable portion.
Recoverable reserves totalled 22.9 million pounds U3O8 (8800 tU) at the time of acquisition. The increase now reported results primarily from discovery of additional reserves through subsequent drilling programmes by RAMC. The full potential of the property remains untested. Several areas of known mineralisation will be subjected to additional drilling in the future. We anticipate that the in situ resources will continue to increase as a result of such drilling. The northern portions of the project hold the greatest potential for discovery of additional uranium reserves.
The Smith Ranch Project area could ultimately be subdivided into three areas, each with the independent potential to be a 1 to 2 million pounds U3O8 per year production centre (see Figure 3).
Reynolds Ranch. A second portion of the property lies to the northeast of the Smith Ranch permit area, and is known as the Reynolds Ranch ISL project. The geology of the Reynolds Ranch area is very similar to that of Smith Ranch, in that the same mineralised sands within the upper unit of the Paleocene-Fort Union formation in the Smith Ranch area continue to the north into the Reynolds Ranch area. The majority of the known reserves to date appear to be localised in the intermediate sands such as the U, S and upper O sands areas, as opposed to the deeper O, M and K sands which host most of the Smith Ranch reserves. Deeper O sand mineralisation is known to be present within the Reynolds Ranch area and holds a considerable amount of potential.
Demonstrated (measured and indicated) reserves total approximately 8.2 million pounds U3O8 (3150 tU) for this area. A recent reserve study by an independent consultant found approximately 11.8 million pounds U3O8 (4500 tU), proven and probable, based on drilling to date, using a grade thickness (GT) outline approximation technique. Based upon this independent study, the present total mineral resources for the area amount to approximately 24.6 million pounds U3O8 (9460 tU).
The initial phase of the Reynolds Ranch development is an 18-month programme of exploration and delineation drilling combined with environmental baseline studies. We anticipate that the geological information gained from this programme will be sufficient to arrive at a decision regarding the scale of commercial development for this property. The baseline environmental studies will position RAMC to seek federal and state approvals to begin construction.
It is expected that a substantial increase in uranium resources will result from the programme, to more than 30 million pounds U3O8 (11 500 tU). Such a resource will support a facility similar to Smith Ranch. Construction could begin as early as 1999 if warranted by market conditions. This schedule would provide significant added production for RAMC in 2000 and beyond.
Northwest Unit. A third area to the northwest of Smith Ranch is an exploration target. Referred to as the Northwest Exploration Area, it consists primarily of lands acquired by RAMC in 1990 and 1991. On the whole it has been very sparsely drilled with demonstrated reserves of only 1.5 million pounds U3O8 (580 tU), yet it is known that numerous ore trends criss-cross the area. An adequate assessment of its full commercial potential will require a substantial long term drilling effort.
The project currently is in compliance with all regulatory licence/permit requirements.
Once an ore body is targeted for production, wells (12 to 15 cm in diameter) are installed in redetermined patterns. Over the course of their operational lives, these wells may be used to inject leaching fluids, to recover uranium rich solutions, and finally to restore the groundwater. These cased wells are carefully constructed and sealed so that the leaching solution does not escape or migrate to any other underground areas or aquifers. Uranium production from a set of wells typically lasts for only one to two years, followed by groundwater restoration. As a result, well-field planning and installation is an intense ongoing production activity throughout the project life.
Approximately fifteen such units will be required to develop the total project area. Two to three mining units may be in production at any one time, with additional units in various states of development and/or restoration. A mining unit will be dedicated to only one production zone and typically will have a flow rate in the range of 190 l/s. Aquifer restoration of a mining unit will begin as soon as practicable after mining in the unit is complete. If a mined-out unit is adjacent to another unit being mined, restoration of a portion of the unit may be deferred to minimise interference with the operating unit. The size and location of the mining units will be defined based on final delineation of the ore deposits, performance of the area and development requirements.
The well-field pattern will be the conventional five-spot pattern, which is a square with four injection wells at the corners and a centrally located recovery well. It will, however, be modified as necessary to fit the shape of the orebody. The cell dimensions will vary depending on the formation and the characteristics of each orebody. Spacing of injection wells will vary from 23 to 46 m apart. All wells will be constructed to serve as either injection or recovery wells. This permits flow directions to easily be changed to maximise uranium recovery and to optimise groundwater restoration.
Maximum well spacing (injector to injector) of a five-spot pattern has two effective limitations: the width of the ore body, and a hydrologic/geochemical bound of about 46 m. The first is an essential design element to avoid the deliberate flowing of lixiviate through unmineralised areas where gangue minerals can consume the leaching chemicals (oxygen) and diminish the process efficiency. The latter is a practical limitation beyond which it has proven difficult to provide sufficient oxygen and hydrologic control to sustain high uranium grades (concentrations) in the produced fluid.
In each mine unit more lixiviate will be produced than injected. This creates a localised hydrological cone of depression or pressure sink. This pressure gradient provides containment of the lixiviate by causing natural groundwater movement from the surrounding area toward the mine unit. It is expected that the over-production or bleed rates will be a nominal 0.5% of the production rate for the Q sand mining unit and a nominal 1.5% for the O sand mining unit.
Well Completion. Monitor, production and injection wells will be drilled to the top of the target completion interval with a truck mounted rotary drilling unit using native mud and a small amount of commercial viscosity control additive. The well will be cased and cemented to isolate the completion interval from all overlying aquifiers. The cement will be placed by pumping it down the casing and forcing it out of the bottom of the casing and back up the casing-drill hole annulus. The well casing will be Schedule 40 PVC which is available in 6 m joints. Typical casing will have 127 mm nominal diameter with a minimum wall thickness of 6.55 mm and a pressure rating of 1480 kPa. Figure 6 shows the well completion method.
Three casing centralisers located approximately 9, 27 and 46 m above the casing shoe are placed on the casing to ensure it is centred in the drill hole and that an effective cement seal results. The cement volume for each well is 110% of the calculated volume required to fill the annulus and return cement to the surface. The excess is to ensure that cement returns to the surface. Occasionally the drilling may result in a larger annulus volume than anticipated and cement may not return to the surface. In this situation the upper portion of the annulus will be cemented from the surface.
After the cement has cured, the plug is drilled out and the well completed. The well is then air lifted to remove any remaining drilling mud and cuttings. A small submersible pump is used for final clean up and sampling. If sand production or hole stability problems are expected, Johnson wire wrapped screen or a similar device may be installed across the completion interval.
Well Casing Integrity. After a well is completed but before it is operational, a mechanical integrity test (MIT) of the well casing will be conducted. In the MIT, the bottom of the casing adjacent to or below the confining layer is sealed with a downhole packer or other suitable device. The top of the casing is then sealed and a pressure gauge is installed inside the casing. The pressure in the sealed casing is increased to a minimum of 20% above the maximum anticipated operating pressure of 791 kPa. The well is closed, and all fittings are checked for leaks. After the pressure is stabilised, pressure readings are recorded at two minute intervals for ten minutes.
If a well casing does not meet the MIT, the casing will be repaired and retested. If a repaired well passes the MIT, it will be employed in its intended service. If a well defect occurs at depth, the well may be plugged back and recompleted for use in a shallower zone provided it passes a subsequent MIT. If an acceptable MIT cannot be obtained after repairs, the well will be plugged. A new well casing integrity test will be conducted after any well repair using a downhole drill bit or under-reaming tool.
Monitor wells will be drilled and constructed in the same manner as production and injection wells and all three types of wells must pass the MIT.
The processing facilities consist of two ion exchange (IX) plants and a central processing plant (CPP). The initial IX plant (IX-A) is located next to the CPP, while the second IX facility will be a satellite unit (IX-B). The leaching solution is circulated through the IX plant, where the uranium is extracted from the enriched leach solution using an ion exchange resin.
The IX facilities are equipped with resin loading and bleed treatment circuits. Each facility can process 190 l/s (3000 US gallons per minute) of lixiviate. Ion exchange resin is transferred by pipeline between IX-A and the CPP. Truck trailers will be used for IX-B transfer. The CPP elutes resin from both IX facilities. The precipitation, product filtering, drying and packaging circuits can process up to 5600 pounds U3O8 (2.15 tU) per day or 2 million pounds U3O8 (770 tU) per year.
Resin Loading. The resin loading circuit in each IX facility consists of six pressurised vessels, each containing 14.2 m³ of anionic ion exchange resin. These vessels are configured as three parallel trains for two-stage downflow loading. Booster pumps are located upstream and downstream of the trains.
As the uranium in solution enters the IX facility, the upstream booster pumps pressurise the fluid to 791 kPa. The dissolved uranium in the pregnant lixiviate is chemically absorbed onto ion exchange resin. Any sand or silt entrained in the pregnant lixiviate is trapped by the resin bed like a traditional sand filter. The barren lixiviate exiting the second stage will normally contain less than 2 mg/litre of uranium. This fluid will be pressurised to 791 kPa by booster pumps and returned to the well-field for re-injection.
The lixiviate is composed of native groundwater, carbon dioxide and oxygen. When the resin becomes saturated with uranium, it is removed from the circuit and transferred to the central plant. The barren leach fluid is refortified with carbon dioxide and oxygen and re-injected into the orebody to recover additional uranium. Because the leaching solution is continually recirculated, water consumption from this process is very small.
Bleed Treatment. The bleed fluid is treated to remove radium mobilised by the ISL mining process as well as residual uranium normally contained in the barren leach solution. Uranium removal is accomplished by additional ion exchange treatment in a single train of two-stage downflow vessels. Radium removal is effected with conventional barium/radium sulphate co-precipitation. A filter press removes the barium/radium sulphate precipitant.
Elution Circuit. When resin in a first stage IX vessel is loaded with uranium, the vessel is isolated from the normal process flow. The resin is transferred in 14.2 m³ lots to the CPP. At the CPP, the resin passes over vibrating screens with water to remove entrained silt particles and other fine trash. It is gravity fed into pressurised downflow elution vessels for uranium recovery and resin regeneration.
Using a three stage elution circuit, 170 m³ of eluate contact 14.2 m³ of resin to create 57 m³ per elution. The eluate is prepared by mixing quantities of saturated sodium chloride (salt) solution, saturated sodium carbonate (soda ash) solution, and water. The salt solution is generated in salt saturators (brine generators). Saturated soda ash solution is prepared by passing warm water (>41°C) through a bed of solid soda ash.
Precipitation Circuit. In the elution circuit, the uranyl dicarbonate ions are removed from the loaded resin and converted to uranyl tricarbonate by a small volume of strong sodium chloride/soda ash solution. The resulting rich eluate contains sufficient uranium for economic precipitation. Sulphuric acid is added to the rich eluate to break the uranyl carbonate complex, which liberates carbon dioxide and frees uranyl ions. The acidic, uranium rich fluid is pumped to agitated tanks where hydrogen peroxide is added in a continuous circuit to form an insoluble uranyl peroxide compound.
Ammonia is then added to raise the pH to near neutral for digestion. The uranium precipitate (slurry) gravity flows to a 11.6 m diameter thickener. The uranium depleted supernate solution overflows the thickener to surge tanks for disposal via a deep injection well.
Filtering, Drying and Packaging. After precipitation, the settled yellowcake is washed, filtered, dried and packaged in a controlled area. Washing removes excess chlorides and other soluble contaminants. Filtering and dewatering is done in a filter press. The filter cake is then moved to holding tanks located above the yellowcake dryers.
The yellowcake is dried in one of two low-temperature (less than 121°C) vacuum dryers, which are totally enclosed during the drying cycle. The off-gases generated during the drying cycle are filtered and scrubbed to remove entrained particulates. The water sealed vacuum pump also provides ventilation while the cake is loaded into drums. Compared to conventional high temperature drying by multihearth systems, this dryer has significantly lower airborne particulate emissions. By operating at low temperatures and under a vacuum, no measurable quantities of insoluble uranium solids are produced, further reducing environmental and occupational risks. This drying technology requires a high purity feed stock because operating temperatures are not sufficient to volatilise contaminates.
The dried yellowcake product is packaged in 208 litre (55 US gallon) steel drums for storage and shipment by truck to another licensed facility for further processing. All yellowcake shipments will be made in compliance with applicable regulations. The vacuum pump system is employed during packaging to minimise airborne particulate emissions.
Solid waste volumes will be nominal, in the range of 20 t per year. Radium bearing sludges and discarded ion exchange resin contain low level radioactivity and, hence, require disposal at NRC approved sites. Such wastes are disposed in the tailings structures at RAMCs Ambrosia Lake facilities near Grants, New Mexico.
To avoid the costs of pumping large volumes of water over long distances, RAMC will use satellite ion exchange facilities. These facilities will be assembled and used at various well-fields, recovering uranium there by means of the ion exchange resin. As portions of the resin from these units become loaded with uranium, the resin will be transported in tank trucks to the CPP for stripping. The stripped resin will then be washed and returned by truck to the satellite units for reuse.
By serving several satellite well-fields with one processing plant, it is possible for RAMC to mine isolated ore bodies that may not be individually sufficient to justify the construction of separate processing facilities.
Smith Ranch Operating Plan
The 2 million pounds U3O8 per year rate of production will be sustained until reserves are exhausted. The most recent geological studies place the recoverable resource above 26 million pounds U3O8 (10 000 tU) for the permitted areas. This would support full production through to 2010, giving a productive project life of 14 years.
generalised well-field development schedule and production plan
has been formulated based upon the following assumptions:
To ensure careful management of the start up of individual recovery wells, blocks of no more than 20 wells are started during any given month. New wells are being regularly added during the first nine operating months until full flow capacity is achieved.
The scheduled start up of wells may be adjusted either up or down to meet the production goal for a given month or year. The key is that these schedules serve as a guide to developing a cased well installation plan which ensures that sufficient wells are always available to meet the production goal. The installation plan in turn becomes the basis for budgeting drilling expenditures and guides the geologists in their ore delineation and well-field development efforts.
The feed concentration of uranium in waters entering the ion exchange plant is analogous to the head grade of ores in conventional mining. Grade control or feed concentration control is achieved in ISL mining by varying the number of wells in operation and their operating lives. The average concentration of a well or well-field is heightened by shortening its life. Conversely, the recovery of mineable uranium associated with the well is increased by extending the well life.
Thus, an inherent flexibility exists over any period of time or quantity of production to adjust well-field installation and operating costs. If well life is shortened, a higher feed grade and lower operating cost will follow, but at the expense of higher well-field investments. Similarly, the well life can be extended to increase uranium recoveries and to reduce well-field investments. This, however, leads to lower head grades and higher operating costs.
Production from Smith Ranch is planned to be about 400 000 pounds U3O8 (150 tU) in 1997, rising to 1.5 million pounds in 1998. By 1999 and beyond the full design capacity of 2 million pounds U3O8 (770 tU) is expected to be achieved.
Advantages of ISL Technology
There are at least six advantages of ISL technology over conventional techniques. First, a significantly smaller initial capital investment is required. Conventional operations require costly milling facilities, where the mined ore is physically crushed and ground to expose the uranium minerals. ISL operations do not require milling operations. Rather, the uranium is extracted by a selective chemical process which recovers the leachable mineral without the need for milling facilities, equipment and labour.
Second, the extensive front end capital and lead time required for underground shafts and related facilities are avoided. Similarly, surface mine development costs and lead times for overburden stripping are absent.
Third, ISL is an extremely labour-efficient mining method. RAMCs total workforce for the Smith Ranch project consists of less than 100 employees while annually producing 2 million pounds U3O8. This labour productivity compares favourably with the high grade open pit mines at Key Lake and Rabbit Lake in Saskatchewan.
Fourth, the flexibility of ISL mining allows for adjustments in the production rate to accommodate market conditions without severely impacting production costs. Fifth, unit costs at ISL production facilities are generally below US$15 per pound U3O8, placing these projects among the most competitive uranium projects in the world.
Finally, ISL mining is an environmentally sound technology that causes fewer disturbances, and consequently reduced liability. Further, the restoration of impaired groundwater and solid waste disposal are ongoing components of project planning, design and operation. This integrated approach helps RAMC ensure that the dual objectives of an environmentally sound, yet economically attractive, project are fulfilled.
Airborne dispersion modelling studies were conducted to evaluate the potential radionuclide exposures at and near the project. Radioactive particles emitted from the project are forecast to be less than 1% of their respective maximum permissible concentrations set by the NRC, and orders of magnitude below any known levels of finite risk.
To ensure effective and safe operation of Smith Ranch, a number of environmental monitoring programmes will be instituted. These include airborne emissions monitoring, pre-operational monitoring, operational well-field monitoring, pipeline monitoring, and liquid effluent monitoring.
The operational well-field monitoring programme is the most basic and the most practical means of avoiding environmental problems. Its primary purpose is to detect and correct any condition which could lead to the escape of leaching fluid from its proper designated areas. It is designed to monitor the pressure and movement of the leaching fluid during operation.
Two systems of monitor wells exist: horizontal wells, which detect any lateral movement of the leaching fluid near the ore body; and vertical wells, which detect any unwanted vertical movement of the leaching solution. The horizontal wells surround the entire well-field, at 125 to 150 m intervals. The vertical wells are positioned above and below the ore body within the well-field, with one well per every four acres of well-field. An illustration of the operational well-field monitoring programme is shown in Figure 5.
RAMC will carefully control the flow rates and pressures of all operating wells and interconnecting pipelines, while monitor wells will be regularly sampled to determine reservoir pressures and water quality. These data are used to maintain the proper production-injection balance for the mining unit, to confirm that injection pressure limits are not exceeded, and to assure that no unwanted fluid movements are occurring.
The Smith Ranch project will be a competitive and environmentally friendly source of uranium production for many years to come.
© copyright The Uranium Institute 1997 SYM9798