Geological setting South-central Kazakhstan geology is comprised of a large relatively flat basin of Cretaceous to Quaternary age continental clastic sedimentary rocks. The Chu-Sarysu basin extends for more than 1,000 kilometres from the foothills of the Tien Shan Mountains located on the south and southeast sides of the basin, and merges into the flats of the Aral Sea depression to the northwest. The basin is up to 250 kilometres wide, bordered by the Karatau Mountains on the southwest and the Kazakh Uplands on the northeast. The basin is composed of gently dipping to nearly flat-lying fluvial-derived unconsolidated sediments composed of inter-bedded sand, silt and local clay horizons. The Cretaceous and Paleogene sediments contain several stacked and relatively continuous, sinuous “roll-fronts” or oxidation reduction (redox) fronts hosted in the more porous and permeable sand and silt units. Several uranium deposits and active uranium ISR mines are located at these regional oxidation roll-fronts, developed along a regional system of superimposed mineralization fronts. The overall stratigraphic horizon of interest in the basin is approximately 200 to 250 metres in vertical section. The Inkai deposit is one of these roll-front deposits. It is hosted within the Lower and Middle Inkuduk horizons and Mynkuduk horizon which comprise fine, medium, and coarse-grained sands, gravels and clays. The redox boundary can be readily recognised in core by a distinct colour change from grey and greenish-grey on the reduced side to light-grey with yellowish stains on the oxidized side, stemming from the oxidation of pyrite to limonite. The sands have high horizontal hydraulic conductivities. Hydrogeological parameters of the deposit play a key role in ISR mining. Studies and mining results indicate Inkai has favourable hydrogeological conditions for ISR mining. Mineralization Mineralization in the Middle Inkuduk horizon occurs in the central, western, and northern parts of the MA Area. The overall strike length is approximately 35 kilometres. Width in plan view ranges from 40 to 1,600 metres and averages 350 metres. The depth ranges from 262 to 380 metres, averaging 314 metres. Mineralization in the Lower Inkuduk horizon occurs in the southern, eastern, and northern parts of the MA Area. The overall strike length is approximately 40 kilometres. Width in plan view ranges from 40 to 600 metres and averages 250 metres. The depth ranges from 317 to 447 metres, averaging 382 metres. Mineralization in the Mynkuduk horizon stretches from south to north in the eastern part of the MA Area. The overall strike length is approximately 40 kilometres. Width in plan view ranges from 40 to 350 metres and averages 200 metres. The depth ranges from 350 to 528 metres, averaging 390 metres. Mineralization comprises sooty pitchblende (85%) and coffinite (15%). The pitchblende occurs as micron- sized globules and spherical aggregates, while the coffinite forms tiny crystals. Both uranium minerals occur in pores on interstitial materials such as clay minerals, as films around and in cracks within sand grains, and as replacements of rare organic matter, and are commonly associated with pyrite. Deposit type The Inkai uranium deposit is a roll-front type deposit. Roll-front deposits are a common example of stratiform deposits that form within permeable sandstones in localized reduced environments. The Cretaceous and Paleogene sediments contain several stacked and relatively continuous, sinuous “roll-fronts”, or redox fronts hosted in the more porous and permeable sand and silt units. Microcrystalline uraninite and coffinite are deposited during diagenesis by ground water, in a crescent-shaped lens that cuts across bedding and forms at the interface between oxidized and reduced ground. Sandstone host rocks are medium to coarse grained were highly permeable at the time of mineralization. There are several uranium deposits and active ISR uranium mines at these regional oxidation roll-fronts, developed along a regional system of superimposed mineralization fronts.

Mining at Inkai is based upon a conventional and well-established ISR process. ISR mining of uranium is defined by the IAEA as:

“The extraction of ore from a host sandstone by chemical solutions and the recovery of uranium at the surface. ISR extraction is conducted by injecting a suitable leach solution into the ore zone below the water table; oxidizing, complexing and mobilizing the uranium; recovering the pregnant solutions through production wells; and finally, pumping the uranium bearing solution to the surface for further processing.”

ISR mining at Inkai is comprised of the following components to produce a uranium-bearing lixiviant (an aqueous solution which includes sulphuric acid), which goes to settling ponds and then to the processing plants for production as yellowcake:

• Determination of the GT (grade x thickness) cut-off for the initial design and the operating period. The design sets a lower limit to the pounds per pattern required to warrant installation of a pattern before funds are committed, and the operating cut-off applies to individual producer wells and dictates the lower limit of operation once a well has entered production.

• Preparation of a production sequence, which will deliver the uranium-bearing lixiviant to meet production requirements, considering the rate of uranium recovery, lixiviant uranium head grades, and wellfield flow rates.

• Wellfield development practices, using an optimal pattern design, distribute barren lixiviant to the wellfield injectors, and then collect lixiviant, which carries the dissolved uranium, back to the MPP, Sat1 or Sat2, as the case may be.

The above factors are used to estimate the number of operating wellfields, wellfield patterns and wellfield houses over the production life. They also determine the unit cost of each of the mining components required to achieve the production schedule, including drilling, wellfield installation and wellfield operation.

There is ongoing wellfield development to support the current production plan.

There are three processing facilities on the MA Area: the Main Processing Plant (MPP) and two satellite plants, Sat1 and Sat2. The existing MPP, Sat1 and Sat2 circuit capacities were estimated using Inkai daily process summaries, which were subsequently demonstrated since 2019 by actual annual production. The MPP has an ion exchange (IX) capacity of 2.7 million pounds U3O8 per year and a product drying and packaging capacity of 8.3 million pounds U3O8 per year. Sat1 and Sat2 have respective IX capacities of 6.0 and 2.3 million pounds U3O8 per year.

Collectively the MPP, Sat1 and Sat2 have the capacity to produce about 8.3 million pounds U3O8 per year depending on the grade of the production solution. Construction work for a process expansion of the Inkai circuit to 10.4 million pounds U3O8 per year is in progress. The expansion project includes an upgrade to the yellowcake filtration and packaging units and the addition of a pre-dryer and calciner.

The process consists of the following major steps:
• uranium in-situ leaching with a lixiviant;
• uranium adsorption from solution with IX resin;
• elution of uranium from resin with ammonium nitrate;
• precipitation of uranium as yellowcake with hydrogen peroxide and ammonia;
• yellowcake thickening, dewatering, and drying;
• packaging of dry yellowcake product in containers.

Ion exchange resin adsorption (loading).
Wellfield acid solution, containing the leached uranium (pregnant solution), is pumped from the selected wellfield(s) via pipelines to a settling pond and then to the IX circuits for adsorption of the contained uranium. The use of IX for recovery of uranium from leach solutions is based on the existence of uranyl sulphate complexes. The uranyl sulphate anions are selectively adsorbed onto solid synthetic IX resin beads with fixed ionic sites. The resin bed is retained in IX vessels where resin is contacted with pregnant solution.

Once the resin in an IX column is fully loaded with uranium, the column is isolated from the continuous IX circuit and the resin is retained for elution or transferred with push water to an elution vessel. In the case of the MPP, the pregnant solution can be directed to one of the adsorption column trains. Each train is capable of performing resin adsorption and then operated in the desired mode of elution. In the case of Sat1, the pregnant solution reports to either an adsorption column train or a semi-batch adsorption column. In the case of Sat2, pregnant solution reports to a semi-batch adsorption column.

Resin elution (stripping).
In the elution process, uranium that has been adsorbed onto the IX resin during the adsorption cycle (loaded resin) is desorbed from the resin using ammonium nitrate. The eluate produced from this step is stored in pregnant eluate tanks.

At the MPP and Sat1, loaded resin can either be retained in the vessel for elution or hydraulically conveyed to a vessel specifically designed for elution within the circuit. Loaded resin can also be transferred between the two plants for elution based on available elution capacity. At Sat2, loaded resin is hydraulically transferred from the adsorption vessel to an elution vessel for elution.

Denitrification.
After the uranium has been stripped from the resin in the elution process, the adsorption sites on the resin are initially left in a nitrate form. The adsorption sites on the resin must be denitrified and converted to a sulphate form for re-use in the IX circuit. Denitrification is accomplished by contacting the resin with a solution of sulphuric acid and process water in a denitrification vessel. Each plant has a denitrification vessel to complete this step.

Precipitation.
Eluate from Sat1 and Sat2 is transported to and stored with the MPP eluate before the eluate is directed to the precipitation circuit. Hydrogen peroxide is added to the precipitation tanks to induce precipitation. The pH of this stream is adjusted in the precipitation tank by the addition of anhydrous ammonia.

The precipitation tanks are operated in a cascade configuration to allow the required retention time for the precipitation reaction to proceed to completion. The final yellowcake slurry is discharged from the last tank in the series and pumped into a thickener.

Yellowcake product thickening.
The precipitated slurry from the precipitation circuit flows into a thickener. The contained yellowcake slurry is thickened and is pumped to filter presses.

Filter press operation.
The yellowcake slurry from the yellowcake thickener underflow reports to the filter presses. The slurry is first washed and then dewatered in the filter presses.

Drying.
The dewatered yellowcake from the filter press is then pumped into rotary vacuum dryers where the yellowcake product is produced.

The vacuum dryers are totally enclosed during the drying cycle to assure zero emissions. The off-gases and steam generated during the drying cycle are filtered and condensed to collect entrained particulates and moisture within the process system.

Packaging.
Once the dryer contents have cooled, a measured amount of dried yellowcake is transferred through a rotary valve to a drum. The drums are collected into lots before being shipped.

- subscription is required.