Langer Heinrich Uranium Project — 2024 Technical Report

The 2024 technical report details the established alkaline leach and ion exchange processing route for the Langer Heinrich Uranium Project, referencing design parameters, historical operating data from 2014 to 2018, and planned improvements for the restart.

Report context

This technical report, dated 2024, addresses the Langer Heinrich Uranium Project located in the Erongo Region, Republic of Namibia. The processing facility described employs a sodium carbonate leaching flowsheet with continuous and fixed-bed ion exchange, followed by precipitation to produce tri-uranium octoxide (U₃O₈). Although certain process, reagent and utility stream changes have been implemented for the Restart Project, the flowsheet does not deviate fundamentally from that operated until closure in 2018. In targeting increased throughput and improved efficiency, certain equipment has either been replaced with new equipment, modified or removed.

Processing route

Ore handling and feed preparation

The feed preparation area consists of two parallel circuits (Circuit 1 and Circuit 2), each comprising a run-of-mine (ROM) tip and primary jaw crushers feeding the scrubbing circuits. Trucks deliver ore from the pits to the blending stockpiles at the ROM pad adjacent to the process plant. Selective ore recovery from the stockpiles maintains a 500–600 ppm U₃O₈ equivalent feed. This recovery is made by front end loaders, which load trucks and dump the ore onto a grizzly over the primary jaw crusher’s feed bin. The grizzly is sized to restrict the feed size to the plant to less than 500 mm. The primary crushers reduce the ore to less than 130 mm, as required by the scrubbers.

Scrubbing and recycle crushing

The scrubbing area consists of two parallel circuits. Circuit 1 uses two pneumatic, tyre-driven scrubbers (Stage 1 and 2) in parallel, whilst Circuit 2 uses a larger single-girth gear-driven scrubber (Stage 3). The Stage 3 scrubber has the same capacity as the combined capacity of the Stage 1 and Stage 2 scrubbers. The purpose of the scrubbers is to remove the uranium-containing carnotite, which has been deposited on the outside of the calcrete agglomerates and other competent material in the ore. The rotating scrubber breaks down the calcrete that holds the agglomerates together and then liberates the uranium-bearing coating from the quartz pebbles and agglomerates. After scrubbing, screened oversize (+10 mm) is discharged to a recycle crushing circuit where it is screened at 45 mm. The +45 mm fraction is sent to the secondary crusher, and the -45 mm portion to the tertiary crusher. The -10 mm ore is transferred onto the scrubber feed conveyor while the plus 10 mm is conveyed back to the tertiary crusher for re-crushing. The -10 mm material is sent to the classification circuit.

Classification circuit

The classification circuit, consisting of cyclones and Hydrosort classifiers, separates the less than 500 μm material, which is uranium rich, from the greater than 500 μm material which is barren. All barren material (approximately 40% w/w of ROM feed) is sent to a barren material stockpile in the plant, from where it is removed as needed. The uranium-rich material is fed to the pre-leach thickener.

Leaching

The leach circuit consists of two pre-leach thickeners operating in parallel, two 4,000 m³ leach feed surge tanks, a 4-stage heat recovery unit and two leach modules that operate in parallel. Beneficiated -500 μm slurry material is pumped to one of two pre-leach thickeners, where it is thickened to an underflow density of up to 50% solids by mass with the assistance of flocculant. Thickener overflow is recycled back to the scrubbing process. The thickener underflow is pumped to surge tanks which decouple the classification circuit from the downstream slurry circuit. The surge tanks have a buffer capacity of approximately 12 hours. The slurry is then pumped to a conditioning tank where density adjustment is carried out, if required, using process solution.

The cold leach feed slurry is heated in a four-stage barometric heat transfer unit (flash splash) whilst simultaneously cooling the hot leach discharge. This process heats the cold leach feed to approximately 70°C and cools the leach discharge to approximately 45°C. The hot leach feed is split equally between the two leach trains. Leach Train 1 consists of six 1,800 m³ concrete tanks, and Leach Train 2 consists of two 3,600 m³ concrete and two 1,800 m³ steel tanks. Both trains cascade the leachate from one tank to the other in series. All leach tanks are fitted with agitators to ensure optimal slurry mixing. The sodium carbonate and sodium bicarbonate levels in both leach trains are continuously monitored and added if required to maintain the target of pH 10.4. Direct steam dosing is utilized in the first two tanks of each module to raise the temperature from 70°C to the targeted 90°C.

Counter current decantation

The CCD circuit consists of 11 thickeners arranged in series to achieve seven stages of washing and two clarifiers, which operate in parallel. The tailings system consists of a cluster of dewatering cyclones, a cyclone overflow thickener and an in-plant tailings pumping system. The CCD and tailings system serves to minimise soluble metal losses to the tailings storage facility (TSF) area by washing leached solids with wash liquor (barren solution) from the ion exchange plants and industrial water. Flocculant is dosed to each thickener to assist with solids settling. The clarifiers remove residual suspended solids and neutralise bicarbonate in the pregnant liquor solution before IX processing.

Fixed-bed ion exchange

The FBIX plant consists of two modules operating in parallel. Each module consists of 12 separate fixed bed ion exchange columns. The purpose of the FBIX plant is to concentrate the uranyl carbonate ion and to reject impurities, primarily vanadium. The FBIX sequence consists of lag, lead and elution. Pregnant liquor solution from the CCD circuit is stored in the PLS tank and then fed to the FBIX columns in the lead/lag loading mode through two distribution manifolds. Once the resin is fully loaded, it is eluted with sodium bicarbonate to strip the resin of uranium into a high-grade pregnant solution (concentrated eluate). After that, the columns are put back into an adsorption stage, and the process repeats itself.

The Stage 3 IX circuit comprises four NIMCIX fluidised bed columns, of which two are used for adsorption and two for elution. Production is prioritized through the NIMCIX plant, which has lower operating expenditure and higher recovery.

NIMCIX and bicarbonate recovery process

The NIMCIX plant consists of two modules operating in parallel. Each module comprises an adsorption and elution column, auxiliary tankage, and pumps. PLS feeds the adsorption columns and leaves as barren solution. Eluant solution feeds the elution columns and leaves as an eluate solution. The primary purpose of the NIMCIX plant is to concentrate the soluble uranium in the PLS. A secondary purpose is to separate impurities such as vanadium. The NIMCIX operation comprises several steps within the adsorption and elution sequence.

Concentrated eluate from both the NIMCIX and FBIX circuits contains sodium bicarbonate that is neutralised during the precipitation of sodium diuranate using sodium hydroxide (caustic soda) in the BRP. Sodium bicarbonate is used to elute the uranium from the IX resin. This process consumes approximately 30% of bicarbonate. The remaining 70% of bicarbonate is neutralised by adding caustic soda before the uranium precipitation. Approximately 25% of total operating costs for the Project are attributable to bicarbonate and caustic soda consumption.

In 2015, the BRP plant was commissioned to recover sodium bicarbonate between the IX elution and precipitation process steps. The BRP process uses membranes to separate the majority of the sodium bicarbonate, and this process is similar to a reverse osmosis plant. By recovering bicarbonate, fresh consumption is reduced by 68%. In addition, caustic soda consumption was reduced by 53%, as not as much is required anymore to neutralise the bicarbonate. Uranium recovery has increased by 2% due to the positive impact on site carbonate and the water balances. This technology has enabled LHU to lower operating costs by approximately 20%.

Precipitation and final product recovery

The concentrated eluate from the BRP plant is mixed with a caustic solution to increase the pH to over 12.8 in the sodium diuranate reactors in order to produce sodium diuranate (SDU) precipitate. The SDU slurry is thickened, and the barren SDU solution is recycled to enable recovery of the entrained reagents. The thickened SDU is then pumped to a wash tank to wash out entrained sodium carbonate and then pumped to a batch precipitation tank, where it is re-dissolved in sulphuric acid at a pH of 3.6. Once all SDU is dissolved, hydrogen peroxide is added at a controlled rate, together with sodium hydroxide, which causes the uranium to precipitate as UO₄·nH₂O. The use of hydrogen peroxide in the re-precipitation stage also reduces the precipitate’s vanadium content to a level necessary for all converters.

Drying and drumming

This is a batch process. Following centrifuging (three units, one operational and two standby), the solids are fed to an oil-heated dryer using an enclosed screw feeder. Drying takes place at about 300°C for one hour to drive off free and crystalline water. The dry powder (final uranium oxide product U₃O₈) is then packaged in drums, weighed and sealed in preparation for transportation. Final product specification is greater than 97% U₃O₈.

Tailings

The tailings are pumped to the TSF. Process solution is recovered from the TSF via a combination of decant barges and an underdrainage system. This achieves a water recovery of approximately 40% v/v.

Planned process improvement

Part of the LHU restart plan involves the debottlenecking of the beneficiation circuit and the downstream hydrometallurgical circuits. Elemental Engineering was engaged to evaluate various process improvement opportunities using process simulation. A SysCAD dynamic surge and availability model of the beneficiation circuit, leach, CCD and NIMCIX circuits were constructed to evaluate the impact of various scenarios on production throughput. Elemental Engineering highlighted the following key outcomes arising from their study:

• Beneficiation circuit throughput is constrained by various reliability and process issues, with the primary downtime factors being big rocks, chokes, water supply and equipment/electrical integrity.
• Reduction of downtime events and process upsets would enable plant ore throughput to be increased up to 5.5 Mt per annum.
• Installation of an 8,000 m³ leach feed surge tank would assist in increasing ore throughput.
• Analysis of mining pit data showed that Pits A, B, C, D and stockpiled material at MG3 negatively impact thickener densities as well as recoveries.
• The majority of poor recoveries observed was caused by soluble U₃O₈ losses to the tailings.
• Analysis of 2017 process data classified minor and major failures at the NIMCIX area. In order to maintain the required PLS throughput, the minor and major failure frequencies would need to be reduced by a factor of 3 with resin loading above 20 g/L.
• Installation of a PLS pond does not improve plant throughput.

Based on the results of the debottlenecking study, Elemental Engineering recommended the following actions:

• Improve equipment reliability at the beneficiation circuit by eliminating or reducing identified downtime events.
• Install a leach feed surge facility with a total volume of 8,000 m³.
• Maximise resin loading at the NIMCIX circuit to maintain desired PLS flow throughput.
• Increase thickener/CCD underflow densities by having a higher solids bed-inventory and an even distribution of thickener feed across parallel operating units.
• Increase equipment reliability at the NIMCIX continuous ion exchange circuit by reducing identified minor and major downtime events.
• Implement a downtime system to track and monitor equipment reliability performance at the hydrometallurgical plant.
• Re-evaluate the need for a PLS pond after the installation of the leach feed surge tank.
• Application of the constructed surge and availability model to evaluate commissioning and operating scenarios in more detail and to aid in the development of process control philosophy.

Lycopodium was commissioned by Paladin to recommend modifications to existing, and provision of new, plant and equipment to enable LHU to achieve the revised production targets. This was based on a new mine schedule with maximum plant capacity of 5.5 Mtpa. In July 2021, Lycopodium detailed their proposed modifications and new equipment requirements in their Restart Project Value Improvement Study. Key assumptions included overall utilization ROM to pre-leach thickener of 90% and overall utilization leach to product recovery of 95%. Paladin further expanded on availabilities and utilizations as follows: beneficiation availability 94%, beneficiation utilization 96%, overall beneficiation run time 90%, and overall hydrometallurgical run time 95%.

The restart project includes several process upgrades which aim to debottleneck throughput rates, improve runtime and process recovery. Those upgrades associated with improved recovery include: upgrade of primary cyclone clusters; addition of a second Hydrosort unit (teeter bed); upgrade of thickener feed wells and feed dilution systems to improve solids settling and underflow densities; addition of leach feed surge tanks to improve downstream process stability and control; upgrade of tailings dewatering system to improve soluble loss and reduce water loss to the TSF; and addition of a UO₄ thickener to reduce recycling of metal to the front end of the process.

Key reported parameters

Technical qualifications

The following limitations apply to the data and projections presented in this report. Run of mine feed tonnage ranged between 250 kt and 350 kt per month from July 2014 to March 2018. Overall uranium recovery has generally been above 80% and in later years ranged between 85% and 90%. Historical recoveries in certain months show management intervention in addition to inherent leach characteristics of the ore. The planned throughput of 5.5 Mtpa is significantly higher than that achieved in recent years and assumes that the predictions of the Elemental Engineering dynamic surge and availability model are realised. It was noted that ion exchange resin needs to be replaced every two years.

Source: NI 43-101 Technical Report on Langer Heinrich Uranium Project, Erongo Region, Republic of Namibia, Paladin Energy Limited, 2024, Section 17 Recovery methods.