Overview

Deposit type

• Sedimentary

Summary:

The Rössing uranium deposit lies within the central part of the late Precambrian Damara orogenic belt that occupies an area approximately 50 km wide and extends northeast for over 100 km in west-central Namibia.

The Damara lithology consists mainly of folded, steeply dipping metasediments (gneiss, schist, quartzite, and marble) arranged in a northeast-southwest striking belt.

The geology of the mining area at Rössing is associated with a dome structure and occurs in pegmatitic granite known as alaskite, which intruded into meta-sediments. The Rössing ore body is unique in that it is the largest known deposit of uranium occurring in granite. The nature and grade of uranium ore is extremely variable and can be present as large masses or narrow inter-bands within the barren meta-sediments.

All the primary uranium mineralisation and most of the secondary uranium mineralisation occurs within the alaskite. However, the alaskite is not uniformly uriniferous, and much of it is un-mineralised or of sub-economic grade.

Uraninite is the dominant ore mineral (55 per cent); secondary uranium minerals constitute 40 per cent, while the refractory mineral betafite makes up the remaining 5 per cent. Ore grades at the mine are very low, averaging 0.035 per cent. The uranium ore consists of 70-90 per cent alaskite and is subdivided into four ore types, according to the composition of the host rock.

Mining Methods

• Truck & Shovel / Loader

Summary:

Mining is done by blasting, loading and hauling from the open pit before the uranium-bearing rock is processed to produce uranium oxide.

The open pit measures 3.5 km by 1.5 km and is 420m deep.

The pit void is mined by a conventional truck-and-shovel operation, with mining being conducted in 15 m benches. Pit ramps are 40 m wide and established at a maximum 10% gradient. The central benches of the pit are generally in excellent condition – a result of good pre-split blasting techniques. The upper and lower benches are in poorer condition as a result of over-blasting, potentially affecting the stability of the pit rim. Nevertheless, the rocks making up the pit walls, despite being heavily jointed, have high strength values. There is also little seismic activity in the area. Sudden rockfalls and failures are thus rare.

Ore is extracted from the hard rock by blasting. The high energy fuel explosive used, HEF 260, is made up on site with 60 per cent High Energy Fuel (ANCN Solution, old oil, diesel, Megas Emulsifier – E21 and sulphamic acid) and 40 per cent ammonium nitrate prills. Blasting takes place on average twice a week, using approximately 150 tonnes of explosives per blast. Up to 30,000 tonnes of explosives are consumed per year.

The stockpiles have a combined footprint of more than 120 ha. The rock dumps’ footprint increased in both the western and eastern areas of the open pit, with waste dump 2 increasing to 1.4 ha and waste dump 7 to 3.0 ha. In general, rock disposal sites are established as close to the major mining areas as possible.

The Rössing Uranium LoME from 2027 to 2036 was approved by the Rössing Board in February 2023. One month later, a 13-year contract was signed with Beifang Mining to commence with a full contract mining service from 2024 to 2036. By the end of 2023, Beifang had mobilised a new fleet of heavy mining equipment (“HME”) to site, together with an experienced workforce trained to operate this equipment. The first blast was taken in the new Phase 4 pushback, ahead of schedule, on 21 December 2023.

The upper benches of the Phase 4 pushback will be mined concurrently with the final benches of the Phase 2/3 pushback at the bottom of the pit. The latter will supply most of the ore until the end of 2026, while mining waste in Phase 4 to expose more ore from 2027 onwards.

While mining continues in both areas until the end of 2026, Rössing will continue to operate its remaining HME, after which Beifang will take over all mining from 2027 onwards.

Comminution

Crushers and Mills

Summary:

Crushing
Ore from the open pit is delivered in 140 and 180 tonne haul trucks to the primary crushers, where two gyratory crushers reduce the ore to less than 160 mm in size. A conveyor belts transports the crushed ore to a coarse ore stockpile with a live capacity of some 80,000 tonnes.

It passes through a further series of crushers and screens until the particles are smaller than 19mm. After weighing, the fine ore is stored.

Coarse ore is withdrawn from the stockpile by vibrating pan feeders, feeding directly onto a coarse ore reclaim conveyor. This conveyor discharges the ore to a pre-screening plant where all fines are removed and the coarse material returned to the surge bin ahead of the secondary crushers. The ore is further processed through secondary, tertiary and quaternary stages of crushing and screening, delivering a final product of less than 19 mm in size to the fine ore stockpile. The crushing circuit is equipped with an adequate system of dust extraction and collection into covered lugger bins. There are, in total, ten collection systems that provide extraction points from the reclaim tunnel to the fine ore storage bin.

Grinding
The final stage of size reduction employs four Marcy rodmills operating in parallel. This milling stage comprises two modules that can be operated independently. Each module consists of two rodmills which feed into six leach tanks respectively. Grinding in the rodmills is a wet process, with feed water that can be any one or a combination of fresh water, return dam solution from the tailings impoundment and seepage water from the seepage dam. The final particle size leaving the rodmills is 1.1 mm in diameter on average.

The four rod mills, which are 4.3 m in diameter, are utilised as required by production levels and operate in parallel.

Processing

• Sulfuric acid (reagent)
• Calcining
• Vacuum filtration
• Solvent Extraction
• Crush & Screen plant
• Agitated tank (VAT) leaching
• Counter current decantation (CCD)
• Acid tank leaching
• Resin adsorption
• Elution
• Ion Exchange (IX)
• Roasting

Summary:

The run of mine material from the open pit is fed through primary and secondary crushers to the processing plant. The metallurgical process is a conventional acid leach with ion exchange solution concentration and solvent extraction purification, followed by the precipitation of ammonium diuranate and roasting to produce uranium oxide.

At full capacity, the processing plant can produce 4,500 tonnes of uranium oxide each year.

Leaching
A combined leaching and oxidation process takes place in large mechanically agitated tanks. The uranium content of the pulped ore is oxidised by ferric sulphate and dissolved in a sulphuric acid solution.

The resulting slurry is pumped from the rodmills to the leaching section where it is mixed with sulphuric acid, ferric iron and manganese dioxide in a series of six leach tanks. The first tank in the series (290 m3 capacity) is considerably smaller than the other five (1,450 m3 capacity), thus ensuring adequate mixing of reagents and leach feed.

The steel leaching tanks are rubber-lined and mechanically agitated. Retention time in the leaching section is 8-9 hours at a temperature of 35°C, with uranium extraction of 85-90%. Gases and fumes generated during the leaching process are captured on top of the leach tanks by means of scrubbing units. The reagents used for leaching are:
• Ferric iron to oxidise the uranium from a tetravalent to a soluble hexavalent state. Ferric iron is obtained by reacting iron oxide with 93% sulphuric acid in special Rössing designed reactor vessels. Iron oxide (haematite) is brought in by truck in 1 m3 mega bags.
• 93% sulphuric acid for extraction. Sulphuric acid is imported through the harbour in Walvis Bay, railed to site and stored in large acid tanks prior to being delivered to the leach tanks.
• Manganese dioxide to oxidise ferric iron to ferric. Manganese dioxide ore is delivered to the harbour in Walvis Bay by ship and then railed to site and stored in a storage bunker. It is transported by front end loader to a crushing, grinding and thickening plant adjacent to the leach modules where a finely ground slurry is produced and delivered to the leach tanks as part of the extraction process.

Filtration, Drying And Roasting
The addition of gaseous ammonia to the ‘OK liquor’ raises the solution pH, resulting in precipitation of ammonium diuranate, which is then thickened to a yellow slurry.

The ammonium diuranate is recovered on rotating drum filters as yellow paste, known as ‘yellow cake’.

Final roasting drives off the ammonia, leaving uranium oxide. The final product is then deposited in metal drums. Neither ammonium diuranate nor uranium oxide are explosive substances.

The Sands / Slimes Split
Pulp leaving the final leach tanks flows into a ten-way motorised pulp distributor and thence to 10 hydro cyclones. A sand/slime split occurs here with the slime fraction (cyclone overflow) directed to a counter current decantation (CCD) thickener circuit. The coarse sand fraction (cyclone underflow) reports to one of ten primary rotoscoops. There are 20 rotoscoops in each module arranged as 10 discrete pairs, a primary and secondary unit each, providing a two stage sands washing circuit. Barren solution from the continuous ion exchange plant is used as the wash medium on all second stage units. Washed sands are removed from the second stage rotoscoops by a conventional conveyor belt.

The Slimes Washing – Ccd Thickeners
Slimes (cyclone overflow) washing is carried out using a five stage CCD thickener circuit (see Figure 3.5). The first stage consists of four identical thickeners with the slimes fraction distributed equally to two of them. The third and fourth thickeners are used as clarifiers. First stage thickener underflows are re-combined and progressively pumped through four further stages of thickening and re-pulping, thus five washing stages are achieved. Continuous ion exchange (CIX) barren solution is introduced into the fifth washing stage. This runs counter current to the slime flow, and provides the wash medium taking up the uranium. First stage thickener overflow, called “pregnant solution”, contains uranium (uranyl sulphate), at a concentration of 0.180 g/L.

Continuous Ion Exchange
First stage CCD thickener overflow (pregnant solution) is pumped to a pregnant solution storage tank situated near the CIX plant. Tank discharge is by four pumps, each delivering to one line of the CIX contactors. The Rössing CIX plant is built on the Porter system, which uses the upward flow of pregnant solution to fluidise a bed of ionic resin beads in a series of six contactor chambers per line. The flow of pregnant solution is counter current to the resin movement. There are four lines of CIX contactors with six chambers in each line. Resin transfer from one contactor to the next is carried out by air lifter units of which there are six per contactor. Loaded resin from contactor 1 in each line is transferred to the elution columns. Three elution columns per line of contactors are provided; these take the form of fibreglass lined mild steel pressure vessels. Sulphuric acid (at 10% concentration) is passed through the resin bed, stripping the uranium from the resin beads during its passage. Stripped resin is then returned to the co ntactor line and the uranium rich concentrated eluate is pumped to solvent extraction. The eluate has a uranium concentration of 4 – 5 g/L.

Solvent Extraction
Concentrated eluate containing 4 to 5 g/L uranium is pumped to solvent extraction as the aqueous phase of the extraction process . The organic phase is Shellsol, containing alamine 336 and isodecanol. Extraction, i.e. transfer of uranium from the aqueous to the organic phase, is carried out in five stages of counter current contact using Davy Powergas mixer settler units. The loaded solvent is then passed through a two unit clean water scrubbing stage prior to a four unit stripping stage where the loaded solvent (organic) is mixed with a 7% ammonium sulphate (aqueous) solution under pH control with aqueous ammonium hydroxide. Uranium is stripped into an aqueous phase and is pumped to the final product recovery plant as OK liquor (concentrated uranium diuranate solution) containing 8 to 20 g/L uranium.

Final Product Recovery
OK liquor, the chemical solution containing uranium trioxide, is pumped to the FPR building from the SX plant. The first stage of final recovery is the precipitation of ammonium diuranate (yellowcake) from the OK liquor. This is carried out in an agitated precipitation tank. Gaseous ammonia is added to raise and maintain the pH of 7.3. Precipitation tank discharge gravitates to a yellowcake thickener. Thickener overflow (ammonium sulphate) is returned to the SX strip mixer settlers while underflow material is pumped to a two stage washing section. Washing is carried out by two drum filters in series equipped with overhead water sprays. Filter cake from each stage of washing is re-pulped with process water. Re-pulped second stage filter cake is fed into one of the two multi-hearth calcining furnaces. Each furnace has six hearths and is heated to 700°C on the final hearth. The yellowcake feed is calcined to uranium oxide and is discharged via a hammer mill to an automatic drum filling plant. Final product at + 98.5% U3O8 is dispatched in sealed drums, each drum automatically washed and dried and weighing + 450 kg.

Drum filter replacement
Drum filters are used in the final product recovery section, in a two-stage filtration process, purposed to filter yellow cake from thickener underflow slurry into the roaster feed tank. Two drum type vacuum filters are used at Rössing, one of which was prioritised for replacement in 2023, due to operability and mechanical integrity challenges.

Pipelines and Water Supply

Summary:

Infrastructure connected to Rössing includes a water supply pipeline and storage reservoirs; four (4) with capacity of 80 000m3 and additional six (6) in construction to provide combined 60 000m3 storage by 2022.

Water for the central coastal region is provided by the parastatal bulk water supplier, NamWater, which sources fresh water from the Desalination plant at Wlotzkasbaken. NamWater distributes the water via a network of pump stations, reservoirs and pipelines to Henties Bay, Swakopmund and Walvis Bay, Langer Heinrich Uranium Mine, Husab Mine, Rössing, and Arandis.

Freshwater use
Water demand is met by the local bulk water supplier, NamWater, via a pipeline from the base reservoirs in Swakopmund and is sourced from the Orano desalination plant near Wlotzkasbaken. Freshwater supply continues to be a challenge for our operation, as our demands are not always met due to engineered or otherwise natural challenges experienced by the suppliers.

NamWater’s Rössing terminal reservoir is connected to the mine with a 600-mm pipeline.

Khan River water use
Saline groundwater from the Khan River aquifer, in conjunction with biodegradable dust suppressant polymers, is used for the purpose of haul road dust suppression in the open pit. The business is permitted to abstract 870,000m3 per annum from the aquifer. In 2023, there were no abstractions made from the Khan River, which represents an absolute reduction from 4,780m3 (0.55% of permitted annual volume) which was abstracted in 2022.

Water management
All spillages in the processing plant are captured and channelled to a large recycle sump for reuse. Effluents from the workshops are treated to remove oils and sewage is processed in the onsite sewage plant. These semi-purified effluents are used in the open pit for dust suppression.

At the deposition pool (active paddy) of the TSF, water is recycled and reused on a continuous basis in the processing plant, minimising surface evaporation and infiltration into the tailings pile. Water that infiltrates the TSF is recovered by pumping boreholes and open trenches installed on the facility itself to reduce the volume of underground water within the tailings pile.

Seepage control systems are also employed outside the TSF. They include a surface seepage collection dam to capture water from the engineered tailings toe drains, cut-off trenches in sand-filled river channels, dewatering boreholes situated on geological faults and fracture systems on the downstream, western side of the facility. All systems are designed to lower the water table to the extent that flow towards the Khan River is interrupted. The recovered water is reused in the processing plant.

Production

Operational metrics

Personnel

Job Title	Name	Email	Profile	Ref. Date
General Manager Operations	Martin Tjipita			Jul 8, 2024
General Manager Sustainability	Liezl Davies			Jul 8, 2024
Maintenance Superintendent	Mathew Tueutjiua			Jul 8, 2024
Managing Director	Johan Coetzee	Johan.Coetzee@Rossing.com.na		Dec 31, 2023
Operations Superintendent	Messag Kamati			Jul 8, 2024
Project Superintendent	Martin Shikongo			Jul 8, 2024