Rössing Uranium’s operations consist of two distinct activities: the first is mining uranium-bearing rock, while the second is processing this ore into uranium oxide for the world’s nuclear energy market, which fuels the generation of electricity. Our attention is directed towards creating shareholder value and maintaining a secure and viable business, as well as ensuring that we remain a long-term contributor to Namibia’s economy.
The uranium located in our mining licence area is embedded in very hard and abrasive granitic rock, known as alaskite. To mine the necessary volume of ore and waste, the mine must conduct blasting operations regularly.
Electric and diesel-powered shovels load uranium-bearing rock onto haul trucks, which transport the ore to the primary crushers for the first stage in the crushing process.
From there the crushed ore is conveyed to the coarse ore stockpile, where it is reclaimed and put through additional crushing stages in the Fine Crushing Plant, before the processing stage of operations begins.
Blasting preparations underway in the open pit.
In 2020, we mined 19.4 million tonnes of rock (13 per cent less than in 2019) of which 9.2 million tonnes was economic uranium-bearing ore (7 per cent more than in 2019), and 10.0 million tonnes were waste and low-grade ore (including 0.2 million tonnes dumped in-pit). This equates to a waste-to-ore strip ratio of 1.09, which is significantly lower than 2019 (1.60). The waste-to-ore ratio will continue to decrease as the open pit gets deeper.
Mining operations were forced to slow down between March and June while controls were implemented to combat the spread of COVID-19 on-site. This had an impact on ore supply, which was mitigated by depleting run-of-mine stockpiles and reducing cut-off grades to meet tonnage requirements, albeit at lower grade.
As a result of this, ore milled increased from 8.0 million tonnes in 2019 to 8.7 million tonnes in 2020.
Milled uranium grade of 334 parts per million (ppm) was 12 per cent lower than 2019, while ore blending was tightly controlled to support higher plant recoveries. Higher tonnes and recovery offset the lower grades to deliver 1.6 per cent more metal in 2020 relative to 2019.
While COVID-19 controls dominated the health and safety effort across the mine, the mining operation recorded zero ‘all injuries’ for 2020. Progress was made with regards to several health, safety and environmental (HSE) initiatives, including geotechnical meshing to mitigate rock-fall risk; trialling of a fatigue management system on the haul trucks; construction of a ramp to access water at the bottom of the open pit for dust control; and to dewater the pit ahead of mining the lower benches.
Improvements in other areas included the upgrading of the radiometric truck scanners for grade control; trialling of down-hole logging tools and progressing a geo-metallurgical test work programme to optimise process recoveries.
At a strategic level, an updated view of the Phase 4 pushback was completed that will support a more detailed study in 2021 and 2022.
Looking ahead, productivity and cost improvement initiatives will focus on blasting efficiencies and optimising the mining sequence, together with anticipated reductions in the mining fleet.
Nearly 20 engineering projects were undertaken during 2020, of which four are discussed here.
VARIABLE SPEED DRIVES FOR CCD FEED PUMPS AND SMALL THICKENERS
Rössing Uranium have been using hydraulic variable speed couplings (VSC) to vary pump speed for flow control processes on the CCD feed pumps. A VSC makes use of old technology: mechanical devices are coupled directly to a motor and then hydraulic fluid is used to perform speed control on pumps. Historically, Rössing has experienced frequent failure on the VSCs.
In addition, the installation and alignment of hydraulic VSCs is labour intensive and contributes directly to extended plant downtime, resulting in significant production losses. The small thickeners underflow pumps were also being run on fixed speed, which is not appropriate for flow control and can be very inefficient in terms of power consumption.
It was on this basis that an alternative technical solution was proposed involving the installation of 3.3kV medium voltage (MV) variable speed drives (VSDs) to replace the VSCs, and to also install 525V low voltage (LV) VSDs to replace the fixed speed on flow control.
The VSDs were installed on CCD’s feed pumps line 1 and line 2, as well as on four small thickener underflow pumps. The project was successfully commissioned in December 2020. To enhance safety, the start/stop panels were fitted with protective covers against spillage. A housing was constructed for the MV VSDs, with adequate air conditioning installed. The newly-installed motors were directly aligned to the V-belts on each pump.
(From left to right) Members of the engineering team: Nestor Hamalwa (Mechanical engineer), Eliaser Silvanus (Mechanical engineer), Hanna Uunona (Mechanical engineer) and Wilhelmina Kamati (Electrical engineer graduate) at a planning session.
WATER STORAGE CAPACITY INCREASE
Historically Rössing Uranium has suffered many water shortages for operations. The trend over the years shows regular sulphur outbreak events in the ocean, resulting in the shutting down of the Orano desalination plant, with reduced inflow to NamWater reservoirs at its Swakopmund base and therefore reduced inflow to the Arandis reservoirs from which Rössing’s fresh water is being supplied.
These incidents resulted in production outages directly related to the unavailability of fresh water supply to the mine. Several options were considered and evaluated to increase the reliability in fresh water supply to the mine.
After a due diligence investigation on various options, the Board approved a capital project in 2020 to increase the water storage capacity to complement the storage capacity of NamWater’s reservoirs.
A suitable tank supplier was identified that will deliver six tanks to the mine. Each tank will be able to contain 10,000m3 of potable water. The tanks will be delivered on site in containers in mid-2021: the six tanks will be installed adjacent to the existing NamWater reservoirs.
The total increase in water storage capacity will thus be 60,000m3, providing Rössing Uranium with approximately seven to eight days of additional fresh water supply for operations. In the second quarter of 2021, the earthwork preparation and base construction on which the tanks are to be installed, will commence.
CIX & SX STRUCTURAL UPGRADE
Severe structural deterioration has been noticed at the mine, specifically at the Continuous Ion Exchange (CIX) and Solvent Extraction (SX) Plants. Acid spillage over the years has undermined the interface between column supports and the structural concrete founding slab supporting the vessels. Structural integrity assessments were done in 2016 and again in 2019 to determine the condition of the existing structures and to recommend repair methodologies to sustain the existing structures.
Following these assessments, two projects were approved to restore the structural integrity of the areas of these plants most affected by the deterioration. Both projects were completed successfully with restored concrete flooring, steel structures and acid proofing, which ensured the structural integrity of both sections where the work was implemented.
Going forward, major projects for 2021 include:
- Increase in water storage capacity
- New FPR roaster
- Pipe re-routing at the CIX trench
- Major refurbishment of leach tank 4/1
- Upgrading of crusher mainframe
- Upgrading of scrubber leaching, and
- Rehabilitation of the westerly dewatering wellfield.
Y3 PADDOCK BUTTRESS AND E2/Z2 ADDITIONAL PADDOCKS
The availability of deposition areas has decreased at the Tailings Storage Facility (TSF). As such, a geotechnical site investigation was carried out in 2018 on the TSF. Part of the findings of the site investigation was that the mine would no longer be able to safely deposit on two of the major paddocks. This implied that there is a need to identify and develop additional deposition areas, and to also bring back a previously abandoned paddock.
The reinstatement of the previous paddock was on condition that the Y3 Paddock also be buttressed before any form of commissioning for deposition is done. Additionally, two new paddock areas have been identified as Z2 and E2 with Y3 being scheduled for buttressing. This decision to continue with the above project was also endorsed by the TSF Review Board.
PROCESS SAFETY MANAGEMENT
Process safety management (PSM) is a systematic approach of controlling the unwanted release of hazardous substances, process solutions or fires and explosions that have the potential to significantly impact the health and safety of employees, the environment or the business.
During the previous year, Rössing Uranium’s PSM steering committee decided on four main process safety hazards. These four process safety hazards are managed with strict engineering and administrative control strategies. The four hazards identified were:
- anhydrous ammonia gas,
- concentrated sulphuric acid,
- fire in the solvent extraction and final product recovery plant, and
- engulfment due to large processing tank failures.
In the latter part of 2019, it was identified that the engineering standards and manuals currently being used, are outdated. The PSM team was tasked to identify the shortcomings and embark upon updating of these standards and manuals as an improvement project in 2020, together with the normal day-to-day control strategies of the mine’s four main process safety hazards.
Due to the COVID-19 pandemic, an external audit could not be conducted in 2020 because of travel restrictions. However, the mine contracted consultants with over 15 years experience in process safety management in different processing plants all over the world to assist in the process safety improvement project. The assistance was started remotely due to travel restrictions.
The process safety management improvement project focusses on evolving it more specific to Rössing Uranium but still complying to international standards. From 2020 onwards, the PSM team reports to a newlycreated engineering governance department, namely Asset Management. The project will assist the asset management planning, training, HSE, operations and maintenance departments to ensure continuous management of process safety hazards at the mine.