Tag Archives: SAIMM

Mining network needs to align on safe tailings dam design, SRK’s Spies says

Safer tailings storage facilities (TSFs) – or tailings dams – can be achieved when mine owners, contractors and engineering consultants work closely together, says SRK Consulting’s Linda Spies.

Speaking after a recent Southern African Institute of Mining and Metallurgy (SAIMM) conference focusing on tailings dams, Spies, Senior Geotechnical Engineer at SRK Consulting, said that mining executives today required more assurance that their tailings dams are safe, with controls becoming much stricter. Greater transparency was also being demanded by other stakeholders such as investors and communities, she added.

“After several hundred lives were lost in two well-publicised tailings dam failures in Brazil, in 2015 and 2019, awareness of tailings dam risks has been raised within the mining industry and in the public eye globally,” she said. “These latest failures were especially significant insofar as senior management at the mining companies were for the first time being implicated directly with charges of manslaughter and environmental damage.”

She noted that while conferences on this topic usually involved mainly tailings dam practitioners and academics, this event had strong representation from owners; contractors, who are responsible for tailings dam construction; and consultants, who design TSFs and monitor their construction.

“This meant that the discussion was more holistic and valuable, enriched with insights from these various perspectives,” she said. “This is vital in promoting innovation, safety and environmental and social responsibility in the design, operation and closure of tailings dams.”

While the tone of the event was serious considering recent failures, there was also an optimism flowing from a showcasing of best practice in the field and how this was being successfully applied. In her own case study presentation on a lined tailings dam at a South African platinum mine (Impala’s Marula dam), Spies highlighted the complexities introduced by the liner requirement – and how good drainage design and quality assurance were an important part of the solution. (see Getting lined tailings storage facilities right below)

Among the key issues discussed at the conference was whether upstream tailings dams should be allowed – as this was one of the commonalities in the recent Brazil failures. High-level input was given in a panel discussion by senior leaders from a mining company, a law firm and an insurance firm, including technical opinions from tailings industry expert and specialist geotechnical engineer Adriaan Meintjes, a Partner and Corporate Consultant from SRK.

According to SRK Principal Hydrogeologist and Numerical Modeller, Sheila Imrie, who also presented at the event, tailings is rightly receiving considerable attention from a combined engineering and scientific perspective and will continue to do so in the future.

“The continued application of the latest technologies by the industry’s top experts is critical,” Imrie said. “Industry must also ensure that sufficiently detailed research, monitoring and numerical modelling informs the future design and current management of tailings dams.”

She presented a paper on ‘3D Seepage Modelling in Tailings Storage Facility Analysis and Design for Low Permeability Lined Basins’ with SRK Civil Engineer, Wesley Rouncivell. A key aspect of the safe operation of tailings dams into the future involves comprehensive and rigorous monitoring of these facilities on a regular and real-time basis, they said.

In another SRK presentation, GIS Specialist, Ansu Louw, and Civil Engineer, Riaan van der Colf, gave their insights on a ‘GIS-enabled, Web-based TSF Monitoring Solution’ by SRK to enhance monitoring of tailings facilities.

Getting lined tailings storage facilities right

The inclusion of a liner in a tailings dam brings many environmental benefits, but also increased complexity in design, construction and operation, Spies says.

In her presentation – ‘Design of an HDPE-lined platinum tailings facility in South Africa’ – at the SAIMM Tailings Storage Conference, in Gauteng, recently, Spies highlighted the importance of well-designed drainage systems. These are vital to drawing down the phreatic surface, reducing the seepage gradient and minimising the liquefaction potential of tailings, she said.

She also emphasised high construction standards to ensure tailings dams successfully limit seepage, and outlined a series of quality control and assurance measures.

Weir Cavex hydrocyclones prove their worth at South Africa diamond mine

Weir Minerals’ Cavex® hydrocyclones have been put to the test at a diamond mine in South Africa’s Northern Cape Province, proving the technology can be applied in dense medium separation (DMS) plants treating diamondiferous material, according to the company.

In her presentation to the Southern African Institute of Mining and Metallurgy (SAIMM) diamond conference in Johannesburg in 2018, Weir Minerals Africa’s Senior Process Engineer, Boitumelo Zimba, said the hydrocyclones improved plant efficiency and produced 40% more tonnage than the mine’s target.

“As the Cavex hydrocyclone is tried and tested in hard-rock mining and coal classification, the Cavex 360° laminar spiral inlet profile was used as a basis for the development of a dense medium cyclone,” Zimba said. “Individual casting patterns were developed and produced in order to fabricate the Cavex dense medium hard chrome cyclone with the exact laminar spiral feed chamber that exists when moulded out of rubber.”

The customer required a solution that could offer at least six months wear-life, and a probable error of separation (Ep) of no greater than 0.08 at a cut density of 3.1 t/m³. Tracer tests were used to monitor the efficiency of the separation achieved by the Cavex hydrocyclones to ensure all of these requirements were met.

“Ep values achieved were 0.042 for the 4 mm tracer tests and 0.035 for the 8 mm tracer tests, which were below the set maximum target of 0.08 from the mine,” Zimba said. “This highlighted the benefits and improved efficiencies of the Cavex laminar spiral feed inlet.”

The lower the Ep – or probable error of separation – the more efficient the separation; it is defined as half the difference between the density at which 75% is recovered to sinks, and that at which 25% is recovered to sinks, Weir said.

“The customer’s tracer tests on the Cavex hydrocyclones showed that cut points of 3.08 t/m³ were achieved for both the 4 mm and 8 mm tracers,” Zimba said. “This was within the performance levels of 3.1 t/m³ that the customer had specified.”

Initially, the hydrocyclones were commissioned to treat only fines at the diamond plant – the minus 8+1 mm material. Later however, the mine decided to run a combined DMS, after which the full DMS size range of minus 20+1 mm was treated through all the fines DMS hydrocyclones.

“The unique design of the laminar spiral inlet geometry delivers sharper separation and maximises capacity while delivering a longer wear-life than conventional involute or tangential feed inlet designs,” Weir says. “By providing a natural flow path into the hydrocyclone body the design allows the feed stream to blend smoothly with the rotating slurry inside the chamber, reducing turbulence and improving separation efficiency.”

Zimba explained: “Combining our cone and spigot components in the hard metal range is an important contribution to the reduction in turbulence. Another vital factor is the Cavex inlet design with 360° scroll; this design was proven through extensive computational fluid dynamics analysis as well as our multiple installations to date.”

Weir Minerals also conducts ongoing research and development on methods to minimise turbulence on assembled casted components. The Cavex hydrocyclones are designed with a variety of inlet sizes to accommodate a wide top size at specified medium-to-ore ratios. The inlet sizes range from 0.2 to 0.33 as a function of the hydrocyclone diameter.

“The Cavex CVX hydrocyclone also has a wide range of vortex finder sizes to maintain separation efficiency at different operating yields and spigot sizes. The vortex finder sizes range from 0.4 to 0.5 as a function of cyclone diameter, and are designed to maintain a strong air-core at different spigot sizes,” Weir says.

To prolong life and efficiency, the hydrocyclones can also be manufactured with different materials.

“Cavex CVXA hydrocyclones are hard-wearing and are cast in 27% chromium iron for maximum abrasion resistance; components are designed for ease of maintenance, with all surfaces joined with a layer of epoxy cement,” the company says.

Weir Minerals Africa operates two foundries in South Africa – one at its Isando facility and the other at its Heavy Bay Foundry in Port Elizabeth. “This allows the organisation to cast items in-house leveraging its local foundry personnel’s knowledge, experience and expertise, ensuring that the highest standards are maintained,” Weir says.

“This approach ensures optimal life of the hydrocyclone in operation, and reduced maintenance costs by replacing worn parts in situ. It also eliminates the risk of any adverse effects on performance arising from mixing old and new hydrocyclone components. Further, safety on site is enhanced by minimising the maintenance work necessary on the installed hydrocyclones.”

Zimba said future work will include the investigation of various alloys to combat high wear rates on some of the hydrocyclone components, in particular the vortex finder and the cone sections. “This will allow longer operation and plant stability,” she said.