Tag Archives: HPGR

Multotec pulping chute advances at Ekapa open opportunities for fines scrubbing tech

The performance of Multotec’s pulping chutes at Ekapa’s diamond treatment operation in Kimberley, South Africa, over the past couple of years has, the company says, opened the door to quicker and more cost effective fines scrubbing.

According to John Britton, Technical Consultant at Multotec, the two pulping chutes have achieved outstanding results, helping the customer’s facility to cost effectively increase the throughput of its Combined Treatment Plant (CTP).

“At our recent two-year inspection of the plant, we found that the wear rate on the ceramic lining of the wave generator was only 20 mm over that 24-month period,” Britton says. “Each chute was processing 380 t/h of recrushed kimberlite product with 380 cu.m of water, rushing down a 28° incline.”

Multotec’s patented wave generators use gravity to create a constant turbulent mixing action in the slurry flow that releases the mud, clay and slime sticking to the kimberlite particles. The chutes are positioned to receive material from the high pressure grinding rolls’ interparticle tertiary crushing circuit. Multotec’s engineered alumina ceramic tiles give the chutes and wave generators high wear resistance, it says.

“The chutes exceeded our expectations in how well they separated the clay from the kimberlite ore and broke up clay balls in the material stream,” Britton says. “This has really demonstrated the long-term capacity of our design to deliver results with hardly any maintenance or operator intervention.”

He highlights that the chutes are stationery structures that rely on the kinetic energy being created by the in-rush of slurry flow over the wave generators. This makes the solution much simpler and less energy-intensive than traditional rotary scrubbers with motors, drives and gearboxes. The chute can also achieve its results much quicker, as the material flow passes through in just three to four seconds.

Ekapa CEO, Jahn Hohne, says he has been impressed by how well the chutes have performed as an alternative to a considerably more costly scrubber circuit, and having delivered a 20% increase in throughput through the plant and making a positive economic contribution to overall efficiency. Hohne says he admired Multotec’s innovation capability and looked forward to even further improvements in the design.

Britton notes that, after conducting the wear inspection of the chutes, there were modifications Multotec was planning. One of these related to the retarder bars, which slow down and divert the slurry flow.

“We believe we can achieve even better results if we remove some of the retarder bars and install another set of wave generators,” he says. “Our results suggest that this will get the ore material even cleaner, before it reports to the screen, the conveyor belt and finally the dense medium circuit.”

The success of the pulping chutes at Ekapa has led to considerable interest from other diamond producers in southern Africa, he added.

Kwatani wins major screening order from Central Asia copper mine

Competing with leading OEMs from around the world, vibrating screen specialist OEM Kwatani says it has snatched a mammoth export order for over 70 screens from a mining operation in Central Asia.

The order was signed in April with a large copper mine in the region, which boasts a production rate of 35 Mt/y. According to Kwatani General Manager Sales and Service, Jan Schoepflin, the machines will be rolled out and delivered over a tight schedule of just eight months.

Kwatani, now part of the Sandvik group within the Sandvik Rock Processing Solutions division, is already hard at work manufacturing the large and medium-sized screens at its South Africa-based manufacturing facility.

“This is Kwatani’s largest order to date and is probably the largest single order for screens ever placed with a company in Africa,” Schoepflin says. “We are proud to have won such a prestigious bid in the face of intense competition, showing how our global reputation has been growing.”

The order is for large double-deck multi-slope screens, which feed high pressure grinding rolls, as well as for single-deck linear screens feeding concentrators. The screens in this order will be installed on isolation frames to minimise the extent to which dynamic loads affect the plant’s building structures, the company says.

Kwatani says it is well known for its design, manufacture and servicing of large, robust screens which are engineered for tonnage.

“As the largest OEM for vibrating screens and feeders in Africa, we have had great success on the continent and abroad with our large ‘banana’ screens,” Schoepflin says. “These and our other custom-engineered screens have been supplied to over 50 countries to date.”

The stringent and lengthy technical adjudication for this project was conducted for the mine by two leading international project engineering houses. The size and value of the order ensured all the mining industry’s foremost screen suppliers participated in the bid. Other indicators of the order’s scale are that the screens will consume around 700 t of steel, and will altogether be fitted with 21,000 screening panels.

Schoepflin notes that an important consideration for customers is not only the proven quality and performance of its screens, but Kwatani’s ability to deliver on time.

“Any large capital expenditure decision on a mine is taken with time-sensitive factors in mind,” he says. “For instance, the delayed delivery of critical equipment can prevent a mine from meeting its planned production targets. This undermines the financial basis for that decision – an eventuality that no mine can afford.”

The end-customer and the project houses, therefore, had to have full confidence in Kwatani’s capacity.

With growing demand from a buoyant mining sector, the company recently added another 3,000 sq.m to its existing 17,000 sq.m facility in Spartan, Johannesburg. Its design and manufacturing capabilities are ISO 9001:2015 certified, ensuring that the latest order to Asia will comply with the highest global standards, he says.

“We also pride ourselves on the quality and resilience of our supply chain, which underpins our ability to manufacture to demanding deadlines,” Schoepflin says. “We carefully select our supply partners – most of whom are local enterprises – and collaborate closely with them to build their sustainability and responsiveness.”

To keep the project’s schedule on track, dedicated in-house project managers and procurement specialists meet regularly with supply partners to ensure a smooth and streamlined process. This has required alignment of all local and global procurement, including motors, drives and steel. The company’s agility allowed contracts and prices to be tied down for timeous delivery, despite the global supply chain disruption that lingers from the COVID-19 lockdowns, Kwatani says.

Kwatani will conduct training of the mine staff in maintenance and troubleshooting, so that they can fulfil these essential duties independently. The mine will be able to source all the necessary spares from Kwatani, who will also send an engineer or technician to site to supervise and sign off on certain major tasks.

Meeting delivery deadlines and avoiding penalties will require detailed logistical planning for the completed units, Schoepflin notes. The screens will be delivered in batches to a South African port, and shipped as break bulk due to their size. Production of the screens is expected to be complete by early 2023.

Wood tradeoff study puts HPGR, POx processing ahead at De Grey’s Mallina gold project

Prefeasibility process engineer Wood Australia has completed a comprehensive nine-month trade-off study into the preferred process flowsheet design for De Grey Mining’s Mallina gold project, selecting a process flowsheet that incorporates high pressure grinding roll (HPGR) and pressure oxidation (POx) technology.

The project, which includes the Hemi Deposit, is in the Pilbara region of Western Australia.

In late 2019, De Grey made a large scale, high value, near surface gold discovery at Hemi – an intrusion-hosted form of gold mineralisation new to the Pilbara region that, the company says, shows a scale of mineralisation not previously encountered in the Mallina Basin. The company currently has 6.9 Moz of measured and indicated resources declared at the project, with plans to turn this into an open-pit mining operation down the line.

The findings have come out ahead of the full PFS, which is due for announcement in the September quarter of this year.

The trade-off study has confirmed that Hemi mineralisation has excellent recovery and is amenable to HPGR and POx processing technologies, the company said. The process route chosen has demonstrated advantages relative to other processing technologies including:

  • Proven and accepted technology for the scale of operation and style of mineralisation;
  • Lower capital and operating costs;
  • Higher gold recovery between 93% and 95% depending on average feed grades;
  • Circa-20% lower energy consumption;
  • Circa-25% lower reagent (lime) consumption;
  • Circa-25% lower CO2 emissions;
  • No heat addition required to sustain – or cooling to control – the POx process; and
  • Robust and proven equipment.

The flowsheet selections have the benefit of lower carbon emissions through lower energy requirements and lower greenhouse gas emissions as a result of improved neutralisation and consequent lower lime consumption, De Grey added.
“Further studies are in progress as part of the PFS on the carbon intensity and greenhouse gas emissions for the Mallina Gold Project development,” it said.

The currently envisaged flowsheet at Hemi sees ore crushed and ground in the comminution circuit before being fed to the flotation circuit. Any gravity recoverable gold will be recovered prior to flotation with the use of, for example, a Knelson or Falcon concentrator. Test work has shown gravity recoverable gold is present in the Hemi and regional mineralisation, and the extent of gravity-recoverable gold will continue to be assessed through test work.

The flotation circuit will process gold bearing sulphides in Hemi ore producing a “low mass pull” gold-rich sulphide concentrate. The POx circuit is designed to receive the gold-rich sulphide concentrate from the flotation circuit. The POx circuit will have a throughput of 8% (800,000 t/y) of the throughput of the comminution circuit.

The POx circuit will convert the sulphide concentrate to a gold bearing residue amenable to standard carbon in leach (CIL) processing. The underflow from flotation is also amenable to standard CIL processing. Both streams will enter the CIL circuit followed by electrowinning to produce gold bars on site. This has numerous benefits for the POx circuit including lower capital and operating costs compared with projects that require whole of ore treatment through POx.

Tailings from the CIL circuit will be pumped to a tailing storage facility.

Hemi mineralisation has two significant and attractive mineralogical characteristics that lead to the overall expected metallurgical recovery of between 93% and 95% at expected mined grades, namely:

  • The majority of gold at Hemi can be floated into a low mass pull concentrate that recovers very high levels of sulphides and gold ahead of oxidation; and
  • The flotation tail contains gold that can be successfully recovered using standard CIL processing.

The crushing circuit will include a primary gyratory crusher, a secondary cone crusher and. The secondary cone crusher will operate in closed circuit with a sizing screen while the HPGR will operate in closed circuit with wet sizing screens to produce a nominal less than 7 mm mill feed. The grinding circuit will consist of two ball mills with conventional pinion drives each with their own classification circuit.

The oxidation circuit throughput for Hemi is proposed to be 800,000 t/y, or 8% of the proposed comminution circuit throughput of 10 Mt/y. The oxidation circuit will treat the gold-bearing sulphide concentrate generated by the flotation circuit. The POx circuit will consist of flotation concentrate thickening and storage, POx utilising autoclave technology and neutralisation in association with the flotation tail prior to co-leaching in a CIL circuit.

The oxidation circuit will be designed to have sufficient storage capacity prior to the autoclave to allow for maintenance shutdowns without the need for a mill shutdown. This decouples the comminution and oxidation circuits ensuring that each circuit does not impact on the availability of the other.

Kwatani’s mill discharge screen expertise to pay off at Namibia gold mine

Namibia’s mining scene is seeing an exciting expansion and technological innovation at a leading gold mining operation, with Kwatani supplying five mill discharge screens – all custom designed and manufactured at its Gauteng facilities.

Kim Schoepflin, CEO of Kwatani, says her company has a long history in Namibia and a strong footprint across various commodities there – including an established presence at this gold mine. It has worked with the engineering, procurement and construction contractor and the end-customer for two to three years on conceptualising the optimal solution.

“The mine is gearing up to increase its production by 50%, to take advantage of the strong gold price,” Schoepflin says. “Our role was to ensure that our discharge screens meet their exact process requirements – with our efficiencies of up to 95% – while delivering mechanical integrity for minimal maintenance downtime.”

The expansion includes the installation of two latest-technology mills – a high-pressure grinding roll (HPGR) and a vertical mill – which will boost production while reducing energy demand. Kwatani’s mill discharge screens, each measuring 3-m wide by 8-m long, will handle the coarse and fine material from the HPGR and the vertical mill. The company will also supply three silo feeders of 1.2 m by 2.5 m in size, to feed material from the silo to conveyors.

“Our screen design optimises the retention time on the deck, allowing for better screening and stratification,” Schoepflin says. “Due to the volume of slurry and water sprayed onto the screens, the added retention time assists with better drainage at lower cut points.”

The coarse screens were designed at a decline, and feature a larger screening media aperture with higher amplitude and stroke. Together with lower speed, this achieves better screening efficiency for the coarser particles. The fine horizontal screens, with smaller aperture screening media for the finer feed, were designed with a higher speed and lower amplitude and stroke; this will optimise the screening efficiency of the finer feed to these screens.

She also highlights the attention paid to the isolation of the vibrating screens. In this case, Kwatani engineers selected rubber buffers, which have higher dynamic loads but are more suited to wet applications and screens with a heavier mass.

“The number and type of buffers were defined according to the mass of the screens,” Schoepflin says. “The selection of rubber buffers for larger screens also assists with start-up and shutdown time, allowing the screens to come to rest more effectively.”

For these five screens, Kwatani, now part of Sandvik Rock Processing Solutions,  designed and supplied custom counter-balance frames to minimise the dynamic load to the plant infrastructure. The company’s screen technology includes designing its exciters in-house. This ensures that screens receive the necessary G-forces for optimal material stratification and screening, matching customers’ process requirements with the best possible efficiencies.

“To make sure our screens cope with the high capacity demands of modern processing plants, we rigorously test all units in our in-house testing facility before dispatch,” Schoepflin said. “These units began their journey to Namibia at the end of November 2021, and our team will support the commissioning when the customer requires.”

Kışladağ and Weir Minerals on the HPGR-backed gold recovery trail

The story that led to the installation of a Weir Minerals Enduron® high pressure grinding roll (HPGR) at Eldorado Gold’s Kışladağ heap leach operation in Turkey is a fascinating read, as well as a great example of the benefits of using such technology.

Back in March 2018, Eldorado announced it would suspend mining to evaluate processing options for the operation. This decision followed extensive laboratory tests that indicated gold recoveries would continue to trend downwards around the base of the open pit where mining was underway.

This suspension, plus further engineering and test work, led to the company advancing the potential development of a mill project. The transition away from its heap leaching roots to a possible mill and carbon-in-leach (CIL) process would have added significant capital costs and shortened the mine life significantly.

Before making this significant capital decision, Eldorado paused to take time to undertake the necessary technical work and sought the technical collaboration of Weir Minerals on a solution.

“It was a very challenging period,” George Burns, President & CEO of Eldorado Gold Corporation, told IM. “Kışladağ is a cornerstone asset in our portfolio. It required collaboration with our geologists, metallurgists, site teams and technology providers, including Weir, working together on a solution.”

(Credit: Eldorado Gold)

In late 2018, results showed increased recoveries from an extended leach cycle. Following a deeper understanding of the geometallurgical drivers of the sulphide component of the deposit, improved heap leach recoveries were realised by optimising the metallurgical conditions. With these improved recoveries confirmed, the heap leach plan was revised in early 2019. Eldorado announced plans to resume mining, crushing, stacking and heap leaching at Kışladağ, and suspended plans to build the processing plant.

The decision came following metallurgical test work on the material placed on the heap leach pad in 2018. Gold recovery had increasingly exceeded expectations throughout the year, providing a new, positive heap leaching outlook beyond the near term. At the same time, Eldorado worked with Weir Minerals on the potential use of an HPGR at the operation.

HPGR creates a finer particle size, which helps to liberate the gold particles, resulting in increased recoveries.

An improved understanding of the leaching process on its low-grade ore and the potential of this cost-effective grinding addition provided it with the confidence to continue heap leaching beyond the short-term time horizon previously envisaged.

“Our collaboration with Weir on this effort is an excellent example of how Eldorado collaborates with technology leaders and seeks out solutions,” Burns said. “We believe this is a strength of the company’s core business values. We are agile and flexible ‒ a good example in both business and operations to find innovative, technical solutions and demonstrate prudent capital discipline. Ultimately, the solution was the best technical and economic decision for Eldorado.”

Testing, testing, testing

“The relationship between Weir Minerals’ and Kışladağ goes back to 2013,” Bjorn Dierx, Global Product Manager Enduron HPGR, told IM.

The OEM had been provided with samples on several occasions to investigate different flowsheet possibilities.

“The benefits of HPGR in heap leaching recovery were known by the site’s crew,” he said.

Enduron technology was tested at the quaternary crushing stage before heap leaching, in the quaternary crushing stage before ball milling and at the tertiary crushing directly before heap leaching.

All the time, the mine operator, Tuprag, Eldorado Gold’s subsidiary in Turkey, was evaluating the impact on gold recovery.

Although HPGR in closed circuit with screening was also tested, most of the test campaigns were focused on a configuration with so-called ‘Partial Product Recycling’ (PPR), according to Serhat Onol, Weir Minerals Senior Process Engineer.

“This system includes splitter plates underneath the rolls which ‘cut’ a proportion of the product discharge and reverts this back to the HPGR head feed,” he explained. “This recycle stream can be adjusted online to adapt the product grind towards the downstream requirements.”

PPR is not an option for every application but for Tuprag – due to the feed and desired product size – all specifications showed it was the best route.

“The hybrid solution with screening serves to increase the flexibility and to control the circulating load to the HPGR,” Onol said.

With capacity rates of around 4,200 t/h at Kışladağ, the screening area requirement was reasonably high, he explained.

“The hybrid solution uses screening only for the recirculating stream: the centre product of the HPGR reports to downstream leaching, whereas the rest is recirculated,” he said. This not only removes the fines re-entering the HPGR and, thus, reduces the circulating load, but also avoids the over-grinding of fines before leaching.

The PPR option, itself, is a very flexible operation, with the adjustable discharge splitter plates providing the best circuit flexibility in terms of throughput and product size, according to Onol.

(Credit: Eldorado Gold)

Great expectations

With the main driver of the HPGR installation being an improved gold recovery scenario, leading to an increased heap leach life, the pressure has been on Weir Minerals to come up with the goods.

The final flowsheet, which includes a 2.4 m diameter by 2.2 m long Enduron HPGR with the capacity to process 4,200 t/h, is much simpler than the existing circuit, according to Dierx, with less equipment to maintain, control and monitor.

“A single Enduron HPGR will replace all of the five existing tertiary crushers of which liners would have an average lifetime of circa-one month with a crusher availability of 85%,” he said. “The HPGR tyres have a wear life close to 18 months, with the HPGR achieving a high asset availability of more than 95%.

“Additionally, as a result of the HPGR combined with the hybrid PPR system, the existing four tertiary screens are also being decommissioned.”

Not only has the HPGR alleviated the use of this equipment, it is also set to boost that bottom line gold recovery.

“During testing, it was determined that the circuit configuration and HPGR operating conditions, such as pressure, have a direct influence on the gold recovery,” Dierx said. “The current expectation is that the average recovery increase after the commissioning of the Enduron solution will be approximately 4%.”

This could bring gold recovery to approximately 56%, as was declared in a 2020 press release from Eldorado that highlighted a 15-year mine life at Kışladağ with an average annual production of 160,000 oz.

In action

One of the largest brownfield HPGRs Weir Minerals has ever installed has just processed its first material at Kışladağ, which is testament to the hurdles both the Weir Minerals and Tuprag teams overcame during the height of the COVID-19 pandemic.

“Despite the challenges we faced during the pandemic, we were able to fully install the machine, including pre-commissioning, in only 22 weeks,” Dierx said.

(Credit: Eldorado Gold)

This was achieved by minimising the amount of work carried out on site via pre-site testing and modular HPGR assembly.

“As the available footprint in existing sites is limited, the unique Enduron design (length:diameter ratio) not only improves the grinding efficiency but also allows for easier implementation with less civil requirements,” Dierx said.

The machine has the potential to be digitally connected to the Weir Synertrex® IoT platform where operators can benefit from direct access to maintenance specialists, who will be monitoring performance and provide necessary operating guidance.

And the Weir Minerals team is confident more Enduron HPGR installations will follow the one at Kışladağ.

“We are very proud of the product’s recognition by our customers as the Enduron HPGR has been selected for all major greenfield HPGR projects in the hard-rock space,” Dierx said. “Despite all the key Enduron differentiators, it is not only merely about the product but particularly the wider experience across Weir Minerals in both the upstream and downstream processes via our wide product portfolio.

“Particularly in these brownfield applications, the system is not operating in a vacuum and every process change influences how the overall circuit works. This requires tacit knowledge, which Weir Minerals holds across their global teams.”

Eldorado’s Burns concluded: “We are pleased to implement a solution that increases gold recovery and supports a 15-year mine life at Kışladağ, allowing Eldorado to continue to provide employment and economic opportunity in the region, as well as provide a solid foundation for future growth.

“Kışladağ has been the cornerstone asset of Eldorado for over a decade, producing over 3 Moz of gold and generating significant value for all stakeholders during that period. This project is a testament to our exceptional team and technology partners working together to execute in challenging circumstances during the pandemic.”

Enter Engineering, thyssenkrupp to tackle Tebinbulak iron ore deposit in Uzbekistan

Enter Engineering and thyssenkrupp AG have signed an Agreement of Intent that could see the engineering procurement and construction (EPC) contractor take the exclusive role as construction partner in building an integrated mining metallurgical complex at the Tebinbulak iron ore deposit in Uzbekistan.

The pact, worth €50 million ($58 million), comes on top of a signed agreement for the start of preparatory work on the project, including a contract for the supply of equipment, its design, supervision during installation and commissioning at the facility.

The high pressure grinding roll (HPGR) technology will be used to help process up to 60 Mt/y of iron ore, according to the EPC firm.

The implementation period for Enter Engineering’s construction role is two years with the plant launch anticipated for September 2023.

Bakhtiyor Fazylov, Chairman of the Board of Directors of Enter Engineering, said: “We are delighted to partner with a leading global company such as thyssenkrupp. Applying German standards, we will create a high-quality raw material base for the domestic metallurgical industry. This project also embodies all the goals Enter Engineering strives for: protecting Uzbekistan’s national interests in the international market, supporting the interests of domestic consumers and creating jobs.”

Reza Poorvash, CEO thyssenkrupp Mining Technologies Europe and Asia, said: “To date, more than 140 units of HPGR equipment have been sold in the mining industry. In the CIS countries, thyssenkrupp takes a leading position among mining companies that use this technology, in practice confirming the high quality and reliability of the German brand.”

Roman Karl, Managing Director thyssenkrupp Mining Technologies CIS, added: “We are delighted to partner with such a well-known company in Uzbekistan as Enter Engineering, who have a long track record of successful execution in major engineering construction projects.

“The project will use one of the most energy efficient and innovative technologies to significantly reduce energy consumption. HPGR has been used since 1985 in the cement industry, and since 1986 in the mining industry for use in the grinding process to ensure a high level of product fineness. Full integration of this technology within Industry 4.0 is also important.”

The Tebinbulak complex is significant for Uzbekistan because of its multiplier effect. As well as creating new jobs in remote areas, it will help develop domestic iron ore to provide the country’s existing metallurgical complexes with raw materials. It will also support development of infrastructure, creation of service enterprises and an increase in trade between countries.

Tebinbulak is located in the Karauzyak district of Karakalpakstan, in the north-west part of Uzbekistan. The field covers 5.2 sq.km and comes with a predicted mine life of 27 years.

Cooperation between Enter Engineering and thyssenkrupp is supported at a high inter-governmental level, with the agreement signing ceremony attended by Alisher Sultanov, Uzbekistan’s Minister of Energy.

Swiss Tower Mills Minerals backs Coalition for Eco-Efficient Comminution

Swiss Tower Mills Minerals AG (STM) has become the latest sponsor to support the work of the not-for-profit Coalition for Eco-Efficient Comminution (CEEC).

An innovative company that has successfully translated the vertical stirred milling technology of industrial minerals to hard-rock minerals processing, STM’s support of CEEC’s work was a natural fit for the company, according to Managing Director, Ralf Hesemann.

“The uptake of new technology in the mining industry is traditionally a slow process,” Hesemann said. “Tapping into a trusted independent body that communicates the latest technical findings on efficient comminution practices is a win-win for both of us.

“I look forward to our collaboration.”

Swiss-based STM developed the Vertical Regrind Mill (VRM) and released it to the minerals market in 2012. More than 60 of the stirred media grinding mills have been sold to mines across the Americas, Europe, Africa, Asia and Australia. For fine and ultra-fine grinding applications, it is marketed under the name HIGmill, through the exclusive partner Metso:Outotec. For coarse regrind applications, STM offers the VRM mill directly to customers in the minerals market.

Since the grinding principle of multi-compartment grinding offers substantial energy savings, a new stirred mill has been developed for coarse grinding applications up to 6 mm feed size, the Vertical Power Mill™ (VPM). Mill sizes range from 700 kW to 12,500 kW with high flow rates, and potential energy savings of up to 40%. Due to its small footprint, STM is marketing the VPM as a viable ball mill replacement in HPGR circuits or for capacity increase in existing plants.

The energy savings are achieved through uniquely designed rotors and stator rings in a vertical arrangement that enable high power intensities, even with relatively low tip speeds, STM says. This results in higher energy efficiency, a smaller footprint and the potential for increased recoveries. Power intensities of 200-300 kW/cu.m are typical, and operational tip speeds range between 6-12 m/s, depending on application and mill size.

CEEC Director, Chris Rule, said it was encouraging to see energy efficient, stirred media mills being installed by industry as a step towards more sustainable mining practices, in line with ESG considerations and net zero emissions commitments.

One of the first HIGmills be commissioned, in 2015, was a 700 kW mill for a copper concentrate regrind application at the Kevitsa mine in Finland. Several papers have been published on the energy efficiency and metallurgical performance of this mill, including an Outotec paper presented at Comminution Capetown 2016, and ‘A Review of Published Full-Scale Stirred Mill Results’ by Michael Larson, Molycop, USA, presented at the SAG 2019 Conference.

The technology will also be installed at the Iron Bridge Magnetite Project in Western Australia. The joint venture between Fortescue Metals Group and Formosa Steel IB Pty Ltd is the world’s first large-scale plant without horizontal milling. The flowsheet consists of a two-stage HPGR circuit feeding in total 10 advanced HIGmill grinding mills.

Rule said stirred mill grinding technology had been well proven for decades in industrial mineral applications such as in the opacifiers, fillers, ceramics, paint and pharmaceutical industries.

“We commend STM for translating this technology to mineral processing, offering miners an energy-efficient, low footprint alternative to high-intensity ball milling,” Rule said.

“Having STM on board as a CEEC sponsor means greater opportunities for us to learn about and share alternative comminution approaches. This support from our valued sponsors over the past 10 years is what enables CEEC to help keep industry aware of demonstrated advances that help mining leaders tackle the challenges of reducing the energy consumption, emissions and overall footprint of their operations.”

Hesemann said declining ore quality meant energy efficient comminution was becoming a more critical stage for realising profit.

“We’re proud of the part our technology plays in lowering the footprint of mineral processing, while at the same time decreasing capital expenditure and operating expenditure and improving the bottom line.

“Being a CEEC sponsor will enable us to more widely share any advances in this field, as well as learning from the global network of industry experts that CEEC brings together through its events and online resources.”

Pictured is the factory acceptance test success for a new 50,000 litre Vertical Regrind Mill (VRM50000)

eHPCC: the future of grinding in mining?

A lot has been made of the potential of high pressure grinding rolls (HPGRs) to facilitate the dry milling process many in the industry believe will help miners achieve their sustainability goals over the next few decades, but there is another novel technology ready to go that could, according to the inventor and an independent consultant, provide an even more effective alternative.

Eccentric High Pressure Centrifugal Comminution (eHPCC™) technology was conceived in 2013 and, according to inventor Linden Roper, has the potential to eliminate the inefficiencies and complexity of conventional crushing and/or tumbling mill circuits.

It complements any upstream feed source, Roper says, whether it be run of mine (ROM), primary crushed rock, or other conventional comminution streams such as tumbling mill oversize. It may also benefit downstream process requirements through selective mineral liberation, which is feasible as the ore is comminuted upon itself (autogenously) in the high pressure zone via synchronous rotating components. Significant product stream enrichment/depletion has been observed and reported, too.

As IM goes to press on its annual comminution and crushing feature for the April 2021 issue – and Dr Mike Daniel, an independent consultant engaged by Roper to review and critique the technology’s development, prepares a paper for MEI Conferences’ Comminution ’21 event – now was the right time to find out more.

IM: Considering the Comminution ’21 abstract draws parallels with HPGRs, can you clarify the similarities and differences between eHPCC and HPGR technology?

MD & LR: These are the similarities:

  • Both offer confined-bed high-pressure compression comminution, which results in micro fractures at grain boundaries;
  • Both have evidence of preferential liberation and separation of mineral grains from gangue grains at grain boundaries; and
  • Both have an autogenous protective layer formed on the compression roll surfaces between sintered tungsten carbide studs.

These are the differences:

  • eHPCC facilitates multiple cycles of comminution, fluidisation and classification within its grinding chamber, retaining oversize particles until the target product size is attained. The HPGR is a single pass technology dependent on separate materials handling and classification/screening equipment to recycle oversize particles for further comminution (in the event subsequent stages of comminution are not used);
  • Micro factures around grain boundaries and compacted flake product that are created within HPGRs need to be de-agglomerated with downstream processing either within materials handling or wet screening. In some instances, compacted flake may be processed in a downstream ball mill, whereas, in eHPCC, preferential mineral liberation is perfected by subsequent continuous cycles within the grinding chamber until mineral liberation is achieved within a bi-modal target size (minerals and gangue). The bi-modal effect differs from ore type to ore type and the natural size of the minerals of interest;
  • The preferential liberation of mineral grains from gangue grains generally occurs at significantly different grain sizes, respectively, due to the inherent difference in progeny hardness. eHPCC retains the larger, harder grains, hence ensuring thorough stripping/cleaning of other grain surfaces by shear and attrition forces;
  • eHPCC tolerates rounded tramp metal within its grinding chamber, however does not tolerate high quantities of sharp, fragmented tramp metal that create a non-compressible, non-free-flowing bridge between roll surfaces, which risks the damage of liner surfaces;
  • The coarse fraction ‘edge effect’ common in HPGR geometry is not an issue with eHPCC. In fact, the top zone of the eHPCC grinding chamber is presumed to be an additional portion of the primary classification zone within the grinding chamber. The oversize particles from the internal classification process are retained for subsequent comminution;
  • The maximum size of feed particle (f100) entering the eHPCC is not limited to roll geometry as is the case with HPGRs (typically 50-70 mm). eHPCC f100 is limited to feed spout diameter (for free flow) and dependent of machine size ie eHPCC-2, -5, -8 and -13 are anticipated to have f100 60 mm, 150 mm, 240 mm and 390 mm, respectively. The gap between rolling surfaces is greater than the respective f100; and
  • eHPCC technology shows scientifically significant product stream enrichment.

IM: What operating and capital cost benefits do you envisage when compared with typical HPGR installations?

MD & LR: Both operating and capital cost benefits of the eHPCC relative to HPGR technology are due to the eHPCC not requiring the pre-crushing and downstream classification equipment required by HPGRs.

The eHPCC operating cost benefits are associated with eliminating maintenance consumables, downtime, reliability issues and energy consumption associated with the equivalent HPGR downstream equipment listed above.

The eHPCC capital cost benefits are associated with eliminating the real estate (footprint) and all engineering procurement and construction management costs associated with the equivalent HPGR upstream/downstream equipment listed above. eHPCC flowsheets are likely to be installed as multiple ‘one-stop’ units that maintain high circuit availability due to ongoing cyclic preventative maintenance.

IM: Where has the design for the eHPCC technology come from?

LR: It was invented in early 2013 by me. I then pioneered proof-of-concept, prototyping, design and development, culminating in operational trials in a Kazakhstan gold mine in 2020. A commercial-grade detailed design-for-manufacture has since been undertaken by a senior team of heavy industry mechanical machine designers and engineers.

IM: In your conference abstract, I note that the eHPCC technology has been tested at both laboratory and semi-industrial scale with working prototypes. Can you clarify what throughputs and material characteristics you are talking about here?

LR: The first iteration of the technology, eHPCC-1, was tested at the laboratory scale from 2013-2015. This proof-of-concept machine successfully received and processed magnetite concentrate, copper-nickel sulphide ore, alkaline granite, marble and a wolfram clay ore dried in ambient conditions. The typical throughput was between 200-400 kg/h depending on the feed size, particle-size-reduction-ratios (dependent of grain size) and target product size. The feed size was limited to a maximum of 25 mm to ensure free flow of feed spout.

Alkaline granite: eHPCC-2 coarse product (left) and fine product (right)

MD & LR: From 2016-2020, we moved onto the semi-industrial scale testing with the eHPCC-2 (two times scaled up from eHPCC-1). This was designed for research and development (R&D) and tested on magnetite concentrate, alkaline granite, and hard underground quartz/gold ore. The throughput capabilities depended on the geo-metallurgical and geo-mechanical properties of feed material, such as particle size, strength, progeny (grain) size and particle size-reduction-ratios (subject to confined bed high pressure compression). Larger-scale machines are yet to be tested against traditional ‘Bond Theory’ norms.

The eHPCC, irrespective of the outcomes, should be evaluated on its ability to effectively liberate minerals of interest in a way that no other comminution device can do. The maximum feed size, f100, at the gold mine trials was limited to 50 mm to ensure free flow through the feed spout. R&D culminated in pilot-scale operational trials at the Akbakai gold mine (Kazakhstan), owned by JSC AK Altynalmas, in 2020, where SAG mill rejects of hard underground quartz/gold ore were processed. The mutual intent and purpose of the tests was to observe and define wear characteristics of the eHPCC grinding chamber liners (roll surfaces). These operational trials involved 80% of the feed size being less than 17 mm and a variety of targeted product sizes whereby 80% was less than 1 mm, 2 mm, 2.85 mm and 4.8 mm. The throughput ranged from 1-5 t/h based on the size.

IM: What throughputs and material characteristics will be set for the full-scale solution?

LR: There will be a select number of standard eHPCC sizes. Relative to the original eHPCC-1, the following scale-up factors are envisaged: -2, -3, -5, -8, and -13. These are geometrical linear scale-up factors; the actual volumetric capacity is a cube of this factor, with adjustments for centripetal acceleration. Currently -13 times seems to be the maximum feasible size of the present detailed design philosophy, but there are no foreseeable limitations in terms of feed materials with exception to moist clay. Clay was successfully processed after drying the feed in ambient temperatures during testing. Further testing of moist clays blended with other materials that can absorb the moisture as they comminute would be desirable.

IM: Other HPGRs can also be equipped with air classification technology to create dry comminution circuits. What is the difference between the type of attrition and air classification option you are offering with the eHPCC?

MD & LR: Two modes of comminution occur in the particle bed of eHPCC repetitively and simultaneously. First, confined bed pressure compression breakage occurs at a macro level that promotes shear/compression forces greater than the mineral grain boundaries. Second, Mohr-Coulomb Failure Criteria (shear/attrition) that completes the separation of micro fractures on subsequent cycles takes place.

The nip angle between the rotating components of eHPCC technology never exceed 5°. During the decompression and fluidisation portion of the cycle, the softer species – which are now much smaller – are swept out of the fluidised particle bed against centrifugal and gravitational forces by process air. The larger species, influenced by centripetal acceleration, concentrate at the outer diametric and lower limits of the conical rotating grinding chamber, continuing to work on each other during each subsequent compression phase.

HPGRs are limited to one single-pass comminution event, requiring downstream external classification and subsequent recycling/reprocessing of their oversize and/or flake product.

IM: How will it improve the mineral liberation and separation efficiency compared with other grinding solutions that combine both?

MD: eHPCC technology could compete with the Vertical Roller Mill and Horomill, however, eHPCC is likely to be more compact with high intensity breakage events contained within the all-inclusive system of breakage, classification and removal of products.

IM: When was it most recently tested and over what timeframe?

LR: The eHPCC-2 pilot plant was mobilised, setup and commissioned in March 2020, but its operation was suspended until June 2020 due to COVID-19 quarantine restrictions and a need to cater to abnormal amounts of ball fragments in the feed, the latter of which pushed the treatment of tramp metal to the extreme. The machine operated for the months of June and July using liners constructed of plasma transferred arc welded (PTAW) tungsten carbide (TC) overlay. During this period, a total of 795 t was processed at various targeted product sizes, with, overall, an average throughput of 3 t/h (nominally 265 operating hours) processed.

Side view of pilot system including feed hopper and weigh-scale feeder (right), feed conveyor (middle foreground), control and auxiliaries (middle background), eHPCC-2 (left foreground), dust bag-house (left background) and product conveyor and stockpile (not shown left background)
Front-end loader filling feed hopper with SAG mill rejects f80 18 mm

The PTAW-TC overlay was deemed unsustainable as it was consumed rapidly and demanded continuous rebuilding due to the high pressure intensive abrasive wear on the convex cone. The pilot plant operation was mostly suspended during the month of August while an alternative tungsten carbide studded liner, analogous to HPGR studded rolls, was manufactured for simulating a trial of this studded liner philosophy. The studded liner philosophy was operated in the eHPCC-2 in Kazakhstan for sufficiently long enough to ascertain the creation of the autogenous protective wear layer of rock between the studs, with the simulation trial deemed a success. The design philosophy shall be adapted on the commercial-grade eHPCC.

eHPCC-2 TungStud™ as-new (left) high-pressure-air-cleaned (middle) and brushed (right)

The pilot plant was demobilised from the Akbakai site laydown area on September 10, 2020, to release the area for construction of a non-related plant expansion. The operational experiences of the pilot plant at Akbakai provided valuable knowledge and experience pertaining to mechanical inertia dynamics and design for eliminating fatigue within eHPCC components.

IM: Aside from the test work on trommel oversize at the Kazakhstan gold mine, where else have you tested the technology?

LR: eHPCC has no other operational experiences so far. Investment and collaboration from the industry to progress the commercialisation of eHPCC is invited. The commercial-grade eHPCC-2.2 is designed and ready for manufacture.

IM: Is the technology more suited to projects where multiple streams can be produced (fines, coarse piles, etc)?

LR: eHPCC is configurable to meet the demands and liberality of a diverse spectrum of feed materials and the potential downstream extractive processes are complementary to eHPCC product streams. Therefore, it would be incorrect to categorise it as more suitable in any one niche; it is configurable, on a case-by-case basis, to meet the liberality of the specific progeny of the feed.

IM: What energy use benefits do you anticipate by creating a one-step comminution and classification process over the more conventional two-step process?

MD & LR: The energy saving benefits include:

  • Elimination of tumbling mill grinding media consumption;
  • Elimination of the liberal wastage of randomly directed attrition and/or impact events that indiscriminately reduce the size of any/all particles (gangue or precious mineral) with the conventional tumbling mill; and
  • Elimination of energy consumption of the materials handling systems between the various stages of comminution and classification, be it dry belt conveying, vibrating screens, classifiers, cyclone feed pumps, cyclones and their respective recirculating loads that can be upward of 300% of fresh feed.

IM: Do you anticipate more interest in this solution from certain regions? For instance, is it likely to appeal more to those locations that are suffering from water shortages (Australia, South America)?

MD & LR: We suspect the initial commercialisation growth market to be from base metals producers seeking to expand or retire existing aged/tired comminution classification capacity, followed by industry acknowledgement of the technology’s potential to shift the financial indicators of other potential undeveloped projects into more positive territory. This latter development could see the technology integrated into new projects.

In general, the technology will appeal to those companies looking for more efficient dry comminution processes. This is because it offers a pathway to rejection of gangue at larger particle sizes, early stream enrichment/depletion and minimal overgrinding that creates unnecessary silt, which, in turn, hinders or disrupts the integrity of downstream metallurgical extraction kinetics, and/or materials handling rheology, and/or tailings storage and management.

LR: There are a number of rhetorical questions the industry needs to be asking: why do we participate in the manufacture and consumption of grinding media considering the holistic end-to-end energy and mass balance of this (it’s crazy; really why?)? Why do we grind wet? What are the barriers preventing transition from philosophising over energy efficiency, sustainability etc and actually executing change? Who is up for a renaissance of bravely pioneering disruptive comminution and classification technology in the spirit of our pioneering forefathers?

The more these questions are asked, the more likely the industry will find the solutions it needs to achieve its future goals.

Dr Mike Daniel’s talk on eHPCC technology will be one of the presentations at the upcoming Comminution ’21 conference on April 19-22, 2021. For more information on the event, head to https://mei.eventsair.com/comminution-21/ International Mining is a media sponsor of the event

SNC-Lavalin to manage construction of Coeur’s Rochester silver-gold mine expansion

SNC-Lavalin has been awarded a $30 million contract by Coeur Rochester Inc, a wholly-owned subsidiary of Coeur Mining, to provide construction management services for the Plan of Operations, Amendment Number 11 (POA 11) expansion project, at Coeur’s Rochester mine near Lovelock, Nevada, USA.

The contract commenced in the December quarter and is estimated to be completed by the end of 2022. This win is aligned with SNC-Lavalin’s new strategy moving forward in the Services segment, it said.

The POA 11 expansion project includes the construction of a new crushing plant, including a primary, secondary and tertiary crushing circuit (high pressure grinding rolls), a new heap leach pad (272 Mt), a new Merrill-Crowe process plant (62,509 litres/min), and upgrades to existing electrical utility system infrastructure, including a new substation and power distribution lines.

Coeur says this will more than double planned annual crusher throughput capacity from around 12.7 Mt to over 25.4 Mt, post-expansion. This will see average annual silver and gold production total over 8 Moz and some 80,000 oz, respectively, for the initial 10 years, post-expansion

SNC-Lavalin said: “This mandate is well aligned with our expertise in silver, gold and base metal project delivery as well as our commitment to delivering real value to our clients.”

SNC-Lavalin’s offices in Reno, Nevada, and Toronto, Ontario, will continue to support the construction management phase of the project. In addition, a team based locally at the site will manage construction-related activities.

César Inostroza, Senior Vice-President, Mining & Metallurgy, SNC-Lavalin, said: “SNC-Lavalin’s Mining & Metallurgy strategic plan is gaining traction with this mandate. It is an example of the mining services work that our team is winning across our core geographies, including the USA. SNC-Lavalin and Coeur continue to foster a strong relationship that finds and executes services solutions to create world-class operations

“This award is a testament to the continued partnership between SNC-Lavalin and Coeur. It leverages our knowledge of the Rochester mine and engineering expertise from the previous phase of this project and expands our work in the US.”

Terrence FD Smith, Coeur’s Senior Vice President and Chief Development Officer, added: “The strong business partnership between Coeur and SNC-Lavalin will help ensure a robust project delivery for Rochester, paving the way for improved performance in the future.”

Since approval of the initial Plan of Operation in 1986, the Rochester mine has undergone periodic mine plan amendments to support development projects and continued operations. The POA 11 proposes another mine life extension, which is expected to maintain the current workforce and support full production activities at Rochester until 2033.

AngloGold Ashanti confirms caving plans in Colombia

The Massmin 2020 crowd got a glimpse of just what will be required to build Colombia’s first underground caving mine during a presentation from AngloGold Ashanti’s Lammie Nienaber this week.

Nienaber, Manager of Geotechnical Engineering for the miner and the presenter of the ‘Building Colombia’s first caving mine’ paper authored by himself, AngloGold Ashanti Australia’s A McCaule and Caveman Consulting’s G Dunstan, went into some detail about how the company would extract the circa-8.7 Moz of gold equivalent from the deposit.

The Nuevo Chaquiro deposit is part of the Minera de Cobre Quebradona (MCQ) project, which is in the southwest of Antioquia, Colombia, around 104 km southwest of Medellin.

A feasibility study on MCQ is expected soon, but the 2019 prefeasibility study outlined a circa-$1 billion sublevel caving (SLC) project able to generate an internal rate of return of 15%. Using the SLC mining method, a production rate of 6.2 Mt/y was estimated, with a forecast life of mine of 23 years.

The MCQ deposit is a large, blind copper-gold-silver porphyry-style deposit with a ground surface elevation of 2,200 metres above sea level (masl, on mountain) and around 400 m of caprock above the economic mineralisation.

Due to the caving constraints of the deposit, the first production level to initiate caving (undercut) is expected to be located around 100 m below the top of the mineralisation at 1,675 masl (circa-525 m below the top of the mountain), with the mining block extended around 550 m in depth (20 production levels at 27.5 m interlevel spacings).

The main ore transfer horizon is located 75 m higher in elevation than the mine access portals at 1,080 masl and the proposed valley infrastructure. The initial mining block will be accessed by twin tunnels developed in parallel for 2 km at which point a single access ramp will branch up towards the undercut; the twin tunnels will continue another 3.7 km to the base of the SLC where the crushing and conveying facilities will be located.

The company is currently weighing up whether to use tunnel boring machines or drill and blast to establish these tunnels.

Nienaber confirmed the 20 level SLC panel cave layout would involve 161 km of lateral development and 14 km of vertical development. There would be six ore pass connections on each level, four of these being ‘primary’ and two acting as backups. The crusher would be located on the 1155 bottom production level.

Due to the ventilation requirements in Colombia the mining fleet selected for Quebradona is predominantly electric, Nienaber said, adding that the units will initially be electric cable loaders powered by 1,000 v infrastructure.

Fourteen tonne LHDs were selected for the production levels based on their speed, bucket size (enables side-to-side loading in the crosscut and identification of oversize material) and cable length, the authors said. On the transfer level, 25 t loaders were specified to accommodate the shorter tramming lengths and limited operating areas (there are a maximum of two loaders per side of the crusher due to the layout).

As battery technology improves in the coming years, the selection of loader sizes may change as additional options become available, according to the authors.

The selection of the present Sandvik fleet was predominantly based on the electric loaders and the OEM’s ability to provide other front-line development and production machines required to undertake SLC mining, the authors said.

This decision also accounted for the use of automation for the majority of production activities, with the use of a common platform seen as the most pragmatic option at this stage.

It has also been proposed that the maintenance of the machines be carried out by Sandvik under a maintenance and repair style contract since there is a heavy reliance on the OEM’s equipment and systems.

An integrated materials handling system for the SLC was designed from the ore pass grizzlies, located on the production levels, to the process plant.

Due to the length of the ore passes (up to 500 m), and the predicted comminution expected by the time the rock appears on the transfer level, larger than industry standard grizzly apertures of 1,500 mm have been selected.

The design criteria for the underground crusher was that it needed to reduce the ore to a size suitable for placement on the conveyor belt and delivery to the surface coarse ore stockpile, after which secondary crushing prior to delivery at the process plant will be undertaken.

Assuming the maximum size reduction ratio for the crusher of circa-6:1 at a throughput rate of 6.2 Mt/y, a 51 in (1,295 mm) gyratory crusher was selected. This crusher is also suitable to support block cave mining should the conversion of mining method occur, according to the authors.

The process plant will include high pressure grinding rolls as the main crushing unit on the surface, supported by a secondary crusher to deal with oversize material. The ore then feeds to a ball mill before being discharged to the flotation circuit.

The gold-enriched copper concentrate will be piped to the filter plant for drying and the removal of water down to a moisture content of 10%, according to the company, while the tailings will be segregated to pyrite and non-pyrite streams before being distributed to one of two filter presses.

Dry stacking of the tailings will be used, with the pyrite-bearing tailings being encapsulated within the larger inert tailings footprint.

With the feasibility study due before the end of the year – and, pending a successful outcome – the proposed site execution works could start in the September quarter of 2021, Nienaber said.