Tag Archives: HPGR

Metso Outotec delivers ‘next evolution’ in high pressure grinding rolls with HRCe

Comminution of minerals, Environmental, Mineral processing, Mining services, Sustainable mining, , , , ,

Metso Outotec has launched the “next evolution of the high pressure grinding roll”, with the delivery of its HRC™e HPGR.

The original HRC HPGR was launched back in 2014 by Metso (now Metso Outotec), pioneering the use of flanges and non-skewing design. The grinding performance that brings energy efficiency, lower circulating loads and increased throughput is now strengthened with an additional evolution in design, Metso Outotec says.

The new HRCe comes with a decreased installation capital expenditure compared with the original HRC. Changes in design allow for maximum productivity with proven technology that leads to superior grinding efficiency.

Christoph Hoetzel, Head of Grinding business line at Metso Outotec, said: “We are very excited about the new HRCe, which combines proven technology and customer-focused evolutions. Metso Outotec is the only OEM that has been able to design and develop reliable flanged HPGR technology that has demonstrated superior performance for many years in the mining industry. We will continue utilising our proven technology but have evolved the design to maximise value for our customers and superior grinding efficiency.”

The high throughput comes from the elimination of the edge effect with the flange design, which will ultimately maximise the amount of crushed material, the company says. With the anti-skew assembly, customers will find faster restarts and no downtime from skewing events, according to Metso Outotec.

The HRCe also comes with a large feed size acceptance of 60-120 mm and improved energy efficiency compared with similar HPGRs, the company says. It also boasts typical capacities of 1,810-6,930 t/h.

Key benefits of the new HPGR include:

  • Improved energy efficiency of up to 15%;
  • Lower circulating load of up to 24%;
  • Increased throughput of up to 19%;
  • Elimination of edge effect from combination of proven flange design and anti-skew assembly; and
  • Elimination of downtime caused by skewing events.

Latest Kamoa-Kakula copper studies reaffirm project’s world-class status

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The latest economic studies on Ivanhoe Mines and Zijin Mining Group’s majority-owned Kamoa-Kakula project in the Democratic Republic of Congo have indicated the asset could become the world’s second largest copper mining complex.

First production at Kamoa-Kakula is less than a year away, but the project partners have continued with a series of economic studies that emphasise the world-class nature of the orebodies within their control.

The headline maker is the results of a preliminary economic assessment that has evaluated an integrated, multi-staged development to achieve a 19 Mt/y production rate at the mine, with peak annual copper production of more than 800,000 t.

At the same time, a prefeasibility study (PFS) has been carried out to look at mining 1.6 Mt/y from the Kansoko mine, in addition to 6 Mt/y already planned to be mined from Kakula, to fill a 7.6 Mt/y processing plant at Kakula.

A definitive feasibility study (DFS) has also evaluated the stage-one, 6 Mt/y plan at Kakula, which is currently being constructed and is less than a year away from producing first copper, according to Ivanhoe Co-Chair, Robert Friedland.

While the operation looks to have the scale of a world-class asset, it will also have top ranking ‘green’ credentials, according to Friedland.

“The Kakula mine has been designed to produce the world’s most environmentally-responsible copper, which is crucial for today’s new generation of environmentally- and socially-focused investors,” he said.

“Zijin shares our commitment to build the new mines at Kamoa-Kakula to industry-leading standards in terms of resource efficiency, water and energy usage, and minimising emissions. We are blessed with ultra-high copper grades in thick, shallow and flat-lying orebodies – allowing for large-scale, highly-productive, mechanised underground mining operations; and access to abundant clean, sustainable hydro electricity to power our mines – providing us with a distinct advantage in our goal to become the world’s ‘greenest’ copper miner and be among the world’s lowest greenhouse gas emitters per unit of copper produced.”

The project recently retained Hatch of Mississauga, Canada, to independently audit the greenhouse gas intensity metrics for the copper that will be produced at Kamoa-Kakula.

The Kamoa-Kakula Integrated Development Plan (IDP) 2020, as the companies refer to it, builds on the results of the previous studies announced in February 2019.

DFS to 6 Mt/y

The new DFS incorporates the advancement of development and construction activities to date, and has once again confirmed the outstanding economics of the first phase Kakula Mine, Ivanhoe said.

It evaluates the development of a stage one, 6 Mtpa underground mine and surface processing complex at the Kakula deposit with a capacity of 7.6 Mt/y, built in two modules of 3.8 Mt/y, with the first already under advanced construction (see photo). It comes with an internal rate of return of 77% and project payback period of 2.3 years.

The first module of 3.8 Mt/y commences production in the September quarter of 2021, and the second in the March quarter of 2023. The life-of-mine production scenario provides for 110 Mt to be mined at an average grade of 5.22% Cu, producing 8.5 Mt of high-grade copper concentrate.

The Kakula 2020 DFS mine access is via twin declines on the north side and a single decline on the south side of the deposit. One of the north declines will serve as the primary mine access, while the other decline is for the conveyor haulage system, which was recently commissioned.

The primary ore handling system will include a perimeter conveyor system connected to truck load-out points along the north side of the deposit. The perimeter conveyor system will terminate at the main conveyor decline.

The mining method for the Kakula deposit is primarily drift-and-fill using paste backfill (around 99%); with the exception of a room-and-pillar area close to the north declines, which will be mined in the early years of production. The paste backfill system will use a paste plant located on surface connected to a distribution system that includes a surface pipe network connected to bore holes located at each connection drive on the north side of the orebody, the company says.

The Kakula concentrator design incorporates a run-of-mine stockpile, followed by primary cone crushers operating in closed circuit with vibrating screens to produce 100% passing 50 mm material that is stockpiled.

At the end of August, the project’s pre-production surface ore stockpiles totalled an estimated 671,000 t grading 3.36% Cu, including 116,000 t of high-grade ore grading 6.08% Cu.

The crushed ore is fed to the high pressure grinding rolls operating in closed circuit with wet screening, at a product size of 80% (P80) passing 4.5 mm, which is gravity fed to the milling circuit.

The milling circuit incorporates two stages of ball milling in series in closed circuit with cyclone clusters for further size reduction and classification to a target grind size of 80% passing 53 micrometres (µm).

The milled slurry is pumped to the rougher and scavenger flotation circuit where the high-grade, or fast-floating rougher concentrate, and medium-grade, or slow-floating scavenger concentrate, are separated for further upgrading. The rougher concentrate is upgraded in the low entrainment high-grade cleaner stage to produce a high-grade concentrate.

The medium-grade or scavenger concentrate together with the tailings from the high-grade cleaner stage and the recycled scavenger recleaner tailings are combined and further upgraded in the scavenger cleaner circuit. The concentrate produced from the scavenger cleaner circuit, representing roughly 12% of the mill feed, is re-ground to a P80 of 10 µm prior to final cleaning in the low entrainment scavenger recleaner stage.

The scavenger recleaner concentrate is then combined with the high-grade cleaner concentrate to form final concentrate. The final concentrate is then thickened and pumped to the concentrate filter. Final filtered concentrate is then bagged for shipment to market.

The scavenger tailings and scavenger cleaner tailings are combined and thickened prior to being pumped to the backfill plant and/or to the tailings storage facility. Backfill will use approximately half of the tailings, with the remaining amount pumped to the tailings storage facility.

Based on extensive test work, the concentrator is expected to achieve an overall recovery of 85%, producing a very high-grade concentrate grading 57% copper. Kakula also benefits from having very low deleterious elements, including arsenic levels of 0.02%.

7.6 Mt/y PFS

The PFS evaluating mining 1.6 Mt/y from the Kansoko mine envisages an average annual production rate of 331,000 t of copper at a total cash cost of $1.23/lb copper for the first 10 years of operations, and annual copper production of up to 427,000 t by year four. This comes with an internal rate of return of 69% and project payback period of 2.5 years, according to Ivanhoe.

Development would see Kakula-Kansoko benefit from an ultra-high, average feed grade of 6.2% Cu over the first five years of operations, and 4.5% Cu on average over a 37-year mine life.

There are currently two mining crews at Kansoko, in addition to the 10 mining crews (three owner crews and seven contractor crews) currently at Kakula, with the ability to increase this number to fast-track the development of Kansoko, Ivanhoe said.

19 Mt/y option

The Kamoa-Kakula 2020 PEA presents initial production from Kakula at a rate of 6 Mt/y, followed by subsequent, separate underground mining operations at the nearby Kansoko, Kakula West and Kamoa North mines, along with the construction of a 1 Mt/y of concentrate direct-to-blister smelter. The smelter section of the study saw China Nerin Engineering act as the main engineering consultant with Outotec providing design and costing for propriety equipment.

The Kamoa North Area comprises five separate mines that will be developed as resources are mined out elsewhere to maintain the production rate at up to 19 Mt/y, with an overall life in excess of 40 years, Ivanhoe says.

For this integrated 19 Mt/y option, the PEA envisages $700 million in remaining initial capital costs, with future expansion at Kansoko, Kakula West and Kamoa North funded by cash flows from the Kakula mine, resulting in an internal rate of return of 56.2% and a payback period of 3.6 years.

This shows the potential for average annual production of 501,000 t of copper at a total cash cost of $1.07/lb copper during the first 10 years of operations and production of 805,000 t/y of copper by year eight, Ivanhoe said.

“At this future production rate, Kamoa-Kakula would rank as the world’s second largest copper mine,” the company said.

Multotec solution scrubs up well at Ekapa Minerals diamond plant

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A revolutionary new concept in fines scrubbing is proving to be a game changer for Ekapa Minerals at its Combined Treatment Plant (CTP) in Kimberley, South Africa.

The innovation, developed by Multotec Wear Linings, is processing both virgin underground kimberlite as well as tailings for retreatment at the CTP. The solution is effectively a pulping chute that scrubs and washes the re-crushed product after it has passed through the high pressure grinding rolls (HPGR) inter-particle tertiary crushing circuit.

The important advantage here, according to Multotec Wear Linings Projects Sales Manager, John Britton, is that it performs the scrubbing action faster and more efficiently than a traditional rotary scrubber would, and at much lower cost.

Multotec commissioned two of these pulping chutes at Ekapa Minerals in late 2019, where they have been operating consistently and in line with expectations. With the use of patented wave generators, the pulping chute uses the gravitational energy from the slurry flow to create a constant turbulent mixing action that releases the mud, clay and slime sticking to the kimberlite particles.

According to Ekapa Minerals CEO, Jahn Hohne, the pulping chutes are a welcome contribution to the company’s cost saving efforts, and a clear demonstration of Multotec’s expertise in developing value-adding solutions in the mining sector.

“The dual chute pulping plant is ideally suited to de-conglomerating the HPGR cake product and is exceeding expectations in efficiency and effectiveness at over 600 t/h, which is a major relief on the existing overloaded pair of CTP scrubbers,” he said. “The net result is a meaningful increase of up to 20% throughput capacity of the entire processing plant which substantially improves the economy of scale of CTP, feeding directly to the bottom line.”

Britton highlighted the efficiency of the system, which is able to aggressively scrub the material in just three to four seconds as it passes through the chute. This represents just a fraction of the usual retention time in a rotary scrubber, which is three to four minutes, according to the company. He also emphasises the drastic reduction in running cost which the pulping chute achieves.

“From our experience of plant layouts and flow diagrams, it is clear that fines scrubbers are significant contributors to a plant’s capital, operating and maintenance costs,” Britton said. “Scrubbers are equipped with large drives with gears and gearboxes to rotate the drum. They are high consumers of power and require mechanical component maintenance which means higher operating costs.”

Substantial structures and supports are also needed for the scrubber and its drive mechanisms. In designing the pulping chute, Multotec sought a simplified solution, Britton says. In addition to improving scrubbing efficiency, the objective included reducing the cost of replacing scrubber liners and the downtime that this demanded. The cost of replacing the steel shell of a scrubber – which is constantly subject to stress, wear and fatigue – was another cost to be considered.

“The pulping chute, by contrast, is a stationery and much simplified innovation, focused on the scrubbing of fines less than 32 mm in size,” the company said. “Slurry deflectors located at the top end of the scrubbing chute direct at least part of the slurry away from the scrubbing chute floor. This curls into an arched form which flows backwards into the approaching flow of slurry, creating the turbulent scrubbing effect.”

Britton said: “We custom-design the chutes to suit the application and can increase chute capacity to up to 800 t/h. This is achieved with no moving parts, bearings, hydraulic packs or girth gears; the only power required is to supply material and water to the receiving chute. These actions are also required to feed the scrubber, then gravity takes over and provides the required energy.”

Maintenance is also streamlined by designing the chute in segments. Should one segment be wearing more than others, it can be quickly removed and replaced – putting the chute back into operation while the original segment is refurbished as a spare.

Britton says the pulping chute has drawn interest from other diamond producers in southern Africa, Australia and Canada. It can also be applied in commodity sectors such as coal, platinum, chrome, iron ore and mineral sands.

thyssenkrupp navigates South Africa lockdown to replace platinum mine HPGR roll

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As the COVID-19 pandemic tightens its grip, thyssenkrupp Industrial Solutions says it is assisting customers in maintaining operational efficiencies through sustainable service delivery and innovative technologies.

“The global economic crisis, as a consequence of the COVID-19 pandemic, has put the drive for efficiency into top gear,” Philipp Nellessen, CEO of thyssenkrupp Industrial Solutions Sub Sahara Africa, said. “Fundamental to this drive is cutting-edge technology. Through our ongoing investment in people and R&D and our over 200 years of expertise, we are able to develop advanced technologies to assist mining and other industries in achieving maximum operational efficiencies.”

Although the South Africa mining industry was not operational during national lockdown Level 5, critical repairs were still permitted. As an essential service provider, thyssenkrupp has been delivering maintenance and repair as well as rebuild work to local mines.

The company assisted a platinum mine in Limpopo Province with a roll change on one of thyssenkrupp’s flagship products, a high pressure grinding roll (HPGR).

Nico Erasmus, thyssenkrupp Industrial Solutions Sub Sahara Africa Head of Service Operations, explained: “The scope of work required a rebuild on the HPGR set as well as the installation of the hardware on the mine site, making this our largest project in the national lockdown period.

“We are very pleased that even in a complete lockdown situation, we were able to complete the project in a healthy and safe manner, in excellent co-operation with our customer.”

The customer had “excellent controls” in place and thyssenkrupp complemented the risk mitigation with its own additional preventative protocols, he added.

Procedures included pre-selection of a team that falls inside the recommended age and health categories, pre-screening at both thyssenkrupp and customer sites, limiting the amount of people on shifts and in spaces, adhering to stringent hygiene measures (hand sanitising, wearing face masks, social distancing, cleaning of surfaces, tools and equipment), and implementing special transport and accommodation measures.

According to Erasmus, despite several challenges, the team adapted quickly to all the controls while still being responsive enough to get the work done safely and within the scheduled timelines.

“The transport of super loads (two trucks with 120 t loads each) was a real challenge, but our logistics team rose to the occasion and got the loads on site in no time and ready for installation,” Erasmus said.

To remain operational and continue seamless service delivery to customers, thyssenkrupp has implemented all necessary policies in line with South Africa Government COVID-19 regulations.

These include possession of all essential services permits and strict entry control protocols for employees, visitors and suppliers at all premises. Employees are required to attend mandatory training sessions conducted by the OSH department, wear all necessary personal protective equipment, sanitise regularly and maintain social distancing.

A dedicated COVID-19 committee has been set up to assess changing regulations and risks associated with office and site working environments, the company said.

“With the majority of employees working from home, we have faced our fair share of challenges but the process was very well organised with IT managing it all incredibly well ensuring that everybody was equipped in time,” Erasmus said. “We only had one day of downtime at our essential service workshop site.”

Wrapping up, an optimistic Nellessen says he is in no doubt that South Africa/Sub-Sahara Africa will recover.

“The people here are incredibly brave and innovative and companies will find their way out of the crisis,” he said.

“Despite tough times ahead for some industries, the mining sector continues to show growth and here I foresee a restart and a good recovery, depending on mining commodities probably taking anything between three to 12 months to reach previous and required pricing levels.”

New innovations help Freeport Americas cut GHG emissions

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Successful innovations in mining, processing and reporting saw Freeport-McMoRan’s Americas division significantly outperform greenhouse gas (GHG) emission reduction targets in 2019, the company has reported in its annual sustainability publication.

On an absolute basis, the division’s total GHG emissions for this part of the business remained stable at 4.8 Mt, which was 30% lower than the company’s “Business As Usual” projections, while, on an intensity basis, Americas’ performance improved significantly with carbon intensity per metric tonne of copper produced decreasing by 18% versus 2012 levels and coming in 30% lower than Business as Usual.

The company said, in 2019, the Americas division undertook a significant effort to analyse its GHG emissions in the Americas back to 2012.

This work enabled it to identify “levers” for change in the future and reaffirmed its approach to asset optimisation and processing innovation.

Over the last decade, the division, which includes assets such as Morenci and Cerro Verde, has developed and implemented industry leading technologies for leaching of oxide ores, implemented step change crushing technologies that reduce energy demand by over 30% per tonne of milled material and developed a new, highly efficient process for leaching sulphide concentrates that replaces traditional smelting and refining, it said.

“We also have implemented an asset management strategy where we rebuild engines, frames and truck beds, resulting in the reuse of approximately 70% of a typical haul truck,” it added.

The latter’s net result is over $1 billion in capital avoidance, and an estimated GHG emissions avoidance of 325 t of CO2 equivalent per truck, or more than 150,000 t in the last decade, the company said. This is based on the rebuild of 465 haul trucks that the company has carried out with Caterpillar dealer Empire Cat.

“In addition, the gradual decarbonisation of country-level energy grids, combined with specific power purchase contract terms for renewables, allows us to maintain our focus on lowering operating costs while reducing the amount of GHGs emitted per metric tonne of product,” Freeport said.

Between 2012-2016, ore grades at the company’s Americas operations decreased, requiring more ore to be both moved and processed to produce the same amount of copper. This resulted in emissions climbing during the period.

However, the company took the following actions which countered its increasing emissions trend.

In 2014-2016, it installed new highly efficient milling technology (high pressure grinding roll technology) at Morenci and at Cerro Verde, which enabled significant improvements in absolute emissions intensity as well as significant production gains at both sites, it said.

From 2014 through to 2019, the company also saw a significant decrease in the carbon intensity of its electricity consumption due to Peru and Arizona grid decarbonisation trends.

In 2018, meanwhile, advances in information allowed the company to switch to a “market-based approach” for a significant portion of its delivered electricity, enabling Freeport to reflect actual emissions versus estimates calculated using the standard published grid factors provided by regulators.

Looking forward, the company said it expected to achieve similar success as it did in the last decade at its Americas operations.

“We have set a corporate target to achieve an additional 15% reduction in carbon emissions per metric tonne of copper produced in the Americas by 2030, using a 2018 baseline,” it said.

“Over the next several years, the company will be focused on recovery from COVID-19 impacts by maintaining safe and financially viable operations as well as supporting the economic recovery of the communities where we operate.

“As business conditions allow, we will look for opportunities to invest in innovative mining and processing technologies as a means of working towards our 2030 emissions reduction goal, as well as to further develop our climate change strategy.”

In total, Freeport saw its Scope 1 and Scope 2 emissions (combined) drop from 10.1 Mt of GHG emissions in 2015 to just over 8 Mt in 2019, the report showed.

Los Andes Copper engineers a Vizcachitas alternative

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It is a combination of improved technology, reduced fine grind requirements and maintenance benefits that led to Los Andes Copper replacing the SAG and ball mill crushing circuit proposed in its Vizcachitas copper-molybdenum project preliminary economic assessment (PEA), with a three-stage crushing circuit that uses high pressure grinding roll (HPGR) technology in the tertiary crushing stage, according to Executive Chairman, Fernando Porcile.

In the middle of a prefeasibility study on the Vizcachitas project, Los Andes recently issued an update on the study progress.

A delay of PFS publication to the March quarter of 2021 due to the onset of COVID-19 impacting some of the metallurgical test work and field work at the project might have been the key takeaway for investors, but those in the mining technology game will be focusing on the revised process flowsheet being put forward at the Chile project.

One of the big changes was seen at the front end on the comminution side.

In the close to year since issuing the June 2019 PEA, and with the arrival of Porcile and his team, the company’s understanding of its orebody characteristics and the technology available to it as a new greenfield project owner has grown.

Porcile said the ore at Vizcachitas is very suitable to this energy efficient HPGR technology, with metallurgical test work showing an HPGR circuit can reduce the sensitivity to changes in hardness, providing a product that is more consistent in size. This will help reduce major process fluctuations downstream – where there have also been some changes.

The P80 target grind size of 240 microns hasn’t changed much – moving up to a P80 of 240-300 microns – but the SAG and ball mill circuit has been replaced with a three stage crushing circuit using secondary crushers in open circuit and HPGR as a tertiary crusher in closed circuit.

On the preliminary comminution process flowsheet, this includes the use of a Metso Superior™ MKIII primary gyratory crusher, feeding three Nordberg® MP2500™ cone crushers, which move into 40,000 t crushed ore bins. This material is then conveyed to two Metso HRC™ 2600 HPGRs.

Los Andes says the configuration of secondary cone crushers in an open circuit avoids the use of a coarse ore stockpile and recirculation conveyor belts – reducing dust emission sources – while the closed reverse grinding circuit allows less production of fines, which is helpful for the follow-on thickening and filtration stages.

On top of this, the secondary crushing and grinding plant in this setup is close to the primary crusher, which also reduces coarse ore conveying costs.

Porcile said HPGR technology has moved on a long way in the last decade and now represents a more reliable proposition than using the SAG and ball mill circuit previously proposed.

“There is much less risk associated with using HPGRs in a new operation,” he told IM. “Large SAG mills not only take up lots of space within the plant, they can also come with teething problems during start up.”

He added: “HPGRs used to come with lots of wear problems, meaning you had to replace the rollers often. The maintenance on them is that much better now; the rollers do not wear out as quickly and, when they do, you can easily replace them.”

On top of the obvious benefits in energy consumption that come with using HPGR technology, there are positives that can be felt further down the process flowsheet.

“We are very confident that HPGR is the best alternative for our project due to the nature and quality of our ore,” Porcile said. “We produce very little fines, which has an impact on the way we deal with tailings.”

The combination of a lack of fines and low presence of clays (mainly kaolinite) has helped filtration performance in test work, indicating that a dry-stacked tailings solution may be viable at Vizcachitas, Porcile said.

This could provide an up to 50% reduction in water consumption compared with the PEA at Vizcachitas. It could also see some 82% of water recovered throughout the process, in addition to a significant reduction in infrastructure requirements.

“We go from having infrastructure in two valleys in the PEA to one in the PFS,” Porcile said on the latter point.

One may think creating a dry-stacking operation at a 110,000 t/d throughput mine would prove costly and difficult, but the lack of fines and low presence of clays already mentioned means the process is a lot simpler to other dry-stacking projects currently on the table across the globe, according to Los Andes.

Test work to date has indicated that coarse material from the plant (plus-400 microns) could produce a cake with 14%-18% moisture through the use of belt conveyors. This material currently makes up 87% of the envisaged tonnage.

Only 13% of tonnage classed as fines (less than 400 microns) would have to go through pressure filters to produce a 16-19% moisture cake, according to the company.

Porcile says these belt filters work just as well as pressure filters on the coarse material from Vizcachitas but are that much more cost effective.

“Belt filters come with high filtration rates, are low cost (in terms of capex) and are reliable,” Porcile said. “In the study, we envisage saving pressure filters only for the very top level of material.”

While it is too early to talk about the impact these changes will have on the capital expenditure and net present value numbers to be included in the PFS, expect the $1.87 billion and $1.8 billion (after tax and with an 8% discount), respectively, to change.

Los Andes Copper addressing Vizcachitas project energy and water needs in PFS

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Los Andes Copper has ideas on adding to the number of large open-pit mines in Chile’s copper industry with the development of its Vizcachitas project, but it is eyeing up a different route to many of them that includes the use of energy-efficient HPGR technology and dry-stacked tailings.

In an update on its pending prefeasibility study (PFS), the company said it was re-evaluating the conceptual plan it laid out in its June 2019 preliminary economic assessment, which envisaged a base case 110,000 t/d operation using a SAG mill grinding circuit and thickened tailings dam.

The PFS is currently underway and areas of work being advanced include processing, the tailings facility, infrastructure, geology, the mine plan, environmental and social and community engagement, it said.

While delaying some of the metallurgical test work and field work, the current COVID-19 situation had not impacted the progress of the main engineering study, according to Los Andes. “All employees and subcontractors are working from home where possible and only a small group of individuals are working to prepare samples in the company’s Santiago core storage area,” it said.

The full PFS is not expected until the March quarter of 2021, but the company did outline some engineering leaps it has made since the PEA publication.

It said test work had shown that a HPGR circuit is feasible for the project and could provide “enhanced project economics with lower energy consumption and increased operating flexibility”.

The PEA outlined a SAG and ball mill crushing circuit with a target grind size of P80 (240 microns), but the more recent test work had shown room for an alternative with a three-stage crushing circuit using secondary crushers in open circuit and HPGR as a tertiary crusher in closed circuit. This circuit would target a grind size of P80 between 240-300 microns, the company said.

Such a change would avoid the use of a coarse ore stockpile, reduce energy consumption, reduce maintenance, and reduce the project footprint, it said.

HPGRs have previously been used at Chile mining operations, including the Compañía Minera del Pacífico-owned Mina Los Colorados iron ore mine and KGHM’s majority-owned Sierra Gorda operation.

Los Andes clarified: “HPGR technology has been identified as the most attractive grinding alternative given the data obtained from the preliminary test work conducted to date.”

The next big advance was made on the tailings side, with the company saying test work had shown that the project is amenable to filtering and dry-stacked tailings.

“This change would significantly reduce the project’s water consumption, footprint and environmental impact,” it said. It would also, one would expect, provide a much smoother environmental permitting route for Vizcachitas considering the negative sentiment surrounding thickened tailings dams in the industry.

There are knock-on benefits to this move too, with the reduced footprint required for dry-stacked tailings meaning all project infrastructure could fit into one operating complex in the Rocin Valley of Chile, around 150 km northeast of Santiago. The PEA previously outlined the use of infrastructure in both the Rocin Valley and the Chalaco Valley.

The preliminary filtration circuit Los Andes is working with shows the coarse fraction (87% of total tailings) could be filtered in belt filters, with the fine fraction (13%) filtered in pressure filters.

Recent studies on other dry-stack tailings project have tended to use either belt filters or pressure filters, but Los Andes said the combination of the two added flexibility to the tailings filtration operation at Vizcachitas and reduced operational risks due to variability of the finer fraction in tailings.

This would see the company require 12 belt filters and three filter presses for the 110,000 t/d copper-molybdenum operation.

According to the company, dry-stacked tailings would:

  • Reduce water consumption by around 50%;
  • Reduce the project’s footprint;
  • Be better suited for areas of high seismic activity;
  • Be transported by trucks or conveyors;
  • Eliminate the need for a traditional dam wall; and
  • Reduce the environmental risk by avoiding contact with ground water.

SNC-Lavalin delivering on new strategy with Rochester POA11 project win

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SNC-Lavalin says it has been awarded a contract to provide engineering, procurement and overall project management services for the Rochester POA11 project in Nevada, USA, by Coeur Rochester Inc, a wholly-owned subsidiary of Coeur Mining.

This phase of the project is estimated to be complete by October 2020, according to the company.

The project is anticipated to include a 20 Mt/y crushing plant, including a primary and secondary crushing circuit as well as a high pressure grinding roll circuit, a 13,750 gpm (52,049 litres per minute) Merrill-Crowe process plant, a new substation with power distribution and new heap leach pad.

Since approval of the initial plan of operation in 1986, the Rochester Mine has undergone periodic mine plan amendments to support mine development projects and continued operations. The mine plan amendment (termed Plan of Operations Amendment Number 11, or simply ‘POA 11’) proposes another mine life extension, which would maintain the current workforce and operate the mine at full production until 2033, SNC-Lavalin said. Coeur says it expects to produce 27,000-33,000 oz of gold and 4-5.5 Moz of silver in 2020.

The Rochester POA11 project is located 160 km northeast of Reno near Lovelock, Nevada. The Rochester mine is an open-pit operation that produces silver and gold. Mining methods include typical open-pit techniques where ore and waste rock are drilled, blasted, crushed, loaded and hauled to either leach pads (ore) or rock disposal sites.

This mining and metallurgy contract win is aligned with the company’s new strategy moving forward towards engineering services and greater growth, SNC-Lavalin said.

The Montreal-based company will provide overall project management services and integrate the engineering performed by various service providers under one set of specifications, procurement policies, standards, systems and procedures, it said. Services will be provided out of its offices in Toronto, Canada, with local support from the Reno, Nevada, branch. This mandate will include additional support such as public consultations, community engagement and working with the local community to address any impacts on the public, housing and accommodations during the project period.

César Inostroza, Senior Vice-President, Mining & Metallurgy, SNC-Lavalin, said: “As a first project with Coeur Mining, we look forward to building a long-term relationship and supporting our client to develop their silver and gold mine in Nevada.

“This mandate is well aligned with our services-based strategy for mining and metallurgy projects. This is one of multiple mining projects we have recently been awarded in the US market, and we see great potential in expanding our capabilities in the region. We look forward to contributing to our client’s project success through our extensive technical and project experience.”

Weir Minerals gives its skew view on HPGRs

Comminution of minerals, Environmental, Equipment maintenance, Mineral processing, Mining equipment, Mining maintenance, Mining services, Power supply for mines, , , , , ,

With industry demand for high pressure grinding rolls (HPGR) on the up, Weir Minerals is arguing that skewing is a vital feature for modern HPGRs to reduce wear, save downstream energy and ensure optimal grinding across the whole feed.

The company was sharing its findings following the publication of a new white paper.

Weir said: “With their excellent throughput capacity, low maintenance requirements and energy efficiency, HPGRs are fast becoming a go-to for greenfield projects looking to maintain their margins despite commodity price pressures and declining ore grades.”

The mineral processing company said, in the June quarter, that it had registered strong demand for its Enduron® HPGR technology during the three-month period, later on in the year confirming a major order, which included this comminution equipment, from Fortescue Metals Group for its Iron Bridge magnetite project in Western Australia.

Henning Knapp, HPGR Process Team Leader for Weir Minerals, said the applications from this equipment have evolved from the cement production days of the 1980s and are increasingly being deployed as tertiary and quaternary crushers in mineral comminution circuits, dealing with tougher ores including iron, gold, copper and diamonds.

“As any engineer will tell you, it’s almost impossible to eliminate feed variance and segregation completely. In the past, this has posed a critical challenge for HPGR operators – but dynamic skewing such as that featured in the Enduron HPGR, maintains optimal pressure across the entire feed.”

Traditionally, HPGR manufacturers have shied away from skewing designs, for fear of roller misalignment creating unfavourable load distributions, and preventing the use of flanged guards to reduce the edge effect, the company said. “However, Weir Minerals’ unique roller bearings design allows for skewing alongside effective edge guards, reducing wear and promoting better grinding.”

The downside of static rollers

A HPGR reduces particles by compressing and crushing the feed between two equally sized, parallel rollers rotating in opposite directions, with a small gap between them. This compresses the feed to 80% of its solid density, where the force of the rollers pushes the rocks against each other and exceeds their compressive strength.

“Inter-particle comminution avoids the direct component wear caused by conventional comminution techniques, and applies immense pressure, up to 27,000 kN, across the entire particle size distribution, which creates the higher proportion of fines HPGRs are renowned for,” says Knapp.

However, segregated feeds can result in markedly uneven particle sizes across the width of the feed, creating high, abrasive pressure on one side of the roll and insufficient pressure on the other. It will also produce a coarser product, requiring more work downstream, according to Weir.

“To compensate for the edge effect, a lateral wall or ‘cheek plate’ is deployed on either side to prevent material exiting the gap between the rollers sideways. The closer this is to the rollers, the better – but that has prevented engineers from introducing the flexibility needed to cope with feed segregation,” explains Knapp.

How Enduron HPGRs skew to maintain optimum pressure

To accommodate this uneven pressure Enduron HPGRs use a spring-loaded lateral wall which not only reduces the edge effect (maintaining a gap of as little as 1 mm) but is specifically designed to facilitate roll skew.

As shown above, an uneven feed will lead to high pressure on one side and not enough on the other. Having one roller skew will facilitate larger material at one end while ensuring the smaller particles on the other side receive enough pressure to be ground down: it maintains an even pressure distribution across the entire feed, saving energy and reducing wear, Weir says.

“The degree to which the Enduron HPGRs skew is largely dependent on the width of the roll, with longer rolls skewing about 5 mm for every metre the roll is wide. However, the effect of even small changes can be significant on local pressure peaks,” says Knapp.

“The skewing should be managed by an advanced control system, which steers the rolls to satisfy the desired output pressure. This system also ensures the skew isn’t too great or maintained for too long, which both disrupt the compressive bed.”

In the case of prolonged or excessive skewing, Enduron HPGRs send a signal notifying the supervising control system and operating staff. Prolonged skewing generally is indicative of a disturbance or fault in up-stream facilities, such as low bunker filling, upstream crusher wear, screen deck wear, or conveyor failure, Weir says.

“Where static rolls suffer from differential pressure, creating undesired product, consuming more energy and suffering additional wear, Enduron HPGRs maintain optimum pressure across the entire feed thanks to their skewing, spring-loaded lateral walls,” Weir said.

Knapp concluded: “When dealing with competent mineral feeds in real-world conditions, there’s simply no substitute for the Enduron HPGR’s ability to maximise performance with skewing.”

Weir Minerals says Enduron HPGRs crush the competition

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Weir Minerals says its range of Enduron® high pressure grinding rolls (HPGR) make for the perfect pebble crushers, offering highly efficient reduction and generating substantial amounts of fines that reduce the energy required for downstream milling.

These units also reduce water and energy consumption, two resources that miners are actively looking at within their operations.

In the company’s June quarter results, Weir noted that it had seen strong demand for its Enduron HPGR technology, adding that the company had been contracted to support a large greenfield development in the UK in the period.

Whether recirculated through primary milling or separated and sent to a dedicated downstream pebble mill, pebble crushing is an energy-intensive operation that ties up a site’s limited resources, Weir says.

“With their high throughput and capacity for dealing with competent ores, HPGRs make ideal pebble crushers,” the company said. The Enduron HPGR’s low operating costs (owing to its long component wear life and low specific energy requirements) makes it a competitive inclusion in pebble crushing circuits, offering short payback times, according to the company.

Ranging in size from 25-90 mm, pebbles are oversized material produced from autogenous and semi-autogenous grinding, which are too coarse to be crushed by larger lumps of ore and steel balls and too fine to act as grinding media themselves.

As such, pebbles (or critical particle size material) reduce the efficiency of any mill they’re returned to, increasing power consumption and decreasing throughput, Weir says.

When pebbles comprise a large proportion of a (S)AG mill’s feed as they’re returned multiple times, the proportion of large particles which have the power to crush with the force of their impact is reduced and new particles are instead subjected to additional attrition and abrasion. “This can over-grind fines, producing unsuitable ultra-fines,” Weir says.

Regardless of whether they’re receiving feed directly from an upstream SAG mill or further reducing pebbles that have passed through a dedicated cone crusher, HPGRs offer highly efficient reduction, generating substantial amounts of fines that reduce the energy required for downstream milling, Weir says.

“The fineness of products is one of the key compromises in conventional pebble circuits, with pebble crushers unable to maintain high throughput without sacrificing the proportion of well reduced particles.”

By virtue of their variable roll speeds, HPGRs can maintain high levels of throughput without generating a coarser product, allowing a significant amount of product to bypass downstream mills via pre-classification, the company explained.

To obtain the greatest efficiency, an appropriate control system should be selected to monitor and maintain the material level in the HPGR feed chute and control the roll speed and apply optimal operating pressure based on the presented pebble feed rate and quality, according to Weir.

One thing to note when deploying a HPGR in a pebble crushing circuit is that truncated feed (one with a narrow size distribution) may cause higher wear on the surface of the machine’s rollers than encountered in other applications. This is due to the more “mobile” particles generating a weaker autogenous wear layer where the coarse pebble fragments chip away at the coating on the roll-surface.

Oversized rocks that are larger than the machine’s operating gap will further wear away at the roller surface, making the use of a safety screen advisable if the preceding crusher’s output isn’t strictly controlled, Weir says.

Similarly, when placed after a (S)AG mill, a significant quantity of oversized or tramp materials can disrupt HPGR operations. “With their unique ability to dynamically skew their bearings to accommodate varying feed conditions, Enduron HPGRs cope better than other HPGRs under these conditions,” the company said.

However, to further reduce damage to wear materials, a well-designed detection and removal system should be applied, Weir advises. “This would consist of a tramp magnetic separator, a metal detector, and a subsequent tramp metal rejection facility. Such a system should preferably be installed as close as possible to the HPGR, preferentially directly ahead of the HPGR feed chute.”

In circuits with particularly heterogenous ore competencies, such as transition gold ores or coarsely-banded iron ores, HPGRs should be run at variable speeds to ensure throughput is maintained regardless of the feed conditions, according to Weir.

The company concluded: “With the ability to maintain this high level of throughput across a variety of ore types without compromising the fineness of their product, Enduron HPGRs represent an ideal, energy-efficient addition to most pebble crushing circuits.”