Tag Archives: pressure oxidation

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.

Lifezone hydromet tech blueprint puts Kabanga Nickel in pole refining position

Kabanga Nickel is ready to put its ‘money where its technology is’ in the pursuit of production from a highly prospective nickel-copper-cobalt asset in Tanzania, according to Keith Liddell, Executive Chairman.

Having been granted access to a project that has had more than $290 million spent on it by previous owners such as Barrick Gold and Glencore between 2005 and 2014, including 587,000 m of drilling, the company is coming at the Kabanga project with a fresh set of eyes and a plan that aligns with the government’s in-country beneficiation requirements.

The outcome of this previous investment is an in-situ mineral resource of 58 Mt at 2.62% Ni, containing more than 1.52 Mt of nickel, 190,000 t of copper and 120,000 t of cobalt. This resource is in the process of being updated with the latest modelling software.

The Barrick-Glencore joint venture also outlined a mine plan in a draft feasibility study that looked to recover 49.3 Mt of ore at 2.69% nickel equivalent from the two primary orebodies – North and Tembo. Again, Kabanga is re-evaluating this strategy, having identified several opportunities to enhance project outcomes including a development plan that facilitates higher production rates and access to high-grade ore earlier in the mining schedule.

Yet, the biggest departure from the previous plans for Kabanga is the “mine to metal” concept that Liddell and Dr Mike Adams, Senior Vice President: Processing & Refining, have been marketing.

This is part of the reason why the Tanzanian Government signed a binding framework agreement with Kabanga Nickel earlier this year that resulted in a joint venture company called Tembo Nickel Corp (owned 84% by Kabanga Nickel and 16% by the Government of Tanzania) to undertake mining, processing and refining to Class 1 nickel with cobalt and copper co-products near the asset.

Unlike the plethora of smelter plans being drawn up in the likes of Indonesia and the Philippines – two other countries attempting to keep more ‘metal value’ in-country – Kabanga’s plan hinges on a hydrometallurgical refining route.

This isn’t a carbon copy of the high pressure acid leaching (HPAL) technology the industry is used to hearing about – most of the time for the wrong reasons. The hydrometallurgy Kabanga is talking about is more in keeping with the process Vale uses at Long Harbour in Canada, Adams pointed out.

“There’s hydrometallurgy and then there’s hydrometallurgy,” he told IM. “HPAL is incredibly different to the Lifezone hydrometallurgy we are proposing at Kabanga, which is dealing with sulphide concentrates. Our process is effectively 17% of the HPAL carbon footprint; HPAL has a much higher carbon footprint than smelting, let alone what we are proposing.

“Our technology comes with lower temperatures and pressures, and the materials of construction are nowhere near as exotic as HPAL. It is more economic and more environmentally friendly than both HPAL and smelting.”

The ‘Lifezone’ Adams mentioned is Lifezone Limited, a technology and development company established by Liddell to exclusively own and develop the patented rights to the Kell Process – a unique hydrometallurgical process. Although devised to treat platinum group metals and refractory gold ores without smelting or the use of cyanide, and with major energy savings, cost benefits and a significantly reduced environmental impact (CO2 and SO2) over conventional technologies, the Kabanga team is keen to draw from Lifezone’s experiences when it comes to devising the refining plan in Tanzania.

They and much of the South African platinum industry are looking at developments at Sedibelo Platinum’s Pilanesberg Platinum Mines (PPM) operation on the Bushveld Complex where a 110,000 t/y beneficiation plant employing the Kell Process is currently being constructed. This plant has the capacity to produce 320,000 oz/y of platinum group metals at the refinery end, with seven refined metal products set to be produced on site.

If Sedibelo, which Liddell is a shareholder of, can achieve such a feat, it will become the first South African PGM operation producing refined PGM, gold and base metal products on site. At the same time, this metal production would come with some 82% less energy consumption and the associated significant reduction in carbon emissions, plus improved recoveries and lower operating costs, than conventional off-site PGM smelting.

But, back to Tanzania, where the aim is to deploy hydromet technology with a specifically designed flowsheet to leach and refine the base metals. End products from the Kabanga refinery will be Class 1 nickel and cobalt metals with >99.95% purity readily saleable to customers worldwide, as well as A-grade copper cathode for the Tanzanian market, according to the company.

Not only is this different to conventional pyrometallurgical nickel sulphide smelting and refining – which, according to Liddell comes with around 13 t of CO2 emissions per tonne of Class 1 nickel metal, compared with the 4 t of CO2 emissions per tonne of nickel (Nickel Institute industry baseline numbers) with the Lifezone hydrometallurgical route – it also removes the need to transport and export concentrate long distances to European, North American or Asian smelters and refineries for further processing.

Such benefits and plans go some way to answering the questions around how Kabanga is holding a nickel-copper-cobalt asset that many battery metal investors and mining companies would be interested in.

Kabanga Nickel is putting Lifezone’s hydrometallurgy expertise to the test at the project in Tanzania

The majors might not be ready to offer up a plan featuring in-country beneficiation with new technology, but Kabanga and Lifezone are.

“As you know, the industry is very conservative – no-one wants to be first, they want to be second,” Liddell said. “As technology providers, we’re going to be first and second – first with the Kell Process plant in South Africa and second with the hydromet plant at Kabanga.

“We have ownership in those so, in effect, we are putting our money where our technology is. In a conservative industry, you have to do this.”

Liddell is right.

Take battery-electric vehicles or hard-rock cutting technology on the mobile equipment side of the mining business. The OEMs, to gain market traction, had to invest in the technology, build prototypes and mine-ready vehicles and then convince the miners to test them at their sites – most of the risk was held with the tech providers, not the miners.

While Lifezone will have to take on similar technology and financial risks for industry buy-in, all the billed benefits of its hydromet technology fit the mining industry ESG and productivity brief, making it a technology that has applications beyond Kabanga, Tanzania and nickel.

According to the company, it represents an architecture of several well-proven “breakthrough” hydromet process technologies – namely pressure oxidation of sulphide minerals, selective solvent extraction of metals and selective metal absorbents – that realise the value of all waste streams, both in-process and by constructing local, regional and global circular economies.

It comes with higher metal recoveries, lower costs, lower environmental impact, a less complex flowsheet, shorter production pipeline and reduced value lockup for those companies employing it. This means metal production comes sooner, more metal is produced at a lower cost and with a lower footprint and less potentially payable metal is left in the waste stream due to a lack of viable processing options.

The main unit operations at Kabanga are likely to include aqueous pressure oxidation in an autoclave to dissolve the sulphides and remove the base metals; copper refining by SX-EW; iron removal to purify the solution for cobalt and nickel refining; cobalt refining by SX-EW; and nickel refining by SX-EW. This could result in 40,000-50,000 t/y of nickel metal as cathode, powder or briquette, alongside 8,000 t of copper cathode and 3,500 t/y of cobalt cathode or rounds.

The refinery blueprint – designed in a modular manner to bolt on additional process trains, according to Liddell and Adams – could see Tanzania become the multi-metals processing hub it has eyes on, processing material from across East Africa and retaining more value in-country. Down the line, it could align itself even closer with the battery metals sector by producing precursor products that gigafactories are calling out for.

Beyond Kabanga Nickel, Liddell sees potential for applying this hydromet concept at existing smelting operations to lower the footprint and operating cost of operations.

“The hydromet process uses anywhere between one fifth and one third of a smelter’s electricity input,” he explained. “You can replace a 50 MW electric smelter with a 10 MW hydromet plant. At the same time, the process allows refiners to get more metal out of the concentrate. This means the lower energy draw and increased revenues can pay back the money invested in a hydromet plant.”

For operations looking to incorporate more renewables, this reduced power draw is a major selling point.

Similarly, for countries like South Africa looking to retain or grow its metal production blueprint while weaning themselves off coal amid routine power blackouts, the concept stacks up.

“In South Africa, you could end up producing the same amount of metals off a much lower power base, and it’s then much cheaper to green up that electricity,” Liddell said.

The potential is vast, and Kabanga Nickel has an 18-month program currently ahead of it to start development.

This one-and-a-half-year plan follows the recent issue of a mining licence that allows the company to get on the ground – symbolised by the drill rig (pictured above) that is about to start turning on site.

Over this timeframe, the plan is to update the existing feasibility study numbers and bolt a refinery module onto it, explore avenues with metallurgical drilling to boost the concentrate grade and re-work the mine design to access the two orebodies simultaneously. The latter is one of the ways the team could access more value sooner in the production process.

All of this could set the company up to start production from Kabanga in 2024-2025, 1-2 years after the Kell Process goes live at Sedibelo’s operation and in time for a further run up in battery metals demand and, most likely, more governments legislating for in-country beneficiation.

Kabanga Nickel and Lifezone’s plans could end up being a future tried-and-tested blueprint.

Petropavlovsk gears up for refractory gold push with Pioneer plant launch

Petropavlovsk has announced the “technical launch” of the flotation plant at its Pioneer operations in Russia’s Far East, becoming the second facility in the gold miner’s portfolio able to process refractory gold ore and produce flotation concentrate.

Denis Alexandrov, CEO of Petropavlovsk, said: “The successful launch of the Pioneer flotation plant represents a key strategic milestone for the company. We are pleased to have commissioned the facility slightly ahead of the mid-year target we set when I joined the company last year.

“The new plant will enable Petropavlovsk to take full advantage of Pioneer’s substantial refractory ore reserves while providing an additional source of own-mined concentrate for our state-of-the-art Pressure Oxidation (POX) Hub.”

The new Pioneer flotation plant has the capacity to process 3.6 Mt/y of refractory gold ore. Once fully operational, the plant is expected to deliver more than 100,000 t/y of refractory gold concentrate for treatment at its POX Hub, the company says.

The opening of the Pioneer flotation plant doubles the group’s capacity to process refractory gold ore which, including the existing Malomir flotation plant, now stands at 7.2 Mt/y. Pioneer is expected to become fully operational by July and to produce around 60,000 t of concentrate in 2021.

Petropavlovsk said the construction of a third line at the Malomir flotation plant remains on track, and will add an additional 1.8 Mt/y of flotation capacity from the September quarter of 2022, bringing the total combined group capacity to 9 Mt/y.

“The launch of Pioneer flotation and expansion at Malomir will reduce the reliance of the POX Hub on treating lower-margin third-party concentrates,” the company added.

MOGAS eyes high-pressure acid leach, POX market growth with Watson Valve buy

MOGAS Industries has completed the acquisition of assets of Watson Valve, a US-based turnkey manufacturer of severe service valves for industries including mining.

Watson has a global install base of over 3,400 valves, primarily in the mining industry, but also encompassing the oil & gas and chemical industries, MOGAS said.

“This strategic purchase expands MOGAS’ global mining reach on valve supply and valve repair services, as well as adjacent market opportunities especially pertaining to the autoclave market,” it said. “It also provides an opportunity for MOGAS to build and strengthen its technology-driven vision for the niche pressure leach industry – both high-pressure acid leach, as well as pressure oxidation – by including long-standing mining customers to its portfolio, especially in the North American region.

MOGAS says it is committed to supporting and servicing the additional customer base brought about by this purchase, using its extensive global network of in-house and authorised repair centres.

Matt Mogas, MOGAS President and CEO, said: “This acquisition allows MOGAS to expand its product portfolio and get a step closer to achieve our vision as the dominant severe service technology company. We would like to offer our customers more options, and will continue to leverage our years of field experience to further enhance the Watson product line.”

Polymetal to expand pressure oxidation gold treatment in Russia

The Board of Polymetal International has approved the expansion of pressure oxidation operations at its operations in Russia and authorised the immediate start of construction at its POX-2 project.

A recently released feasibility study on the project showed that the second POX line would meaningfully increase the value of Polymetal’s refractory reserve base, comprising approximately 55% of total ore reserves, processing concentrates from its Kyzyl, Nezhda, Mayskoye, and Voro mines.

The project is expected to generate significant economic benefits as all refractory concentrates will be retained for in-house processing as opposed to selling to third-party offtakers. It will result in the incremental production of approximately 30,000-35,000 oz/y of gold from the same amount of feedstock and will, on average, lower total cash costs by $ 100-150/oz per ounce for 500,000 oz of annual gold production, according to Polymetal.

POX-2, which is immediately adjacent to the current Amursk POX facility in Amursk, Russia, will also allow Polymetal to create capacity for treatment of third-party refractory concentrates, a market which has grown considerably in Russia and globally in recent years, it said.

The project’s base case post-tax net present value (10% discount) was measured at $112 million and factored in a $1,200/oz gold price, 65 RUB/$ exchange rate and a total of 4.3 Mt of concentrate containing 9.3 Moz of gold processed from Kyzyl, Nezhda, Mayskoye, and Voro over a period of 23 years.

Pre-production capital expenditures were estimated at $431 million and would be entirely funded out of company’s operating cash flows, Polymetal said.

The plant’s design throughput capacity would be 250,000-300,000 t/y of concentrate, depending on the levels of sulphur content. The maximum sulphide sulphur processing capacity, meanwhile, was 48,000 t/y.

“This would complement the 200,000 t/y of concentrate and 30,000 t/y of sulphur capacity of the existing Amursk POX facility,” Polymetal said, adding that the new facility would use a titanium-lined steel autoclave operating at 240˚С and a pressure of 43 bar.

Hatch Inc will be responsible for the basic engineering, detailed engineering, POX procurement support and the supply of custom-made equipment for high-pressure and acidic processing areas, according to Polymetal. Polymetal Engineering is responsible for other processing areas, general site layout, and infrastructure.

Vitaly Nesis, Group CEO of Polymetal, said: “POX-2 leverages our core technical capabilities and creates substantial value. It also fully de-risks our business model by eliminating dependence on concentrate offtake markets. Emerging trends in the global gold mining industry make POX-2 a crucial element of the company’s long-term strategy”.

Polymetal envisages the start of detailed engineering and construction in the June quarter, receipt of all permits in the March quarter of 2020, delivery of the autoclave on-site in the September quarter of that year and completion of civil construction works around a year later.

Completion of the main equipment installation is scheduled for the March quarter of 2022, followed by completion of external infrastructure and mechanical completion and start of commissioning activities in the September and December quarters of that year, respectively.

The end of commissioning and first production could take place in the September quarter of 2023, with full ramp-up by the end of that year.

POX-2 will share some of the external infrastructure (gas main, access road, water main) with the existing POX facility. Additional electricity supply will be provided via a new dedicated power line from the regional 110 kW grid, Polymetal said.

The project will include a new hydrometallurgical area (POX proper), carbon-in-leach and intensive cyanidation areas, an oxygen plant, an upgrade to the existing dry tailings facility, reverse osmosis water treatment facility, and several smaller infrastructural facilities (warehouses, maintenance areas, etc).

POX-2 is designed for processing double refractory concentrates, which contain micron gold particles encapsulated in sulphides (pyrites and arsenic pyrites) together with high concentrations of organic carbon. “High carbon content drives high sorption activity (preg-robbing) and dictates the use of high-temperature (240˚С) pressure oxidation compared with medium-temperature (200˚С) oxidation utilized at the existing Amursk POX facility,” Polymetal said.

“Pressure oxidation was selected as the most feasible processing technology for double refractory ores. It is able to achieve gold recoveries of 96% by utilising high temperatures, elevated pressure and oxygen to recover encapsulated gold, while conventional cyanidation methods would result in sub-optimal recovery rates of 20-40%. Completed metallurgical tests on Kyzyl and Mayskoye high-carbon concentrates confirm the recovery rate of 96%.”

Polymetal’s Amursk POX facility, in 2018, produced 308,000 oz of gold-equivalent from 170,000 t of processed concentrate for a 96.7% POX recovery.

Petropavlovsk nears first gold production at POX plant

Petropavlovsk has made significant progress on the commissioning its Pressure Oxidation (POX) Hub project at the Pokrovskiy mine in the Russian Far East, with first refractory ore concentrate processing scheduled for November 28.

During the week commencing November 5, the group’s in-house POX experts together with Outotec, MOGAS Systems & Consulting and representatives from various equipment manufacturers, successfully commenced hot commissioning of the first of four autoclaves, associated flash tanks, high pressure circuits and concentrate re-grinding and lime preparation sections of the POX facility.

The hot commissioning process involved filling autoclave 1 with an acid solution that replicates the usual operational conditions under which the autoclave is processing refractory concentrate. The autoclave vessel was heated in stages over a period of three days, before being allowed to cool down over a period of two days.

“The hot commissioning process helped to expose certain minor defects, including a leak caused by a faulty seal within an agitator. All defects have now been rectified and the autoclave is being heated in preparation for final commissioning tests with refractory ore concentrate, scheduled for November 28,” Petropavlovsk said.

The flash tanks and receivers associated with autoclave vessel 1 have also successfully passed the hot commissioning stage.

In the update today, management also confirmed both the cold and wet commissioning of all other principal equipment at the POX and filtration sections of the plant have been completed, with wet commissioning confirming the quality of the welding and piping work at the POX section of the plant.

The concentrate loading, re-grinding and lime preparation sections (formerly part of the Pokrovskiy resin-in-pulp plant) have also been commissioned, and first concentrate and limestone are currently being loaded into the plant ahead of autoclave commissioning using refractory ore concentrate.

The oxygen plant has been fully commissioned and is being prepared to commence oxygen production to supply autoclave 1 once tests on refractory concentrate begin later this week.

Petropavlovsk says the company is on track for maiden gold production from the POX plant shortly, with a plan to ramp up to sustainable commercial production throughout 2019.

The development of the POX hub is aimed at supporting estimated production of 500,000-550,000 oz/y over the next five years, up from 420,000-450,000 oz expected this year.