Eriez has supplied more than 70 HydroFloat coarse particle flotation (CPF) units throughout the world for applications that include copper, lithium, base metals, gold and other minerals, and recently successfully demonstrated its effectiveness for increasing Fe content in iron ore concentrates, according to the company.

Blast furnaces use most of the iron ore mined today, but greener, more sustainable technologies are gaining ground – and they bring a demand for ore-based products with higher Fe content and reduced contaminants. Here’s how the industry is meeting the challenge.

By Russell A. Carter, Contributing Editor

The economic health of the iron ore production sector is closely linked to the global steel market. While stating the obvious, it’s also necessary to point out that this is not a linear relationship; price trends for a ton of steel versus a ton of ore or pellets might vary independently due to various factors, but overall it’s not a complicated arrangement: The world needs steel, and steelmaking needs iron ore. 

Increasingly though, the world wants green steel, and the industry’s gradual shift to low-carbon, less environmentally impactful metal production will be accompanied by new challenges in how iron ore is sourced and processed. In order to meet their decarbonization targets, steelmakers are assessing their options for eventual replacement of basic oxygen furnaces (BOFs} with greener technology such as direct reduction iron (DRI) plants that are more energy efficient and less polluting – but also less forgiving when it comes to furnace feedstock quality. 

DRI requires higher iron content, lower acid gangue content and less phosphorus – properties not characteristic of the typical hematite product that constitutes the bulk of current iron ore output. As explained in a white paper published last June by the Institute for Energy Economics and Financial Analysis (IEEFA), about 70% of the world’s steel is produced in BOFs and the global steel industry remains largely focused on utilizing coal-consuming furnace operations, giving iron ore miners an incentive to continue producing sinter-grade output.

Magnetite ores offer significantly higher grades of Fe content, but usually have minimal value as raw ore and require expensive and, in some cases, complex processing to produce concentrates or pellets suitable for premium furnace feedstock. There are numerous magnetite projects in progress or in various planning stages, but prior experience with failed or troubled projects in Australia and Canada, for example, illustrates that development of a magnetite mine can be an expensive, drawn-out process – one that’s further exacerbated by ongoing supply-chain and shipping delays.

Yet, from the steelmakers’ perspective, a gradual conversion to DRI technology is necessary, logical and mostly a matter of timing. Here’s how United States Steel’s executives described the process during a corporate earnings conference call in mid-2022: “It’s not a matter of if, it’s when and where when it comes to DRI,” said Kevin Lewis, US Steel’s vice president of investor relations and financial planning and analysis, in response to a question from a stock analyst. “The investment that we are making to produce DR-grade pellets further expands the optionality we have to advance a DRI strategy in the future.”

Lewis said the company’s near-term focus will remain on pig iron produced from conventional blast furnaces, but it has “no regrets [on our] decision to invest in DR-grade capabilities at Keetac. It’s our best ore body. It’s our longest life of mine and a very logical choice to add that capability to blast furnace pellet production capabilities, and that puts us in a great position moving forward to explore DRI.” 

Keetac is the company’s $150-million project to retool its operation at Keewatin, Minnesota, to product high-grade DRI pellets from taconite ore. In addition to producing DR-grade pellets to ultimately feed EAFs, the production facility will maintain flexibility to continue producing blast furnace grade pellets.

Richard L. Fruehauf, the company’s senior vice president and chief strategy and sustainability officer, added: “We’re focused on pig [iron] first and foremost because of the benefit pig iron gives you versus DRI in the furnace. But DRI is an opportunity for the future, and with the announcement of the float plant at Keetac, that allows us to get started. We see a lot of commercial opportunity, and there are potentials for partnerships that we might look at as well in the future.” 

In other major iron ore mining locales such as Western Australia’s Pilbara, mining companies are working closely with steelmaking customers, tech startups and research organizations to develop technologies aimed at ensuring future market demand for their hematite lump and fines products, which range between 58%-62% Fe content – a level sufficient for blast furnace feed but not for DRI processes. 

At the FT Mining Summit held in October 2022, BHP CEO Mike Henry outlined the company’s strategy.  “Certainly, we are planning to supply the existing steel industry. We have made changes both to our iron ore portfolio and our coking coal portfolio, to upgrade the average quality of our products. In the case of iron ore, we have improved the iron content and lump content through the development of the South Flank mine. 

“We believe that if steelmakers seek to decarbonize, they will want to move to more efficient blast furnace steel production. That is going to require higher quality iron ore, and we have shifted our portfolio in that direction, and higher quality coking coal,” said Henry. 

In addition, as this issue was being prepared BHP announced an agreement with project management and professional services firm Hatch, to design an electric smelting furnace pilot (ESF) plant. The facility is aimed at demonstrating a pathway to lower carbon dioxide intensity in steel production using iron ore from BHP’s Pilbara mines. 

The pilot facility would be intended to test and optimize production of iron from an ESF, which is capable of producing steel from iron ore using renewable electricity and hydrogen replacing coking coal, when combined with a DRI step. BHP said estimates show that reductions of more than 80% in CO2 emission intensity are potentially achievable processing Pilbara iron ores through a DRI-ESF pathway, compared with the current industry average for the conventional blast furnace steel route.

In South Africa, Anglo American and H2 Green Steel recently agreed to work together on low-carbon steelmaking value chains. The companies will study and trial the use of premium-quality iron ore products from Anglo American’s Kumba mining operation in South Africa and Minas-Rio in Brazil, as feedstock for H2 Green Steel’s DRI production process at its plant in Boden, Sweden. The ability to use lump iron could complement the iron pellets needed for DRI, and increase flexibility in H2 Green Steel’s production process, according to the two companies.

Also in Sweden, steel producer LKAB’s next-generation pelletizing plant is under development. “Our ambition is to replace ten percent of the carbon input with hydrogen by 2026,” said Fredrik Normann, project manager at LKAB. The company’s pellet processing operations comprise six pelletizing plants. Four of these, in Kiruna and Svappavaara, are grate-kiln plants that pose more of a technical challenge for conversion when compared with the two straight-grate plants operated by the company,.

“Heating in the pelletizing plants is the major source of carbon dioxide emissions in the process.  Addressing the heating issue in the grate-kiln plants is a challenge,” said Björn Åström, also a project manager at LKAB. 

“In the case of kiln plants we have to consider a very great degree of flaming and heat transfer to the product. That also makes the need for new process technology a much more difficult problem to solve and we have to develop the solution ourselves,” said Normann. 

Anglo American is confident that it can find markets for its South African and Brazilian iron ore products as steelmakers look for sources of higher grade iron ore. The company is primarily a lump ore producer but also markets sinter fines and pellets.

According to the company, the solution lies partly in the use of biomass and oxygen, but mainly hydrogen. The KK2 grate-kiln plant in Kiruna will be the testbed, according to Normann. “This plant is suitably equipped for development and has the lowest production, which makes it ideal for initial testing.” However, LKAB’s pellet operation in Malmberget will be the first to convert; its straight-grate configuration will make transition to the new fuel technology much easier, said LKAB.

The project ties in with LKAB’s participation in the HYBRIT initiative established by SSAB, LKAB and Vattenfall to develop new technology for hydrogen-based iron- and steelmaking with the aim to establish a fossil-free value chain from the mine to finished steel product. In June 2021, the HYBRIT-initiative succeeded in producing what it claimed to be the world´s first hydrogen-direct reduced sponge iron at a pilot plant.

The Shape of Things to Come

Hand in hand with the commercial opportunities provided by upgraded iron-ore metallics are significant issues facing iron ore miners, such as energy conservation, competition for available water resources and the looming question of how to minimize tailings volumes generated by processing higher tonnages of lower-grade material. If all of these factors could be distilled into a trio of one-word themes describing the future of this sector, they would be: Higher. Acquire. Drier.

First, higher. While DRI is one of the principal vehicles identified by the iron and steel sector as a means to approach net-zero decarbonization status, its current implementation caters to high-grade ore with Fe content of 67% or more, and there isn’t an abundance of sources for this grade of material. If the industry carries through on a large scale with its announced plans to use green hydrogen to fuel substantially higher production from DRI technology, new sources of high iron-content feed will be needed, and according to the IEEFA report , the amount of additional DR-grade iron ore capacity that will be operational by, say, 2030 is far from certain. 

“In its 2021 iron ore project review, Wood Mackenzie provides data on planned mine projects that are earmarked to start producing ore this decade with Fe content of 67% or higher,” according to the IEEFA report’s authors. “This list totals 213 Mtpa of new capacity, almost all of them magnetite projects. However, Wood Mackenzie considers only 41 Mt of this potential new iron ore capacity to be ‘probable’ or ‘highly probable’ with the remaining four-fifths considered only ‘possible.’”

Recent iron ore processing improvements offered by Eriez include development of a wider wet drum and hybrid magnetic element designed to enable higher iron recovery. This graph illustrates a recovery comparison beween hybrid and conventional 100% ceramic wet drums at an iron ore mine in Chile.

There are multiple pathways that can be followed on a quest to produce more green steel with DRI, the IEFFA report notes, and discovery of new high-grade deposits is just one of them, along with other options that include further processing of existing ores to improve the grade, and technology solutions that enable the use of lower-grade iron ore in DRI processes.

That’s where the ‘acquire’ theme enters the picture. Iron ore producers are actively investing money and resources to acquire technical knowledge and equipment that will allow them to remain competitive in a changing market – one that is likely to reward suppliers of high Fe-content ore-based products with premium prices and shareholder approval. In order to reach their goals, producers have the flexibility of choice to: 1) work closely with traditional process-equipment vendors to optimize their production flowsheets; 2) investigate and adopt new technologies – developed in house or through strategic partnerships – designed around green production concepts; or 3) both.

E&MJ spoke with two well-known industry suppliers that recognized an opportunity to apply their joint expertise and product lines; in mid-2022, Eriez and Weir Minerals announced a cooperative agreement to develop new flotation systems designed to increase the selective recovery of coarse particles in a broad range of applications, including iron ore beneficiation, by applying flotation fundamentals to gravity separation. The technology, Coarse Particle Flotation (CPF), also holds promise for reducing water and energy consumption and producing safer tailings, according to the two companies.

Eriez Manufacturing Co., founded more than 80 years ago by a grain salesman who invented a magnetic-separation device for removing ferrous contaminants from grain-mill product streams, has steadily expanded its product and services portfolio to encompass mineral flotation, metal detection and material handling equipment. Weir Minerals is a full-service, pit-to-plant supplier of equipment and services spanning an entire flowsheet from comminution to tailings. We invited executives from both companies to comment on the specific advantages their in-house technologies offer users, with focus on iron ore applications.

Eric Wasmund, vice-president-global flotation business at Eriez, said “Eriez has invested considerable time and effort in developing new products as well as improving existing products to ultimately help iron ore customers increase production while reducing the number of units of equipment.”

As an example, Jose Marin, Eriez’s director-minerals and materials processing, pointed out that the development of a wider wet drum and hybrid magnetic element allows for higher volumes of slurry and higher iron recovery at the beginning of the process. “This effectively reduces the footprint of the magnetic concentrators, reducing the overall rejects of magnetite in the tails.”

He provided a graph (above) that illustrates the recovery comparison between the hybrid and the conventional 100% ceramic wet drums at an iron ore mine in Chile. The orange line represents the grade recovery of the hybrid wet drums while the blue line represents conventional 100% ceramic drums.

He went on to explain that the company’s Magnetic Mill Liners are highly desirable in iron ore mines because of the magnetic susceptibility of the ore. “There are mills that have effectively operated more than 10 years in magnetite beneficiation plant with the same MML liners.

“Eriez supplied a set of Magnetic Mill Liners (MML) to NEXA in Peru, which helped NEXA win a safety award. The MML uses magnetic fields to adhere to the surface of the shell of the mill, eliminating hundreds of nuts that are typically used to secure the metallic or rubber liners inside the mill.

“The MML consists of numerous individual sections similar to tiles (approximately 12 in. long, 10 in. wide and 4 to 6 in. thick) that weigh a fraction of what conventional liners weigh. MML tiles are moved inside the mill without need of any specialized cranes. Each section of liner weighs from 20 to 40 kilograms (44-88 lb), making it easy for crews to install them by hand.

“There are no bolts or nuts to secure the liners in the shell. This eliminates the challenge of torquing and re-torquing the nuts after installation and following a short period of operation. This later action alone helps the mill to have higher operational availability,” he concluded.

Jose Concha, HydroFloat global product manager for Eriez, described the potential benefits that HydroFloat technology offers iron ore producers, extending to savings in capital investment, upkeep and operational expenses. “Eriez is working with several iron ore producers to implement the HydroFloat CPF technology for improving both sustainability and profitability,” said Concha. “It’s been proven with other types of minerals (base metals, phosphate, potash, lithium and others) that HydroFloat can efficiently recover particles that are fully and poorly liberated, particles two to three times bigger than conventional cells can recover. Being able to recover coarser particles in the HydroFloat permits concentrator plants to coarsen the grinding product, resulting in significant reduction in energy consumption.”

He noted that CPF produces coarser tailings, with P80 estimated to be over 500 µm. This type of material behaves like a sea sand, having high hydraulic conductivity, thereby improving the water recovery and producing coarser material at high solids concentrations. These coarse tailings can be used in combination with advanced dewatering processes like Anglo American’s patented Hydraulic Dry Stacking (HDS), filters, dewatering screens and other ways to improve water recovery and to dispose of final tailings in safer ways.

“As more HydroFloat CPF projects are developed, we have found ways this technology can improve the profitability of projects, especially when it comes to identifying benefits from the mine to final tailing disposal,” said Concha. “HydroFloat is considered a pre-concentration technology that facilitates the removal of coarse gangue at the early stages of the process. This has a positive impact on the Capex and Opex of projects. For greenfield projects, CPF will allow reduction of grinding mill size, reduction of the volume of the conventional flotation plant, reduction of the cost of the tailing storage facility and more.

“For brownfield projects, CPF will allow an increase in the plant throughput without the need to install more primary mills or keeping the same throughput when harder ores are processed. Additionally, by coarsening the grinding product, it is possible to reduce the generation of ultrafine particles, which improves flotation performance and global recovery.”

He pointed out that reduction in Capex, Opex and improvements in recovery have allowed a reduction of the cut-off grade in some projects, permitting the development of profitable projects that process low-grade ores, and in some cases, bringing the possibility to expand the mine reserves. 

Jose Marin, director-minerals and materials processing, told E&MJ that Eriez had recently completed a laboratory test program at its Research Center in Pennsylvania for an iron ore mine to evaluate the feasibility of producing high-purity iron ore concentrate. In this test program, the HydroFloat CPF technology was successfully demonstrated to increase Fe content to 67% while the SiO2 content was reduced to 1% while maintaining +90% stage recovery of Fe. A feasibility study was performed with very favorable results. After incorporating the results of this test program, the project is advancing to the execution stage.

He said Eriez also developed a pilot plant wet drum which consists of a single unit with multiple interchangeable components. The basic unit is a 48-in.-diameter by 16-in.-wide (12-in. magnet width) pilot plant wet drum with the hybrid element coupled with an efficient self-leveling tank that is suitable for cobber or rougher stages. In addition, the company offers an interchangeable countercurrent tank recognized worldwide as the most effective tank for the cleaning or finisher stages. There are also two available magnetic elements for the cleaners and finishers.

Marin said Eriez can supply a unit that “can replicate every single stage of a magnetite concentrating plant whether it uses rougher-cleaner-finisher or rougher-scavenger-cleaner or any other combination. This unit alone allows plants or laboratories to simulate actual performance of the 48-in. diameter wet drum which is the workhorse of magnetite concentration.”

Changing the Game

Peter Lempens, Weir Minerals’ director-sustainable mining technology, brought us up to speed on that company’s efforts in flowsheet optimization.

“We have proven technologies that we’re configuring in new, innovative flowsheets to optimize processes and equipment performance. For instance, our Enduron HPGR continues to deliver significant energy savings compared to traditional SAG and ball mills – up to 40%, depending on the application. When the HPGR is combined with air classification and/or followed by a vertical stirred mill – which we offer our customers through our partnership with Swiss Tower Mills Minerals (STM) – we are able to deliver a game-changing solution for more efficient comminution. Crucially, rather than solely focusing on size reduction, we’re making sure that the energy we apply is actually being converted into recoverable product. 

“Traditional mill circuit flowsheets are inefficient, with 40%-60% of the slurry returned to the mill for reprocessing,” he noted. “These recirculated loads obviously reduce the throughput and capacity of the mill. The reconfigured HPGR-vertical stirred mill flowsheet, in comparison, significantly reduces slurry recirculating load and delivers stable and consistent performance, despite high feed variability. 

“The addition of air classification – another proven technology Weir Minerals is utilizing in innovative ways – allows for efficient, large capacity dry particle classification. The Enduron HPGR with air classifier beneficiates between stages, which means there isn’t any unnecessary processing of waste and, therefore, the miner is able to maximize the downstream capacity.”

Weir Minerals developed an innovative flowsheet for Fortescue Metal’s Iron Bridge project, designed to ensure that “energy isn’t applied to rocks that don’t result in recoverable metal.”

Lempens said the company’s product offering is backed by a team of experts who “not only know the equipment inside-out, but also have process experience, while the Weir Technical Centers allow us to carry out test work and partner with miners to develop solutions based on their specific needs and unique site requirements. And this work isn’t limited to the laboratory. We also support our customers with full-scale demonstrations, from circuit design through to on-site sampling and reporting.”

Bjorn Dierx, global product manager-Enduron HPGR, explained that Weir Minerals has taken an integrated approach, linking comminution with mineral recovery, in the circuit design at Fortescue Metal Group’s (FMG) Iron Bridge magnetite mine. “The innovative flowsheet – with Enduron HPGRs with air classifiers feeding vertical stirred mills – was co-developed with FMG and validated by extensive test work and an on-site demonstration plant. It is an industry-leading example of sustainable magnetite processing and a game-changer for the mining industry, more broadly. It is, after all, the world’s first large-scale plant without tumbling mills,” he noted.

“It’s a project that really demonstrates what’s possible when an OEM, like Weir Minerals, has a strong working relationship with a miner, like FMG. They challenged our team to develop a flowsheet that maximized recoverable metal at the lowest cost and environmental impact. This required a deep understanding of the mineralogy, which was backed by extensive test work campaigns – including a three-year on-site pilot test program – that saw numerous flowsheet iterations before the HPGRs with air classifiers and vertical stirred mills were chosen. 

“The innovative flowsheet delivers energy savings by ensuring that energy isn’t applied to rocks that don’t result in recoverable metal, while coarse dry magnetic separation as inter-stage beneficiation between the Enduron HPGRs allows for the rejection of over 20% of the barren material,” said Dierx. “Moreover, by combining the micron-sized grinding with dry air classification, we are able to further minimize water addition prior to feeding it into the highly efficient vertical stirred mills. These, in turn, prevent overgrinding by minimizing mill retention time, while also making use of internal classification.”

Joining Forces

Rio Tinto recently reported that it had proven the effectiveness of its low-carbon iron-making process using ores from mines in Australia in a small-scale pilot plant in Germany, and is planning the development of a larger-scale pilot plant.

Rio Tinto’s BioIron process uses raw biomass instead of metallurgical coal as a reductant and microwave energy to convert Australian Pilbara iron ore to metallic iron in the steelmaking process. BioIron, according to the company, has the potential to support near-zero CO2 steel-making, and can result in net negative emissions if linked with carbon capture and storage.

Rio Tinto said the process has been tested extensively in Germany by a project team involving Rio Tinto, a large Nordic process equipment supplier and the University of Nottingham’s Microwave Process Engineering Group. Development work was conducted in a small-scale pilot plant using batches of iron ore and biomass briquettes. The process will next be tested on a larger scale at a continuous pilot plant with a capacity of one metric ton per hour. Plant design is underway and Rio Tinto is considering suitable locations for its construction.

BioIron works using lignocellulosic biomass including agricultural by-products (e.g. wheat straw, canola stalks, barley straw, sugar cane bagasse) or purpose-grown crops. The biomass is blended with iron ore and heated by a combination of combusting gases released by the biomass and high-efficiency microwaves that can be powered by renewable energy.

Rio Tinto said it is aware of complexities involving biomass supply and is working to ensure only sustainable sources of biomass are used. Accordingly, the company is undertaking a benchmarking study of biomass certification processes.

Meanwhile, Fortescue Metals, Primetals Technologies, Mitsubishi Corp. and voestalpine signed a Memorandum of Understanding (MoU) underpinning an alliance aimed at designing and engineering an industrial-scale prototype plant with a new process for net-zero-emission ironmaking at the voestalpine site in Linz, Austria. The collaboration will also investigate the implementation and operation of the plant.

The new ironmaking process will be based on Primetals Technologies’ HYFOR and Smelter solutions. HYFOR is a direct reduction process for iron ore fines that doesn’t require agglomeration. A pilot plant has been in operation since late 2021, and Primetals Technologies said it has run numerous successful test campaigns over the last year including successful trials on Fortescue’s Pilbara iron ore products.

The technology employs an electrical furnace for melting and final reduction of DRI based on lower-grade iron ores. Fortescue’s main responsibility in the project is to provide knowledge about iron ore quality and preparation. In addition, Fortescue will supply various iron ores for the new plant.

During the project planning phase, an industrial-scale prototype plant with a capacity of between three to five tons of green hot metal per hour will be designed, reportedly the first solution to link a hydrogen-based direct reduction plant for iron ore fines with a Smelter.

Although the main goal of the project planning phase is to support decision-making for a go-ahead on construction of a prototype plant capable of continuous operation, and from that to gain the know-how needed for a commercial full-scale plant, another target is to investigate the use of various types of iron ores to produce DRI, hot briquetted iron (HBI) and hot metal and, as a next step, draw conclusions about the process steps, both individually and in various combinations.

Hydrogen used in the new plant will mainly come from Verbund, an electric utility which operates a proton exchange membrane (PEM) electrolyzer in Linz. The plant will be upgraded to accommodate compression and storage of hydrogen gas before use in the combined HYFOR and Smelter plant.

Less Water, Less Coal

Brazil’s Vale, the world’s largest iron ore producer, has been active on several fronts to develop technologies capable of making iron ore processing environmentally cleaner, drier and more efficient. The company reported that by 2023 it will have invested roughly $21 billion to expand the use of dry processing, with the goal of ultimately reaching a level of 70% dry processing in effect throughout its Brazilian operations.

In mid-March, Vale reported that it had, for the first time, produced commercial-quality pellets on an industrial scale without using anthracite coal. In a test carried out in a pellet plant in Vargem Grande, Minas Gerais state, Vale said it replaced coal with biocarbon to fire the pellets. Biocarbon is a renewable, zero-emission product obtained by carbonizing biomass. The test began by replacing 50% of the coal with biocarbon, before gradually rising to 100%. In total, approximately 50,000 metric tons of pellets were produced, of which 15,000 tons were a result of using 100% certified biocarbon.

Earlier this year, Vale began commissioning the Gelado project in Carajás, Brazil, aiming at producing high-quality pellet feed by reusing tailings that have been deposited in the Gelado dam since 1985, when Vale began operations in the region. Initial production capacity for the $485-million project will be 5 million tons per year.

The company said that following the conversion of its Carajás Plant 1 to natural moisture (dry) processing over the next few years, the Gelado project will ramp up to handle 10 million tons per year of tailings, representing more than 8 million tons of downstream product from its pelletizing plant at São Luís. According to the company, the Fe content of the tailings is already high – in the range of 63% – and magnetic separation will produce a concentrate with even higher metal content for delivery to the plant.