Vale says it plans to invest up to $100 million to build an industrial plant for dry magnetic concentration of low-grade iron ore, bolstering its efforts to eradicate wet tailings facilities at its mines.
The technology, known as FDMS (fines dry magnetic separation), is unique, Vale says, and has been developed by New Steel – a company it acquired in late 2018.
The capacity of the plant, which is expected to be installed in Minas Gerais, will be 1.5 Mt/y, with the project due to start up by 2022. Vale estimates that, in 2024, 1% of all the company’s production will use this technology, whose patent is already recognised in 59 countries.
With New Steel, Vale estimates that, in 2024, 70% of production will come from dry or natural moisture processing, without adding water to the process and without using tailings dams. Today, the company produces 60% of its iron ore using natural moisture processing. Of the remaining 30% of production using wet processing, 16% will have filtered and dry-stacked tailings, it said.
By this point, only 14% will continue using the conventional method, with wet concentration and tailings disposal in dams or deactivated extraction sites, compared with 40% of current production. The investment is all part of Vale’s $1.8 billion filtering and dry stacking plan, which it laid out in 2019.
The first units to use the FDMS technique will be the Vargem Grande complex (in Nova Lima), Pico, Cauê and Conceição mines (in Itabira), and Brucutu mine (in São Gonçalo do Rio Abaixo).
According to the President of New Steel, Ivan Montenegro, a pilot plant for FDMS will start operating at the Ferrous Metals Technology Center (CTF, Centro de Tecnologia de Ferrosos), in Nova Lima (Minas Gerais) in the June quarter, with the investment amounting to almost $3 million. The unit will be able to concentrate 30 t/h of dry ore, using magnetic separation technology with rare earth magnets.
“Through this process, New Steel can deliver a concentrate with iron content up to 68%, from poor ore with content up to 40%, depending on its chemical and mineralogical composition,” Vale said. “Currently, this concentration is produced by the method known as flotation, which uses water. In flotation, the tailings are usually disposed of in dams. With the dry concentration technology developed by New Steel, the tailings will be stacked.”
Vale said it is already studying methods to use these dry stack tailings as an input for the civil construction industry, in addition to other initiatives, such as co-products.
The pilot project at CTF is the second carried out by Vale. Between 2015 and 2017, a similar plant was successfully operated at Fábrica mine, in Minas Gerais, it said. These results were essential for Vale to see the potential of FDMS, according to Montenegro. “The technology, however, has been tested since 2013. At the time, the equipment allowed a concentration of 5 t/h, rising to 15 t/h in 2015 and up to 30 t/h in 2017,” it said.
To be aligned with Vale’s future projects, the company is working on the development of large-capacity magnetic separators of up to 100 t/h.
According to Technical Director of New Steel, Mauro Yamamoto, more than 10,000 test samples of ore from the Iron Quadrangle region of Minas Gerais have already been analysed by the company. Yamamoto points out that, today, with technology, 90% of the iron ore from a low-content deposit can be efficiently recovered.
Currently, New Steel seeks to reduce operating costs by using industrial microwaves to dry the product. It aims to replace natural gas dryers, thereby cutting energy costs in half. “It is a sustainable process, but we have the challenge of making it more competitive,” Montenegro said.
Vale’s Director of Ferrous Metals Value Chain, Vagner Loyola, said the company has been developing technology to increase dry processing for years. Over the last decade, Vale invested almost $17.8 billion to deploy and expand the dry – or natural moisture – processing of the iron ore produced in Brazil. Over the next five years, it estimates it will invest $3.1 billion in similar processing facilities to achieve the goal of 70% dry production.
In Pará, almost 80% of production already uses this technology in Vale’s North System. The main plant in Carajás, Plant 1, is being converted to use natural moisture processing; from its 17 processing lines, 11 already use dry processing and the remaining six wet processing lines will be converted by 2023.
The treatment plants at Serra Leste (in Curionópolis) and the S11D complex (in Canaã dos Carajás) do not use water to treat the ore. At the S11D complex, for example, the use of the natural moisture processing route allows water consumption to be reduced by 93% when compared with the conventional method of iron ore production.
In Minas Gerais, dry processing was expanded from 20% in 2016 to 32% in 2019. Today, this type of processing is used by several units, such as Brucutu, Alegria, Fábrica Nova, Fazendão, Abóboras, Mutuca, and Pico. “In Minas Gerais operations, all the units that could be converted to dry processing production are already in operation,” Loyola explains. “Then, we are using tailings filtering and stacking as well as the dry concentration technology from New Steel to reduce the use of dams.”
Dry processing is associated with the quality of the iron ore from the mine face. In Carajás, as the iron content is already high (above 65% Fe), the material is only crushed and screened to be classified by size (granulometry). In some mines of Minas Gerais, the average content is 40% Fe in itabirite. To increase its grade, the ore is concentrated through processing with water and the tailings are disposed of in dams. Then, the high-grade ore resulting from this process can be transformed into pellets at the pelletising plants to increase the added value of the product.
The plants that use dry processing in Minas Gerais depend on the availability of high-grade ore – around 60% – that can be found in some mines of the state. To achieve the required quality and be included in Vale’s product portfolio, this ore must be blended with the ore from Carajás – this blending is carried out at Vale’s Distribution Centers in China and Malaysia.