The mine tailing dam spill at BHP and Vale’s Samarco iron ore operations last year killed 19 people and had devastating effects on the environment.
Occurring in Minas Gerais, a south-eastern Brazilian state, the spill injured more than 50 people and contaminated the water supply of several towns.
But can these tailings dam environmental disasters potentially be avoided with new processing technologies?
Brazilian company New Steel have developed a new dry iron ore tailings process to make mining more environmentally sustainable.
It involves the dry recovery of iron ore fines and super fines from mining wastes, low grade run of mine (ROM), or compact itabirite.
The method does not use water to process iron ore, instead it transforms mining tailings – with low iron content and no commercial value – into high iron content and low contaminants, making it economically viable.
As iron ore must be composed of grades of at least 58 per cent, mining companies stack the lower grade material on tailings dumps.
This material with low iron content is then processed and iron is separated from other materials, particularly silica (sand), from these stacks. In doing this, the company can produce a highly pure iron ore concentrate in an industrial scale by obtaining a premium product of up to 68 per cent iron, as well as being able to make use of particles as small as 0.01mm, thus generating high recovery rates compared to existing methods.
The moisture content of the ore is reduced through a mechanical stir dryer (using natural gas or biomass), and is classified into various fractions. The ore is then separated magnetically using a magnetic separation unit (FDMS).
The drying process increases particle segregation, with the technology’s air classifier able to separate particle sizes down to 0.01 mm. Whereas existing dry separation processes work for relatively coarse particles greater than 0.55mm, the FDMS technology can separate fine particles up to 0.01mm, increasing efficiency.
The technology aims to improve the recovery of iron ore still contained in wastes or low grade ROM making it possible to obtain iron ore concentrate with 68 per cent iron, and ultimately providing high metallurgical and mass recoveries.
New Steel CEO Gustavo Emina said, “Before the invention, the only technology available to raise the content of very fine iron ore particles was flotation, but flotation is water-sensitive and is not economically sustainable in the current scenario of pricing, making any new project unfeasible, as it demands high spending.”
Emina explained to Australian Mining, “In this dry process no water is used thus there is no need for tailing dams.”
This will have significant benefits compared to wet processing methods as the effects of tailing dam bursts have not only been felt in Brazil, but more recently in the Solomon Islands as well.
The collapse of the dam on the island’s Gold Ridge mine released millions of litres of toxic water containing arsenic and other heavy metal tailings into waterways towards communities further downstream. The project, sold by St Barbara to local landowners, already faced a number of previous environmental concerns due to heavy rainfall, flooding, and cyclones with its tailing dam close to collapse. Last year the government declared the mine a disaster area after tropical cyclone Tracey brought heavy rains that filled the dam to near overflow.
Emina further outlined the advantages of the process; such as heightening the value of otherwise marginal deposits and increasing the output and export capacity of iron ore producers through beneficiation of their mining waste.
It reduces the impact on the environment by storing and recovering tailing stockpiles to produce a higher ore grade, and avoiding environmental issues associated with tailing dams such spills and seepage.
Other advantages include a low energy consumption rate and its ability to increase the life of a mine. Dry processing plants also have a reduced size compared to traditional facilities.
As the waste generated after the iron ore is extracted is mainly sand, it can be used as a byproduct in the construction of houses, schools and other facilities, enhancing its sustainability.
“The greater efficiency of the FDMS generates a dry clean waste with five per cent iron that can be used by the cement or ceramic industry,” Emina added.
The technology has been undergoing trials since 2010 in Brazil with the company’s operation of the first experimental dry processing plant in Minas Gerais.
The Brazilian Institute of Industrial Property (INPI) ranked the patent application as a Green Patent due to its sustainability. New Steel also received an award in the innovation category at the international Platts Global Metals Awards, considered the ‘Oscar’ of mining.
The patent has been approved in the United States and is also being processed in 26 other countries.
Negotiations to implement the new technology in the US are underway.