Clean mining

Various projections show that the demand for critical minerals such as copper, nickel, and lithium, will increase significantly in the next five to 10 years. In the case of copper, this is due not only to the future growth in the demand for electricity due to the development of global economies, but also to the greater use of this metal in projects and technologies that are being developed to have access to cleaner energies and reduce carbon dioxide (CO₂) emissions.

According to Wood Mackenzie, a consultancy, it is estimated that under the 1.5 accelerated energy transition (AET) scenario, the additional volume of primary copper that will be required is 9.7 million tonnes. This additional demand is equivalent to almost a third of the current refined copper consumption. Meeting this demand will be a challenge because even if the current primary production rate were to be maintained and recycling rates improved, it would not be possible to meet the expected demand. However, the scenario is even more worrisome, since it is becoming more complicated and time-consuming to develop mining projects.

According to another consultancy CRU, the development of a new open pit copper project may take more than a decade. On the other hand, many of these projects are located in places with social or political complexities or limited access to water, energy, qualified technical personnel, and infratructure to operate them. The combination of these factors could jeopardize the development of greenfield projects that could help mitigate the potential supply crisis of this metal.

In addition, there are also technical challenges to solve, for example it is known that as the years go by, the deposits become poorer; some time ago the Chilean Copper Commission (Cochilco) published that between 2000 and 2016 the average copper grades of the main mining companies in Chile fell by more than 50%. This means that to produce the same amount of copper today it is necessary to process more than twice as much ore as was needed 20 years ago. This brings with it other complications, such as higher energy consumption, higher water consumption, higher talings generation, which in addition to making the processes more complex, could also mean greater risks and possible environmental impacts that must be evaluated and mitigated during its execution. It is also widely known that as the exploitation of the deposit deepens, the ore tends to become harder with more complex mineralogies, which usually ends up negatively impacting the processing capacity and affecting the recovery, which in the end decreases the production of valuable elements.

Currently, having a profitable mining project is not enough to be successful. Mining projects also need to be respectful of the surrounding communities and the environment. To this end, new policies, practices and technologies need to be implemented during the development of these projects, so that more profitable and environmentally sustainable projects can be developed.

The authors of this article believe that this is feasible and that although it will involve taking risks to implement new practices and technologies, which may be heresy in the mining industry, an industry that has historically been characterized by being conservative, it is believed that the implementation of innovation, rather than an option or fad, will be a necessity if operations are to be feasible in the long term.

Recently, there have been encouraging advances in the development and implementation of new and more efficient technologies to be used in mineral processing, such as pre-concentration technologies like bulk and ore sorting, hydrometallurgy technologies that allow recovering copper from low grade sulphide ores such as Jetti, and the coarse particle flotation developed by Eriez, which allows recovering efficiently particles two to three times coarser than conventional flotation technologies.

Coarse particle flotation

Coarse particle flotation (CPF) is a modern technology compared to conventional flotation technologies. The HydroFloat CPF technology has been operating industrially for 20 years. Recently the interest in the mining industry has been growing, because in addition to the metallurgical-economic benefits, it has been seen that this technology can positively impact the entire value chain and provide benefits for the development of cleaner and more sustainable mining. The HydroFloat CPF is a fluidized bed coarse particle flotation machine that has solved the restrictions of buoyancy and froth recovery using a fluidized bed, an upward flow of fluidizing water and countercurrent operation in conditions like a plug flow reactor.

Lower energy consumption and CO₂ emissions

Having the possibility of efficiently recovering coarser particles by flotation allows coarser grinding, thus making it possible to reduce energy consumption per tonne of ore processed. Several independent studies carried out by Anglo American, Ausenco, Capstone, Fluor and others, have found that through the implementation of CPF processes it would be possible to reduce the energy consumption in concentrators by 10% to 20%, reaching, in some cases, even higher values. In addition, it is expected that the consumption of milling media per tonne of ore processed will decrease, which, in addition to reducing operating costs, will also have a positive impact on the reduction of CO₂ emissions.

The possibility of being able to efficiently float coarser particles will be especially important for operations that expect to have to deal with harder and lower grade ores in the coming years.

Improved water recovery and tailings management

On the other hand, having the possibility to float coarser particles will also provide the opportunity to generate coarser tailings. Several studies have found that depending on the mineralogy and liberation of the processed ore, the implementation of HydroFloat CPF pre-concentration projects could allow the rejection of between 30% to 45% of the total mass processed as gangue in coarse fractions, with P80 above 400 µm to 500 µm, which improves the hydraulic conductivity of these tailings and facilitates water recovery, and disposal is safer.

On this topic, Anglo American has recently published the results of its patented hydraulic dry stacking (HDS) technology implemented at pilot scale at El Soldado. This technology intercalates coarse sand (e.g., tailings from the CPF plant) between layers of fine tailings. According to Anglo American, this novel form of tailings disposal has improved water recovery by more than 80%, and it disposes tailings in a more stable and safer way.

But in addition to this, different studies, for example, the one carried out by Professor Jan Miller of the University of Utah, have found that the HydroFloat CPF technology allows the recovery of coarse particles with very low liberation; it is estimated that 1.5% to 5% of exposed hydrophobic surface is sufficient for a particle to be efficiently recovered by HydroFloat. In other words, the particles contained in the tailings of the HydroFloat CPF cell, besides being coarse, have very little exposed sulfides, in most cases the sulfides are totally encapsulated, which would limit their reactivity, and reduce acid generation in drainage water in tailing dams.

On the other hand, these coarse tailings (usually 100% over 150 µm) generated in the HydroFloat CPF have a high solids concentration, usually above 60%, and a narrow particle-size distribution (5:1 ratio between the coarsest to the finest particle), allowing them to be easily dewatered. New tailings disposal technologies (e.g., HDS and comingling) could take advantage of the production of coarse tailings generated in the CPF process and provide a more economical and environmentally friendly solution by generating tailings with more favorable geotechnical and geochemical properties for their safe disposal, compared to conventional techniques.

Although these new innovative technologies are a great advance in the safe disposal of tailings, the goal is to have mining operations where no tailings are generated. Although this may seem an unrealistic challenge, there are already studies in this field, such as one conducted by the University of Queensland and the University of Geneva, which has been investigating the generation of a co-product called “ore sands” that could be used as a raw material in the construction industry. In another recent study conducted by the University of Queensland in conjunction with Newcrest, a comprehensive characterization of the tailings from the HydroFloat CPF cells installed at Cadia was carried out, in which it was found that the analyzed sample appears to be suitable for use as a raw material in the construction industry.

Better use of natural resources

Another field related to the development of cleaner and more efficient mining has to do with the better use of our natural resources, either through the economic processing of historical low-grade stockpiles, or through the increased recovery of valuable elements in the flotation process. It is widely known that conventional cells are highly efficient in recovering the elements of interest contained in a narrow range of particle sizes, in most cases in the 20 µm to 150 µm range. However, in the milling process a wide range of particles are generated, which means that in most concentrators that use conventional cells, the greatest losses of valuable elements occur in the –20 µm and +150 µm fractions. In the case of copper plants, this can represent losses ranging from 10% to 20% of the total copper processed.

Through the use of high intensity cells such as the Eriez StackCell it is possible to recover more than 50% of the copper that is lost in the ultrafine fractions (e.g. particles contained in the cleaner scavenger tailings), and with the use of the HydroFloat CPF cell it is generally possible to recover more than 70% of the copper that is lost in the coarse fractions (rougher tailings at +150 µm).

Through the application of these technologies, it is possible to increase the production of the valuable elements without the need to mine more ore. According to a study carried out by McKinsey the application of the CPF process throughout the industry could result in an annual copper production of 500,000 to 1.5 million additional tonnes by 2032, without the need to extract more ore than the mines evaluated are already mining. CMJ

Jose Concha is global HydroFloat product manager at Eriez, and Eric Wasmund is vice-president, global flotation business, Eriez flotation division.

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