Nano steps for the minerals industry

Materials World magazine
,
1 Aug 2017

Dr Barrie O’Connell CEng argues how nanotechnology could benefit the minerals industry.

Nanotechnology is an emerging area of science that is being introduced to our everyday lives, from its uses in the engineering of surfaces such as the application of waterproofing to its development in graphene. Nanotechnology could be used to the advantage of the mineral processing engineer from its use in froth flotation, where traditional collectors could be replaced with superior performing ‘nano-collectors’, and in ore bodies that have not previously been considered amenable to in-situ leaching that could be targeted by ‘nanotech leachates’ that selectively extract strategic metals and minerals. 

Without geological or mineralogical constraints, in-situ nanotech leaching could change the way metals are extracted and negate the need to mine ore from the ground. The potential economic benefits of nanotechnology offer immense and worthy debate and development. This technology may be of particular importance to the European mining industry for the recovery of strategic metals and minerals from deposits that are currently uneconomic to mine. Europe’s dependency on metals sourced outside of the EU is an issue that the European Commission is currently addressing through various research initiatives such as the flexible and mobile economic processing technologies (FAME) through the Horizon 2020 programme. 

Faced with ever decreasing head grades and the need to grind complex ores finer, mining companies often adopt the strategy by increasing the amount of ore they process in an attempt to remain economically viable. There is an increasing demand to improve efficiencies in existing circuits, although in reality this will be limited by the capability of these existing technologies. Furthermore, it is unlikely that operational metallurgists will be able to make game-changing advances to existing circuits until new technologies are introduced.

Nanoscale vs microscale

Nanotechnology refers to the engineering, measurement and understanding of nanoscaled materials and devices. The science of materials behaves differently at the nanoscale in comparison to the microscale. The nanoscale refers to the length of measurement where 1nm is one billionth of a metre or one thousand times smaller than a micrometre. Nanotechnology applies to the scale between 1–100nm. At the nanoscale, materials can take on entirely new properties – for example, quantum confinement, where electrons within nanoparticles become progressively restricted by the physical size of the material, and as such, their quantum behaviors can be altered. In quantum confinement, with the use of ultraviolet light, 5.5nm silicon nanoparticles emit a red spectrum. By progressively reducing the silicon particle size to 2.3nm, the colour emitted by the material changes from orange, yellow, green and eventually blue at each discrete particle size.

Another property is the surface area that materials exhibit at the nanoscale – a 1cm cube can be broken down into smaller cubes that increase the overall surface area. The resultant cubes are dissected into smaller cubes, increasing the surface area two fold. For instance, a cube with a volume of 1cm3 sees its surface area increased from 6cm3 to 60,000,000cm3 when broken down into individual 1nm-sided cubes. This property lends itself to the chemical industry, where chemical reactions are influenced by surface area. Further applications in the materials industry include coating surfaces only a few atoms thick to manipulate surface chemistries, creating properties such as hydrophobicity used for self-cleaning glass. 

Industrial uses 

Today, nanotechnology is used in a variety of applications ranging from sportswear, pharmaceuticals, cosmetics, environmental technologies and self-cleaning glass. The universality of the technology means that its application continues to grow, impacting a number of disciplines in engineering and science.  

Examples where the properties of nanotechnology are used for industry include:

  • Strength – various nanomaterials have been used as filler materials to enhance the properties of structural and non-structural polymers used in aircraft construction. The application in heavy industry such as the aerospace and construction industries continues to grow. 
  • Surface area – due to its high surface area, the technology is used in the sunscreen and cosmetic industry as less material can be used to do more. 
  • Structure – Lockheed-Martin, USA, developed and patented a molecular filtration membrane called perforene, which can desalinate seawater by using 1% of the energy of existing desalination systems. 
  • Weight – much like aerospace, lighter and stronger materials will be useful for creating vehicles that are fuel efficient and safer. Merida Bicycles, UK, has increased the impact resistance of bike components by up to 40%. 

The application of this technology is immense. By 2020, the industry is predicted to be worth US$75.8bln – no doubt this will continue to expand.

Nanotechnology and metallurgy 

The mining industry relies on tried and tested technology where performance and risk factors are understood. It could be argued that there is a natural reluctance to expedite the introduction of new technologies and that merging of such technologies is based upon numerous trials. In addition, the mineral processing industry has not recently seen any major technological advancement since the development of technologies such as carbon-in-pulp and bioleaching. The reluctance by industry could be one of two things – the perceived risk factors or a common belief that major improvements to existing technologies can’t be made. Decreasing head grades coupled with increased mineralogical complexity, mines are forced to increase the amount of ore to remain economical and efficient. Moreover, there is a fundamental need to develop new technologies of extraction that are more efficient and cheaper to operate. 

Nanotechnology could provide an opportunity to improve metallurgical and cost efficiencies for the treatment of ores, decrease the energy usage of processing plants and improve environmental aspects of tailings and water disposal. Researchers are developing ways to mass-produce graphene, which could one day be used to fabricate items such as impellers and mill liners. Research is also underway into its potential for cleaning organic and inorganic pollutants, as derived from oil spills. The minerals industry could use this technology for the application of the treatment of acid mine drainage or process discharge water.

Fundamental to the success of any mine is the presence of a water supply. But, as water is a resource that is growing increasingly scarce. Given the challenges faced when looking to operate mines in geographic areas with poor water resources, the ability to generate process water from seawater is attractive. Today’s desalination plants, typically using reverse osmosis, are expensive and time consuming. Recent research has shown that nano-filtration could be an alternative desalination method, requiring some 100 times less energy. The technology uses a graphene membrane that is perforated with small holes (0.05µm), allowing only the small water molecules to pass through while larger ions are unable to penetrate the membrane.  

Other research involves removing natural organic matter, biological contaminants, organic pollutants, nitrates and arsenic from groundwater and surface water. The removal of organics and arsenic from process waters entering bio-oxidation circuits could also be applied to the minerals industry. The selective manipulation of mineral surfaces could be of huge benefit to the minerals industry in mineral separation process such as froth flotation. For example, by manipulating the surface tension of minerals to selectively enhance their wettability for effective separation in the development of nano-collectors. In addition, the technology could be used to form inhibitors and depressants thus potentially replacing alternative toxic reagents such as cyanide in flotation circuits.

More so, developing new lixivants – nano-leachates – for the recovery of base and precious metals could be favourable over traditional lixivants, where the application of benign chemicals could make in-situ leaching more environmentally friendly, paving the way forward for projects that have previously stalled based on social-environmental concerns. One company exploring nanotechnology in the mining industry is NTI Nanotechnology Corporation, Canada. NTI is looking to undertake trials at Port Hedland’s iron ore mine, Australia, where dust has become an environmental and health issue. It is proposed that nanoparticles would be used to bind the dust together forming heavy agglomerates that are less likely to become airborne. FAME and other similar projects under the European Commission funded Horizon 2020 programme are investigating how the European deposits can be mined and used economically, sustainably and in a more environmentally friendly way. The success of ensuring a secure supply of raw materials is critical to Europe’s economic success.

In achieving the European Commission’s goal, other non-traditional technologies and sciences should be explored as alternative solutions to the challenges facing the European mining industry. As such, continued collaborative research involving academic and industrial organisations is paramount. Work has already begun with encouraging results, demonstrating the potential application of the technology to the minerals industry, with hope for further R&D in future.

Dr Barrie O’Connell CEng is a chartered engineer with more than 18 years experience, ranging from pilot and industrial plant operations to research and consultancy. Barrie is currently Principal Mineral Processing Engineer at Wardell Armstrong, UK.