Not a waste

Materials World magazine
,
3 May 2015

Mine wastewater treatment services and technologies look set to become big business again. Guy Richards explains why.

With miners forced to scour ever more remote – and often arid – regions for ore bodies of falling quality, and under increasingly stringent environmental legislation, the industry is facing fresh challenges over how it deals with the huge quantities of water it consumes. 

This is prompting predictions of a worldwide rebound in the water treatment market. For example, according to industry analyst Frost and Sullivan, demand for treatment equipment and services alone is expected to be worth US$3.6bln by 2016, while a report by consultancy Bluefield Research estimates that the total mine water market – which includes water infrastructure such as reservoirs, pipelines and dewatering systems as well as the equipment and services – will be worth US$17bln by the end of 2019, a growth of 49% on 2013 levels.

Growth factors

Bluefield report author Erin Bonney Casey says there are several factors driving this growth. ‘First is the cyclical nature of the mining sector, as well as the growing demand for natural resources as the global economy recovers,’ she says. ‘As mines are developed in increasingly remote and water-scarce regions, they are turning to alternative water supplies such as desalinated seawater and treated municipal wastewater, which require higher investment levels than traditional groundwater or surface water sources. Water must also be sourced from further away, increasing the cost of water transport infrastructure.’

Regulations specifying stricter limits on mine wastewater are another driver, she says, an issue that is more acute in developed countries such as the USA and Canada, where regulations are tighter. 

She adds, ‘As part of the mining sector boom that peaked in 2012, companies were trying to get new mines and mine expansions operational as quickly as possible. Now that commodity prices have fallen, miners are turning their eyes to improved efficiencies that can drive down production costs. As a result, water inputs – an increasingly expensive piece of the value chain – are receiving more attention at operating mines.

‘There is also the issue of a mine’s social licence to operate. Over the past few years, mining companies have started to publish annual sustainability reports, with targets to reduce their impact on water resources. This is partly in response to some high-profile conflicts over water resources with local populations that have caused expensive work stoppages, so it is important for mining companies to be seen to be managing water resources responsibly,’ she says. 

Frost and Sullivan estimates that half of its US$3.6bln estimate will be accounted for by the services element, and that two-thirds of that will be for operation and maintenance. In addition, there is a shift taking place in the way services are provided. Frederick Royan, Global Research Director for Environment Markets at Frost and Sullivan, says, ‘New business models are emerging that look at the value proposition of treatment. Before, water treatment was handled by separate companies. Now, it’s one company to look after the entire operation – including the risk element. It’s an holistic approach now.’

Bonney Casey agrees, adding, ‘As water and wastewater systems become larger and more complex, some mines are choosing to outsource their operations to firms that specialise in water through long-term operations contracts of 10 years and more. Water specialists are also interested in pursuing these types of contracts, as the mining sector offers higher margins than typical municipal systems.’

Specialised services

Service providers are getting smarter about how they deliver solutions, and in tandem with that is the development of new technologies for treating wastewater, whether it be for subsequent release into the environment, re-use at the mine, or to recover any valuable metals in the water to offset remediation costs.

One of these, called Virtual Curtain, removes metal contaminants including copper, lead and uranium from wastewater, allowing the treated water – said to be of rainwater quality – to be safely discharged. It uses hydrotalcites, minerals often found in indigestion tablets, to trap the contaminants. The technique was developed by Australia’s national science agency, CSIRO, after it was discovered that the hydrotalcites could be formed from aluminium, iron and magnesium, common contaminants already present in many types of wastewater. 

The company commercialising the technology says precipitates of the hydrotalcites encapsulate high concentrations of metals, often at ore grade. In addition, using contaminants already in the wastewater avoids the need for expensive infrastructure and complicated chemistry to treat the waste. 

Using what is already in the wastewater is the inspiration behind a technology, previously covered in October 2014’s Materials World, being researched in the UK at the University of Exeter’s Environment and Sustainability Institute, although here the focus is on algae. 

The Institute’s AVaRICE project is investigating the use of acid- and metal-tolerant algae in the valorisation and remediation of metal-contaminated effluents such as acid mine drainage (AMD). Its main aim is to grow naturally occurring algae in AMD, and convert the biomass into a ‘bio-crude’ to produce oil that can be used as fuel or other organic compounds. But it has the added advantage that the algae tend to remove at least some of the contaminating metals in the process, which could then be recovered. 

This gives the potential for treating contaminated wastewater, though one of the researchers, Dr Chris Bryan, says the water would probably need some further treatment. ‘These are early days,’ he says. ‘We are conducting experiments to address some key questions around algae growth rates and metal removal rates. We hope to publish the results at the end of this year, but the project has the potential to reduce remediation costs and produce valuable products.’ 

Another approach is to use sulphide precipitation, such as the ChemSulphide technology from Canadian company BioteQ. This works by adding biological or chemical sources of sulphide to the water to selectively precipitate dissolved metals out of it, again allowing the treated water to be safely discharged or re-used on site. 

Equally promising is selective extraction using resins, such as the Molecular Recognition Technology from Utah-based IBC Advanced Technologies, a non-ion exchange process that uses organic chelating agents or ligands. It incorporates small beads of silica gel or polymer substrates to which the selective ligand has been chemically attached. The beads are packed into fixed-bed columns, the feed solution is passed through the column and the target metal is selectively removed. 

Tusaar, based in Colorado, also offers a non-ion exchange technique, but this is based on granulated activated carbon, and is said by the company to be able to target and isolate more than 45 metals from a single source in one pass-through process. The metals can then be recovered and again, the treated water re-used or discharged.

Reducing the costs

It is still too early, however, to say which of these approaches or any others will prove the most economical, according to Dr Bob Kleinmann, Vice President of the International Mine Water Association (IMWA). He also sounds other notes of caution. ‘Metal values are extremely low right now, with the exception of some of the truly precious metals, such as gold,’ he says. ‘But I do believe that we will begin to see metal recovery from mine water as a way to defray water treatment costs once metal values recover.

‘However, once the metals of potential value are recovered, you still have to treat the water to discharge standards, so I think a reasonable objective is to defray water treatment costs by offsetting them with metal recovery, rather than extracting enough metals to make a profit. There just aren’t enough metals of value in mine water to make it pay for all of the costs of water treatment,’ he says. ‘My prediction is that metal recovery will eventually be a niche market occupied by some technology-savvy companies that will make a profit by agreeing to take over water treatment responsibilities for a fee.’ 

That should suit the miners, who are notoriously conservative when it comes to adopting new technologies. In any event, Dr Kleinmann says change is being forced on them. ‘Regulations are the stick here, and the biggest example of that is how total dissolved solids discharge limits have already forced the mining industry to lower sulphate concentrations in treated mine water in many parts of the world. This will only increase in the future as good-quality water becomes more valuable. ‘Regulations have often driven innovation’, he says.