Getting the most out of precious metals
The recovery of precious metals from process and waste streams has turned into a multi-million business over the last 10 years. And it is one that spans countless industries and attracts steadily-intensifying competition. Although the game is clearly already on for those organisations that have developed ‘scavenger’ techniques to rescue these sought-after metals, a huge part of this market remains wide open.
By Lydia Heida
Increased demand and advanced technologies have provided a major lift for the precious metals sector. For example, the fine chemical and pharmaceutical industries are increasingly dependent on palladium-based catalysts while gold and platinum figure strongly in chip and wafer production for the electronics industry.
At the same time, mining and refining companies are faced with declining ore grades, resulting in concentrates with higher impurity content and leading to a large, complex residue stream. Companies around the world have felt the unwanted repercussions as loss of precious metals simply means losing money.
A handful of innovative companies are leading by example. New and sophisticated metal scavengers can bring the amount of precious metals in a liquid stream down to one part per million or even parts per billion.
‘Our metal scavengers have recovered over 2.5 tonnes of precious metals in five years,’ says Jamie Conway-Baker, business manager of Johnson Matthey’s water division which covers the pharmaceutical, industrial and refining sectors among others. ‘This represents a value of about £50 million (US$ 85 million) at today’s market prices.
Chemical ‘magnets’
University of London spin-off project PhosphonicS is one of the frontrunners in this field thanks to its range of modified silica beads that trap trace elements of precious metals from liquid streams like a ‘chemical magnet’.
These small and porous beads have a very high surface area and can hold a large amount of metals. PhosphonicS has characterised 200 compounds that are bound to the silica and is able to recover platinum group metals as well as gold and silver.
‘About 30 to 40% of our business is aimed at purification applications, where the primary purpose of the scavenger is to clean up the product – for example, in the pharmaceutical, fine chemical and electronics industries,’ says the company’s chief executive officer Dr Linda Bell.
‘Recovering precious metals for their value; these metals stem either from a catalyst in a chemical process or from mining or refining streams.’
‘The other part is about recovering precious metals for their value. These metals stem either from a catalyst in a chemical process or from mining or refining streams. Also in the electronics industry, some processes that are using precious metals – such as the manufacturing of printed circuit boards or semi-conductors – are offering a recovery opportunity.’
If a waste stream from an electronics application contains gold and platinum, it might be that one scavenger is better at removing gold and the other is better at removing platinum, ‘and so both are incorporated into the final process’, Bell adds.
Various sizes of installation are available, with the costs proportionate to the scale. ‘A relatively small installation would cost a few thousand Euros and a big application could cost from half a million up to Euro 2 million (US$ 675 000 to US$ 2.7 million),’ she continues.
This can be a slurry process, a fixed bed column, or a lead and lag process. A successful operation involves the loading of about 10 to 80 g of precious metal per kg of silica.
Plenty of opportunities
Globally, over 100 companies are using or testing PhosphonicS’ metal scavengers. The company has local representation in countries extending all the way from South Africa to the Asia-Pacific region and is looking to set up operations in the USA and Russia.
The recovery of precious metals is of particular interest to countries such as China which has limited natural resources. ‘They have to import a lot of precious metals, and it is very important for them to recover as much as possible,’ stresses Bell.
In low concentration streams across the chemical, petroleum and other industries, around US$ 1.5 billion of recoverable metal is being lost globally, PhosphonicS states on its website.
The recovery of precious metals is of particular interest to countries such as China which has limited natural resources.
‘It is difficult to say how much of the market is still uncovered,’ Bell comments. ‘Mining and refining companies will tend to use traditional chemical processes. If they were to decide to use more scavenging technology, then that would drive very significant growth.’
Some of the market is captive – for example, by Johnson Matthey. ‘They use their own scavengers and their partners will also make use of these scavengers,’ Bell explains.
To offer a viable alternative to Johnson Matthey, PhosphonicS has a non-exclusive refining partnership with German precious metals and technology company Heraeus which will take the loaded scavengers and recover 97% of the metal on them.
‘It is an exciting technology, with applications that we are still developing worldwide,’ Bell declares. In the next 12 to 18 months, the team will bring some new technology to the market, focused on the recovery of precious metals in the chemical and pharmaceutical industries.
Targeting ‘the last 5%’
France-based Magpie Polymers is also a notable rhodium or ruthenium. ‘As far as I know, we are the only company worldwide that uses these types of phosphines in scavengers,’ says co-founder and ceo Dr Steve van Zutphen. ‘It creates a selective bond with precious metals and can be used in waste water treatment, as well as in optimising refining processes. Other scavenging technology can recover up to 95% of metals; we target the last 5%.’
Magpie Polymers’ most important application is the recovery of platinum and palladium from silver refining. ‘In the last process step, electrolysis is used to purify silver,’ Van Zutphen explains. ‘During this step, our scavengers can recover platinum and palladium out of the silver, which creates a purer silver and isolates the platinum and palladium that can be sold separately.’
In Europe, a number of silver refiners are now using Magpie Polymers’ scavengers ‘because previously there wasn’t a good solution to this problem’, according to Van Zutphen.
Apart from the recovery of precious metals from liquid streams in the refining and mining sectors, Magpie Polymers also has clients in the plating industry. The company is already working for a mining company in South Africa where it is running a pilot project to recover precious metals from its waste stream.
‘Due to labour strikes, this project has been on hold for the last few months, but hopefully the mine will be up and running again soon,’ he notes. As for the business potential of metal scavengers, Van Zutphen states: ‘If we could accommodate half of the miners and refiners worldwide with one or two niche applications for our scavenging technology, we would be very busy for the coming years.’
Cradle-to-cradle
UK-headquartered Johnson Matthey distinguishes itself from PhosphonicS and Magpie Polymers by virtue of the range of so-called backbones it can offer – a fibre, a silica, a silica polymer composite and a resin – and the number of chemical compounds that can be attached to these, according to Jamie Conway- Baker.
Sulphonic acid, vinyl pyridine, mercapto and thiourea groups most commonly give scavengers the right selectivity of metals. As for the process, customers can choose between a fixed bed column, which is sometimes used in series to increase overall contact time, a filter press, or a stirred tank or batch approach.
‘There is a lot more opportunity out there than is exploited at the moment.’
‘We continuously optimise between the three – backbone, chemical compound and process – to create the best solution for the customer,’ says Conway-Baker. ‘Since our precious metal refinery is one of the largest worldwide that recycles materials of secondary sources, we could tailor our material to suit that refining circuit and offer a full cradle-to-cradle approach.’
Bell is insistent on one point: ‘There is a lot more opportunity out there than is exploited at the moment.’
In the last 10 years, Johnson Matthey has acquired several companies that have developed metal scavenging technology in order to build their own portfolio, including Smoptech, Reaxa and Purity System Incorporated.
This portfolio is now large enough to cover the whole range of industries that need scavenging technology for either purification applications, waste water treatment or the recovery of precious metals – mainly gold, platinum, palladium, iridium, rhodium and ruthenium – for their value.
Lot of head room
‘Currently, we are developing a unique range of products that are based on silica polymer composite,’ says Conway-Baker. ‘The silica surface has a nano-layer of polymer on it and it is possible to attach lots of different compounds to it. This really opens up a whole new area since these composites can be used for the recovery of intermediate metals such as indium, gallium, bismuth, tellurium and rare earth metals.’
‘Many of these metals are still not efficiently recovered. For example, old tailings are becoming attractive for the recovery of metals as the grade is approaching what is now coming out of the mine.’
Regarding rare earth metals, Conway-Baker acknowledges the socio-political argument about security of supply. ‘But looking at the economics, rare earths are available now on the market,’ he points out.
‘It is a long-term play how we can efficiently separate and refine those from different sources. People are simply not going to pay 10 times the amount of money for such metals because they come from a recycling source.’
The overall volume of precious metals recovered today is ‘still very low’ and so there is ‘a lot of head room in the market to look at greater recoveries’, according to Conway-Baker, with China hailed as a ‘key market’ for the near future.
Johnson Matthey already has ‘a dedicated laboratory for metal scavengers’ at its Shanghai location, plus sales offices and some manufacturing facilities. ‘The experience and exposure in the Chinese market are already in place,’ Conway-Baker notes.
He believes Johnson Matthey’s water division will generate hundreds of millions of pounds of revenue in the next five to 10 years. ‘Our goal is to be a leading provider of niche technology processes, and metal scavengers will be part of this,’ he declares.
‘Lost in waste water’
Nanotechnology seems to be the new direction for metal scavengers, as this is also the central focus of the CERAMPOL project which aims to achieve a new generation of nanostructured membranes based on ceramic and polymeric materials with enhanced affinity to heavy metals.
Two years ago, this project was started up with a grant of nearly Euro 3.5 million (US$ 4.75 million) from the EU’s Seventh Framework Programme for Research as part of its commitment to create economic growth and jobs in Europe.
‘A lot of metals are still lost in waste water and end up in waterways or the sea.’
Spain’s Leitat technology centre is co-ordinating the project which has drawn in partners from various European countries, among them the Dutch University of Twente, Norwegian ceramic filter and membrane producer KeraNor, Spanish engineering firm Técnicas Reunidas and Johnson Matthey.
‘A lot of metals are still lost in waste water and end up in waterways or the sea,’ explains Dr Mirko Faccini, co-ordinator of CERAMPOL. The project is aimed at recovering rare earth metals from mining industry waste water and precious metals from the fine chemicals, pharmaceutical, electronics, refining and mining industries.
‘We work with polymer nanofibres which are modified so they have a high selectivity for a certain metal,’ Faccini notes. ‘The recovery rate is much higher than any other company that manufactures metal scavengers has now on the market. Also, the resistance to water flow is really low which saves energy.’
Europe in ‘weak’ position
At present, the team is focusing on gold, platinum and some of the rare earths, namely europium and yttrium. After analysing water streams from the Johnson Matthey refining process, for example, these rare earth metals were found in the highest concentrations.
In future, it is believed that CERAMPOL’s metal scavengers could cover the whole range of rare earths and precious metals. CERAMPOL’s technology is ready to enter the scaling-up phase. ‘We expect that the first pilot plant, which will be located in Spain, will be built in the coming months,’ Faccini states.
Looking further ahead, Faccini believes use of precious and rare earth metals will continue to increase across various sectors such as the electronics and solar industries. He argues that Europe is in a ‘weak’ position because the market for rare earths is dominated by China.
‘Here, there are no opportunities to mine these metals, so it is a good idea to recover them as much as possible,’ he contends. ‘This will have a huge value in the future, to protect the European market and its industry from such a monopoly.’
Published: August 2014 in Recycling International.