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20 December 2021 5 min read

Up to 69 different metals are buried in the world’s e-waste stockpile, most of which ends up in landfill. Valuable metals could be recovered using a more economical and environmentally friendly approach to recycling known as biomining.

E-waste – discarded mobile phones, computers, TVs, batteries and other electrical and electronic equipment – is one of the world’s fastest growing waste streams, due to increased digitisation of products, shorter product life-cycles and fewer repair options.

In 2019, humans generated approximately 54 million metric tonnes of e-waste, of which only 17 per cent was recycled.

Most ends up in landfill, contaminating soil, groundwater and waterways.

Closing the loop

A team of CSIRO and Murdoch University researchers recently reviewed global trends in materials recovery from e-waste and identified opportunities and barriers to establishing new industries in Australia and New Zealand.

They noted the value of recoverable materials in the world’s e-waste stockpile is an estimated US$60 billion.

This stockpile includes 69 different metals – precious metals like gold and silver; base metals like copper, cobalt and nickel; and increasingly critical rare earth elements.

From a financial perspective, the feasibility of recovering strategic metals from e-waste will depend on the costs involved – of collection, transport, sorting and disassembly, shredding, milling, and metallurgical processing to extract and concentrate the metals.

From a sustainability perspective, recovering metals and materials from e-waste offers potential environmental and societal benefits.

These include reducing the volume of e-waste going to landfill and associated environmental impacts; ‘closing the loop’ in material life-cycles; and reducing the energy use, emissions and impacts of mining and minerals refinery operations.

Biomining a ‘high-grade ore’

CSIRO’s Dr Anna Kaksonen has been working with CSIRO colleagues Dr Naomi Boxall, Dr Ka Yu Cheng, Christina Morris and Jonovan Van Yken, and Murdoch University's Prof. Navid Moheimani and Prof. Aleksandar Nikoloski to explore prospects for biomining metals from e-waste.

Biomining is already used at a large scale to bioleach metals from low-grade ores and biooxidise refractory sulfidic gold ore concentrates before cyanidation.

Currently, 10–15 per cent of the world’s copper and about 5 per cent of the world’s gold are mined this way.

Dr Kaksonen points out that primary ore resources are becoming progressively depleted globally, making e-waste a more critical resource for the minerals sector.

“E-waste is like a high-grade ore – it's often called an urban mine,” she says.

“For example, there is up to 100 times more gold in a tonne of mobile phones than in a tonne of gold ore.

“Currently, much of the e-waste collected in Australia is still shipped overseas for value recovery. There’s an economic opportunity for Australia to develop local processing options so that the metals’ value could be recovered here.”

Metals bioleaching from milled PCBs

The CSIRO-Murdoch University team’s current research focuses on the development of innovative bioprocesses for extracting base and precious metals from milled printed circuit boards (PCBs).

The work is funded through the Western Australian Government’s New Industries Fund Waste Sorted e-waste grants.

PCBs – found in most electronics – are particularly rich in valuable base and precious metals, including copper, nickel and zinc, and gold, silver and palladium. 

“Conventional hydrometallurgy typically uses strong chemical acids or cyanide for leaching metals, but this results in toxic waste streams,” says Dr Kaksonen.

The research conducted by the team so far has included characterisation of the content of various metals in the milled PCBs and evaluation of the effect of pulp density on bioleaching base metals from milled PCBs in the laboratory.

The researchers are currently evaluating the efficiency of precious metal bioleaching.

Australian urban mines and mobile refineries?

Dr Kaksonen hopes a successful outcome will lead to further research to optimise the bioprocesses and determine their economic feasibility, in terms of the value of extracted metals in relation to pre-processing and processing costs.

She hopes to one day see mobile e-waste ‘biorefining’ units in Australia, which would offset the comparatively high costs of transporting PCBs and other e-waste to central locations for processing.

“The benefit of biotechnology is that it can be applied at relatively small scales, and scaled up or down, unlike smelters, which are fixed infrastructure and require high-volume feedstocks to be economic,” says Dr Kaksonen.

Business ventures like Germany's BRAIN BioXtractor and New Zealand-based Mint Innovations have already begun to use biomining and biorefining to isolate base metals and precious metals such as gold from e-waste in urban and mobile processing facilities.

Metals in waste Li-ion batteries

Dr Boxall, Dr Kaksonen, and Dr Cheng have also explored opportunities and challenges for recovering metals from lithium-ion (Li-ion) battery waste.

Two of the laboratory-scale bioreactors used by the Perth team to assess the feasibility of microbial solutions to leach metals from shredded and milled printed circuit boards.

In 2015, Li-ion batteries accounted for 24 per cent of all batteries purchased in Australia.

They are used in handheld, portable and rechargeable products, as well as electric vehicles and renewable energy equipment.

The estimated value of metals in one tonne of Li-ion battery waste is between $AU4,500 and $17,000, with most of that value due to cobalt.

Dr Boxall and her colleagues have successfully demonstrated the lab-scale application of bioleaching to extract lithium, cobalt, nickel, manganese and copper from Li-ion battery waste.

However, as the research team have noted, the potential value of metals in Li-ion batteries – particularly cobalt – depends on many unpredictable and intersecting factors.

Many countries have already started developing new battery technologies that use less cobalt, which may in turn reduce the value of battery waste.

Lithium is another metal subject to dramatic fluctuations in its commodity price, which is set to rise with increasing demand for electric vehicles (EV) and off-grid storage devices.

Battery waste and materials forecasting

This is where CSIRO’s recently developed Physical Stocks and Flows Framework (PSFF) tool can help the industry more realistically test assumptions about future supply and demand trends for manufacturing materials.

The CSIRO team released a report on the application of the tool to testing assumptions about the future supply of EV battery metals, particularly cobalt, lithium and nickel.

Critical Energy Metals Mission-in-development lead, Dr Jerad Ford, says the PSFF tool takes into account factors not currently accounted for in traditional forecasting models, which ignore the dynamics of global materials flows and expected changes in underlying technologies.

Future demand for cobalt and nickel mined from primary ores, for example, may be impacted by changes in battery chemistry, more rapid EV uptake, and higher levels of recycling.

This could result in unexpected gluts, shortages and other fluctuations, instead of progressively rising demand trends.

For industry, the PSFF tool could be used to model market assumptions for any major new technology requiring a new mix of metals.

Dr Ford’s colleague, Dr Jim West, says CSIRO’s aim in developing the tool is to “help Australian industry identify risks and opportunities on the path to a low carbon future”.

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