Demand for some of the world’s key metals and minerals is set to outstrip supply in the coming years.
To take copper as an example, the International Energy Agency (IEA) forecasts that the copper market could face a supply deficit of 30% by 2035. This will be an all-too-familiar issue for those in the mining industry, and issues like declining ore grade are well understood. But as these deficits loom, innovators are increasingly looking for new sources of valuable metals and minerals beyond traditional projects. One of the sources they are looking at is mine wastewater, which is full of dissolved metal ions.
Traditionally, low and variable concentrations of target substances and the chemical complexity of mixtures have made it difficult to extract resources from many wastewaters in sufficient quantities and purities to make economic sense. Incumbent technologies also face downsides such as the generation of secondary waste.
Now, however, startups and academic researchers alike are developing technologies that have sufficient scalability and selectivity to make resource recovery economic – even for tough wastewater streams and tailings facilities. This is opening up new opportunities for mining companies to turn wastewater from a liability into a new revenue stream.
‘Scavenging’ metals with selective filters
One company working in this space is Finland’s Weeefiner, which has developed 4D Scavenger – a highly selective technology that uses 3D-printed, chemically porous filters to capture dissolved metals from industrial water streams, including mines.
As water flows through the system, the target metals, such as copper, are selectively extracted and concentrated into a high-quality, metal-rich product that can be used directly or further refined. This enables the recovery of metals that would otherwise be lost in wastewater.
Instead of bulk treatment, Weeefiner’s technology is designed to target specific metal ions, a crucial feature as mining water streams are complex and contain many dissolved elements at varying concentrations.
The system is built into a standardised shipping container, and this modular design allows for easy transportation and rapid deployment.
The technology is applicable across a wide range of mining water streams, including process water, Pregnant Leach Solution (PLS), SX/EW bleed streams, Acid Mine Drainage (AMD), and tailings-related water streams.
In operational mines, the technology enables recovery of valuable metals from process streams, improving efficiency and reducing losses. At closed or legacy sites, it enables recovery of remaining metals from mine-impacted water while reducing environmental risks and long-term treatment costs.
Heat- and chemical-free critical mineral extraction
As countries attempt to diversify their sources of critical minerals – for both geopolitical and environmental reasons – a range of circular solutions are emerging beyond the wastewater space. Lithium-ion battery recycling, for example, is growing rapidly. However, many of these solutions rely on large thermal and chemical inputs to separate and purify the target materials, and this is also true of conventional ore processing.
For MIT spinout SiTration, the exciting thing about wastewater is that it provides an opportunity for circular extraction of minerals without the need for acid, high temperatures, or intense chemical processing.
The company uses a combination of two technologies – Silicon Electro-Extraction (SEE) and Silicon Nano-Filtration (SNF) – to efficiently and profitably recover critical minerals from a range of mining wastewaters, even when those streams are complex and dilute. Crucially, these technologies utilise electricity and membranes, with no need for heat or chemical inputs.
The company’s ground-breaking porous silicon membrane technology is both highly durable and tuneable – meaning that the sizes of the membrane’s pores can be adjusted to recover a range of materials. Silicon Electro-Extraction (SEE), meanwhile, utilises electrochemistry to further isolate and extract the target materials.
The combination of these technologies enables efficient and low-cost material recovery compared to traditional resource-intensive mining and battery recycling technologies.
SiTration has already teamed up with Rio Tinto to apply its technology to mining wastewaters and has received funding from BHP’s venture arm.
Extracting water treatment chemicals from AMD
It may be notorious for polluting rivers and groundwater, but researchers from Heriot-Watt University and the University of South Africa have discovered that AMD can paradoxically be a tool for delivering clean water.
The cross-border research team has developed and tested a method for extracting ferric iron from AMD before converting it into ferric chloride – a chemical widely used for water treatment.
In lab experiments, the ferric chloride recovered from the AMD was found to achieve 99% removal of pollutants such as aluminium, iron, and chromium from river water.
To precipitate iron from the AMD, the researchers used magnesium oxide nanoparticles, which were derived from cryptocrystalline magnesite, a material locally available at mine sites in South Africa. The iron was then reacted with widely available hydrochloric acid to produce ferric chloride.
"This could be a low-energy and low-carbon practical solution to a problem that blights communities around the world and has lasting health, ecological and economic impact,” explains Dr Spyros Foteinis from Heriot-Watt University’s Research Centre for Carbon Solutions – a collaborator on the research.
The researchers believe this solution could be scale up to an industrial level and could be particularly useful at tackling pollution from legacy mines.
From copper to cleaning chemicals, innovators are finding new ways to extract value from mining wastewater. In the process, they are unlocking new revenue streams and providing greater access to the key minerals the world will need in the coming decades.
