Secondary raw materials from aqueous streams: VITO closes the metal loop

Companies in the metallurgical industry often generate large volumes of liquid waste. They usually process that aqueous waste, or have this done by another party, but the costs of that processing can mount up. For this reason, large metal companies are keen to find a way of closing the loop.

But reducing the costs of processing the aqueous waste streams is not the only incentive to close the loop. In most cases, while waste streams contain various metals in low concentrations, their total mass is not insignificant given the large volumes. Some metals are even critical, meaning they are scarce and therefore expensive, and need to be imported from outside the European Union. If metal companies are able to recover these critical metals from their waste streams, they will be able to kill two birds with one stone.

Gas diffusion electrode

VITO has developed a unique technology for treating these industrial waste streams and for recovering the critical metals: a patented electrochemical process. "Our technology is based on capacitative electroprecipitation," explains Metin Bulut, Business Development Manager at VITO. "We use a gaseous diffusion electrode (an electrochemical circuit that is also used in fuel cells, for example, ed.) to induce a reaction that oxidises the metals and then results in their precipitation. The cathode and anode are also made of carbon in the form of a very fine matrix, and this enables us to adapt the structure easily, allowing a wide range of metals to be recovered." A selection from that range, by increasing atomic number, includes boron and magnesium, chromium and manganese, and cobalt and copper.

The carbon matrix in the cathode is partly hydrophobic (water-repelling) and hydrophilic (water-attracting). One side of it is also coated with a Teflon layer, which only allows air particles to pass through and therefore keeps the matrix separate from the liquid medium. "Normally, a reduction reaction takes place at the cathode," continues Bulut, "but in our set-up the cathode oxidises the metal ions. This causes the metals to cluster and precipitate as sediment, which we can separate."

Nanocrystals

The technology was developed as part of VITO’s research into sustainable chemistry. It was originally intended to facilitate the production of what we call nanocrystals – minuscule crystals composed of just a hundred atoms – that have extraordinary properties precisely because they are so small (for example, they emit light whose colour depends on their own size).

Critical metals are usually what we refer to as rare earth metals, which are incorporated in all kinds of electronic equipment and which can be recovered and reused from E-waste through the practice of urban mining. VITO’s technology, however, focuses on liquid industrial waste streams, where the metals are rather pre-sent in low concentrations. "During our research into nanocrystals, we discovered that we could also use our technology to extract metals from liquid streams, an application that we knew had commercial potential. Although the Flemish subsoil is rich in quartz and clay, primary metal sources are rather scarce, which means we rely on secondary sources from waste streams."

Get-A-Met

Until very recently, there was no way of efficiently extracting metals from a liquid medium in such small concentrations, and in such a way that the metals could also be reused, and therefore valorised. In the Get-A-Met project, which is being supported by the Strategic Initiative Materials (by VLAIO) and which involves KU Leuven and Ghent University, even a provisional business model has already been developed. This shows that the technology has a good chance of being used in the metal industry. This is due to the technology’s many strengths: it is flexible (it can be used for different metals), efficient (over 99 percent of the metal fraction is recovered!) and relatively cheap (around forty euro cents per m³ of waste water).

The business model shows that the recovery and valorisation can be organised in different ways. While metal companies can, of course, acquire the technology themselves, they can also outsource the processing of their waste streams to a specialised company. "This company is then paid for waste disposal, for example, while it returns the recovered metals to the market itself," explains the business development manager. A rough estimate of the potential revenue from the valorisation was also already developed in the model: around two million euros - and this being within the consortium of stakeholders behind Get-A-Met. "If we are able to roll out the technology throughout Flanders, we will achieve gross revenue of ten million euros. Besides, this does not even take into account the savings that were made as a result of lower water treatment costs.

Open to collaboration

Over the next two years (the Get A Met project runs from 2016 until 2020), we will be investigating how the technology can be scaled up to greater processing capacity, and then commercialised. "We possess the technology and the know-how together with KU Leuven and Ghent University," says Bulut, "and as always, we are open to collaboration with commercial partners, whether or not in the form of contract research. For example, we could investigate specific waste streams within a single company and adapt our technology accordingly. In the longer run, it is possible, of course, to set up a spin-off or outsource the technology under licence. The most important thing now is to properly assess the value we can create using the combination of waste water treatment and the valorisation of critical metals. We want to know to which extent closing critical metal loops in a range of industrie