Can we help the green transition by extracting arsenic from contaminated sites?

Historically, arsenic has been used for, for example, pest control or impregnation of wood. In some cases, it has left major pollution problems, and arsenic itself is carcinogenic.

However, arsenic is also found in a metallic form, which is valuable and plays an important role in the future.

»For decades, we have tried to get arsenic as far away from humans as possible. But something interesting is happening with arsenic in terms of society. This is because the economic importance of arsenic is changing. The reason is that it is used in a number of products that are necessary to transition from fossil fuels to green energy systems, especially high-speed electronics, batteries and alloys,« says Case van Genuchten, Senior Researcher at the Geological Survey of Denmark and Greenland, GEUS.

Some semiconductors, which are used in microchips, also contain arsenic. Within the green transition, semiconductors are also included in, for example, solar cells, satellites and computers.

The vast majority of the metallic arsenic used in semiconductors is currently obtained from mining in China. Within the EU, there is a limited production of arsenic, but the majority is still purchased from outside.

Case van Genuchten is heading a project that, with support from Independent Research Fund Denmark (DFF), will try to extract arsenic from contaminated sites and reuse it to produce semiconductors.

Hope for a contaminated site in Hillerød

One of the starting points for the research is a plot of land in Hillerød, which previously belonged to the wood impregnation company A/S Collstrop - Dansk Træimprægnering.

Here, arsenic-containing impregnating agents were injected into timber to prevent the wood from decomposing.

»Decades ago, the regulation of arsenic was not very good, and therefore Collstrop did not do it in a very clean way. So, they ended up contaminating the soil with huge amounts of arsenic. There are 100 tons of arsenic in this one place. If you drink water with arsenic, it is very toxic to humans, just as it can harm plants and animals that live in the area,« says Case van Genuchten and continues:

»So, the Capital Region of Denmark has spent decades figuring out what to do with the site. They have used established methods, which for arsenic is containment. So, you prevent arsenic from moving around in the environment and contaminating more soil and more groundwater. But it can also be a potential resource.«

In addition to the Collstrop site in Hillerød, the researchers will also make use of a gold mine in the town of Yellowknife in northwestern Canada. 

Arsenic occurs naturally in connection with various types of metal ore, and therefore arsenic ends up being a waste product in mining. 
In Canada, they have chosen to freeze the 237,000 tons of arsenic waste to prevent the contamination from spreading. The total clean-up of the mine is expected to cost just more than four billion Canadian dollars, or about 20 billion kroner, to maintain this solution. 

»So we've been in contact with the authorities in Canada for several years now, and they're very excited about the idea of cleaning up and recycling the arsenic,« says Case van Genuchten.

Building on previous research

The practical part of the research will first and foremost uncover what is the most effective method for washing the arsenic out of the soil from the Collstrop site and the gold mine in Canada. This means that the researchers will test everything from caustic soda to citric and acetic acid.

When the arsenic is out of the soil, it is put in water and a reducing agent containing sulphur is added to the mixture. It converts the arsenic in the water into metallic arsenic.

The reaction is well known, as it has been tested in a previous DFF-funded project carried out by GEUS. Here, the focus was on cleaning groundwater of arsenic.

»I hope that we can achieve a semiconducting material that is extracted from waste. At the same time, we can gain greater knowledge about how we can convert different types of arsenic pollution into valuable materials,« predicts Case van Genuchten, concluding:

»We will try to convert this pollution into a material that is currently actively imported into the EU. The imported metallic arsenic comes from traditional mining, and environmental scientists know very well how destructive mining can be for the environment. So we hope that this can become a much more sustainable way of producing a material that is needed to transition from fossil fuels to green energy systems.«

The project is scheduled to go on for four years.