Waste to wash away old sins

Mining has been and still is an important industry in Sweden; it has had a strong impact on the country’s development. The large quantities of mining waste collected over the years can however be harmful to both human health and the surrounding environment.

In a doctoral thesis in environmental science, Lotta Sartz presents a solution that is both simple and cost-effective. By using certain waste products from other industries the pH value of the acidic leachate that releases and transports the metals from the tailings can be increased, thus stopping the pollution.

Makes the water more acidic

- At the same time, this is an advantage for the industrial companies that would otherwise have to pay to take care of their waste products, says Lotta Sartz.

Her method is used primarily in the historic mine sites where metal was mined from sulphide ore, which represents about three quarters of the mines. When the sulphides, which are sulphur compounds, come into contact with oxygen, oxidation turns them into sulphates, which are easily soluble salts that lower the water’s pH value, that is, making the water more acidic. This means that heavy metals such as copper, zinc, cadmium and lead are released from the waste piles and spread into the environment. As historic mining methods were less efficient than they are today, the historic mining waste has higher concentrations of metal. Since much of the industrial waste consists of alkaline by-products and therefore have a high pH value, it can be used for counteract purposes – it can either be introduced directly into the mine waste, or used as a filter where the leachate flows out.

Full-scale tests

Lotta Sartz’s research is based on both laboratory and field-scale experiments, and includes alkaline by-products from four different industries: the lime industry, the steel industry, the pulp industry, and the power generation industry.

- The results show that some of these materials have the ability to neutralize the mine waste or leachate from the mine waste and reduce the mobility of heavy metals. So now we are taking the next step to test them in full scale.

Lotta Sartz has also developed a “test kit” with experiments in different scales, making it easier to plan and carry out post-treatment of historic mine waste deposits.

In addition to her PhD work, Lotta Sartz is working as an environmental chemist within the EU financed project Bergskraft Bergslagen.

Text: Ingrid Lundegårdh
Photo: Mattias Bäckström and Lotta Sartz