Bioprocess for reducing sulphate and nitrate in mine waste water

Forrum Recycling and Waste Solutions AB were nominated as one of three finalists for the Swedish Mining Innovation Award in 2019, for a microbiological-based wastewater treatment process for lowering the sulphate and nitrate content of mine waste water. The concept is being tested at pilot scale at LKAB Svappavaara and consists of a prefiltration stage and a free floating biobed reactor.

structures for microbes to attach to in wastewater treatment
Plastic pieces give a surface for the microbes to attach to, to prevent them being washed out with the water.

Most mines face challenges meeting discharge limits on the allowable amount of sulphates and nitrates in the mine waste water. A summary of the wastewater treatment solution developed by Fortum is presented in a Youtube video. Mine waste water treatment is a focus of work package WP5 in the SEESIMA project.

Rare Earth Minerals recovery from mining waste

A rather negatively-oriented article recently highlighted the developments in the Rare Earth Mineral industry in China. Unfortunately the article is rather light on technical details, choosing to highlight the environmental impacts. According to the article there have been many ‘pirate’ operations extracting Rare Earth Elements (REE), and extraction techniques include in situ leaching where chemicals are pumped into soil to dissolve and extract the elements from the soil. It is mentioned that other extraction techniques are in use and under development with lower impacts.

As posted earlier, LKAB in Sweden is studying the recovery of REE from iron ore tailings, and NW Russia have existing commercial operations doing this. The waste chemical mentioned in the article on China, “ammoniacal nitrogen” sounds like a potential resource for fertiliser production, or at least can be treated in an analogous manner to the treatment of sulphate in mining waste water being studied in the SEESIMA project WP5.

An article with more technical detail on the Chinese REE industry can be found here, This article focuses on the ion absorption type of REE deposits, which are only found in China. Although only representing less than 3% of China’s REE deposits, they have a higher content of medium and heavy REE and simpler extraction, being easily extracted by ion exchange with ammonium sulphate solutions. This is the basis for the in situ leaching processes, which avoided the environmental impact of open excavation.

Experimental work on sulphate reduction underway

Breakdown of sulphur-containing minerals often results in the release of sulphate (such as with acid mine drainage). One way to combat the environmental problems that this causes is to use certain types of bacteria that reduce the sulphate back to sulphur or sulphide compounds.

Sulphate reduction and metal sulphide removal experiments are going on at the University of Oulu. Sulphate reducing bacteria are cultivated in bottle scale and tested for utilization of KemiCond treated sewage sludge and succinate. At the same time synthetic mining water is treated, and iron is recovered as FeS. Furthermore, tests with other low-cost carbon sources and real mining waters, as well as reactor experiments are planned to be started in the autumn 2019.

sulphate reduction experiment over 2 weeks
Sulfate-reducing bacterial consortium cultivated in synthetic mining water at 6 °C with succinate as a carbon source.
continuous flow reactor for sulphate reduction experiments
Continuous up-flow reactor built up for biological sulfate reduction experiments

For more details, contact Hanna Virpiranta