Nitrogen removal in low pH and heavy metal contaminated mine wastewaters

Finland has a long mining history and the number of new mining projects has Increased since Finland joined the EU in 1995 [K. Mattila, G. Zaitsev, J. Langwaldt, 2007]. In Finland, the range of commodities exploited by the mining industry, fall under the operational jurisdiction of the Mining Act (503/1965). Mining industry in Finland is also important for regional employment. Together with natural stone and aggregate industry, mining industry employs around 12000 persons with annual turnover of 1700 million euros. It is estimated that each employee at mining industry creates other three or four jobs, increasing significance of the employment [GTK, 2012].
Especially in Finland nitrate concentrations in rivers are increasing [EEA, 2004]. The total amount of extracted rock has been increasing significantly since the 1950s.
In 2006, the total output of Finnish mining activities was 30.646.467 tons [Geological Survey of Finland, 2007]. About 0.2-0.3 and 0.5-1.0 kg of explosives per ton of
extracted rock are applied in open pit and underground mining, respectively (Oy Forcit Ab). In Finland, the total annual consumption of explosives might be about 12.000 tons (0.4 kg/ ton of rock). In a study by Forsberg and Åkerlund (1999) about 17% of applied explosives are transported with the ore to the refinement and barren rock piles. The study by Forsberg and Åkerlund (1999) and a survey at Kemi mine indicate that about 0.03% and 1% w/w of nitrogen in all loaded explosives, respectively, are discharged into the aquatic environment.
The annual consumption of explosives in the Suhanko and Talvivaara mine project will be about 8000 to 12000 tons with a potential release of 80 to 120 tons of total nitrogen into the nearby water bodies if up to 1% of the total nitrogen in applied explosives are directed to the aquatic environment.
Furthermore, the extraction of groundwater to prevent flooding of mines, leachate discharge from barren rock piles and discharge of wastewater from the ore processing into tailing ponds results in large amounts of mine effluents in the order of several m3/min or million m3/year per mine. Discharge of nitrogenloaded mine waters from the barren rock piles is largest during spring and after heavy rainfall events. The discharge of large volumes of nitrogen-loaded water in spring is critical since microbial activity is thought to be low after the cold winter. Barren rock plies are a long-term source of ammonia and nitrate release.
Small streams and water bodies have only limited capacity to handle excessive N-loads and are at risk of eutrophication.