Nitrogen removal with bioreactors in mining environments

Snow-covered mining environment. Photo.

Nitrogen behavior in mining environments is investigated in terms of the release of nitrogen compounds from rock waste deposits, and the removal of nitrogen from mine waters in denitrifying bioreactors.

Contact information: Albin Nordström, Roger Herbert

Nitrogen release from undetonated ammonium-nitrate based explosives used in mining is an environmental issue that is just beginning to be recognized. Undetonated ammonium nitrate is readily soluble in water and quickly enters into the mine drainage. The nitrogen in these waters is primarily in the form of nitrate (NO3-) and ammonium (NH4+) with lesser amounts of nitrite (NO2-), which is eventually discharged to the environment. In the cold climate of northern circumpolar areas, aquatic ecosystems are often nutrient-limited, and even small nitrogen loadings could impact water bodies. In addition, a significant issue is the presence of nitrite and the generation of ammonia (NH3), both of which have toxic effects on aquatic ecosystems. 

Nitrogen leaching from rock waste

Nitrogen compounds adsorb to rock waste that is removed from the mine and deposited on the ground surface. With the percolation of rainfall and snowmelt through the deposit, nitrate and ammonium are leached from the rock waste.

Two rock waste deposits have been created at LKAB’s Kiruna iron ore mine to study the processes controlling nitrogen release. Starting in Spring 2015, temperature and water content changes will be monitored in the rock material. Water discharge and water chemistry will be studied in water discharging from the base of the deposits. The aim of the study is to provide a better understanding of the hydrological processes controlling fluid flow in waste rock dumps at low temperatures.

Nitrogen removal in denitrifying bioreactors for mine water treatment

A low-cost solution for treating mine drainage with nitrate is a fixed-bed denitrifying bioreactor system, which is a passive or semi-passive surface or subsurface structure containing a porous organic material through which water flows. During water flow through the anaerobic regions of the bioreactor, dissimilatory reduction of NO3- to N2 is promoted by the denitrifier community.

Based on a series of laboratory experiments and a previous bioreactor study in Malmberget, a pilot-scale bioreactor has been constructed at LKAB’s Kiruna iron ore mine. The aim of the study is to provide an improved understanding of the dominating biogeochemical processes in a bioreactor system, and how biofilms with high denitrification rates develop and are maintained.

This project is part of the larger research project “MiNing - Reduction of nitrogen discharges in mining processes and mitigating its environmental impact” funded by VINNOVA, LKAB and Boliden AB over the period 2013 – 2016. 

Snow-covered mining environment with a car. Photo.
LKAB’s Kiruna iron ore mine