Reduction of Acid Rock Drainage from the Lokken Sulphide Ore Mine by Diverting Acid Drainage from Surface Waste into the Flooded Mine

摘要

The Laken sulphide ore mine (1654-1987) has for the last 100 years been the most polluting mine in Norway. About 6.2 million tonnes of acid-generating waste are disposed of in the area. Up to 1983 the main source of pollution was the highly acidic mine water. In the following years the most polluting part of the mine, the Wallenberg Mine, was flooded by natural inflow during 8 years. At the end, acid drainage from the dumps were diverted into the flooded mine giving the ingoing water a retention time of about 1 year. The purpose of this measure was to raise the pH of the ingoing seepage by contact with the alkaline bedrock. Ferric iron is precipitated and copper ions are trapped on pyrite surfaces at elevated pH values. The measure worked very well for 10 years. A 95 % reduction in the total copper loadings from the area was achieved. In 2002 the pH of the outgoing water dropped from 5.5 to below 3. The neutralising capacity of the mine is exceeded. At the end of 2008 it is obvious that the measure has come to an end. The metal loadings from the flooded mine have increased substantially in the latest years and new abatement plans have to be implemented as soon as possible.