Long-term evaluation of acid rock drainage mitigation measures in large lysimeters

In the course of a German–Romanian scientific project, large lysimeters with a volume of up to 65 m3 were used for up to 3 years long experiments on controlling acid rock drainage formation in three different types of pyritic mine waste: (A) weathered 6 years old waste rock material, (B) sorted, freshly broken, low-grade ore, and (C) unweathered tailings material. An addition of sodiumdodecylsulphate (SDS) partly reduced the activity and number of metal sulphide oxidizing bacteria of the type Acidithiobacillus ferrooxidans but did not kill the bacteria. Consequently, the release of metals and sulphate from mine waste was not significantly reduced. The application of the biocide isothiazolinone (Kathon RH 886) reduced the release of Cu, Zn, Fe and sulphate between 5% and 50% for different types of mine waste. A cover of organic material only achieved a moderate reduction of the heavy metal and sulphate release from the weathered 6 years old waste rock material: Cu was reduced by 50%, Zn by 30%, Fe by 90%, and sulphate by 40%.