Prevention of Acid Mine Drainage (AMD) by using sulfur-bearing rocks for a cover layer in a dry cover system in view of the form of sulfur

Acid Mine Drainage (AMD) is one of the environmental problems caused in mining operation. The exposure of sulfide minerals in rocks to water and oxygen in the excavation process leads to AMD. The cover system has been constructed to prevent AMD in many cases in Indonesia for the availability and low-cost maintenance. Waste rocks are classified into Potentially Acid Forming (PAF), which is sulfur-bearing rocks, or Non Acid Forming (NAF) based on the results of geochemical analysis in the system. PAF is covered by NAF to prevent the contact of PAF with water and oxygen for the prevention of AMD in many cases in Indonesia. However, it is difficult to construct the cover system due to the shortage of NAF when most of waste rocks are PAF materials in the field. Tere are additionally varieties of PAF materials due to the content of sulfur in rocks in the field: some of them are unlikely to be the source of AMD. For the reasons, sample analysis of the waste rocks obtained in coal mines in Indonesia and the leaching test were conducted in order to discuss the use of some of PAF materials for the cover layer in such a case. The results indicated that it can be possible to use some of PAF materials in which most of sulfur compounds are readily-soluble for the cover layer instead of NAF after the reduction of the potential of acid production of rocks. Meanwhile, the rocks in which most of sulfur compounds are sulfide minerals have to be preferentially backfill in the dumping site since they can contribute to AMD for a long-term. The form of sulfur in rocks, therefore, should be taken into account to select PAF to utilize for the cover layer. This new concept of the cover system in which some of PAF materials are used for the cover layer makes the construction of the cover system without a large amount of NAF possible to prevent AMD in the mine.