Abstract
Acid Mine Drainage (AMD) which occurs when sulfide minerals are exposed to water and oxygen with an excavation is one of the serious environmental problems in the world. A dry cover system is generally constructed in waste dump for the prevention of AMD in Indonesia by virtue of low cost and availability of waste rocks for a cover layer. However, the failure of the system caused by the lack of information related to the construction of cover system in mines, which leads to AMD, has been reported recently in Indonesia. In this study, the field investigation was conducted in pit and waste dump in open cast coal mine in Indonesia with the aim of obtaining the information on the construction of a cover layer and backfilling conditions of waste rocks in the waste dump. The rock samples taken in two areas of the mine were analyzed by geochemical analysis and sequential extraction with acids. The results indicated that Net Acid Producing Potential (NAPP) of the rocks in the waste dump down to 100 cm depth in both areas was from 10 to 30 kg H2SO4/ton, suggesting that Potentially Acid Forming (PAF) was backfilled in a cover layer. The backfill of PAF was contrary to the concept of cover system, which caused the failure of constructing a cover layer. The cause of the failure was likely attributed to the shortage of cover rocks which are classified as Non Acid Forming (NAF) or the failure of proper placement of them by an operational problem in the areas. Moreover, the results of the extraction with acids suggested that the form of iron and sulfur has to be taken into account to discuss the occurrence of AMD.
Highlights
The negative impacts on the nature of coal development by open cast mining have been reported with expansion of coal production recently in Indonesia
The rocks classified as uncertain rocks are backfilled in waste dump in this mine as Potentially Acid Forming (PAF) within the operation to minimize the risk of Acid Mine Drainage (AMD) after mine closure
These results indicated that more than 50% of waste rocks produced in the operation in the areas consisted of PAF assuming that uncertain rocks are PAF
Summary
The negative impacts on the nature of coal development by open cast mining have been reported with expansion of coal production recently in Indonesia. Acid Mine Drainage (AMD), which is a serious environmental problem, is attributable to the contact of sulfide minerals with water and oxygen in excavation activities in mining. This problem affects the nature in the field [1]; it has to be prevented within the operation of mines. The generation of acidic water proceeds with the dissolution of sulfide minerals such as pyrite (FeS2), followed by the reaction that Fe2+ changes into Fe3+ through oxidation by oxygen (Equations (1) and (2)) [2].
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