Construction of Dry Cover System for Prevention of Acid Mine Drainage at Mine Waste Dump in Open Cast Coal Mines, Indonesia

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.

Effects of pH-Induced Changes in Soil Physical Characteristics on the Development of Soil Water Erosion

“…At pH > 6, the repulsion between negatively charged soil particles resulted in decreases in I P and LL, leading to the development of soil erosion by water. The pH conditions can change the risk of soil water erosion through the change in physical characteristics of soils and this can develop over time at mine sites since mining operations contribute to changes in pH (e.g., through the generation of acidic water during the construction of waste dumps and the use of limestone) [13,16]. Considering that there were not large differences in soil texture, physical properties of soil, and minerals among the simulated soil samples, the difference in pH conditions affected the erosion rate of the soils through changes of the physical properties of the soils with zeta potential changes.…”

“…According to past research, the extent of soil erosion by water varies with pH. Acid mine drainage, which commonly occurs at the waste dumps of mining sites, causes acidic conditions with a pH of approximately 2 develop over time [13][14][15]. This acidification changes the physical properties of soils, including the shear strength and Atterberg limits [16,17].…”

Emerging Strategies for Mitigating Acid Mine Drainage Formation and Environmental Impacts: A Comprehensive Review of Recent Advances

“…Therefore, some researchers have encouraged to look for cost-effective and environmentally friendly methods to prevent the formation of AMD (Bai et al, 2021;Demers et al, 2017). Based on previous studies, oxygen barrier (dry and water cover) (Matsumoto et al, 2016;Moncur et al, 2015) and surface passivation techniques can be applied to prevent AMD formation (Zeng et al, 2013) . In general, the dry cover method is often used to prevent the formation of AMD (Lu et al, 2013) .…”

Characterization of Mine Waste and Acid Mine Drainage Prediction by Simple Testing Methods in Terms of the Effects of Sulfate-Sulfur and Carbonate Minerals

“…A cover system is an example of an isolation method, i.e., the use of an impermeable sheet to create a water shield with cement [8,9]. In this system, mining waste rocks, classified as non-source rocks for AMD, are commonly used as cover materials due to their low cost and easy use at mine sites compared to the abovementioned materials [10][11][12]. A cover layer comprising non-source rocks inhibits the supply of oxygen to sulfide minerals throughout the waste dump [13].…”