区分 |
甲 |
氏 名 |
Mokhamad Candra Nugraha
Deni |
| 論文題名 | Acid mine drainage generation due to physical rock weathering at dumping site in coal mine, Indonesia |
| （インドネシアの石炭鉱山におけるダンピングサイトの物理的な岩石風化による酸性鉱山排水の発生） |
| Coal mining in Indonesia has an important
role for the current and future national economic growth. Most of the
Indonesia coal is for export market with the total value around US$ 6.53
billion in 2007, increased from previous years. Domestic coal consumption
also increased from 30.7 million tons in 2003 to 49 million tons in 2007,
mostly used for electric power generation. However, coal mining activity may cause the changes of initial environment condition and give impacts to the social life area around the activity. One of the environmental risks is acid mine drainage (AMD) generation. AMD generation is produced when sulphidic materials are oxidized by the oxygen and water, and the results of those processes are transported and discharged to the receiving environment. Many factors influence the AMD generation and transport of its product that inherently have correlations with climatic condition. One of the methods to prevent AMD generation is dry dump cover system that is proposed to minimize the influx of water and oxygen. In the tropical area where high rainfall and temperature occur, local climate events can potentially affect the integrity of a dry cover system. Rock weathering that is caused by cyclical drying and wetting condition can break the cover material to be finer size of particles, thus possibly reducing the saturated hydraulic conductivity brought about by the compaction processes of the surface material. Finer size of particles can also increase the total reactive surface area, thus increasing the rate of pyrite oxidation, and leading to AMD generation subsequently. Having considered the tropical climate condition with high rainfall and temperature of Indonesia, the study is intended to investigate the potency of physical and chemical rock weathering and their impacts to the engineering aspects of waste rock dumping area construction to prevent AMD generation. The dissertation describes and discusses the role of waste rock weathering and its influences to the processes of AMD generation, and consists of seven chapters as follows: Chapter 1: This chapter describes the general background of study, including the processes of AMD generation and the concept of dry dump cover systems, problem description and associated previous studies, the objective of study, and the approaching methods towards the solutions of the problems. Chapter 2: This chapter describes the general description of physical and chemical characteristics of waste rock in Indonesia, particularly at coal basin areas. It could be suggested that the potency of AMD generation in Indonesia is severe and needs to be deemed as an important aspect in the mining operation, including at PT. Kaltim Prima Coal (KPC), as the case location of this study. Even though the management of AMD generation at KPC has been recognized as one of the best practice in Indonesia, some aspects should also be studied and improved in order to get appropriate, practicable, and effective long-term management. There were three high risk events relating to AMD generation at KPC i.e. improper management of Non Acid Forming (NAF) and Potentially Acid Forming (PAF) waste rocks, shortfall of NAF, and shortfall of topsoil. Reviewing current management controls and developing some corrective actions are required in order to prevent AMD generation. Chapter 3: This chapter describes the detailed investigation of in situ waste rocks and waste rocks from dumping areas, in order to understand the background of conditions associated with AMD generation at the mine site. The results indicated that in situ waste rocks geochemically had a potency of AMD generation upon exposed to the air and water, which are two important factors in oxidation processes, and it would be faster due to rock weathering occurrences that increasing the total reactive surface area for chemical reactions. On the other hand, the results of investigation for the waste rocks from dumping areas suggested that rock weathering possibly can minimize the potency of AMD generation by creating finer size of particles and clay that can act as a barrier against oxygen diffusion and water infiltration into and within the dump. Chapter 4: This chapter describes the further investigation about rock weathering. The rates of physical rock weathering were different for sandstone, mudstone, and siltstone, and those samples also had different impacts to the water quality. Furthermore, from the column experiment, physical factor of the waste rock at the surface layer had a significant role to influence discharged-water quality. This condition was attributed to the interaction processes of geochemical characteristics of waste rock, weathering processes, water saturation, water retention time, and oxygen concentration on the layers. Chapter 5: This chapter describes the application of previous findings, including the investigation of applicability of mixing NAF and PAF waste rocks. Laboratory column experiments concluded that mixing of NAF and PAF with blending method had a lower potency of AMD generation than that with layering method, after the occurrence a shock loading of discharge-water constituents at the beginning of the experiment. Furthermore, in blending method, the armoring of PAF by NAF occurred due to higher compositions of NAF material, and it also influenced the oxidation processes. Chapter 6: This chapter describes the column experiments in the field, in order to understand the influences of climate condition, using compositions with 0 – 30% of PAF with blending method. The results showed that both physical and geochemical conditions of material changed along the time of experiment. Initially, physical condition i.e. increasing bulk density of material took a role in determining the condition of the column, subsequently affecting the geochemical processes. From this experiment, it was obvious that physical and geochemical conditions of material can not be dissociated one to another in determining the discharged-water quality. In addition, the result of analyses for intrinsic oxygen rate (IOR) suggested that the rates of oxygen diffusion were getting lower due to increasing of bulk density of material. It is however important to note that the rates of oxygen consumption for oxidation purposes were low, and this consequently suggested that available oxygen was not the oxidation rate-determining factor. Chapter 7: This chapter describes the conclusions of study and recommendations for further improvement. Having gone through the foregoing analyses, the study concluded that physical weathering of waste rock at KPC mine site, which is influenced by tropical climatic condition with high rainfall and temperature, has a potency to increase the performance of surface layer of waste rock at dumping area due to finer size of particles and clay formation. Furthermore, in case of mixing of NAF and PAF, physical weathering of waste rock also has a characteristics to reduce the oxidation of PAF materials by the armoring processes of PAF by NAF materials. |