Acid Mine Drainage (AMD) problem is considered as one of the serious problems in mining operation in the world. This problem is generated due to sulfide minerals in waste rocks. Sulfide minerals are very commonly included in any types of crustal rocks, resulting in AMD and a negative impact on the ecosystem. In this research, some experiments were conducted with the rocks sampled in the open pit coal mine in Indonesia to understand the effects of the rock condition on acidic water generation. The result indicated that wetting and drying process affected the disintegration of rocks caused by both physical and chemical factors in the rock sample. Hence, AMD generation is promoted due to both factors while waste rocks are stored in tailings in the current system. It suggests that the system for waste rock management should be improved to prevent AMD generation.

1. Introduction

Mining operation often results in environmental problems. Acid Mine Drainage (AMD) is one of them and considered as serious problem due to the bad influence on the nature. Acidic water is generated when rocks containing sulfide minerals are exposed to oxygen and water. Pyrite is oxidized by oxygen, and the main oxidants are oxygen and ferric ion as shown in Eq. (1) and Eq. (4) in the reaction. Ferrous ion is initially dissolved from pyrite Eq. (1) and ferrous ion is oxidized to ferric ion by oxygen Eq. (2). The pH decreases with the promotion of the reaction above. Oxidation of pyrite is, moreover, accelerated by ferric ion Eq. (4) because ferric ion is strong oxidant. Depending on pH, ferric ion is precipitated as ferric hydroxide Eq. (3). This reaction does not happen at low-pH.

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