Encapsulation is a typical method used to prevent potential acid mine drainage (AMD) in overburden piles. In this method, Potentially Acid-Forming (PAF) material is covered with either Non-Acid-Forming (NAF) material or alkaline material to minimize water infiltration and/or oxygen diffusion through rock pores. The physical and chemical characteristics and thickness of the NAF material layer are critical factors affecting the successful prevention of AMD. Therefore, this study evaluated the method of NAF material layering using laboratory-scale column leaching tests. NAF layers with a ratio of 25 and 50% were used to cover PAF material containing pyrite and jarosite sourced from the Sangatta and Bengalon mining areas, East Kalimantan. The physical and chemical characteristics of leachate collected from samples watered on a weekly wet-dry cycle were analyzed by kinetic tests over a period of 23 weeks. The results showed a trend of increasing pH values and decreasing sulfate and metal concentrations in the leachate. This study shows that NAF layering is an effective method to prevent or minimize the generation of AMD.

The quality of pit lake water during development and final condition is affected by various factors, including geochemical characterization of materials of a pit wall, which may consist of in-situ and backfilling materials. This research aims to obtain a geochemical characterization of pit wall materials using 3 main laboratory tests and analysis, namely static test, mineralogical and elemental composition analysis, and kinetic test using free draining column leach test. Static test results show that 5 of 6 samples exhibit low paste pH and NAG pH. Pyrite is found in four samples and is responsible for acid mine drainage production. Some samples contain acid-consuming carbonates and oxides such as calcite and periclase. Four samples exhibit leachates’ pH values lower than 3,00, mostly during all cycles. Alongside the lithostratigraphic distribution of pit wall rocks, these results imply a potential occurrence of acid mine drainage that will become a critical issue for water quality development and final condition in pit lake formation. Therefore, these results become essential feedback for the stakeholders to plan and implement acid mine drainage management to minimize the adverse impact of acid mine drainage in pit lakes. Immediate understanding of the geochemical characteristics of leachates from pit wall rock, which control the overall mine water quality.

No abstract