Weathering Behavior of Overburden-Coal Ash Blending in Relation to Overburden Management for Acid Mine Drainage Prevention in Coal Surface Mine

Encapsulation of potentially acid forming (PAP) material with non-acid forming (NAF) material is counted as one of the best practices in overburden management for a sustainable prevention of acid mine drainage (AMD) in surface coal mine. In some mines, however, where only limited amount of non-acid forming material is available, appropriate overburden management methods should be developed. Those include the compaction technique of NAP as well as the use of ash from coal fired power plant (fly- and bottom ashes) as blending material in capping material. In both cases, understanding of weathering behavior of capping material is important. The weathering process of blending of overburden and coal combustion ash was simulated in the laboratory using free draining column leach test. Different blending schemes were studied in different columns. The weathering process was simulated by spraying deionized water once per day, and leachates were collected and analyzed. Infiltration rate was also observed. X-ray diffraction and fluorescence analyses were also conducted to identify the mineral composition of the samples. The simulations were conducted within 14 weeks. From the different configuration of the samples in general, it can be concluded that the weathering process played an important role in controlling the infiltration rate, and furthermore could increase the capability of capping material to prevent infiltration into the PAF material. The use of coal fly- and bottom ash could also improve the capping performance.