Physical and geochemical characteristics of coal mine overburden dump related to acid mine drainage generation

The presence of water and oxygen are some of the important factors influencing the oxidation rate of sulfide minerals within overburden dumps. In overburden dumps, the availability of water and oxygen is strongly controlled by the physical structure of the dump, as well as the surface climate and geochemical reaction within the dump. In this study, a series of field investigations, physical and geochemical laboratory characterization were conducted in order to evaluate internal physical structure and geochemical characteristics of coal mine overburden dumps. The study found that a multi bench structure consisting of 10 m height of inter-fingered slope layer is formed as the effect of the end dumping technique. In addition, overburden material was characterized to have high clay content and low durable characteristic when interact with water. These characteristics couple with mining equipment traffic has result in a compacted layer on the surface of each bench lift which then controls the groundwater flow path within the dumps. Moreover, the geochemical characteristics were random, alternating among potentially acid forming and non acid forming materials within the inter-fingered layer. Those alternate geochemical characteristics may control acidification-neutralization reaction of infiltrated water, precipitation of secondary mineral and determines the quality of the overburden dump drainage, subsequently. The internal structure formed and the spatial heterogeneity of geochemical characteristics in overburden dump controls the acid drainage inhibition process within the dumps.