Potential evaluation of acid mine drainage production by coal washing wastes: A case study of Mehmandoost plant, NW Damghan

Acid mine drainage (AMD) as the most important environmental issue in mining sites is considered a significant source of environmental pollution.  AMD is typically produced by the oxidation of sulphide minerals, especially pyrite. The present study aims to investigate the acid production potential of the wastes of Mehmandoost coal washing plant located in NE Damghan. For this purpose, mineralogical, geochemical, and statistic tests were carried out on 7 representative coal washing waste samples. The obtained results show that although coal washing wastes are not enriched in Cu and Mn, they are moderately enriched in Ni and Co, significantly enriched in Cr, Sb and Zn, strongly enriched in Cd and As, and extremely enriched in Pb and Mo. The main mineral phases presented in the studied samples include quartz, muscovite, clinochlore, kaolinite, illite, montmorillonite, calcite and pyrite. In most of the studied samples, the pH and electrical conductivity (EC) of the saturated paste is <3 and > 2000 μm/cm, respectively. Moreover, in most samples the Net Neutralization Potential (NNP) is < -20. Also, in most of the samples, the Net Acid Production Potential (NAPP) is positive and the Neutralization Potential ratio (NPR) is < 3. The pH of Net Acid Formation (NAG pH) of these samples is < 4.5 and the ratio of Acid Neutralization Capacity to Maximum Acid Potential Acidity (ANC/MPA) is < 1. According to the results of static tests, there is a possibility of production of acidic drainage by the studied samples, therefore, taking suitable management measures to control acid production in the area is of crucial importance.