Geochemical Characterisation of Waste Rock Dump and Its Potential to Predict Acid Mine Drainage

Abstract

This paper evaluates the potential of the abandoned Anyankyirem waste rock dump located in Obuasi to cause acid mine drainage (AMD). Twenty (20) rocks were collected from various locations of the dump site and their elemental and physicochemical compositions were examined. XRD analysis was conducted on the samples to assess the mineralogy. Acid Base Accounting (ABA) test was used to ascertain the AMD potential of the dump. The ABA test comprises calculating the acid neutralization capacity (ANC) and maximum potential acidity (MPA) of the various samples. The MPA and ANC values were used to compute the rock samples' net acid production potential (NAPP). To help with acid mine drainage prediction, a column leaching experiment was carried out. Leachates were collected for over a period of 20 weeks. Physiochemical parameters of the leachates were determined as well as its chemical analysis and estimation of dissolution of calcium carbonate and weathering rate. From the column leaching experiment, rate of weathering of calcium carbonate throughout the 20-week leaching experiment was 3.6%. The ICP-MS and ICP-AES was used to determine the concentrations of heavy metals and major elements from the samples. Iron recorded the highest concentration of 7783.65 mg/kg and the lowest of 0.645 mg/kg was recorded in Bi. The sulphur and carbon contents of the samples ranged from 0.1 to 1.61% and 0.23 to 2.53% respectively. From ABA test and the column leaching test results, Anyankyirem waste rock dump is not acid generating.