Determining Acid and Metalliferous Drainage Potential of Waste Rock on a Mine

Acid and Metalliferous Drainage (AMD) is recognised as serious environmental problem in the mining industry. This is because environmental issue of AMD poses serious threat to water quality, vegetation cover and social licence of the mining operations. AMD occurs when reactive sulphide bearing materials are exposed to oxidising conditions. It has now become imperative for some mining companies to test sulphide bearing minerals for their AMD potential before major mining excavations are done. This work determines the AMD potential of fifty (50) waste rock samples from a Mine using Acid Base Accounting (ABA) techniques. Mineralogical studies on the sample indicated that the major sulphide mineral assemblages present were pyrite, arsenopyrite and chalcopyrite. Paste pH showed that 20% of the samples had undergone weathering and as such AMD generation had already started. Approximately 22% of the sample had conductivity levels between 1000 to 10,000 µS/cm and this shows a typical AMD chemical characteristic of high salinity. Acid Base Accounting showed that 32% of the samples were acid generating. Exactly 16% were non-acid forming and 52% were uncertain. The analysis showed that the potential for AMD generation exists for the waste rock material and can affect the local environment, specifically water quality if preventive measures are not taken. Keywords: Sulphide, Waste Rock, Acid Base Accounting, Paste pH, Conductivity

Natural oxidation of coal tailings from Middelburg area (South Africa), and impact on acid-generation potential

SYNOPSIS The aim of this study was to determine the acid-generating potential of coal mine tailings located in the Middelburg area, South Africa, using conventional assessment techniques. Four coal-tailing samples were collected from different layers of a coal-tailing pile. The acid-base accounting (ABA), acid-buffering characteristic curve (ABCC), and net acid generation (NAG) methods were used in conjunction with a mineralogical investigation to assess the potential of acid mine drainage (AMD) formation from the tailings. The results showed that the top layer of the pile, which was exposed to the atmosphere, was most likely to form AMD, exhibiting the lowest paste pH (2.5) and ABA of zero kg H2SO4 per ton. The ABA results were compared to ABCC results and mineralogical calculations to confirm the findings. The results from the ABCC test and calculations based on mineralogy indicated that the ABA method overestimates the effective or readily available acid neutralization capacity (ANC) and the true MPA of each sample; only three of the four samples could therefore be classified as acid-forming, but with low acid-generating capacity. Although the findings show that the top layer of the coal tailings in the Middelburg area is most likely to form AMD, it is important for future studies to further investigate the kinetics of acid formation. Keywords: acid mine drainage, acid-base accounting, mineralogy, net acid generation, coal mine tailings.

The Acid-Base Accounting (ABA) of Overburden Rock to Predict Acid Mine Water in Kasai Coal Mining, Indonesia

The Acid-Base Accounting (ABA) and TCLP methods from overburden samples collected from the coal mine in Kasai were undertaken to predict pre-mining acid mine water quality. Maximum potential acidity (MPA), acid neutralization capacity (ANC), net acid generation (NAG), net acid producing potential (NAPP) and ANC/MPA ratios were determined on the Acid-Base Accounting (ABA) protocol. Most of the samples from KS-10, KS-11 and KS-12 show the pH of NAG of overburden ranges from 5.53–7.86 negatively net acid neutralization potential (NAPP). The ANC/MPA ratio varied from 1.09–26.60 and is classified as non-acid-forming except at an interval depth of 7.00–9.00 m in KS-12, where it is classified as uncertainty. The potentially acid mine water detected in KS-39 at an interval depth of 16.00–36.00 m was classified as potential acid forming (PAF), indicated by a positive NAPP, a low ratio of ANC/MPA (below 1.0) and high dissolved metal iron.