Abstract:
Classification of waste is an essential part of waste management to limit potential
environmental pollution; however, global systems vary. The objective was to understand the waste
classification of high density sludge (HDS) from acid mine drainage (AMD) treatment, according to
selected global systems. Three sludges from two limestone treatment plants, and three others from
a limestone and lime treatment plant from the Mpumalanga coalfields of the Republic of South
Africa (RSA) were evaluated. Systems for the RSA, Australia, Canada, China, and the United States
Environmental Protection Agency (USEPA) were considered. The USEPA system rated all six
sludges non-hazardous, Canadian and Chinese systems allocated a hazardous status to one sludge
from the limestone treatment plants based on Ni solubility. The RSA system considered two of the
sludges from limestone treatment plants to be higher risk materials than did the other countries.
This was due mainly to the RSA system’s inclusion of Mn and use of appreciably lower minimum
soluble levels for As, Cd, Pb, Hg, and Se. None’s use of lime resulted in higher soluble Mn.
Minimum leachable concentration thresholds for Cd, Hg, Pb, As, and Se in the RSA system were
below method detection limits for Toxicity Characteristic Leaching Procedure (TCLP) extracts,
making the guidelines impractical, and revision is advised. Considering all the systems, the
probability that the HDS from the coalfields of Mpumalanga, South Africa will be classified as
hazardous waste increases if the material is only subjected to limestone treatment because of Ni
solubility.
