Assessing Environmental Risks Associated with Ultrafine Coal Wastes Using Laboratory-Scale Tests

Characterisation of the risk of acid rock drainage is typically achieved through the quantification of acid-generating and acid-consuming components present within a sample using initial laboratory-scale, chemical static tests. Such tests, however, consider ARD generation under chemical conditions and do not account for the role of micro-organisms. Their focus is exclusively on the net potential for acid generation, with no account of metal deportment or the relative rate of acid generation and consumption. The present study investigates the ARD potential of two ultrafine coal wastes samples using the standard static tests as well as the UCT biokinetic test to account for microbial ARD generation. The deportment of metal species under each test condition was also considered. The UCT biokinetic test results supported the static test classification, adding provided preliminary kinetic data on the ARD generation. Sequential chemical extraction tests allowed for differentiation of the host minerals according to their leaching potentials, providing supporting evidence for the deportment of metal species under the characterisation tests, thereby improving the knowledge base on which to classify coal wastes as benign or otherwise.