Abstract:

Single net acid generation (NAG) testing is a standard static-testing procedure used within the mining industry to classify the acid rock drainage (ARD) potential of a mine material. The single-addition NAG test is generally appropriate for materials with low sulfide-sulfur contents (i.e., typically less than 1% which is equivalent to about 2% pyrite). High-sulfide and high-carbonate materials require a sequential-testing procedure to yield accurate classification results. Currently, there are no published recommendations for Sequential NAG testing, specifically the number of steps required or criteria for the termination of testing, to guide testing and classification of mine materials with higher sulfide-sulfur and carbonate concentrations. Specific analytical procedures are often adopted on a case-by-case base to promote complete consumptive reactivity of acid-producing and acid-neutralizing mineralogical assemblages. This paper recommends optimal Sequential NAG testing procedures based on mass-balance and batch-geochemical-modeling considerations for a range of material sulfur and carbon contents. The recommendations provided herein are meant to inform the ARD characterization community to support the best practice application of static geochemical testing procedures and material classification as potentially acid generating (PAG) and non-PAG.

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Stuart Miller