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Open AccessArticle

Implications of Sulfur Speciation on the Assessment of Acid Rock Drainage Generating Potential: A Study of South African Coal Processing Wastes

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Minerals to Metals Initiative, Department of Chemical Engineering, University of Cape Town, Rondebosch, Cape Town 7700, South Africa
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Centre for Bioprocess Engineering Research, Department of Chemical Engineering, University of Cape Town, Rondebosch, Cape Town 7700, South Africa
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Author to whom correspondence should be addressed.
Minerals 2019, 9(12), 776; https://doi.org/10.3390/min9120776
Received: 22 October 2019 / Revised: 9 December 2019 / Accepted: 9 December 2019 / Published: 12 December 2019
(This article belongs to the Special Issue Pollutants in Acid Mine Drainage)
The presence of sulfur in coal processing wastes can lead to environmental impacts, such as acid rock drainage (ARD). However, not all sulfur species are acid-forming, and the implications of sulfur speciation when assessing acid rock drainage potential by means of static chemical tests are not well understood. This study set out to evaluate the implications of different sulfur forms on the assessment of acid rock drainage potential using static laboratory-scale tests and to investigate the reliability of methods for the analysis of such forms for the case of three South African coal processing wastes. Both the International Organization for Standardization (ISO) 157:1996 and Australian Coal Association Research Program (ACARP) C15034 protocols were found to be suitable tools for analyzing the different forms of sulfur. Acid-generating sulfur forms constituted between 53% and 64% of the total sulfur in the wastes evaluated, with the maximum potential acidity (MPA) and net acid-producing potential (NAPP) values calculated on the basis of acid-forming sulfur being significantly lower than those calculated on the basis of total sulfur content. Results also showed that the partial conversion of sulfur species under the relatively aggressive conditions of the acid-neutralizing capacity (ANC) and net acid generation (NAG) tests may overestimate the potential acid generating potential in the case of coal. These findings highlight the uncertainties associated with standard ARD static tests and the importance of taking sulfur speciation into account when calculating the MPA for coal processing wastes. View Full-Text
Keywords: sulfur forms; coal processing wastes; acid rock generating potential; acid-base accounting; net acid generation sulfur forms; coal processing wastes; acid rock generating potential; acid-base accounting; net acid generation
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MDPI and ACS Style

Moyo, A.; Amaral Filho, J.R.; T.L. Harrison, S.; Broadhurst, J.L. Implications of Sulfur Speciation on the Assessment of Acid Rock Drainage Generating Potential: A Study of South African Coal Processing Wastes. Minerals 2019, 9, 776.

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