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A systematic approach to sulphidic waste rock and tailings management to minimise acid rock drainage formation
Expanded Title:One of the major environmental issues in the mining industry is that of Acid Rock Drainage (ARD), caused by the disposal of sulphide-bearing wastes. Re-examination of the manner in which waste materials are disposed from the mineral processing and extraction stages of metal recovery is required to relieve the environmental burden created and reduce the time frame of risk. In this study, the approaches to the removal of risk through removal of sulphur species were considered through a review of key work and a set of case studies addressing specific mineral wastes. Aspects of disposal of dump rock and tailings from mining operations processing mineral sulphides (especially pyrite) have been addressed, with the focus of reducing capacity to form ARD through removal of the sulphidic component of the waste. The understanding of the factors governing ARD generation from dump rock and tailings (similar to those governing mineral bioleaching) has been used to improve categorisation, separation and planned disposal of its components to mitigate ARD generation. While flotation and accelerated bioleaching have been used in the case studies to demonstrate sulphide removal by separation and reaction, a review of suitable unit operations is provided. Further, use of acid base accounting and net acid generation methods as static chemical methods for evaluating ARD potential is supported by the development of a biokinetic test for assessing ARD potential under an environment more cognisant with the ARD generating environment, as well as providing kinetic data over a shortened time frame to conventional kinetic tests. The biokinetic test also delivers solutions through which to analyse metal deportment through ARD. A case study using flotation for the physical separation of sulphide from tailings allowed the demonstration of the concept of risk removal. A chalcopyrite-rich values stream and two tailings streams were prepared. The small volume tailings stream, accounting for 10% of the volume, was characterised by an increased sulphide concentration of 3.9% while the bulk tailings stream (90%) contained 0.21% sulphide and was non-acid forming. In a second case study using reaction to remove the sulphide fraction, the relative impacts of removal of acid neutralising and acid forming capacity were apparent, with the rate of the former exceeding that of the latter and being largely complete within 50 days. Further, the addition of a low amount of finely divided pyrite was demonstrated to augment biological sulphide oxidation and the concomitant sulphide removal. A third, preliminary, case study on coal desulphurisation by flotation was unable to demonstrate significant separation of total sulphur from coal ultra-fines, both visual observation and net acid generation (NAG) prediction tests demonstrated a significant separation of sulphidic sulphur, with the majority of the acid-generating sulphidic sulphur reporting to the concentrate fraction, resulting in an acid-forming concentrate while the residual tailings showed an increased NAG pH and reduced acid forming ability over the feed material. Physical separation of sulphidic materials from tailings has been demonstrated to provide the major tailings fraction as non-acid forming while the reactive gangue may be contained in a small fraction of the tailings for additional recovery of values, utilisation of the sulphide or contained disposal.
Date Published:01/07/2010
Document Type:Research Report
Document Subjects:Mine water - Mine water treatment
Document Keywords:Environment, Water Quality
Document Format:Report
Document File Type:pdf
Research Report Type:Standard
WRC Report No:1831/1/10
ISBN No:978-1-77005-991-7
Authors:Harrison S; Broadhurst JL; Van Hille R; Oyekola O; Bryan C; Hesketh A; Opitz A
Project Leader:Harrison S
Project No:K5/1831
Organizations:Minerals to Metals Initiative; Department of Chemical Engineering, University of Cape Town
Document Size:3 641 KB
Attachments:EXECUTIVE SUMMARY 1831.pdf
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