Geochemical and mineralogical laboratory methods in waste rock drainage quality prediction

Document identifier: oai:DiVA.org:ltu-75747
Keyword: Natural Sciences, Earth and Related Environmental Sciences, Geochemistry, Naturvetenskap, Geovetenskap och miljövetenskap, Geokemi, Extractive waste characterisation, Drainage water, ARD, NRD, ABA test, NAG test, SEM, Applied Geochemistry, Tillämpad geokemi
Publication year: 2019
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Abstract:

Harmful substances containing acid or neutral rock drainages (ARD and NRD) are a major challenge related to the management of extractive industry wastes. This issue is particularly related to deposits containing sulphide minerals, which are prone to oxidization under the influence of atmospheric oxygen and water. The drainage quality depends mainly on the mineralogical and chemical composition of the extractive wastes, and especially on the ratio of acid-producing and neutralizing minerals, combined with reactions catalysed by microbes. Since harmful drainages play a major role in the generation of environmental issues for extractive industry, the accurate prediction of the drainage quality is of utmost importance. To design appropriate extractive waste facilities and drainage management, the characterisation of extractive wastes and assessment of the behaviour of the waste material is essential already before the actual mining activities start.

Several methods have been developed to characterize extractive waste materials and to predict their short and long term behaviour, including e.g. geochemical laboratory tests, static tests and longer term kinetic tests, and geochemical modelling. The characterisation methods for assessing the ARD risk can be divided into static and kinetic tests. Static tests are short term laboratory analyses, usually used for preliminary investigation and screening. Kinetic tests are longer term tests, revealing information on the time scale of drainage events. Commonly used static tests for ARD prediction include acid–base accounting (ABA) tests and the net acid generation (NAG) test. Since acid and neutralisation potential largely depend on the ratio and quality of acid-producing and neutralizing minerals, mineralogical calculations could also be used for ARD prediction. The mobility of potentially harmful substances from extractive waste can be preliminary assessed using different geochemical laboratory tests, including selective extraction and leaching methods. The most commonly used selective extraction method in Finland is the aqua regia (AR) extraction. In addition to some silicates and secondary precipitate minerals, it is intended to dissolve elements bound especially to sulphide phases. A less commonly used method for element mobility prediction is the analysis of the single addition NAG test leachate.

In this study, several Finnish waste rock sites were investigated and the performances of different preliminary drainage quality test methods evaluated and compared. The assessed acid production potential methods included the ABA test as presented in the standard EN 15875, the single addition NAG test as presented in the AMIRA guidebook, and a SEM mineralogy-based calculation. The assessed methods for element mobility prediction included the single addition NAG test leachate analysis and the AR extraction.

According to the results, pyrrhotite seems to be the main mineral contributing to acid production, and the silicate minerals the main contributors to the neutralisation potential at the most Finnish waste rock sites. Since silicate minerals appear to have a significant role in ARD prevention, the behaviour of these minerals in mining environment should be more thoroughly investigated. In the investigated Finnish waste rocks, Co, Cr, Cu and Ni often occurred as elevated concentrations, and the most widely abundant harmful elements in the waste rock drainages were Co, Cu, Ni and Zn. The results suggest that an acid production prediction based on SEM mineralogical calculation is at least as accurate as the commonly used static laboratory methods. The AR extraction indicates well which elements might occur as elevated concentrations in the drainage. Also the NAG test leachate analysis performed well in element mobility assessment, but only when the NAG test leachate was sufficiently acidic, the leachate pH being below of 3-6, depending on the element of interest.

Authors

Teemu Karlsson

Luleå tekniska universitet; Geovetenskap och miljöteknik; Geological Survey of Finland GTK
Other publications >>

Lena Alakangas

Luleå tekniska universitet; Geovetenskap och miljöteknik
Other publications >>

Päivi Kauppila

Geological Survey of Finland GTK
Other publications >>

Andrew Barnes

Geochemic Ltd
Other publications >>

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    header: 
        identifier: oai:DiVA.org:ltu-75747
        datestamp: 2021-05-24T23:02:32Z
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                version: 3.7
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                recordContentSource: ltu
                recordCreationDate: 2019-08-29
            identifier: 
                978-91-7790-429-8
                978-91-7790-430-4
                http://urn.kb.se/resolve?urn=urn:nbn:se:ltu:diva-75747
            titleInfo: 
                @attributes: 
                    lang: eng
                title: Geochemical and mineralogical laboratory methods in waste rock drainage quality prediction
            abstract: 
Harmful substances containing acid or neutral rock drainages (ARD and NRD) are a major challenge related to the management of extractive industry wastes. This issue is particularly related to deposits containing sulphide minerals which are prone to oxidization under the influence of atmospheric oxygen and water. The drainage quality depends mainly on the mineralogical and chemical composition of the extractive wastes and especially on the ratio of acid-producing and neutralizing minerals combined with reactions catalysed by microbes. Since harmful drainages play a major role in the generation of environmental issues for extractive industry the accurate prediction of the drainage quality is of utmost importance. To design appropriate extractive waste facilities and drainage management the characterisation of extractive wastes and assessment of the behaviour of the waste material is essential already before the actual mining activities start.
Several methods have been developed to characterize extractive waste materials and to predict their short and long term behaviour including e.g. geochemical laboratory tests static tests and longer term kinetic tests and geochemical modelling. The characterisation methods for assessing the ARD risk can be divided into static and kinetic tests. Static tests are short term laboratory analyses usually used for preliminary investigation and screening. Kinetic tests are longer term tests revealing information on the time scale of drainage events. Commonly used static tests for ARD prediction include acid–base accounting (ABA) tests and the net acid generation (NAG) test. Since acid and neutralisation potential largely depend on the ratio and quality of acid-producing and neutralizing minerals mineralogical calculations could also be used for ARD prediction. The mobility of potentially harmful substances from extractive waste can be preliminary assessed using different geochemical laboratory tests including selective extraction and leaching methods. The most commonly used selective extraction method in Finland is the aqua regia (AR) extraction. In addition to some silicates and secondary precipitate minerals it is intended to dissolve elements bound especially to sulphide phases. A less commonly used method for element mobility prediction is the analysis of the single addition NAG test leachate.
In this study several Finnish waste rock sites were investigated and the performances of different preliminary drainage quality test methods evaluated and compared. The assessed acid production potential methods included the ABA test as presented in the standard EN 15875 the single addition NAG test as presented in the AMIRA guidebook and a SEM mineralogy-based calculation. The assessed methods for element mobility prediction included the single addition NAG test leachate analysis and the AR extraction.
According to the results pyrrhotite seems to be the main mineral contributing to acid production and the silicate minerals the main contributors to the neutralisation potential at the most Finnish waste rock sites. Since silicate minerals appear to have a significant role in ARD prevention the behaviour of these minerals in mining environment should be more thoroughly investigated. In the investigated Finnish waste rocks Co Cr Cu and Ni often occurred as elevated concentrations and the most widely abundant harmful elements in the waste rock drainages were Co Cu Ni and Zn. The results suggest that an acid production prediction based on SEM mineralogical calculation is at least as accurate as the commonly used static laboratory methods. The AR extraction indicates well which elements might occur as elevated concentrations in the drainage. Also the NAG test leachate analysis performed well in element mobility assessment but only when the NAG test leachate was sufficiently acidic the leachate pH being below of 3-6 depending on the element of interest.

            subject: 
                    @attributes: 
                        lang: eng
                        authority: uka.se
                    topic: 
                        Natural Sciences
                        Earth and Related Environmental Sciences
                        Geochemistry
                    @attributes: 
                        lang: swe
                        authority: uka.se
                    topic: 
                        Naturvetenskap
                        Geovetenskap och miljövetenskap
                        Geokemi
                    @attributes: 
                        lang: eng
                    topic: Extractive waste characterisation
                    @attributes: 
                        lang: eng
                    topic: drainage water
                    @attributes: 
                        lang: eng
                    topic: ARD
                    @attributes: 
                        lang: eng
                    topic: NRD
                    @attributes: 
                        lang: eng
                    topic: ABA test
                    @attributes: 
                        lang: eng
                    topic: NAG test
                    @attributes: 
                        lang: eng
                    topic: SEM
                    @attributes: 
                        lang: eng
                        authority: ltu
                    topic: Applied Geochemistry
                    genre: Research subject
                    @attributes: 
                        lang: swe
                        authority: ltu
                    topic: Tillämpad geokemi
                    genre: Research subject
            language: 
                languageTerm: eng
            genre: 
                publication/licentiate-thesis
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                Published
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                        Karlsson
                        Teemu
                    role: 
                        roleTerm: aut
                    affiliation: 
                        Luleå tekniska universitet
                        Geovetenskap och miljöteknik
                        Geological Survey of Finland GTK
                    nameIdentifier: 
                        teekar
                        0000-0001-9034-3880
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                        authority: ltu
                    namePart: 
                        Alakangas
                        Lena
                    role: 
                        roleTerm: ths
                    affiliation: 
                        Luleå tekniska universitet
                        Geovetenskap och miljöteknik
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                        leal
                        0000-0001-7291-8505
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                        Kauppila
                        Päivi
                        Ph.D
                    role: 
                        roleTerm: ths
                    affiliation: Geological Survey of Finland GTK
                    @attributes: 
                        type: personal
                    namePart: 
                        Barnes
                        Andrew
                        Ph.D
                    role: 
                        roleTerm: opn
                    affiliation: Geochemic Ltd
            originInfo: 
                dateIssued: 2019
                publisher: Luleå University of Technology
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                @attributes: 
                    type: series
                titleInfo: 
                    title: Licentiate thesis / Luleå University of Technology
                identifier: 1402-1757
            location: 
                url: http://ltu.diva-portal.org/smash/get/diva2:1346855/FULLTEXT01.pdf
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