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| Titel |
‘Low-acid’ sulfide oxidation using nitrate-enriched groundwater |
| VerfasserIn |
Michael Donn, Naomi Boxall, Nathan Reid, Rebecca Meakin, David Gray, Anna Kaksonen, Thomas Robson, Denis Shiers |
| Konferenz |
EGU General Assembly 2016
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| Medientyp |
Artikel
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| Sprache |
en
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 18 (2016) |
| Datensatznummer |
250136103
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| Publikation (Nr.) |
 EGU/EGU2016-17072.pdf |
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| Zusammenfassung |
| Acid drainage (AMD/ARD) is undoubtedly one of the largest environmental, legislative and
economic challenges facing the mining industry. In Australia alone, at least $60m is spent on
AMD related issues annually, and the global cost is estimated to be in the order of tens of
billions $US. Furthermore, the challenge of safely and economically storing or treating
sulfidic wastes will likely intensify because of the trend towards larger mines that process
increasingly higher volumes of lower grade ores and the associated sulfidic wastes and lower
profit margins.
While the challenge of managing potentially acid forming (PAF) wastes will likely
intensify, the industrial approaches to preventing acid production or ameliorating the effects
has stagnated for decades. Conventionally, PAF waste is segregated and encapsulated in
non-PAF tips to limit access to atmospheric oxygen. Two key limitations of the ‘cap
and cover’ approach are: 1) the hazard (PAF) is not actually removed; only the
pollutant linkage is severed; and, 2) these engineered structures are susceptible to
physical failure in short-to-medium term, potentially re-establishing that pollutant
linkage.
In an effort to address these concerns, CSIRO is investigating a passive, ‘low-acid’
oxidation mechanism for sulfide treatment, which can potentially produce one quarter as
much acidity compared with pyrite oxidation under atmospheric oxygen. This ‘low-acid’
mechanism relies on nitrate, rather than oxygen, as the primary electron accepter and the
activity of specifically cultured chemolithoautotrophic bacteria and archaea communities.
This research was prompted by the observation that, in deeply weathered terrains of
Australia, shallow (oxic to sub-oxic) groundwater contacting weathering sulfides are
commonly inconsistent with the geochemical conditions produced by ARD. One key
characteristic of these aquifers is the natural abundance of nitrate on a regional
scale, which becomes depleted around the sulfide bodies, and where pH remains
neutral.
The "low-acid" oxidation of sulfides with nitrate as an electron acceptor has been
demonstrated at the laboratory scale. In 90-day microcosm respirometry experiments, we
exposed a mixture of pulverized quartz and pyrite -rich ore to natural, high-nitrate
groundwater and inoculated the microcosms with a culture of aerobic and anaerobic
nitrate-dependent iron and sulfur-oxidising microorganisms, which were enriched from ore,
groundwater and activated waste water. Incubations were performed under both oxic and
anoxic conditions, in addition to abiotic controls. Initial results show that oxidation of the
sulfides under nitrate-rich and microbially enhanced conditions does produce less acid than
the same material under oxic conditions, and to some degree can match the models as
long as oxygen ingress can be controlled. These results are the focus of further
research into how this process can be enhanced and whether it can be applied in the
field.
Nitrate-driven oxidation of sulfides could potentially be used as a new approach to reduce
acid generation and leaching of contaminants from waste dumps, in a passive or actively
managed process designed to deplete and/or ameliorate (i.e. through surface passivation) the
mineralogical hazard. Developing our understanding of biological aspects of these processes
may also allow testing of longer-term "bio-caps" for various tailings and dump materials. |
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