- Title
- Investigation of the reaction mechanism for reactive ground
- Creator
- Conroy, Gregory Lawrence
- Relation
- University of Newcastle Research Higher Degree Thesis
- Resource Type
- thesis
- Date
- 2021
- Description
- Research Doctorate - Doctor of Philosophy (PhD)
- Description
- Reactive ground is the spontaneous reaction of ammonium nitrate (NH4NO3) within a blasthole, resulting in fuming, fire and even detonation of loaded explosive. It is associated with sulphide ores and characterised by an induction period, during which visible signs of reaction may be observed, followed by a rapid increase in reaction rate and the generation of gases, leading to thermal runaway and decomposition of NH4NO3. Cyclic voltammetry has been used with laboratory grade FeS2 to examine the initial stages of the reaction mechanism with the aim of identifying the low temperature reactions that lead to the rapid acceleration of reaction rates. It was found that fresh FeS2 did not show reaction until cycled to potentials greater than 0.8V vs SCE. Surface analytical techniques of SEM, XPS and XRD found that oxidation through heating in air or water produced FeSO4 on the surface, which were further oxidised to Fe(III). Examination of the first cycle of a voltammogram could be used to identify the presence of FeSO4 or mixed Fe(III) salts on the surface, which was found to be associated with increased sample reactivity. The onset of a visible reaction between FeS2 and NH4NO3 in conducted to the Australian Explosives Industry Safety Group (AEISG) standard was found to correspond with a rapid change in electrolyte potential. This change in electrolyte potential was consistent with the oxidation of Fe(II) through the reduction of NO3-, and was found to occur in the absence of FeS2. The rate of reaction is affected by temperature, mass transport of reactants to and from the FeS2 surface and heat flux. Differences in reactivity between samples was found to be affected by FeSO4 and Fe(III) on the surface, water content and FeS2 concentration. The surface of acid washed FeS2 was examined after reaction. After reaction at 55oC, FeSO4 crystals were found to cover the FeS2 surface. After reaction at temperatures >75oC, FeSO4 was not present on the surface, and the surface was found to be pitted and chemically etched. Urea, which is known to inhibit reaction, did not inhibit the formation of FeSO4 on the FeS2 surface. A reaction mechanism was proposed that is consistent with the observed reactions between FeS2 and NH4NO3. This reaction mechanism differs to that proposed by other authors as NO2-, formed from the reduction of NO3-, is not a catalyst that ‘builds up’ in the initial reaction stage but is an intermediate that is generated and consumed by multiple reaction steps. The acceleration of reactions is due to changes in reactor temperature and reactant concentration.
- Subject
- reactive ground; ammonium nitrate; pyrite; FeS₂; voltammetry
- Identifier
- http://hdl.handle.net/1959.13/1488600
- Identifier
- uon:52491
- Rights
- Copyright 2021 Gregory Lawrence Conroy
- Language
- eng
- Full Text
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| View Details Download | ATTACHMENT01 | Thesis | 7 MB | Adobe Acrobat PDF | View Details Download | ||
| View Details Download | ATTACHMENT02 | Abstract | 427 KB | Adobe Acrobat PDF | View Details Download |