Results
Table 1 - Results for Testing using the AEISG Code of Practice
Table 2 - Results for Testing using the QMR Reactive Ground Test
Figure 1 – AEISG Test Temperature Plot for Sample 5071C027
Figure 2 – AEISG Test Temperature Plot for Sample 5071C028
Figure 3 – AEISG Test Temperature Plot for Sample 5071C029
Figure 4 – Samples 5071C028 and 5071C029 contained a large amount of visible pyrite
Figure 5 – Samples 5071C028 and 5071C029 reacted violently when testes as per the QMR Reactive Ground
Figure 6 – Sample 5071C027 under the microscope showed trace pyrite
Under a microscope all samples were confirmed to contain pyrite (refer to Figure 4 and Error! Reference source not found.). Prior to testing as per the AEISG Code of Practice each sample was assessed for reactivity risk based on pH, carbonate and amount of reactive sulphide using the QMR Reactive Ground Test (refer to Table 1 and Table 2 for results of both tests). Testing as per the AEISG Code of Practice resulted in sample 5071C028 testing as marginal and samples 5071C027 and 5071C029 as not reactive. The QMR Reactive Ground Test confirmed that sample 5071C027 was not reactive as the sample had only trace sulphide content. The QMR Reactive Ground Test also identified coal was inhibiting a reaction in samples 5071C028 and 5071C029 and that these samples will spontaneously react if subjected to acidic conditions (refer to Appendix 1)
Conclusion:
Sample 5071C028 was found to be marginal and samples 5071C027 and 5071C029 as not reactive when tested as per the AEISG Code of Practice. The QMR Reactive Ground Test confirmed sample 5071C027 was not reactive and that samples 5071C028 and 5071C029 contain a significant amount of pyrite that is prevented from reacting by the coal that each sample contains (with sample 5071C028 not having sufficient coal content to produce a not reactive test when tested as per the AEISG Code of Practice). Samples 5071C028 and 5071C029 will cause the spontaneous detonation of a blast hole in acidic conditions. (Refer to Appendix 1)
Appendix 1 – Temperature Graphs
Case Study: Spontaneous Detonation in Coal Mines
Purpose of Study
The purpose of this case study is to present the result of an investigation into the possible cause of spontaneous detonations in coal mines.
BAckground
There have been instances of spontaneous detonations at coal mines despite routine testing for reactivity as per the AEISG Code of Practice. This is a study of a possible mechanism for these reactions.
Sample Containing mostly Coal Tested as Per the AEISG Code of Practice and qmr reactive ground test
A sample containing coal was tested using the AEISG code of practice. The result was that the sample was non-reactive as no temperature Isotherm was identified and there was no visible reaction. The QMR Reactive Ground test identified that the sample contained a large amount of sulphide by the instantaneous rise in temperature and reaction (refer to Tables 1 & 2).
Table 3 - Results of AEISG Code of Practice for Reactivity Screening
Table 4 – Results for QMR Reactive Ground Test
Affect of sponcom
To access the effect of sponcom on the sample it was heater to 950°C for 60 minutes. After heating the pH was measured and remained at 6. When tested as per the AEISG code of practice a 0.75°C isotherm occurred on initial heating but no significant reaction.
Affect of Acid
To access the effect of acid on the sample, 10 grams of the sample was placed in a beaker and 10 grams of swimming pool acid was poured on top of the sample. A few spoonsful of Ammonium Nitrate Prill was then added. There was no mixing or heating with the mixture starting at a temperature of 12.7°C just after the prill was added.
NOx was observed after addition of prill, and a significant reaction occurred a few minutes later. (Refer to Figure 1,2 and 3).
Figure 1 – Temperature of mixture of the sample, acid and prill
Figure 2 – NOx observed immediately after prill added
Figure 3 – A significant reaction occurred after a few minutes
Conclusion
These initial tests indicate that acid is the likely cause of spontaneous detonation of blast holes due to reactivity. Sources of acid include acid mine drainage and oxidation of pyrite in holes left open for an extended period of time. The AEISG Code of Practice is unable to identify conditions leading to spontaneous detonation. The QMR reactive Ground Test provides a correct assessment of the risk of a reaction.