Results
Ten grab samples were supplied and tested as per the QMR Reactive Ground Test and the AEISG Code of Practice Reactivity Screening Test. The QMR Reactive Ground Test results showed no samples are reactive. The QMR Reactive Ground Test identified that sample RG_WEST49LAU_009 would result in an incorrect positive reactivity test when tested as per the AESIG Code of Practice (refer to Table 1 and Figures 1 to 4). This is due the the sample being acidic and containing trace sulphide. The weathering agent added, as per the AEISG Code of Practice, causes a further increase in acidity and trace amounts of pyrite will readily react causing a temperature rise and physical reaction. Trace levels of sulphide do not have the capacity to supply sufficient heat to cause a reactivity event in blasting (refer to the Appendix).
As none of these samples were suitable for testing of inhibited products, a previously tested reactive sample was selected for retesting. The sample RG_WN47LEB024_003 as shown in Figure 6 was selected. A subsample of areas with visible pyrite associated with coal was prepared (RG_WN47LEB024_003coal) and a subsample with no visible pyrite (RG_WN47LEB024_003nocoal) was prepared. Each of the samples were tested as per the QMR Reactive Ground Test and the AEISG Code of Practice. Both samples were found to be reactive (refer to Table 1 and Figures 6 and 7). Additionally, 9 grams of both subsamples were mixed and tested as per the AEISG Code of Practice with water used instead of acidic weather agent. The sample reacted in a few hours indicating a propensity of these sample to react with nitrate; Therefore these samples are highly reactive.
Table 1 Results for Testing using QMR Reactive Ground Test and the AEISG Code of Practice
Figure 1 -AEISG Temperature graph for samples RG_WEST49LAU_001 to RG_WEST49LAU_009 with RG_WEST49LAU_009 having a 2°C Isotherm on heating
Figure 2 – AEISG temperature graph of RG_WEST49LAU_009 showing temperature isotherm
Figure 3 Both RG_WEST49LAU_009 and RG_WEST49LAU-007 exhibited a physical reaction when tested as per the AEISG Code of Practice
Figure 4 Microscope analysis of RG_WESTLAU49-009 indicated approximately 0.1% pyrite content
Figure 5 – Sample RG_WN47LEB024_003 is acidic and contains pyrite
Figure 6 – RG_WN47LEB024_003coal spontaneously reacts when tested as per the AEISG Code of Practice
Figure 7 – RG_WN47LEB024_003nocoal spontaneously reacts when tested as per the AEISG Code of Practice
Figure 8– 9 grams of RG_WN47LEB024_003nocoal + 9 grams RG_WN47LEB024_003nocoal reacts when tested as per the AEISG Code of Practice with water substituted for acidic weathering agent.
Conclusion:
None of the 10 grab samples are suitable to be used for testing of inhibited products; However, the previously tested Samples RG_WN47LEB024_003coal and RG_WN47LEB024_003nocoal are highly reactive. Sample RG_WN47LEB024_003coal being the most suitable sample for testing of inhibited products due to the higher pyrite content than sample RG_WN47LEB024_003nocoal .
Assessed By:
Dr G. Cavanough
Date:
16th June 2022
Appendix 1 – Trace Sulphide in Acidic Ground
Purpose of Study
The purpose of this case study is to highlight the benefits of using the QMR Reactive Ground Test as compared to the AEISG Code of Practice for Reactivity Screening in that the AEISG Code of Practice gave positive result for this acidic sample containing a small amount of reactive sulphide. The AESIG Code of practice relies on the addition of an acidic mixture of ferrous and ferric ions to accelerate the reaction of sulphide so, in a short time, the samples can be deemed as reactive or non-reactive. The result of testing this sample as per the AEISG screening test would be that the ground is classified as reactive and inhibited products are required. The use of inhibited products will increase the cost and complexity of blasting operations and result is post blast fume due to having to using emulsion products. To accurately assess the reactivity of a sample the QMR Ground Test determines all factors that will cause reactivity including pH, carbonates content, sulphide content and coal content. The QMR Reactive Ground Test will replicate the results of the AEISG test in a maximum of 90 minutes whereas the AEISG Test can take up to 28 days.
The QMR Reactive Ground Test has a risk assessment module that uses the test measurements in conjunction with on bench conditions to access the actual risk of reactivity. On bench conditions that affect the probability of reactivity include:
Hole temperature
The rate of carbonate consumption increases with temperature *
Loading
Augur loading can cause high level of pyrite in a small seam to fall back to the bottom, so there is localised high concentrations of pyrite.*
The presence of sponcom and oxidised sulphide
Oxidisation of sulphide will result in acidic conditions.*
Sleep time*
The rate of carbonate consumption increases with temperature and reducing the sleep time can reduce the risk.* AEISG Code of Practice for Elevated Temperature and Reactive Ground
BAckground
Three samples, from different locations in the same pit, were tested to determine if there was any reactivity. The names of the samples and sample locations are not disclosed, and samples are identified as Case Study B Sample 1, Case Study B Sample 2 and Cast Study B Sample 3.
Testing As per the AEISG Code of Practice.
On testing as per the AEISG code of practice at a temperature of 55°C over a period of 7 days one sample was found to be reactive (refer to Table 1).
Table 1. Results for Testing as per the AEISG Code of Practice
Testing using the QMR Reactive Ground test
The QMR Reactive ground test is designed to replicate the results of the AEISG Code of Practice Test in a maximum of 90 minutes. The test consists of measuring the pH, carbonate and sulphide content of the sample. Table 2 shows that the QMR test gives the same results are the AEISG test.
Table 2. Results for Testing QMR Reactive Ground Test
QMR Reactive Ground risk Assessment
The QMR Reactive Ground Test Software also has a risk module based on the QMR Reactive Ground Test results and “on” bench conditions. The AEISG test result and the replicated test result provided by measurement by the QMR Reactive Ground test may indicate the sample is reactive. For this acidic sample with 0.4% reactive ASIEG Test Procedure has resulted in a false positive test. To provide a true assessment of reactivity the QMR Reactive Ground Test results and “on” bench conditions can be entered into the risk assessment module. Figure 2 shows the risk assessment screen for Case Study Sample 5 and gives the calculated risk as “not reactive”.
The major contributor to this result being the low level of reactive sulphide as describes in the next section of this case study.
Figure 1 - QMR Reactive Ground Risk Assessment for Cast Study B Sample 1.
Confirmation of ASsessment as not reactive
Background
The QMR Reactive Ground Test determines the amount of the amount of reactive sulphide in a sample by the temperature increase as described below for manufacture samples containing different amounts of reactive sulphide.
Figure 2 shows the logs of temperature for the manufactured samples tested using the QMR Reactive Ground Test. Using this data in a plot of % pyrite as a function of temperature rise gives a linear relationship; Therefore, the amount of pyrite contained in a sample is a function of the temperature rise (refer to Figure 3).
Figure 2- Temperature Logs for samples containing different levels of pyrite (the drop in temperature is due to addition of ammonium nitrate and the resulting rise in temperature is due to the reaction of sulphide and the added nitrate.)
Figure 3 – % Pyrite as a function of Temperate rise (from Temperature Logs shown in Figure 2)
The accuracy of this method to determine the amount of reactive sulphide can be demonstrated through using the QMR regression from the plot in Figure 3 with independent data.
Figure 4 -
A typical temperature versus time trace for the reaction between pyrite and ammonium nitrate in the adiabatic calorimeter. The period between time = 0 and point B is the induction stage, B-C is the intermediate stage, and the ignition stage starts at C.**P Priyananda, A M Djerdjev, J Gore, C Neto, J K Beattie, B S Hawkett, “Premature detonation of an NH4NO3 emulsion in reactive ground”, Journal of Hazardous Materials, 283 (2015) 314 – 320.
Data from independent researchers* is shown in Figure 4. This gives an approximate 260°C temperature rise for a 41.6% sulphide mixture. Using the QMR regression a 260°C temperature equates to a sample containing 40% pyrite which is in close agreement with the value from the independent researchers.
Heat Energy
The QMR Reactive Ground Test determined that Case Study B Sample 1 contained 0.4% sulphide through the measurement of a 1.8°C rise in temperature.
Q=mc∆t Equation 1
Where Q = heat energy, m=mass substance(60g) , c = specific heat of substance(4200J/kg K)) and Δt(1.8°C) is the change in temperature.
Using equation 1 for the temperature rise of Case Study B Sample 1 gives a total heat energy of 432 joules from the reaction of 0.4% reactive sulphide (i.e. 0.04 grams reactive sulphide in the 10 gram sample of ground used in the QMR Reactive Ground Test).
If, in a blast hole, a reaction between sulphide and nitrates occurs with a resulting rise of 100°C, the amount of heat energy required would be 20000 joules. (This value calculated using Equation 1 with specific heat value for AN emulsion of 2000 J/kg K). If a reaction with 0.04 grams of the sulphide in Case Study B Sample 1 generates 453.6 joules, a 100°C temperature rise of the 100 gram sample will require 1.85 grams of reactive sulphide. Considering, that during loading of blast hole there is fallback, contact, mixing and exposure of the explosive product to the ground around where Case Study B Sample 1 was taken there would need to be 462 grams of Case Study Sample 1 mixing intimately with ammonium nitrate. Clearly more than 100grms of ammonium nitrate would be required to provide mixing with this amount of material. If 1kg or ammonium nitrate is intimately mixed with 462 grams of Case Study Sample 1 the temperature rise would be 10°C. Therefore there is no likelihood of a reaction generating sufficient to cause initiation. Case Study B Sample 1 does not contain enough reactive sulphide to result in a reactivity event.
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