OFFICIAL guidelines, the test duration was typically set to safety buffer included 4 times the desired field sleep time for up to 7-day sleep times. For example, a 7-day sleep time requires a 28day test with no reaction. The isothermal test was extended and modified in several ways to enable analysis of much longer sleep times: • Sample Selection: highly reactive ground samples. Four rock samples from various mine sites were obtained, all of which had previously “failed” a routine sleep time test, meaning they caused a reaction even with an inhibited explosive. Using such highly reactive samples ensured that any test method developed would be robust; if these samples could be safely inhibited for 90 days, typical reactive ground would be well under control. • Inhibitor Variation: Unlike the standard test which uses a fixed formulation, the inhibitor content was systematically changed to observe its effect on reaction induction time. By spanning a range of inhibitor levels, the relationship between inhibitor concentration and the time to reaction was determined. Rather than simply a pass/fail of one formulation an “inhibitor budget” was predicted for the application. • Test Duration: Each test was run until either a clear exothermic reaction occurred (an exotherm greater than 2oC) (AEISG, 2020) or until significantly more than 90 days was reached with no reaction observed. • Synthetic Standard Sample: In addition to the four mine-site samples, a synthetic reactive ground standard was developed for controlled experiments. This “pyrite standard” was used in a subset of trials to see if lab-generated samples followed the same trends as real samples from mine sites. Each test produced a time–temperature record. From these, the induction time (time to reaction onset) for each inhibitor level and sample was extracted. If no reaction occurred, the induction time was recorded as “>90 days”. These data formed the basis for our analysis of inhibitor efficacy. Data analysis identified a function which could be used to extrapolate the inhibitor level required for a long sleep time test, based on the standard 28-day test. It is worth noting that many layers of conservatism were built into the new test process to provide large safety buffers. This is because reactive ground testing uses a small number of small samples, and the variability of sulphide distribution in any given orebody is usually not quantifiable. Accelerating Rate Calorimetry (ARC) To complement the isothermal tests, Accelerating Rate Calorimetry (ARC) was also used to study the samples. ARC is an adiabatic thermal analysis technique that reduces heat loss to the environment to study self-heating behavior. In simpler terms, the ARC simulates worst case conditions, like loaded blast holes, where heat and gases cannot easily dissipate.
RkJQdWJsaXNoZXIy MTM0Mzk2