The Effect of Inert Salts on Explosive Emulsion Thermal Degradation

Ammonium nitrate fuel oil (ANFO) explosive emulsions are comparatively safe, effective and low-cost products for mining operations. They consist of a supersaturated ammonium nitrate solution dispersed as droplets in a continuous fuel phase. Here we apply a previously developed bench-top Nuclear Magnetic Resonance (NMR) Pulsed Field Gradient (PFG) technique to monitor the emulsion droplet size distribution in ANFO explosive emulsions as a function of time stored at an elevated temperature of 50 °C; we thus investigate the subtle effect of adverse storage conditions on emulsion stability. Storage at 50 °C for 12 weeks lead to a ∼60 % increase in mean droplet size, whereas a sample stored at 21 °C experienced no change in mean droplet size. The addition of inert salts (calcium nitrate or sodium nitrate) to the ammonium nitrate solution was also considered in terms of their ability to enable stable storage of the emulsions at 50 °C. An addition of 5 wt% calcium nitrate to the aqueous phase was required to suppress any thermal degradation of the explosive emulsions whilst a much lower dosage of only 1 wt% sodium nitrate was required to realise the same stabilizing effect.