Explosive Emulsion Characterisation using Nuclear Magnetic Resonance

Abstract

Explosive emulsions are frequently employed in mining operations as they offer a comparatively robust, safe and effective product. These are typically formulated as concentrated ammonium nitrate solutions dispersed in an oil phase in the form of a highly concentrated water‐in‐oil emulsion. Being highly concentrated, determining the droplet size distribution (which is critical to assessing long‐term emulsion stability and explosive effectiveness) of these emulsions is challenging. Here we demonstrate that this is readily achieved using bench‐top Nuclear Magnetic resonance (NMR) Pulsed Field Gradient (PFG) techniques. The initial mean droplet size is shown to decrease with an increase in the concentration of ammonium nitrate or emulsifier or when inert salt was added to the composition, it was found to increase as the concentration of the aqueous (oxidiser) phase was increased. The emulsion droplet size distributions were observed to remain constant for a 3‐month period over the composition range explored.

The Effect of Inert Salts on Explosive Emulsion Thermal Degradation

“…The explosive emulsion is a blend of oxidiser and fuel phase, where the oxidiser phase is a supersaturated ammonium nitrate solution and the fuel phase comprises of the oil and emulsifier [10]. The formulation of explosive emulsions on a laboratory scale replicates the industrial process (e. g. [30]) and the procedure remains consistent with our previous work [26] as follows:…”

“…The explosive emulsion is a blend of oxidiser and fuel phase, where the oxidiser phase is a supersaturated ammonium nitrate solution and the fuel phase comprises of the oil and emulsifier [10]. The formulation of explosive emulsions on a laboratory scale replicates the industrial process (e. g. [30]) and the procedure remains consistent with our previous work [26] as follows: * The oxidiser phase is prepared by gradually adding the ammonium nitrate and the inert salts (if required) into preheated water whilst being stirred continuously at 80°C. The oxidiser phase preparation is deemed complete when all salts have dissolved completely at 80°C.…”

“…The standard explosive emulsion formulation was retained from that used in previous work [26]. This consists of a 7 wt% fuel phase and a 93 wt% oxidiser (aqueous) phase.…”

“…The degree of restriction on self‐diffusion experienced by the dispersed phase molecules is related to the droplet size; this phenomenon is exploited to determine the emulsion droplet size. The successful implementation of the pulsed field gradient technique for emulsion droplet sizing has been detailed in our previous explosive emulsion study [26] as well a number of previous publications concerning emulsions (e. g. [23–25, 34, 37–39]).…”

“…The use of Nuclear Magnetic Resonance (NMR) Pulsed Field Gradient (PFG) techniques for the determination of emulsion droplet size distributions has been widely validated (e. g. [20][21][22]) across a range of emulsion systems [20] including concentrated emulsion (e. g. [23][24][25]). In previous work [26], such NMR PFG techniques were employed to conduct a series of parametric studies to investigate the influence of various formulation characteristics of ANFO explosive emulsions on both initial mean emulsion droplet size and how the droplet size distribution evolved over 12 weeks storage at room temperature (~21°C). Droplet size measurements were successfully validated against optical droplet size determination on diluted samples.…”