Development of two-component gassing system to sensitize explosive emulsions

Abstract

This study investigated explosive emulsions used in civilian mining for breaking rocks. These emulsions were highly concentrated (mass fraction greater than 90 %) and consisted of a dispersion of an aqueous solution of industrial grade ammonium nitrate in a fuel phase containing surface active agents. For such emulsions to detonate, they must be sensitized. This is usually done by generation of gas bubbles (voids) in-situ via a gassing reaction, whereby a gassing component is added to the emulsion to react with ammonium nitrate (present in large quantity), which is a one-component method. In this method, any excess of gassing agent gives rise to an undesired extent of gassing reaction, resulting in poor blasting performance. This study reports an alternative approach to sensitizing explosive emulsions, by using a two-component gassing system, one (KI) that was added to the fuel phase or to ammonium nitrate solution in a pre-determined amount prior to emulsification, and the other (H2O2) added to the explosive emulsion after manufacture, when sensitization was required. Thus, the primary goal of this research was to carry out a phenomenological study of the dependence of H2O2 and KI concentrations, as well as the effect of pH on the emulsion density over time, with a view to shedding light on the factors controlling the final gassed emulsion density, and on optimizing the process. Blasting experiments were also conducted to compare the performance of the new method to the one currently being used. Three industrial fuel phases were selected for this study: F800, Bullfinch and R602/45. The H2O2 solution (30 wt%) and KI concentrations were varied from 0.09 to 7.80 wt% and 0.004 to 0.1 wt% respectively. The pH values ranged from 4.4 to 6.5. The research showed that the stoichiometric reaction between KI and H2O2 was dominant rather than the catalytic decomposition of H2O2. It was also found that when KI was added to the fuel phase, the rate of density change increased and the final gassed emulsion density decreased with increasing H2O2 concentration. As with the effect of H2O2, an increase in rate of density change and a decrease in final emulsion density with increasing KI concentration were observed. For KI concentrations of 0.008 wt% (F800) and 0.004 wt% (Bullfinch and R602/45), the reference density was reached and the excess of H2O2 did not affect the extent of gassing reaction or the final gassed emulsion density. Unexpectedly, emulsions in which KI was added to the ammonium nitrate solution yielded exactly the same results. Interestingly, it was demonstrated that regardless of the phase in which KI is initially added prior to emulsification, the gassing reaction neither occurred in the fuel nor the aqueous phase but at the interface formed by the fuel and aqueous phases. Blasting experiments showed that emulsions sensitized by the new method (two-component system) yielded velocities of detonation 7 to 11% lower than the current method (one-component system). This was probably due to the differences in porosity of emulsions sensitized by different methods. The studies conducted have shown that the use of the two-component (H2O2 and KI) gassing system is suitable to regulate the extent of the gassing reaction in explosive emulsions for pH < 6.0. The two-component gassing system could be used in the explosives industry where consistent blasting performance is required.