AU2020267239A1 - Explosive composition and method of making the same - Google Patents

Abstract

An explosive composition, comprising: a heavy ANFo component comprising: ammonium nitrate prills; a fuel oil; an emulsion component; and a phyllosilicate-based 5 bulking agent. The emulsion component may comprise oxidizing salts. The bulking agent may comprise a plurality of bulking agent particles. The bulking agent has a density that is less than the heavy ANFo component i.e. the ANFo component that is being replaced. 16 16762841_1 (GHMatters) P112297.AU.1

Description

Explosive composition and method of making the same

Technical field This disclosure relates generally to heavy ammonium nitrate fuel oil (ANFo) explosives used to charge blastholes, such as those used on mine sites.

Background Heavy ANFo is a mixture, in varying ratios, of ammonium nitrate prills and fuel oil, which makes up the ANFo component, and an emulsion which forms the heavy component. The specific density of a heavy ANFo composition depends on particular ratios of the [emulsion]:[ANFo component]. An emulsion is generally required when water is present in a blasthole as the emulsion protects the ANFo component from water ingress (i.e. the emulsion imparts the ANFo with water resistance). However, increasing an amount of emulsion added to the ANFo increases the density. The negative aspects of increasing the density include fume generation post-detonation, the fines and dust that are produced after detonation, and excessive pre-conditioning of surrounding rock mass and expense.

To reduce the density of heavy ANFo whilst still maintaining the chemical properties of the heavy ANFo, filler materials can be substituted for a certain percentage of the heavy ANFo composition. Filler materials or "bulking agents" have been used with varying degrees of success, from failure to allow the composition to detonate through to successful detonation. Some filler materials are successful at detonation but are not economically viable, some filler materials have unacceptable physical characteristics such as exaggerated abrasiveness in relation to the batching equipment, some filler materials can induce dust borne irritations, some fillers are difficult to handle when trying to form the heavy ANFo mixture, and some filler materials are environmentally undesirable. Examples of previous filler materials include wood meal, saw dust, bagasse, Styrofoam, polystyrene and rice husks.

It is to be understood that, if any prior art is referred to herein, such reference does not constitute an admission that the prior art forms a part of the common general knowledge in the art, in Australia or any other country.

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Summary The disclosure provides an explosive composition, comprising: a heavy ANFo component comprising: ammonium nitrate prills; a fuel oil; an emulsion component; and a phyllosilicate-based bulking agent. The emulsion component may comprise oxidizing salts. The bulking agent may comprise a plurality of bulking agent particles. The bulking agent has a density that is less than the heavy ANFo component i.e. the ANFo component that is being replaced.

An advantage of using phyllosilicate-based bulking agents to reduce a density of heavy ANFo is that, in some embodiments, phyllosilicate-based bulking agents provide free flowing heavy ANFo mixtures. Phyllosilicate-based bulking agents may not cause exaggerated abrasion, thereby reducing wear and tear on material handling equipment which may help to reduce maintenance costs. Phyllosilicate-based bulking agents may also be more environmentally friendly compared with other bulking agents, such as polystyrene-based bulking agents which can persist in plastic form and/or generate C02 upon detonation of the heavy ANFo. Phyllosilicate-based bulking agents may also produce significantly less static compared with other bulking agents, such as those based on polystyrene, making their handling easier compared to more static-prone materials.

The bulking agents may be kiln dried. The agents may be in an expanded form. The bulking agents may have a density less than 0.8g/cc, such as 0.4g/cc to 0.7g/cc. It should be noted that the bulking agent can be formed from more than one type of bulking agent, and the density of the bulking agent is determined by an overall density of a mixture of bulking agents and is not limited to the density of a single bulking agent particle. For example, two different bulking agents having different densities may be used to form the bulking agent, where the overall density of the bulking agent is determined by the relative proportions of the two different bulking agents. The bulking agent particles may be spherical. The bulking agent particles may have a diameter ranging from about 6 mm to about 18 mm.

The composition may further comprise a gassing agent that can react prior to detonation to form a gas that becomes distributed as bubbles in the emulsion component. The gassing agent may comprise two or more reagents that can react with 2

16762841_1 (GHMatters) P112297.AU.1 one another to generate the gas bubbles distributed in the emulsion. The gassing agent may be a chemical gassing agent.

The oxidizing salts may include metal nitrate salts. The emulsion may have a density of at least 1.3g/cc. A ratio of [ammonium nitrate prills]:[fuel oil] may range from about 90:10 to 98:2. A ratio of [ammonium nitrate prills-fuel oil]:[emulsion] may range from about 90:10 to about 35:65.

The disclosure also provides a method of forming an explosive composition, comprising: mixing: ammonium nitrate prills;fuel oil; an emulsion; and a phyllosilicate based bulking agent; wherein the ammonium nitrate prills, fuel oil and emulsion form a heavy ANFo and the bulking agent has a density that is less than the heavy ANFo.

The bulking agent may be as set forth above. The mixing step may be provided by auguring two or more components of the composition together. For example, the ammonium nitrate prills, fuel oil, emulsion and bulking agents may be mixed together by auguring. The bulking agent, ammonium nitrate prills and emulsion may be first mixed together followed by mixing in the fuel oil. The ammonium nitrate prills, emulsion and fuel oil may be first mixed together followed by mixing in the bulking agent.

The bulking agent may be mixed by using a pulsed mixing protocol where only a portion of a required amount of bulking agent is mixed with each pulse based on a timed cyclic delivery. The method may further comprise mixing a gassing agent with emulsion. The gassing agent reacts to form bubbles that are distributed in the emulsion. The step of providing the gassing agent may comprise adding two or more reagents that react with each other upon mixing to form a gas. The composition may be as set forth above. The method may further comprise charging a blasthole with the explosive composition.

The disclosure also provides a method of charging a blasthole, comprising charging a blasthole with the explosive composition as set forth above.

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Detailed description of embodiments An embodiment provides an explosive composition. In an embodiment, the composition comprises a heavy ANFo component comprising: ammonium nitrate prills; a fuel oil; an emulsion component. The emulsion component can comprise oxidizing salts. The composition can also include a phyllosilicate-based bulking agent. The bulking agent can have a plurality of particles. The bulking agent has a density that is less than the heavy ANFo component it is replacing. Accordingly, a density of the composition can be changed by adding relatively more or less amounts of bulking agents compared to a given mass of heavy ANFo and/or by selectively changing a density of the bulking agent.

For heavy ANFo mixtures having a high percentage of emulsions, for example ANFo mixtures that are used to charge particularly wet blastholes, a mass of the heavy ANFo required to fill a blasthole is greater than for a heavy ANFo having less emulsion for the same blasthole. Increasing the amount of the emulsion in the ANFo component increases the amount of fuel oil required per blasthole. Therefore, the use of a phyllosilicate-base bulking agent helps to reduce a density of the heavy ANFo mixture, and therefore reduce its mass, so that the amount of heavy ANFo required per blasthole decreases to reduce costs.

The reason why an emulsion is required for wet blastholes is that in the absence of the emulsion the water would dissolve some of the ammonium nitrate prills which alters the ratio of [ammonium nitrate]:[fuel oil]. This can reduce the blasting effectiveness of the explosive composition (i.e. will lead to non-full order detonation) and also lead to the production of undesirable blast products, such as NOx rather than N 2 . Providing an emulsion makes the ANFo more "resistant" to water in the blasthole.

The emulsion has a discontinuous aqueous phase comprising of droplets of an aqueous solution of one or more oxidizing salts, such as inorganic oxidizing salts, and a continuous water immiscible organic phase in which the droplets are dispersed. Generally speaking, the emulsion provides resistance to water by coating the ammonium nitrate prills with the continuous water immiscible organic phase so that any water present in the blasthole cannot come into contact with and dissolve the ammonium nitrate prills. 4

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The phyllosilicate-based bulking agent can be used in the explosive composition in its natural state, such as vermiculite, clay or pearlite. In an embodiment, the phyllosilicates-based bulking agent is kiln dried. In an embodiment, kiln drying provides a heating process to expand the phyllosilicate-based bulking agents. For example, clay aggregate can be dried in a kiln drying process to cause expansion of the aggregate to form an expanded phyllosilicate-based bulking agent. Accordingly, in an embodiment the phyllosilicate bulking agent is in an expanded form. Expanded phyllosilicate-based bulking agents have a significantly reduced density compared to non-expanded phyllosilicate-based bulking agents. In an embodiment, a combination of expanded and non-expanded phyllosilicate-based bulking agent is used in the explosive composition. The expanded bulking agent has a density less than the non-expanded bulking agent. Adjusting a ratio of [expanded]:[non-expanded] bulking agents can help to provide a bulking agent with specific densities, which may help to more finely tune a resulting density of the explosive composition.

The greater the difference between the density of the heavy ANFo and the phyllosilicate-based bulking agent, the greater the ability the bulking agents have to reduce the density of the heavy ANFo blend. ANFo generally has a density of about 0.85g/cc. Heavy ANFo density ranges from 0.95g/cc to 1.35g/cc depending of the ratio of emulsion to ANFo. In an embodiment the bulking agent has a density of less than about 0.8g/cc. In an embodiment the density of the bulking agent ranges from about 0.4g/cc to about 0.65g/cc. The phyllosilicate-based bulking agent may have an average density of about 0.5g/cc. In an embodiment, a bulking agent is formed from expanded, clay-based phyllosilicate particles having a roughly spherical geometry, where a density of the bulking agent is about 0.4g/cc to about 0.65g/cc. In an embodiment, a diameter of spherical phyllosilicate-based bulking agent particles ranges from about 6 mm to about 18 mm. A bulking agent formed from spherical phyllosilicate particles may have a density of about 0.4g/cc to about 0.65g/cc and may not be prone to settling out of the mix and may flow well to feed into the process unit. An issue with some bulking agents is that they do not flow well in a mobile processing unit (also referred to as a "sensitizing unit") that is used to form an explosive composition. Spherical particles are exemplary, and in some embodiments the

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16762841_1 (GHMatters) P112297.AU.1 particles may have a shape and geometry other than spherical, such as elongate, planar, oval, cuboid, and so on.

A size and geometry of the bulking agent particles may determine the ability of the bulking agent to change a density of the heavy ANFo. For example, a size and geometry that favours tight packing of the phyllosilicate particles will adjust a density of the heavy ANFo differently to a size and geometry that favours less tight packing. A bulking agent with a narrow particle size distribution may allow the bulking agent to more consistently adjust a density of a heavy ANFo when compared to a wider particle size distribution. A density of the bulking agent may be based on a size of the bulking agent particles. In one embodiment the bulking agent particles are spherical. For example, spheres of smaller size can pack together more than spheres of a larger size. As an example, spheres of around 4mm in diameter can pack down more to have a density of around 0.8g/cc, spheres of around average 10mm diameter have a density of around 0.5g/cc, and spheres of around 20mm have a density of around 0.3g/cc. Accordingly, a density of the bulking agent may be adjusted by selecting a size distribution of the particles that form the bulking agent.

The oxidizing salts in the emulsion may be nitrate-based. For example, the oxidizing salts can include ammonium nitrate, calcium nitrate, sodium nitrate and any combination thereof. However, the disclosure is not limited to the use of nitrate-based oxidizing agents and any other industry accepted oxidizing salts may also be used. The fuel oil component may be fuel oils, mineral oils, or waxes. Diesel, for example, may be used as the fuel oil. In an embodiment, the emulsion component has a density of at least 1.3g/cc. In an embodiment a viscosity of the emulsion is in the range of 22 000 - 60 000 cP (Brookfield Viscometer #7 spindle at 20 rpm) at 49 °C.

In an embodiment the composition has a gassing agent. The gassing agent reacts prior to detonation to form bubbles that are distributed in the emulsion, so the gassing agent can be considered a chemical gassing agent. The presence of bubbles helps to reduce the density of the emulsion. The gassing agent may have two or more reagents that can react with one another to form the gas and bubbles. Acetic acid and sodium nitrite / sodium thiocyanate are used as the gassing agent in an embodiment. The gassing agent (e.g. the reagents) may be added individually to the emulsion by the 6

16762841_1 (GHMatters) P112297.AU.1 mobile processing unit used to form the explosive composition, or the emulsion may be pre-dosed with the gassing agent. For example, when the gassing agent has two or more reactants, one of the reactants can be added to the emulsion well before the emulsion is required to form heavy ANFo, and the other of the reactants can be added to the emulsion just prior to charging a blasthole with heavy ANFo.

Chemical gassing agents are not usually used for heavy ANFo as the sensitivity is provided by the ANFo component of the blend. Sensitivity means the ability of the explosive composition detonation. Sensitivity is dependent on density. The purpose of gassing the emulsion is to reduce the density of the emulsion which allows the product to be sensitive enough to be initiated. If the heavy ANFo is too dense, it will not detonate. Heavy ANFo used up to a ratio of approximately 50:50 [ANFo]:[emulsion] (i.e. heavy ANFo with 50% emulsion) does not necessarily have enough emulsion to require gassing as the ammonium nitrate prills provides enough of a reduction in density and increased sensitivity in order to be able to be detonated. For compositions with over 50% emulsion, the ammonium nitrate prills are not sufficient alone to provide the sensitivity required to allow the combined product to detonate. Gassing agents may be used in addition of the bulking agent to help reduce a density of the heavy ANFo. The amount of gassing agent used is such that it allows full order detonation. In an embodiment, an amount of gassing agent is <5 wt.% of the heavy ANFo (i.e. the explosive composition).

A ratio of the [ANFo]:[emulsion] in some embodiments ranges from about 90:10 to about 35:65. Heavy ANFo having up to 65% emulsion is considered an augured product, whereas beyond 65% emulsion the product can be pumped or augured. The properties and handling requirements of an augured product vs a pumped product differ. Embodiments of the disclosure are generally directed to an augured product i.e. having an emulsion ratio up to a maximum of 65%. As a ratio of [ANFo]:[emulsion] ranges from 90:10 to 35:65, a density of the heavy ANFo ranges from about 0.85 g/cc to about 1.35 g/cc. As the percentage of emulsion in the heavy ANFo increases, the density increases, which increases bulk product costs and increased powder factor, which is a contributing factor in the generation of NOx post blast fume. Generation of NOx is undesirable and indicates sub-optimal detonation conditions. Using

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16762841_1 (GHMatters) P112297.AU.1 phyllosilicate-base bulking agents helps to reduce a density of the explosive composition and may help to reduce the generation of NOx during detonation.

In an embodiment, a ratio of [ammonium nitrate]:[fuel oil] ranges from 90:10 to about 98:2 by mass. In an embodiment a ratio of [ammonium nitrate]:[fuel oil] is 94:6. In an embodiment the fuel oil is diesel, mineral oil and/or recycled oil/diesel blend.

The explosive composition of this disclosure is formed on site using a mobile processing unit or sensitizing unit. As ANFo is classified as a Class 1 explosive, mixing on site avoids the need to transport ANFo. To form the explosive composition, the ammonium nitrate prills, fuel oil, emulsion and phyllosilicate-based bulking agent can be mixed together in a single step. In an embodiment, the ammonium nitrate prills, emulsion and bulking agent are first mixed, and this mixture is then mixed with the fuel oil to form the heavy ANFo. In an embodiment, the ammonium nitrate prills, emulsion and fuel oil are first mixed, and this mixture is then mixed with the bulking agent. In an embodiment the emulsion and ammonium nitrate prills are first mixed, followed by mixing with one of the bulking agent and fuel oil, and then followed by mixing with the other of the bulking agent and fuel oil.

The bulking agent may be added using a timed injection. For example, only a portion of a calculated amount of bulking agent required to decrease the density of the heavy ANFo by a known amount may be added. Each portion may be added (e.g. injected) to the heavy ANFo based on a timed cyclic delivery. Each portion addition may be considered a "pulse" of addition, where a number of pulses are used to mix the required calculated amount of bulking agent. For example, the bulking agent may be added in 10 "pulses" where 10% of the amount of bulking agent required is added during each pulse. Using pulsed addition may help to ensure that the bulking agent is homogenously distributed in the explosive composition. Other mixing protocols may be used, for example mixing the emulsion and fuel oil together first, then mixing in the ammonium nitrate prills and bulking agent. The specific mixing protocol used may be determined by the capability of the mobile processing unit and/or blasthole conditions. In an embodiment mixing is provided by an auger. The auger used to mix the explosive composition may be the augur used to charge a blasthole with the explosive.

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In an embodiment, forming the explosive composition includes adding a gassing agent to the heavy ANFo. The gassing agent is generally added to the emulsion component. The component of the explosive composition may determine in which component the gassing agent is first mixed with. For example, for a gassing agent that is water soluble, the gassing agent may be first mixed with the emulsion component. However, if the gassing agent is hydrophobic / lipophilic, the gassing agent may be added to the fuel oil component. If the gassing agent is a solid it may be added to the ammonium nitrate prills and/or bulking agent. The gassing agent reacts to form a gas that forms bubbles that become distributed in the heavy ANFo. In an embodiment the bubbles tend to reside in the emulsion once a blasthole has been charged with the heavy ANFo. In an embodiment, the gassing agents are selected and/or mixed into the explosive composition such that the evolution of bubbles does not begin until the explosive composition is augured into a blasthole.

Examples Exemplary embodiments will now be described by way of example only. Exemplary embodiments of heavy ANFo compositions are shown in Table 1. The components outlined in Table 1 were mixed together and charged down a 150 mm blasthole and then detonated. A primer was used to initiate detonation of the columnar composition. The ammonia nitrate emulsion (ANE) comprises acetic acid, and for Samples 1-4 having a commercially available gassing agent component (T4), the T4 reacts with acetic acid to result in the formation of gas bubbles that are distributed in the emulsion. ANFo was omitted from Sample 2 which acted as a control.

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Table 1. Composition of exemplary heavy ANFo blends having phyllosilicate-based bulking agents.

Tube 0 Primer Initial Density Final Nett Mass ANFo4 ANE 1 T4 2 Gasser ratio Gasser ratio LECA3 Wt. ratio Sample (mm) (g) Kg/cc Density (Kg) (Kg) (Kg) (Kg) to Emusion to total product (Kg) ANE/ANFo/LECA Kg/cc (tw. w~t

1 150 340 1.19 1.006 18 3.6 11.61 0.09 0.78 0.5 2.7 65:20:15

2 150 340 1.093 0.907 18 0 12.503 0.097 0.78 0.54 5.4 70:00:30

3 100 340 1.161 1.089 13 2.6 8.385 0.065 0.78 0.5 1.95 65:20:15

4 150 340 1.162 0.896 18 3.6 11.61 0.09 0.78 0.5 2.7 65:20:15

5 150 340 1.148 1.148 18 3.6 11.7 0 0 0 2.7 65:20:15

6 150 340 1.202 1.202 18 6.3 9 0 0 0 2.7 50:35:15

7 150 340 0.873 0.873 18 8.1 7.2 0 0 0 2.7 40:45:15 1ANE: Ammonium Nitrate Emulsion; includes acetic acid. 2 T4 reacts with acetic acid in the ANE to form bubbles; acetic acid and T4 together act as the gassing agent.

3LECA: Light Expanded Clay Aggregate; spherical in geometry with a diameter ranging from 6mm - 18 mm. 4 [ammonium nitrate]:[fuel oil] ratio of 94:6.

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In the claims which follow and in the preceding description, except where the context requires otherwise due to express language or necessary implication, the word "comprise" or variations such as "comprises" or "comprising" is used in an inclusive sense, i.e. to specify the presence of the stated features but not to preclude the presence or addition of further features in various embodiments.

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Claims (28)

Claims

1. An explosive composition, comprising: a heavy ANFo component comprising: ammonium nitrate prills; a fuel oil; an emulsion component; and a phyllosilicate-based bulking agent; wherein the bulking agent has a density that is less than the heavy ANFo component.

2. The composition as claimed in claim 1, wherein the bulking agent is kiln dried.

3. The composition as claimed in claim 1 or 2, wherein the bulking agent is in an expanded form.

4. The composition as claimed in any one of claims 1 to 3, wherein the bulking agent has a density less than 0.8g/cc.

5. The composition as claimed in any one of claims 1 to 4, wherein the bulking agent has a density ranging from 0.4g/cc to 0.7g/cc.

6. The composition as claimed in any one of claims 1 to 5, wherein the bulking agent comprises a plurality of particles, the particles including spherical particles.

7. The composition as claimed in claim 6, wherein the bulking agent particles have a diameter ranging from about 6 mm to about 18 mm.

8. The composition as claimed in any one of claims 1 to 7, further comprising a gassing agent that can react prior to detonation of the composition to form a gas that becomes distributed as bubbles in the emulsion component.

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9. The composition as claimed in claim 8, wherein the gassing agent comprises two or more reagents that can react with one another prior to detonation of the composition to generate the gas bubbles distributed in the emulsion.

10. The composition as claimed in any one of claims 1 to 9, wherein the emulsion component comprises oxidizing salts that include metal nitrate salts.

11. The composition as claimed in any one of claims 1 to 10, wherein the emulsion has a density of at least 1.3g/cc.

12. The composition as claimed in any one of claims 1 to 11, wherein a ratio of

[ammonium nitrate prills]:[fuel oil] ranges from about 90:10 to 98:2.

13. The composition as claimed in any one of claims 1 to 12, wherein a ratio of

[ammonium nitrate prills-fuel oil]:[emulsion] ranges from about 90:10 to about 35:65

14. A method of forming an explosive composition, comprising: mixing: ammonium nitrate prills; fuel oil; an emulsion; and a phyllosilicate-based bulking agent; wherein, when mixed, the ammonium nitrate prills, fuel oil and emulsion form a heavy ANFo component and the bulking agent has a density that is less than the heavy ANFo component.

15. The method as claimed in claim 14, wherein the bulking agent is kiln dried.

16. The composition as claimed in claim 14 or 15, wherein the bulking agent is in an expanded form.

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17. The method as claimed in any one of claims 14 to 16, wherein the bulking agent has a density of less than 0.8g/cc.

18. The method as claimed in any one of claims 14 to 17, wherein the bulking agent comprises a plurality of particles that include particles that are spherical.

19. The method as claimed in claim 18, wherein the bulking agent particles have a diameter ranging from about 6 mm to about 18 mm.

20. The method as claimed in any one of claims 14 to 19, wherein the mixing step is provided by auguring.

21. The method as claimed in any one of claims 14 to 20, wherein the bulking agent, ammonium nitrate prills and emulsion are first mixed together followed by mixing in the fuel oil.

22. The method as claimed in any one of claims 14 to 20, wherein the ammonium nitrate prills, emulsion and fuel oil are first mixed together followed by mixing in the bulking agent.

23. The method as claimed in any one of claims 14 to 22, wherein the bulking agent is mixed by using a pulsed mixing protocol where only a portion of a required amount of bulking agent is mixed with each pulse based on a timed cyclic delivery.

24. The method as claimed in any one of claims 14 to 23, further comprising mixing a gassing agent with emulsion, the gassing agent reacting to form bubbles that are distributed in the emulsion prior to detonation.

25. The method as claimed in claim 25, wherein the step of providing the gassing agent comprises adding two or more reagents that react with each other upon mixing prior to detonation to form a gas.

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26. The method as claimed in any one of claims 14 to 25, wherein the composition is as claimed in any one of claims 1 to 13.

27. The method as claimed in any one of claims 14 to 26, further comprising charging a blasthole with the explosive composition.

28. A method of charging a blasthole, comprising charging a blasthole with the explosive composition as claimed in any one of claims 1 to 13.

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