AU2013204063B2

AU2013204063B2 - Water Resistant ANFO Equivalent and Method of Use

Info

Publication number: AU2013204063B2
Application number: AU2013204063A
Authority: AU
Inventors: Peter BELLAIRS
Original assignee: BELLAIRS JENNIFER ANNETTE
Current assignee: BELLAIRS Jennifer Annette
Priority date: 2012-08-22
Filing date: 2013-04-11
Publication date: 2016-05-05
Anticipated expiration: 2033-04-11
Also published as: AU2013204063A1

Abstract

A method for forming a water resistant explosive composition, the method including the steps of forming an explosive agent into a particulate or prill, applying one or more physical barrier layers to minimise or prevent ionic exchanges with the explosive agent and combining with a fuel source.

Description

I WATER RESISTANT ANFO EQUIVALENT AND METHOD OF USE TECHNICAL FIELD [0001] The present invention relates to ANFO explosives and particularly to ANFO explosives which are physically rather than chemically inhibited. BACKGROUND ART [0002] The use of explosives to break rock is an intrinsically hazardous process. There are situations where a specific additional hazard may exist due to the possible unwanted reaction between an explosive and the rock being blasted. In such situations the unwanted reactions may result in premature detonations with potentially fatal results. The reactions can be caused by rock chemistry, temperature or a combination of both. [00031 The Australian Explosives Industry And Safety Group Inc (AEISG) Code of Practice - Elevated Temperature and Reactive Ground provides the following definitions: "Elevated temperature" - material that is above 55'C and includes both hot ground and high temperature ground conditions as defined in AS2187.2-2006. "Elevated temperature products" - explosive products that have been formulated and/or packaged and tested to withstand a nominated temperature for a recommended period of time before they will deteriorate or become unstable and possibly decompose violently or explode. "High temperature ground" - High temperature blasting is defined as the blasting of material at 100'C or greater [AS 2187.2-2006 - Section 12.7] "Hot ground" - material shall be defined as hot if its temperature is 55'C or more but less than 100'C [AS 2187.2-2006 - Section 12.6.1] "Inhibited product" - explosive product that chemically suppresses the reaction between nitrates and sulphides. "Reactive ground" - rock that undergoes a spontaneous exothermic reaction after it comes into contact with nitrates. The reaction of concern involves the chemical oxidation of sulphides (usually of iron or copper) by nitrates and the liberation of potentially large amounts of heat. The process is unpredictable and can be so violent that it results in mass explosions. [0004] When dealing with the issue of elevated temperature ground and/or reactive ground, there are four main ground conditions that can apply as illustrated in Figure 1. [0005] For the case of both elevated temperature and reactive ground conditions, the risks associated with these conditions need to be considered during product selection and in determining operational requirements. [0006] The reaction of nitrates with sulphide containing minerals is an auto-catalysed process that can, after some induction time, lead to a runaway exothermic decomposition even if the starting temperature of the mixture is at an ambient temperature. The induction stage or the first stage occurs in the presence of water (only small amounts) in the rock mass so that ionic exchanges can occur. [00071 Natural oxidative weathering of iron sulphides such as pyrites by atmospheric oxygen generates solutions of ferrous ions and acid. This process occurs whenever the sulphides are exposed to air along cracks, in drilled holes, in the muck pile after blasting, on pit walls and in old stopes. No nitrates are required for this to occur. Iron Sulphides + Oxygen + Water = Ferrous Ions + Sulphuric Acid [0008] This reaction is exothermic and can lead to hot blast holes for particularly reactive ores. This temperature increase can be as little as 2'C or as much as several hundred degrees. [0009] On contact with ammonium nitrate, the ferrous and acid species from weathering can begin to catalyse the breakdown of nitrate. The breakdown process is auto-catalytic in that it generates its own catalysts as it proceeds. Nitrates + Iron Sulphides + Ferrous Ions + Sulphuric Acid = Nitric Oxide + Ferric Ions + HEAT [0010] The nitric oxide is the catalyst to the second stage of the ammonium nitrate reactive ground reaction. The nitric oxide and ferric ions produced in this stage react with more pyrites, generating more ferrous ions and sulphuric acid. Iron Sulphides + Nitric Oxide + Ferric Ions - Ferrous Ions + Sulphuric Acid [0011] Although these reactions are exothermic, their rate may be initially so slow that little or no temperature rise is detectable. This is due to the concentration of catalytic species building -J up to some critical level. The time taken for this to occur is often referred to as the induction period. [0012] When sufficient catalysing species have built up, the reaction rate increases sharply and the heat generated causes the temperature to become so high that a rapid, potentially violent decomposition of the remaining ammonium nitrate is inevitable. Nitrates + Fuels (sulphides, diesel etc) + Heat gives EXPLOSION [00131 A variety of solutions have been provided to answer the problem of using explosives in elevated temperature and/or reactive ground conditions. [0014] U.S. Pat. No. 5,159,153 (Cranney et al.), acknowledged the well-known problem that certain sulfide/pyrite ores are reactive (that is, reactive ground) with ammonium nitrate, and that when a blasting agent containing ammonium nitrate is used in a borehole, heat generated in the borehole by such reactivity can cause premature detonations. The Cranney et al. patent refers to U.S. Bureau of Mines Reports of Investigation Nos. 7187 (hereinafter, "Report 7187") and 8373 (hereinafter, "Report 8373") and U.S. Pat. Nos. 3,447,982 and 3,708,356 as disclosing use of urea to inhibit any reaction of AN (ammonium nitrate) or ANFO (ammonium nitrate and fuel oil) with reactive ores. [0015] This urea dosed explosive composition is an inhibited product which chemically suppresses the reaction between nitrates and sulphides. [0016] When dealing with elevated temperature ground, the main methods of dealing with the problems created are to minimise sleep time (the period of time that an explosive is left in a blast hole until it is fired. The time is measured from the time of loading until the time of firing) of the explosive charge and/or through the choice of bulk, packaged and initiating product formulated and/or packaged to withstand elevated temperatures. [00171 It will be clearly understood that, if a prior art publication is referred to herein, this reference does not constitute an admission that the publication forms part of the common general knowledge in the art in Australia or in any other country. SUMMARY OF INVENTION [00181 The present invention is directed to water resistant ANFO or ANFO equivalent, which may at least partially overcome at least one of the abovementioned disadvantages or -r provide the consumer with a useful or commercial choice. [0019] With the foregoing in view, the present invention in one form, resides broadly in an explosive composition including an explosive agent and a fuel source wherein the explosive agent is provided with one or more physical barrier layers to minimise or prevent ionic exchanges with the explosive agent. [0020] In an alternative form, the present invention resides in a method for forming a water resistant explosive composition, the method including the steps of forming an explosive agent into a particulate or prill, applying one or more physical barrier layers to minimise or prevent ionic exchanges with the explosive agent and combining with a fuel source. [0021] In yet another alternative form, the present invention resides in a method for blasting in reactive ground conditions wherein the method includes the use of an explosive composition including an explosive agent and a fuel source wherein the explosive agent is provided with one or more physical barrier layers to minimise or prevent ionic exchanges with the explosive agent. [0022] In yet another alternative form, the present invention resides in a method for blasting in elevated temperature conditions wherein the method includes the use of an explosive composition including an explosive agent and a fuel source wherein the explosive agent is provided with one or more physical barrier layers to minimise or prevent ionic exchanges with the explosive agent. [0023] In still another alternative form, the present invention resides in method for blasting in reactive ground conditions wherein an explosive composition is formed first into a prill or particulate form and then one or more physical barrier layers about the prilled or particulate composition. [0024] In a further alternative form, the present invention resides in a method for blasting in elevated temperature conditions wherein an explosive composition is formed first into a prill or particulate form and then one or more physical barrier layers about the prilled or particulate composition. [0025] The present invention is based about physical separation or isolation of the explosive agent from external conditions. This will preferably minimise the production of catalytic species which will lengthen the induction period of the reactive ground reaction. [0026] Prevention of ionic exchange with the explosive agent is not required but is preferred. Even if the ionic exchange with the explosive agent can be minimised or slowed, then the sleep time of the composition can be extended, even in elevated temperature or reactive ground conditions. [0027] The explosive composition of the present invention could also include lower density explosives that utilise water resistant explosive agent prill or granules as well. These lower density explosives would typically be used in dry ground applications and static water conditions where blastholes are dewatered with but may be used without liners. [0028] The fuel is preferably provided in or attached to one or more of the coating layers that surround the explosive agent. [0029] The explosive agent of the present invention may be any agent suitable for use in explosives. Particularly, the explosive agent will normally be or include an oxidising agent such as certain alkali metal salts, alkaline earth salts and ammonium salts commonly used in explosives. One preferred example of such an explosive agent is ammonium nitrate. [0030] The explosive agent may be selected from those which are well known in the art including oxidative explosives such as ammonium nitrate, urea nitrate, sodium nitrate, calcium nitrate, ammonium perchlorate and the like and any combination of two or more of the above. [0031] Preferably, the explosive agent is ammonium nitrate. [0032] It is particularly preferred that the explosive agent is provided as a prill, particulate material or granule. [0033] Preferably, the fuel will also be provided in a solid form. The fuel will typically be selected from the group consisting of rubber, plastics such as polystyrene, polyethylene and polybutylene, gilsonite, solid form unexpanded polystyrene, acrylonitrile-butadiene-styrene, waxed wood metal, rosin and the like. The rubber may be natural or synthetic or a mixture thereof. [0034] More preferably, the fuel is natural and/or synthetic rubber and/or a plastic such as polystyrene, polyethylene and polybutylene. [0035] In a preferred embodiment the solid fuel is natural and/or synthetic rubber. [0036] Other materials may be added to the composition at any stage as desired by an operator.

V [00371 Preferably, at least one of the physical barrier layers is formed from a water resistant or hydrophobic material. A suitable convenient class of materials with the desired properties are polymeric materials. Other suitable materials include waxes and materials such as stearates, particularly calcium stearate or paraffin based materials including modified paraffin wax. Silanes, particularly modifies silanes could also be used. [0038] Preferably one or more barrier layers are provided as a surface coating. An effective layer may require more than one layer. The layers may have different properties. Preferably the one or more layers are applied as a thin film. [0039] The one or more barrier layers may provide a chemical barrier layer preventing, minimising or slowing ionic exchange with the explosive agent but preferably a physical barrier layer is provided for the explosive agent. [0040] Where a polymeric material is used, any polymeric material may be used. A polymeric fluid may be used which results in the explosive agent being coated, and/or the fuel being coated or a composition containing both being coated. Use of certain polymeric materials may result in the fuel and explosive agent being bonded together such as with an adhesive or simply held close together, but not in actual physical contact, such as by a viscous agent or material in which they can be embedded. For example, providing a barrier layer or coating on the explosive agent may allow fuel, particularly solid fuel to be bonded to the coated explosive agent. [0041] In this form, the polymeric material preferably maintains the explosive agent and the fuel in even distribution throughout the composition. Suitably, the polymeric material is selected from the group consisting of a polyisobutene, a polystyrene, a polyethylene and a polybutylene. [0042] Preferably, the polymeric material comprises polyisobutene lactones, alkanolamine derivative, such as Anfomul P3000. [0043] The polymeric material used as the physical barrier layer may be any polymer which further results in adherence or adhesion of the fuel and the explosive agent, although this is not strictly necessary. This may be achieved by use of a polymer to coat the explosive agent prill or particulate and which has inherent adhesive properties, which results in the generation of some kind of attraction between the two surfaces or which holds the two components in close vicinity due to its viscosity or to components being in some way embedded within it. The polymeric material may be fluid upon application and may or may not increase in viscosity or solidify thereafter, depending mostly on the viscosity required to adhere the explosive agent and the fuel together. [0044] Preferred polymeric materials are of the polyisobutene type or liquefied plastics such as a polystyrene, polyethylene, or polybutylene gel. [0045] The polymeric materials can be liquefied in a volume of a suitable organic solvent such as toluene, benzene, petrol and the like in order for application. Typically, once the layer has been applied, the solvent material will be removed, normally by evaporation. [0046] Particularly preferred polymeric materials are polyisobutene lactone derivatives, polyisobutene succinic acid derivatives and polystyrene gel. More preferably, the polymeric adherent is a polyisobutene lactone alkanolamine derivative. An example of this kind of polymeric material is commercially available from Croda Australia under the name Anfomul P3000. Although other polymeric materials are suitable it has been found that Anfomul P3000 appears to chemically react with the surface of the oxidative explosive agent and polymerises with the rubber solid fuel particles to give an explosive composition that is particularly stable to physical handling and maintains the fuel in intimate contact with the explosive agent. [00471 The composition may further comprise fuel oil. This fulfils the same role as with traditional ANFO and, while not essential, may be a useful addition to the explosive composition. [0048] In the case of the water resistant ANFO equivalent as provided by the present invention, diesel is not used as a fuel but preferably crumbed rubber or another fuel less preferably. This is especially advantageous when only a small portion of the mine is at elevated temperature which are most of the applications world wide. [0049] The water resistant ANFO equivalent of the present invention can also be used in the lower temperature end of high temperature blasting (100 C to 160'C inclusive) as the preferred fuel, rubber and the ANFO have the following melting points: Rubber - 170'C Ammonium Nitrate - 169.9'C. [0050] The surface coatings that include the crumbed rubber may also offer slight protection for the rubber and the preferred nitrate prill from heat.

[0051] In one form of this invention, the final explosive composition including the water resistant explovie agent prill is combined with a fuel source to form a prilled, pelleted or granulated final product for ease of filling boreholes using conventional equipment. [0052] Any of the features described herein can be combined in any combination with any one or more of the other features described herein within the scope of the invention. [0053] The reference to any prior art in this specification is not, and should not be taken as an acknowledgement or any form of suggestion that the prior art forms part of the common general knowledge. BRIEF DESCRIPTION OF DRAWINGS [0054] Various embodiments of the invention will be described with reference to the following drawings, in which: [0055] Figure 1 is an illustration of the four main ground conditions that can exist when dealing with elevated temperature ground and/or reactive ground. DESCRIPTION OF EMBODIMENTS [0056] According to a particularly preferred embodiment of the present invention, a water resistant explosive equivalent and method of use is provided. [00571 The explosive composition includes an explosive agent provided with one or more physical barrier layers to minimise or prevent ionic exchanges with the explosive agent and a fuel source. Typically the ionic exchange occurs in the presence of water, even very small amounts and therefore the main aim of the one or more barrier layers is to "waterproof' the explosive agent. [0058] The explosive agent is provided as a prill, a small aggregate of a material, most often in a spherical shape due to the nature of the formation of the prill. [0059] One or more barrier layers are provided as a surface coating to cover the exterior of the prilled explosive agent. An effective layer may require more than one layer and the layers may have different properties. [0060] The one or more barrier layers may provide a chemical barrier layer preventing, minimising or slowing ionic exchange with the explosive agent but preferably a physical barrier layer is provided for the explosive agent. [0061] Whilst there are a variety of methods that could be used, two preferred methods of waterproofing the explosive agent are as follows. [0062] The first waterproofing technique involves the use of calcium stearate/paraffin gel as waterproofing agents. The water proofing agents can be dissolved in an organic solvent and applied by sequential coating and solvent evaporation steps. Normally, there will be a three coating steps with intervening solvent evaporation steps. [0063] This technique is best performed using fluidised bed technologies that prevent or at least minimise particle agglomeration and allow the uniform application of the waterproofing agents while maintaining the flowability of the explosive agent particles. The layers can be applied to particles of ammonium nitrate prill or particulate sequentially coated with calcium stearate, paraffin gel and/or formulations containing a mix of both calcium stearate and paraffin gel. Using this coating method it is possible to prevent the ingress of water into the explosive agent particulate or prill for extended periods without loss of explosive capacity. [0064] Additional layers may be provided to allow mixture with an appropriate fuel source. [0065] An alternative waterproofing method involves the use of paraffin wax. Ammonium nitrate prill or particulate can be sequentially coated with medium to high melting point (>50'C) paraffin wax dissolved in an organic solvent or coated directly with molten wax. Again, this application is best performed using fluidised bed technologies that prevent particle agglomeration and allow the uniform application of the waterproofing agents while maintaining the flowability of the explosive agent particles. [0066] In this way large particles ranging from 5-10mm of wax encrusted explosive agent can be formed if necessary. These are prevented from aggregation before desired by a final surface coating of microfine talc, diatomaceous earth, bentonite or zeolite. Depending on the depth of coating, the wax encrusted particles may be made completely waterproof for a period of 48 hours without loss of explosive capacity. Other waxes that may be useful include various vegetable waxes, silicone waxes and organo-silicone waxes. [00671 Various other additives, as discussed previously, may be incorporated into the waterproof explosive agent coating as desired. Further, when it comes to the addition of the fuel to the explosive agent, other useful additives such as catalyst material may be added.

IU [00681 Hence, the explosive compositions of the invention can be used in many wet environs where formerly only more costly slurries, water gels, emulsions and water resistant products could be used. This provides a useful and more economic alternative to the consumer. [00691 In a particularly preferred embodiment, crystals of urea nitrate or calcium nitrate are first provided with a surface coating to prevent ingress of water. Rubber particles of 30 mesh size or less as the fuel source are mixed with the coated crystals. Once uniformly combined, a mixture consisting of polymeric adherent, such as Anfomul P3000, and fuel oil is added to provide a final explosive composition of urea or calcium nitrate 85% to 95%, rubber particles 5% to 15%, fuel oil/polymeric adherent mix 3% to 7 % and, optionally, iron catalyst 0.25% to 1%. This mix provides a relatively insoluble explosive composition that may be used when water has entered the borehole or where explosion delays after borehole filling would allow the uptake of moisture thus reducing the efficiency of the explosion. [00701 Typically, fuel is mixed with the explosive agent at the time of filling the borehole to form an explosive composition of from 85% to 99% explosive agent and from 1 % to 15% fuel. This embodiment enables polystyrene waste products, as well as rubber waste such as from tyres, to be utilised as a fuel source and so provides flexibility in sourcing fuels. [00711 In the present specification and claims (if any), the word 'comprising' and its derivatives including 'comprises' and 'comprise' include each of the stated integers but does not exclude the inclusion of one or more further integers. [0072] Reference throughout this specification to 'one embodiment' or 'an embodiment' means that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment of the present invention. Thus, the appearance of the phrases 'in one embodiment' or 'in an embodiment' in various places throughout this specification are not necessarily all referring to the same embodiment. Furthermore, the particular features, structures, or characteristics may be combined in any suitable manner in one or more combinations. [0073] In compliance with the statute, the invention has been described in language more or less specific to structural or methodical features. It is to be understood that the invention is not limited to specific features shown or described since the means herein described comprises preferred forms of putting the invention into effect. The invention is, therefore, claimed in any of its forms or modifications within the proper scope of the appended claims (if any) appropriately interpreted by those skilled in the art.

Claims

1. A reactive ground explosive composition for use in reactive ground including an ANFO or ANFO equivalent explosive agent and a fuel source, wherein the ANFO or ANFO equivalent explosive agent is provided with one or more physical barrier layers impermeable to ionic exchange for minimising or preventing ionic exchanges with the ANFO or ANFO equivalent explosive agent and delaying or preventing an exothermic reaction when in the reactive ground.

2. A reactive ground explosive composition as claimed in claim 1 wherein the fuel source is provided in or attached to one or more of the barrier layers.

3. A reactive ground explosive composition as claimed in either claim 1 of claim 2 further including at least one lower density explosive that utilises a water resistant ANFO or ANFO equivalent explosive agent prill or granules.

4. A reactive ground explosive composition as claimed in any one of the preceding claims wherein the fuel source is provided in or attached to one or more of the physical barrier layers that surround the ANFO or ANFO equivalent explosive agent.

5. A reactive ground explosive composition as claimed in any one of the preceding claims wherein the ANFO or ANFO equivalent explosive agent is provided as a prill, particulate material or granule.

6. A reactive ground explosive composition as claimed in any one of the preceding claims wherein the fuel source is provided in a solid form.

7. A reactive ground explosive composition as claimed in any one of the preceding claims wherein the fuel source is selected from the group consisting of rubber, plastics such as polystyrene, polyethylene and polybutylene, gilsonite, solid form unexpanded polystyrene, acrylonitrile-butadiene-styrene, waxed wood metal, rosin, any of which are natural or synthetic or a mixture thereof.

8. A reactive ground explosive composition as claimed in any one of the preceding claims wherein the fuel source is natural and/or synthetic rubber and/or a plastic such as polystyrene, polyethylene and polybutylene. 12

9. A reactive ground explosive composition as claimed in any one of the preceding claims wherein at least one of the physical barrier layers is formed from a water resistant or hydrophobic material.

10. A reactive ground explosive composition as claimed in claim 9 wherein a suitable class of materials with the desired properties are polymeric materials.

11. A reactive ground explosive composition as claimed in claim 9 wherein a suitable material is selected from the group including waxes and materials such as stearates, particularly calcium stearate or paraffin based materials including modified paraffin wax.

12. A reactive ground explosive composition as claimed in claim 9 wherein a suitable material is a silane, particularly a modified silane.

13. A reactive ground explosive composition as claimed in any one of the preceding claims wherein one or more barrier layers are provided as a surface coating about combined ANFO or ANFO equivalent explosive agent and a fuel source.

14. A reactive ground explosive composition as claimed in any one of the preceding claims wherein more than one barrier layer is provided.

15. A reactive ground explosive composition as claimed in any one of the preceding claims wherein the one or more barrier layers provide a physical barrier layer operating chemically to prevent, minimise or slow ionic exchange with the ANFO or ANFO equivalent explosive agent.

16. A reactive ground explosive composition as claimed in claim 1 or claim 2 wherein a polymeric material is provided as a barrier layer which also maintains the ANFO or ANFO equivalent explosive agent and the fuel source in even distribution throughout the composition.

17. A reactive ground explosive composition as claimed in any one of the preceding claims wherein a polymeric material used as the at least one barrier layer comprises polyisobutene lactones, or an alkanolamine derivative.

18. A reactive ground explosive composition as claimed in any one of the preceding claims wherein a polymeric material used as the at least one barrier layer is liquefied in a 13 volume of a suitable organic solvent such as toluene, benzene, petrol and the like in order for application and once the barrier layer has been applied, the solvent material is removed.

19. A reactive ground explosive composition as claimed in any one of the preceding claims further including fuel oil.

20. A reactive ground explosive composition including a water resistant ANFO or ANFO equivalent explosive agent as claimed in any one of the preceding claims is prilled then combined with a fuel source to form a prilled, pelleted or granulated final product.

21. A method for forming a water resistant explosive composition for use in reactive ground, the method including the steps of: i. forming an ANFO or ANFO equivalent explosive agent into a particulate or prill, ii. applying one or more physical barrier layers impermeable to ionic exchange for minimising or preventing ionic exchanges with the ANFO or ANFO equivalent explosive agent and delaying or preventing an exothermic reaction when in the reactive ground and iii. combining the coated ANFO or ANFO equivalent explosive agent with a fuel source.

22. A method for blasting in reactive ground conditions wherein the method includes the use of a reactive ground explosive composition including an ANFO or ANFO equivalent explosive agent and a fuel source wherein the ANFO or ANFO equivalent explosive agent is provided with one or more physical barrier layers impermeable to ionic exchange for minimising or preventing ionic exchanges with the ANFO or ANFO equivalent explosive agent and delaying or preventing an exothermic reaction when in the reactive ground.

23. A method for blasting in elevated temperature conditions wherein the method includes the use of a reactive ground explosive composition including an ANFO or ANFO equivalent explosive agent and a fuel source wherein the ANFO or ANFO equivalent explosive agent is provided with one or more physical barrier layers impermeable to ionic exchange for minimising or preventing ionic exchanges with the ANFO or ANFO equivalent explosive agent and delaying or preventing an exothermic reaction when in the reactive ground. 14

24. A method for blasting in reactive ground conditions wherein an ANFO or ANFO equivalent explosive composition is formed first into a prill or particulate form and then one or more physical barrier layers impermeable to ionic exchange are formed about the prilled or particulate composition.

25. A method for blasting in elevated temperature conditions wherein an ANFO or ANFO equivalent explosive composition is formed first into a prill or particulate form and then one or more physical barrier layers impermeable to ionic exchange are formed about the prilled or particulate composition.