CN1307551A - ANFO composition - Google Patents

Abstract

An explosive composition comprising ammonium nitrate granules, fuel oil and a propellant selected from the group consisting of inorganic ammonium compounds, organic ammonium compounds, amides, carbonates and nitrates, with the proviso that the propellant is not ammonium nitrate, And wherein the content of the throwing agent is greater than 5% by weight.

Description

Ammonium nitrate/fuel oil composition

The invention relates to an explosive composition, in particular to an ammonium nitrate/fuel oil (ANFO) composition suitable for blasting soft media such as overburden and coal seams.

Detonation of explosive compositions releases energy in various forms. Two of these energy release types are of particular importance in controlling blasting to ensure that the size distribution and dispersion of the blasting layer is as desired, and they are fragmentation energy and heave energy. Fracture energy (commonly referred to as impact energy) determines the ability of an explosive composition to shatter the surrounding medium. Blasting hard media such as rock requires explosive compositions with high fragmentation energy. Throwing energy (commonly referred to as foaming energy) determines the ability of an explosive composition to move material around it. When blasting soft media such as overburden or coal seams, explosive compositions with low fracture energy and higher throw energy are preferred.

ANFO and ANFO-based explosive compositions are widely used in civilian applications, such as mining operations. ANFO is a substantially oxygen balanced mixture of ammonium nitrate particles coated with fuel oil. Typically, ANFO contains 94% by weight ammonium nitrate and 6% by weight fuel oil. ANFO is widely used in civil blasting operations mainly because of its low cost, easy production, easy operation and charging, and its convenience and performance as a bulk system. Despite the lack of water resistance, ANFO and ANFO-based explosive compositions are suitable for dry explosives. ANFO and ANFO-based explosive compositions generally provide too high a fragmentation energy when used to blast soft media, so techniques such as air spacing have been employed to reduce the fragmentation energy released during detonation. Other techniques for reducing or controlling the energy of the explosion include diluting the explosive composition with an inert material, loosening the explosive composition with a low density material (inert or fuel), inflating or blowing the explosive composition with microspheres, and the like. The use of air-staged charges and other fragmentation energy reduction techniques also has the effect of reducing throwing energy. A reduction in throw energy is generally undesirable since it is desirable to maintain or at least minimize the loss of throw energy while reducing the fragmentation energy to allow the explosive composition to act on the cover.

In open cut or quarry blasting, the blastholes are usually spaced evenly along the bench at a consistent interval and determined by the amount of ANFO required for blasting. However, each run will typically have areas of harder and softer material. While fragmentation energy can be reduced for softer areas by, for example, air-staged charges, the concomitant localized reduction in throw energy results in increased dispersion of the overburden and increases the difficulty and cost of its collection. It would be desirable to have a method of varying the fragmentation energy of ANFO or ANFO-based explosive compositions which maintains the throw energy or at least avoids a reduction in throw energy as much as possible.

We have now discovered an ANFO explosive composition which has reduced fragmentation energy but which retains the desired level of throw energy. Advantageously, the explosive compositions of the present invention can be modified to provide the desired balance of fragmentation and throwing energies, and can be readily varied within and between boreholes to provide optimum blast performance.

The present invention provides a kind of explosive composition, and it contains ammonium nitrate particle, fuel oil and throwing agent (heaveagent), wherein said heaving agent is selected from inorganic ammonium compound, organic ammonium compound, amide, carbonate and nitrate, condition It is a throwing agent other than ammonium nitrate, wherein said throwing agent is present in an amount greater than 5% by weight.

The explosive composition of the present invention comprises ammonium nitrate and fuel oil, a mixture of which is commonly referred to in the art as "ANFO". Explosive compositions for use in the present invention preferably contain sufficient fuel oil so that the explosive composition is substantially oxygen equilibrated (taking into account the presence of oxide salts, fuel oil, sensitizers and other additives in the explosive). "Substantially oxygen balanced" means that the mixture has an oxygen balance of greater than about -25%, preferably in the range of -10% to +10%. If the explosive composition is used alone, the composition should be substantially oxygen balanced. However, if an emulsion or other explosive is blended with ANFO, the final blended explosive composition should be oxygen balanced.

Preferably, the content of fuel oil is about 2%-10% (weight) of the total weight of ammonium nitrate and fuel oil. More preferably, the content of fuel oil is about 3%-6% by weight. Advantageously, the use of a propellant reduces the fuel oil requirements of the explosive composition. The preferred weight ratio of ammonium nitrate to fuel oil is in the range of 97:3 to 96:4.

Ammonium nitrate particles suitable for use in ANFO explosives are known in the art. Suitable ammonium nitrate particles may be separate discrete particles such as spherical particles, granules, agglomerates and fines. Low porosity ammonium nitrate particles suitable for use in the explosives of the present invention are taught in US Patent No. 4,736,683.

A small portion of the ammonium nitrate component can be replaced by other inorganic oxidizer salts known in the art, including alkali metal nitrates (such as sodium nitrate and potassium nitrate) and perchlorates or alkaline earth metal nitrates (such as calcium nitrate, magnesium nitrate and barium nitrate) and perchlorate. These additional components are usually added in amounts up to about 20% by weight, more usually up to about 15% by weight, based on the weight of ammonium nitrate.

Ammonium nitrate is preferably coated with an anti-caking agent. Ammonium nitrate coatings are known in the art. Ammonium nitrate can be coated with, for example, clays such as bentonite, talc, or metal salts of aliphatic monocarboxylic acids of 6 to 24 carbon atoms. The metal component of the salt may be an alkali or alkaline earth metal, such as sodium, zinc, copper, magnesium, potassium, calcium, barium and strontium. The fatty acid may be caproic acid, heptanoic acid, caprylic acid, capric acid, lauric acid, myristic acid, palmitic acid, stearic acid, oleic acid, or tallic acid, among others. Preferably, the coating is magnesium stearate or a mixture of magnesium stearate and magnesium oxide.

The amount of anti-blocking agent that can be used is preferably 0.1 to 1% by weight, more preferably about 0.1% to 0.2% by weight, based on the weight of the inorganic oxidizing agent salt to be coated. When the coating is a metal salt of a fatty acid such as magnesium stearate, lesser amounts of anti-caking agents may be used.

The fuel oils used in the explosive compositions of the present invention are those known in the art to be suitable for ANFO. Fuel oil, especially No. 2 fuel oil and No. 2 diesel fuel, are typical (and preferred) fuels for use in formulating with ammonium nitrate to form the explosive compositions of the present invention. The performance specifications of No. 2 fuel oil are well known: flash point above 38°C, 90% distillation point 228 minimum, -338°C maximum, maximum Saybolt universal viscosity at 38°C for 38 seconds (3.6cSt) (ASTM D396-84 fuel oil standard specifications). Specifications for No. 2 diesel fuel are also well known (flash point above 52°C) and are described in ASTM D975, Standard Specification for Diesel Fuel Oils. Petroleum fractions (sometimes referred to as crude or partially refined oils) are also suitable fuel components. Various other commercially available liquid hydrocarbons may be used. Virtually any liquid hydrocarbon which can be mixed in liquid form is suitable for use in formulating the explosive. Fuel oil may be partially or fully replaced by one or more other oxidizable materials such as other hydrocarbon fractions derived from petroleum and similar fractions derived from other fossil fuels. These include heating oil, diesel fuel, jet fuel (particularly Type "A" jet fuel), oil, kerosene, lubricating oil, coal distillate, kerogen extract (from shale oil), and the like. Oils derived from vegetable and animal sources as well as synthetic products such as alcohols (e.g., having chains of 8 to 16 carbon atoms or more), glycols, amines, esters, ketones, and refined mineral oils (liquid at room temperature) may also be used. , preferably with a flash point above 38°C) instead of fuel oil. Saturated fatty acid-type co-fuels suitable for carbonaceous fuel components include caprylic, capric, lauric, palmitic, behenic, and stearic acids. Higher alcohol-type co-fuels suitable for use in the carbonaceous fuel component include hexanol, nonanol, lauryl alcohol, cetyl alcohol, and stearyl alcohol. Other miscible carbonaceous materials for use as co-fuels in carbonaceous fuel components include vegetable oils such as corn oil, cottonseed oil, and soybean oil. If desired, carbohydrate materials may be added as auxiliary fuels, typical examples of which are mannose, glucose, sucrose, fructose, maltose and molasses.

Small amounts of high melting point waxes (melting point at least 38°C, usually less than 1% by weight of the fuel) can also be used as carbonaceous fuel components. Waxes useful in carbonaceous fuel components include petroleum-derived waxes such as petrolatum wax, microcrystalline wax, and paraffin wax; mineral waxes such as ozokerite and montan wax; animal waxes such as spermaceti; and insect waxes such as beeswax and Chinese wax.

Petroleum oils of any desired kinematic viscosity may be used as a component of carbonaceous fuels, which may include oils having kinematic viscosities ranging from thin liquids to those liquids (small amounts) that are too thick to flow at ordinary temperatures . Typical petroleum stocks have kinematic viscosities in the range of about 5 to 4000 cSt at 25°C.

Most preferably, the fuel oil (comprising any such petroleum oil) has a kinematic viscosity of less than about 200 cSt, more preferably between about 2 and 100 cSt (measured at 25°C).

The explosive compositions of the present invention are substantially dry. Preferably, the explosive composition contains less than 1% by weight water, more preferably less than about 0.5% by weight water, most preferably about 0.2% by weight water.

Various modifiers, thickeners and sensitizers conventionally employed in the art may be incorporated into the explosive compositions of the present invention. For example, energy enhancers such as aluminum, magnesium, aluminum-magnesium alloys, ferrophosphorus, high-silicon cast iron, lead and its salts, and trinitrotoluene may be added.

The ANFO compositions of the present invention can be sensitized with sensitizers such as those known to those skilled in the art. Suitable sensitizers include polystyrene beads. US Patent No. 4,889,570 teaches that a water repellant such as guar gum can be applied as a coating of ammonium nitrate.

The explosive compositions of the present invention may be prepared by any of the continuous, semi-continuous or batch processes currently used to prepare ANFO explosive compositions. When the fuel source is a mixture of one or more oils, it is advantageous to mix the oils before adding the ammonium nitrate.

The throwing agent may be selected from inorganic ammonium compounds, organic ammonium compounds, amides, carbonates and nitrates, provided that the throwing agent is not ammonium nitrate, and wherein the throwing agent is present in an amount greater than 5% by weight.

Inorganic ammonium compounds include ammonium salts, ammonium double salts and mixtures thereof. Preferred inorganic ammonium compounds include ammonium sulfate, ammonium chloride, ammonium carbonate, ammonium bicarbonate, ammonium thiosulfate, ammonium thiocyanate, ammonium sulfonate and ammonium phosphate. Preferred double salts include ammonium sulfate nitrate, ammonium phosphate nitrate and calcium ammonium nitrate. A preferred inorganic ammonium containing double salt is ammonium sulfate nitrate. We have found that fertilizer grade ammonium sulfate nitrate is particularly suitable for use in the present invention.

Organic ammonium compounds suitable for use in the present invention include ammonium acetate, ammonium oxalate, ammonium tartrate and ammonium citrate.

Carbonates suitable for use in the present invention include calcium carbonate and sodium carbonate. Nitrates suitable for use in the present invention include calcium nitrate. Amides suitable for use in the present invention include urea and dicyandiamide. It is especially preferred to use 20-30% urea in the present invention. Urea in this amount is particularly effective in reducing the detonation velocity of the explosive composition while producing a significant volume of gas. Urea is also a suitable throwing agent because of its low cost.

The level of propellant used in the explosive composition of the present invention is greater than 5% by weight. Throwing agents are readily employed up to about 60% by weight. Preferably, the propellant is present in an amount of 20 to 40% by weight of the explosive composition.

We have found that the addition of propellants to ANFO or ANFO-based explosive compositions substantially reduces the oxygen balance of the composition. As a result, the amount of fuel oil required to achieve an oxygen balanced explosive composition is reduced. The reduction in fuel oil, and the reduction associated with the replacement of ANFO with a propellant, results in a significant reduction in the fuel oil requirements of the explosive composition, while substantially maintaining the propellant energy.

The preferred particle size of the throwing agent is in the range of 1 to 10 mm in diameter. The optimal particle size depends on the charge size (diameter). In large-diameter blastholes (such as blastholes for blasting overburden or coal seams (150 to 320 mm blastholes)), it is advisable to use larger-diameter propellants. The preferred particle size is about 1 to 2 mm. Ammonium sulfate nitrate (fertilizer grade) is a preferred slinging agent and is readily available as 85% particle size in the 2 to 5 mm range with an average particle size of 2.8 to 3.5 mm.

The compositions of the present invention can be prepared by mixing a throwing agent with a premixed ammonium nitrate/fuel oil composition. Alternatively, the compositions of the present invention can be prepared by mixing porous ammonium nitrate particles with a throwing agent and subsequently mixing this mixture with fuel oil.

While not wishing to be bound by theory, applicants have performed a number of theoretical calculations to evaluate the possible performance of the explosive compositions of the present invention. In Tables 1 and 2 below, theoretical calculations obtained using the "Ideal Explosives Code" ("IDEX") to calculate the properties of ideal explosives are reproduced.

Table 1 ASN/ANFO(98/2) 0/100 20/80 30/70 40/60 50/50 60/40 _O2 balance 12.89 7.87 5.35 2.84 0.33 -2.18 Density(g/cc) 0.82 0.86 0.89 0.91 0.94 0.96 Reaction heat (MJ/kg) 2.37 2.1 1.97 1.84 1.7 1.57 Ideal VoD(m/s) 4476 4481 4490 4506 4529 4550 CJ temperature (K) 2307 2147 2068 1988 1905 1822 Gas volume (L/kg) 1080 1050 1040 1020 1010 994 REE, to 100MPa (standard) 68 62 59 56 53 49 RBS, to 100MPa (standard) 70 67 65 64 62 59

Table 2 ASN/ANFO(94/6) 0/100 20/80 30/70 40/60 50/50 60/40 _O2 balance -1.32 -3.5 -4.59 -5.68 -6.77 -7.86 Density(g/cc) 0.82 0.86 0.89 0.91 0.94 0.96 Reaction heat (MJ/kg) 3.82 3.13 2.8 2047 2.14 1.8 Ideal VoD(m/s) 1288 1227 1197 1166 1133 1096 CJ temperature (K) 3041 2676 2499 2318 2131 1937 Gas volume (L/kg) 1070 1050 1040 1020 1010 1000 REE, to 100MPa (standard) 102 87 79 71 64 56 RBS, to 100MPa (standard) 105 94 87 81 75 68

While not wishing to be bound by theory, it is believed that the propellant plays an important role in the detonation reaction process. The main effects are on the rate of energy release, degree of combustion and gas production.

The rate of energy release is controlled by the detonation velocity and the length of the reaction zone. It is believed that the addition of the propellant had a delayed effect on detonation. The reduction of VOD allows more energy to be used as throwing energy in the rock fracture process.

It is believed that the reduction of VOD is achieved by the decomposition reaction of ammonium nitrate occurring during the chemical interaction, and then absorbing the heat released during the decomposition of competing reactions. The detonation temperature is also reduced in the compositions of the present invention.

It can be considered that the critical diameter of the drug zone is a function of the length of the reaction zone when the throwing agent is added. The reaction zone length is very short (2-10 mm) for fast detonating explosives and very long (35-37 mm) for slower detonating explosives. We have found that a significant slowing of the reactions within the blast front allows more energy to be used for the expansion of the residual gas behind the C-J plane.

The addition of so-called inert substances, such as sodium chloride, to explosive compositions results in a reduction in VOD which is generally proportional to the amount of the substance added. However, the main difference between an inert substance and a propellant is that the inert substance does not produce gas when detonated. Contrary to the present invention, the addition of an inert substance results in a reduction in the total gas volume per kilogram of explosive composition.

We believe that the materials specified in the present invention play an important role in the decomposition process of ammonium nitrate explosives.

It can be considered that the rate-determining step of ammonium nitrate combustion is the decomposition reaction of ammonia gas and nitric acid;

(1)

    ＜

In our opinion, the throwing agent inhibits or delays the above-mentioned reaction process through the following factors:

(i) Decomposition produces excessive ammonia gas, so that the above decomposition equilibrium is obviously shifted to the left, for example

(2)

Ammonium oxalate > ammonia + oxalic acid

(ii) Urea, dicyandiamide or other reducing substances are mixed with nitric acid or nitrogen oxides generated during the decomposition of ammonium nitrate in reaction (1). It is believed that unoxidized ammonia gas will accumulate in the reaction zone and the combustion process in reaction (1) will be inhibited or delayed.

(3)

Nitric acid + urea > urea nitrate

Therefore, it can be considered that the throwing agent acts as a retarder in the decomposition reaction of ammonium nitrate. Reactions (2) and (3) shift the equilibrium of reaction (1) to the left, so it can be considered that they control the rate of energy release.

The interaction of the throwing agent with the ammonium nitrate blasting agent allows the following reactions to proceed completely:

(4)

It is believed that pushing reaction (4) toward exotherm may be due to the removal of excess oxygen by reacting with ammonia gas produced by the decomposition of the retarder in reaction (2).

(5)

Even small amounts of combustible substances can prevent exothermic decomposition, which releases significant heat, from proceeding.

It is believed that the decomposition into gaseous components can be facilitated by the use of ammonium salts of weak acids, ie ammonium salts with lower decomposition temperatures (by reaction 2).

Ammonium nitrate is a highly oxygenated molecule, containing one oxygen per molecule in excess of that required for complete combustion of its hydrogen (via reaction 4).

When heat is present, this excess oxygen is then available for oxidation of the hydrogen atoms of the amino groups in the added ammonium salt (via reaction 5). The oxidation of ammonia (in ammonium salts) generates the heat required for the conversion of acid groups (in ammonium salts) to gaseous products.

(6)

In addition to the above, the decomposition of ammonium nitrate into ammonia gas and nitric acid also requires heat.

(1)

The addition of propellant to ANFO-based blasting agents according to the present invention appears to have a retarding and slightly desensitizing effect on the explosive decomposition process. In addition, the throwing agent appears to provide a thermal energy surplus due to the oxidation of the amino groups (see reaction (5) above) and a thermal energy deficit due to the acid group decomposition reaction.

Throwing agents are believed to have a significant effect on chemical reactions and thermochemistry. The rate of chemical energy release is extremely important in the rock-destroying performance of explosives. The energy distribution of fragmentation energy and throw energy determines the ability of an explosive to move material around it.

The formulations of the present invention effectively control the transfer of throwing energy by slowing down the chemical reactions in the blast front (visible by the reduction of the VOD value and the extension of the length of the reaction zone (critical diameter)). In addition, the composition provides a substantial amount of gas and is therefore advantageous for efficient blasting in soft overburden and coal seam applications.

It is believed that the propellant generates a large number of gas molecules during detonation by reacting with ammonium nitrate spherical particles.

Direct oxidation of fuel oil by spherical ammonium nitrate particles produces large quantities of very hot, and therefore often very energetic, gases.

Advantageously, the present invention provides an easily adjustable explosive composition which can control the rate of energy release while maintaining the production of large volumes of gas. Using the compositions of the present invention, pre-drilled boreholes can be loaded with explosive compositions having specifically selected energy release rates for each borehole or even for different regions within each borehole. Utilizing the energy-adjustable explosives of the present invention provides better control over the location of overburden fractures and potentially reduces or eliminates backside fractures of blastholes.

Advantageously, the composition of the present invention can be made to have different energy and energy release by changing the ratio of the propelling agent incorporated into the explosive composition at the time of production and by pre-estimating the loading of the explosive composition into the borehole speed. ANFO-based explosive compositions are usually produced by mixing ammonium nitrate pellets with fuel oil on-site by bulk trucks. The method of in situ production of ANFO based explosive compositions is easily adapted to produce the explosive compositions of the present invention. The ammonium nitrate particulate material and propellant may be premixed and the explosive composition of the present invention may be produced in the usual manner.

Advantageously, the mobile explosive production facility may also include a storage facility, so that the amount of propellant can be conveniently controlled by controlling the rate at which the propellant is metered into the explosive production process. This makes it easy to vary the composition of the explosive from borehole to borehole and within any particular borehole. Local variations in blast area geology can also be taken into account by providing appropriate energy release (even within a blasthole).

The propellant can be incorporated into the ANFO-based explosive composition in such a way that the propellant is mixed with the ammonium nitrate particles prior to incorporation into the fuel oil, or the propellant can be incorporated into the ANFO composition already mixed.

Advantageously, the compositions of the present invention reduce the generation of coal fines, reduce overburst, improve formation and placement of rock overburden, thereby providing enhanced drag marking and earth excavation efficiency, and potentially eliminating ground reaming.

We have also found that the incorporation of a propellant reduces the amount of fuel oil in the explosive composition. Typically, the ammonium nitrate fuel oil composition is oxygen balanced with 94% by weight porous ammonium nitrate spherical particles and 6% by weight fuel oil. Fuel oil is the most expensive component, so by incorporating a gas generating agent according to the present invention, the amount of fuel oil required can be reduced. For example, it is believed that effective blasting can be obtained with a 97:3 ANFO composition combined with a propellant. In fact, we have found that the selection of slinging agents such as urea and other reducing agents can eliminate the need for fuel oil in blasting agents.

Although the ANFO explosive compositions of the present invention may be used alone, these explosives may also be used in admixture with emulsion or hydrogel explosives known in the art.

Throughout the description of this application and the following claims, unless the content requires otherwise, the word "comprising" should be understood as meaning including one or more complete things or steps described, but not excluding any other one or more complete thing or step.

The invention will now be further described with reference to the following non-limiting examples.

Examples 1 to 3

Comparative Examples CE1 and CE2

Mix the ANFO blasting agent prepared from ammonium nitrate spherical particles and fuel oil in the proportions shown in Table 3 with ammonium sulfate nitrate (if any). The densities of the resulting blasting agents are shown in Table 3. Examples 1 to 3 and Comparative Example CE2 had an AN:FO ratio of 96:4.

table 3 Example number CE1 CE2 1 2 3 Ammonium nitrate spherical particles ¹ 94 96 67.2(96) 57.6(96) 48.0(96) fuel oil ² 6 4 2.8(4) 2.4(4) 2.0(4) ammonium sulfate nitrate - - 30.0 40.0 50.0 Density(g/cc) 0.80 0.82 0.86 0.88 0.89

1. Ammonium nitrate spherical particles:

NITROPRIL ^TM Explosive Grade Ammonium Nitrate Granules, supplied by Orica Australia Pty Ltd

2. Fuel oil: No. 2 fuel oil

3. Ammonium sulfate nitrate:

Provided by BASF

60% ammonium sulfate

40% ammonium nitrate

Then, test the dry blasting agent to measure the speed of detonation. Two lengths of optical fiber with clean cut ends are inserted into the explosive in the test cardboard tube, separated by a known distance (typically 100mm). Connect the other ends of the two lengths of fiber to the two connectors of an electronic timer capable of timing the light pulse from start to mark stop signal. The optical fiber located in the charge bag near the priming agent is the starting signal for the timer and should be connected to connector 0. Another fiber stops the timer and should be connected to connector 1.

A timer times the light pulse as the blast front passes through the start and end fibers, expressing this time in milliseconds. The detonation velocity is calculated from the time required for the detonation wavefront to travel from the first fiber segment to the second fiber segment.

Explosive charges contained in cardboard tubes of different diameters are detonated. The critical diameter is determined by the smallest charge diameter to achieve 100% detonation of the charge.

Calculate the relative effective energy available, the relative bulk energy available, and the gas volume.

The results of these tests are shown in Table 4.

Table 4 Example number CE1 CE2 1 2 3 VOD(km/s) Unconstrained cartridge diameter 120mm 3.3 2.7 1.9 fail fail 152mm 3.6 3.0 2.4 1.6 1.3 185mm 3.9 3.2 2.6 2.2 1.5 200mm 4.3 3.3 2.8 2.4 2.1 250mm 4.5 / 3.1 / 2.4 Critical Diameter (mm) >100 >100 >120 >150 >150 Available Energy: Relatively Effective (ANFO) 100 87 71 66 60 Relative volume (ANFO) 100 89 76 73 67 Gas volume (L/kg) 1080 1070 1040 1020 1010

Examples 4 to 8

Comparative example CE3

Following the procedure described in Example 1, a dry ANFO blaster was prepared from the ingredients listed in Table 5.

table 5 Example number CE3 4 5 6 7 8 Ammonium nitrate spherical particles ¹ 94 67.2(96) 79.2(97) 57.6(96) 73.6(97) 82.2(97) fuel oil ² 6 2.8(4) 2.8(3) 2.4(4) 2.4(3) 2.8(3) ammonium sulfate nitrate / 30.0 / 40.0 / / Ammonium sulfate ⁴ / / 18.0 / 24.0 / Ammonium bicarbonate ⁵ / / / / / 15.0 Density(g/cc) 0.80 0.87 0.88 0.88 0.89 0.88

1. Ammonium nitrate spherical particles:

NITROPRIL ^TM Explosive Grade Ammonium Nitrate Granules, supplied by Orica Australia Pty Ltd

2. Fuel oil: No. 2 fuel oil

3. Ammonium sulfate nitrate:

Provided by BASF

60% ammonium sulfate

40% ammonium nitrate

4. Ammonium sulfate: provided by Incitec Industrial Chemicals

5. Ammonium bicarbonate: Provided by Spectrum Distributors

The dry blasting agent, which is substantially oxygen equilibrated, was tested according to the procedure described in Example 1 and the results are shown in Table 6.

Table 6 Example number CE3 4 5 6 7 8 VOD(km/s) Unconstrained cartridge diameter 120 mm 3.3 f f / / 2.8 150 mm 3.6 2.1 1.6 f f 3.2 185 mm 3.9 2.6 2.3 1.6 1.5 3.1 Critical Diameter (mm) >100 >120 >120 >150 >150 >200 Available Energy: Relatively Effective (ANFO) 100 71 72 66 67 / Relative volume (ANFO) 100 76 77 73 74 / Gas volume (L/kg) 1080 1040 1040 1020 1040 960

Examples 9 to 11

Comparative Examples CE4 and CE5

Following the procedure described in Example 1, a dry ANFO blaster was prepared from the ingredients listed in Table 7.

Table 7 Example number CE4 CE5 9 10 11 Ammonium nitrate spherical particles ¹ 94.0 96.0 67.2(96) 48.0(96) 80.0 fuel oil ² 6.0 4.0 2.8(4) 2.0(4) / Ammonium nitrate ⁶ / / 24.0 ^* 40.0 ^* / Urea 7 / / 6.0 ^* 10.0 ^* 20.0 Density(g/cc) 0.80 0.82 0.80 0.78 0.79

1. Ammonium nitrate spherical particles:

NITROPRIL ^TM Explosive Grade Ammonium Nitrate Granules, supplied by Orica Australia Pty Ltd

2. Fuel oil: No. 2 fuel oil

3. Ammonium sulfate nitrate:

Provided by BASF

60% ammonium sulfate

40% ammonium nitrate

6. Ammonium nitrate: provided by Incitec Industrial Chemicals

7. Urea: Provided by Incitec Industrial Chemicals

The dry blasting agent was tested according to the procedure described in Example 1, and the results are shown in Table 8.

Table 8 Example number CE4 CE5 9 10 11 VOD(g/cc) Unconstrained cartridge diameter 90mm f f 2.3 1.8 100mm / / 2.5 / 120mm 3.3 2.7 2.9 2.6 152 mm 3.6 3.0 3.2 2.9 185mm 3.9 3.2 3.3 2.9 f 200mm 4.3 3.3 3.2 / 2.1 250mm 4.5 / 3.5 3.3 2.8 Critical Diameter (mm) >100 >100 >60 >80 >200 Gas volume (L/kg) 1080 1070 1070 1070 1070

Claims (16)

1. An explosive composition comprising ammonium nitrate prills, fuel oil and a heave agent, wherein the heave agent is selected from the group consisting of inorganic ammonium compounds, organic ammonium compounds, amides, carbonates and nitrates, with the proviso that the heave agent is not ammonium nitrate, wherein the heave agent is present in an amount greater than 5% by weight.

2. An explosive composition accordingto claim 1 wherein the heave agent is an inorganic ammonium compound selected from the group consisting of ammonium sulfate, ammonium chloride, ammonium carbonate, ammonium bicarbonate, ammonium thiosulfate, ammonium thiocyanate, ammonium sulphonate and ammonium phosphate.

3. An explosive composition according to claim 1 or 2 wherein the heave agent is an inorganic ammonium compound selected from the group consisting of ammonium sulphate nitrate, ammonium phosphate nitrate and calcium ammonium nitrate.

4. An explosive composition according to any one of claims 1 to 3 wherein the heave agent is ammonium sulphate nitrate.

5. An explosive composition according to claim 1 wherein the heave agent is an organic ammonium compound selected from the group consisting of ammonium acetate, ammonium oxalate, ammonium tartrate and ammonium citrate.

6. An explosive composition according to claim 1 wherein the heave agent is a carbonate selected from the group consisting of calcium carbonate and sodium carbonate.

7. An explosive composition according to claim 1 wherein the heave agent is calcium nitrate and is present in an amount of more than 20% by weight of the explosive composition.

8. An explosive composition according to claim 1 wherein the heave agent is an amide selected from urea and dicyandiamide.

9. An explosive composition according to claim 8 wherein the heave agent is urea.

10.An explosive composition according to any one of claims 1 to 9 wherein the heave agent is present in the explosive composition in an amount of from 20 to 40 weight percent.

11. An explosive composition according to any one of claims 1 to 10 wherein the size of the heave agent is in the range 1 to 10 mm in diameter.

12. The explosive composition of claim 11 wherein the particle size is in the range of 1 to 2 mm.

13. An explosive composition according to any one of claims 1 to 12 wherein the fuel oil is present in an amount of from 3 to 6% by weight, based on the weight of ammonium nitrate and fuel oil.

14. An explosive composition according to any one of claims 1 to 12 wherein the weight ratio of ammonium nitrate to fuel oil is in the range 97: 3 to 96: 4.

15. An explosive composition according to any one of claims 1 to 14 wherein the fuel oil is selected from diesel No. 2 fuel.

16. An explosive composition substantially as hereinbefore described with reference to the accompanying drawings and/or examples.