NO890869L - EXPLOSION MIXTURE, AND PROCEDURE FOR ITS PREPARATION. - Google Patents

Description

The present invention relates to an explosive mixture and in particular such a mixture comprising a mixture of an emulsion explosive and solid ammonium nitrate particles.

Emulsion explosive mixtures have been well received in the explosives industry due to their excellent blasting properties and ease of handling. Emulsion explosive mixtures now in common use in industry were first described in the US. 3,447,978 and comprises as components: (a) a discontinuous, aqueous phase comprising separated droplets of an aqueous solution of inorganic, oxygen-releasing salts, (b) a continuous, water-immiscible, organic phase in which the droplets are dispersed, ( c) an emulsifier which forms an emulsion of the droplets of oxidizing salt solution in the continuous, organic phase and (d) a discontinuous gas phase.

More recently, explosive mixtures comprising a mixture of a water-in-oil emulsion and a solid, particulate ammonium nitrate (AN), such as ammonium nitrate "prills" or ammonium nitrate "prills" coated with fuel oil (referred to as ANFO) have become popular due to the reductions in costs due to the incorporation of a significant proportion, for example 5 to 50% AN.

Preparations comprising mixtures of a water-in-oil emulsion and AN (or ANFO) are described, for example, in Australian Patent Application No. 29408/71 and US Patents 3,161,551 and 4,357,184. A serious problem with prior art mixtures is evident when the mixtures are loaded into wet boreholes.

Although the tendency for solid AN prill to break up or dissolve in water is somewhat reduced by the presence of the emulsion component, collar charging with previously known emulsion/prill mixtures in water-containing boreholes results in a significant reduction in blasting performance.

As a result, it has heretofore been necessary when emulsion/AN mixtures are charged into water-containing boreholes to pump the product to the bottom of the hole using a long delivery hose to fill the hole by moving the water above the rising explosive column.

However, this pumping technique does not allow the fast loading rates that can be achieved when the mixtures are loaded from the top of the borehole using techniques such as spiral drawdown. Often those using such explosives, in addition to having to accept a slower charge rate in wet boreholes, also had to maintain two sets of equipment for charging boreholes depending on the prevailing weather conditions.

It has now been found that by choosing a water-in-oil emulsion

with a viscosity in the range of from 25,000 to 60,000 cP, the water resistance of a mixture of water-in-oil emulsion and solid, particulate ammonium nitrate is significantly increased while the mixture maintains a consistency suitable for collar charging.

There is thus provided an explosive mixture comprising a mixture of 45 to 95% by weight of the mixture of a water-in-oil emulsion comprising a discontinuous, aqueous phase comprising at least one oxygen-releasing salt, a continuous, water-immiscible, organic phase and a water -in-oil emulsifier,

and 5 to 55% by weight of the mixture of solid particulate ammonium nitrate and wherein the Brookfield viscosity of the water-in-oil emulsion is in the range of from 25,000 to 60,000 cP.

When used here, the term Brookfield viscosity refers to the viscosity measured at 60°C using a Brookfield RVT viscometer with spindle no.7 at 50 rpm.

my. It is preferred that the Brookfield viscosity of the water-in-oil emulsion is in the range of 28,000 to 40,000 cP.

A number of factors affect the viscosity of the emulsion component, such as the nature of the oil and the water-in-oil emulsifier, as well as their interaction. These features can be balanced without too much experimentation to provide a Brookfield viscosity within the characteristic range of from 25,000 to 60,000 cP.

The emulsion explosive component in the mixture may contain auxiliaries, for example the void agent such as gas bubbles, porous particles or balloons to reduce the density agent which stabilizes the void agents and solid particulate material such as carbon or aluminium.

Such materials affect the viscosity of the mixture in the same way as the solid, particulate ammonium nitrate and the water-in-oil emulsion's Brookfield viscosity is therefore determined on the water-in-oil emulsion free of auxiliaries.

The water-immiscible, organic phase component in the water-in-oil emulsion in the mixture according to the invention perceives the continuous "oil" phase in the water-in-oil emulsion and is the fuel. Examples of organic fuels include aliphatic, alicyclic and aromatic compounds and mixtures thereof which are in a liquid state at the composition temperature. Suitable organic fuels can be selected from fuel oil, diesel oil, heating oil, distillate, petroleum, naphtha, wax (for example microcrystalline wax, paraffin wax and crude paraffin), paraffin oils, benzene, toluene, xylenes, asphalt materials, polymeric oils such as polymers of olefins with low molecular weight, animal oils, fish oils and other mineral, hydrocarbon or fatty oils and mixtures thereof. Preferred organic fuels are liquid hydrocarbons generally referred to as petroleum distillates, such as gasoline, petroleum, fuel oils, heating oils and paraffin oils.

The organic fuel in the continuous phase of the water-in-oil emulsion component typically comprises from 2 to 15% by weight and preferably 3 to 10% by weight of the water-in-oil emulsion component in the explosive mixture according to the invention.

Typically, it has been found that oils having a viscosity in the range of from 4 to 1,000 and preferably 6 to 200 centi-stoke are particularly suitable for providing a water-in-oil emulsion with the characteristic viscosity range of from 25,000 to 60,000 cP. It is particularly preferred that the organic fuel in the emulsion component of the mixtures according to the invention comprises at least one paraffin oil.

It has generally been practice in the field to use diesel oil or fuel oil no. 2 in the emulsion phase of the emulsion/AN mixtures. However, it has been found that the use of paraffin oil is particularly suitable for preparing mixtures with a high resistance to water absorption.

The emulsifier in the water-in-oil emulsion can be selected from a wide range of emulsifiers known in the art. Examples of emulsifiers include alcohol alkoxylates, phenol alkoxylates, poly(oxyalkylene) glycols, poly(oxyalkylene) fatty acid esters, aminal oxylates, fatty acid esters of sorbitol and glycerol, fatty acid salts, sorbitan esters, poly(oxyalkylene) sorbitan esters, fatty amino alkylates, poly(oxyalkylene) glycol esters , fatty acid amides, fatty acid amide oxylates, fatty amines, quaternary amines, alkyloxazolines, alkenyloxazolines, imidazolines, alkylsulfonates, alkylarylsulfonates, alkylsulfosuccinates, alkylphosphates, alkenylphosphates, phosphate esters, lecithin, copolymers of poly(oxyalkylene)glycols and poly(12-hydroxystearic acid) and mixtures thereof. Among the preferred emulsifiers are 2-alkyl- and 2-alkenyl-4,4'-bis(hydroxymethyl)oxazoline, the fatty acid esters of sorbitol, lecithin, copolymers of poly(oxyalkylene)glycols and poly(12-hydroxystearic acid) and mixtures thereof and in particular sorbitan mono-oleate, sorbitan sesqui-oletate, 2-oleyl-4,4'-bis(hydroxymethyl)oxazoline, mixture of sorbitan sesquioleate, lecithin and a copolymer of poly(oxy-alkylene) glycol and poly(12-hydroxystearic acid) , poly[alk(en)yl]-succinic acid and derivatives thereof, and mixtures thereof.

Although a range of emulsifiers can be used in the preparation of the compositions according to the invention, it has been found that a particularly high water resistance is achieved when the water-in-oil emulsion component has a viscosity in the range of 25,000 to 60,000 cP and the emulsifier component comprises a condensation product of an amine and a poly[alk(en)yl]succinic acid and/or anhydride.

Typical examples of condensation products of an amine and poly[alk(en)yl]succinic acid and/or anhydride may include esters, imides, amides and mixtures thereof. Preferably, said emulsifier has an average molecular weight in the range of 400 to 5,000.

In said poly[alk(en)yl]succinic acid-based emulsifier, it is preferred that the hydrocarbon chain is obtained by polymerization of a mono-olefin and the polymer chain will generally contain from 40 to 500 carbon atoms.

Preferably, the poly[alk(en)yl] part is obtained from olefins containing from 2 to 6 carbon atoms and in particular from ethylene, propylene, 1-butene and isobutene. The emulsifier can be obtained from poly[alk(en)yl]succinic anhydride. Such emulsifier derivatives are described in Australian Patent Application No. 40006/85.

Such derivatives are commercially available materials, which are prepared by an addition reaction between a polyolefin containing an unsaturated end group and maleic anhydride, optionally in the presence of a halogen-containing catalyst. The succinic acid or anhydride residue in the above compounds can be reacted to introduce a polar group. In general, said polar group is monomeric, although oligomeric groups containing no more than approx. 10 repeated units can be used. Examples of suitable polar groups may include polar groups obtained from polyols such as glycerol, pentaerythritol and sorbitol or an internal anhydride thereof (for example sorbitan), from amines such as ethylenediamine, tetraethylenetriamine and dimethylaminopropylamine and from heterocyclic compounds such as oxazoline or imidazoline. Suitable oligomeric groups include short-chain poly(oxyethylene) groups (i.e., those containing up to 10 ethylene oxide units).

Formation of emulsifiers for use according to the invention can be carried out by conventional methods depending on their chemical nature.

To prepare a derivative of poly(alk(en)yl)succinic acid comprising a polar group obtained from an alcohol or an amine, the acidic group or anhydride thereof may be reacted with the hydroxyl or amino group by heating the two components together in a suitable solvent in the presence of a catalyst if desired.

The emulsifiers may be of a non-ionic character, but they may alternatively be anionic or cationic in nature, as for example when the hydrophilic part contains the residue of a polyamine or a heterocyclic compound.

Preferred emulsifiers are poly(isobutylene) succinic anhydride derivatives and most preferably condensates thereof with amines such as ethanolamine.

Typically, the emulsifier component in the mixture according to the present invention comprises up to 5% by weight of the emulsion component in the mixture. Higher proportions of emulsifier can be used and can serve as an additional fuel for the mixture, but in general it is not necessary to add more than 5% by weight of emulsifier to achieve the desired effect.

In particular, it has been found that the use of a poly(isobutylene) succinic anhydride/amine condensation product in combination with a paraffin oil in the mixture according to the invention provides particularly good water resistance and is well suited for collar charging in significant volumes of water.

It is preferred that the mixture according to the invention further comprises voiding agents which can for example be in the form of fine gas bubbles dispersed in the mixture, hollow particles (often referred to as microballoons), porous particles or mixtures thereof.

Techniques for the production of gas-added emulsion explosives are well known in the art and include mechanical stirring, injection or bubbling of the gas through the mixture or chemical generation of the gas in situ.

The preferred method for introducing a gas phase is by in situ chemical gas formation. Suitable chemicals for in situ generation of gas bubbles include peroxides, such as hydrogen peroxide, peroxide nitrates, such as sodium nitrite, nitrosamines, such as N,N'-dinitroso-pentamethylenetetramine, alkali metal borohydrides such as sodium carbonate. Catalytic agents such as thiocyanate or thiourea can be used to accelerate the decomposition of a nitrite gas supply agent.

When used, the voiding agent can be added before or after the emulsion is mixed with the ammonium nitrate particles. However, it is generally preferred that the voiding agent be added to a mixture of the emulsion and the particles.

Typically, the voiding agent comprises 0.05 to 50% by volume of the emulsion explosive component at ambient temperature and pressure. More preferably, the voiding agent is present when used, in the range of 10 to 30% by volume of the emulsion explosive component and preferably the preferred bubble size of occluded gas is below 200 µm. More preferably, at least 50% of the gas component will be in the form of bubbles or microspheres with an internal diameter of 20 to 200 pm.

It has been found that the presence of a dispersed gas phase significantly improved the water resistance of the composition according to the invention, when a gas bubble stabilizing agent is also present.

Such means are described in co-pending Australian Patent Application No. 40968/65.

There is thus provided an explosive mixture comprising from 45 to 95 percent by weight of the total mixture of a water-in-oil emulsion comprising a discontinuous, aqueous phase comprising at least one oxygen-releasing salt, a continuous, water-immiscible, organic phase, a water-in -oil emulsifier and at least one agent which can facilitate the production of gas bubbles in the presence of said water-immiscible, organic phase and 5 to 55 percent by weight of the total mixture of solid, particulate ammonium nitrate, and where said water-in-oil emulsifier is selected from the group consisting of condensation products of an amine and a poly[alk(en)yl]succinic acid and/or -anhydride and mixtures thereof.

The ability of various agents to facilitate the production of small gas bubbles in the mixture according to the invention can be determined by means of a foam stabilization test.

In another aspect of the invention, an explosive mixture is thus provided as described above, where the agent referred to is further characterized in that it has properties that provide a suitable stabilizing effect and which is determined by means of a foam stabilization test as described below. In the aforementioned foam stabilization test, 0.2 parts by weight of active ingredient of the relevant agent or mixture of agents to be tested is added to and mixed with 100 parts by weight of diesel fuel. 5 ml of the mixture is placed in a graduated cylindrical vessel of 15 ml internal diameter. The mixture is shaken for 15 seconds. A foam forms on the surface of the mixture. The volume (V5) of the foam is measured 5 minutes after the mixture has been shaken using graduations on the vessel. The foam volume (V60) is measured again after 60 min. after the shaking is finished, the vessel and mixture being kept at a temperature of 18 to 22°C during this time. A foam stability parameter ø60/5 is calculated from the foam volumes using the formula

It has been found that the agents or mixtures of agents in which the V5 value was equal to or greater than 1 cubic centimeter and had a ø<60>/<5> equal to or greater than 0.3 provide the desired gas bubble stabilizing effect in this embodiment of the invention. Foam stabilizers which are preferred for use in the compositions according to the invention are therefore those which have a V5~ value equal to or greater than 1 cubic centimeter and a 0.3 value equal to or greater than 0.3, determined by means of the foam stabilization test described above.

The most preferred gas stabilizing agents are nonionic fluoroalkyl esters available for example under the trademark "FLUORAD".

When the gas bubble stabilizer is used, it will typically be present in the range of 0.0001 to 5.0% by weight of the emulsion component in the mixture and preferably in the range of 0.001 to 1%.

Suitable oxygen-releasing salts for use in the aqueous phase of the mixture according to the invention include the alkali and alkaline earth metal nitrates, chlorates and perchlorates, ammonium nitrate, ammonium chlorate, ammonium perchlorate and mixtures thereof. The preferred oxygen releasing salts include ammonium nitrate, sodium nitrate and calcium nitrate. More preferably, the oxygen-releasing salt comprises ammonium nitrate or a mixture of ammonium nitrate and sodium or calcium nitrates.

The oxygen-releasing salt in the emulsion component in the mixtures according to the present invention comprises from 45 to 95% and preferably from 60 to 90% by weight of the total emulsion component in the mixture. In mixtures where the oxygen-releasing salt comprises a mixture of ammonium nitrate and sodium nitrate, the preferred composition range for such a mixture is from 5 to 80 parts sodium nitrate for every 100 parts ammonium nitrate. In the preferred mixtures according to the present invention, the oxygen-releasing salt component therefore comprises from 45 to 90% by weight (of the emulsion component) ammonium nitrate or mixtures of from 0 to 40% by weight (of the emulsion component) ammonium nitrate.

Typically, the amount of water used in the mixture according to the present invention is in the range of from 1 to 30% by weight of the emulsion component. Preferably, the amount used is from 5 to 25%, and more preferably from 6 to 20% by weight of the emulsion component.

Preferably the ratio of water-in-oil emulsion: solid particulate ammonium nitrate is in the range of 45:55 to 70:30 and more preferably 45:55 to 60:40.

The term ammonium nitrate particles is used here to include mixtures of "prilled" ammonium nitrate, which may optionally be coated with a fuel component as, for example, in the case of the well-known ANFO mixtures.

Typically, the solid, particulate ammonium nitrate will comprise up to 10% weight/weight of fuel oil, as approx. 6% is preferred. At approx. 6%, the solid, particulate ammonium nitrate is essentially oxygen-balanced.

In a further embodiment of the invention, a method for producing the mixture described above is provided, the method comprising mixing from 45 to 95 parts by weight of a water-in-oil emulsion and from 5 to 55 parts by weight of a solid, particulate ammonium nitrate.

The water-in-oil emulsion can be prepared in a preliminary process comprising: Dissolving the oxygen-releasing salt in water at a temperature above the "fudge<11> point of the salt solution, preferably at a temperature in the range of 25 to 110°, to provide an aqueous salt solution;

combining the aqueous salt solution, the water-immiscible organic phase and the water-in-oil emulsifier with rapid mixing to form a water-in-oil emulsion and mixing until the emulsion is smooth.

In a preferred embodiment of this method, the method further comprises mixing the emulsion component or one or more components thereof with a gas bubble stabilizing agent and an agent capable of generating gas bubbles in situ.

As described above, the present invention provides significant advantages when charging water-containing boreholes.

There is therefore also provided a method for charging a water-containing borehole comprising pouring an explosive as described above into the water-containing borehole from a position near the collar of the water-containing borehole.

The term "pouring" means that the explosive mixture is released from its container or means of transport. It is preferred that the explosive mixture is transported by transport screw to the collar of the borehole and released from a position above the collar.

There is also provided a method for blasting in a water-containing borehole comprising the steps of charging a water-containing borehole as described above and detonating the explosive.

It is a particular advantage of the mixtures according to the invention that they detonate well even when poured from the vicinity of the borehole collar into significant water depths.

Typically, the mixtures according to the invention can be detonated well even when the explosive/water weight ratio is less than 10 and preferably in the range of from 1/1 to 6/1.

There is also provided a method for blasting comprising detonating an explosive mixture as described above in water, where the weight ratio between explosive and water is less than 10 and preferably in the range of from 1/1 to 6/1.

The invention shall now be illustrated, but in no way limited to, the following examples in which the term Brookfield viscosity is used to refer to measurements made at 20"C using a Brookfield viscometer with spindle No. 7 at 50 rpm .

Example 1 and merging example A

The explosives in example 1 and comparative example A

with the compositions shown in table 1, was prepared using the following method.

An aqueous solution was prepared by mixing the ammonium nitrate, CN, water and acetic acid. The mixture was heated to approx. 80°C and was added to a rapidly stirred mixture of the oil and the emulsifier. When the addition was finished, stirring was continued until the emulsion was smooth (about 60 sec.).

ANFO (comprising particulate ammonium nitrate on which 6% by weight of fuel oil had been absorbed) was mixed with the emulsion and the gas stabilizer was then added with the mixture, followed by the addition of the gas forming solution. The water-in-oil emulsion of the explosive mixture of Example 1 prepared according to this method had a Brookfield viscosity of 30,000 cP.

The water-in-oil emulsion of the explosive mixture in Comparative Example A had a Brookfield viscosity of 10,000 cP.

The mixtures prepared according to the above procedure were tested as follows: The explosive (15 kg) is poured down a 4 m high (150 mm diam.) artificial borehole with a 200 mm diam. packing on the bottom containing water (15 kg). The gasket was removed and excess water from the top. The explosive was then ignited with a 400g "ANZOMEX" (trademark) igniter.

The mixture of Example 1 successfully detonated when performed in the above test, but the mixture of Comparative Example A did not detonate.

Examples 2 and 3

The explosives from examples 2 and 3 with the compositions shown in table 2 were produced using the following method.

An aqueous solution was prepared by mixing the ammonium nitrate and water. The mixture was heated to approx. 80°C and was added to a rapidly stirred mixture of the oil and the emulsifier. When the addition was finished, stirring was continued until the emulsion was smooth (approx. 60 sec.).

The ANFO (comprising particulate ammonium nitrate on which 6% by weight of fuel oil had been absorbed) was mixed with the emulsion and the MICROBALLOONS were then added by mixing.

The water-in-oil emulsion in the explosive mixture of Examples 2 and 3 had a Brookfield viscosity of 34,560 - 38,560 CP.

The mixtures from examples 2 and 3 showed little loss of AN from ANFO when immersed in water.

The mixture from Example 2 gave 88% shock when detonated in water-containing boreholes.

Example 4

The mixture from example 2 was prepared and added gas chemically to a density of 1.10 g/cm<3>.

The mixture from Example 4 gave 83% of full energy (shock and bubble) when detonated in water-containing boreholes.

Example 5

The mixture of Example 2 was prepared except that the paraffin oil was replaced with fuel oil.

The mixture from Example 5 gave 85-90% of full energy (shock and bubble) when detonated in water-containing boreholes (200 mm diam.).

Example 6

The mixture of Example 5 was prepared except that the PIBSA emulsifier was replaced with sorbitan mono-oleate.

The mixture from Example 6 gave 81-86% of full energy (shock and bubble) when detonated in water-containing boreholes (200 mm diam.).

Claims (10)

1. Explosive mixture, characterized in that it comprises a mixture of 45 to 95% by weight of the mixture of a water-in-oil emulsion comprising a discontinuous, aqueous phase comprising at least one oxygen-releasing salt, a continuous, water-immiscible, organic phase, a water-in-oil emulsifier and 5 to 55% by weight of the mixture of solid particulate ammonium nitrate, and wherein the Brookfield viscosity of the water-in-oil emulsion is in the range of 25,000 to 60,000 cP, preferably 28,000 to 40,000 cP . 2. Explosive mixture according to claim 1, characterized in that the water-in-oil emulsion comprises a discontinuous phase with a viscosity in the range of from 4 to 1000 centi-stoke, preferably 6 to 200 centi-stoke. 3. Explosive mixture according to one of claims 1 or 2, characterized in that the discontinuous phase comprises a paraffin oil. 4. Explosive mixture according to any one of claims 1 to 3, characterized in that the emulsifier comprises a condensation product of an amine and a poly[alk(en)yl] succinic acid and/or anhydride, preferably a condensation product of ethanolamine and polyisobutylene succinic anhydride. 5. Explosive mixture according to any one of claims 1 to 4, characterized in that the explosive mixture comprises: 45-95% by weight of a water-in-oil emulsion comprising a discontinuous, aqueous phase comprising at least one oxygen-releasing salt, a continuous , water-immiscible, organic phase, a water-in-oil emulsifier and at least one agent that can facilitate the production of gas bubbles in the presence of said water-immiscible, organic phase, and 5 - 55% by weight of the total mixture of solid, particulate ammonium nitrate , and where the water-in-oil emulsifier is selected from the group consisting of the condensation products of an amine and a poly[alk-(en)yl] succinic acid and/or anhydride and mixtures thereof. 6. Explosive mixture according to any one of claims 1 to 5, characterized in that the explosive mixture comprises a water-in-oil emulsion and a solid, particulate ammonium nitrate in the ratio, water-in-oil emulsion: solid, particulate ammonium nitrate, in the range 45:55 to 70:30, preferably 45:55 to 60:40. 7. Explosive mixture according to any one of claims 1 to 6, characterized in that the solid, particulate ammonium nitrate comprises fuel oil which constitutes less than 10% by weight of the solid, particulate ammonium nitrate, preferably 6% by weight of the solid, particulate ammonium nitrate. 8. Method for producing a mixture according to any one of claims 1 to 7, characterized in that 45 to 95 parts by weight of a water-in-oil emulsion is mixed with from 5 to 55 parts by weight of a solid, particulate ammonium nitrate, wherein the method preferably comprises a preliminary method which comprises: Dissolving the oxygen-releasing salt in water at a temperature above the "fudge" point of the salt solution, preferably at a temperature in the range from 25 to 110°C, to give an aqueous salt solution, Combining the aqueous salt solution, the water-immiscible organic phase and the water-in-oil emulsifier with rapid mixing to form a water-in-oil emulsion emulsion and mix until the emulsion is smooth. 9. Method for charging an explosive mixture according to any one of claims 1 to 7 in a water-containing borehole, characterized in that the explosive mixture is poured into the water-containing borehole from a position near the water-containing borehole's collar. 10. Method for blasting in a water-containing borehole, characterized in that an explosive mixture according to any one of claims 1-7 is loaded into a water-containing borehole and the explosive is detonated, the weight ratio between the explosive mixture and the water being less than 10, and more preferably, the weight ratio between the explosive mixture and the water is in the range of from 1/1 to 6/1.