IL22073A - Slurried blasting explosives - Google Patents

Description

This invention relates to improved slurried blast #ing explosives which consist essentially of one or more organic explosives and one or more inorganic oxygen-supplying salts slurried in an aqueous solution of said inorganic oxygen-supplying salts. Thus water, in an amount between about 8 and 26% by weight, is an essential ingredient of such explosive compositions.

The above slurried explosives are now well known and some of them containing trinitrotoluene (T.N.T.), ammonium nitrate (A.N.) and water are described, for example, in Canadian patent No. 619,653 issued on 9th May, 1961 to M.A.

Cook and H.E. Farnam, Jr. They have found wide acceptance and use in recent years, particularly in open-pit mining, quarrying and construction operations. They are safe to use because of their insensitivity to blasting cap detonation, economical, and because of their high borehole loading density characteristics, very powerful.

It has been found, however, that aqueous slurried explosive compositions comprising inorganic oxygen-supplying salts and particulate organic explosives frequently have poor storage properties even when containing gelling agents such as the mannogalactans suggested by G.M. Barany and J.D. Mclrvine in Canadian patent No. 617,006 dated 21st March, 1961. Over relatively short periods of time, particularly where there are wide variations in temperature during storage, for example, between daytime and night, the gel is thinned by the salts going into solution during warm periods which thinning causes the slurries to separate into solids and a supernatant liquid layer. This segregation, of course, destroys the homogeneity of the mixture, making it subject to failure to propagate in boreholes in the field. Furthermore, a homogeneous gelled ft present, for example, in boreholes as has been demonstrated by G.M. Barany and J.D. Mclrvine in the above-mentioned patent. However, when segregation of the slurries occurs, resistance to water attack and penetration is reduced and this in turn reduces the sensitivity of the composition and can result in detonation failure in use. Also, when they segregate, the salts recrystallize and bridge during cool periods causing the slurries to lose to a large degree their flowability, which property is essential in achieving the optimum borehole loading densities mentioned heretofore.

Furthermore, loss of flowability makes the slurries difficult to load, for example, by pouring into boreholes in the field. Consequently, factory manufactured explosive slurries have normally proven most attractive to the trade under conditions of short term storage at relatively low ambient temperatures, the latter factor having some tendency to reduce the segregation of the solid and liquid ingredients. It has been particularly found that under tropical climatic conditions, these slurries have a reduced -useful storage life, the ingredients tending to segregate more rapidly than in temperate climates.

It has been proposed in the above-mentioned patent .No. 617,006, to overcome the problem of segregation of ingredients by adding a critical amount of borax to mannogalactan-containing slurries to give a more cohesive gel. It is believed that the borate ions in the borax "cross-link" the mannogalactan-thickened slurries to give improved cohesiveness and provide a product of improved resistance to ingredient segregation.

However, while the addition of borax under carefully controlled conditions can give a satisfactory cohesive gelled slurry, it has been found that on an industrial scale, it has not been fails to take effect at all if the borax is added before the" mannogalactan swells or the slurry becomes firm and cohesive so quickly that it soon cannot flow and cannot be pumped or poured, into packages. In Canadian patent No. 658,202 J.D.

McIrvine proposes the use of slow dissolving fused glassy tetraborates instead of borax. These tetraborates have a delayed, cross-linking effect but like borax cross-linked slurries, the tetraborate-containing slurries tend to be less sensitive to explosive initiation than slurries which do not contain borate ions.

In another means of overcoming the problem of segregation of ingredients in explosive slurries, some users have resorted to the on-site mixing of the slurries followed by immediate loading into boreholes. However, even this procedure-may permit segregation of ingredients to take place in the boreholes unless charged boreholes are detonated without delay. Furthermore, this on-site mixing of the slurries can normally only be justified on an economic basis by the large users of explosives. The small user of explosives who is un-able to support the cost of on-site mixing and raw material storage facilities and yet wishes to take advantage of the additional power and low cost of explosive slurries, must resort to the use of a factory-manufactured and factory-packaged product.

The problem of segregation of ingredients and other disadvantages of explosive slurries, may in part be overcome by increasing the quantity of gelling agent and/or decreasing the quantity of water used in the slurry mixture. Either or both ..of these remedies will have the effect of forming a thick, f rm., product which resists segregation over long periods of storage even at elevated temperatures. Such a method, however, borehole. Additionally, the cost of the product would necessarily rise due to increased ingredient costs as well as resultant production and packaging difficulties.

It is the primary object of this invention to provide an improved slurried explosive composition which is resistant to segregation of its ingredients over long periods of storage. Other objects of the invention will appear hereinafter.

The improved slurried explosive composition of this invention comprises at least one inorganic oxygen-sup-plying salt, a particulate organic explosive, a gel-forming or thickening polysaccharide, water, a metallic chromate selected from the group consisting of sodium and potassium dichromate in an amount ranging from 0.005% to 0.1% by weight of the composition, zinc chromate in an amount ranging from 0.05% to 1.0% by weight of the composition and barium chromate in an amount ranging from 0.1% to 1.0% by weight of the composition, and optionally, a cross-link delaying agent in an amount ranging from 0.002% to 0.1% by weight of the composition.

The addition of the above metallic chromates or di-chromates in the amount indicated to an explosive slurry has the desirable effect of almost completely eliminating any tendency of the slurry to separate into solid and liquid layers in storage because the metallic chromate ion has a cross-linking effect on the gel-forming polysaccharide, thereby producing a cohesive slurry which is very resistant to water penetration. It has been found, however, that for effective cross-linking in the absence of a cross-link delaying agent, the addition to an explosive slurry of these segregation-prevention additives must normally be delayed for at least one-half hour, that is, until such time as the polysaccharide gelling agent has had an opportunity to adequ segregation-prevention additive is incorporated before the gelling agent has adequately swelled, either no thickening will occur or the rate of thickening will be greatly reduced. If, on the other hand, the cross-linking additive is added about one-half hour after the addition of the gelling agent, the gel becomes so stiff nearly immediately that it becomes extremely difficult to package. In addition, such a delay for the purpose of allowing the gelling agent to take up water has an adverse effect on the efficiency and the cost of manu- facture of slurry explosives. Because the slurry has already been allowed to become very thick, mixing at this stage will result in occlusion of air and a decrease in the sensitivity of the slurry.

On the other hand, it has been surprisingly discovered that the addition of a cross-link delaying agent in the amounts indicated has the advantageous effect of delaying the cross-linking action of the metallic chromate ion o the polysaccharide, thereby permitting the slurry to remain free-floWing for a period sufficiently long to enable easy packaging. The action of the cross-link delaying agent is such that it does not interfere with the normal swelling of the gelling agent but only delays the cross-linking action of the chromate ion. It is not necessary, therefore, to delay the incorpora-tion of the cross-linking and segregation-prevention additive into the composition so long as the cross-link delaying agent has been added to the slurry. Packaging of the slurry may begin as soon as a homogeneous and sufficiently thickened mixture has been prepared usually within 5 mins. of the polysaccharide addition. Suitable cross-link delaying agents are metal citrates, metal tartrates, citric acid, tartaric acid and gluconic acid. slurries in explosive factories under controlled and safe -V. conditions and store the mixtures for long periods of time without segregation of the solid and liquid ingredients. The" slurries so prepared possess the additional and advantageous property of remaining both cohesive and yet flowable at all but the lowest ambient temperatures encountered in the field permitting their loading to optimum density in boreholes.

Equally adavantageous as mentioned above is the delayed cross-linking characteristic of the slurries, which property permits economies in mixing, handling and packaging in the explosives factory. Additionally it has been found that slurries cross-linked using the delayed chromate system, unlike the borate cross-linked slurries disclosed in above-mentioned Canadian patent No. 658,202 which tend to be less sensitive to initiation, are slightly more sensitive than non-cross-linked slurries.

Preferred slurried blasting explosive compositions according to this invention contain from 30% to 75% by weight of at least one inorganic oxygen-supplying salt, from 15% to 40% by weight of a particulate organic explosive, from 0.2% to 2.0% by weight of a gel-forming or thickening polysaccharide, from 0.01% to 0.5% by weight of the cross-linking and segregation-preventive additive, from 0.005% to 0.05% by weight of a cross-link delaying agent and from 8% to 25% by weight of water.

A very suitable inorganic oxygen-supplying salt for inclusion in the explosive composition of this invention is ammonium nitrate. It is in some cases advantageous to replace some, suitably up to 50%, or all of the ammonium nitrate by other metal nitrates such as sodium, barium, potassium and calcium nitrates to achieve, for instance, increased strength or fluidity. A more fluid mix can also be obtained by the use of a small percentage of urea. The particle size of the inorganic oxygen-supplying salts is not critical and powdered, granulated, prilled or crystalline forms may be used or all or part of the salts may be predissolved in all or part of the water.

The organic explosives suitable for use in the blasting agents of this invention are described herein as "particulate". By "particulate" it is intended to exclude liquid explosives such as nitroglycerine and nitroglycol and to indicate that the explosive should be in a powdered, granular, flaked or pelleted form. A very suitable organic explosive is T.N.T. (trinitrotoluene) although a large class of organic explosives that can be made in particulate form is suitable for use in this invention either as such or in admixture with T.N.T. or each other but in many cases they prove more expensive than T.N.T. This class includes penta-erythritol tetranitrate (P.E.T.N.), tetryl, cyclotrimethyl-enetrinitramine (R.D.X.), pentolite (being .a mixture of approximately equal parts of T.N.T. and P.E.T.N.) and composition B (being a mixture of about 60% by weight of R.D.X. and about 40% by weight of T.N.T. , plus a little wax). Smokeless powder is also considered as an organic explosive for the purpose of this invention.

The gel-forming or thickening polysaccharides are preferably mannogalactans such as guar gum or carob seed.

The slurried explosive composition of this invention may be prepared in any suitable type of mixing equipment, but preferably the mixer should have no rapidly moving parts and should have a folding action combined with a lifting of material from the bottom of the mixer to the top. The conventional "ribbon type" mixer is particularly suitable for this purpose. A preferred mixing procedure is to mix together and water. After a few minutes of mixing, the particulate organic explosive may be added and dispersed and the crosslink delaying agent added. The gelling or thickening agent may then be added as a dry powder or mixed with a small quantity of ethylene glycol or glycerine as a dispersion medium and the whole composition mixed until homogeneous.

The desired final temperature of the mixture should be from 40° to 140°F. in order that the slurry can be packaged most satisfactorily. To achieve the desired final temperature it may be ncessary that the water ingredient be added hot or as a hot solution of one or more of the inorganic oxygen-supplying salts or, alternatively, a heated mixer may^be used.

The following Table and Figures illustrate the improved explosive composition of this invention but the latter is in no manner to be limited in scope to the embodiments described.

The compositions shown in Table were prepared in the first manner above described and placed in glass cylinders 20" high. The inches of segregated fluid at the top of the column after storage at 90°F. is shown for the times indicated. Compositions are expressed as percent by weight of total.

T A B L E Ingredients Mix 1 Mix 2 Mix 3 Mix 4 Mix 5 Mix 6 Ammonium nitrate 55.5 55.4 37.6 37.5 37.6 37.5 Sodium nitrate 8.0 8.0 23.3 23.3 18.3 18.3 Water 14.9 14.9 12.6 12.6 12.6 12.6 T.N.T. flake 10.0 10.0 12.5 12.5 — — ■ T.N. T. pellet 10.0 10.0 12.5 12.5 15.0 15.0 Smokeless powder - - - - 15.0 15.0 P.E.T.N. - — — - - - Compos tion "B" — - — - — — Guar flour 0.6 0.6 0.5 0.5 0.5 0.5 Glycol 1.0 1.0 1.0 1.0 1.0 1.0 Zinc chrornate - 0.1 — 0.1 - 0.1 Potassium dichrornate - - — — - — Potassium tartrate — — — — - — Tartaric acid~ - 0.005 - 0.005 — 0.005 Barium chrornate — — — — — — Gluconic acid — — — — — — Storage Temperature °F 90 90 90 90 90 90 Days in storage 26 47 28 68 20 50 Segregation in 20" column 1" nil 1" nil 1" 1/8" Fig. 1 illustrates the change in viscosity of two similarly cross-linked slurries, the one containing a cross-link delaying agent and the other containing no crosslink delaying agent. The compositions used were the same as that shown as Mix No. 2 in the Table. Beaker-size laboratory batches only were used. The viscosity of the compositions were determined at 3 to 5 minute intervals after the addition of the gel-forming agent by means of a Bropkfield viscometer. Line "A" illustrates the sudden change which takes place in the viscosity of a slurry when the cross-linking and segregation-prevention additive (zinc chromate) is added to a thickened slurry after about 30 minutes of the addition of the gelling agent (guar flour) , that is, after the guar has had a chance to take up water and swell. It can be seen that the viscosity change is nearly immediate reflecting a sudden cross-linking and rendering the slurry too cohesive and stiff for easy packaging. The broken line branch of line "A", called line "A-l" reflects the gradual increase in viscosity of a slurry where only a thickening agent (guar flour) has been added. Such a slurry does not crosslink and will break down into solid and liquid layers a short time after manufacture. (See Table - Mix 1) . Line "B" illustrates the gradual increase in viscosity of a slurry containing zinc chromate as a cross-linking and segregation-prevention additive and tartaric acid as a cross-link delaying agent. The increase in viscosity of such a composition (due to the onset of cross-linking) occurs at from about 8 to 24 hours after the addition of the guar flour and is consequently beyond the range of the graph. The composition of line "B" remained cohesive and resistant to segregation of its ingredients for long periods after manufacture (See Table - Mix 2) , Line "C" illustrates the reduced rate of increase in viscosity of a slurry composition wherein the sparingly soluble zinc chromate and guar flour are added to the slurry at the beginning of the mixing cycle and wherein no crosslink delaying agent is employed. The lack of the cross-link delaying agent appears to effect the ability of the guar flour to take up water and produce a cohesive gel. It is suspected that the zinc chromate "ties up" at least part of the gelling agent, preventing adequate thickening. Although such a slurry eventually thickens and cross-links, because of the lower viscosity during and immediately after packaging there is danger of segregation before cross-linking occurs. Line "D" illustrates the almost complete lack of thickening and immediate segregation of a slurry composition wherein completely soluble sodium dichrornate and guar fluor are added to the slurry at the beginning of the mixing cycle and wherein no cross-link delaying agent is employed. The lack of the crosslink delaying agent appears to result in the immediate "tying up" of all of the gelling agent, almost completely preventing thickening.

Fig..2 illustrates an effect similar to that shown in Fig. 1 except that different combinations of cross-linking and segregation-prevention additives and cross-linking delaying agents are employed. Line "A" illustrates the sudden change which takes place in the viscosity of a slurry when the cross-linking and segregation-prevention additive (potassium di-chromate) is added to a thickened slurry after about 30 minutes of the addition of the gelling agent (guar flour), that is, after the guar has had a chance to take up water and swell.

It can be seen that the viscosity change is nearly immediate reflecting a sudden cross-linking and rendering the slurry increase in viscosity of a slurry where only a gelling agent' (guar flour) has been added. Such a slurry does not cross-link and will break down into solid and liquid layers a short time after manufacture (See Table - Mix 1) . Line "B" illustrates the gradual increase in viscosity of a slurry containing potassium dichromate as a cross-linking and segregation-prevention additive and potassium tartrate as a cross-link delaying agent. The increase in viscosity of such a composition (due to the onset of cross-linking) occurs at from about 13 to 17 hours after the addition of the guar flour and is shown in Fig. 3.

The composition of line "B" remained cohesive and resistant to segregation of its ingredients for long periods after manufacture (See Table - Mix 7) .

Claims (12)

■ Having now particularly described and ascertained the nature of our said invention and in what manner the same is to b performed, we declare that what we claim is: SLURRE frt-R$TJN&

1. An explosive composition resistant to segregation of its ingredients over long periods of storage consisting essentially of a thickened aqueous slurry of solid explosive material, said slurry comprising at least one inorganic oxygen- supplying salt, at least one particulate organic explosive, a gel-forming polysaccharide, water and a metallic chromate selected from the group consisting of sodium and potassium dichromate in an amount ranging from 0.005% to 0.1% by weight of the slurry, zinc chromate in an amount ranging from 0.05% to 1.0% by weight of the slurry and barium chromate in an amount ranging from 0.1% to 1.0% by weight of the slurry.

2. An explosive composition as claimed in Claim 1 also containing a cross-link delaying agent.

3. An explosive composition resistant to segregation of its ingredients over long periods of storage consisting essentially of a thickened aqueous slurry of solid explosive material, said slurry comprising from 8 to 26% by weight of water, from 30% to 75% by weight of at least one inorganic oxygen-supplying salt, from 15% to 40% by weight of at least one particulate organic explosive, from 0.2% to 2.0% by weight of a gel-forming mannogalactan, and a metallic chromate selected from the group consisting of sodium and potassium dichromate in an amount ranging from 0.005% to 0.1% by weight of the slurry, zinc chromate in an amount ranging from 0.05% to 1.0% by weight of the slurry and barium chromate in an amount ranging from 0.1% to 1.0% by weight of the slurry.

4. An explosive composition as claimed in Claim 3 also containing from 0.002% to 0.1% by weight of the slurry, of a cross-link delaying agent.

5. An explosive composition as claimed in Claim 1 wherein the inorganic oxygen-supplying salt is selected from the group consisting of the nitrates of ammonium, sodium, barium, potassium and calcium and mixtures thereof.

6. An explosive composition as claimed in Claim 3 wherein the inorganic oxygen-supplying salt is selected from the group consisting of the nitrates of ammonium, sodium, barium, potassium and calcium and mixtures thereof.

7. An explosive composition as claimed in Claim 1 wherein the particulate organic explosive is selected from the group consisting of trinitrotoluene, composition B, pen-tolite, pentaerythritol tetranitrate, cyclotrimethylenetri-nitramine and smokeless powder and mixtures thereof.

8. An explosive compostion as claimed in Claim 3 wherein the particulate organic explosive is 'selected from the group consisting of trinitrotoluene, composition B, pentolite, . pentaerythritol tetranitrate, cyclotrimethylene-trinitramine and smokeless powder and mixtures thereof.

„ 9. An explosive composition as claimed in Claim 1 wherein the gel-forming polysaccharide is a guar flour.

10. An explosive composition as claimed in Claim 3 wherein the gel-forming mannogalactan is a guar flour .

11. An explosive composition as claimed in Claim 2 wherein the cross-link delaying agent is selected from the group consisting of tartaric acid, gluconic acid, citric acid, metal citrates and metal tartrates.

12. An explosive composition as claimed in