IL34412A - Blasting slurry compositions containing calcium nitrate and method of preparation - Google Patents

Description

Blasting Slurry Compositions Containing Calcium Nitrate and Method of Preparation BLASTING SLURRY COMPOSITIONS CONTAINING CALCIUM NITRATE AND METHOD OF PREPARATION This Invention pertains, to explosive, blasting slurries con* ta lrilng aqueous solutions of ammonium nitrate and other powerful Inorganic Oxidizers plus thickeners, fuels and sensitizers. Such slurry compositions are commonly made up of an aqueous solution of ammonium nitrate, to which sodium; nitrate may be added. The solution is thickened with guar gum and/or starch to a viscous heavy liquid or gel, and sensitized usually with high energy fuels such as powdered . aluminum and or self-explosives such as TNT. In some cases the liquid component has Included non-aqueous but water-compatible liquids , such •as alcohols , glycols , amides such as formamlde , and analogous liquids. Typical of such slurries; are those described In U . S. Patent Νο·» 2 , 930, 685 and U . S. Reissue Patent No. 25, 695 to Cook and Fa mam, also In U.S. Patents NosV 3, 249 , 474, '476, and '477 , 3, 382, 117, and others. Some of these have suggested possible use of calcium nitrate a s ah Ingredient of such slurries. As far as the present Inventors are aware, however, no substantial or practical use has been made of this Ingredient.

' One reason that calcium nitrate has not. been used to any substantial extent Is the fact that Is quite Insensitive, as are most aqueous slurries. They are often quite difficult to detonate. Considerable effort has been expended tn developing slurries which are "sensitive enough for practical use as Industrial explosives . Thus, the use for Is well known. Also, the use of self-explosive particles distributed throughout the slurry, such as granules of TNT, grains of smokeless . owder, and the like/ and combinations of such with aluminum, etc. , are known. Furthermore ,. the sensitivity-contributing effect of tiny gas bubbles, especially of entrapped a ir bubbles, ha s been recognized and suggested as being desirable . Even with these effective sensitizers, however, calcium nitrate as a substantial and significant ingredient of bla sting slurry cornposltlons has not been used In practice and its use, a s a rule has hot been considered feasible, as far as the present Inventors are aware.

The presence of. water In such slurries, of course, detracts greatl from the Ir sensitivity. However, In order to maintain the desired liquidity of fluidity for mixing, pumping and/or pouring the slurries Into boreholes for Immediate use , or. Into packages for storage, substantial proportions of some kind of liquid usually are required.

Thus, commercially usable slurries ordinarily contain as much as 12 to 20% by Weight, or more , of wtater. Somewhat lower proportions can be used if fluidity for pumping is not needed. Where the particulate materials are present. In a variety of particle sizes , aluminum particles, -for Instance , less liquid Is required for a given viscosity. Generally speaking, any combination of calcium nitrate as an oxidizer, with Its known insensltlvlty, and of relatively high water content In a blasting slurry would be expected to be so dead or Insensitive as to be impractical. Moreover, calcium n Itrate u s ua lly conta Ins considerable water of crystallization and this "would appear to be a deterrent to Its use. o tent runs about 14% m re or less b wei ht In m calcium nitrate .

Contrary to the . disadvantages suggested above, the present Inventors have found that calcium nitrate can be used effectively and In substantial proportions in aqueous blasting slurries, with several advantages that the prior art seems not to have recognized. Among such advantages are the following: . ' " ·' .. a . Calcium nitrate slurries can be made having relatively high density or specific gravity, ' as compared with slurries made up primarily of ammonium nitrate and other conventional Ingredients. b. The slurries of the present. Invention requite cons added water to render them fluid, due to release of the water of crystallization normally present In calcium nitrate , When made by the process of . this invention; the water requirements can be reduced further and advantageously by substitution of ethylene glycol or analogous organic Hquld for part or most of the water. ; c, ' ....The cost of calcium nitrate i slurries Is relatively low. d. Calcium nitrate per se can easily be produced In situ and In the field. and, using dheap starting materials. e. . Where explosive sensitizers are used, proportions required can' be substantially reduced, as compared with general practices In the art. ^ ■ ' :- . . · . . ' ■ '; f . The congelation temperature or. "fudge" point of slurries contain-. Ing calcium nitrate can be lower, other things be ing equfb or, alternative iy, larger total salt proportions can be used without raising the fudge , point. This Is an advantage . of this Invention.

A further advantage of the use of calcium nitrate, according to the present Invention, Is the possibility of using products of higher density. Conventional slurries often are sensitized In part by Inclus ion of fine bubble s of a ir or other ga ses provided the ir densities are not too high . They do not appear to respond very Well to sensitization by such V . ga s bubbles when made with densities exceeding about 1. 4 grams per - , ·.. cubic centimeter. This limitation appears not to apply In the same degree to the slurrie s . of the present Invention. ■ .· . '■ ..

* I present commercial practice, a solution of the oxidizer . 10 salt, which Is usually, ammonium nitrate or a combination of sodium nitrate and ammonium nitrate * Is dissolved In hot waiter. Thereafter, ; fuel's and/or sensitizers, etc. , In solid particulate form and usually Insoluble In the liquid are added to the solution. As the resulting slurry cools , It reaches a point at which the ' salts In solution begin to precipitate , . causing a rapid, thickening or solidification/ The temperature at which this occurs Is. the . so-called "fudge " point and It varies with the composition. It Is desirable to have a fudge point low enough that necessary mixing and pumping, of the slurry can be accomplished before • ., the material starts to solidify, that is , before the fudge point Is reached. 2 pi The use of calcium nitrate , contributing liquid as It does by relea se of at least some of Its water of crystallization either lowers the fudge point or, alternatively* makes It pos sible to use more total oxidizer In the solution without ra ising the fudge point. This Is n Important a spect of this Invention.

The Invention will be explained further b giving specific exam les of com ositions Incor oratin It.

A series of samples, of explosive slurry were made up, simply using calcium nitrate to replace part of the. normal ammonium nitrate and/or sodium nitrate, as follows. Parts shown are percentage . by weight.

■ TABLE I ■ V' · ···'■· - ■ . . . A ·, ■ .. ' B. , . c .' . D ' ' Ammonium nitrate 42 45 . 45 . 55.2* Sodium nitrate : ._ 10 10 — Calcium nitrate V 37 i ' 36.5 36.5 36.8* Water 12 . 8.5 8.5 8.0* Guar Gum thickener 0.1 0.1 0.1 0.25 .Ethylene glycol ' , 0*2 — . — 0.5 Propylene glycol ..·' . 1.0 1.0 ~- TNT ("Pelletol") : 16 _— . — Gllso lte 3.7 6.0 , 6.0 — Aluminum ■- coarse. r- . 9.0 9.0 — Aluminum - fine , , 1.0 1.0 . ~ Smokeless powder . ; ' ^ Density .. — 1.40 @ 1.34@ — '."■·■■', :' - ■ ..,·,;.': :·ν'·':. ■■.;:' ■_.· 54° C 54° C . - ' Composition A was prepared by dissolving the sodium nitrate first in warm water,. 0° C ; then adding the ammonium nitrate and calcium nitrate together. In these tests a Norwegian calcium nitrate was used, this composition was not tested for detonation but would be lengths six times the diameter. The 2 " charges failed to detonate completely but the larger charges were all fired successfully with a standard booster. For Composition D the proportions starred mad© up i 00% of the solution. For sensitizer, 28 parts of HSSP double base smokeless powder was used. This product had a solution density (before addition of smokeless : powder) of 1.61. Density after addition of the SP was hot determined. This product fired in a 2-lnch column with a standard "2A" booster. " Another series of tests were made, starting with a standard oxidizer solution S j. which Was made . up of the following Ingredients, parts by weight.

Ammonium nitrate (AN) 32. 5 or 35.9% Calcium nitrate (CN) 37. 0 or 40, 8% Sodium nitrate (SN) 5. 5 or .6. 06% Water 5. 5 . or . 6. 06% Ethylene glycol 10. 0 or: l i . 03% Guar gum - commercial 0. 2 · or 0. 22% The sodium nitrate was dissolved first In the water and then t e calcium nitrate and ammonium nitrate were added together . to the solution. Temperature of this mixture was about 70° C . Water of crystallization released from the calcium nitrate helped maintain liquidity. This total mixture had a pH of about 4. 5 and an oxygen balance of about +11%,. . e guar gum was dispersed in the ethylene glycol and the resulting, dispersion added to the oxid zer mixture. The resulting compost aqueous solution of the same salts. It as cooled down to about 50° C before adding particulate fuel or sensitizer Ingredients In the form. of various pro-mixes mentioned below. This solution had a "fudge " point (congelation temperature) of about 35° C .

In order to cross-link ,the gum to get higher viscosity and thus prevent segregation of suspended fuel particles, etc. , a cross-linking agent or In some cases a combination of oxldlzer-reducer agents was used. A typical agent, "designated "A" , was a 50/50 solution of potassium or sodium dlchromate. Gallic acid or potassium antimony tartrate was used as reducing agent In a number of examples . In some of these, gassing. agents, such as nitrous acid or ammonium, sodium or .potassium nitrite ere added In very small proportions , sometimes with melamlne or thiourea to accelerate aeration. Hydrogen peroxide was used In some cases , along with traces of potassium iodide or manganese dioxide to catalyze decomposition. In some cases It was difficult to thicken slurries with pH aboce 3* 0. In these a small amount of nitric acid wa s used to lower the pH slightly. Thus 0. 55' cc. of 58% ' ' ' ' ' ' ί'. ' { ' ' ' . '·. ■ ■ "' ' ' · ■ nitric acid per 100 g. of slurry brought pH down to 3. 0 and 0. 2 cc. brought It to a level between (1. 0 and 2. 0. Thiourea speeded up the thickening and also increa sed the gassing rate, when ammonium, potas-s lum or sodium nitrite were used. Gassing agents are useful not only to reduce density but also. to Increase sensitivity. Numerous gassing agents are available, as will readily be understood by those skilled In the art.

Slurries were made · up using ground pitch or gllsonlte alone, the explosive cplumn may be under sufficient hydrostatic or super- Imposed pressure that the charge Will not detonate * or at least will not lidetonate all the way. ' A particular object, realized in thls Invention, Was to obtain stable; gassed slurries that can be detonated In 2 1/2-lnch columns or larger; at temperatures as low as 5° C and under pressures of up to 50 psl. The products described in Table III above meet these requirements. Many, perhaps most, of the blasting slurries of the prior art fall far short of the latter requirement. .

The use of ethylene glycol with Its fuel value and Its low- temperature solvent properties, as a significant. Ingredient Is one Impor- taht feature . Another is the use of calcium itrate which makes It possible tp use higher total proportions of oxidizer for a given fudge point. . A mixture of oxidizers containing ammonhim nitrate and sodium nitrate with calcium nitrate Is usually preferred. As noted above, a fudge . point as low as 35° C is quit© remarkable and some of these products have such. The use of an effective cross-linking system, such a s dlchromate-galllc acid or other oxldatlon-reductlpn combinations , which are reasonably independent of pH is Important. Slurries of low pH (high acidity) are excessively corrosive to mixing nd pumping . equipment. Hence, a thickening system not dependent on low pH is advantageous. In situ mixing and pumping of blasting agents has many advantages. Separate ingredients which are non-explosive Individually c¾n be combined at the mine and pumped directly to the borehole before they get too viscous for pumping through hoses. Hence, controlled viscosity, which builds up slowly enough to permit mixing and pumping Intrusion In the gel, Is important. Compositions of this Inventio have all these desirable properties, Including density control when the slurry Is under the pressure of a tall column in a borehole. They may Include combinations of calcium nitrate with other Inorganic oxidizer salts such as nitrates, chlorates and.perchlorates.

Preferably, the slurries of this Invention Include at least 5% by weight of ethylene glycol as a fuel and liquid extender, at least 10% of calcium nitrate, a stable thickening system, and enough gassing agent to keep the slurry at density not exceeding 1.20 g/cc. under 50 pel pressure. Particularly preferred are slurries containing at least 8% of ethylene glycol, at least 20% of calcium nitrate, and less than 8% added water.

Variations In Ingredients and proportions, including use of self-explosive particles In some cases and other types and varieties of fuels can be made within the scope of this invention as will be obvious to those skilled in the art.

Claims (10)

What is claimed is»

1. A pumpable andRurable aqueous slurry blasting composition of low water oontent and high sensitivity) comprising a liquid phase which includes a solution of powerful oxidizer salriis selected from the group which consists of inorganic nitrates, ohlorates and perohlorates and inoluding at least 10$ by weight) based on the total composition» of calcium nitrate, said liquid comprising water and water-compatible organic liquid having fuel value and low temperature solvent properties, a sufficient quantity of gas in the form of tiny bubbles being dispersed throughout said liqud phase to substantially enhance the sensitivity of thf whole composition to detonation^ and a storage stable, strongly cross-linked thickener or gel former ealeoted from the group which oonsists of polysaccharide gums and starches in proportions sufficie t to permanently hold said gas bubbles dispersed in situ and also to inhibit segregation of solid particles suspended in the liquid phase and inhibit intrusion of bofcehola water into said composition*

2. * Composition according to Claim 1 wherein said water-compatible organic liquid is selected from the group consistin of alcohols, glyools, amides, and analogous nitrogen containing liquids*

3. Composition aocordlng to Claim 1 wherein said water-compatible brganlo liquid Is propylene glycol*

4. · Composition according to Claim 1 wherein said water-compatible organio liquid is formamide. Ί

5. * Composition 8$ of ethylene glyool a'combination oxidation-

6. * Composition according to Claim 1 wherein the slurry contains sufficient gassing agent to hold its density below 1*2 grams per oubio centimeter under a pressure of 50 psi.

7. * Composition according to Claim 1 in which there is at least 20 by weight, based on total composition, of calcium nitrate. ■ ' i ■

8. Composition aooording to Claim 1 whioh inoludes at least 8$ of ethylene glyool*

9. than &fo of water, not inoluding vjater of crystallization associated with said calcium nitrate.

10. Composition according to Claim 1 which includes at least of ethylene glycol, at least 10$ of oaloium nitrate, an oxidation-reduotion cross-linked gel forme j and sufficient gassing agent to keep the slurry density "below 1.2 g/oo. unde a pressure of 50 pal. 11· Composition according to Claim 1 which inoludes finely divided aluminum as a fuel.