US3473983A - Slurry blasting composition containing sulfur and having high sodium nitrate content - Google Patents

Description

United States Patent 3,473,983 SLURRY BLASTING COMPOSITION CONTAINING SULFUR AND HAVING HIGH SODIUM NITRATE CONTENT Melvin A. Cook and Lex L. Udy, Salt Lake City, and

Robert B. Clay, Bountiful, Utah, assignors to Intermountain Research and Engineering Company, Inc., a corporation of Utah No Drawing. Filed Aug. 7, 1968, Ser. No. 750,759

Int. Cl. C06b 1/00 US. Cl. 14941 13 Claims ABSTRACT OF THE DISCLOSURE BACKGROUND AND PRIOR ART Since the invention a few years ago of aqueous explosive blasting slurries, these have been based generally on the use of high proportions of ammonium nitrate (e.g. US. Patents 2,930,685 and Reissue 25,695 to Cook and Farnam). Numerous suggestions have been made for using sodium nitrate (SN) as an ingredient. Some of the latter suggestions, on their face, might appear specifically to indicate that ammonium nitrate (AN) and sodium nitrate (SN) are in fact freely interchangeable, but this is not the case. Those who have had extensive experience with use of sodium nitrate in explosives, especially in aqueous slurry explosives, are Well aware that compositions containing substantial proportions of this particular ingredient tend to be quite dead, i.e. are highly insensitive. In many cases they cannot be detonated at all; in most cases they are very difficult to detonate. For this reason, in the practical art, sodium nitrate has been used, if at all, only in small proportions, ammonium nitrate being the primary oxidizer in nearly all cases. That is, despite occasional and usually unsupported suggestions of the possibility of using large proportions of sodium nitrate in blasting slurries of the type mentioned above, high SN slurries either have not been used at all or, if occasionally used, they have required very large and correspondingly expensive proportions of powerful sensitizers. For example, when particles of self-explosive sensitizers, such as TNT are used, they must be used in larger than normal quantities if and when high proportions of sodium nitrate, and correspondingly low proportions of ammonium nitrate, or none of the latter, are used as oxidizer. Where fuel type sensitizers, such as particulate metals are employed, e.g. fine aluminum particles, the latter must be used in much larger quantities with high sodium nitrate than with normal high ammonium nitrate low-sodium nitrate slurries. Specifically, a proposed composition in the prior art which suggested use of about equal quantities of AN and SN indicated that as much as 25% of the total composition should be particulate aluminum. By contrast, with most of the oxidizer in the form of AN, by weight of the same aluminum appeared to be satisfactory. In another example, which suggested use of 36% by weight, based on total slurry, of sodium nitrate, along with 20% of ammonium nitrate, the requirement for a similar aluminum sensitizer was indicated to be 20%, by

3,473,983 Patented Oct. 21, 1969 "ice weight, based on the total composition. Aluminum is one of the most costly ingredients of aluminum sensitized slurries. Obviously, it is highly desirable to minimize its requirements.

It has been suggested, in US. Patents 3,249,477 and 3,282,752, issued to Clay and Udy, two of the present inventors, that by using in aqueous slurries of high ammonium nitrate content, sodium nitrate and sulfur in combination, keeping their relative proportions within certain limits, the sensitivity of the slurries could be improved. It was suggested that a reaction occurs between the sodium nitrate and the sulfur which results in production of sodium sulphate plus gaseous nitrogen, oxygen, etc., with desirable results. Even in those cases, however, use of sodium nitrate in proportions equalling or exceeding the ammonium nitrate quantity was not suggested because at the time it was not considered feasible. The known difficulties at the time these inventions were made of detonating explosive mixtures which included sodium nitrate in quantity were sufiicient to preclude even a suggestion by the patentees that sodium nitrate could be used in high proportions. This was notwithstanding the fact that sodium nitrate is often available in large quantities. In some parts of the world it occurs naturally and is much less expensive than ammonium nitrate.

Surprisingly, it has now been discovered and is an important aspect of this invention that aqueous slurry blasting agents of adequate sensitivity and good explosive performance can be made, using low cost sensitizers, while employing relatively very high proportions of sodium nitrate in the oxidizer. As a matter of fact, quantities of commercial grade sodium nitrate substantially exceeding the quantities of ammonium nitrate employed in AN-SN slurries can be so used, without encountering high sensitizer costs. To produce efiective blasting slurries at low cost, which slurries include such high proportions of sodium nitrate, is therefore an important object of this invention.

A further object is to prepare high sodium nitrate slurries of low cost which can be tailormade to desired strength and performance standards by relatively simple variations in ingredients and compounding procedures, e.g. by simply adding and/or changing proportions of metallic and non-metallic fuel or sensitizer ingredients.

The method by which the above are accomplished is a further feature and object of this invention.

DESCRIPTION OF PREFERRED EMBODIMENT Blasting compositions made according to the present invention include 10 to 20% of liquid by weight, based on the total composition. The preferred liquid is water, although, if desired, part of it may be a water miscible organic fluid such as ethyl alcohol, methyl alcohol, ethylene glycol, diethylene glycol, glycerol, formamide, or the like. In any case, a major proportion of the liquid preferably is water. The composition comprises a. major proportion by weight of oxidizing salt, preferably ammonium nitrate and sodium nitrate, of which a major portion is the latter. Depending on the permissible cost, aluminum may be included in proportions of 0.5 to 12% of the total, by weight. This aluminum should be of good sensitizing grade and therefore should include at least 0.4%, based on the total composition, of paint grade aluminum or fine aluminum of equivalent sensitizing properties. Overall, the composition should comprise enough sulfur to bring the sodium nitrate/sulfur weight ratio within limits of four to nine, preferably five to seven. The composition must contain enough supplemental fuel, preferably a carbonaceous fuel selected from the group which comprises finely ground gilsonite and finely ground coal, preferably bituminous, to bring the overall oxygen balance within limits of :10%.

The composition preferably is made up by preparing what may be called a standard solution of oxidizer, made up of 25 to 30%, based on the total by weight of ammonium nitrate, to of sodium nitrate, and 10 to of water. To this is added a small amount of viscosity increasing agent. The purpose of the latter is to fix against escape from or coalescence within the eventual slurry or the liquid phase thereof, numerous fine gas bubbles, e.g. air bubbles.

To proportions of 50 to 60% by weight, of the solution just described, are added solid particles comprising 23 to 30% by weight of dry or particulate sodium nitrate and 10 to 27% of particles selected from at least n pre-mix. In a preferred method, two premixes are provided, one a lean or economy mix, and the other an aluminum-rich powerful or maximum mix. Each of these contains enough sulfur, aluminum, supplemental fuel and supplemental thickener to make certain that whichever is selected, or whatever portion may be drawn from both, a reliably detonable blasting agent will be produced.

A blasting slurry made up of inexpensive ingredients and giving good performance in actual blasting tests was made up as follows:

Example I Ammonium nitrate in proportions of 28.9%, by weight, based on the total composition, and about 12.5% of commercial grade Chilean sodium nitrate were dissolved in hot water (temperature 30 C.). Proportions of water were 15.2% by weight of the total slurry. In 0.4% of ethylene glycol, 0.2% of guar gum was dispersed, this mixture then being added to the solution just described, to impart a slightly increased viscosity to the solution. The oxidizer solution, as used in this example, made up about 57% of the total weight of the slurry.

An additional quantity of 28.5% by weight, based on the total, of the same Chilean commercial grade sodium nitrate was added to the slightly thickened solution, along with a dry pre-mix of particulate ingredients made up of the following materials in weight proportions totaling 14.8%, based on the total slurry, as follows:

On mixing the sodium nitrate and the pre-mix into the solution, some air was entrapped so that the slurry which resulted had a density of 1.28 g./cc., somewhat lower than theoretical. Total thickener was 0.4% of guar gum and 2.1% of starch. Depending on the rate of addition of the particulate solids and the vigor of mixing, the degree of such aeration may be varied as desired. Preferably, enough aeration is included to lower the density by at least 5% from theoretical, and up to as much as or or more. This particular slurry settled somewhat in the borehole; its density at the time of shooting was 1.31 g./cc. In a slurry having a normal unaerated density of, say 1.45 grams per cc., the aerated density may be varied as desired between about 1.40 and 1.05 g./cc. In exceptional cases, this density may be brought below 1.0, but such low density ordinarily is not desirable, especially when the slurry is to used in boreholes which contain water. Under such circumstances, the slurry preferably should be dense enough to sink in the Water and not be lifted up or out of the borehole. The above slurry performed very satisfactorily in blasting hard rock in a large mining operation using boreholes of six inches and larger diameter, 30 to 100 feet in depth.

Example II A more powerful slurry was made up by simply adding more aluminum powder, to a total of 10% of the 4 weight of the slurry, to the premix, while reducing the sulfur by 1% and the gilsonite by 3%. The high aluminum slurry costs more than the slurry of Example I but it is substantially more powerful. Its final composition by weight, overall, was as follows:

Percent Ammonium nitrate 27.7 Sodium nitrate 38.1

Water 14.3 Ethylene glycol 0.4 Guar gum 0.4 Sulfur 5.0

Gilsonite 2.5 Aluminum 10.0

Starch 2.1

It will be noted, particulary, that the above compositions have essentially the same quantity of oxidizer. Both contain substantially more sodium nitrate than ammonium nitrate and both contain about six to eight times as much sodium nitrate as sulfur. The proportions of sulfur may be increased moderately, often with advantage, to /5 or more of the weight of sodium nitrate. The general ratio of sulfur to sodium nitrate is discussed in the Clay and Udy patents mentioned above. For compositions of sodium nitrate content so high that it exceeds ammonium nitrate, as in the present invention, the preferred ratio limits of sodium nitrate to sulfur are narrow, i.e. between four and nine, preferably between five and seven. Sulfur content may desirably be a little higher with low sensitizer content (aluminum) than with high.

These are important advantages in the flexibility and interchangeability of the compositions of the present invention. Basically, a single liquid solution is thereby made adaptable to a variety or family of related compositions covering a rather wide use spectrum. Starting with an aqueous solution of ammonium nitrate and sodium nitrate, which need not be changed at all in composition, a small amount of a thickener is added, preferably a glycol dispersion of guar gum, as noted above. The dry ingredients to be blended into the liquid in varying proportions for slurries of different blasting power are placed for convenience in three different compartments or bins. One contains the undissolved sodium nitrate. Another contains an economy pre-mix, as in Example I. The third contains the high grade or power explosive pre-mix, as in Example II.

The economy pre-mix may be varied somewhat in composition but preferably it contains about 4 to 8% by weight, based on the total composition, of pulverized sulfur, about 5 to 6% of powdered gilsonite, coal, or equivalent carbonaceous fuel, about 1% of fine aluminum powder, at least part of which, and preferably all, is a fine flaked paint grade aluminum. To this may be added around 2% of a starch, preferably tapioca flour. It is desirable to include a small amount of guar gum. Specifically, this economy mix is preferably just like the dry premix of Example I above although, as noted, the proportions of the various components may be varied within fairly narrow limits. The combination of the fine paint grade aluminum and carbonaceous fuel, plus the sensitizing effect of sulfur when used with sodium nitrate, is adequate to insure that a slurry containing only the economy pre-mix can be detonated by means of a booster of moderate size and power.

The high-grade or maximum power pre-mix, as it may be called, corresponds in general to that used in Example II above. Proportions of 4 to 7% sulfur (preferably around 5 to 6%), a small quantity of carbonaceous fuel, which may be gilsonite, bituminous coal or the like, and mixtures, preferably 2 to 3%, and about 10% or 8 to 12% of aluminum of various particle sizes from paint grade (-325 mesh Tyler) to 20-mesh or even larger, and a starch or flour type thickener as well as a small amount, say 0.2%, of guar gum. In a particularly suitable high-grade pre-mix, there was aluminum of grades or particle sizes distrbuted as follows:

The use of a small amount of guar gum in either the economy or the high grade pre-rnix adds a delayed thickener component so that a slurry which is mixed mechanically and pumped immediately to a borehole will begin to thicken up by the time it reaches the borehole. This prevents sedimentation or separation of the sensitizer solids, aluminum particles, etc., from the slurry which otherwise might fail to detonate by reason of desensitization.

By placing the economy pre-mix in one bin or container and the high grade pre-mix in another, either may be supplied selectively to mix with the standard or nearly standard solution. In this way, an economy slurry or a very powerful or high-grade slurry (referred to herein elsewhere as a maximum power slurry) may be produced by merely selecting the appropriate pre-mix and combining it with the solution. It will be understood that the dry sodium nitrate also will be added. An overall economy mix has less than 2% aluminum, along with a carbonaceous fuel suflicient for good oxygen balance, 12 to 20% of water, a major proportion of oxidizer of which more than half is sodium nitrate, and suitable thickener. It contains enough sulfur to give a SN/S radio of at least four and not more than eight. For a more expensive and powerful mix, the aluminum is increased several fold, as noted above, and other ingredients are reduced enough to make room for the aluminum. In this case, sulfur may be as low as A; of the sodium nitrate or as high as A. Enough carbonaceous fuel, up to 3%, is used to maintain good oxygen balance.

Instead of choosing only one of the extremes of economy blasing slurry and the high-grade, by mixing the two separate pre-mix compositions in various ratios, a slurry of any desired blasting power between the two extremes may readily be produced with full assurance that it will be reliable and detonable. A mechanical system, such as a mobile pump and mixer unit or so called pump truck may be used, as described, for example, in US. 3,303,738 or 3,361,023. In such a system, the standard solution of oxidizer (containing in this case both ammonium nitrate and sodium nitrate dissolved in water, with a small amount of viscosity increasing agent or thickener) is drawn from a tank into a mixing zone. Dry particulate ingredients such as sodium nitrate, an economy pre-mix and/or a highgrade pre-mix are fed by angers, vibrators or other devices, from their respective bins to the mixing zone where they are stirred into and suspended by the solution. The resulting slurry composition, now made explosive by the combination of liquid and solid components, may be packaged and stored for future use or it may be flowed or pumped directly into a borehole for blasting.

Obviously, the feed rate for either pre-mix may be varied anywhere between full feed and zero so that either may be fed to the mixing zone to the exclusion of the other or both may be fed in predetermined proportions. The feed rate or ratio, of course, will be such as to add the proper proportions of solids to the solution to obtain a blasing slurry of the desired composition. By merely controlling the relative feed rates of the two pre-mixes, while allowing solution flow and delivery of dry sodium nitrate to proceed at fixed or standard rates, any desired slurry quality between the economy grade and the high grade may be obtained with precision.

While the examples given above generally include at least a small amount of fine aluminum, usually 0.4% or more, and the flaked paint grade aluminum of commerce is a particularly desirable and effective sensitizer, it is not always necessary to include this fine aluminum or, if included, it can be used in proportions as low as 0.1% of the weight of total slurry, as the following examples show.

Example III A solution was made up of the following ingredients, parts by weight based on total slurry being given:

Ammonium nitrate 31.5 Sodium nitrate 13.5 Water 15.0 Guar gum 0.15

Ethylene glycol 0.3

The guar gum was first dispersed in the ethylene glycol and this dispersion was added to the solution which was heated to about 35 C. to achieve full soltuion of the oxidizer salts.

A dry premix was made up of the following:

Sulfur (finely powdered) 7.0 Gilsonite (powdered) 6.0 Guar gum 1.0

Example IV Example III was repeated, except that 5.9 parts of gilsonite was used instead of 6 parts and 0.1 part or percent of fine flaked paint grad aluminum was added. This composition detonates more easily than the composition of Example III and is preferred where the ambient or borehole temperatures are cooler. In general, it is preferred to use at least 0.1% of the fine aluminum if the borehole temperature is below about 15 C. In many cases, the extra cost of using 0.4% or even more of fine paint grade aluminum will be justified because of its superior sensitivity and blasting strength.

While use of 25 to 30%, or up to 35%, of ammonium nitrate, as a minor part of the oxidizer salt, is ordinarily preferred because ammonium nitrate is less difficult to sensitize and detonate than sodium nitrate, lesser quantities, down to 15%, can be used in some cases. 20 to 35% of ammonium nitrate is usually employed. Sodium nitrate limits are 20 to 50%, preferably 23 to 40% overall. Also, the ammonium nitrate can be replaced in part, or even wholly in some cases, by ammonium chlorate or perchlorate and/or by sodium or potassium chlorate or perchlorates. Here again the limits are 15 to 35 preferably at least 20% and more preferably at least 25%. A major distinguishing feature of the present invention, of course, is the use of sodium nitrate as a major part of the oxidizer (i.e. over 50% of it by weight), and the balancing of this sodium nitrate by use of sulfur within limits of one fourth to one ninth of the weight of sodium nitrate, plus of course the requisite sensitizers or fuel-sensitizer material to bring oxygen balance between as already noted.

The use of a standard solution, including 15 to 35 by weight, based on total slurry, of ammonium nitrate or equivalent, and 5 to 20% sodium nitrate, to which a rich and a lean premix plus undissolved sodium nitrate can be added in variable proportions to get a tailor-made" slurry of almost any reasonable desired performance characteristics is a particular feature also.

The compositions described and their manner of preparation, as explained above, facilitate the tailoring to order of a variety of explosive slurries to fit varying blasting requirements exactly and at minimal cost while using large proportions of sodium nitrate as oxidizer. By using pro-mixes made up as described above, the user can be certain that no combination selected will fail to detonate by reason of fuel or sensitizer deficiency. At the same time, the use of large proportions of sodium nitrate, where it is a cheap commodity, as it is in many areas, will keep costs at a particularly low level, regardless of the grade of blasting agent prepared. In broad terms the compositions of this invention comprise a major proportion of oxidizer salt of which a major part is sodium nitrate, up to 15% of aluminum, preferably not over 12% (a large part or in some cases all of the aluminum may be coarser, cheap grades), 10 to 20% of liquid, the major part of which is water, enough carbonaceous fuel to bring the oxygen balance with about il%, and enough sulfur to fall within a SN/ S ratio range of four to nine by weight. Sugar and other cabohydrates may be used in the fuel. The slurry should include a thickener as a rule, although unthickened slurries made pastry or heavy with suspended solids often can be fired successfully without a thickener as such. The liquid phase is preferably 80% or more water, although various water miscible liquids may constitute up to 50% of the liquid. Preferably the liquid is used to dissolve the ammonium nitrate (or a chlorate or perchlorate substitute for ammonium nitrate) and only part of the sodium nitrate. It is usually desirable thus to form a standard soltuion to which various proportions of the dry ingredients may be added, within the limits given above. That is, the standard soltuion can be used for a number of different slurries. In this way blasting agents of varying strength but good sensitivity can be made, without large variations in total oxidizer or in sodium nitrate content.

While it has been indicated above that a mechanical mixing and slurry delivery system may be used to advantage, it will be understood that a mechanical mixing and/or pumping system is not always necessary. Mixing and/or ingredients will be so chosen as to incorporate at least a small quantity of air or other gas. Indeed, it is usually quite ditficult to avoid inclusion of at least a small amount of air as fine bubbles. These help sensitize the slurry, as is now well known. The slurries may be made up by adding and mixing ingredients, both liquid and solid, by manual means or in various ways. The slurry products so obtained may be used immediately or may be stored in tanks or packages for future use. In the latter case, and where aluminum is a sensitizer, addition of a small amount of a phosphate or analogous stabilizer to prevent premature aluminum-water reactions is desirable, as explained in US. Patent No. 3,113,059. Various other modifiers may be added or used, as will readily be apparent to those skilled in the art. Other fuels, oxidizers, sensitizers, etc., may be added as needed.

It is intended by the claims which follow to cover the above suggested modifications, and any others which would suggest themselves or be obvious to those skilled in the art as broadly as the prior art properly permits.

What is claimed is:

1. A slurry blasting agent composition having a substantially continuous liquid phase and comprising a major proportion by weight of an oxidizing agent selected from the group which consists of ammonium, alkali metal and alkaline earth metal nitrates, chlorates and perchlora-tes, and mixtures thereof, at least 15 and not more than 35% by weight, based on the total composition, of said oxidizing agent being other than sodium nitrate and a major part of said oxidizing agent being sodium nitrate, to 20% of liquid comprising water, 0 to 12% of aluminum, a sufiicient proportion of sulfur to bring the sodium nitrate/sulfur weight ratio within limits of four to nine, and enough solid carbonaceous fuel to bring oxygen balance within limits of i10%.

2. Composition according to claim 1 which comprises enough thickener in the liquid phase to entrap and hold fine gas bubbles to reduce the composition density from unaerated level by at least 5%.

3. Composition according to claim 1 which contains less than 2% aluminum.

4. Composition according to claim 1 which comprises about 50 to 60% by weight of a solution made up essentially of water, ammonium nitrate, sodium nitrate and a small amount of thickener in said solution, and 40 to 50% of solid matter comprising 12 to 20% of sodium nitrate, the total sodium nitrate being over 50% of total oxidizer salt present, 0.5 to 10% of particulate aluminum, at least 0.1% of which is paint grade aluminum, and a supplemental thickener in addition to said small amount in said solution.

5. Composition according to claim 4 which comprises about 0.4% of fine grade aluminum and at least 5% of carbonaceous fuel.

6. Com-position according to claim 1 which includes at least 4% of fine paint grade aluminum.

7. Composition according to claim 1 which comprises 8 to 12% of aluminum and not to exceed about 4% of carbonaceous fuel aside from the thickener.

8. Composition according to claim 1 which comprises about 10% of aluminum and 2 to 4% of carbonaceous fuel selected from the group which consists of gilsonite and coal.

9. The process of preparing blasting agents of various blasting energies which comprises preparing a standard solution of about 15 to 35%, based on the total composition, of ammonium nitrate, about 5 to 20% of sodium nitrate, about 10 to 20% of water, and a small amount of viscosity increasing agent, then adding selectively to about 50 to 60% of said solution a sufficient amount of particulate sodium nitrate to bring total sodium nitrate content above total content of ammonium nitrate but not above 50% of the total slurry, and about 10 to 27% of one or more pre-mix compositions selected from premixes of high aluminum content and of low or zero aluminum content respectively, each of said pre-mixes containing a solid carbonaceous fuel, a supplemental thickener and enough sulfur to bring the overall sulfur content within sodium nitrate/sulfur weight ratio limits of nine to four, whereby any selected blasting agent composition will necessarily contain enough sulfur, fuel and sensitizer to assure a reliably detonable slurry of good strength, regardless of relative proportions of the two premixes.

10. Process according to claim 9 wherein the pre-mixes each contain at least 2% of carbonaceous fuel.

11. Process according to claim 9 wherein the standard solution contains at least 20% of ammonium nitrate.

12. Process according to claim 9 wherein the standard solution contains at least 25% of ammonium nitrate and sufficient thickener to entrap tiny air bubbles for adding sensitivity to detonation.

13. Process according to claim 9 wherein the total premix employed contains at least 0.1% by weight, based on total slurry, of fine paint grade aluminum.

References Cited UNITED STATES PATENTS 3,282,752 11/1966 Clay et al. 149-22 3,092,528 6/1963 Loving l4973 X BENJAMINE R. PADGE'IT, Primary Examiner S. I. LECHERT, Assistant Examiner US. Cl. X.R.