US3764421A - Method of making nh4no3-h2o-fo composition - Google Patents

Abstract

IMPROVED BLASTING COMPOSITIONS ARE PROVIDED BY ADDING WATER, IN CONTROLLED AMOUNTS, TO A PRILLED ANFO (MIXTURE OF PRILLED AMMONIUM NITRATE AND FUEL OIL), AGING THE MIXTURE UNTIL THE CONTAINED PRILLS CAN BE CRUSHED BY PRESSING BETWEEN THE FINGERS AND THEREAFTER COMPLETING THE MIXING OF THE INGREDIENTS UNTIL A PRODUCT IS OBTAINED IN WHICH A SUBSTANTIAL AMOUNT OF THE PRILLED AMMONIUM NITRATE HAS BEEN CONVERTED TO FINELY-DIVIDED SOLIDS AND THE DENSITY OF THE RESULTING MIXTURE IS GREATER THAN THE DENSITY OF THE PRILLED ANFO STARTING MATERIAL.

Description

Iii-ted StatcS Patent 3,764,421 METHOD OF MAKING NH N0 -H O-FO COWOSITION Jared W. Clark, 1604 London Heights Road, Charleston, W. Va. 25314 No Drawing. Filed Sept. 5, 1972, Ser. No. 286,617 Int. Cl. C06b 1/04 US. Cl. 149-46 2 Claims ABSTRACT on THE DISCLOSURE BACKGROUND OF THE INVENTION Field of invention This invention relates to blasting compositions and is particularly directed to the so-called ANFO-based explosive compositions employed during mining operations. More specifically, the present invention is concerned with a method of producing improved ANFO-based blasting compositions which comprises the addition of small amounts of water and a sequence of critical steps which results in the production of such improved blasting compositions.

The prior art Historically, dynamite, a mixture of nitroglycerin, nitroglycol and other ingredients such as ammonium nitrate, sodium nitrate, sawdust, buckwheat hulls and limestone chips, has been the principal explosive which has been employed for blasting during mining and earth-moving operations.

Other more costly explosives are used in devices such as blasting caps, detonating fuse, primers and shaped charges. However, it has recently been discovered that ammonium nitrate is a very effective explosive when it is combined with various suitable oxidizable materials. See the article on Dynamite Industry is Quietly Fading Away: Fertilizer Product Gains Most of Market, The Wall Street Journal, May 18, 1971, page 40.

In recent years dynamite has been replaced, to a great extent, by ANFO which is a mixture of ammonium nitrate (AN) and fuel oil (F0). The principal reason for this replacement is the superior explosive character of ANFO and its considerably lower cost. In fact, as the aforementioned article discloses, today, 70% of the explosive market is captured by ANFO.

However, the low density and water sensitivity of ANFO have limited their usefulness in some blasting operations. Although water sensitivity can be overcome by packaging the ANFO in water-tight containers, their low density (of about 0.85) causes them to float in waterfilled vertical blast holes thus making it difiicult to load the ANFO packages to the bottom of such holes. Consequently, separation between these packages results in failure or incomplete propagation of the detonation throughout the entire charge.

One method of increasing the bulk density of ANFO is to pack such compositions in rigid containers. When packed to densities ranging from about 1.0 to 1.2, the containers will sink in water-filled, vertical blast holes. Packaging ANFO in such containers has met with only 3,764,421 Patented Oct. 9, 1973 "ice limited acceptance, however, because of the relatively high cost of rigid containers as compared with flexible polyethylene bags or polyethylene-lined cloth bags. Also, packaging ANFO in these containers is a relatively slow operation as compared to filling bags with ANFO and requires special equipment such as auger packers or mechanical vibrators.

Another method for increasing the bulk density of ammonium nitrate compositions is to eliminate or partially eliminate the void spaces between solid particles of ammonium nitrate. This can be accomplished by partially or completely dissolving the ammonium nitrate in water. The amount of added water is usually in the range of 10 to 15 percent by weight.

Sensi-tizers, such as finely-divided aluminum, or explosives, such as TNT, are used in most of these products in order to make them sensitive to detonation by commercial primers. In these formulations, thickening agents (e.g., guar gum and synthetic water-soluble polymers) and cross-linking agents, such as formaldehyde, borax and potassium antimonyl tartarate are employed to prevent or minimize separation of solid or liquid phases. Some of these compositions are water-compatible to the extent that they can be used in Water-filled blast holes without the benefit of water-tight containers. They are highly effective for use in water-filled holes and are also used where a high loading density is desired such as for bottom-hole boosting. These compositions, however, are more expensive as compared to ANFO and their use has been largely limited to applications where Water is a serious problem, or in hard rock where their use is justified by high drilling costs.

SUMMARY OF THE INVENTION Improved ANFO-based blasting compositions are provided by adding water, in controlled amounts, to a prilled ANFO, aging the resulting mixture until the contained prills can be crushed by pressing between the fingers and thereafter completing the mixing of the ingredients until a substantial amount of the prilled ammonium nitrate has been converted to finely-divided solids. The density of the resulting mixture is greater than the density of the prilled ANFO starting material.

DETAILED DESCRIPTION OF THE INVENTION It has now been unexpectedly discovered that the foregoing limitations of ANFO-based blasting compositions can be overcome by treating a prilled ANF'O' composition in a series of critical steps which results in the production of ANFO-based compositions of increased density These compositions, when packaged in flexible, Water-impervious containers, are particularly suitable for use in water-filled blast holes. Thus it has been found that the addition of water to prilled ANFO results in a weakening of the prill structure to the extent that complee break-down to much smaller particles takes place on further mixing in equipment of the type commonly used for mixing prilled ammonium nitrate with fuel oil. The amount of water which is added is usually from about 1 to about 8 weight percent and preferably from about 1 to about 3 Weight percent based on the weight of the mixture of prilled ammonium nitrate and fuel oil. The time required for weakening of the prill structure will vary and is dependent on the porosity of the ammonium nitrate and its prior history such as length of time and aging conditions. Aging overnight usually results in adequate loss of prill structure which is indicated by softening of the prills until they can be crushed between the fingers. Break-down of the ANFO prills, on further mixing, is readily apparent and the density of the resulting material Was found to be greater than the density of prilled ANFO.

The procedure, described herein for the preparation of the ANFO-based blasting compositions of this invention, are particularly suitable for carrying out in the field shortly before their intended use, thus minimizing required storage facilities. Mixing equipment can be the same as those used for mixing fuel oil with ammonium nitrate and similar equipment can be used for bagging and charging the blast holes.

Although in most instances no separation of an oil phase, nor a separation of an aqueous solution of ammo nium nitrate have been observed, even after prolonged storage, such separation, if any, are ordinarily insignificant and do not interfere with the detonating characteristics of the improved compositions of this invention. Also, caking does not present a serious problem in using these compositions. Ordinarily, it has been observed that these compositions tend to cake somewhat, particularly during storage in hot weather. However, the caked materials can be readily broken up. In any event, when the caked materials are detonated while in water-impervious bags, the blasting results have not been significantly different from blasting results obtained with similar compositions in which no caking has been observed.

The processing procedures described in this invention can be applied to compositions other than prilled ammonium nitrate and fuel oil. Thus, ammonium nitrate may be partially replaced with other nitrates such as sodium nitrate and calcium nitrate. Fuel oil may be partially or wholly replaced with other oxidizable materials such as other hydrocarbon fractions derived from petroleum and similar fractions derived from other fossil fuels. Oils derived from plant and animal origins are also suitable and synthetic products such as alcohols, glycols, amines, esters and ketones may also be used instead of fuel oil.

The present invention may be further illustrated by the following examples.

EXAMPLE 1 Prilled ANFO (500 grams), consisting of 6% diesel number 2 fuel oil and 94% prilled, low-density, fertilizergrade ammonium nitrate, was hand-mixed with 30 grams of water in a polyethylene bag at ambient temperature. Partial loss of the prilled structure took place during mixing of the ANFO with water as evidenced by softening of the prills to the extent that they could be crushed between the fingers. After aging this mixture for a period of approximately 10 days, there was no noticeable change in appearance. There was no separation of an oil phase or of an aqueous solution of ammonium nitrate, and no caking was observed.

EXAMPLE 2 Prilled ANFO (2500 grams), consisting of 6% diesel number 2 fuel oil and 94% prilled, low-density, fertilizergrade ammonium nitrate, was hand-mixed with 150 grams of Water at ambient temperatures. Approximately equal amounts of this mixture were charged to three separate, open-top, 12-ounce, tin-plate cans. A number 6 commercial blasting cap with attached'fuse was inserted in one can. A 16-inch piece of SO-grain Primacord (Primacord is a trade name for a detonating fuse manufactured by the Ensign Bickford Company) was formed into a loop by taping the ends together and inserted into a second can. A similar loop of ZOO-grain Primacord was inserted into a third can. Blasting caps, with attached fuses, were taped to the ends of the Primacord loops. When these charges were set off, no detonation was observed in the charge in which only the blasting cap had been inserted. This was evidenced by the fact that the can was ruptured by the blasting cap but the ANFO was scattered around the can on the ground and there was no crater formation. However, detonation was observed in the charges containing the SO-grain and the ZOO-grain Primacord loop as evidenced by fragmentation of the cans, absence of ANFO and small craters in the ground where the cans have been placed. These results demonstrate that the sensitivity of 4 the mixture is about the same as ANFO and that mixing, bagging, aging and charging to blast holes presents no unusual safety problems.

EXAMPLE 3 Prilled ANFO (400 lbs.), containing 6% diesel number 2 fuel oil, was charged to a rotary-drum, cement-type mixing unit and mixed with 6% water to which had been added approximately 20% of oil-treated ammonium nitrate (ANFO). The approximately resulting composition of the mixture was 88% ammonium nitrate, 6% diesel number 2 fuel oil and 6% water. ANFO was added to the water in order to prevent freezing at the ambient temperature which was below 32 F.

The diesel number 2 fuel oil, contained in the ANFO, was colored by the addition of one gram of an oil-soluble red dye per gallon of oil. The color of the ANFO was a light pink and this color was retained in the mixture of ammonium nitrate, fuel oil and water. The contents of the mixing unit were discharged into a bagging bin and loaded into polyethylene bags (approximately 50 lbs.) These bags were aged at ambient temperatures for 14 days. The previously described loss of prill structure was observed during the mixing operation and during aging. After the 14-day period, the contents of the bags were recharged to the rotary-drum cement-type mixing unit and mixed for 15 minutes.

The resulting product was a mixture of finely-divided ammonium nitrate solids with the added fuel oil and water. The added fuel oil and water were retained by the ammonium nitrate to the extent that no separation was observed over a period of several weeks. The density obtained by light tapping of a filled container was 1.1 which was increased to 1.2 by hand packing of the mixture.

A sensitivity test was conducted in accordance with the test described in Example 2. There was no detonation when using number 6 and number 8 blasting caps. However, there was partial detonation with a IOU-grain Primacord loop and a strong detonation with a ZOO-gram Primacord loop.

EXAMPLE 4 For hundred pounds of prilled ammonium nitrate containing 6% number 2 diesel fuel oil was charged to a rotary-drum, cement-type mixer as in Example 3. The oil contained in this mixture also contained a red dye to provide coloration for the mixture. One gallon of water was added to the mixer and the mixture blended for 15 minutes. The resulting mixture was then charged to 50-pound bags which were stored at ambient conditions.

There was little evidence of prill breakdown during the 15 minutes mixing interval. However, after standing overnight, the prills could be broken down partially by slight tamping and the density of this mixture was determined to be 0.9 gm./cc. which could be increased to 1.1 gm./ cc. by hand-packing.

When the mixture was tested for its detonation characteristics as in Example 2, no detonation was observed with number 6 and number 8 blasting caps but the mixture detonated with both IOU-grain and ZOO-grain Primacord loops.

From the foregoing description it is readily apparent that the process of this invention affords providing an improved blasting composition which is particularly suitable for blasting operations in water-filled blast holes. In accordance with this invention the density of the resulting product will be greater than about 1 and it is preferably from about 1.1 to about 1.2. Although this increased density may be achieved by the critical process steps employed herein, in those instances where, for one reason or another, the density of the resulting composition is somewhat less than 1, it has been observed that this density may be increased to the desired range by simply hand-packing the resulting composition.

What is claimed is:

1. A process for the preparation of ammonium nitratebased blasting compositions which comprises:

(a) adding water to a mixture of prilled ammonium nitrate and fuel oil in which the oil constitutes from about 4 to about 8 weight percent of the ammonium nitrate, said water being used in an amount of from about 1 to 8 weight percent based on the weight of said mixture of prilled ammonium nitrate and fuel oil.

(d) continuing mixing of the resultant mixing until a nitrate fuel oil prills have been substantially completely coated with water,

(0) discontinuing said mixing and aging the resulting mixture for a period of time suflicient to produce a composition in which the contained prills have been substantially converted to finely-divided solids, and

(d) continuing mixing of the resultant mixture until a product is obtained having a greater density than the density of the starting prilled ammonium nitrate-fuel oil mixture.

2. The process of claim 1 wherein said mixture is aged for a period of time sufiicient to produce a composition which, after continued mixing, produces a product having a density of from about 1.0 to about 1.2.

References Cited UNITED STATES PATENTS 3,305,414 2/1967 Hodgson 149-46 3,394,038 7/ 1968 Minnick et al 14946 X 3,450,582 6/1969 Sheeran 14946 X 3,558,749 1/ 1971 Rank et al 1492 X STEPHEN J. LECHERT, JR., Primary Examiner US. Cl. X.R.

Patent No 3 9 7 A21 Dated October 9 1973 Jared w. Clark Inventor (s) It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

.Column 2 line A, "packaging" should read packing Column 12, line 56, "complee" should read complete Column-4, line 10 (line 5 of Example 3), "approximately" should read -1-: approximate Column L, line 59 (the penultimate line of Example 5), "gram" should read. gr I I I Column 4, line Ah (line 1 of Example A), "for" should Q read Four I colu n '5, lines 11-13 should be deleted and (b) mixing the resulting mixture until the ammonium nitrate fuel oil prills have been substantially completely coated with water,

should be inserted therefor.v

Signed and sealed this 20th day of August 197A.

(SEAL) I Attest: V r 7 MecoyM. GIBSON, JR. c. MARSHALL mm Attesting Officer Commissioner of Patents I FORM Po-1050 (10-69) v USCOMM-DC oo.a7e. i 9 U GOVERNMENT PRINTINQ OFFICE l9! 0-386-334.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 7 h I Dated October 9, 1973 Jared w. Clark Inventor(s) It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

I Column 2 line A, "packaging" should read packing Column 2, line 56, "complee" should read complete Column I, line 10 (line 5 of Example "approximately' should read approximate Column line 39 (the penultimate line of Example 5),' "gram" should read. grain Column line l l- (line 1 of Example I) "for" should read Four I i I Column 5, lines 11-15 should be deleted and (b) mixing the resulting mixture until the ammonium nitrate fuel oil prills have been substantially completely coated with water,

should be inserted therefor.

Signed and sealed this 20th day of August 197 (SEAL) Attest: p 7 MeCO M. GIBSON, JR. c. MARSHALL DANN Attesvting Officer Commissioner of Patents FORM 90-1050 ($59) uscoMM-Dc scan-Poo U.$. GOVERNMENT PRINTING OFFICE 2 I9, -'3'3Il,