202530WO 98/13318CA 02265905 1999-03-11PCT/N097/00262Water Resistant Explosive CompositionAmmonium nitrate fuel oil explosives, hereafter called ANFO, have today adominant position in the worldâs total use of commercial explosives. ANFO is basicallymade of two components, namely ammonium nitrate (AN) as oxidiser, and ï¬iel oil (F0)as fuel.The reason why ANFO has this dominant position as the world's most used explosive, ismainly because the explosive consists of two rather cheap raw materials, besides beingvery easy to produce.ANFO can either be produced in a factory, or be produced directly at the userâssite. When produced at a factory, ANFO is usually ï¬lled in bags containing 25 or 1000KGs.ANFO prills have good ï¬ow properties, that is, they ï¬ow easily in pipelines, andthey are specially well suited for bulk loading with pneumatic loading equipment. ANFOis then filled in a pressure vessel, usually called .a âpressure potâ, and compressed air witha pressure of 3-6 bar is applied. By means of a valve at the outlet of the pressure pot,which opens and closes, the ANFO is blown down to or into the bore holes.The greatest disadvantage with the ANFO-explosives is their lack of waterresistance. Usually this problem is solved by blowing the bore holes free for water bymeans of compressed air immediately before charging, and then carry out the blasting assoon as possible after loading. In many cases this method works well in order to chargeANFO in water ï¬lled bore holes, except for cases when cracks in the rock will lead thewater into the bore hole after having loaded the ANFO.Lots of work has been done in order to make the ANFO more water resistant.However, new additives that will make ANFO more water resistant, will at the same timeresult in both a more expensive and complicated product to manufacture. Consequently,the main advantage with ANFO, namely low price, will be reduced, and other waterresistant explosive alternatives will become more competitive.From the patent literature there are two known principles for making ANFO waterresistant:One of the methods recommends adding a certain percentage of an emulsion explosive tothe ANFO. This is described in US-patents No. 4.111.727 and 4.181.546. The explosive2030W0 98I133l8CA 02265905 l999-03- llPCT/N097/002622resulting from this is called Heavy ANFO, and is usually classiï¬ed as a special type ofexplosive. Besides, Heavy ANFO can not be loaded by means of pneumatic loadingequipment. Normally, Heavy ANFO will not be considered as a water resistant ANFO.The other method described is adding so called water thickening agents to theANFO. These agents will then âreactâ with the water, making this highly viscous andthereby stopping further penetration of water into the product.US-patent No. 4.933.029 describes a water resistant ANFOâexplosive where thewater resistance is achieved by using a water thickening agent like guar gum. In additionto this, it is known to use water repellent agents, like fatty acids, wax, etc. Also ï¬llerslike talc, glass, expanded perlite, sulphur, etc-., may be used for preventing water topenetrate into the ANFO.US-patent No. 5.480.500 describes such a water resistant ANFOâexplosive. In thispatent the water resistance is achieved by both applying a water thickening agent as guargum, and simultaneously adding a particulate ï¬lling agent, for instance pulverisedammonium nitrate in order to stop penetration of water into the ANFO.The characteristic feature by applying above mentioned product in accordancewith the technique already known, is the fact that one will allow some water to penetrateinto the explosive, resulting in a reaction with the ANFO. This again will form a barrieragainst further water penetration. At areas where the water has âreactedâ with ANFO inorder to form a barrier against further water penetration, the ANFO in this area isdamaged. The degree of water penetration into the ANFO is often used as a measure ofhow good the water resistant ANFO in question really is.In US-patent No. 5.480.500 the water penetration in the ANFO is measured bypouring 100 ml cold water in the middle of an ANFO column which is ï¬lled in a 1000 mlgraduated cylinder. During 15 seconds the water is carefully poured at top of theexplosive column. The water resistant ANFO and the water is left for one hour, forthereafter to measure how deep the water has penetrated into the ANFO. The best resultin the above mentioned patent was a water penetration of 5,5 cm. In bore holes withï¬owing water this means that the explosive will have a layer of 5.5 cm where the ANFOis damaged by water and cannot contribute to detonation. Furthermore, if one should puttodayâs water resistant ANFO in a bore hole partly ï¬lled with water, the explosive wouldbe mixing with the water, and one would have a mixture unable to detonate.2030W0 98ll3318CA 02265905 l999-03- llPCT/N 0971002623The present invention provides a water resistant ANFO-product which willdetonate even when poured into a bore hole partly ï¬lled with water. Therefore, thisconcept is not based on the previously known principle that the water âreactsâ withANFO and forming a barrier for preventing further water penetration into the ANFO-explosive.The invention with this current water resistant ANFO patent, is that it utiliseswater in the bore hole so that the dry ANFO and water in the borehole form a slurry. Thiswater resistant ANFO may thus be described as an âinstant slurryâ of the watergel type.A watergel-slurry is characterised by consisting of dissolved salts of nitratesand/or perchlorate, and the water content may vary from approx. 10 to 30 %. The slurryis thickened with various types of gums and will also often contain some undissolvedsalt, usually ammonium nitrate. A watergel slurry is usually sensitised either bychemical gassing or by addition of porous particles such as hollow micro balloons orexpanded perlite.The water resistant ANFO in accordance with the current invention (âinstantslurryâ) may therefore consist of the same components (except for water, which ispresent in the bore hole) known from the patent literature related to a watergel slurry.In accordance to the current invention, it is possible to apply any chemical gassingreagent responding to water in the bore hole, which will develop gas bubbles sensitisingthe explosive. Some examples of gassing reagents which may be used are: Sodiumbicarbonate. aluminium, nitrite (particularly sodium nitrite) and calcium carbide.In order to get the first three previous mentioned substances to respond to waterdeveloping a gas, the water has to have a low pl-I-level. Consequently, the bore holewater has to be made acidic by ensuring that the water resistant ANFO also contains anacid, lowering the pl-I-level sufficiently for a reaction and development of gas. It ispreferred to use one or more of organic acids chosen amongst citric acid, tartaric acid,ascorbic acid or acetic acid. It may also be used an inorganic acid which lowers thewater's pH in an adequate way.The two last-mentioned gassing reagents will easily decompose or react, whenstored for a longer period together with AN and small amounts of humidity always beingpresent in the ANFO. These should therefore be given at protecting water soluble layer, forinstance through a micro encapsulation process.202530W0 98I133l8CA 02265905 l999-03- llPCT/NO97I002624Sodium bicarbonate (NaHCO,) is the preferred gassing reagent because it is cheap, easyto use, and has storage stability together with ANFO. Sodium bicarbonate can be used involumes from 0,1 to 10 % by weight of the total mixture. The preferred volume is from0,5 % by weight to 5 % by weight. Together with sodium bicarbonate it is preferred touse citric acid as a pH lowering agent, in amounts of 0,5 to 10 % by weight of the totalmixture. The preferred amount of citric acid used together with sodium bicarbonate is 2to 7 % by weight.In combination with a gassing reagent, solid density reducing agents may beadded. These agents are well known from the slurry literature and include hollow microballoons, perlite, foamed glass, volcanic ash or other porous particles with open or closedpores which have an adequate low volume density.As thickening agent for water in accordance with the invention, it may be usedseveral different types and combinations. These are also known from the patent literature,both concerning water resistant ANFO and watergel slurry. Some examples of suchthickening agents are: Guar gum, xanthan gum, CMC (carboxymethyl cellulose), varioustypes of alginates and âsuper-absorbentsâ used in modern napkins and sanitary towels.These water thickening agents must tolerate salts in the water, and must have an ability tothicken the water with a suitable speed (that is during 1-10 minutes).It is possible also to cross-link the thickened gum. As cross-linking agent may forexample potassium pyroantimonat or sodium dichromate be used. Generally, thethickening agent(s) should be present in an amount of 0.1 °/o to 10 %. based on the weightof the explosive mixture. The preferred amount will be from 2 % by weight to 7 % byweight.When a water resistant ANFO. according to the invention, with added sodiumbicarbonate and an organic acid is poured into a bore hole where water is present, forinstance with water some meters from the bottom of the bore hole and up, the ANFO willsink to the bottom and expel the water upwards, at the same time as parts of the ANFOwill start dissolving. The added acid will also dissolve in the water, and lower the pH sothat sodium bicarbonate will start to decompose and develop CO2 -gas. The developed gaswill force the water which is in the process of being thickened further up in the dryANFOâcolumn. This lowers the concentration of water in the bottom of the bore hole,and makes it more easy to detonate.2035W0 98/13318CA 02265905 l999-03- llPCTIN097/002625In order to avoid too high water concentration in the bottom of the bore hole, thethickening agent should not thicken the water too fast, but gradually as the gassingdevelops and starts pushing the water further upwards into the dry ANFO-column.To avoid a too high water concentration in the bottom charge, it may also be beneï¬cial touse an ANFO-mixture with partly crushed prills, because this will also expel the watermore effectively.ExamplesTo simulate a partly ï¬lled bore hole, we used a steel tube with a diameter of 64mm and a length of 400 mm. The tube was filled with water up to a level of 65 mmabove the bottom, that means approx. 16 % of the tube length (or volume) was ï¬lled withwater.The various test explosives were poured directly into the water until this was expelled andthen further until the tube was completely ï¬lled. The bottom of the tube was closed bymeans of a strong tape, and immediately after the tubes had been ï¬lled with ANFO, thetop of the steel tube was closed with a second strong tape, which however, was perforatedwith small holes to let out the excess gas.The steel tubes were test shot using a 150 gram primer attached to the bottom of the tubes,and the velocity of detonation (VOD) was measured at the uppermost 100 mm of the steeltube.Table 1 shows results with some test mixtures compared to two of Scandinaviaâscommercially available water resistant types of ANFO, namely Aqanol and Solarnon.In the examples various water resistant ANFO mixtures were ï¬lled in 64 mm steeltubes which in advance had 16 % of the total tube volume ï¬lled with water. The velocitydetonating (VOD) was compared with the before mentioned commercial water resistantANFO explosives, and with ANFO-mixtures without gassing reagent.â CA 02265905 1999-03-llW0 98/ 13318 PCT/N097/002626TABLE 1The components are given in % by weight of the total mixtureExample No. 1 2 3 Tâ 4 5 " 6 "AN-prill 83,5 % 85,5 % 84,0 % 86,0 %Fuel oil 4,0 % 4,0 % - 5,0 %Glycol - - 9,0 % -Urea 2,0 % 2,0 % - -Guar gum F-21 4,0 % 4,0 % 4,0 % 4,0 %Citric acid 4,0 % 4,0 % - 3,0 %Tartaric acid - â 1,5 % -Sodium 2,0 % - 1,5 % 2,0 %bicarbonateBorresperse 2â 0.5 % 0,5 % - -Aqanol 100 %Solamon 100 %VOD (m/s) F 3â F 3â 2 400 F 3â 3 100 2 900I) _2):3):â Examples according to the inventionSodium lignosulphonate from Orkla ASAFail (no detonation)