Low-density granular blasting agent for use in mining

Abstract

The invention relates to the development of a low-density granular Oxidizing Agent (PAN), the ingredients of which do not segregate and are conferred with explosive properties through the simple mixture thereof with combustible ingredients, thereby producing a low density granular Blasting Agent (PANFO). PANFO has many applications in the mining industry, in both open-pit and underground operations, said agent being suitable for use alone in applications intended to control damage to the banks or mixed other explosives typically used in the industry. According to the invention the density of the mixture can be adjusted to the conditions of the rock to be blasted and, consequently, the fragmentation requirements can be maximised. When used as a diluent of standard ANFO prill, the low-density reactive nature of PANFO eliminates the risks of detonation failures, associated with the segregation of the ingredients of the mixture, regardless of the desired degree of dilution or the level of segregation produced during pit loading.

1 . A low density granular Blasting Agent, CHARACTERIZED in that it comprises three basic components: low density inert particles, an oxidizing aqueous solution and a liquid combustible of the fuel oil type. 
     
     
         2 . The low density granular Blasting Agent of  claim 1 , CHARACTERIZED in that said low density inert particles are selected from natural rocks of volcanic origin such as perlite and other porous and absorbent rocks such as pumice, vermiculite, bentonite, expanded clays and the like, capable of absorbing and retaining aqueous solutions. 
     
     
         3 . The low density granular Blasting Agent of  claim 2 , CHARACTERIZED in that the perlite is selected from said inert particles. 
     
     
         4 . The low density granular Blasting Agent of  claim 3 , CHARACTERIZED in that the perlite is an inert material obtained from siliceous rocks wherein its more distinctive characteristic with respect to similar volcanic rocks is its capacity of being expanded when subjected to high temperatures, becoming a very light and absorbent material. 
     
     
         5 . The low density granular Blasting Agent of  claim 4 , CHARACTERIZED in that the expanded perlite is used in granular form with particle sizes between 0.5 millimeters and 15 millimeters, and densities from 50 kg/m 3  to 350 kg/m 3 . 
     
     
         6 . The low density granular Blasting Agent of  claim 5 , CHARACTERIZED in that the expanded perlite has preferably a size comprised in the range from 2 millimeters to 10 millimeters. 
     
     
         7 . The low density granular Blasting Agent of  claim 6 , CHARACTERIZED in that the preferred density of the expanded perlite is between 80 kg/cm 3  and 200 kg/cm 3 , as at said range perlite preserves an adequate capability to absorb and retain liquid, while maintaining sufficient mechanic strength. 
     
     
         8 . The low density granular Blasting Agent of  claim 1 , CHARACTERIZED in that the aqueous oxidizing solution is selected from alkali metal nitrates, alkaline earth metal nitrates, alkali metal chlorate, alkaline earth metal chlorate, alkali metal perchlorates, alkaline earth metal perchlorates, urea nitrates, guanidine nitrates and any mixture thereof. 
     
     
         9 . The low density granular Blasting Agent of  claim 8 , CHARACTERIZED in that the selected aqueous oxidizing solution is ammonium nitrate and is used in the form of an oversaturated solution at temperatures higher than ambient temperature. 
     
     
         10 . The low density granular Blasting Agent of  claim 9 , CHARACTERIZED in that concentration of the saturated ammonium nitrate solution used is in the range of from 70% to 96% by weight of ammonium nitrate and the corresponding saturation temperatures thereof are approximately 35° C. and 125° C. 
     
     
         11 . The low density granular Blasting Agent of  claim 1 , CHARACTERIZED in that said liquid combustible of the fuel oil type is selected from naphtha compounds such as: fuel oil, gas oil, kerosene and/or mixtures thereof; paraffin compounds such as mineral oils, light lubricant, waxes and/or mixtures thereof; vegetable compounds such as sunflower, corn oil and/or mixtures thereof, and other compounds such as sucrose, glucose, fructose, maltose and molasses and/or mixtures thereof. 
     
     
         12 . The low density granular Blasting Agent of  claim 11 , CHARACTERIZED in that the selected liquid combustible is of the fuel oil or gas oil type or mixtures thereof. 
     
     
         13 . A process for preparing the granular Blasting Agent of  claim 1 , CHARACTERIZED in that the low density inert particles, preferably expanded perlite, are placed in contact with the high temperature oxidizing aqueous solution, preferably of ammonium nitrate and the liquid combustible of the fuel oil type, in accordance with a determined order. 
     
     
         14 . The process for preparing the Blasting Agent of  claim 13 , CHARACTERIZED in that crystallization of the oxidizing aqueous solution salts, preferably ammonium nitrate, within the porous spaces of the low density inert particles, preferably expanded perlite, will occur as a result of the natural water cooling and evaporation process of water within the oxidizing aqueous solution. 
     
     
         15 . The process for preparing the Blasting Agent of  claim 14 , CHARACTERIZED in that the more concentrated the ammonium nitrate solution, the more crystals will be precipitated by cooling and the less water will be necessary to evaporate in order to complete crystallization and drying. 
     
     
         16 . The process for preparing the Blasting Agent of  claim 15 , CHARACTERIZED in that the thus formed ammonium nitrate crystals remain trapped within perlite pores and in a thin surface layer without the possibility of segregation unless proceeding to physical destruction of the aggregate. 
     
     
         17 . The process for preparing the Blasting Agent of  claim 16 , CHARACTERIZED in that the expanded perlite acts as a carrier for ammonium nitrate salts, giving rise between them to a low density granular Oxidizing Agent (PAN), the latter being a non explosive granular product whose final density shall mainly depend on the degree of porosity of the perlite used. 
     
     
         18 . The process for preparing the Blasting Agent of  claim 17 , CHARACTERIZED in that if it is necessary to reduce ammonium nitrate crystallization on the surface of the expanded perlite and prevent the generation of a thicker coating layer that increases density of the low density granular Oxidizing Agent (PAN), it is convenient to promote draining of the excess solution, by excess meaning that amount above the retention capacity of the perlite granules. 
     
     
         19 . The process for preparing the Blasting Agent of  claim 18 , CHARACTERIZED by working with an oversaturated solution whose temperature runs 20° C. to 30° C. above the saturation temperature corresponding to the solution concentration. 
     
     
         20 . The process for preparing the Blasting Agent of  claim 19 , CHARACTERIZED in that said oversaturated solution may or may not comprise other dissolved salts such as urea, sodium nitrate and calcium nitrate. 
     
     
         21 . The process for preparing the Blasting Agent of  claim 20 , CHARACTERIZED in that it includes an initial classification stage to eliminate the excess of fine material from inert particles of the expanded perlite, followed by a soaking or wetting stage of the expanded pertlite with the ammonium nitrate aqueous solution at a high temperature, and finally a natural or induced drying stage. 
     
     
         22 . The process for preparing the Blasting Agent of  claim 21 , CHARACTERIZED in that the granular mixture preferably includes a drying stage. 
     
     
         23 . The process for preparing the Blasting Agent of  claim 22 , CHARACTERIZED in that among the various types of dryers, the more efficient for drying said granular products are rotary kilns or belt dryer equipments with countercurrent hot air flows, as well as fluidized bed furnaces. 
     
     
         24 . The process for preparing the Blasting Agent of  claim 23 , CHARACTERIZED in that the liquid combustible of the fuel oil type can be added moments before it is loaded into the blastholes, in a way similar to that employed with prilled ammonium nitrate used in the production of mixtures of prilled ammonium nitrate and fuel oil (called ANFO). 
     
     
         25 . The process for preparing the Blasting Agent of  claim 24 , CHARACTERIZED in that the liquid combustible of the fuel oil or gas oil type is added to the granular Oxidizing Agent (PAN) at ratio such that the resulting composition is oxygen balanced, which means approximately 6% of the weight corresponding to the ammonium nitrate crystals precipitated in the perlite. 
     
     
         26 . The process for preparing the Blasting Agent of  claim 25 , CHARACTERIZED in that a combustible ratio in a range from 6% to 10% is used to ensure the presence of a sufficient amount of combustible in intimate contact with the ammonium nitrate crystals. 
     
     
         27 . The process for preparing the Blasting Agent of  claim 26 , CHARACTERIZED in that the low density granular Blasting Agent is mixed with other explosives in order to increase initiation sensitivity and/or adjust performance to operating requirements. 
     
     
         28 . The process for preparing the Blasting Agent of  claim 27 , CHARACTERIZED in that the other explosives include the typical products used in the mining industry such as ANFO, slurries and explosive emulsions, as well as fines of military explosives including pentaerythrol tetraamine, cyclo-1,3,5-trimethylene-2,4,6-trinitramine), trinitrotoluene, nitroguanidine, cyclotetramethylene tetranitramine and similar products known in industry. 
     
     
         29 . Use of a Blasting Agent of  claim 1 , CHARACTERIZED in that it is capable of controlling rock fragmentation and damage, its ingredients do not segregate due to density differences, its composition may be oxygen balanced making it suitable for open pit and underground mining operations; prior to being mixed with the combustible ingredient (fuel oil) it is classified as a granular Oxidizing Agent, thus having fewer risks and less handling, transportation and storage restrictions, while its granular nature allows the use of existing mechanized mixing and blasthole loading technologies, alike those being used for standard ANFO brills.