Dubrovnik International ESEE Mining School – DIM ESEE 2020 Small mining sites – Innovation in exploitation and processing October 12th – 16th, 2020 IUC Dubrovnik, Croatia Advanced blasting solutions for exploitation in small mining sites Ass. Prof. Peter Shishkov | eng. Nadezhda Stoycheva PhD-student| University of Mining and Geology “St. Ivan Rilski”, Sofia, Bulgaria Historical overview of rock fracturing Before blasting - from primitive tools, pick and hammer to fire ➢ In pre-historical times, miners used primitive tools for digging. ➢ Mining shafts were dug out by hand or using stone tools, making the entire process too long. ➢ During the ancient period, the pick and hammer were replaced with fire to carve tunnels and reach greater depths at a faster rate. ➢ By burning of dry woods near the rock face, the stones were weakened and fractured. I. Historical overview of explosives Black powder (BP) In the late Middle Ages mining technology jumped forward again when miners started using explosives to break up large rocks. ▪ Roger Bacon published the formula of black powder around 1242. ▪ Berthold Schwartz invented the gun around the end of 13th Century, which resulted in further refinement of BP. ▪ Blasting with powder replaced “fire setting” for loosening rock around the beginning of the 17th Century. ▪ BP was first used for blasting in Hungary, where a small gold mine began an experiment that changed mining forever. ▪ On Feb. 8, 1627, a new age started for the mining industry: the Age of blasting. I. Historical overview of explosives Black powder (BP) ▪ The crew of Oberbiberstollen of Schemnitz would tried also to attack the rock, not with fire and vinegar, but with black powder. ▪ It began by using a striking rod with a large hammer, forcing horizontal holes into the face of the drift. ▪ Drilling a hole needed a crew of 5 men – one who would hold and turn the striker bar, three men with heavy sledgehammers who would take turns striking the bar, and one man who was in time-out. ▪ Each hole was filled with small amounts (about 16 – 20 g) black powder. ▪ A reed-pipe with well stuffed black powder was placed into the hole as a primitive delayer, and a wooden plug was inserted into the end to keep everything tight. ▪ An explosion occurs around half minute after ignition of the end of the “reed-fuse”. ▪ Black powder is a deflagrating explosive, meaning it burns rapidly but does not detonate and it does not produce a shockwave. This was not an age of optimization of blasting. The focus was on completing the job and spreading the technology to other mines. The actual development, formulations and history are heavily debated today. I. Historical overview of explosives Detonating explosives • The first detonating explosive has been developed • Ascanio Sobrero invented the nitroglycerin in 1847 in 1608, The name of this explosive was lost to experimenting to find a new medicine for angina. history. • Two laboratory accidents • In 1659, the first ammonium nitrate compound was produced by treating of NH4CO3 with HNO3. • Began to used in mining • Fulminating silver was invented in 1786. • Immanuel Nobel (Alfred Nobel’s father), built a small factory in 1861 in Sweden At that time, priming explosives were not heavily utilized and considered too sensitive to be used in a • Alfred lost his brother and a chemist during a large practical manner. plant explosion I. Historical overview of explosives Dynamite • Invented by accident, after spilling nitroglycerin and absorbing it with diatomaceous earth (kieselgur). • The resulting solid after saturation of porous earth with nitroglycerin, reduced the instability of "nitro“, but could be detonated by a blasting cap. • Dynamite (from dynamis – meaning power). • Patented in 1867. In later years, sugar cane and wood pulp replaced kieselgur in it’s formula. • Advantages: - more powerful than black powder; - higher velocity of decomposition (detonation); - more effective in breaking rocks (not only moved them, but broke them apart). • Shortcomings: - would freeze; - sensibility to heat and mechanical impacts; - exudes toxic nitro fumes, that cause headaches; - ageing with migration of the nitroesters. The dynamite was one of the greatest inventions for the explosive industry and led to rapid advances in commercial blasting. Over 340 000 tons manufactured in 1955. I. Overview of explosives Trinitrotoluene (TNT) • Invented in 1863; • Used in production of dyes. • Explosive properties discovered by, Carl Häussermann, in 1891. • TNT was valued partly because of its insensitivity to shock and friction, with reduced risk of accidental detonation • It was additionally desensitized in amorphous form. To detonate, it must be triggered by a pressure wave from a starter explosive, called an “explosive booster”. • TNT neither absorbs nor dissolves in water, which allows it to be used effectively in moisturized environments ❑ Advantages: • TNT became the mostly used explosive material after - enough powerful with higher velocity of First World War. detonation; • It was used until the end of 20th Century as sensitizer and - water resistant and heavier than water; fuel in various compositions and as individual explosive - sustainable molecules. • The relative effectiveness factor (RE factor) or TNT ❑ Shortcomings: equivalent is a significant trace in the explosive science. - poisonous, carcinogenic; • TNT is toxic, pollutant and carcinogenic. - low sensibility to commercial detonators; • After 1990 explosive manufacturers began to remove it - strongly negative oxygen balance, toxic carbon from the receipts of commercial and military explosives. monoxide; - ageing with thermal decomposition in open-air. I. Overview of explosives through the years Modern explosives - after nearly a century, dynamite was replaced by explosives that were even safer and cheaper – ammonium nitrate-based explosives: ➢ Fine-grade and coarse-grade dry blends of AN and TNT (ammonites) were presented on the market after 1930s. ➢ Water-gel (slurry) explosives - in the 1950s Melvin Cook, tryed to add water to explosives to create a pumpable explosive product. - in same time, miners in Europe and USSR also realized, that when using rough-dispersion ammonites in wet boreholes, the blasting effect is better than in dry conditions; - manufacturers decided to put water in ammonites and to pack the mixtures; - “gelatinized explosive suspensions” was developed to solve the “water problem” with ammonium nitrate products; - in the beginning, market was not great; - use increased with development of equipment for ❑ Slurry advantages: better economics impact, drilling large diameter holes; increased loading density, low sensitivity, water - water gels was transformed later, by adding in first AN and then substituting TNT with a liquid explosive: resistance, no nitroesters. monomethylamine nitrate; - in the 1970s, research began to remove the high ❑ Slurry shortcomings: needs sensitizer, not for explosive from water gels and emulsions were made; small blast-holes. I. Overview of explosives through the years Modern explosives ➢ ANFO (Ammonium Nitrate Fuel Oil) explosives • Around 1950s, Bob Akre decided to experiment with developing a new type of explosive. • Akre had seen major disasters caused by AN and he wanted to see if he could develop an explosive from AN fertilizer. • He tried to mix AN fertilizer with different substances (molasses) in cement mixer and take them to his coal pit. • Later, Akre began adding fine coal. • Other mines started to request the new products to them. • Segregation of the ingredients led to the addition of waxes and/or oil as the fuel. ❑ ANFO advantages: easier to load, cheaper, and • Dupont introduced NITRAMON in 1935 and safer than dynamites. called his products “Blasting Agents” • ANFO replaced the dynamite in dry holes. ❑ ANFO shortcomings: desensitized by water; • Over 998 million tons was manufactured in booster needed. 1974. I. Overview of explosives through the years Modern explosives Changing of “the goals” in blasting techniques and technologies through the centuries, concerning evolution of characteristics of industrial explosives: ➢ rock breaking (with BP), ➢ crushing with powerful explosives (NG, dynamite), ➢ better fragmentation (with TNT, dry blends), ➢ safer blasting activities (with ANFO, water-gels), ➢ limitation of adverse effects (with slurry, emulsion, +Nonel), ➢ economy & blasting efficiency (bulk blasting agents + electronic timing) ... The most popular commercial explosives after 2000 year are: ❑ ANFO, ❑ slurries, ❑ emulsion blasting agents, ❑ cap-sensitive emulsions ❑ heavy blends. Their main preferences are: ✓ lower price, ✓ regulated energy output, ✓ more environmental friendly ingredients, ✓ improved safety conditions for storage, transportation and handling. II. Detonation and it’s impact over solid ambience Types of explosive’s decomposition: ➢ thermal decomposition, The level of destruction of surrounding rock is in ➢ combustion, close relation with the rate of energy releasing as a result of explosive’s decomposition. ➢ deflagration, ➢ detonation • Explosion is a general term for an accelerated release of energy generating extreme temperatures, releasing of gases and expanding volume. • Explosions may be: - supersonic as in the case with high explosives, - subsonic of low explosives (like BGP, fireworks or SFX-pyrotechnics). • Deflagration and detonation are two ways in that energy could be released suddenly. • Deflagration - when the combustion process propagates below subsonic speeds (slower