Protection layer mining

Peide Sun, Xuefu Xian. 1998. Solid-gas coupled analysis for safety range of upper protective layer mining. Chinese Journal of Rock Mechanics Engineering. 17(supp) 932-936 (in Chinese with English abstract). 

Powder sheathed with various protective layers. It is used mainly for mining and quarrying operations. The flame developed is transmitted along a preselected path to the pyrotechnic charge, where it can either initiate the chge directly or initiate one or several squibs that are used as chge igniters... 

Maier, Bur. Mines Techn Paper, 1925,360 Southard and Nelson, J.A.C.S., 1937,59,911. A protective layer of another liquid, e.g. concentrated sulphuric acid, may be used King and Partington, J.C.S., 1926, 128, 925 (chlorine dioxide). 

In summary, super-long fully-mechanized caving face was used for mining as a protective layer, its high productivity and high efficiency advantages were not fully reflected, and the large amount of gas emission threatened the safety of face production. 

Theory and practice showed that mining using super-long fully-mechanized caving face as lower protective layer had problems of large gas... 

Liulin, 2010. Rational protection range of lower protective layer and application in pressure-relief gas extraction. Xuzhou China university of mining and technology. 

Hao Zhiyong, et al. 2007. Numerical simulation and analysis of the law of overlaying strata movement in the mining of protective layers of coal seams based on UDEC. China Mining Magazine, 16(7) 81-84. 

A typical setting of equipment for a sulfur well and the principles of mining are illustrated schematically in Eigure 1. Eirst, a hole is drilled to the bottom layer of the salt-dome cap rock with equipment of the same type as that used in oil fields. Three concentric pipes within a protective casing are placed in the hole. A 20-cm pipe inside an outer casing is sunk through the cap rock to the bottom of the sulfur deposit. Its lower end is perforated with small holes. Then, a 10-cm pipe is lowered to within a short distance of the bottom. Last and innermost is a 2.5-cm pipe, which is lowered more than halfway to the bottom of the well. 

The intimate mixing of oxidizer and fuel in emulsions give these explosives much higher detonation velocities when compared to ANFO. For example, in 150 mm diameter PVC ANFO has a velocity of about 4000 m/sec, and a sensitized emulsion would have a velocity closer to 6000 m/sec at a density of 1.20-1.25 g/cc. Also, the layer of oil surrounding each oxidizer solution droplet protects the emulsion from extraneous water intrusion and subsequent deterioration of the explosive. Many studies have shown that when mining operations use emulsion explosives rather than ANFO, which has basically no water resistance, the amount of nitrate salts in mine ground water is reduced considerably. This can be a very important factor in today s environmentally conscious mining and explosives industry. 

In German coal mines, two different protective circuits are established method A uses a common concentric conductor (kz and t in Fig. 12.3(d)) as a protective earthed (PE) conductor. The semiconductive layer (pp) is used as a monitoring conductor (UL) with (z) an uninsulated copper conductor to lower the longitudinal resistance. Between PE and UL, a sinusoidal monitoring... 

An investigation of the surface composition and chemical state of three naturally weathered arsenopyrite samples exposed for periods ranging from 14 d to 25 yr showed that the arsenopyrite surface has an effective passivating layer that protects the mineral from further oxidation (Nesbitt and Muir, 1998). The same samples were then reacted with mine-waste waters, which caused extensive leaching of the arsenopyrite surface below the oxidized overlayers. The acidic nature of the solution caused dissolution of the previously accumulated ferric arsenite and arsenate salts. 

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