Coal Mining Methods

Two major coal mining methods is underground coal mine and surface mine.
Underground Coal Mine
There are two methods of underground Coal mine, room-and-pillar mine and longwall mine. Room and pillar mining method is done by cutting coal mine area then conveys it to a waiting shuttle car which transports it to the conveyor belt to be moved to the surface and no explosion is needed.  After reach a specified distance, the continuous miner is backed out and roof bolts are put in place.  The process is repeated until the coal seam is mined.
Longwall method involves pulling a cutting machine of the coal seam.  This machine has a revolving cylinder with tungsten bits that shear off the coal.  Longwall mining involves making careful planning to ensure there is geological support before starting mining activities. Depth of coal surface varies in depth of 300 – 1000 feet. The mine roof is supported by large steel supports, attached to the longwall machine.  As the machine moves forward, the roof supports are advanced and The coal falls into a conveyor system which carries it out of the mine to surface.  Nearly 75 percent of the coal can be removed using this method.  The remaining 25 percent of underground production is produced by conventional mining which uses explosives to break up the coal for removal.
Surface mine
Surface mine is also called a Open Mine, this method only has economic value when the coal near to the surface. To do this, company must gather an information about climate, soil composition, wildlife and government regulation of surface mine. With open mine method, about 90% of coal could be taken. Open mine involves lot of tools including dragline, hydraulic shovel, excavator, treadmill and mine trucks to transport the coal to the surface. The coal and soil separated with explosive, then the materials transported to the surface through a pulley puller or with shovels and trucks. Once the coal is removed, the land is returned to the desired contour and Native vegetation or trees are planted.
Coal Processing
The coal processing depending on the content and purpose. This coal may only need a simple process, or may require complex manufacturing processes to get specific coal quality. To separate coal and other material, the raw coal separated into fractions of various sizes then this raw material released into tank containing liquid with specific gravity, lighter materials will float and can be separated, stone and other materials which are heavier and will sink discarded as waste.
Smaller fraction is processed according to differences in density as the centrifuge. Centrifuge is a machine that reproduces an old very quickly, so that separates solid and liquid inside the container. Alternative methods using different surface content of coal and waste. In flotation, the carbon particles are separated in the bubbles produced by air blown into the immersion of water containing chemical reagents. Recent technology developments helps improve good quality of coal.

How to Determine Coal Quality : Coal Quality Factors

Coal is a source of energy that can not be renewed. Because the coalification involves several factors, the quality of coal also varies. General Coal quality parameters is the calorie content of moisture, flight substances, ash content, carbon content, sulfur content, size and Grinding Hardgrove Index, and other parameters such as elemental analysis in the ash content (SiO2, Al2O3, P2O5, Fe2O3, etc.), analysis of the composition of sulfur (pyritic sulfur, sulfate sulfur, organic sulfur), and the melting point of ash (ash fusion temperature ). Taking the example of coal plants, the effects of the above parameters of power generation equipment are as follows:
1. Calorific value (CV)
CV has a great influence on the operation of the sprayer / grinder, charcoal tubes, and Windbox and the burner. The higher the CV of the flow of coal every hour, so the lower your rate adjusted feeder coal.
For coal with a moisture content and Grinding Hardgrove Index same level, then a high CV spray causes operate under its normal capacity (by design), or in other words, the operating ratio will be lower.
2. Coal Moisture
The results for moisture analysis is divided into free moisture (FM) daninherent moisture (IM). The number of calls for a total moisture (TM). The moisture content affects the amount of primary air intake. Coal high humidity requires more primary air for drying the coal to a specific temperature for the spray output.
3. Volatile matter
VM womb affects the perfection of the intensity of burning and fire. The evaluation is based on the ratio of carbon (fixed carbon) substances flight, called the fuel ratio (fuel ratio).  The highest value of the fuel ratio, the amount of carbon in coal is not burned is also growing. If the comparison is a value greater than 1.2, then the contact will be less good, which resulted in lower recording speed.
4. Ash content
The ash content will meet with the combustion gases through the combustion chamber and the conversion in the form of fly ash (fly ash), which amounted to 80 percent and bottom ash as much as 20 percent. The higher ash content, in general, affect the level of fouling (fouling), wear and corrosion of the equipment that passed.
5. Fixed Carbon
Carbon content value obtained by reducing the number 100 with the level of water (moisture), ash content, and the number of flights. These values come up with pembatubaraan level. Carbon levels and the amount of substance used as a flight calculations to evaluate the quality of fuel, ie the fuel value ratio as described above.
6. Sulfur content
Sulfur in the coal pyritic sulfur is divided, sulfate sulfur and organic sulfur. But overall, the evaluation of the sulfur content in coal is expressed in total sulfur (TS). Sulfur content affects the level of corrosion that occurs on the cold side of air heater element, especially when the temperature is lower than the dew point of sulfur, as well as influencing the effectiveness of the precipitator ash detention peralatanelectrostatic.
7. Coal Size
Coal grain size is limited in the range of fine-grained (coal or dust pulverized coal) and coarse grains (mass of coal). The most delicate to the maximum size of 3 millimeters, while the coarse grain sizes up to 50 mm.
8. Grinding Hardgrove Index (HGI)
Devastating performance or mill is designed, in particular, the values of HGI. To download the HGI, their ability to operate lower than the default anyway to generate the level of fineness (fineness) of the same.

What is Coal

Coal is an organic mineral which can be burned andformed from ancient plant residual precipitate which subsequently changed its form due to physical and chemical processes that occur over millions of years. Therefore, the coal included in the category of fossil fuels. The process that turns coal plants is called as coalification.

Variety of ancient plant according to geologic age and location of growth and development, along with the site of deposition (sedimentation) of the plants, the influence of pressure and geothermal rocks and geological changes that occurred are the factors why there are various types of coal. Therefore, the characteristics of coal vary with the field of coal (coal fields) and coating (hard coal).
Formation of coal began in the formative period of the Carboniferous (Carboniferous Period), known as coal, which was the first of the season lasted from 360 to 290 million years ago. The quality of each coal deposit is determined by temperature and pressure as well as the establishment of a long time, referred to as "organic maturity." First process, the plants turn into deposits of peat which later changed its brown coal (lignite) or also called lignite (brown coal). Young coal is coal with the kind of low organic maturity.
After obtaining the effects of temperature and continuous pressure over millions of years, lignite will experience changes that gradually increase the organic maturity and youth to change coal into sub-bituminous coal (sub-bituminous). Chemical and physical changes continued until the coal becomes harder and darker color to form bituminous coal (bituminous) or coal (anthracite). Under the right conditions, an increase of more mature organic, continued to form anthracite.

In coalification process, the organic maturity, actually describes the change in concentration of each major element of the coal-forming. The following example shows the analysis of each element in each coalification stage. coalification process at higher levels, carbon levels will increase, while the hydrogen and oxygen is reduced. Because the level of general coalification can be associated with the quality or the quality of coal, coal with low coalification also called low-grade coal, materials such as lignite and sub-bituminous are generally more gentle with the fragile and without color brightness as the ground, have high levels of moisture (humidity) is high and the low carbon content, so the energy content is also low. The higher the quality of coal, generally the hardest color and compact, elegant black and will be more. Also, humidity levels would be reduced, while the carbon will increase, so the greater its energy content.

The Coal is Classified based on the level coalification usually becomes a general indicator to determine the intended use. For example, coal or coal boiler is called thermal or steam coal, used to fuel many power plants, industrial combustion at large, such as brick or tile, and cement industries, while metallurgical coal (coking coal, coke or coal) is used for industrial iron and steel industries and chemicals. Both types of coal were included in the bituminous coal. The anthracite coal used for mineral ore sintering process, the process of manufacture of electrical electrodes, burning lime, and for the manufacture of smokeless briquettes.
Before its used, the coal must be known in advance the quality. This meant that the specifications of the machine or equipment that use coal as fuel, in accordance with the quality of coal being used, so the machines can function optimally and durable.

How is Pumice Formed

Pumice stone is a type of light-colored stone, made of laminated glass bubbles. These stones are formed from magma acid by the action of volcanic eruptions that separate materials into the air, then runs in the horizontal transport and accumulate as pyroclastic rocks. Vesicular pumice has a high ecological value, containing a large number of cells (cellular structure) due to expansion of gas bubbles in it, and generally is as loose material or fragments of volcanic breccia. While the minerals in the pumice are:

• Feldspar 
• Quartz
• Obsidian
• Cristobalite
• Tridymite

How is Pumice Formed?
Pumice stones occur when the acid magma to the surface and extensive contact with the air suddenly. Foam cup with gas in it the opportunity to come out and suddenly hardened magma. Pumice fragments are generally made when a volcano terlemparkan size of pebbles to.

Pumice stones are generally found as surface melt or flow, loose parts, or fragments of volcanic breccia. Floating obsidian can also be made by heating, so the gas. Heating is carried out on obsidian from vulcano, the temperature required to transform an average 880oC obsidian pumice. Obsidian density initially decreased to 0.416 2.36 after treatment was also floating in the water.

Floating hydraulis properties. White pumice gray, reddish yellow, vesicular texture varies with the size of the hole the better with the structure oriented to each other or not skorious with holes. Sometimes the gap is filled by zeolite or calcite. These rocks are resistant to frost (frost) is not hygroscopic (water-sucking). Has the nature of introductory low heat. Compressive strength 30-20 kg/cm2. The main composition of the amorphous silicate minerals.
The types of stone that the physical structure and the formation of the same origin with pumicit pumice, volcanic cinter, and snails. While the minerals in the pumice are feldspar, quartz, obsidian, cristobalite, and tridymite.

The Earth's Atmosphere Layers

The Earth’s atmosphere is composed of 78% nitrogen (N2) and 21% oxygen (O2).  Most of the remaining 1% is composed of argon, Water Vapor, and Carbon Dioxide. The force of the Earth’s gravity and the amount of gas cause a sea-level pressure of approximately 14 lbs/ in2 or 1 bar.  This pressure decreases rapidly with increasing elevation; that is, at a higher elevation, the amount of gas is less, causing a lower atmospheric pressure. The average temperature near the surface of the Earth is about 60º F.  This regulation of temperature is a result of the reflection of incoming solar radiation by the atmosphere coupled with the blanketing effect, caused by carbon dioxide and water vapor. The amount of carbon dioxide in the Earth’s atmosphere is about 0.04% and The water vapor amount varies from 0.1% in cold, dry regions to 3% in warm, wet regions.

Earth Atmosphere Layers
The atmosphere of the Earth is estimated to be about 600 miles thick.  However, because there is no set boundary where the atmosphere ends, this estimation is somewhat arbitrary.  Nevertheless, the Earth’s atmosphere can be divided into several distinct layers identified using temperature changes, chemical composition, movement, and density.

• Troposphere  The lowest level of the Earth’s atmosphere is referred to as the troposphere.  It contains about 90% of the atmosphere’s mass.  Moreover, this layer is characterized by convection currents.  These convection currents are generated by the Sun’s radiation heating the ground and lower atmosphere.  The warmer air near the surface expands and rises, and is replaced by downdrafts of cooler air from above. Convection currents in the troposphere generate nearly all weather phenomena.
• Stratosphere – The layer of the atmosphere directly above the troposphere is the stratosphere.  Ozone Layer is in the upper part of the stratosphere, the Sun’s ultraviolet light creates a layer of ozone through a process called photochemistry.  Ozone is a form of oxygen containing three atoms per molecule
• Mesosphere – The atmosphere reaches its coldest temperature of around -170° F in the mesosphere. This is also the layer in which a lot of meteors burn up while entering the Earth's atmosphere.
• Thermosphere – The thermosphere is a region in which temperatures again increase with height.  This temperature increase is caused by the absorption of energetic ultraviolet and x-ray radiation from the Sun.

The Earth is heated more near the equator than at the poles.  Because of this, the atmosphere  redistributes much of the solar energy from warmer regions to cooler ones, which causes the formation of a global atmospheric circulation.  This circulation is usually represented in a simplified form, but in actuality, the system is quite complicated.  There are many factors that contribute to the complexity of the system, including:

• Landmasses obstructing circulation patterns.
• The tilt of the Earth’s axis causing seasonal variations.
• Coriolis Effect – The Earth’s rotation generates the deflection of large air masses.  This phenomenon is known as the Coriolis Effect and is responsible for rotating weather systems such as hurricanes.

The Earth’s atmosphere did not always consist of the same relatively stable mixture of gases that we breathe today.  The present atmosphere is the result of very gradual changes that began soon after the Earth formed.

• Primordial Atmosphere – The first atmosphere of the Earth was composed of hydrogen, helium, methane (CH4), ammonia (NH3), water vapor and low amounts of oxygen.  This atmosphere was swept away by intense solar winds – vast streams of particles composed primarily of electrons and nuclei of hydrogen and helium emitted by the Sun.
• Secondary Atmosphere – The present atmosphere of the Earth is the result of the release of gases dissolved in molten rock, a process called outgassing (similar to gases observed in present-day volcanic eruptions).  The principal components of this “new” atmosphere were probably water vapor, carbon dioxide and nitrogen.  However, it did not contain oxygen.  The oxygen of the Earth’s atmosphere was slowly added, primarily by green plants through the process of photosynthesis.  As the Earth continued to cool, clouds formed and great rains occurred.  These torrential rains eventually filled the ocean basins.  This event not only diminished the amount of water vapor in the atmosphere, but also carried away most of the carbon dioxide as well.  Eventually, large amounts of the carbon dioxide within the oceans were chemically incorporated into carbonate rock.

How to Mining Gold: Gold Mining Methods

Gold is a chemical element with the symbol Au  and an atomic number of 79. And gold has been a valuable and highly sought-after precious metal for jewelry, and other arts since long before the beginning of recorded history. Now Gold is also used in industrial applications in ceramics, electrical, and electronics applications.

Gold Mining Methods
Panning
Panning was a manual technique of washing gold. Water and dirt are put in the pan the Submerge the pan in water and then shake the pan in a circular motion under water or with water in it.  Since gold was the heaviest metal, it would sink to the bottom. Panning is the easiest technique of gold prospecting in the Gold Rush period. The standard gold pan is 16 inches in diameter, 2 1/2 inches deep and made of sheet iron.
The Stamper Battery
The Stamper Battery was a large machine. It extracted gold from rocks by crushing them. The Stamper Battery was very expensive and had a series of heavy weights  attached to it. The Stamper Battery was powered by an engine.
Sluicing
Sluicing was a common mining method during the Gold Rush period. The sluice box is placed in a stream to catch the water-flow and gold bearing material or a screen is placed on top of the box. As the water passed through the screen gold and other heavy metals would settle behind the riffles or slats. Other light metals would float away.
Puddling
Puddling tubs were larger versions of gold pans. The tub was usually a round barrel made of wood or metal. The miner would add clay and fill the tub with water. The miner would then stir the tub and this would separate the gold from the clay.
The Windlass
Windlasses were used in shallow shaft to lift the dirt to the surface. The windlass was a very slow method of mining and only worked for about 40 metres. The windlass required little skill to build and is made from simple materials and could be easily moved. Over the windlass a windsail would be attached to provide ventilation to the shaft.
The Dolly Pot
The Dolly Pot  was a small hand operated mortar and pestle. The Dolly Pot was also a rock crusher used to sample for ores and especially gold. Most Dolly Pots were made from mercury bottle.
The Long Tom
The Long Tom looked like sluice box but much bigger. The Long Tom measured 12 to 15 feet long. It was mainly made of wood and had a metal bottom with riffles and slats.
Tunnel Mining
Tunnel mining is what most people think of when they imagine mining. Tunnel mining was used to source the veins of gold that apparently went down. It consists of excavating tunnels, shafts and galleries to gain access to ore deposits within hard rock. This is done in modern times either with explosives, boring machines or both. The TauTona and Savuka Gold Mines of South Africa compete for the title of being the world's deepest underground mines--for any mineral, not just gold--both having dug deeper than 3,700 feet.

How to Identifying Mineral

Geologists have identified more than 3,000 minerals. Most common minerals are formed of more than one element, such as gold and silver, are made of single elements. All minerals is always solid and have a characteristic crystal structure.
Mineral characteristic, A mineral must has this following criteria:
•   found in nature and occurs naturally,
•   inorganic,
•   has a crystal structure (arrangement of atoms),
•   has a specific range of chemical compositions,
•  has characteristic physical properties (shape and volume).

How to identifying a mineral
Geologists use the physical properties of minerals to identify them and every mineral has specific characteristic that can be used to classified them. The physical properties of minerals are:

Hardness, every mineral has different hardness, hardness of minerals is seeing as how easy its to scratch. The hardness scale usually used to measure mineral hardness is Mohs hardness Scale. To check a mineral’s hardness, scratch it with the hardness of one of a set of reference minerals, then see where it fits on the Mohs’ Scale.
The hardness of mineral based on mohs scale

1. Talc
2. Gypsum
3. Calcite
4. Fluorite
5. Apatite
6. Orthoclase
7. Quartz
8. Topaz
9. Corundum
10. Diamond

Color, Some minerals vary in their color and only few of them have special characteristic of color. Mineral color is not good method to identify a mineral.
Density, is the mass of mineral. One method of measuring the density of a sample entails the use of one dense liquid and another miscible liquid of lower density. A solution of the two substances is created in which a crystal of the mineral in question remains suspended and neither sinks nor floats.
Fracture , takes place when a mineral sample is split in a direction which does not serve as a plane of perfect or distinct cleavage. A mineral fractures when it is broken or crushed. Fracture does not result in the emergence of clearly demarcated planar surfaces; minerals may fracture in any possible direction. Descriptions of fracture include splintery, jagged, and conchoidal  defined as the smooth curves found on broken glass. 
Cleavage,   may be determined by the examination of surfaces which have actually broken. It may also be determined by inspection of the interlacing systems of cracks which permeate the structure of certain specimens. These systems of cracks are beautifully apparent within transparent crystals such as fluorite or calcite.
Luster, is another identifying trait of minerals. It is how shiny the mineral appears or whether they are opaque or transparent.  A mineral’s luster can be described as adamantine, pearly, silky, dull, resinous and vitreous, A common type of mineral luster is vitreous, meaning “like glass.” 
Streak
Since mineral color cannot always be used to identify a mineral, geologists sometimes use streak. Streak is a mineral’s fine powder. To look at streak, powder the mineral or run it along a ceramic plate. Not all minerals have identifiable streak; quartz, for example, would be more likely to scratch the ceramic plate. Metallic minerals have the best streak.

How Do Minerals Form

Minerals can form in two ways: 

Crystallization of melted materials

• Minerals form as hot magma cools inside the crust, or as lava hardens on the surface.  When these liquids cool to the solid state, they form crystals.  

Crystallization of materials dissolved in water ( form by Evaporation )

• If you have a hot water solution (sugar and hot water), when the water cools the atom(s) leave the solution and crystallize as minerals.
• A SOLUTION is a mixture in which one substance dissolves in another.

Sedimentary Rock Process

Lithification (greek : lithos = rock) is a process whereby freshly unconsolidated deposits of sediments are converted into rock. The main processes of lithification are Compaction, Cementation and Crystallization. The physical, chemical and biologic changes that occur under conditions of pressure (up to 1 kb) and temperature (maximum range of 100C to 300C) that are normal to the outer part of the Earth's crust to the deposited sediments from the time of their initial deposition to their lithification and after it are known as diagenesis. So the definition of diagenesis is any chemical, physical, or biological change undergone by a sediment after its initial deposition and during and after its lithification. In very thick sedimentary sequences, diagenesis may grade into metamorphism, and the sediment will change from a sedimentary rock to a meta-sedimentary rock to a metamorphic rock.
Some geologists restrict the term to the initial phase of post-sedimentary changes, occurring in the zone where the sediment is still unconsolidated, the process being complete when the sediment has been converted to a more or less compact sedimentary rock. In this usage, the term is equivalent to early diagenesis as used in the U.S. The main processes of diagenesis are:
Compaction
Definition:  Compaction is the process by which the volume of sediment is reduced as the grains are squeezed together. The reduction in volume as the pore space is reduced helps to hold the rock together by binding the grains closer together and increasing the friction between grains. Intergranular fluid is expelled as volume is reduced. The degree of compaction is controlled by such factors as grain shape, sorting, original porosity, and the amount of pore fluid present.
Recrystallization
Definition: Recrystallization is a process in which physical or chemical conditions induce a reorientation of the crystal lattices of mineral grains. These textural changes cause the sediment to become lithified. It occurs in response to such factors as pressure, temperature, and fluid phase changes. It also occurs because of solution and reprecipitation of mineral phases already present in the rock.
Solution
Solution refers to the process in which a mineral is dissolved. As fluids pass through the sediment, the unstable constituents will dissolve and are transported away or are reprecipitated in nearby pores where conditions are different. The dissolution of soluble minerals by a solution under saturated with respect to that mineral depends on pH, Eh, temperature, pressure, PCO2, ion strength etc. Common minerals to dissolve are evaporates such as halite, sylvite and anhydrite. This process is important because it commonly leads to secondary porosity. Pressure solution is a process that occurs as pressure is concentrated at the point of contact between two grains in the sediment. This causes solution and subsequent migration of ions or molecules away from the point of contact, towards an area of lower pressure where the dissolved phase can be reprecipitated.
Cementation
Cementation is the process in which chemical precipitates (in the form of new crystals) form in the pores of a sediment or rock, binding the grains together. Some common cements are quartz, calcite and hematite, but a wide variety of cements are known, such as aragonite, gypsum, and dolomite. Pressure solution produces locally derived cement, but many cements consist of new minerals previously in solution in the fluid phase. Cementation reduces porosity by filling in the pore spaces between the grains.
Higher pH and higher temperatures favor carbonate cements. Lower pH and low temperatures favor quartz or chert cements. Syntaxial overgrowths are formed when cement growth occurs as and an extension of existing detrital "crystal".
The reverse process, called decementation, also is thought to occur. There is evidence that decementation has occurred in calcareous sandstones, in which case the calcareous cement or grains are dissolved in the same manner as the solution of limestones. The frosted and etched surfaces of quartz grains in some friable and loosely cemented sandstones seem to indicate the former presence of a carbonate cement that has been leached.
Authigenesis Or neocrystallization
Authigenesis (neocrystallization) is the process in which new mineral phases are crystallized in the sediment or rock during diagenesis. These new minerals may be produced:
•    By reactions involving phases already present in the sediment (or rock)
•    Through precipitation of materials introduced in the fluid phase, or
•    From a combination of primary sedimentary and introduced components.
This process overlaps with weathering and cementation. It usually involves recrystallization and may result in replacement. Authigenic phases include silicates such as quartz, alkali feldspar, clays and zeolites; carbonates such as calcite and dolomite; evaporite minerals such as halite, sylvite and gypsum, as well as many others.
Replacement
Replacement involves the essentially simultaneous dissolution of existing minerals and the precipitation of a new mineral in situ.