A mill is a device that breaks solid materials into smaller pieces by grinding, crushing, or cutting. Such comminution is an important unit operation in many processes. There are many different types of many types of materials processed in them. Mills were powered by hand, working animal, wind or water. Today they are powered by electricity; the grinding of solid materials occurs through mechanical forces that break up the structure by overcoming the interior bonding forces. After the grinding the state of the solid is changed: the grain size, the grain size disposition and the grain shape. Milling refers to the process of breaking down, sizing, or classifying aggregate material. For instance rock crushing or grinding to produce uniform aggregate size for construction purposes, or separation of rock, soil or aggregate material for the purposes of structural fill or land reclamation activities. Aggregate milling processes are used to remove or separate contamination or moisture from aggregate or soil and to produce "dry fills" prior to transport or structural filling.
Grinding may serve the following purposes in engineering: increase of the surface area of a solid manufacturing of a solid with a desired grain size pulping of resources In spite of a great number of studies in the field of fracture schemes there is no formula known which connects the technical grinding work with grinding results. To calculate the needed grinding work against the grain size changing three semi-empirical models are used; these can be related to the Hukki relationship between particle size and the energy required to break the particles. In stirred mills, the Hukki relationship does not apply and instead, experimentation has to be performed to determine any relationship. Kick for d > 50 mm W K = c k Bond for 50 mm > d > 0.05 mm W B = c B Von Rittinger for d < 0.05 mm W R = c R with W as grinding work in kJ/kg, c as grinding coefficient, dA as grain size of the source material and dE as grain size of the ground material. A reliable value for the grain sizes dA and dE is d80; this value signifies.
The Bond's grinding coefficient for different materials can be found in various literature. To calculate the KICK's and Rittinger's coefficients following formulas can be used c K = 1.151 c B − 0.5 c R = 0.5 c B 0.5 with the limits of Bond's range: upper dBU = 50 mm and lower dBL = 0.05 mm. To evaluate the grinding results the grain size disposition of the source material and of the ground material is needed. Grinding degree is the ratio of the sizes from the grain disposition. There are several definitions for this characteristic value: Grinding degree referring to grain size d80 Z d = d 80, 1 d 80, 2 Instead of the value of d80 d50 or other grain diameter can be used. Grinding degree referring to specific surface Z S = S v, 2 S v, 1 = S m, 2 S m, 1 The specific surface area referring to volume Sv and the specific surface area referring to mass Sm can be found out through experiments. Pretended grinding degree Z a = d 1 a The discharge die gap a of the grinding machine is used for the ground solid matter in this formula.
In materials processing a grinder is a machine for producing fine particle size reduction through attrition and compressive forces at the grain size level. See crusher for mechanisms producing larger particles. In general, grinding processes require a large amount of energy. A typical type of fine grinder is the ball mill. A inclined or horizontal rotating cylinder is filled with balls stone or metal, which grind material to the necessary fineness by friction and impact with the tumblin
Cupellation is a refining process in metallurgy, where ores or alloyed metals are treated under high temperatures and have controlled operations to separate noble metals, like gold and silver, from base metals like lead, zinc, antimony or bismuth, present in the ore. The process is based on the principle that precious metals do not oxidise or react chemically, unlike the base metals. Since the Early Bronze Age, the process was used to obtain silver from smelted lead ores. By the Middle Ages and the Renaissance, cupellation was one of the most common processes for refining precious metals. By fire assays were used for assaying minerals, that is, testing fresh metals such as lead and recycled metals to know their purity for jewellery and coin making. Cupellation is still in use today. Native silver is a rare element, it is found in nature combined with other metals, or in minerals that contain silver compounds in the form of sulfides such as galena or cerussite. So the primary production of silver requires the smelting and cupellation of argentiferous lead ores.
Lead melts at 327°C, lead oxide at 888°C and silver melts at 960°C. To separate the silver, the alloy is melted again at the high temperature of 960°C to 1000°C in an oxidizing environment; the lead oxidises to lead monoxide known as litharge, which captures the oxygen from the other metals present. The liquid lead oxide is absorbed by capillary action into the hearth linings; this chemical reaction may be viewed as: Ag + 2Pb + O2 → 2PbO + AgThe base of the hearth was dug in the form of a saucepan, covered with an inert and porous material rich in calcium or magnesium such as shells, lime, or bone ash. The lining had to be calcareous because lead reacts with silica to form viscous lead silicate that prevents the needed absorption of litharge, whereas calcareous materials do not react with lead; some of the litharge evaporates, the rest is absorbed by the porous earth lining to form "litharge cakes". Litharge cakes are circular or concavo-convex, about 15 cm in diameter, they are the most common archaeological evidence of cupellation in the Early Bronze Age.
By their chemical composition, archaeologists can tell what kind of ore was treated, its main components, the chemical conditions used in the process. This permits insights about production process, social needs or economic situations. Small scale cupellation is based on the same principle as the one done in a cupellation hearth; the minerals have to be crushed and smelted to concentrate the metallic components in order to separate the noble metals. By the Renaissance the use of the cupellation processes was diverse: assay of ores from the mines, testing the amount of silver in jewels or coins or for experimental purposes, it was carried out in small shallow recipients known as cupels. As the main purpose of small scale cupellation was to assay and test minerals and metals, the matter to be tested has to be weighed; the assays were made in the cupellation or assay furnace, which needs to have windows and bellows to ascertain that the air oxidises the lead, as well as to be sure and prepared to take away the cupel when the process is over.
Pure lead has to be added to the matter being tested to guarantee the further separation of the impurities. After the litharge has been absorbed by the cupel, buttons of silver were formed and settled in the middle of the cupel. If the alloy contained a certain amount of gold, it settled with the silver and both had to be separated by parting; the primary tool for small scale cupellation was the cupel. Cupels were manufactured in a careful way, they used to be small vessels shaped in the form of an inverted truncated cone, made out of bone ashes. According to Georg Agricola, the best material was obtained from burned antlers of deer although fish spines could work as well. Ashes have to be ground into a fine and homogeneous powder and mixed with some sticky substance to mould the cupels. Moulds were made out of brass with no bottoms. A shallow depression in the centre of the cupel was made with a rounded pestle. Cupel sizes depend on the amount of material to be assayed; this same shape has been maintained until the present.
Archaeological investigations as well as archaeometallurgical analysis and written texts from the Renaissance have demonstrated the existence of different materials for their manufacture. Different recipes depend on the expertise of the assayer or on the special purpose for which it was made. Archaeological evidence shows that at the beginnings of small scale cupellation, potsherds or clay cupels were used; the first known use of silver was in the Near East in Anatolia and Mesopotamia during the 4th and 3rd millennium BC. the Early Bronze Age. Archaeological findings of silver and lead objects together with litharge pieces and slag have been studied in a variety of sites, metallurgical analysis suggests that by people were confidently extracting silver from lead ores so the method would have been known earlier. During the following Iron Age, cupellation was done by fusing the debased metals with a surplus of lead, the bullion or result product of this fusion was heated in a cupellation furnace to se
Underground mining (hard rock)
Underground hard rock mining refers to various underground mining techniques used to excavate hard minerals those containing metals such as ore containing gold, iron, zinc, nickel and lead, but involves using the same techniques for excavating ores of gems such as diamonds or rubies. Soft rock mining refers to excavation of softer minerals such as coal, or oil sands. Accessing underground ore can be achieved via a decline, inclined vertical shaft or adit. Declines can be a spiral tunnel which circles either the flank of the deposit or circles around the deposit; the decline begins with a box cut, the portal to the surface. Depending on the amount of overburden and quality of bedrock, a galvanized steel culvert may be required for safety purposes, they may be started into the wall of an open cut mine. Shafts are vertical excavations sunk adjacent to an ore body. Shafts are sunk for ore bodies. Shaft haulage is more economical than truck haulage at depth, a mine may have both a decline and a ramp.
Adits are horizontal excavations into the side of a mountain. Adits are used for horizontal or near-horizontal ore bodies where there is no need for a ramp or shaft. Declines are started from the side of the high wall of an open cut mine when the ore body is of a payable grade sufficient to support an underground mining operation, but the strip ratio has become too great to support open cast extraction methods, they are often built and maintained as an emergency safety access from the underground workings and a means of moving large equipment to the workings. Levels are shaft to access the ore body. Stopes are excavated perpendicular to the level into the ore. There are two principal phases of underground mining: development production mining. Development mining is composed of excavation entirely in waste rock in order to gain access to the orebody. There are six steps in development mining: remove blasted material, installing support or/and reinforcement using shotcrete etceteras, drill face rock, load explosives, blast explosives.
To start the mining, the first step is to make the path to go down. The path is defined. Before the start of Decline all preplanning of Power facility, drilling arrangement, ventilation and, muck withdrawal facilities are required. Production mining is further broken down into long hole and short hole. Short hole mining is similar to development mining. There are several different methods of long hole mining. Long hole mining requires two excavations within the ore at different elevations below surface. Holes are loaded with explosives; the holes are blasted and the ore is removed from the bottom excavation. One of the most important aspects of underground hard rock mining is ventilation. Ventilation is the primary method of clearing hazardous gases and/or dust which are created from drilling and blasting activity, diesel equipment, or to protect against gases that are emanating from the rock. Ventilation is used to manage underground temperatures for the workers. In deep, hot mines ventilation is used to cool the workplace.
Ventilation raises are used to transfer ventilation from surface to the workplaces, can be modified for use as emergency escape routes. The primary sources of heat in underground hard rock mines are virgin rock temperature, auto compression, fissure water. Other small contributing factors are blasting; some means of support is required in order to maintain the stability of the openings that are excavated. This support comes in two forms. Area ground support is used to prevent major ground failure. Holes are drilled into the back and walls and a long steel rod is installed to hold the ground together. There are three categories of rock bolt, differentiated by, they are: Point anchor bolts are a common style of area ground support. A point anchor bolt is a metal bar between 20 mm – 25 mm in diameter, between 1 m – 4 m long. There is an expansion shell at the end of the bolt, inserted into the hole; as the bolt is tightened by the installation drill the expansion shell expands and the bolt tightens holding the rock together.
Mechanical bolts are considered temporary support as their lifespan is reduced by corrosion as they are not grouted. Resin grouted; the rebar used does not have an expansion shell. Once the hole for the rebar is drilled, cartridges of polyester resin are installed in the hole; the rebar bolt is spun by the installation drill. This mixes it. Once the resin hardens, the drill spinning tightens the rebar bolt holding the rock together. Resin grouted. Cable bolts are used around large excavations. Cable bolts are much larger than standard
Mining is the extraction of valuable minerals or other geological materials from the earth from an ore body, vein, reef or placer deposit. These deposits form a mineralized package, of economic interest to the miner. Ores recovered by mining include metals, oil shale, limestone, dimension stone, rock salt, potash and clay. Mining is required to obtain any material that cannot be grown through agricultural processes, or feasibly created artificially in a laboratory or factory. Mining in a wider sense includes extraction of any non-renewable resource such as petroleum, natural gas, or water. Mining of stones and metal has been a human activity since pre-historic times. Modern mining processes involve prospecting for ore bodies, analysis of the profit potential of a proposed mine, extraction of the desired materials, final reclamation of the land after the mine is closed. De Re Metallica, Georgius Agricola, 1550, Book I, Para. 1Mining operations create a negative environmental impact, both during the mining activity and after the mine has closed.
Hence, most of the world's nations have passed regulations to decrease the impact. Work safety has long been a concern as well, modern practices have improved safety in mines. Levels of metals recycling are low. Unless future end-of-life recycling rates are stepped up, some rare metals may become unavailable for use in a variety of consumer products. Due to the low recycling rates, some landfills now contain higher concentrations of metal than mines themselves. Since the beginning of civilization, people have used stone and metals found close to the Earth's surface; these were used to make early weapons. Flint mines have been found in chalk areas where seams of the stone were followed underground by shafts and galleries; the mines at Grimes Graves and Krzemionki are famous, like most other flint mines, are Neolithic in origin. Other hard rocks mined or collected for axes included the greenstone of the Langdale axe industry based in the English Lake District; the oldest-known mine on archaeological record is the Ngwenya Mine in Swaziland, which radiocarbon dating shows to be about 43,000 years old.
At this site Paleolithic humans mined hematite to make the red pigment ochre. Mines of a similar age in Hungary are believed to be sites where Neanderthals may have mined flint for weapons and tools. Ancient Egyptians mined malachite at Maadi. At first, Egyptians used the bright green malachite stones for ornamentations and pottery. Between 2613 and 2494 BC, large building projects required expeditions abroad to the area of Wadi Maghareh in order to secure minerals and other resources not available in Egypt itself. Quarries for turquoise and copper were found at Wadi Hammamat, Tura and various other Nubian sites on the Sinai Peninsula and at Timna. Mining in Egypt occurred in the earliest dynasties; the gold mines of Nubia were among the largest and most extensive of any in Ancient Egypt. These mines are described by the Greek author Diodorus Siculus, who mentions fire-setting as one method used to break down the hard rock holding the gold. One of the complexes is shown in one of the earliest known maps.
The miners crushed the ore and ground it to a fine powder before washing the powder for the gold dust. Mining in Europe has a long history. Examples include the silver mines of Laurium. Although they had over 20,000 slaves working them, their technology was identical to their Bronze Age predecessors. At other mines, such as on the island of Thassos, marble was quarried by the Parians after they arrived in the 7th century BC; the marble was shipped away and was found by archaeologists to have been used in buildings including the tomb of Amphipolis. Philip II of Macedon, the father of Alexander the Great, captured the gold mines of Mount Pangeo in 357 BC to fund his military campaigns, he captured gold mines in Thrace for minting coinage producing 26 tons per year. However, it was the Romans who developed large scale mining methods the use of large volumes of water brought to the minehead by numerous aqueducts; the water was used for a variety of purposes, including removing overburden and rock debris, called hydraulic mining, as well as washing comminuted, or crushed and driving simple machinery.
The Romans used hydraulic mining methods on a large scale to prospect for the veins of ore a now-obsolete form of mining known as hushing. They built numerous aqueducts to supply water to the minehead. There, the water stored in large tanks; when a full tank was opened, the flood of water sluiced away the overburden to expose the bedrock underneath and any gold veins. The rock was worked upon by fire-setting to heat the rock, which would be quenched with a stream of water; the resulting thermal shock cracked the rock, enabling it to be removed by further streams of water from the overhead tanks. The Roman miners used similar methods to work cassiterite deposits in Cornwall and lead ore in the Pennines; the methods had been developed by the Romans in Spain in 25 AD to exploit large alluvial gold deposits, the largest site being at Las Medulas, where seven long aqueducts tapped local rivers and sluiced the deposits. Spain was one of the most important mining regions, but all regions of the Roman Empire were exploited.
In Great Britain the natives had mined minerals for millennia, but after the Roman conquest, the scale of the operations increased as the Romans needed Britannia's resources gold, silver
Gold panning, or panning, is a form of placer mining and traditional mining that extracts gold from a placer deposit using a pan. The process is one of the simplest ways to extract gold, is popular with geology enthusiasts because of its low cost and relative simplicity; the first recorded instances of placer mining are from ancient Rome, where gold and other precious metals were extracted from streams and mountainsides using sluices and panning. However, the productivity rate is comparatively smaller compared to other methods such as the rocker box or large extractors, such as those used at the Super Pit gold mine, in Kalgoorlie, Western Australia, which has led to panning being replaced in the commercial market. Gold panning is a simple process. Once a suitable placer deposit is located, some alluvial deposits are scooped into a pan, where they are gently agitated in water and the gold sinks to the bottom of the pan. Materials with a low specific gravity are allowed to spill out of the pan, whereas materials with a higher specific gravity sink to the bottom of the sediment during agitation and remain within the pan for examination and collection by the prospector.
These dense materials consist of a black, magnetite sand with whatever stones or metal dust that may be found in the deposit, used for source material. While an effective method with certain kinds of deposits, essential for prospecting skilled panners can work but a limited amount of material less than the other methods which have replaced it in larger operation. Pans remain in use in places where there is limited capital or infrastructure, as well as in recreational gold mining. In many situations, gold panning turns up only minor gold dust, collected as a souvenir in small clear tubes by hobbyists. Nuggets and considerable amounts of dust are found, but panning mining is not lucrative. Panning for gold can be used to locate the parent gold veins which are the source of most placer deposits. Gold pans of various designs have been developed over the years, the common features being a means for trapping the heavy materials during agitation, or for removing them at the end of the process; some are intended for use with mercury, include screens, sharp corners for breaking ice, are non-round, or are designed for use "with or without water".
Edward Otho Cresap Ord, II, a former Army officer and co-owner of several mines, patented several pan designs including designs for use with mercury or dry. Pans are measured by their diameter in centimeters. Common sizes of gold pans today range between 10–17 inches, with 14 inches being the most used size; the sides are angled between 30° to 45°. Pans are manufactured in high-impact plastic. Russia iron or heavy gauge steel pans are traditional. Steel pans are stronger than plastic pans; some are made of lightweight alloys for structural stability. Plastic gold pans resist rust and corrosion, most are designed with moulded riffles along one side of the pan. Of the plastic gold pans and red ones are preferred among prospectors, as both the gold and the black sand stands out in the bottom of the pan, although many opt for black pans instead to identify gold deposits; the batea, Spanish for "gold pan", is a particular variant of gold pan. Traditionally made of a solid piece of wood, it may be made of metal.
Bateas are used in areas where there is less water available for use than with traditional gold pans, such as Mexico and South America, where it was introduced by the Spanish. Bateas are larger than other gold pans; the yuri-ita, Japanese for "rocking plate" is a traditional wooden gold pan used in Japan. Unlike other gold pans, it is rectangular in shape with a concave cross section and is sealed off at one end with the other end open; as the Japanese name implies, the gold is panned with a rocking motion
Froth flotation is a process for selectively separating hydrophobic materials from hydrophilic. This is used in paper recycling and waste-water treatment industries; this was first used in the mining industry, where it was one of the great enabling technologies of the 20th century. It has been described as "the single most important operation used for the recovery and upgrading of sulfide ores"; the development of froth flotation has improved the recovery of valuable minerals, such as copper- and lead-bearing minerals. Along with mechanized mining, it has allowed the economic recovery of valuable metals from much lower grade ore than previously. Descriptions of the use of a flotation process have been found in ancient Greek and Persian literature suggesting its antiquity. During the late nineteenth century, the process basics were discovered through a slow evolutionary phase. During the early twentieth century, it revolutionized mineral processing around the globe. Occurring chemicals such as fatty acids and oils were used as flotation reagents in a large quantity to increase the hydrophobicity of the valuable minerals.
Since the process has been adapted and applied to a wide variety of materials to be separated, additional collector agents, including surfactants and synthetic compounds have been adopted for various applications. Englishman William Haynes patented a process in 1860 for separating sulfide and gangue minerals using oil. Writers have pointed to Haynes's as the first "bulk oil flotation" patent, though there is no evidence of its being field tested, let alone used commercially. While in 1877 the brothers Bessel of Dresden, introduced their commercially successful oil and froth flotation process for extracting graphite, considered by some the root of froth flotation. However, because the Bessel process was used on graphite not gold, copper, zinc, their work has been ignored by most historians of the technology. Seventy-seven year old inventor Hezekiah Bradford of Philadelphia invented a "method of saving floating material in ore-separation” and received U. S. patent No. 345951 on July 20, 1886.
He had received his first patent in 1834 invented machinery to separate slate from coal during the 1850s-1860s, invented the Bradford Breaker, still in use by the coal industry today. His "Bradford Ore Separator," patented 1853 and improved over the decades, was used to concentrate iron and lead-zinc ores by specific gravity, but lost some of the metal as float off the concentration process; the 1886 patent was to capture this "float" using surface tension, the first of the skin-flotation process patents, eclipsed by oil froth flotation. It is uncertain if his 1886 patented "flotation" process was introduced. On August 24, 1886, Carrie Everson received a patent for her process calling for oil but an acid or a salt, a significant step in the evolution of the process history. By 1890, tests of the Everson process had been made at Georgetown and Silver Cliff and Baker, Oregon, she abandoned the work with the death of her husband, before perfecting a commercial successful process. During the height of legal disputes over the validity or not of various patents during the 1910s, Everson's was pointed to as the initial flotation patent -- which would have meant that the process was not patentable again by contestants.
Much confusion has been clarified by historian Dawn Bunyak. The recognized first successful commercial flotation process for mineral sulphides was invented by Frank Elmore who worked on the development with his brother, Stanley; the Glasdir copper mine at Llanelltyd, near Dolgellau in North Wales was bought in 1896 by the Elmore brothers in conjunction with their father, William. In 1897, the Elmore brothers installed the world's first industrial size commercial flotation process for mineral beneficiation at the Glasdir mine; the process was not froth flotation but used oil to agglomerate pulverised sulphides and buoy them to the surface, was patented in 1898. The operation and process was described in the April 25, 1900 Transactions of the Institution of Mining and Metallurgy of England, reprinted with comment, June 23, 1900, in the Engineering and Mining Journal, New York City. By this time they had recognized the importance of air bubbles in assisting the oil to carry away the mineral particles.
As modifications were made to improve the process, it became a success with base metal ores from Norway to Australia. The Elmores had formed a company known as the Ore Concentration Syndicate Ltd to promote the commercial use of the process worldwide. In 1900, Charles Butters of Berkeley, acquired American rights to the Elmore process after seeing a demonstration at Llanelltyd, Wales. Butters, an expert on the cyanide process, built an Elmore process plant in the basement of the Dooley Building, Salt Lake City, tested the oil process on gold ores throughout the region and tested the tailings of the Mammoth gold mill, Tintic district, but without success; because of Butters’ reputation and the news of his failure, as well as the unsuccessful attempt at the LeRoi gold mine at Rossland, B. C. the Elmore process was all but ignored in North America. Developments elsewhere in Broken Hill, Australia by Minerals Separation, led to decades of hard fought legal battles and litigations for the Elm