is there ecocide during coal mining crusher

5 common faults analysis of coal hammer crusher

Coal hammer crusher is important equipment for crushing large raw coal. Its stable operation plays an important role in ensuring the raw coal conveying efficiency of the underground coal mine. We can put forward the corresponding solutions via analyzing the main fault sources and common faults of coal hammer mill crushers. Then improve the hammer coal mill crushers operation reliability, reduce the maintenance difficulty, and make sure the smooth progress of coal mining.

According to the working principle, coal crusher can be divided into two types: hammer crusher and jaw crusher. The hammer mill crushers have large processing capacity that max capacity is 4000tph. So the coal plant mainly uses hammer crushers to crushing raw coal. The power of the hammer crusher general is 90 ~ 400kw, which mainly depends on the rotating parts to drive the hammer up. Then crush the lump coal to the particle size which is easy to transport by the impact force of the hammer falling.

As important equipment of the underground coal mine transportation system, a coal hammer crusher is usually installed in the middle of the climbing section. The large piece of raw coal is transported to the transfer machine by the scraper conveyor and then guided into the hammer crusher by the transfer machine. The coal is crushed into small pieces by a hammer coal crusher and then transported to the ground coal yard.

The coal hammer mill crusher is composed of a bottom groove, crushing frame, hammer shaft, driving and adjusting device, and lubricating system. It has no transshipment function which needs after connecting the crushing bottom groove and connecting slot. Then uses the transshipment machine. The hammer impact crusher frame body is located on the upper part of the bottom groove and installs a crushing hammer shaft in the middle of the frame body. The mechanism is that the hammer shaft is lifted to a certain height through the transmission device which increases the gravitational potential energy. After falling, the hammerhead impacts and squeezes the raw coal at the bottom trough, crushing it to smaller particle sizes. The small coal particle is convenient for continuous conveying by the transfer machine.

According to the power of the equipment, the underground coal hammer crusher adopts two different transmission forms: pulley and retarder. In general, the belt pulley transmission is only used for power below 250kw. The power greater than 250kw is through the reducer.

Analyze fault for the large-scale, high-power hammer mill crusher, it cant diagnose specific faults. If the equipment fault is considered to be caused by the damage of a single component, the diagnosis is too one-sided. The test results may be biased, and the subsequent maintenance of the equipment may not achieve the desired repair effect. Therefore, the failure of a high-power hammer crusher should be considered from various factors, such as the design, processing, installation, commissioning and use.

The design should ensure the stability of the structure and the good dynamic characteristics of the equipment. The unreasonable mechanical structure will lead to the local stress concentration and affect the dynamic characteristics of the equipment. Then they may lead to forced vibration or self-excited vibration and other undesirable phenomena. In addition, the common design and manufacture defects include working speed and the material of the spare part can not meet the design requirements, machining accuracy is too low, poor moving cone balance performance, etc.

The hammer crusher installation, commissioning and maintenance stage may occur crusher parts installation dislocation. The transmission system with the shafting and installation location is not appropriate. The overall equipment geometric parameter adjustment is not good. The installation position of the dynamic cone is not reasonable. All the problems may lead to the equipment large load and poor stability in operation.

In the process of man-made operation, the equipment abnormal opening, closed and adjusted speed improperly. The equipment operated beyond the designed working condition for a long time. Lack of maintenance. Lubrication between the components was insufficient. These also cause the failure of the hammer crusher.

The coal hammer crusher operates for a long time, the parts are easy to wear and deformation. Individual parts may be shaken off, crack or even damage. The dynamic cone changes, spare parts will also be affected by the external environment caused by pitting or corrosion. Or with other parts wear each other. Or affected by vibration which causes uneven settlement of the ground where the equipment is located. At the same time, the increase of clearance between some spare parts, losing fit surface and lowering of fit surface friction will affect the normal work of the hammer mill.

The vibration and the movement of the dynamic cone in the operation of the hammer crusher will cause the dynamic cone ware. Then lead to the eccentricity of the center of gravity of the dynamic cone and the unbalance of the dynamic cone. The problems caused by the unbalance of the movable cone are as follows:

In the rotor system which connects with coupler, misalignment between the two rotors will cause the coupler to deflect. The bearing affected will shorten the service life, affect the stability of oil film, the operation is not smooth. We should increase the monitoring of rotor misalignment faults and focus on the detection of vibration amplitude and phase stability.

The rotor system is affected by factors such as misalignment of the rotor, bending of the shaft, loosening of the foundation, wear of the bearing, improper assembly, etc. It will rub-impact with bearings. Although the torque of the rotor can be balanced when the equipment is running, the speed is greatly affected. The rotor system is unstable, and the overall stability of the equipment decreases.

The main performance: one is the rotor system vibration, the other is the impact of rub-impact on the rotor itself. The combination of the two results in more complex adverse reactions, such as phase reverse displacement and axial trajectory diffusion or turbulence. In the design stage, in order to ensure the stability of the equipment, the gap between the rotating parts and the adjacent parts is relatively small, and the probability of the rub-impact phenomenon is more easily increased.

Oil Whirl is a phenomenon that the rotor of the transmission system moves the wedge oil film around the center of the bearing bush according to the average velocity of oil due to vibration and rotation fluctuation. The main characteristics are the smooth phase. It is obviously affected by lubricating oil characteristics. The trajectory presents a double ring ellipse. The subharmonic generated by the vibration will change with the increase of the rotational speed.

Hammer crusher is rotating vibration equipment. The foundation and fixed foundation bolt vibration during the crusher machine operating. It is easy to cause the bolt loose. At the same time, the bearing pedestal will be loose because of vibration. Vibration amplitude is large, mainly acting in the vertical direction. In order to determine the foundation and bearing pedestal looseness, the vertical vibration signals are detected and compared with the vibration signals of crusher and foundation bolt. If the foundation and the bearing seat are looser, there will be a big difference between the two vibration signals, which should be handled in time to avoid accidents.

The coal hammer crusher is the key equipment for crushing large raw coal in the underground coal. The machine is an important part of the raw coal transportation system. The common problems are design Defects, installation, debugging and maintenance problems, parts wear and deformation, movable cone unbalance, rotor rub-impact, shaft misalignment, etc.

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ecocide in russia | eurozine

Osteuropa focuses on environment and environmentalism in Russia. Including articles on coalmining in the Kuzbass; garbage and governance; the environmental history of the Soviet and post-Soviet eras; and literary ecology, classic and contemporary.

Black gold, Russias poison Eurozine Review 04/2021 Ecocide in Russia Osteuropa 79/2020 Eurozine Review Whither democracy? New Eastern Europe 12/2021 Eurozine Review Digital practices Mittelweg 36 1/2021 Eurozine Review 150 years of Italian emigration Internazionale special issue 2020 Eurozine Review Subscribeto our weekly newsletter In 2021, both the EU and Germany have made climate and sustainability a key topic in their diplomacy with Russia, in the hope that the environment will be one of the few areas where cooperation remains possible. In response, Osteuropa publishes an issue exploring key areas in Russian eco-politics.

In the Kuznetsk Basin in southwestern Siberia, the amount of coal being excavated has trebled over the past two decades, writes Anton Lementuev. Coal is known as the black gold of the region; but for the people living in the region, it is poison. As open-caste mines move ever closer to residential areas, coal dust and other dangerous substances released into the ground water increasingly endanger health, while noise and dirt become ever more a feature of everyday life.

The local government is hand in glove with the coal mining companies and has made the Kemerovo area almost entirely dependent on coal. This has been possible because the demand for coal from the Kuzbass has grown not least in western Europe. Coal mining has made the pit owners extremely wealthy; but for the people of Kemerovo, it means living against the backdrop of an ecological catastrophe.

When Gorbachev opened the door to western consumer goods in the late eighties, the country was inundated with garbage, writes Robert Argenbright. Consumerism ruled the new day, and the volume of solid waste grew exponentially, much of it consisting of previously unseen materials such as polyethylene and polystyrene foam.

Today, Russia does not have a modern, efficient waste policy. There is no attempt to avoid waste, and just four per cent of household waste is recycled. The authorities preferred method of dealing with waste is incineration which often falls short of European safety standards.

However, an increasing number of citizens are protesting against waste disposal sites. So much so that the waste problem has become a problem for the Kremlin. The garbage crisis landed on Putins doorstep, and his need to maintain popularity underlies a fundamental dilemma of the garbage reform: how to pay for it without provoking public discontent?

Klaus Gestwa surveys the development of historical research on the Soviet and post-Soviet environments, and its integral connection to environmentalist movements. The widely held assumption that environmental problems or ecological crises were merely transitionary phenomena en route to communism had led to a trivialization of environmental destruction in the Soviet Union.

In the 70s, ecocide was a much-used term in Soviet environmental history; during and immediately after the collapse of communism, eco-nationalism became a popular concept. More recent research has taken regional, imperial and global historical perspectives. Even if environmental topics are not at the top of the agenda of post-Soviet politics, one can by no means talk of a de-ecologization of the social consciousness.

Leonid Leonov (18991984) was one of the most successful writers in the Soviet Union. His novel The Russian Forest (1953) had print runs in the millions and is regarded as a classic of Socialist Realism. But though heavily programmatic, Leonovs literary works as well as journalism presented surprisingly modern ecological demands, writes Ulrich Schmid. These included sustainable forest management, raising the status of woodland to a legal entity, founding support associations, and the creation of a state nature protection committee. Leonov can be regarded as the founder of public debate on environmental issues in Russia.

Between the eighteenth to the twentieth centuries, there were phases when Russian literature took an intense interest in natural phenomena and ecological issues, writes Lara Rindt. What is less well known is that contemporary Russian literature also frequently takes up ecological and environmental problems, often with a critical stance.

Published 3 March 2021 Original in English First published by Eurozine

Editors from the Eurozine network will finally meet in a hybrid format, in-person in local hubs and online from their own homes on 2 July 2021, closing the evening with a new panel discussion thats open for the general public in a live stream.

Russia and Turkey have moved from confrontation to cooperation. But their shared interests have had deleterious consequences for the Kurds in Syria and Crimean Tatars in Ukraine. Tensions continue in Nagorno-Karabakh and Libya. And their support for right-wing authoritarianism in the Western Balkans is undermining liberal democratic values.

Kultros barai offers a Lithuanian perspective on Russian power play, historic and current; and a Jewish history behind Soviet jazz. Plus: philosopher Algis Micknas on upholding democratic principles through everyday politics.

coal deposits in nigeria, west africa with their locations and uses

Coal Deposits - Some Africa countries like Nigeria is blessed with coal rich states especially Enugu which is known as the the coal city because of its vast coal deposits, other states include;Benue, Kogi, Delta,Kwara,Plateau, Abia,Anambra,Bauchi,Edo, Ondo, Adamawa andImo.

Fossil fuels came up as a result of the remains of dead animals and plants million years ago; an example of such fuels is coal. Coal is a fossil fuel and its a non-renewable energy source because it takes millions of years to form and cannot be renewed by men once depleted.

It was during the civil war that Biafra Coal Corporation, Enugu and Odagbor, later referred to as Okaba coal mine, situated in present day Kogi State were commissioned. After the civil war, these mines were merged into Nigerian Coal Corporation (NCC).

The exit of a number of expatriate professional miners from Britain and Poland, and foundation of crude oil at Oloibiri in commercial quantities were the factors that led to government abandoning the massive coal infrastructure at the mines, which were under the management of NCC.

However, the Federal government has a memorandum of understanding (MoU) of $3.7 billion, which they signed with a Chinese company, HTG-Pacific Energy Consortium, to carry on with power generation from coal deposits in Enugu.

Trading of coal in Nigeria began in 1914, during the country's amalgamation year. It was in this year that the first coal was exported out of the country to the United Kingdom from Port Harcourt, the newly invented port then.

Some of them are O.T. Oils Limited, Victoria Island Lagos (exporter); Globexia, Ikeja Lagos (exporter); Resources Improvement & Manufacturing Company Limited (mining and supply), to name but just a few.

The lighter component which is gaseous (like methane) is forced out from the deposit, with the heavier component becoming richer in carbon undergoing different stages which occurs as follows; plant debris to peat, sub-bituminous coal, bituminous coal, anthracite coal, lignite and graphite which is a pure carbon mineral.

History of coal dates back to thousands of years, and its industrial revolution importance goes to the 19th and 20th centuries. It was said that the Chinese people have used it for over 3,000 years past.

Majorly, there are four (4) types or classifications of coal. They are otherwise called the ranks or grade, which are the slow, natural process during which decomposed organism transform into closely compacted, crispy, harder and more carbon-rich matters.

2. Bituminous or black coal: It's a shiny, smooth coal with volatile content that is relatively of high content. Bituminous coal contains a tar-like substance called asphalt or bitumen, and it's the middle rank coal between subbituminous and anthracite

These dead plants are turned into coal, in other words, fossil fuels, by heat and pressure. Also, it is important to know that fossils consist of hydrocarbon-containing natural resources, which are not from either plants or animal source.

However, since 2015, Vietnam, Philippines, Poland, and Malaysia have been the fastest-growing markets for coal with Vietnam importing 395%, while the other 3 countries imported 177.7%, 152.5%, 121.6% respectively.

Quartzite solid mineral deposits in Nigeria, West Africa can be found in Ekiti, Taraba, Kogi, Kwara and Oyo states. Quartzite is a metamorphic rock that is hard with a non-layered appearance; its colour is of different shades...

Lithium and other mineral resources that Nigeria, Western Africa is blessed with area major means for industrial growth in the country. Lithium is a metal and is soft with a silvery-white colour which changes to a dull...

the common failures of hammer crushers - jxsc machine

As important mining equipment for the underground coal mine coal transportation system, hammer crusher is usually installed in the middle section of the coal transportation system. Raw coal in the middle of the transportation is crushed into small pieces by a hammer crusher and then transported to the ground coal yard. The coal mine hammer crusher consists of the bottom trough, the crushing frame body, the breaker shaft, the transmission device, the adjusting device and the lubrication system. It has no transfer function and needs to be connected with the crushing bottom trough. The hammer crushing frame body is located at the upper part of the bottom groove, and a crusher shaft is installed in the middle of the frame body. Buy hammer crusher

The mechanism of action is that the broken hammer shaft is lifted to a certain height through the transmission device, thereby increasing the gravitational potential energy. After the falling, the hammer head impacts and squeezes the raw coal at the bottom groove, and is crushed to a smaller particle size, which is convenient for continuous transfer of the transfer machine. The coal mine hammer crusher can adopt two different transmission forms of pulley and reducer according to the power of the equipment. Normally, the pulley drive is only used for hammer crushers up to 250 kW, and hammer crushers larger than 250 kW are driven by reducers.

(1) Design processing defects. The design should ensure that the structure of the equipment is stable and the dynamic characteristics are good. Unreasonable mechanical construction will lead to local stress concentration in the hammer crushers, affecting the dynamic characteristics, and thus may cause undesirable phenomena such as forced vibration or self-excited vibration. (2) Installation, commissioning, and maintenance procedures. In the installation, commissioning and maintenance stages of the hammer crusher, the installation of each spare part may be misplaced. The coordination and installation positions of the shaft system in the transmission system are not suitable, the adjustment of the geometric parameters of the whole equipment is not in place, the installation position of the moving cone is unreasonable, etc., and then It may cause problems such as large equipment load and poor stability of the running state. (3) Human error. In the process of human operation, the equipment is abnormally opened, closed and the speed is not properly adjusted. The hammer crusher runs beyond the design working condition for a long time, the equipment lacks maintenance, and the lubrication between the various components is insufficient. It is also a factor causing the hammer crusher to malfunction. (4) Wear and deformation of the components. The hammer crusher runs for a long time, and various components are prone to different degrees of wear and deformation. Individual parts may be detached, cracked or even damaged by vibration, and the deflection of components such as moving cones may change. Parts may also be pitting or corroded by the external environment, or may wear out with other parts or be affected by vibration. Uneven settlement of the location; at the same time, the gap between the individual parts increases, the looseness of the fit, the friction of the mating surface decreases, etc., which will affect the normal operation of the hammer crushers.

The vibration and moving cone action of the hammer crusher will cause the moving cone to wear, which will cause the center of gravity of the moving cone to shift to form an eccentricity, resulting in an unbalanced moving cone. The problems caused by the imbalance of the hammer crushing motor cone are: (1) The moving cone produces an eccentricity, which changes the force state of the rotor to make it unevenly stressed. During the rotating motion, the moving cone repeatedly bends. When the fatigue limit is reached, damage or even breakage may occur. (2) The moving cone is unbalanced, the equipment is out of the design working condition, and the vibration is caused by severe vibration, which interferes with the external environment. (3) During the working process of the rotor, deflection due to uneven force, friction with bearings or other adjacent components not only causes wear of various components in the equipment, but also affects the working efficiency of the equipment. It is a serious safety hazard and should be strengthened. Inspection and timely disposal.

In a rotor system connected by a coupling, misalignment between the two rotors causes the coupling to deflect, and the bearing that is connected is affected by the rotor misalignment, which shortens the service life, affects the oil film stability of the sliding bearing, and the overall operation of the bearing. Poor, resulting in more serious irregular vibrations. The monitoring of rotor misalignment should be increased, and the vibration amplitude and phase stability should be detected.

The rotor system of the hammer crushers is affected by factors such as rotor misalignment, bending of the shaft, looseness of the foundation, wear of the bearing, improper assembly, etc., and friction or even rubbing phenomenon with the bearing. Although the torque that the rotor is subjected to during operation of the equipment can be balanced, the rotational speed is greatly affected, the rotor system is also unstable, and the overall stability of the equipment is degraded. Main performance: First, the rotor system vibrates, and second, the rubbing has an impact on the rotor itself. The two overlap each other, resulting in more complex adverse reactions, such as phase reverse displacement and axial trajectory diffusion or disorder. In the design stage, in order to ensure the stability of the equipment, the gap between the rotating parts and the adjacent parts is relatively small, and it is easier to increase the probability of occurrence of rubbing.

Hammer crusher is rotating vibration equipment. During operation, the ground bolts used for foundation and fixation vibrate, which can easily cause the foundation sinking and the loosening of the anchor bolt connection. At the same time, the bearing seat will also be loosened by the vibration. The vibration amplitude is larger, mainly in the vertical direction. In order to determine the loosening condition of the foundation and bearing seat, the vibration signals in the vertical direction are detected and compared with the vibration signals of crusher and ground bolt. If the foundation and bearing housing are looser, there will be a great difference between the two kinds of vibration signals, so it should be dealt with in time to avoid accidents.

Hammer crusher is the key equipment for crushing large blocks of raw coal in coal mine, and is an important part of the raw coal transportation system. Design and machining defects, installation, debugging, maintenance process problems and man-made operation errors and structural wear and tear, deformation is the main source of hammer crusher fault, moving cone imbalance, rotating shaft misalignment, rotor rubbing.

coal mines - an overview | sciencedirect topics

Coal mines are typically hosted in soft sedimentary rock and caving (goafing) of the roof strata above large mined out areas is normal. Therefore larger magnitude events are expected, along with high attenuation of higher frequency signals. Low stress drops also result in lower dominant frequencies. Coal mining is fast moving, and so the ability to move the system hardware easily is important. Coal mines usually also require intrinsically safe equipment due to the potentially explosive atmospheres.

Coal mine explosions are rare, but they cause the most fatalities. Nearly 8,000 lives have been lost in US coal mines alone. Worldwide figures are much higher. Criteria for both gas and coal dust explosions are discussed. Flammability limits (upper and lower) for all mine gases are discussed. Techniques to determine if a mixture of combustible and inert gases are explosive are presented. Minimum ignition energy (MIE) and minimum temperatures for ignition for both gas and dust are presented. Impact of methane, moisture, particle size, and volatile content of coal on coal dust explosion is discussed. Preventive techniques comprising methane drainage, use of permissible equipment, mixing inert material, such as limestone dust, with coal dust to render it inert are explained. Finally, the use of stone dust barriers to contain the explosion within a section is presented. This limits the extent of damage to mine structures within the section and minimizes widespread losses of life and property.

Coal mines contain hazardous and explosive gases, and there is a potential for long-lasting fires. The OSM estimates that there are currently 4163 acres burning, including 94 sites where hazardous or explosive gas is being emitted from underground mine fires, which can have an effect on humans in the vicinity of the site. The estimated cost of extinguishing these fires is $860 million. The most extreme case in the United States is in Centralia, Pennsylvania, where an underground fire has been burning for longer than 30 years. Attempts to extinguish it have failed, leading the government to buy all the property at a cost of $42 million as well as costs associated with the attempts to fight the fire.

Coal mine activity in Poland has provided millions of tons of coal waste every year, which were used for terrain leveling or were deposited on the dumps. Some part of them have been reclaimed e.g. as a filling material. The technology of dump constructions, their size, and their location have been changed during the whole history of coal mining. Nowadays, the cutback in coal production is apparent; a majority of coal mines are already closed or are in a state of liquidation, but the problem concerning coal waste and its influence on the environment is still serious.

Coal dumps are frequently ignited by anthropogenic activities such as electrical sparks or burning trash in the vicinity of a dump and also by the self-ignition of coal within the dump caused, for example, by the exothermic oxidation of sulfides within the coal (Stracher and Taylor, 2004). Pressure and temperature conditions generated in the dumps during burning, and resulting in contact metamorphism reaching the sanidinite facies, lead to the crystallization of rare minerals such as the fluor-ellestadite found in the dump in Czelad (Ciesielczuk, 2008). The newly formed minerals are usually fine grained but from a mineralogical perspective, are very important because, for example, of the occurrence of previously undocumented mineral phases (Muszyski etal., 2006).

Early in the history of coal mining in Poland, the problem of burning dumps was restricted in scale and neglected. As coal mining developed in importance, changing technologies and increasing amounts of coal waste deposited on enlarging dumps intensified the problem. It is thought that self-ignition of the dumps has resulted in the combustion of at least 50% of the deposited waste. The environmental questions to be investigated are important and urgent.

Coal mine fire is devouring coal seams in major coal-producing countries including China, the United States, India, and Indonesia. Many seams have been burning for decades and some for centuries. Coal fires are a natural phenomenon; however, coal mining by humans has assisted the propagation of these fires and thereby enhancing the environmental pollution (Pone etal., 2007).

The ignition of coal mine fires is of global concern as it may be attributed to significant environmental problems (Stracher and Taylor, 2004; Avila etal., 2014). Environmentally catastrophic effects from coal fires include large amounts of pollutants such as sulfur and nitrogen oxides ((NOx) acidic gases), CO2, particulate matter (PM), organic compounds, fly ash, and potentially toxic trace elements such as arsenic, mercury, and selenium (Finkelman, 2004). Coal fires have killed people, affected entire communities to abandon their homes and businesses, damaged floral and faunal habitats, and are accountable for dangerous land subsidence (Pone etal., 2007). CO2 concentrations exceed those of other gases produced by coal fires; however, CO2 concentrations are not entirely controlled by the coal itself. CO, hydrogen and the hydrocarbons, ethylene (C2H4), propylene (C3H6), and acetylene (C2H2) are monitored as coal-fire detector gases because these are released sequentially as temperature increases during heating. Consecutive temperatures (C) at which release begins in medium volatile bituminous coal are 110, 170, 240, and 300C for CO, H2, C2H4, and C3H6, respectively. Combustion occurs between 110 and 170C, and flames appear at about 200C (Kong etal., 2017).

Pone etal. (2007) found that gases emitted from coal-fire vents in the Witbank and Sasolburg coalfields consist of a complex mixture of hydrocarbons, halocarbons, greenhouse gases (GHGs), and toxic concentrations of CO, benzene, xylene, and toluene. Based on chemical analyses, they characterized these emissions under four principal groups, such as (1) aromatic compounds mostly volatile organic compounds (VOCs) (Benzene, toluene, ethylbenzene, xylenes, ethyltoluene, and trimethylbenzene), (2) aliphatic hydrocarbons (Ethane, propane, butane, pentane, propene, and ethyne), (3) halogenated hydrocarbons (dichloromethane, chloromethane, bromomethane, iodomethane, and trichloromethane), and (4) greenhouse and other gases (CH4, CO2, and CO).

ROM coal is first crushed and screened into different size fractions, coarse (>50mm), small (0.550mm) and fines (<0.5mm). Each size fraction is treated separately by a series of sequential unit operations such as sizing, cleaning and dewatering, which constitute a circuit (Fig. 3.6). In Indian conditions, only three circuits are considered, but the inherent characteristics of raw coal feed determine the configuration of the circuits. It is recommended to split fine coal into fine (0.151mm) and ultrafine (0.15mm) for treatment in separate circuits.

The objective of prewashing is to remove a sufficient quantity of noncombustible material so that the downstream circuit is relieved of any unnecessary loading. Also, it is necessary to minimise the production of fines as fine coal treatment is much more expensive and difficult.

In order to run the parallel circuits efficiently and to maximise overall plant yield, the circuits should run with constant incremental ash. In the case of Indian coking coals, the size demarcation between different parallel streams, especially coarse-coal and small-coal, may disappear, and only the small-coal stream remains. All materials are crushed down to under 13 or 6mm. The parallel circuits need to be fed with a uniform distribution of raw coal as per design.

Coal mines are often cited as the origin of gas sensors, see Section 5.1.1. Despite the numerous different sensing methods available today, gas monitoring, however, within mines remains challenging. Due to the vast lengths and depths of coal mine tunnels, a large sampling density is necessary to ensure the safety of miners. In the past, sensors needed to be directly connected to the processing server, making a large amount of cable and coordination necessary. Today, research exists on wireless monitoring systems [8]. These would be much more flexible and would allow for widespread detection within the mine. For this application, SMOX-based sensors are ideally suited because they are small and inexpensive. They are robust and can handle the harsh environment within mines. The first entirely wireless prototype detection system for mines contains SMOX sensors for CO, methane, propane, and butane. Researchers are optimistic that the entire sensing system (electronics and a sensor node) will cost under $400, with each additional sensor node only costing $250 [8]. By using MEMS technology and pulsed heating, SMOX-based sensors can be powered for several years using a standard battery. Battery-operated detectors not only lead to an increase in stationary devices, but also enabled the development of small portable personal safety devices.

In addition to miners, garbage collectors, and firefighters are in the top ten dangerous jobs in many developed countries. Exposure to toxic gases plays a role in the high mortality rates of all three jobs [66]. Personal safety apparel is already commonplace in these dangerous professions, and textiles are positioned close to the body. This combination makes clothing the ideal place to integrate and couple safety sensors with biometric measurements. Small battery-operated and wireless SMOX-based sensors are well suited, and there are already several prototypes for different smart safety clothing articles. The European project Proetex was aimed at developing smart gear for firefighters. A prototype safety boot with an integrated gas sensor was developed [67].

Research is currently being done on flexible sensors which could be directly integrated into clothing. In the past, ZnO nanorods and nanowires have successfully been synthesized onto fabric materials for several different purposes [68,69]. Lim et al. created a conductive fabric by growing ZnO nanorods onto cotton. Copper wires were then attached to the ZnO as electrodes. Using this setup, it was possible to detect H2 at room temperature. The ZnO nanofiber fabric was stable during mechanical stretching [70]. In the next step, flexible hotplates will need to be coupled with fabric substrates for better sensing results. The field of wearable gas sensing is still very much in its infancy, but the future seems highly promising and would revolutionize personal safety in dangerous jobs (Fig. 5.4).

Figure 5.4. Here the integration of SMOX fibers in fabric is shown. SEM images of (A) cotton fabric substrate; (B) bare cotton fibers; (C) ZnO NR-coated cotton fibers; (D) high magnification images of ZnO NRs on a cotton fiber; (E) photograph of bare and ZnO NR-coated fabric; and (F) ZnO NRs-on-fabric multifunctional sensing device [70,71].

Coal mines essentially consist of long galleries of large length-to-diameter ratio (L/D). Since the onset of systematic research on the propagation of coal dust explosions in mines, large-scale experimental galleries have been a main tool of investigation. The tests in experimental coal mines in the United Kingdom at about 1890, was probably the first of this kind.

Fischer (1957) reported results from coal-dust explosion experiments in a 260-m long experimental coal-mine gallery of equivalent-circle cross-sectional diameter of 3.2m, ie, L/D of about 80. The main purpose of these experiments was to investigate whether deposits of stone dust on shelves in the upper part of the gallery cross section would prevent the propagation of coal-dust explosions in the gallery. However, it appeared that under certain circumstances this stone dust had little effect, and very violent flame acceleration phenomena were observed, as shown in Fig.7.20.

Figure7.20. Time of arrival of bituminous coal dust/air flame as a function of distance from ignition point at closed end of gallery of length 260m and diameter 3.2m. Pressure at closed end as a function of time. Nominal average dust concentration 500g/m3.

The coal-dust explosion was initiated by an explosion of 40m3 methane/air at the upstream closed end of the gallery. The gas was ignited by black powder ensuring both efficient ignition and violent combustion of the gas. The blast from the gas explosion in turn swept up the coal-dust layer of 4kg per m length of gallery on the floor and initiated the self-sustained dust explosion down the entire length of the gallery. The most striking feature of Fig.7.20 is the very constant flame speed of 1040m/s measured from about 50m from the closed end right to the open tube end 200m further down. Fischer associated this with some kind of detonation (see next subsection). The pressure versus time ratio was recorded only at the upstream closed end of the gallery, because the explosion was so violent that all the measurement stations further down the gallery were destroyed. As can be seen, the peak pressure at the closed end was about 5bar (g). It would be anticipated that the pressures further down the gallery were considerably higher.

Jost and Wagner (in Freytag, 1965) have illustrated the various characteristic phenomena occurring during acceleration of premixed gas flames in long one-end-open tubes. There are good reasons for assuming that their overall picture, as reproduced in Fig.7.21, also applies to dust clouds.

Figure7.21. Characteristic phenomena during acceleration of gas or dust flames in one-end-open long tubes, from laminar combustion via turbulent combustion to detonation. VF, flame speed; V2, velocity of the unburnt gas or dust cloud ahead of the flame.

The only major difference is that a dust cloud needs to be generated by raising dust deposits into suspension. This means that stage 1 and possibly also stage 2 in Fig.7.21, the ignition and laminar propagation of the initial flame, respectively, may not be relevant for dust flames. As already discussed, Fischer (1957) used a turbulent gas flame for initiating the dust entrainment and explosion. However, once the dust explosion gets under way, the blast wave generated by it will entrain dust further downstream as already discussed. Therefore all stages of Fig.7.21, from stage 3 and downward, will apply even to dust clouds. The essential reason for the flame acceleration is turbulence generated in the unburnt cloud ahead of the flame due to wall friction when the cloud is pushed toward the open tube end by the expansion of the part of the cloud that has burnt. The cloud combustion rate increases as soon as the flame front reaches the turbulent region of the unburnt cloud. This in turn increases the expansion rate of the combustion products and therefore also the flow rate of the unburnt cloud further ahead. The result is an even higher turbulence level and further increase of the combustion rate.

During all these stages, compression waves will be emitted and propagate toward the open tube end. Because the cloud ahead of the flame is heated due to adiabatic compression, each wave will propagate at slightly higher velocity than the previous one. Ultimately, therefore, they will all catch up with the initial wave and form a strong leading shock front. The turbulent flame front will also, due to the positive feedback mechanism of combustion rate, flow rate, increased turbulence, and turbulence-enhanced increased combustion rate, eventually catch up with the leading shock wave. If the leading shock is sufficiently strong, a switch can occur in the mechanism of flame propagation. Instead of heat being transferred by turbulent diffusion behind the leading shock wave, the dust cloud may become ignited in the highly compressed state inside the leading shock. If the induction time of ignition is sufficiently short, the chemical reaction zone and the propagating shock wave then become closely coupled and propagate through the cloud at constant velocity. This is detonation. However, as already mentioned, flame propagation at a constant high speed will not necessarily have to be a classical detonation, but can also be a high-speed turbulent deflagration supported by wall friction-induced turbulence.

Coal preparation is defined as the process of removing the undesirable elements from run-of-mine (ROM) coal by employing separation processes to achieve a relatively pure, uniform product. These separation processes are based on the differences between the physical and surface properties of the coal and the impurities. Coal preparation would include not only sizing (crushing and breaking), but also all the handling and treating techniques necessary to prepare the coal for market. Table III gives a general overview of the characteristics of different coal types offered in the market.

ROM coal is usually a heterogeneous material with no size definition and can consist of pieces ranging from fine dust to lumps; it is often wet and contains rock and/or clay, making it unsuitable for commercial use, such as in combustion. The objective of coal preparation, in terms of combustibility, is to improve the quality of the coal by removing these extraneous noncombustible materials leading to:

Pretreatment, or size reduction, is a common term used to include the processes of breaking, crushing, and screening ROM coal to provide a uniform coal feed with a certain predetermined top size. The number of stages in the size reduction process will depend on the end use of the coal. For instance, in power generation, the number of stages is more than the number needed for coking coal. In breaking the coal, four types of equipment are available: rotary breakers; roll crushers; hammer mills (ring mills), and impactors.

The Hardgrove grindability index is the index determined after passing 50 g of 1630-mesh dried coal in a standardized ball-and-race mill and sieve this sample through a 200-mesh sieve (ASTM D409) to determine the amount of material going through it.

The rotary breaker causes the coal to break by lifting it to a given height and dropping it against a hard surface. It is a cylindrical unit (operating at low speed) that subjects the coal particles on the liner to undergo centrifugal motion; the liners of the rotary breakers are screen plates that allow peripheral discharge of the properly sized material along the length of the rotary breaker.

The roll crusher is the workhorse of coal size reduction to shear and/or compress the material. It is compactly engineered in the form of a rotating roll and a stationary anvil (single roll crusher) or two equal-speed rolls (double roll crusher) rotating in opposite directions.

The hammer mill is the most commonly used coal pulverizer. In this device, feed coal is impacted by rotating hammers and further by grid breaker plates. Usually a high portion of fines is produced. A ring-type hammer mill (rings instead of hammers) would minimize the amount of fines in the product.

The impactor impacts the coal, which is then projected against a hard surface or against other coal particles. The rotor-type impact mill uses rotors to reduce the size of the material; the shattered material rebounds in the rotor path repetitively until the product is discharged from the bottom.

The sizing process usually follows the crushing process. The three major reasons for sizing the coal are to separate coal into various sizes for marketing, to feed washing and dewatering units, and to recover the solids used to control the specific gravity in these washing devices. Sizing of the coal is performed by screening or classification.

The most common screening method includes bringing each particle against an opening or aperture where the particle will either pass through or be retained. Several screen configurations have been developed, such as the following: (1) the Dutch sieve bend is a fixed screen with no moving parts and is situated at a level lower than the feed, (2) the Vor-Siv, developed in Poland, and (3) the loose-rod deck, developed in the United States by Inland Steel Corp., which consists of steel rods set at a suitable pitch to create the screening aperture.

Although most sizing of coal is performed with screening devices, classifiers are also in use. Classification refers to achieving size separation by exploiting different flow rates through a fluid. It includes dry classification and wet classification. Dry classification uses air as the ambient fluid and involves higher fluid volumes and higher velocities than those found in wet classification.

Coal preparation has been evolving for more than a century and the core of most of the process development work is in the area of separating the impurities from the coal, utilizing the physical difference in specific gravity between the coal and the rock impurities. An overview of the different coal cleaning systems is provided in Table IV.

One of the most successful heavy-medium cleaning processes; involves a large inverted conical vessel with sand in suspension in an upward current of water; increasing or decreasing the amount of sand in suspension causes a change in density of the fluid

After the cleaning process, the coal retains a significant amount of moisture, which can have negative effects on its transport and handling and its calorific value. Therefore, there is a need to reduce the moisture content by either dewatering or drying. Dewatering means mechanically separating water from the coal and drying means separation by thermally evaporating water.

Normally processes a pulp with a low percentage of solids (5 to 20%) and produces a relatively thick suspension by removing a portion of water; solids discharged at the bottom, and water and slimes exit at the top of the unit

Also done is heating the feed slurry (steam filtration) by covering a conventional vacuum filter with a hood and applying steam under the hood to facilitate additional water drainage from the filter cake

crushing and milling | mining of mineral resources | siyavula

In this chapter we build on what was done in the previous two chapters. After learning that rocks contain minerals, we now explore how the minerals may be extracted so that they may be utilised. Mining plays an important role in the wealth of a country. Learners will therefore learn about the mining industry in South Africa and the impact that mining may have on a country and the globe.

The mining industry is an important industry in South Africa. It involves a number of industries working together. Exploration is followed by excavation, which is followed by crushing and milling to reduce the size of the rocks. This is followed by extraction (removing the valuable minerals from the ore) and finally refining. Each of these processes are discussed in this chapter. The idea is not that learners should know all the terms off by heart, but rather that they grasp the bigger picture. A number of different processes are needed with each one dependent on the efficiency of the step before. The flow diagram exercise towards the end of the chapter is meant to consolidate the chapter content and help learners realise the continuous nature of many industrial processes.

A research project is also included in this chapter. Let the learners choose one industry and research the different aspects of mining covered in this chapter for their chosen industry. The following mining industries can be researched: gold, iron, copper, diamond, phosphate, coal, manganese, chromium or platinum group metals (PGMs). Learners could also choose their own.

The projects need to be handed out in the beginning of the term/chapter. Learners can then present their projects at the end of the chapter, by doing a poster or an oral, or both. For the orals, we suggest you work with the language department so that learners can be assessed there as well. If posters are done, then we suggest you put these up for display for the whole school to see. Learners can stand at their posters during breaks where learners from other grades have the opportunity to come and have a look at their work and ask questions about it.

The project has a two-way purpose, firstly for learners to continue learning about doing research, finding information and presenting the information to others, and secondly, for learners to explore careers in this industry. Part of what they should include in their research is a section on careers in mining.

In the previous two chapters you have learnt about the spheres of the Earth especially the lithosphere. The lithosphere consists of rocks, which contain minerals. Minerals are natural compounds formed through geological processes. A mineral could be a pure element, but more often minerals are made up of many different elements combined. Minerals are useful chemical compounds for making new materials that we can use in our daily lives. In this chapter we are going to look at how to get the minerals out of the rocks and in a form that we can use. This is what the mining industry is all about.

You already know that minerals in rocks cannot be used. Many processes are used to make minerals available for our use. We need to locate the minerals. We must determine whether these concentrations are economically viable to mine. Rocks with large concentrations of minerals, are called ores. Mining depends on finding good quality ore, preferably within a small area.

The next step is to get the rocks which contain the mineral out of the ground. Once the ore is on the surface, the process of getting the mineral you want out of the rock can start. Once the mineral is separated from the rest of the rock, the mineral needs to be cleaned so that it can be used.

This project should be handed out in the beginning of the chapter so that learners have time to work on it. Information for the project is provided in the sections in the chapter, but learners also need to find information on their own. Guiding questions are provided to help learners.

One of the most important steps in mining is to find the minerals. Most minerals are found everywhere in the lithosphere, but in very, very low concentrations, too low to make mining profitable. For mining to be profitable, high quality ore needs to be found in a small area. Mining exploration is the term we use for finding out where the valuable minerals are.

Today technology helps mining geologists and surveyors to find high quality ore without having to do any digging. When the geologists and surveyors are quite sure where the right minerals are, only then do they dig test shafts to confirm what their surveying techniques have suggested.

In all these methods we use the properties of the minerals and our knowledge of the lithosphere to locate them underground, without going underground ourselves. For example, iron is magnetic so instruments measuring the changes in the magnetic field can give us clues as to where pockets of iron could be.

Exploration methods are used to find, and assess the quality of mineral deposits, prior to mining. Generally a number of explorative techniques are used, and the results are then compared to see if a location seems suitable for mining.

Remote sensing is the term used to gain information from a distance. For example, by using radar, sonar and satellite images, we can obtain images of the Earth's surface. These images help us to locate possible mining sites, as well as study existing mining sites for possible expansion.

Rare earth elements are a set of 17 elements on the Periodic Table, including the fifteen lanthanides and scandium and yttrium. Despite their names, they are found in relatively plentiful amounts in the Earth's crust.

Geophysical methods make use of geology and the physical properties of the minerals to detect them underground. For example, diamonds are formed deep in the Earth at very high temperatures, in kimberlite pipes of igneous rock. The kimberlite pipe is a carrot shape. The first kimberlite pipe to be detected was in Kimberley in South Africa. The pipe was mined, eventually creating the Big Hole.

Geochemical methods combine the knowledge of the chemistry of the minerals with the geology of an area to help identify which compounds are present in the ore and how much of it is present. For example, when an ore body is identified, samples are taken to analyse the mineral content of the ore.

When colonialists arrived, they realised the potential mineral wealth of South Africa as gold, and later diamonds, were discovered. They ruthlessly took land from the local people wherever minerals were found, completely ignoring their right to ownership and access.

De Beers purchased the mining rights and closed all access to diamond mining areas. Anyone entering the area would be prosecuted and the sale of so-called 'illegal' diamonds was heavily punished. Other large mining companies have tried to claim the right to the minerals that they mine.

Once the ore body has been identified, the process of getting the ore out of the ground begins. There are two main methods of mining - surface mining and underground mining. In some locations a combination of these methods is used.

Surface mining is exactly what the word says - digging rocks out from the surface, forming a hole or pit. In South Africa, this method is used to mine for iron, copper, chromium, manganese, phosphate and coal.

Let's look at coal as an example. For surface mining, the minerals need to be close to the surface of the Earth. Most of the coal found in South Africa is shallow enough for surface mining. Usually the rocks are present in layers. To expose the coal layer, the layers above it need to be removed. The vegetation and soil, called the topsoil, is removed and kept aside so that it can be re-deposited in the area after mining. If there is a layer of rock above the coal face, called the overburden, this is also removed before the coal can be excavated. Once all the coal has been removed, the overburden and topsoil are replaced to help in restoring the natural vegetation of the area. This is called rehabilitation.

There is a growing emphasis on the need to rehabilitate old mine sites that are no longer in use. If it is too difficult to restore the site to what it was before, then a new type of land use might be decided for that area.

When you mine you are digging into solid rock. The rock needs to be broken up into smaller pieces before it can be removed. Holes are drilled in the rock and explosives, like dynamite, are placed inside the holes to blast the rock into pieces. The pieces are still very large and extremely heavy. The rocks are loaded onto very large haul trucks and removed. Sometimes the rocks (ore) are crushed at the mining site to make them easier to transport.

Mining trucks are enormous. They are up to 6 meters tall, that's higher than most houses. These trucks can carry 300 tons of material and their engines have an output 10-20 times more powerful than a car engine.

Often the minerals are not found close to the surface of the Earth, but deeper down. In these cases underground mining, also called shaft mining, is used. Examples of underground mining in South Africa are mining for diamonds, gold and sometimes the platinum group metals (PGM).

The PGMs are six transition metals usually found together in ore. They are ruthenium (Ru), rhodium (Rh), palladium (Pd), osmium (Os), iridium (Ir) and platinum (Pt). South Africa has the highest known reserves of PGMs in the world.

Sometimes the ore is very deep, which is often the case with diamonds or gold ore. In these cases mine shafts go vertically down and side tunnels make it possible for the miners and equipment to reach the ore. A structure called the headgear is constructed above the shaft and controls the lift system into the vertical shaft. Using the lift, it can take miners up to an hour to reach the bottom of the shaft.

The TauTona Mine in Carletonville, Gauteng is the world's deepest mine. It is 3,9 km deep and has 800 km of tunnels. Working this deep underground is very dangerous. It is very hot, up to 55C. To be able to work there, the air is constantly cooled to about 28 C using air-conditioning vents.

South Africa is a world leader in the gold mining industry. We have been doing gold mining for more than a century and our mines are the deepest in the world. Until 2010 we were the leading producer of gold in the world. Gold is a lustrous, precious metal which has a very high conductivity.

Yes it is, the mines are very deep, of the deepest in the world. Mining deep underground is difficult and dangerous because of the heat and lack of oxygen. Rocks can also collapse because of the pressure.

One of the methods used in underground mining is called room and pillar, and is often used for mining coal. Part of the mine is open to the surface and part of it is underground. The coal face is dug out, but pillars of coal are left behind to keep the tunnels open and support the roof. Machines called continuous miners are used to remove the coal. The coal is loaded onto conveyor belts and taken up to the surface for further crushing.

This section looks at methods to get very large rocks crushed and ground until it is as fine as powder. The first concept that needs to come across here is that minerals are inside rocks and by crushing rocks, the minerals are exposed at the surface of the rock fragment. Only then can chemicals be used to extract the mineral. An analogy with a choc chip biscuit is used to demonstrate this principle. The second concept is that a lot of energy is needed to break rocks. This is a very energy-intensive step in the mining industry, and one of the reasons why mining is so expensive.

This lesson can be introduced by demonstrating the principle explained above to the class. Use choc chip biscuits and crush them with your fingers. This is to get the minerals (choc chips) out. The next step is to separate the choc chips from the crumbs - also a step in the mining process.

Mineral crystals are spread throughout rocks, just like chocolate chips are spread throughout a choc chip biscuit. Sometimes we can see the chocolate chips from the outside, but most of the time the chips are not visible because they are inside the biscuit.

The only way to find out how many choc chips there are is to crush the biscuit. In the same way we can sometimes see mineral crystals from the outside of the rock, but mostly we don't know what minerals there are and and what concentrations are inside the rock. The only way to find out is to break the rock into smaller and smaller pieces.

Once we have crumbled the choc chip biscuit, the chocolate pieces can be separated from the crumbs. In the same way in the mining process the valuable minerals can be separated from the unwanted rock. The unwanted rock is called waste rock.

Let's look at an example. You have learnt in the previous chapter that copper minerals are found in rocks. In South Africa, the Bushveld Igneous Complex is an area which stretches across the North West and Limpopo Provinces. Igneous rock with high mineral content is found here. Here they mine for PGMs, chromium, iron, tin, titanium, vanadium and other minerals using open pit and underground mining. The rocks from the mines are transported by conveyor belts to crushers. Jaw crushers and cone crushers break the huge rocks into smaller rocks.

You can demonstrate this to your class by placing some pieces of broken up biscuit into a plastic container with some marbles or ball bearings. Place the lid on the container and then shake it so that the marbles help to crush and break up the biscuit pieces even further.

This process of reducing the size of the rocks requires a lot of energy. Just image how hard it is to break a rock. How much more energy do you think is needed to crush a rock until it is like sand? This is one of the steps in the mining process that is very expensive because energy is needed to drive the process.

Most minerals are found as compounds in rocks. Only a few minerals are found in their pure form, in other words not bound to any other element. Examples of minerals found in their pure form are gold and diamonds (diamonds consist of the element carbon).

Some rocks are used as is, and do not need to be crushed into powder, or involved in minerals extraction. For example phosphate rock itself can be used as a fertiliser, or it can be used to make phosphoric acid. Sand, or the mineral silicon dioxide (SiO2) is used in the building industry. Coal found in sedimentary rock, is crushed into the appropriate size and used as fuel for electricity generation or the iron-making process.

Before the minerals can be used, they need to be separated from the waste rock. A number of different separation techniques are used. These techniques are based on the properties of the minerals. Different minerals are often found together, for example copper and zinc, gold and silver or the PGMs. A combination of techniques are used to separate the minerals from the waste and then the minerals from each other.

Sorting by hand is not a very effective method to separate out the minerals you want. It can only be used in exceptional situation or by individuals, for example many people mine for alluvial diamonds by hand in rivers in Angola. It is a cheap and easy process to do individually, but it is not feasible on an industrial scale.

Iron is a metal with magnetic properties. Iron ore can be separated from waste rock by using magnetic separation techniques. Conveyor belts carry the ore past strong electromagnets which remove the magnetic pieces (containing the iron) from the non-magnetic waste. How do you think this works? Study the following diagram

The magnetic iron ore will fall into the container on the right as it is attracted to the magnetic roller and travels around the bend of the magnet for a longer period, whereas the non-magnetic waste drops straight down due to gravity, as the magnet turns, and falls into the first container on the left.

One of the first methods for mining gold was that of panning, a technique where ore is mixed with water and forms a suspension. When it is shaken, the dense particles of gold sink to the bottom and could be removed.

Let the learners work in groups of three. The value of the activity is the process of doing it, and not so much the end product. Learners will want to separate every single bead in the process and this is not possible, nor does it happen in the mining industry. Valuable materials do end up as waste.

When choosing beads to separate, ensure that there are a variety of shapes, round and flat, small and large. Most plastic beads will float on water, but metallic ones will sink. The piece of carpet is provided to make the tray rough, but still smooth enough for round beads to roll off, and flat beads to stick. Choose the smallest flattest beads to represent the valuable materials.They will remain on the carpet in the tray more easily.

To separate by density, learners can drop the beads into water - some beads will float and others will sink. To separate by size, learners can use the mesh and let the smaller beads fall through into the cup, with the larger ones staying behind.

As an extension, include some beads which are identical in shape and size, but different colours. At this point, learners will want to hand sort them. Tell learners that hand sorting, although effective and is used by individuals, it is a very time-consuming process and therefore almost never done in the mining industry. Ask learners if they have any other ideas. This is where chemical properties come in. For example, tell learners that one colour bead reacts with an acid and the other does not. Get learners to discuss how they would then separate the beads knowing this. A real world example is that silver reacts with chlorine, but gold does not.

As you have seen in the activity, separating a mixture can be done using different properties, depending on the different properties of the beads. There could be a number of different ways to separate the beads depending on which type of bead you want to select (considered to be the most valuable ones).

Size separation is used frequently in mining to classify ore. For example, when iron ore is exported, it needs to be a certain size to be acceptable to the world market. Coal that is used in power stations also needs to be a certain size so that it can be used to generate electricity effectively.

Flotation makes use of density separation, but in a special way. Chemicals are added to change the surface properties of the valuable minerals so that air bubbles can attach to them. The minerals are mixed with water to make a slurry, almost like a watery mud. Air bubbles are blown through the slurry and the minerals attach to the bubbles. The air bubbles are much less dense than the solution and rise to the top where the minerals can be scraped off easily.

The focus of this activity is to illustrate the principle of flotation and for learners to practice explaining their observations. They will have to apply what they know about density to be able to explain what they see. This activity can also be modified by letting the learners predict what they think will happen before they add the peanuts and raisins to the tap water; and again before they add it to the soda water. The outcome might not be what they expected and the value of the activity is for them to try to explain what they see.

The activity can be done as a classroom demonstration, but it is more effective if done by the learners in pairs. The one learner can use the tap water, and the other the soda water. A suggestions is to buy packets of peanuts and raisins separately, otherwise oil from the peanuts can coat the raisins, causing some of the raisins to rise. The raisins can also be rinsed in acidulated water because they are often dressed with oil before sale for visual enhancement.

Learners should observe that the peanuts and raisins sink to the bottom in the tap water and remain there since they are more dense than water. However, in the soda water, the peanuts and raisins initially sink to the bottom, but then the peanuts start to rise. Small bubbles from the soda water attach to the peanuts' oily surface and cause them to rise to the surface.

The methods mentioned so far are all physical separation methods. Sometimes they are sufficient to separate minerals for use, like coal or iron ore. But more often the element that we are looking for is found as a chemical compound, and so will have to be separated by further chemical reactions. For example, copper in Cu2S or aluminium in Al2O3. What is the name for the force that is holding atoms together in a compound?

Once the compound is removed from the ore, the element we want needs to be separated from the other atoms by chemical means. This process forms part of refining the mineral, as you will see in the next section.

There are many different methods used to concentrate and refine minerals. The choice of methods depends on the composition of the ore. Most of the methods however, make use of chemistry to extract the metal from the compound or remove impurities from the final product. We will discuss the extraction of iron from iron ore as an example.

Iron atoms are found in the compounds FeO, Fe2O3 and Fe3O4 and in rocks like haematite and magnetite. South Africa is the seventh largest producer of iron ore in the world. Iron has been mined in South Africa for thousands of years. South African archaeological sites in Kwa-Zulu Natal and Limpopo provide evidence for this. Evidence of early mining activities was found in archaeological sites dating mining and smelting of iron back to the Iron Age around 770 AD.

The first iron mining techniques used charcoal which was mixed with iron ore in a bloomery. When heating the mixture and blowing air (oxygen) in through bellows, the iron ore is converted to the metal, iron. The chemical reaction between iron oxide and carbon is used here to produce iron metal. The balanced chemical equation for the reaction is:

This extraction method is still used today. The bloomery is replaced with a blast furnace, but the chemistry is still the same. Iron ore, a type of coal called coke (which contains 85% carbon) and lime are added to the top of the blast furnace. Hot air provides the oxygen for the reaction. The temperature of a blast furnace can be up to 1200C. The reaction takes place inside the furnace and molten iron is removed from the bottom. Lime (calcium carbonate or CaCO3) is added to react with the unwanted materials, such as sand (silicon dioxide or SiO2). This produces a waste product called slag. The slag is removed from the bottom and used for building roads. Iron is used to make steel. Hot gases, mainly carbon dioxide, escape at the top of the furnace.

For safety reasons, this experiment should rather be demonstrated. Ensure that you wear safety glasses when performing this experiment. It is quite easy to do, but takes a long time to actually react. The blow pipe needs to redirect the flame into the hollow in the block. Blow through the top of the blue part of the flame. Use a straw to extend the blow pipe so that you can stand a bit further away from the flame. Ensure that a steady stream of heat gets right into the middle of the mixture so that it glows red hot for a while. The video link in the Visit box also shows how the experiment is performed (and the mistakes made). The product can clearly be seen in the video.

In this experiment carbon was used to remove the oxygen from the lead(II) oxide. The carbon and oxygen form carbon dioxide, and the lead is left behind as a metal. This is the same process that is used in iron extraction in the blast furnace, that we discussed above. Coke, which is mainly carbon, removes the oxygens from the iron(III) oxide to form carbon dioxide and leaves behind the iron metal.

The iron that is formed in the blast furnace often contains too much carbon - about 4% where it should contain not more than 2%. Too much carbon makes the iron brittle. To improve the quality of the iron, it needs to be refined by lowering the amount of carbon. This is done by melting the metal and reacting the carbon with pure oxygen to form carbon dioxide gas. In this way the carbon is burned off and the quality of the iron improves. The iron can now be used in the steel-making process. Carbon reacts with oxygen according to the following chemical equation:

Most minerals go through chemical extraction and refining processes to purify them for use in making materials and other chemical products. These are then distributed to where they are needed, for example, coal is distributed to coal power stations and slag is distributed to construction groups for building roads. The mining industry supplies the manufacturing industry and the chemical industry with its raw materials, for example iron is distributed to steel manufacturing industries.

Long before diamonds were discovered in the Kimberley area and the Gold Rush in Pilgrim's Rest and Witwatersrand areas in the late 1800s, minerals have been mined in South Africa. At Mapungubwe in the Limpopo Province evidence of gold and iron mining and smelting was found which dates back to the early 11th century AD. However, it was the large scale mining activities that accelerated the development of the country.

South Africa has a wealth of minerals. We are the world's largest producers of chromium, manganese, platinum, vanadium and andalusite; and the second largest producer of ilmenite, palladium, rutile and zirconium. We are the third largest coal exporter, fifth largest diamond producer and seventh largest iron ore producer. Up to 2010 we were the world's largest gold producer, but our gold production has declined steadily over a number of years. We are currently fifth on the list of gold producers.

The Bushveld Igneous Complex has the world's largest primary source of platinum group metals, indicated on the map in light blue. It is one of the most important mining areas in South Africa due to its abundance of minerals.

Learners need to develop their own symbols for each mineral that is mined, and also colour code the map. The map is blank and so they must find out where each town is located and add it to the map. Let them also fill in the name of the city/town/area in which they live. If there are mining activities in your area which is not indicated on this table, let the learners add it to the list. The list provided is not exhaustive, but it is still fairly long. If you want to make the activity simpler, learners can also chose a certain number of minerals to represent.

There are two types of diamond mining, alluvial (which is found on the coast or in inland rivers which have washed through kimberlite pipes) and kimberlite (which is found inland). What is the link between these two types of diamond mining?

This activity is meant to consolidate the knowledge from this chapter. Each industry will have its own unique flow diagram. The idea is for the learners to realise that it is a continuous system where the one process feeds into the next one to produce a useful end product. This activity links up with the research project and should give learners a good guide for doing and presenting their research projects.

Coal mining: Finding coal seams through exploration in Mpumalanga, Free State and KwaZulu Natal mining for coal using open pit mining removing the coal by blasting and drilling loading onto haul trucks and removing from mine crushing the coal sorting into different sizes distribution to power stations electricity generation

Mining has played a major role in the history of South Africa. It accelerated technological development and created infrastructure in remote areas in South Africa. Many small towns in South Africa started because of mining activity in the area. It also created a demand for roads and railways to be built. Most importantly it created job opportunities for thousands of people. Even today many households are dependent on the mining activities for jobs and an income. Mining is an important part of our economic wealth. We export minerals and ore to many other countries in the world.

Mining activities also have a negative impact on the environment. In many cases the landscape is changed. This applies particularly to surface mines (open pit mines), where large amounts of soil and rock must be removed in order to access the minerals. The shape of the landscape can be changed when large amounts of rocks are dug up from the Earth and stacked on the surface. These are called mine dumps. Open pit mines also create very large unsightly and dangerous holes (pits) in the ground that change the shape of the land.

Air and water pollution can take place if care is not taken in the design and operation of a mine. Dust from open pit mines, as well as harmful gases such as sulphur dioxide and nitrogen dioxide, could be released from mining processes and contribute to air pollution. Mining activities produce carbon dioxide. Trucks and other vehicles give off exhaust gases.

If the mining process is not monitored properly, acid and other chemicals from chemical processing can run into nearby water systems such as rivers. This is poisonous to animals and plants, as well as to humans who may rely on that water for drinking.

An example are pollutants (dangerous chemicals), called tailings, left over from gold mining which pose a threat to the environment and the health of nearby communities. Dangerous waste chemicals can leak into the groundwater and contaminate water supplies if the tailings are not contained properly.

There are no specific answers for this activity. It is an open discussion. We suggest that you discuss the impact of mining in South Africa through this activity. The idea is that learners should come up with all the issues and think about the impact of what we as humans do. The answer to solving the issues is not necessarily to close down all mining activity.

Use the following concept map to summarise what you have learnt in this chapter about mining of mineral resources. What are the three types of mining that we discussed in this chapter? Fill these into the concept map. Remember that you can add in your own notes to these concept maps, for example, you could write more about the environmental impacts of mining.

Phalaborwa is home to one of the largest open pit mines in the world. The original carbonate outcrop was a large hill known as Loolekop. Archaeological findings at Loolekop revealed small scale mining and smelting activities carried out by people who lived there long ago. An early underground mine shaft of 20 meters deep and only 38 centimeters wide were also found. The shafts contained charcoal fragments dating the activities to 1000 - 1200 years ago.

In 1934 the first modern mining started with the extraction of apatite for use as a fertiliser. In 1946 a well known South African geologist Dr. Hans Merensky started investigating Loolekop and found economically viable deposits of apatite in the foskorite rock. In the early 1950s a very large low grade copper sulfide ore body was discovered.

In 1964 the Phalaborwa Mine, an open pit copper mine, commenced its operations. Today the pit is 2 km wide. Loolekop, the large hill, has been completely mined away over the years. A total of 50 different minerals are extracted from the mine. The northern part of the mine is rich in phosphates and the central area, where Loolekop was situated, is rich in copper. Copper with the co-products of silver, gold, phosphate, iron ore, vermiculite, zirconia and uranium are extracted from the rocks.

The open pit facility closed down its operation in 2002 and has now been converted to an underground mine. This extended the lifetime of the mine for another 20 years. The mine employs around 2500 people.

2000 million years ago this area was an active volcano. Today the cone of the volcano is gone and only the pipe remains. The pipe is 19 km2 in area and has an unknown depth, containing minerals like copper, phosphates, zirconium, vermiculite, mica and gold.

This mine was a leader in the field of surface mining technology with the first in-pit primary crushing facility. This meant that ore was crushed by jaw crushers before taken out of the mine. They also used the first trolley-assist system for haul trucks coming out of the pit. Today the mine has secondary crushing facilities, concentrators and a refinery on site.

In 1982 a series of cavities with well-crystallised minerals were discovered, for example calcite crystals up to 15 cm on edge, silky mesolite crystals of up to 2cm long and octahedral magnetite crystals of 1-2 cm on the edge.

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