Videos- series (u tube) Videos - series Uploaded on Aug 25, 2010 ++++++++++++++++++++++++++++++++++++++++++++++++ Uploaded on Aug 25, 2010 ++++++++++++++++++++++++++++++++++++++++++++++++++ Published on Dec 20, 2012 ++++++++++++++++++++++++++++++++++++++++++++++++++ LET'S TALK SAFETY ISSUES  Uranium mining - Wikipedia, the free encyclopedia Resource Snapshot (5): Phosphorus - World Resources Forum www.wrforum.org500 × 315Search by image Although the timing of the production peak is uncertain, there is no denial from the fertilizer industry that the quality of the existing phosphate rocks is ...  | Related Links The exact effects of bauxite mining are related to the site. It almost always involves some habitat destruction, soil erosion, loss of biodiversity, or water pollution. These effects can be short term, and followed by regrowth, or severe and permanent http://chemistry123123.blogspot.ca/2012/09/environmental-impact-of-extraction-of.html  EPA to review mountaintop coal mining permits | cleveland.com www.cleveland.com453 × 519Search by image The permits are issued by the Army Corps of Engineers, an agency that has been criticized by environmental groups and has been sued for failing to thoroughly evaluate the environmental impact of    |
Environmental impacts
Cement manufacture causes environmental impacts at all stages of the process. These include emissions of airborne pollution in the form of dust, gases, noise and vibration when operating machinery and during blasting in quarries, and damage to countryside from quarrying. Equipment to reduce dust emissions during quarrying and manufacture of cement is widely used, and equipment to trap and separate exhaust gases are coming into increased use. Environmental protection also includes the re-integration of quarries into the countryside after they have been closed down by returning them to nature or re-cultivating them.
CO2 emissions[edit]
Carbon concentration in cement spans from ≈5% in cement structures to ≈8% in the case of roads in cement.[45] Cement manufacturing releases CO2 in the atmosphere both directly when calcium carbonate is heated, producing lime and carbon dioxide,[46] and also indirectly through the use of energy if its production involves the emission of CO2. The cement industry produces about 5% of global man-made CO2emissions, of which 50% is from the chemical process, and 40% from burning fuel.[47]
The amount of CO2 emitted by the cement industry is nearly 900 kg of CO2 for every 1000 kg of cement produced. In the European union the specific energy consumption for the production of cement clinker has been reduced by approximately 30% since the 1970s. This reduction in primary energy requirements is equivalent to approximately 11 million tonnes of coal per year with corresponding benefits in reduction of CO2 emissions. This accounts for approximately 5% of anthropogenic CO2.[48]
The high proportion of carbon dioxide produced in the chemical reaction leads to a large decrease in mass in the conversion from limestone to cement. So, to reduce the transport of heavier raw materials and to minimize the associated costs, it is more economical for cement plants to be closer to the limestone quarries rather than to the consumer centers.[49]
In certain applications, lime mortar reabsorbs the same amount of CO2 as was released in its manufacture, and has a lower energy requirement in production than mainstream cement. Newly developed cement types from Novacem[50] and Eco-cement can absorb carbon dioxide from ambient air during hardening.[51] Use of the Kalina cycle during production can also increase energy efficiency.
Heavy metal emissions in the air[edit]
In some circumstances, mainly depending on the origin and the composition of the raw materials used, the high-temperature calcination process of limestone and clay minerals can release in the atmosphere gases and dust rich in volatile heavy metals, a.o, thallium,[52] cadmium and mercury are the most toxic. Heavy metals (Tl, Cd, Hg, ...) are often found as trace elements in common metal sulfides (pyrite (FeS2), zinc blende (ZnS), galena (PbS), ...) present as secondary minerals in most of the raw materials. Environmental regulations exist in many countries to limit these emissions. As of 2011 in the United States, cement kilns are "legally allowed to pump more toxins into the air than are hazardous-waste incinerators."[53]
Heavy metals present in the clinker[edit]
The presence of heavy metals in the clinker arises both from the natural raw materials and from the use of recycled by-products or alternative fuels. The high pH prevailing in the cement porewater (12.5 < pH < 13.5) limits the mobility of many heavy metals by decreasing their solubility and increasing their sorption onto the cement mineral phases. Nickel, zinc andlead are commonly found in cement in non-negligible concentrations.
Use of alternative fuels and by-products materials[edit]
A cement plant consumes 3 to 6 GJ of fuel per tonne of clinker produced, depending on the raw materials and the process used. Most cement kilns today use coal and petroleum coke as primary fuels, and to a lesser extent natural gas and fuel oil. Selected waste and by-products with recoverable calorific value can be used as fuels in a cement kiln (referred to as co-processing), replacing a portion of conventional fossil fuels, like coal, if they meet strict specifications. Selected waste and by-products containing useful minerals such as calcium, silica, alumina, and iron can be used as raw materials in the kiln, replacing raw materials such as clay, shale, and limestone. Because some materials have both useful mineral content and recoverable calorific value, the distinction between alternative fuels and raw materials is not always clear. For example, sewage sludge has a low but significant calorific value, and burns to give ash containing minerals useful in the clinker matrix.[54]
Normal operation of cement kilns provides combustion conditions which are more than adequate for the destruction of even the most difficult to destroy organic substances. This is primarily due to the very high temperatures of the kiln gases (2000 °C in the combustion gas from the main burners and 1100 °C in the gas from the burners in the precalciner). The gas residence time at high temperature in the rotary kiln is of the order of 5–10 seconds and in the precalciner more than 3 seconds.[55]
Due to bovine spongiform encephalopathy (BSE) in the European beef industry, the use of animal-derived products to feed cattle is now severely restricted. Large quantities of waste animal meat and bone meal (MBM), also known as animal flour, have to be safely disposed of or transformed. The production of cement kilns, together with the incineration, is to date one of the two main ways to treat this solid effluent of the food industry.
Green cement[edit]
Green cement is a cementitious material that meets or exceeds the functional performance capabilities of ordinary Portland cement by incorporating and optimizing recycled materials, thereby reducing consumption of natural raw materials, water, and energy, resulting in a more sustainable construction material.
The manufacturing process for green cement succeeds in reducing, and even eliminating, the production and release of damaging pollutants and greenhouse gasses, particularly CO2.
Growing environmental concerns and increasing cost of fuels of fossil origin have resulted in many countries in sharp reduction of the resources needed to produce cement and effluents (dust and exhaust gases).[55]
Peter Trimble, a design student at the University of Edinburgh has proposed 'DUPE' based on sporosarcina pasteurii, a bacterium with binding qualities which, when mixed with sand and urine produces a concrete said to be 70% as strong as conventional materials.[56]
Types of modern cement
Portland cement is by far the most common type of cement in general use around the world. This cement is made by heating limestone(calcium carbonate) with other materials (such as clay) to 1450 °C in a kiln, in a process known as calcination, whereby a molecule of carbon dioxide is liberated from the calcium carbonate to form calcium oxide, or quicklime, which is then blended with the other materials that have been included in the mix to form calcium silicates and other cementitious compunds. The resulting hard substance, called 'clinker', is then ground with a small amount of gypsum into a powder to make 'Ordinary Portland Cement', the most commonly used type of cement (often referred to as OPC). Portland cement is a basic ingredient ofconcrete, mortar and most non-specialty grout. The most common use for Portland cement is in the production of concrete. Concrete is a composite material consisting of aggregate (gravel and sand), cement, and water. As a construction material, concrete can be cast in almost any shape desired, and once hardened, can become a structural (load bearing) element. Portland cement may be grey or white...
Limestone
Portland cement is by far the most common type of cement in general use around the world. This cement is made by heatinglimestone(calcium carbonate) with other materials (such as clay) to 1450 °C in a kiln, in a process known as calcination, whereby a molecule of carbon dioxide is liberated from the calcium carbonate to form calcium oxide, or quicklime, which is then blended with the other materials that have been included in the mix to form calcium silicates and other cementitious compunds. The resulting hard substance, called 'clinker', is then ground with a small amount of gypsum into a powder to make 'Ordinary Portland Cement', the most commonly used type of cement (often referred to as OPC). Portland cement is a basic ingredient ofconcrete, mortar and most non-specialty grout. The most common use for Portland cement is in the production of concrete. Concrete is a composite material consisting of aggregate (gravel and sand), cement, and water. As a construction material, concrete can be cast in almost any shape desired, and once hardened, can become a structural (load bearing) element. Portland cement may be grey or white.
limestone
| Composition | |
|---|---|
| Calcium carbonate: inorganic crystalline calciteand/or organic calcareous material |
An ore is a type of rock that contains sufficient minerals with important elements including metals that can be economically extracted from the rock.[1] The ores are extracted from the earth through mining; they are then refined (often via smelting) to extract the valuable element, or elements.
The grade or concentration of an ore mineral, or metal, as well as its form of occurrence, will directly affect the costs associated with mining the ore. The cost of extraction must thus be weighed against the metal value contained in the rock to determine what ore can be processed and what ore is of too low a grade to be worth mining. Metal ores are generally oxides, sulfides, silicates, or "native" metals (such as native copper) that are not commonly concentrated in the Earth's crust, or "noble" metals (not usually forming compounds) such as gold. The ores must be processed to extract the metals of interest from the waste rock and from the ore minerals. Ore bodies are formed by a variety of geological processes. The process of ore formation is called ore genesis.
