Dolomite – A Useful Mineral...

Dolomite – A Useful Mineral Dolomite is also known as dolostone and dolomite rock.  It is a sedimentary rock which primarily consists of the mineral dolomite. It is found in sedimentary basins worldwide. Dolomite rock is similar to limestone rock. Both dolomite and limestone rocks share the same colour ranges of white-to-gray and white-to-light brown (although other colours such as red, green, and black are also possible). Both the rocks have approximately the same hardness, and they are both soluble in dilute hydrochloric (HCl) acid. The original mineral name ‘dolomie’ was given by NT Saussare, in 1792, in honor of the French geologist Deodat Guy de Dolomieu (1750–1801). Dolomite, the rock, contains a large proportion of dolomite the mineral. Ideal dolomite has a crystal lattice consisting of alternating layers of Ca and Mg, separated by layers of CO3 and is typically represented by a stoichiometric chemical composition of CaMg(CO3)2, where calcium and magnesium are present in equal proportions. Dolomite originates in the same sedimentary environments as limestone i.e. in warm, shallow, marine environments where calcium carbonate (CaCO3) mud accumulates in the form of shell debris, fecal material, coral fragments, and carbonate precipitates. Dolomite is thought to form when the calcite in carbonate mud or limestone is modified by magnesium-rich groundwater. The available magnesium facilitates the conversion of calcite into dolomite. This chemical change is known as dolomitization. Dolomitization can completely alter a limestone into a dolomite, or it can partially alter the rock to form a dolomitic limestone. Dolomite is a complex mineral. It is relatively a soft mineral which can be easily crushed to a soft powder. The mineral is an anhydrous carbonate mineral consisting of a double carbonate of calcium (Ca) and magnesium (Mg). It is chemically represented by CaMg(CO3)2 or CaCO3.MgCO3. It theoretically contains...

Dolomite – Its Processing and Application in Iron and Steel Industry Jun28

Dolomite – Its Processing and Application in Iron and Steel Industry...

Dolomite – Its Processing and Application in Iron and Steel Industry Dolomite is an anhydrous carbonate mineral. It is a double carbonate of calcium and magnesium (CaCO3.MgCO3). It is one of the important raw materials used in production of iron and steel. Dolomite contains theoretically 54.35 % of CaCO3 and 45.65 % of MgCO3 or 30.41 % of CaO, 21.86 % of MgO, and 47.73 % of CO2. However, in nature, dolomite is not available in this exact proportion. Hence generally the rock containing in the range of 40 % to 45 % of MgCO3 is usually called dolomite. The main uses of dolomite in iron and steel industry are (i) as a fluxing material (ii) for protection of refractory lining, and (iii) as a refractory raw material. Dolomite in iron and steel industry is normally used in three forms. These are (i) raw dolomite which is also the natural form of dolomite, (ii) calcined dolomite, and (iii) sintered dolomite. When dolomite is used as a fluxing material then it is used as either raw dolomite or calcined dolomite. When dolomite is used for the protection of refractories, it is used in calcined form and when dolomite is being used as a refractory raw material, it is used in the form of sintered dolomite. The uses and form of dolomite in iron and steel industry is shown in Fig 1. Fig 1 Uses and form of dolomite in iron and steel industry Processing of dolomite Dolomite after its mining has to undergo several processing before it can be used in various processes. The basic processes in the production of dolomite are (i) quarrying of raw dolomite, (ii) preparing mined dolomite for its use by crushing and sizing, (iii) calcining of raw dolomite, (iv) processing...

Refractories and Classification of Refractories...

Refractories and Classification of Refractories Refractories are inorganic, nonmetallic, porous and heterogeneous materials composed of thermally stable mineral aggregates, a binder phase and additives. The principal raw materials used in the production of refractories are normally the oxides of silicon, aluminum, magnesium, calcium and zirconium. There are some non-oxide refractories like carbides, nitrides, borides, silicates and graphite. Refractories are chosen according to the conditions they face during their use. Some applications require special refractory materials. Zirconia is used when the material is required to withstand extremely high temperatures. Silicon carbide and carbon are two other refractory materials used in some very severe temperature conditions, but they cannot be used in contact with oxygen, since they oxidize and burn in atmospheres containing oxygen. Refractories are the materials which are resistant to heat and exposure to different degrees of mechanical stress and strain, thermal stress and strain, corrosion/erosion from solids, liquids and gases, gas diffusion, and mechanical abrasion at various temperatures. In simplified language, they are considered to be materials of construction which are able to withstand high temperatures. Refractories are usually inorganic non-metallic materials with refractoriness greater than 1500 deg C. They belong to coarse-grained ceramics having microstructure which is composed of large grains. The basis of body is coarse-grained grog joined by fine materials. Refractory products are a specific sort of ceramics that differs from any ‘normal’ ceramics mainly with their coarse-grained structure being formed by larger grog particles joined by finer intermediate materials (bonding). ASTM C71 defines refractories as ‘non-metallic materials having those chemical and physical properties that make them applicable for structures or as components of systems that are exposed to environments above 538 deg C’. Refractories are to be chemically and physically stable at high temperatures. Depending on the operating environment, they...

Magnesia

Magnesia Magnesia or magnesium oxide (MgO) is a white hygroscopic solid mineral that occurs naturally as periclase. It forms magnesium hydroxide in the presence of water [MgO + H2O = Mg(OH)2], but this reaction can be reversed by heating magnesium hydroxide to separate moisture. Magnesium (Mg) is the eighth most abundant element and constitutes about 2 percent of the crust of the earth. It is the third most plentiful element dissolved in seawater, with a concentration averaging 0.13 %. Although magnesium is found in over 60 minerals, only dolomite, magnesite, brucite, carnallite, and olivine are of commercial importance. Magnesium and magnesium compounds are produced from seawater, well and lake brines and bitterns, as well as from the above mentioned minerals. Magnesite (MgCO3), the naturally occurring carbonate of magnesium (Mg) is one of the key natural sources for the production of magnesia (MgO) and subsequently fused magnesia. It is the world’s  largest source of magnesia. It contains a theoretical maximum magnesia content of 47.6 %. It occurs in two distinct physical forms namely (i)  macro-crystalline and (ii) crypto-crystalline. Crypto-crystalline magnesite is generally of a higher purity than macro-crystalline ore, but tends to occur in smaller deposits than the macro-crystalline form. The word magnesite literally refers only to the natural mineral, but common usage applies this name to three other types of materials, dead burned magnesia (DBM), electro fused magnesia and calcined magnesia also called caustic calcined magnesia. Often magnesia word is replaced by magnesite in these products. These products of magnesite often differ mainly in density and crystal development that results from different levels of heat application. The three products of magnesite are shown in Fig 1. Fig 1 Products of magnesite  Magnesia is an alkaline earth metal oxide. Magnesium oxide is normally produced by the calcinations of...

High Alumina Slag and Blast Furnace Operation May27

High Alumina Slag and Blast Furnace Operation...

High Alumina Slag and Blast Furnace Operation Blast furnace (BF) process of iron making is a process where liquid iron (hot metal) and liquid slag are produced by the reduction of iron bearing materials (sinter and/or pellet and lump ore) with coke and by fluxing of the gangue material of the feed materials. The process is the result of a series of chemical reactions which takes place in the blast furnace. The separation of slag from the hot metal takes place in liquid state. Slag has a lower melting point and is lighter than hot metal. In the blast furnace it is at a higher temperature than the hot metal. Blast furnace slag contain predominantly silica (SiO2), alumina (Al2O3), lime (CaO) and magnesia (MgO) along with smaller amounts of FeO, MnO, TiO2, Na2O, K2O and S. Blast furnace (BF) slag composition has very important bearing on its physicochemical characteristics which influences to a great degree the smooth operation of the blast furnace, slag handling, coke consumption, blast furnace productivity and the quality of the hot metal. Low alumina slag normally has low viscosity, high sulphide capacity and low liquidus temperature as compared to high alumina slag. Blast furnace slag alumina (Al2O3) is mainly dependent on the alumina content of the input materials mainly iron ore. In those cases where iron ore alumina is less than 1 % the alumina content in the slag hardly goes above 10 %. But in some iron ores (normally found in India) alumina content is 2 % and higher. Such ores raise the alumina levels in blast furnace slag to 20 % and higher. To operate a blast furnace with such high alumina slag is quite difficult and need a different type of skill from the blast furnace operators...