Limestone and Lime

Limestone and Lime Limestone is an odorless white, grayish-white or tan material that ranges from sized stone to a granular powder. It is often described as the most versatile mineral. Limestone is the name given to any rock formed which consists mostly of calcium carbonate (CaCO3), but to geologists, limestone is only one of several types of carbonate rocks. These rocks are composed of more than 50 % carbonate minerals, generally containing the mineral calcite (pure CaCO3). Limestone is a sedimentary rock composed mainly of CaCO3. It is formed by the deposition either of the skeletons of small creatures and/or plants (organic limestones), or by chemical precipitation, or by deposition of fragments of limestone rock, on the beds of seas and lakes. Limestones are contaminated to a greater or lesser extent by the deposition of sand or clay which is the source of the impurities usually found in the limestone. Generally there is a difference in quality in a deposit from one layer to the next. The purest carbonates and the most suitable from the production point of view tend to be the thick bedded type. Carbonate deposits may be found in horizontal layers as deposited, or at an angle from the horizontal due to earth movements. They will vary in density, hardness and chemical purity. Limestone rocks are extremely common and make up a significant portion of the crust of the Earth. They serve as one of the largest carbon repositories on our planet. The properties of limestone make it one of the most widely used minerals. Some limestones may contain small percentage of magnesium carbonate (MgCO3). These limestones are known as dolomitic limestones. Impurities (such as clay, sand, organic remains, iron oxide, and other materials) cause limestones to show different colours, especially with weathered surfaces. Limestone may be crystalline, clastic, granular,...

Limestone – Its Processing and Application in Iron and Steel Industry Jul07

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

Limestone – Its Processing and Application in Iron and Steel Industry Limestone is a naturally occurring and abundant sedimentary rock consisting of high levels of calcium carbonate (CaCO3) in the form of the mineral calcite. Some limestones may contain small percentage of magnesium carbonate (MgCO3). These limestones are known as dolomitic limestones. Limestone is also a very important industrial mineral. Its chemical properties make it a valuable mineral for a wide range of industrial/manufacturing uses. Limestone is also one of the vital raw materials used in production of iron and steel. Limestone, by definition, is a rock that contains at least 50 % of CaCO3 in the form of calcite by weight. There can be small particles of quartz (silica), feldspar (alumino-silicates), clay minerals, pyrite (iron sulphide), siderite (iron carbonate), and other minerals associated with the limestone. All limestones contain at least a few percent other materials. The Impurities in limestone can consists of silica (SiO2), alumina (Al2O3), iron oxide (Fe2O3), sulphur (as sulphides or sulphates), phosphorus (P2O5), potash (K2O), and soda (Na2O). Silica and alumina are the main impurities of limestone. The limestone which is used in ironmaking is required to contain at least 85 % of calcium carbonate and a low percentage of alumina. Similarly limestone which is used for steelmaking is required to contain at least 92 % of calcium carbonate and a very low percent of impurities especially the silica percentage. The main uses of limestone in iron and steel industry are (i) as a fluxing material, and (ii) other usage which consists of desulphurizing agent, coating of moulds of pig casting machine, neutralizing of acidic water, water treatment, waste water(effluent) treatment, flue gas treatment, and sludge and sewage treatment. It is also a component of synthetic slag. Limestone is...

Lime and Calcined Dolomite for Use in Steel Plant...

Lime and Calcined Dolomite for Use in Steel Plant Lime is a versatile compound.  Various forms of lime are used in environmental, metallurgical, construction, and chemical/industrial applications etc.  The largest single use of lime is in steel manufacturing, where it serves as a  flux for removing impurities (silica, phosphorus, and sulphur) during refining of steel. The fastest growing use of lime is in environmental applications, where lime is used for treatment of flue gases, wastewater, solid waste, and drinking water. Lime is a white crystalline solid with a melting point of 2572 deg C. It is a basic oxide and is used to react with the acidic oxides (e.g. silica) in various smelting operations. With water it makes milk of lime used for neutralizing acidic waste water. It is also being known as quick lime, lime flux, unslaked lime, and fluxing lime. Lime having some percentage of MgO (usually 2 % to 4 %) is also known as dolomitic lime. Lime is a hygroscopic material and absorbs moisture from the air. With the absorption of moisture it loses its reactivity and gets hydrated. Lime is calcium oxide (CaO) produced on heating (calcination) of limestone (CaCO3) to a temperature of 900 deg C and above (usually 1100 deg C). CaCO3(s) + heat = CaO(s)  +CO2(g) This reaction is reversible. Calcium oxide reacts with carbon dioxide to form calcium carbonate. The reaction is driven to the right by flushing of carbon dioxide from the mixture as it is released. Hydrated lime [Ca(OH)2] is formed by reaction of lime with water (slaking). CaO + H2O = Ca(OH)2 + heat Hydrated lime is also known as slaked lime. It is in the form of a dry white powder. Hydrated lime is an alkali and used for neutralizing acidic solutions. In...

Limestone and dolomite flux and their use in iron and steel plant...

Limestone and dolomite flux and their use in iron and steel plant Limestone is a naturally occurring mineral. The term limestone is applied to any calcareous sedimentary rock consisting essentially of carbonates.  The ore is widely available geographically all over the world. Earth’s crust contains more than 4 % of calcium carbonate. Limestone is basically calcite which is theoretically composed of exclusively calcium carbonate (CaCO3). When limestone contains a certain portion of magnesium, it is called dolomite or dolomitic limestone (CaCO3.MgCO3). Dolomite theoretically contains CaCO3 54.35 % and MgCO3 45.65 % or CaO 30.4 %, MgO 21.9 % and CO2 47.7 %. However, in nature, dolomite is not available in this exact proportion. Hence generally the rock containing 40-45 % MgCO3 is usually called dolomite. When MgCO3 is less than 40 % but more than 20 % then the limestone is called dolomitic limestone. The chemical composition of limestone and dolomite varies greatly from region to region as well as between different deposits in the same region. Therefore, the end product from each natural deposit is different.  Typically limestone and dolomite are composed of calcium carbonate (CaCO3), magnesium carbonate (MgCO3), silica (SiO2), alumina (Al2O3), iron (Fe), sulphur (S) and other trace elements. These minerals are shown in Fig 1 Fig 1 Limestone and dolomite The limestone from the various deposits differs in physical chemical properties and can be classified according to their chemical composition, texture and geological formation. Limestones from different sources differ considerably in chemical compositions and physical structures. The chemical reactivity of various limestones also shows a large variation due to the difference in crystalline structure and the nature of impurities such as silica, alumina and iron etc. The varying properties of the limestone have a big influence on the processing method....

Calcination of Limestone May02

Calcination of Limestone...

Calcination of Limestone Calcination or calcining is a thermal treatment process to bring about a thermal decomposition. The process takes place below the melting point of the product. The name calcination is derived from the Latin word ‘Calcinare’ which mean to burn lime. Limestone is a naturally occurring mineral. It exists nearly all over the world. The chemical composition of this mineral varies greatly from region to region as well as between different deposits in the same region. Therefore, the end product from each natural deposit is different.  Typically limestone is composed of calcium carbonate (CaCO3), magnesium carbonate (MgCO3), silica (SiO2), alumina (Al2O3), iron (Fe), sulphur (S) and other trace elements. Limestone is one of the most basic raw materials employed in the steel industry and is used both in iron making and steel making processes. Lime (CaO) is one of the oldest chemicals known to man and the process of lime production is one of the oldest chemical industries. Quicklime was produced in US as early as 1635 in Rhode Island. Technical progress which was non existing in centuries past, has rapidly advanced the lime industry during the last fifty years in the area of process methods and design. Limestone deposits are wide distributed. The limestone from the various deposits differs in physical chemical properties and can be classified according to their chemical composition, texture and geological formation. Limestone is generally classified into the following types: High calcium – The carbonate content is composed mainly of calcium carbonate with a magnesium carbonate content not more than 5 % (usually less).  Magnesium – This contains magnesium carbonate to about 5 – 20%. Dolomitic -This is also known as dolomite and contains over 20 % of MgCO3. However the maximum MgCO3 content does not exceed...