Clay processing equipment
Clays were formed as a result of natural igneous feldspathic rock weathering – mainly, granites, volcanic glass, tuffs, porphyrites and due to destruction of metamorphic rocks (gneisses), etc.
As a result of weathering, feldspars are transformed into a argillaceous matter which is formed mainly as coalinite minerals.
Such a feldspathic rock decomposition is caused by physical (temperature fluctuations, water freezing, salt crystallisation), chemical (exposure to air oxygen, carbon dioxide, water, organic acids) and biological (activity of microorganisms) weathering types. As a result of physical and chemical weathering, weathering crust is formed on various rocks and fields.
Weathering crust minerals are formed in two ways – synthetic, for example, by transforming feldspar into individual oxides – Al2O3 and SiO2 and coagulation of such oxides into kaolinite composition mineral, and by hydrolysis of primary minerals. Kaolinite, illite (hydromica) and montmorillonite minerals are basic rock-forming minerals of argillous raw material.
"Clay" means a fine detrital sedimentary rock consisting of mineral particles less than 0.005 mm. In terms of chemical composition they represent alumosilicates and attendant impurities of other minerals. As granites with transition variations account for approximately of all pyrogenic rocks, i.e. they are they are more numerous than all others, sedimentary clay rocks contain the maximum quantity thereof (as a product of decomposition of the most common minerals of igneous rocks – feldspars, for example, orthoclase, albite, anorthite).
It has been calculated that 95% of Earth crust is igneous rocks and 5% is sedimentary rocks, only 4%v of which are clays. Clays may be primary clays which were left in location where they had been formed, and secondary clays which were deposited in new locations as a result of alluvial, deluvial, fluvio-glacial, eolian and other processes. Moving by one of such ways, for example, by water, primary clay could get free of admixtures which had been previously present in it, and so it deposited in a purer state in a new location which improved its qualities. This is the way of formation of kaolins which contained high percentage of kaolinite mineral, were highly refractory, contained low percentage of colouring oxides which they were mostly white-coloured before and after burning.
Clays with increased content of percentage of fluxing agents and colouring oxides are classified as a special type – refractory clays, and clays containing significant amount of admixtures (colouring oxides, fluxing agents, etc.) become low-melting clays – these are common clays. Division of argillous raw material in terms of application field classifies clean white kaolin and some refractory clays (white-burning raw material) as groups of porcelain and faience clays, refractory clays as groups of pipe, clinker and terracotta clays, and low-melting clays as groups of pottery, brick and tile, and LECA clays.
A characteristic of Quaternary and Late Tertiary time clays which especially often meet the requirements to argillous raw material for production of bricks, tile, LECA and other ceramic materials and products is presence of significant amount of sand particles and polymineral composition of argillous part. Hydromica prevails among argillous minerals in such rocks usually. Kaolinite and montmorillonite are of less significance, and other minerals (peach, halloysite, etc.) are present as admixtures.
Small amount of kaolinite does not exert any significant influence on increase of burning temperature, and montmorillonite decreases it noteworthily, which is a valuable property in production of building bricks. Some types of bricks and ceramic tiles are manufactured in Russia, USA and some other countries using loesses – widely spread quaternary deposits containing much fine dusty material (50–70%) in addition to sand and clay.
Argillaceous rocks can be loose or stony material. However, irrespective of the state of such rocks, they contain a group of finely-dispersed minerals which impart plasticity, formability (for stony materials after fine grinding) and ability to preserve shape after drying to clay. This group of minerals which are alumosilicates are referred to as clay minerals or clay substance.
Hydromica clays are widely spread in nature in addition to kaolinite clays. They are formed as a result of weathering of calcium silicate rocks in wet climate conditions. They are products of the first chemical weathering stage. The main rock-forming minerals in such clays are hydromica, including glauconite, secondary minerals are kaolinite and montmorillonite. Primary hydromica clays occur in weathering crust of crystalline rocks, secondary ones are represented by continental deposits – lacustrine, alluvial, glacial, marine (shelf) and lagoonal deposits.
A special type of argillaceous rocks is bentonite. It was formed by weathering of effusive tuff rocks, volcanic ashes, etc. (it was named so after American fort Benton near which it was discovered for the first time).
Bentonite consists mainly of montmorillonite group minerals, it also contains some admixtures. It is used for preparing porcelain mixtures, washing solutions for drilling, as an adsorbent for liquid clarification, for preparation of iron ores, etc.
Polymineral clays are formed when sedimentary differentiation of a substance is imperfect. The origin of most of such clays is secondary. They are widely spread in deluvial deposits, in alluvial sediments, occur seldom in marine deposits and sometimes in weathering crust. They contain hydromica, kaolinite, montmorillonite, quartz, mica. They are used for manufacturing coarse ceramics products. Some of their kinds are suitable for producing LECA.
The Samara Strommashina plant offers excellent clay processing equipment. The Strommashina manufactures pyroprocessing equipment – rotary clay kilns, drying drums for drying argillous raw material, clay crushers and screening machines. The Strommashina designs and manufactures high-efficient LECA and building ceramics production lines and provides high-level maintenance of the supplied equipment.