Kaolin deposition

To make kaolin acceptable for use, crude kaolin deposits require beneficiation to remove the associated impurities. The colored impurities, specifically titanifer-ous minerals and iron oxides, are generally removed by reverse froth flotation, high gradient magnetic separation, selective flocculation and/or leaching. 

Clay minerals are widely used in the filler industry and the production of the various types has been described by Hancock and Rothon [85]. The products available range from unaltered kaolin to products produced by calcination. Kaolin deposits are widespread throughout the world. While simple clay minerals are extensively used as fillers in elastomers, their use in thermoplastics is more restricted and the principal products used are those obtained by calcination of ka-olinite. Thus metakaolinite finds application in PVC and silane treated calcined clay in polyamides. The production of these forms only is discussed below. 

Maegdefrau and Hofman (1937) in kaolin deposits, Saraspatak, Hungary. 

Levinson (1955) in hydrothermal kaolin deposit, St. Austell, England. 

Hinckley, D.N., 1961. Mineralogical and chemical variations in the kaolin deposits of the Coastal Plain of Georgia and South Carolina. Penn. State Univ. N.S.F. Tech. Rep., 180 pp,... 

The clay minerals used in this study were kaolinite (AI281205(OH) ), illite (Kj A1jSi2+ (OH)2), and montmorillonite which was approximately 1/2 (Ca, Na)Q (Al, Mg, Fe) (Si, ADqO q (OH). n H2O. The clays were natural samples purchased from Ward s Natural Science Establishment, Inc. The kaolinite sample was obtained from a kaolin deposit in Georgia. X-ray diffraction (XRD) patterns on this material showed peaks only for kaolinite, and scanning electron micro-scope-energy dispersive x-ray (SEM-EDX) analysis yielded peaks for Al, Si, and minor amounts of Ti. The illite was a green shale from New York which Ward s listed as 85% illite. XRD patterns of this... 

Since silicate and aluminum silicate minerals are widely available, they are inexpensive and form the backbone of the traditional high-volume products of the ceramic industry. Their abundance also explains why earthenware products are found in nearly every part of the world. The situation is very different with regard to kaolinite, the essential ingredient, along with feldspar and quartz, needed to make porcelain, by far the finest and most highly prized form of ceramic. Kaolin deposits are more localized. There are excellent deposits, for example, in southwest England. In the United States most kaolin comes from the southeast between central Georgia and the Savannah River area of South Carolina. 

Kaolins are classified as either primary or secondary. Primary kaolins are formed by the alterations of crystalline rocks such as granite. The source of this kaolin is found where it is formed. Conversely, secondary kaolin deposits are sedimentary and are formed by erosion of primary deposits. The secondary deposits contain much more kaolinite (about 85-95%) than the primary deposits, which contain only 15-30%. The balance of the ore consists of quartz, muscovite, and feldspar in the primary deposits and quartz, muscovite, smectite, anatase, pyrite, and graphite in the secondary deposits. Kaolin, also known by the common term clay, is usually open-pit mined in the United States from vast deposits in Georgia, South Carolina, and Texas. The ore is not processed in one singular way. There are also distinct methods of ore benefi-ciation, each adding value to the mineral. 

Kaolin deposits are cored and analyzed before mining to determine quality. Mined clays are then either wet or dry processed by air floatation or water fractionation. Surface-modified clays can be made by treating standard, delaminated, and calcinated grades with surface modifiers. The treatment can be performed by either the supplier or the end user. These surface modifiers include silane, titanate, polyester, and metal hydroxide. The objective of these surface treatments is to increase filler loadings and/or improve physical properties such as melt viscosity, thermal stability, and modulus without loss of physical characteristics. Electrical applications represent the largest use of surface-modified kaolin in plastics. 

Case study IQAotgoo et al., 2008) The Upper Tagus Natural Park is one of the largest and most valuable protected areas in Spain (Guadalajara Province). In this area, a spatial coincidence of extraordinary natural resources takes place. On the one hand, exceptional kaolin deposits occur within sediments of the Upper Cretaceous strata (Utrillas Formation). 30% of the kaolin production of Spain comes frxrm this area, mining being the second economic activity here (13.5% of the local employment). On the other hand, this portion of land supports unique bio and geodiversity in Spain, with distinctive aquatic... 

Seki M, Thurman DW, Oberhauser JP, Komfield JA (2002) Shear-induced orientation in the crystallization of an isotactic polypropylene nanocomposite. Macromolecules 35 2583 Siddiqui MA, Ahmed Z (2005) Mineralogy of the Swat kaolin deposits, Pakistan. Arab J Sci Eng 30 195-218... 

The aspect ratio of the final flake products depends upon the origin of the mica and the processing method. Large flake pegmatite mica and wet milled mica can have aspect ratios in excess of 100. By contrast, processed mica flakes from schist and kaolin deposits tend to have aspect ratios in the area of 30 to 60. 

Dill et aL (1997) Dill, H.G. Bosse, H.R. Henning, K.H. Fricke, A. Ahrendt, H. Mineralogical and chemical variations in hypogene and supergene kaolin deposits in a mobile fold belt the Central Andes of northwestern Peru Mineralum Deposita 32 (1997) 149-163... 

China has numerous kaolin deposits, which were exploited very early on. These fireclays fire white. Depending on the geographical area in question, Northern or Southern China, the composition of these kaohns is a little different. In the North, clays were associated with coal deposits they were rich in alumina (approximately 30%) and low in flux elements (alkaline, alkaline-earths) and iron. It was therefore necessary, in order to fire ceramics, to reach temperatures estimated at 1,200-1,350°C [HAR 98]. In the South, on the other hand, kaohns resulted from the deterioration of igneous rocks and as a result they were enriched with flux elements they could be fired at about 1,200°C. 

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