Secondary kaolin

Secondary kaolins were washed from the original weathering site, naturally beneficiated, and redeposited in large areas of pure kaolin. The major commercial deposits of secondary kaolin in the United States were formed 50 million years ago and occur as a continuous belt stretching along the ancient coastline from Alabama northeast to North 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. 

Sedimentary (secondary) kaolin - In reference to geologie origin, the elay has been eroded and transported fix)m its site of formation and deposited at a distant location. The world s major kaolin belt, the 250 miles between Aiken, SC and Eufala, AL, consists of sedimentary kaolin. 

Primary clay, for example kaolin, is colorless, and when such clay is heated to a high temperature it produces white ceramic materials. Most pottery, however, is colored its color is due to the fact that most of it was, and still is, made not from primary but from secondary clay. Secondary clay contains minerals other than clay, and colored metal ions in them endow the pottery with their color. Iron ions (in iron oxides), for example, tend to make pottery yellow, brown, or red, and manganese ions (in pyrolusite, a mineral composed of manganese oxide) make it either dark or black. 

A second aCGRP-deficient mouse was produced by Hoff et al. (1998) in order to study the role of calcitonin. CGRP mice are born normally, are fertile and live a normal life span. These mice were tested in a model of chronic arthritis, where a mixture of kaolin/carrageenan was injected into the knee joint and in comparison to wild type mice failed to develop secondary hyperalgesia (Zhang et al., 2001). 

Secondary clay has been transported from the site of the parent rock. As a result, this clay has fine particles and might be contaminated with iron, quartz, mica, and carbonate compounds. Ball clays are secondary clays. They are higher in iron content, more fusible, finer in particle size, and more plastic than kaolin clays. 

Bauxite consists of a group of closely related oxides and hydrated oxides, and it is a secondary mineral that results when silica is leached from minerals such as kaolin, Al2Si205(0H)4. The conditions for this type of leaching are favorable in the tropical areas in which bauxite is frequently found. 

In one case, multiple pulmonary kaolin granulomata developed secondary to the use of a liquid kaolin suspension for pleural poudrage to treat recurrent spontaneous pneumothoraces, presumably because the kaolin entered the lung through pleuro-alveolar or pleuro-bronchial openings (4). 

Raw kaolin is mainly extracted by open cast mining. Secondary deposits can be exploited using excavators, whereas primary deposits of kaolin are often washed out of the rock with a high pressure water jet. 

Morad (1986) and Morad et al. (1990). Authigenic K-feldspars occur as overgrowths around detrital orthoclase and microcline in the deeper portions of the Caioba area of the distal domain, where feldspar kaolinization/dissolution was less intense (av. < 1%). In places overgrowths surround secondary pores formed by the dissolution of host grains. 

Judging from the mineral composition of the shales in which such secondary transformations would be reduced to a minimum there could have been only 15-30% detrital illite as a primary constituent in the sandstones of the Hassi Messaoud field whereas the amount of illite detected in the Cambrian siltstones is 30-50%. Consequently, only 1% of secondary quartz could have resulted from the transformation of illite to kaolinite. Thus, widely developed kaolinization of illite and feldspars is accompanied by the liberation of silica in the form of silicic acid which is mostly consumed in the formation of overgrowth on quartz grains. The extent of this silicification, however, is controlled by other factors the chemical nature of the environment created and especially the permeability of the rocks. The lower the permeability, the more intense silicification will be. 

The granite-gneiss has been strongly kaolinized due to weathering. The weathering zone shows secondary enrichment of REE. The average REE-composition is given in Table 2.11. 

Aluminum oxide (AI2O3, alumina, corundum) is the most widely used inorganic chemical for ceramics and is produced from the mineral bauxite using the Bayer process. Bauxite is a mixture of hydrated aluminum oxide with iron oxide (Fe203), silica (SiOi), and titania (TiOi) impurities. It results from the decay and weathering of aluminous rocks, often igneous, under tropical conditions. Like kaolin, bauxite occurs as both primary deposits and secondary deposits. 

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