Kaolin primary processing

The term primary clay refers to those clays that are found in the location in which they were geologically formed. They are found in deposits that contain substantial quantities of other minerals. The kaolin is processed in an aqueous slurry and must be separated... 

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. 

The process of selective flocculation is being used industrially by companies such as the Engelhard Corporation (process for removal of titania from clays), Thiele Kaolin Georgia (separation of titania from clays) and the Cleveland Cliffs Company (beneficiation of nonmagnetic taconites, and separation of silica). Although the primary application of selective flocculation has been in the mineral processing industry, many potential uses also exist in biological and other colloidal fields. These include purification of ceramic powders, separation of hazardous solids from chemical wastes, and removal of deleterious components from paper pulp. 

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. 

Imerys leads the European market for polymer end use. The aforementioned four companies supply the majority of the world s water-washed kaolin and are major exporters of the mineral. Other key producers are Thiele with 1.25 mtpa and Quarzwerke owned by Amberger Kaolinwerke (AKW) with 0.9 mtpa. Other US producers of air-floated grades are KT Clay (owned by Imerys) with >500 000tpa and Unimin with >500 000 tpa. It should be noted that European kaolin comes mostly from primary deposits and does not lend itself to the air-flotation process [10]. 

Reaction (1) shows the calcination of kaolin, which can also be described as a thermal dehydration process that destroys the original layered structure of the system. Reactions (2) and (4) describe the alkahne dissolution of metakaolin resulting in primary condensation structures (aluminosilicate oligomers), which, by further poly condensation reactions (3) and (5) in the alkaline environment, give rise to an infinite number of repeating units, thus resulting in a geopolymeric network [10]. The formation of the aluminosilicate structure was initially simply described as a series of destructive and condensation reactions ... 

Secondary clays are those clays, which have been transported away from their primary source to another location, where they have been deposited as a sediment. The transportation process was usually effective at both mineral separation and at particle size selection, in that only the finer particles remained in suspension long enough to reach the final deposit. Important secondary deposits are foimd in the kaolin belt of south-eastern United States (Alabama, through Georgia into South Carolina) and southwestern England. These clays are very fine with mean particle sizes from 0.1 to 2.0 pm. These are all semi-reinforcing fillers. 

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