Clay classification

Efficient separation of clay at very small particle sizes (1-2 pm) is required to produce good-quality products for the paper coating industry. 

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K1 specific surface clay classification ic l as S.t (given w, f>Gllz)... 

Figure 6.12. Grap/i-Particle Size v Cumulative % Undersize-Clay Classification.

Fiitiire 6.14. Graph - Particle Size v Recovery Clay Classification. 

Figure6.16. Graph-Cut Point v Centrate Rate - Clay Classification.

Table A.4 Clay classification data used in Section 6.4.4...

Clays (qv) are aluminosihcate minerals, some of which have definite chemical compositions. In regard to tar sands, however, clay is only a size classification and is usually deterrnined by a sedimentation method. According to the previous definition of fines, the fines fraction equals the sum of the silt and clay fractions. The clay fraction over a wide range of fines contents is a relatively constant 30% of the fines. 

The production of aluminum begins with the mining and beneficiation of bauxite. At the mine (usually of the surface type), bauxite ore is removed to a crusher. The crushed ore is then screened and stockpiled, ready for delivery to an alumina plant. In some cases, ore is upgraded by beneficiation (washing, size classification, and separation of liquids and solids) to remove unwanted materials such as clay and silica. 

Silt and clay are fine-grained soils in which individual particle size cannot be readily distinguished with the unaided eye. Some classification systems distinguish these particles by size, other systems use plasticity to classify these particles. 

Clay, in one particle classification system, consists of inorganic particles less than 0.005 mm in size. In another system, clay is a fine-grained inorganic. soil that can be made plastic by adjusting the water content. When dried, clay exhibits considerable strength (i.e., clay loses its plasticity when dried and its strength when wetted). Also, it will shrink when dried and expand when moisture is added. 

Figure 2-60 shows a classification system developed by the Lower Mississippi Valley-Division, U.S. Corps of Engineers. Percentages are based on dry weight. A mixture with 50% or more clay is classified as clay with 80% or more silt, as silt and with 80% or more sand, as sand. A mixture with 40% clay and 40% sand is a sandy clay. A mixture with 25% clay and 65% silt is a clay-silt (see intersection of dashed lines in Figure 2-60). 

Soil texture, or appearance, depends on particle size, shape, and gradation. Therefore, using the classification in Figure 2-60 the soil texture can be specified as sandy clay or clay-sand. 

Mechanical attrition is used to remove most of the spent binder. First, dry attrition or abrasion processes crush lumps to grain size. Mechanical abrasion is then used to separate the binder from the sand grains. Sometimes, sand is pneumatically propelled against a metal target plate. The impact of the sand on the plate scrubs off the clay and resin coating from the sand grains. Fines are separated and removed by dry classification. 

Clay is the most important component of soil liners because the clay fraction of the soil ensures low hydraulic conductivity. In the United States, however, there is some ambiguity in defining the term clay because two soil classification systems are widely used. One system, published by the American Society for Testing and Materials (ASTM), is used predominantly by civil engineers.18 The other, the U.S. Department of Agriculture s (USDA s) soil classification system, is used primarily by soil scientists, agronomists, and soil physicists.19... 

Table 4.1 Classification of clays by their uses and properties. (From Singer and Singer, 1963 26. Copyright Chapman and Hall, with kind permission of Springer Science and Business Media.)...

In order to study in more detail the clay minerals, it is first helpful to review briefly the basic structural classification of the silicates in general. Although ultimately complicated, the general progression is logical, and is based on the degree of polymerization of the basic structural unit which is the Si04 tetrahedron (see below). The sequence runs as follows ... 

Table 4.2 summarizes this basic classification and terminology of silicates. It is worth remembering that the term infinite refers here to an atomic scale of measurement, and does not imply that the chains extend to infinity in the mathematical sense of the word The terminology surrounding the silicates and clay minerals, in common with other mineralogical terms, has never been fully systematized, and so the names given are often ill-defined, or not unique to a... 

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