The three major factors which affect bleaching performance are type of clay, bleaching method, and oil quality. These are discussed in order. Under the first are such topics as purpose of clay in industry, source of raw material, clay types, physical structure, effect of activation on structure, variation in effectiveness of clays produced from different raw materials, and mechanism of the clay’s action. Also covered is the effect of the clay’s properties-moisture, apparent bulk density, specific gravity, acidity, pH, hydrated silica, particle-size distribution, and the theory of variability. Under the second are effect of bleaching conditions, such as temperature, time, agitation, temperature of clay addition, vacuum versus atmospheric bleaching; commercial methods including atmospheric batch, vacuum batch, vacuum continuous; and effect of oil quality. Under the third are response of different color pigments to bleaching, effect of moisture, oxidation, and organic impurities in the oil. Of the three factors, oil quality has the greatest influence upon bleaching performance.
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