Bleaching earth, a type of clay found in Asia, England, India, and the US, is processed for its absorbent, bleaching, and filtering properties. It is commonly used to remove color pigments from oils and other chemicals, filter impurities from petroleum products, and as an ingredient in beauty products and anti-diarrheal drugs. After use, spent bleaching earth is processed for reuse or safe disposal.
Bleaching earth, often called fuller’s earth, is a type of clay mined in Asia, England, India, and the United States. Once obtained from the earth, this mineral-rich substance is processed and used for its absorbent, bleaching and filtering properties. After industrial use, the earth must again undergo processing in which it is either recycled for reuse or made safe for disposal.
Attapulgite, bentonite and montmorillonite clays are the substances most commonly found in bleaching earths, singly or in combination. In its raw state, clay contains primarily silica, followed by aluminum. This clay also commonly contains iron, magnesium and calcium. Clay deposits resemble soil and can range in color from buff or tan to yellow or pure white. It is highly absorbent and typically has a smooth, greasy feel.
While it can be used in its natural state, manufacturing facilities commonly subject bleaching earth to scrubbing and heating to minimize moisture content and kill microorganisms. The earth is then dried and the treatment plants pulverize the finished product into small particles. The activated whitening clay is mixed in the form of a slurry with hydrochloric, sulfuric or other acids. The resulting clay is then thoroughly washed, dried and ground.
Manufacturers sell the finished product in grades, which differ in moisture content and particle size. The moisture content can range from 6% to 12% and the particles range in size from 25 microns to the largest pieces which are the same size as those commonly seen in cat litter. Clay acquired the name bleaching earth for its ability to remove color pigments from oils and other chemicals. It can also remove colors commonly associated with carotenoids, chlorophyll and pheophytin.
Bleaching clay also has the ability to absorb unpleasant odors, including those produced by ammonia, sulfur and tar. Manufacturers commonly use this compound to filter impurities from petroleum products, ranging from cooking oil to jet fuels. Combined with salt water, these earth clays are commonly used as a lubricant for oil drilling. Some manufacturers also use the clay substance as an ingredient in beauty products and attapulgite is a constituent of some anti-diarrheal drugs.
The absorbent property of bleaching earth causes it to retain some of the oils or chemicals when used as a filter. These substances may have flammable or otherwise harmful characteristics, making disposal a potential safety risk. Processing plants take this used material, called spent bleaching earth, mix it with solvents, steam clean the clay, and combine the earth with acid. The earth is then subjected to further washing, drying and grinding.
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