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 absorbing, bleaching, and filtering properties. After industrial use, the earth must again undergo processing in which it is recycled for reuse or rendered safe for disposal.
Attapulgite, bentonite, and montmorillonite clays are the substances most commonly found in bleaching earth, individually or in combination. In its raw state, the clay mostly contains silica, followed by aluminum. This clay also commonly contains iron, magnesium and calcium. The 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.
Though it can be used in its natural state, manufacturing plants commonly subject bleaching earth to washing and heating to minimize moisture content and eliminate microorganisms. The earth is then dried, and treatment plants pulverize the finished product into small particles. Activated bleaching earth is mixed in slurry form with hydrochloric, sulfuric, or other acid. The resulting clay then undergoes thorough washing, drying, and grinding.
Manufacturers sell the finished product in grades, which differ in moisture content and particle size. Moisture content may range from 6% to 12% and particles vary in size from 25 microns to the larger pieces that are the same size as commonly seen in cat litter. The clay acquired the name bleaching earth from its ability to remove color pigments from oils and other chemicals. It can also remove the colors commonly associated with carotenoids, chlorophyll, and pheophytine.
Bleaching clay also has the ability to absorb unpleasant odors, including those produced by ammonia, sulfurs, and tars. Manufacturers commonly use this compound to filter the impurities from petroleum products, ranging from food grade oil to jet fuels. Combined with salt water, these earth clays are commonly used as a lubricant for drilling oil. Some manufacturers use the clay substance as an ingredient in beauty products as well, and attapulgite is a constituent of some antidiarrheal medications.
The absorbent property of bleaching earth causes it to retain some of the oils or chemicals when it is used as a filter. These substances may have flammable or otherwise harmful characteristics, making disposal a potential safety hazard. 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 then undergoes further washing, drying, and grinding.