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What Is Bleaching Earth?

By Maggie J. Hall
Updated May 21, 2024
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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.

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Discussion Comments

By anon339665 — On Jun 25, 2013

Having read the main article, I was wondering if anyone has any ideas on how or if the clay can be used again in some other way after it has been used to in the refining/bleaching/deodorizing process of food oils? As I understand it is generally sent to landfill after this process. This seems terribly wasteful of a resource. Any suggestions/information would be hugely appreciated, thank you.

By bythewell — On Mar 17, 2013

This stuff gets used in the film industry a lot, just because, before it gets mixed with acid, obviously, it's pretty safe to use around people. So, whenever someone gets a lot of mud or dirt on their face in a movie, you can be reasonably sure they are covered in this kind of clay earth.

I think it's also used in explosions because it looks better on camera than other kinds of soil. I don't know why exactly that is, but maybe it's because of the colors or just the way it spreads through the air.

By Ana1234 — On Mar 17, 2013

@Fa5t3r - They have been using it for centuries to absorb oils, and I imagine the first people to notice just realized that if cloth was laid on this kind of clay, it became less oily.

I think it was mostly used to get rid of lanolin, which is the natural oil that occurs on sheep's wool.

Then they probably just extended that to thinking, well, if it can get rid of that kind of oil, maybe it will work on my hair, or on this lamp, or so forth.

I've heard it can even be used to help reduce some kinds of radiation, if people are exposed to it.

By Fa5t3r — On Mar 16, 2013

It's amazing how many different ways that clay can be used in industry. I'd never heard of bleaching clay before although the name 'Fuller's earth' clay sounds familiar.

I wonder how they realized it could be used for this kind of thing. Seems like it using clay for bleaching something doesn't appear to be the most natural of applications.

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