I started researching what made fullers earth so effective at bleaching after I saw the absolutely ridiculous prices on carbon chemistry, I hope you all find the information to be useful.
Fuller’s earth is any clay material that has the capability to decolorize oil or other liquids without chemical treatment. Fuller’s earth typically consists of palygorskite, attapulgite, or bentonite.
“attapulgite, sepiolite, and bentonite have common properties and they all can be used as bleaching earth. However, attapulgite and sepiolite may be used as a natural bleaching earth, which does not require acid activation. Bentonite is an acid activated bleaching earth because the necessary surface area and porosity have to be created by an acid treatment (Murray, 2007). On the NOP National List, bentonite is a nonsynthetic allowed substance listed under 7 CFR §206.605.
Acid activation enhances properties already present in the clay. Sulfuric acid is most commonly used in the activation process but hydrochloric acid is also effective. The acid treatment increases the surface area and pore volume thus improving the clays performance in removing color pigments and impurities from vegetable oil and animal fat. Although acid activated bleaching earth is often more effective, it is also more costly.”
Attapulgite TR.pdf (323.6 KB)
“Attapulgite is a magnesium aluminum silicate clay of very fine particle size. It is also known as Fullers Earth and is closely related to Sepiolite mineral. Unlike bentonite (or montmorillonite) attapulgite crystals are needle shaped (acicular) rather than flat or flake-like. Like bentonite they disperse well to thicken, suspend and gel suspensions without flocculation problems.”
The fact that attapulgite has needle like crystals means that it will lend itself very well to filtration by a filter media.
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Edit: added more info and a link
Edit:2: Tried to make it look neat.