Bleaching Earth
What bleaching earth does
Despite the name, bleaching is adsorption, not chemical bleaching: fine clay particles, stirred into hot oil under vacuum, adsorb color pigments (carotenoids, chlorophyll), trace metals, residual soaps from neutralization, and oxidation products, and are then filtered out. The result is a cleaner, lighter, more stable oil ready for deodorization. Bleaching earth is therefore a workhorse consumable of the refining line, and getting its selection and dosage right is central to both oil quality and refining economics.
Natural vs acid-activated grades
Two broad families are used. Natural bleaching earth (fuller's earth / natural bentonite or attapulgite) has moderate adsorptive activity and is gentler and lower-cost. Acid-activated bleaching earth is clay treated with acid to greatly increase surface area and adsorptive power, used where stronger color and impurity removal is needed. Some operations add a little activated carbon for specific pigments or contaminants. The choice depends on the oil, the color target and cost: more active earth removes more but costs more and can retain more oil.
Dosage, oil retention and the cost balance
The defining trade-off is that spent bleaching earth retains oil — typically a meaningful fraction of its own weight — so every extra kilogram of earth dosed both costs money and loses oil with the waste. Refiners therefore optimize dosage to hit the color and quality target with the least earth, rather than over-dosing for margin. Spent earth is also a disposal consideration (it is oily and can be prone to self-heating), so handling and disposal are part of the picture. Good practice matches earth grade and dose to the specific oil and to well-degummed, well-neutralized feed, since earth cannot efficiently fix upstream shortcomings.
Where it is used
Indicative reference
| Parameter | Typical (indicative) |
|---|---|
| Function | adsorption of color, metals, soap, oxidation products |
| Grades | natural / acid-activated (± carbon) |
| Dosage | ~0.5–2% by oil weight |
| Process conditions | ~90–110 °C under vacuum, ~20–30 min, then filtered |
| Oil retention | ~20–40% of the earth's weight (a real yield loss) |
| Key trade-off | dosage vs oil retained in spent earth |
| Feed requirement | well-degummed & neutralized oil |
FAQ
Does bleaching earth actually bleach the oil?
Not chemically — it adsorbs color pigments and other impurities onto clay particles, which are then filtered out. "Bleaching" here means color removal by adsorption.
Natural or acid-activated bleaching earth?
Natural earth is gentler and cheaper; acid-activated earth adsorbs more strongly for tougher color and impurity removal. Match the grade to the oil and color target to avoid over-dosing.
Why is bleaching earth a source of oil loss?
Spent earth retains oil — a fraction of its own weight leaves with the waste. That is why dosage is optimized, not maximized.
Can bleaching earth fix poorly degummed oil?
Not efficiently — it works best on well-degummed, well-neutralized feed. Upstream problems should be fixed upstream, not compensated with extra earth.