Definition
Bleaching earth (in German Bleicherde) is a mineral adsorbent obtained from montmorillonite clay — most often from bentonite raw material — subjected to acid activation. Its task is to purify and decolourise edible and industrial oils: it removes dyes, oxidation products, phospholipids, soaps and trace metals. Tonsil is one of the most recognisable trade brands of bleaching earths; in our fleet the Tonsil 571 FF grade appears regularly — a finely ground powder with a high decolourising capacity.
From the perspective of the terminal in Chorula, bleaching earth is an interesting case: chemically related to bentonite, which we also transload, but processed so that its natural sorption properties are sharpened to the maximum. A light, fine, dusting material that greedily absorbs moisture — exactly the kind that requires a careful, dry supply chain.
Origin and composition
Bleaching earths derive from the same clay rocks as bentonite. The raw material is most often montmorillonite — a mineral from the smectite group with a 2:1 layered structure, in which exchangeable cations and water are accommodated between the silica-alumina packets. It is precisely this layered structure, with a large internal surface area and ion-exchange capacity, that makes the clay a natural sorbent.
Some bleaching earths are natural clays (fuller’s earths), which show a sufficient decolourising capacity without chemical treatment. The vast majority of industrial adsorbents, however, are acid-activated clays. The bentonite raw material is treated with a mineral acid (sulphuric or hydrochloric), which partly leaches aluminium, iron and magnesium out of the octahedral layer, develops porosity and multiplies the specific surface area — from tens to even over 200–300 m²/g. After washing, drying and grinding, a fine powder of strictly controlled particle size and moisture is created.
This kinship with bentonite has practical significance in logistics: these materials behave similarly in transloading — they are dusting, light and water-sensitive — although bleaching earth, as a product deliberately “dried out and starved” in terms of sorption, absorbs moisture even more readily than raw bentonite.
Natural versus activated clays
It is worth separating two families of adsorbents that are colloquially lumped together as “bleaching earths” but which differ in manufacturing method and parameters.
| Feature | Natural clay (fuller’s earth) | Acid-activated clay |
|---|---|---|
| Treatment | drying and grinding of raw material | acid etching, washing, drying, grinding |
| Specific surface area | smaller (tens of m²/g) | large (up to 200–300 m²/g) |
| Decolourising capacity | moderate | high |
| Suspension pH | close to neutral | often acidic |
| Typical application | preliminary purification, sorbents | refining of edible and industrial oils |
In practice the edible-oil industry relies mainly on activated clays, because their high surface area and controlled acidity give a repeatable, strong decolourising effect at a relatively small dose. Natural clays are sometimes cheaper and milder, but they require larger doses, so they generate more spent earth for disposal. From the terminal’s point of view both families behave similarly in transloading — the difference lies in the chemistry and acidity, not in the way the powder is handled.
The mechanism of bleaching
The name “bleaching” is sometimes misleading — it is not about chemical whitening but about adsorption, i.e. the physical and chemical binding of contaminants on the developed surface of the clay. In oil refining, bleaching earth comes in at the bleaching stage (colour winterisation), after degumming and neutralisation, and before deodorisation. The course is as follows:
- Into the hot oil (usually 90–120°C, under reduced pressure) bleaching earth is dosed in an amount of the order of tenths of a percent to a few percent of the oil mass, depending on its quality and the required degree of decolourisation.
- The mixture is intensively stirred for several dozen minutes. During this time the active sites at the edges of the montmorillonite packets bind dyes (chlorophylls, carotenoids, oxidation products), residual phospholipids, soaps and trace metals such as iron, copper or nickel — elements that catalyse the rancidification of the oil.
- The spent earth is filtered off on plate or candle filters. With it the adsorbed contaminants disappear from the product, and the oil gains the desired light colour and oxidative stability.
The effectiveness of the process depends on the specific surface area of the clay, its acidity and particle size. Finer grades, such as Tonsil 571 FF (the FF designation suggests a fine fraction), offer a larger contact surface and faster bleaching kinetics, but at the same time dust more strongly and are harder to filter — a classic compromise between activity and process convenience.
From the refinery’s point of view, choosing a bleaching earth is an optimisation of several variables at once: the degree of oil decolourisation, the cost of the adsorbent, the amount of oil retained in the filter cake (so-called oil retention — product losses that “soak into” the spent earth) and the volume of waste to be managed. A grade that is too active can excessively lower the acidity of the oil or retain too much of it in the cake; a grade that is too mild requires larger doses. That is why plants attach importance to the stability of parameters between deliveries — and why, for us as a transloading operator, it is so important that the adsorbent arrives intact, dry and free of contamination, because any change in its moisture or cleanliness shifts this whole balance.
Applications
Bleaching earths are one of the foundations of the oils and fats industry, but their role reaches further.
Refining of edible oils. The most important segment: rapeseed, soybean, sunflower and palm oils, as well as oils from special seeds, undergo a bleaching stage with activated earth to obtain a light colour, a neutral taste and resistance to oxidation. For food plants the cleanliness of the adsorbent itself matters here — as with materials intended for food contact, the cleanliness regime of the supply chain must not lower the quality of the final product.
Industrial oils and fats. Bleaching earths purify industrial oils, waxes, animal fats and biofuel feedstocks, removing the polar contaminants that interfere with further processing.
Oil regeneration. Activated clays serve to renew spent lubricating, hydraulic and insulating (transformer) oils — they capture degradation products and restore usable parameters.
Carriers, fillers and treatment. Some bleaching earths and related activated clays serve as carriers of active substances, clarifying agents and sorbents in the purification of liquids. These are applications smaller in volume, but exploiting the same feature — a developed surface area and an affinity for polar molecules.
The common denominator of all these applications is single use: bleaching earth works as long as it has free adsorption surface, and once it has filled it — it stops being useful and becomes waste. That is why the scale of adsorbent consumption is large, and deliveries to refineries are regular and repeatable, often seasonal, synchronised with oil processing. For the terminal this means loads that return cyclically, rather than single, one-off transloadings — and it is precisely this regularity that means a material like Tonsil 571 FF becomes a permanent part of the rhythm of work on the yards.
Parameters relevant in transport
For a transloading operator, what matters above all are those features of bleaching earth that determine the way the material is handled and how the means of transport is filled.
| Parameter | Typical value / characteristics |
|---|---|
| Commercial form | fine powder (meal), less often granulate |
| Bulk density (loose) | about 500–800 kg/m³ |
| Particle size | powder, often below 0.1 mm (FF grades — finer) |
| Commercial moisture | usually a few–a dozen-odd percent (grade-dependent) |
| Hygroscopicity | high — the material actively absorbs water |
| Dusting | strong — requires dedusting and respiratory protection |
| Suspension pH | often acidic (acid-activated clays) |
| ADR classification (fresh) | none — transport-inert material |
Two values from this table are most important for us. First — the low bulk density: bleaching earth is a light material, so the degree of filling of a silo tanker is more often decided by the tank volume than by the axle-load limit. Second — the high hygroscopicity, which absolutely forces a dry supply chain. These are the two features that shape the whole transloading regime.
It is worth adding a distinction important from the safety point of view: fresh bleaching earth is transport-inert, but spent earth soaked in oil is already a completely different material — it is sometimes prone to self-heating and self-ignition, is subject to separate requirements and is not what is traded as a bleaching sorbent. At the terminal we deal exclusively with fresh material.
Transport and transloading
Here we move onto ground I know best — because Tonsil 571 FF is a real guest on our yards, not an abstract example from a catalogue sheet. It is one of those adsorbents that regularly passes through the terminal in Chorula, so I can write about its behaviour from practice, not from theory.
Hygroscopicity sets the regime. Bleaching earth was created to absorb — and it does so even when no one asks it to. Any moisture that reaches the powder occupies the adsorption surface and lowers the decolourising capacity, and in the extreme case cakes the material. That is why silo tankers for bleaching earth must be dry and clean, without condensate on the walls, big bags tight and undamaged, and storage takes place under a roof, away from water sources. We write more broadly about the principles of dry powder storage on the occasion of bulk material storage.
Dusting. Fine grades, such as FF, dust intensively. In transloading this means mandatory respiratory protection for staff, dedusting of the big-bag discharge point and careful handling of the stream, so as not to raise the powder. This is a routine activity for the team handling dusting materials, but it must not be neglected — bleaching earth with a meal-like particle size disperses into the air in an instant.
Cleanliness and cross-contamination. Since a significant part of bleaching earths goes to the refining of edible oils, the cleanliness of the tank is not a cosmetic matter here but a requirement. A residue of foreign material from a previous load is a risk of contaminating the adsorbent, and as a result the final product. That is why with bleaching earths we maintain the same discipline as with other sensitive loads — we describe it more broadly in the article on cross-contamination. A clean, dry, dedicated silo tanker is the starting point, not an option.
Transport forms and transloading method. Bleaching earths travel in bulk in silo tankers to large refineries and in big bags with a capacity of 500–1000 kg to smaller recipients. In Chorula we transload Tonsil 571 FF from big bags onto silo tankers by the gravity method, without pneumatics. For a material so fine and hygroscopic this has a double advantage: it does not generate the additional dusting associated with pneumatic conveying and does not force compressed air, which could carry moisture, into the tank. We describe the method in the article on pneumatics-free transloading, and the service itself — on the big bag to silo tanker transloading page.
Bleaching earth shows well that a “chemical material” need not mean a dangerous good. Fresh Tonsil is non-ADR, transport-inert, but it requires discipline: dryness, cleanliness and protection against dusting. These three things will decide whether the adsorbent reaches the refinery fully effective. If you are planning to transload bleaching earth or another hygroscopic powder — in bulk or from big bags — ask our team for a quote; we will match the form, packaging and transport regime to your material.
Related topics
- Bentonite — the montmorillonite rock, the starting raw material of activated bleaching earths.
- Carbon black — another fine, dusting chemical material with demanding transloading.
- Big bag (FIBC) — the basic packaging of hygroscopic powders.
- Pneumatics-free transloading — a gravity method protecting the adsorbent against moisture and dusting.
- Service: big bag to silo tanker transloading and storage of bulk materials.
- Network: bulk material transport by PHS Magnum.
Sources
- Literature on the refining of edible oils — the bleaching stage (adsorption on activated earths), removal of dyes, phospholipids and metals.
- Mineralogy of smectites: montmorillonite, acid activation of clays, specific surface area and porosity of adsorbents.
- Safety data sheets and technical data of commercial bleaching earths (including Tonsil grades).
- Operational practice of the SMIALA terminal, Chorula — Aleksy Pasternak.
