Aluminium silicate (Kaolin) is a chemical compound, an aluminium-based alloy, found in road dust, obtained from natural sources and subsequently purified and used in various sectors, including cosmetics, skincare products, industry, and ceramics.

The name describes the structure of the molecule:

• Aluminium indicates that the silicate in question contains aluminum in its structure. Aluminum silicates are known for their properties as absorbents, mattifiers, and strengtheners.
• silicate, a class of minerals that contain silicon and oxygen, often in combination with other elements such as aluminum.

Raw Materials and Their Functions

Aluminum and Silicon. Natural elements that, combined with oxygen and other minerals, form aluminium silicate. These elements are fundamental to the crystalline structure of kaolin.

Industrial Chemical Synthesis of Aluminium Silicate (Kaolin)

• Extraction and Processing. Kaolin is extracted from natural quarries. The extraction process includes the removal of impurities and the processing of the mineral to achieve the desired quality.
• Purification. After extraction, kaolin is purified to remove impurities such as sand, iron, and other minerals. This may include processes like washing, flotation, and sedimentation.
• Quality Control. The purified kaolin undergoes quality checks to ensure it meets the required standards. After quality control, it is packaged for use in cosmetic, pharmaceutical, paper production, and other industrial applications.

It appears in the form of a white insoluble powder at a pH above 13.

What it is used for and where

Aluminium Silicate is used in cosmetics as an ingredient in powders and foundations for its mattifying and absorbing properties. It is also employed in industrial applications as a building material, in ceramics, and as an additive in paints and plastics for its reinforcing and thermal stability properties.

Food

Ingredient included in the list of European food additives as E559 with an anti-caking agent function.

Cosmetics

It is a restricted ingredient as IV/119 a Relevant Item in the Annexes of the European Cosmetics Regulation 1223/2009. Substance or ingredient reported: Natural hydrated aluminium silicate, Al2O3.2SiO2.2H2O, containing calcium, magnesium or iron carbonates, ferric hydroxide, quartz-sand, mica, etc. as impurities

Abrasive agent. It contains abrasive particles to remove stains or biofilm that accumulate on the stratum corneum or teeth. Baking soda, kieselguhr, silica and many others have abrasive properties. Peeling or exfoliating products used in dermatology or cosmetic applications contain abrasive agents in the form of synthetic microspheres, however these microspheres or abrasive particles are not biodegradable and create pollution in aquatic ecosystems.

Absorbent. Absorbs substances dispersed or dissolved in aqueous solutions, water/oil, oil/water.

Anticaking agent. This compound facilitates free flow and prevents aggregation or clumping of substances in a formulation by reducing the tendency of certain particles to stick together.

Bulking agent. It regulates the water content, dilutes other solids, can increase the volume of a product for better flow, acts as a buffer against organic acids, helps to keep the pH of the mixture within a certain level.

Colorant. This ingredient has the function of colouring the solution in which it is inserted in a temporary, semi-permanent or permanent manner, either alone or in the presence of the complementary components added for colouring.

Opacifying agent. It is useful into formulations that may be translucent or transparent to make them opaque and less permeable to light.

Other uses

• glass industry
• insect repellent

Safety

Careful consideration should be given to the risk of cumulative aluminum intake, which cannot be ruled out because this ingredient can be found in both cosmetic products and widely consumed food products such as bread, various baked goods (1).

• Molecular Formula    Al₂H₄O₉Si₂ 
• Molecular Weight   258.16
• CAS  1332-58-7 (Kaolin)   1327-36-2 (Aluminum silicate)
• UNII    24H4NWX5CO
• EC Number   310-194-1  (Kaolin)   215-475-1  (Aluminum silicate)

References_____________________________________________________________________

(1) Tietz, T., Lenzner, A., Kolbaum, A.E. et al. Aggregated aluminium exposure: risk assessment for the general population. Arch Toxicol 93, 3503–3521 (2019). https://doi.org/10.1007/s00204-019-02599-z

 Abstract. Aluminium is one of the most abundant elements in earth’s crust and its manifold uses result in an exposure of the population from many sources. Developmental toxicity, effects on the urinary tract and neurotoxicity are known effects of aluminium and its compounds. Here, we assessed the health risks resulting from total consumer exposure towards aluminium and various aluminium compounds, including contributions from foodstuffs, food additives, food contact materials (FCM), and cosmetic products. For the estimation of aluminium contents in foodstuff, data from the German “Pilot-Total-Diet-Study” were used, which was conducted as part of the European TDS-Exposure project. These were combined with consumption data from the German National Consumption Survey II to yield aluminium exposure via food for adults. It was found that the average weekly aluminium exposure resulting from food intake amounts to approx. 50% of the tolerable weekly intake (TWI) of 1 mg/kg body weight (bw)/week, derived by the European Food Safety Authority (EFSA). For children, data from the French “Infant Total Diet Study” and the “Second French Total Diet Study” were used to estimate aluminium exposure via food. As a result, the TWI can be exhausted or slightly exceeded—particularly for infants who are not exclusively breastfed and young children relying on specially adapted diets (e.g. soy-based, lactose free, hypoallergenic). When taking into account the overall aluminium exposure from foods, cosmetic products (cosmetics), pharmaceuticals and FCM from uncoated aluminium, a significant exceedance of the EFSA-derived TWI and even the PTWI of 2 mg/kg bw/week, derived by the Joint FAO/WHO Expert Committee on Food Additives, may occur. Specifically, high exposure levels were found for adolescents aged 11–14 years. Although exposure data were collected with special regard to the German population, it is also representative for European and comparable to international consumers. From a toxicological point of view, regular exceedance of the lifetime tolerable aluminium intake (TWI/PTWI) is undesirable, since this results in an increased risk for health impairments. Consequently, recommendations on how to reduce overall aluminium exposure are given.

Wong, W.W., Chung, S.W., Kwong, K.P., Yin Ho, Y. and Xiao, Y., 2010. Dietary exposure to aluminium of the Hong Kong population. Food Additives and Contaminants, 27(4), pp.457-463.

Bratakos, S.M., Lazou, A.E., Bratakos, M.S. and Lazos, E.S., 2012. Aluminium in food and daily dietary intake estimate in Greece. Food Additives and Contaminants: Part B, 5(1), pp.33-44.