From Bentonite to Bleaching Earth: Decolourising Edible Oils

Vegetable and animal oils are indispensable in daily life, yet they carry a large amount of residues, pigments and off-flavour compounds, some of which affect health. As living standards rise, expectations for oil quality, purity and flavour rise with them, so decolourisation, deodorisation and de-gumming become necessary process steps.

Activated bleaching earth is made from bentonite by activation with a strong oxidising agent. During activation, hydrogen ions displace and leach out the calcium, magnesium, potassium and sodium cations held between the layers; at the same time the strong alkali dissolves aluminium ions from the octahedral sheet, clears impurities from the mineral surface and opens the pore channels, so pore volume and specific surface area increase markedly.

The finished product therefore adsorbs more strongly and decolourises more effectively, and is widely used in the refining of vegetable and animal oils. In production the dosage still has to be set from the colour of the crude oil, the target colour and the filtration conditions, and confirmed by a bench trial.