Vegetable oil refining processes, specifically, silica refining and bleaching, require a working understanding of adsorption or more specifically the physico‐chemical interaction between sorbent, substrate and contaminants. An understanding of adsorption theory and the factors affecting adsorption is useful in controlling these processes. Isotherms have been used as mathematical models to describe the relationship between adsorbed and non‐adsorbed molecules. The Langmuir isotherm theoretically describes oil pigment binding as reversible, monolayer chemisorption, where all adsorption sites are energetically equal. However, many systems conform to a Langmuir isotherm without these suppositions necessarily holding true. Langmuir behavior may provide useful practical information on the variables affecting the adsorption, but it does not provide proof of the adsorption mechanism. The Freundlich isotherm is supposed to describe reversible adsorption of a single solute at equilibrium at a fixed temperature. It also has been successfully used to describe pigment adsorption from vegetable oil and, likewise, has empirical value in describing the effect of processing variables on adsorption performance. In reality, pigment binding onto adsorbent clays is irreversible and there will be more than one oil solute competing for adsorption sites. Adsorptive binding of solute to adsorbent involves a number of forces, including chemisorption and physisorption, all of which affect bleaching efficiency. Adsorbent dosage, acidity, moisture in the system, temperature and pressure, all key factors that can be used to control the adsorption process.

Vegetable oil refining process involves a bleaching stage wherein clay mineral is commonly used to promote “bleaching” or removal of contaminants from oil treated at higher temperature and under vacuum. Clay minerals have unique properties including high surface area, porosity, and presence of surface active sites. These important features help the mineral promote adsorption and catalysis of organic contaminants/pigments during bleaching of vegetable oils. Essentially, the process of bleaching is aimed at removing contaminants and undesired components from raw oils to preserve taste and impart quality to the oil. As such, clays have been extensively used in bleaching of vegetable oils and fats. The performance of natural clay mineral is dependent on their physical and chemical processing including steps like grinding, screening, acid activation, pillaring, thermal processing, and addition of functional active ingredients. Bleaching efficacy is also dependent on oil processing variables (including time, temperature, atmosphere, humidity, and agitation) maintained during bleaching process. To this end, classical and mild acid activation and addition of functional additives are the most commonly applied methods in the oil and fats industry. This article will briefly review the nature of active sites and textural properties impacting the robustness of natural and modified bleaching clays.