A Comparative Study of Acid-Activated Aluminium and Ferruginous Smectite in Oxalic Acid of Various Concentrations

Acid activation is a chemical modification of minerals and mainly smectites, in order to enhance their surface properties and reinforce their adsorption capacity for specific ions. Acid-activated clays and, more specifically, inorganic acid-activated calcium montmorillonites are mainly used in the bleaching process of vegetable oils, which are holding third place in the world food consumption after cereals and rice, in order to remove chlorophyll and other undesirable substances from the oils. This study proposes the use of oxalic acid for the acid activation of smectites, in order to modify their surface characteristics and create high-quality bleaching earths. In particular, aluminium and ferruginous smectites are treated with oxalic acid concentrations of 0.5, 0.7 and 1 M, and the structural modifications in the materials after treatment are observed through FTIR analysis, combined with the determination of the main structural metals’ extraction from the smectites. The results showed that ferruginous smectite is more susceptible to oxalic acid activation. The final product has developed vacant spaces in its structure to absorb other ions or molecules, although it retains the structure of smectite. Oxalic acid concentration of 0.5 M is sufficient for achieving this result. The materials produced through the oxalic acid activation are also compared with inorganic acid-activated smectites originating from the same deposits.