Abstract
Understanding clay flotation mechanisms has become amajor concernbecause of the increasing level of environmental contamination ofsoil and ground water by heavy metals and radionuclides. Clays areoften used as sorbents for extracting metals in indirect flotationprocesses but can function simultaneously as defoamers. However, howfoam generation and stability depend on the molecular interactionsbetween the clays and surfactant is still controversial. In the presentstudy, an amine polyethoxylated surfactant was used as a bifunctionalsurfactant that collected clay particles and acted as a foaming agentin the flotation process. The pH conditions strongly affected thesurfactant physicochemical properties, allowing the clay extractionefficiency to be tuned. The interfacial recovery factor of the claysalmost reached 100% under acidic (pH < 6) and neutral (pH 6-10)conditions, whereas it was negative under alkaline conditions (pH> 10), contrary to expectations. To elucidate the mechanisms involvedin the particle flotation process for each of the pH conditions, thebulk and foam phases were analyzed. The effects of electrostatic interactionsbetween the solutes and multiscale structure on the clay extractionbehavior were investigated by electrophoretic measurements, dynamiclight scattering, small-angle neutron scattering, and image analysis.Based on these results, three flotation processes were found dependingon pH range: surfactant foam fractionation at pH > 10; clay particlefoam flotation at pH 6-10; and particle froth flotation atpH < 6.