In situ adsorption study of carboxymethylcellulose and sodium oleate on quartz using a quartz crystal microbalance with dissipation (QCM-D)

Abstract

Adsorption kinetics and conformation of sodium oleate and carboxymethylcellulose (CMC) on the quartz surface in real time remain a challenge in the flotation system of CMC /sodium oleate/quartz. In this work, in situ adsorption characteristics of CMC and sodium oleate on quartz surface was investigated by using quartz surface crystal microbalance with dissipation (QCM-D). QCM-D data showed that the conformations and kinetics were critically dependent on pH and degree of substitution (DS) of CMC. As the degree of substitution of CMC increases, the adsorption layer on the quartz surface becomes looser. There was only one adsorption stage at pH 8 and 12, and the adsorption layer was rigid at pH 12. At pH= 10, the conformation of the adsorbed layer changes from loose to rigid and then to loose again. CMC adsorbs less in the early adsorption stage, and the adsorbed layer is loose. As the adsorption proceeds, the adsorption increases, and the adsorbed layer becomes more rigid. At stage III, the adsorbed layer becomes loose, which is considered to be the formation of a hydrated layer. Under different pH conditions, the adsorption of sodium oleate on the quartz surface had only one stage, and when CMC and sodium oleate were adsorbed one after the other on the surface of the quartz surface, two distinguishable adsorption stages appeared, and the conformation of the adsorbed layer gradually changed from rigid to loose. The change of surface free energy of quartz surface before and after CMC adsorption was also calculated by Washburn kinetic equation and the van Oss - Chaudhuri-Good theory. The results showed that the surface free energy reduced and the hydrophobicity increased after the adsorption of CMC on the quartz surface.