The effects of the adsorption of metal ions and surfactant on the interfacial behavior of silicate minerals

The adsorption and configuration of surfactants and the uptake of metal ions on silicate minerals are important topics of continuing interest in the fields of environmental engineering and mineral processing. The objective of this work has been to investigate the effect of the natural hydrophilicity/hydrophobicity of silicate minerals on the adsorption of surfactant and metal ions from aqueous media, and the resulting effect of the adsorption on the interfacial behavior of the minerals. Quartz was taken as the model for a naturally hydrophilic mineral and talc as the hydrophobic mineral. Their interfacial behavior in aqueous systems was investigated through simultaneous measurements of the zeta potential, adsorption, and turbidity of the suspensions for each sample. Various interfacial phenomena were interpreted not only through the results of these measurements but also with additional information obtained from Hallimond tube flotation, induction time measurements, and solution chemistry of the cationic surfactant and metal ions.; Under the same conditions, the zeta potential of talc was found to be considerably more positive than that of quartz upon the addition of dodecylammonium acetate (DAA) over the entire pH region, suggesting that hydrophobic interactions resulting from the natural hydrophobicity of talc play a significant role in the adsorption. A sharp increase in the zeta potentials of both quartz and talc was observed around the K{dollar}rmsb{lcub}a{rcub}{dollar} of the amine (about pH 10) because of the adsorption of ionic-molecular species and/or the co-adsorption of aminium ions and amine molecules, or possibly heterocoagolation of amine precipitates with the mineral. Adsorption isotherms of DAA on talc can be interpreted in terms of differences in the nature of the hydrophobic faces and hydrophilic edges of talc particles.; Upon adsorption of hydrolyzing lead and cadmium ions, the zeta potential of quartz and talc was reversed from negative to positive and the turbidity of the suspensions changed with the sharp change of the zeta potentials. Good correlation among zeta potential, adsorption and suspension turbidity was observed. The adsorption of lead and cadmium ions was found to be very small in the acidic region but increased rapidly near the pHs where the metal ions start to hydrolyze, indicating specific affinity of the hydrolyzed metal ionic species for the mineral surface. The stability of quartz suspensions was significantly different from those of talc because of differences in their hydrophobicity and surface heterogeneity. Suspensions of quartz were stable and independent of pH except at pHs near the point of zero charge (PZC) where low stability was observed, but the suspension stability could be changed markedly by adding metal ions or surfactants. On the other hand, suspensions of talc were not stable under any experimental conditions, probably due to hydrophobic associations and heterocoagulation among the talc particles.; Titration studies showed that the surface charge of quartz was very low under acidic conditions but increased sharply at about pH 6 because of increasing dissociation of surface silanol groups. The surface charge of the ground quartz agreed well with that reported for precipitated silica, suggesting that it is independent of the crystallinity of the material.