Mechanisms of amine-quartz interaction in the absence and presence of alcohols studied by spectroscopic methods

The adsorption mechanism of long-chain alkylamines and their acetate salts on quartz was investigated using Hallimond flotation, zeta-potential, Fourier transform infrared, and X-ray photoelectron spectroscopy (XPS) studies at neutral pH 6-7. The influence of long-chain alcohols on the adsorption of amines in mixed amine-alcohol on quartz was also examined. It is shown by infrared spectroscopy that in differentiation to the electrostatic adsorption model of Gaudin-Fuerstenau-Somasundaran, amine cations form strong hydrogen bonds with the surface silanol groups. The XPS spectra revealed the presence of neutral amine molecules together with protonated ammonium ions at and above the critical hemimicelle concentration. The acetate counterions were found to influence the amine adsorption. Possible mechanisms of adsorption based on these observations were discussed. For the first time it was proved spectroscopically that coadsorption of long-chain alcohols along with amine cations leads to formation of a closely packed surface layer, as compared to the case of adsorption of pure amine alone at the same concentration. The highest order and packing at the surface are observed when the alkyl chain length of mixed amine and alcohol are the same. The condition of same chain length of amines and alcohols adsorbing at the surface corresponds to maximum flotation recovery. The results also confirmed the synergistic enhancement of amine adsorption in the presence of alcohols. The mechanism for mixed long-chain amine and alcohol adsorption onto quartz is consistent with the primary adsorption species of alkylammonium-water-alcohol complex, where deprotonation of ammonium groups in the adsorbed layer leading to two-dimensional precipitation of molecular amine was illustrated. (C) 2002 Elsevier Science (USA).