In situ investigation of the adsorption of styrene phosphonic acid on cassiterite by FTIR-ATR spectroscopy

Abstract

The adsorption of the flotation collector styrene phosphonic acid (SPA) on cassiterite has been investigated by in situ method employing Fourier transform infrared attenuated total reflectance spectroscopy. This technique offers advantages over ex situ methods of studying adsorption as it allows the evaluation of adsorption kinetics and the effects of pH and other variables to be determined as they occur. Furthermore, spectra of the solution species and adsorbed species may be obtained simultaneously. The nature of the surface complex formed when SPA adsorbs on cassiterite was determined by comparison of its infrared spectrum with those of the free acid and its tin (II) and tin (IV) complexes. The SPA was found to chemisorb by forming a tin (IV) -SPA surface complex over the pH range 2.3–7.5. The fine structure of the spectrum of the adsorbate suggests that the surface complex is bidentate. The monoanion of SPA was the dominant solution species over the pH range 3–5. The kinetics of the adsorption process were determined under conditions which are normally used in industrial flotation practice. A considerable increase in adsorption density was achieved after 1 h, the conditioning time normally used in practice. However, an adsorption plateau was not reached even after 24 h. The rate of adsorption of SPA on tin (IV) oxide was greatest between pH 4.5 and 5.5. It was found that the presence of iron in the cassiterite lattice or adsorbed on the cassiterite surface was not necessary for collector adsorption since adsorption occurred on pure tin (IV) oxide as well as on natural cassiterite. Impurities in the cassiterite (Fe, Mn, Si, S) did not appear to affect adsorption characteristics when compared with pure tin (IV) oxide. The effect of dissolved iron was also investigated and found to have no effect on the nature of the adsorbate.