Slide Background
Slide Background

ADSORPTION OF POLYACRYLATES ON HEMATITE: IN SITU EXAMINATION BY FTIR-ATR AT HIGH AND LOW PH

Fawell, P.D., Kirwan, L.J., van Bronswijk, W.

For the majority of tailing substrates, flocculant adsorption proceeds through the interaction of amide functionalities with neutral surface species. For anionic copolymer flocculants, the acrylate component of the polymer does not directly participate in adsorption, only serving to provide chain extension in solution. The flocculation of bauxite residue with high molecular weight polyacrylates represents an almost unique situation, with the absence of amide functionalities implying a totally different adsorption mechanism.

Direct examination of polyacrylate adsorption within the complex matrix of real liquors and the mixture of residue phases is difficult, making it necessary to focus on model substrates (hematite, goethite) and synthetic liquors. Previous spectral studies have suffered from the need to dry solids following adsorption, potentially altering the adsorbed species. This study presents evidence obtained by Fourier Transform Infrared-Horizontal Attenuated Total Reflection (FTIR-ATR), in which liquors of high pH were pumped over a hematite colloid deposited on a zinc selenide crystal. For the first time in situ information has been obtained for the adsorbed polymer at the solid-liquid interface under a range of conditions.

Both the adsorbed species and the rate of polymer adsorption differ greatly for adsorption at high and low pH, and the critical role of the solution cation at high pH has been confirmed. Detailed analysis of the FTIR-ATR spectra also allows quantification of the adsorbed flocculant. The adsorption behaviour is discussed in terms of the surface structure and charge at high pH.