Surface properties of recycled titanium oxide recovered from paint waste

Aluminium oxide coated rutile pigment was extracted from a paint matrix by means of a thermal recycling process. The objective was to investigate the effect of the recycling process on the surface properties of the pigment. The pigment was analysed using powder x-ray diffraction (XRD), surface area measurements (BET), laser diffraction for particle size analysis and X-ray photoelectron spectroscopy (XPS) before and after the recycling process. Investigations on the zeta potential and the surface charge were performed as well. It was concluded that the rutile crystalline core and the aluminium oxide coating of the pigment were still intact after the recycling process. The particle size distribution of the recycled pigment was slightly broader compared to the virgin pigment. The measured magnitude in zeta potential of the recycled pigment was lower than for the virgin pigment. This difference is thought to be caused by alteration in the surface hydroxyl concentration. Surface charge titrations showed differences between the virgin and the recycled pigment at alkaline pH and at low salt concentrations.