Synthesis of Spinel Color Pigments from Aluminum Dross Waste

Abstract

Spinel-based ceramic color pigments were successfully synthesized from utilization of aluminum dross waste and relevant oxide precursors by solid-state processing. Cobalt ions were selected as a chromophore to produce blue pigments. The conventional oxide route was also carried out for comparison purposes. The spinel phase readily formed when fired at 1100 °C; longer duration yielded a higher degree of purity. No preferential orientation of XRD reflection was observed, indicating random crystallographic arrangement. Phase formation was also confirmed by Fourier Transformed Infrared Spectroscopy (FTIR) which displayed both Co-O tetrahedral and Al-O octahedral which are the main framework for a spinel crystal. Slightly sharper FTIR peaks for the dross route compared to those from the oxide route suggest a difference in crystallinity between the two with different precursors. The particle size distribution was relatively wide (5 – 30 micron), possibly due to a crude nature of the dross precursor. The UV-vis spectra showed absorption in the range of 450-550 nm which is associated with the blue color caused by a shift of the 3d7 electrons of Co2+. The obtained dross-route pigments possessed both a and b color parameters (a = -2.3 to-2.6; b = -3.4 to-4.0) in the negative territory, implying greenness and blueness respectively. The L values were in the 20-30 range. When incorporating into practical glazes, the b parameters unexpectedly became more negative, indicating an even deeper blue tone. This result suggested a high potential for utilization of this dross waste as an alternative precursor source for sustainable production of spinel ceramic pigments.