SYNTHESIS AND CHARACTERIZATION OF IRON OXIDE WASTE-DERIVED RED COLOUR PIGMENT VIA CRYO-MILLING PROCESS

This study compares the effects of the cryo-milling process to the ball-milling process and,thus, suggests an effective technique to convert iron oxide waste into industrial grade red colour pigment. The milling process in this work includes ball-milling at room temperature and cryo-milling at 70 K. The SEM results revealed that cryo-milling, running for 45 minutes, produced the finest particles that were averagely 112 nm. While ball-milling, running for the same period, produced particles with an average diameter of 137 nm. The XRD results confirmed that the samples, had transitioned throughout the hematite phase. The samples that underwent cryo-milling lasting 15, 30, 45 and 60 minutes, respectively, showed noticeable alterations in their colour values. The CIE L*a*b* colour values were analysed for all of the samples and the results indicated that the value of a* for all of the cryo-milled samples was greater than those of the ball-milled samples. This indicated that the cryo-milling process improved the colour properties of the samples and, thus, it is suitable for use as a raw material for red colour pigment production. Generally, the cryo-milling process resulted in significant changes in the colour properties and microstructure.