Chromatic properties of industrial solid waste based strontium M-ferrites.

This paper reports a new black pigment based on strontium hexaferrite (SrM) and its equivalent produced from nearly 94% Fe-rich sludge. The pigments were synthesized following solid sate reaction. The fired powders (at 1000 and 1050ºC) show a clear predominance of SrFe12O19. Also, hematite (-Fe2O3) was detected in variable amounts. These two phases are present in higher quantities in the sludge based pigment, due to the interference of other contaminants. The same observation could explain the difference observed in UV-Vis absorbance spectra in the red-light interval, although similar optical behavior is associated to the rest of the visible region. Further optical measurements, carried out with colorimeter, illustrated that the prepared pigments displayed good colorimetric properties close to those of a commercial pigment. However, the addition of Fe-rich sludge slightly reduced this black colour by increasing the L* and b*, but this should be easily corrected since the variance is slight.