Synthesis and characterization of cobalt doped green ceramic pigment from tannery sludge

Chromium green pigments with good color performance were successfully synthesized with tannery sludge as chromium precursor. Yellowish-green problem, which was observed in green pigment synthesized from tannery sludge, was solved by adding Co2O3. Effects of Co2O3 content and calcination temperature on properties of the pigments were characterized by XRD, SEM, EDS and UV-vis. The XRD and EDS results show that the yellow-green color was mainly attributed to the yellow crystal phase (Mg(FeAl)O4) synthesized during the preparation process. Green ceramic pigment can be prepared by adjusting the blue component (CoCr2O4) proportion, which was achieved with different amounts of Co2O3, to balance the color proportion of yellow and blue in pigments according to subtractive color process. With increasing contents of Co2O3, UV-vis absorption spectra was enhanced in yellow band (~610 nm) but weakened in blue band (~460 nm), and colors of pigments changed from yellow-green to blue. Color performance of the green ceramic pigment (with ~2 wt% Co2O3) was close to that developed from the pigment starting from pure Cr2O3. The leaching amounts of Cr(VI) reduced gradually with the increase of calcination temperatures, which closely related to the morphology of the samples calcined at different temperatures.