Designing of technological scheme for conversion of Cr-rich electroplating sludge into the black ceramic pigments of consistent composition, following the principles of circular economy

Development of method for the complete conversion of Cr-containing electroplating sludge (ES) into the black inorganic pigment was presented. Difficulties related to the ES complex, variable composition and inhomogeneity, where the dominant presence of Cr was followed by: Fe, P, Zn, Ni, Cu, etc., can be overcome by determination of the precise amount of Fe2O3 necessary to be added in order to firmly embed all the heavy metals into the pigment structure (i.e. the Fe0.7Cr1.3O3/FePO4 nanocomposite), taking care not only about weight/molar ratios, but also about average particle size, apparent densities, and volume fraction of the starting materials. As a source of Fe2O3, commercial (p.a.) Fe2O3 and two different Fe-wastes were used, thus completely fulfilling the principles of the circular economy. The obtained black inorganic pigments have consistent composition, no leaching of toxic metals, color (CIE L-a-b-values) comparable with those of commercial pigments and thus have the potential commercial large scale application. © 2021 Elsevier Ltd.