Chromium slag and copper smelting waste slag are solid wastes generated in the process of industrial production of chromium salt and copper metal, respectively. In this study, chromium slag and copper smelting waste slag were used as raw materials to produce black ceramic tiles. It can not only reduce environmental pollution but also increase their utilization value. The chromaticity values of ceramic tiles (L*, a*, and b*), which are color models developed by the International Commission on Illumination, were measured using a colorimeter. The phases and microstructure of the ceramic tile were analyzed by X-ray diffractometer (XRD), scanning electron microscope and energy-dispersive X-ray spectrometry (SEM-EDS), respectively. The effects of different process parameters on the coloring performance of ceramic tiles were also investigated. The results show that the color of ceramic tile is the best when the Fe/Cr ratio is 1.5, the sintering temperature is 1200 °C, the holding time is 30 min and the ceramic tile is cooled in the furnace. The values of L*, a*, and b* are, respectively, 22.5, 0, and −1.6. The compressive strength of ceramic tile and the leaching concentration of Cr(VI) are 127.2 MPa and 3.31 mg/L, respectively, which can meet the relevant national standards.

Stainless steel dust is rich in valuable metal elements including Fe, Cr, Ni and Mn, which can be utilized to prepare Fe–Cr–Ni–Mn series black pigments. Meanwhile, manganese can absorb the majority of the visible light wavelength range, which improves the color rendering performance of Fe–Cr–Ni–Mn series black pigments. However, the coloring mechanism of manganese in the above black pigments is not clear. Therefore, the effect of manganese oxide content on the preparation of spinel-type black pigments from microwave-assisted calcination of stainless steel dust was studied in this work. The results show that with the increase in MnO content in the raw mixture, the crystal plane spacing of black pigments increases from 0.2525 nm to 0.2535 nm, the grain size grows from 61.4619 nm to 79.7171 nm, and the lattice constant grows from 0.8377 to 0.8406 nm. Moreover, the band gap is decreased from 1.483 eV to 1.244 eV, the absorbance increases significantly and has a consistent absorbance in the visible range, and the L*, a* and b* values reduce from 41.8, 0.6, 1.6 to 32.0, 1.0, 0.8, respectively. MnO can react with the spinel in stainless steel dust, forming Mn₃O₄, MnCr₂O₄ and Ni (Fe,Cr)O₄ in the system, with a regular polyhedral structure. The prepared pigments have excellent thermal stability at 1100 °C and good compatibility with transparent glazes, which can be adhered to the surface of ceramic tiles after calcination to demonstrate better compatibility as the content of MnO increases.