Use of industrial wastes in the formulation of olivine green pigments

This work describes the formulation and synthesis of Ni-olivine green pigments from industrial wastes, namely foundry sand and a sludge resulting from the wastewater treatment of the Ni/Cr galvanising process. This second one is considered as hazardous waste since the leached levels of nickel and chromium are above legal concentrations. Pigments were prepared by the solid state reaction method and Ni2SiO4 is formed at only 1050 °C. SiO2 (in excess) and NiCr2O4 are present as secondary phases. By using pure reagents and following similar processing conditions, the Ni-olivine phase is only observed at 1200 °C. The green colour of the pigments is due to spin-allowed transitions of Ni2+ in octahedral M1 and M2 positions. The sample prepared from wastes shows a stronger and darker green hue. The colouring performance of ceramic glazes and bodies is also optimal, confirming the potential of the use of such wastes for ceramic pigments production.