Recycling of chromium-rich leather ashes in porcelain tiles production

Leather residues derived from shoes industry are often incinerated in winter times to warm the working ambient, giving rise to the production of chromium-rich ashes that put environmental problems on its disposal. The power of these ashes as colouring and fluxing agent for industrial porcelain tile formulations and the effects of incorporating different amounts on water absorption and bending strength were evaluated in the present work along a broad sintering temperature range of 1120–1180 °C. The experimental results revealed that the incorporation of these wastes can result in porcelain tiles with superior properties, in terms of water adsorption, density and bending strength. The results also showed the possibility of using these wastes as colouring agents to obtain broad range tonality products from cream to dark brown, depending on the added amount of leather ashes in the formulation and on the sintering temperature. The observed improvements of the final properties of the material and the ability of chromium-rich ashes to replace expensive pigments show that their incorporating in porcelain tiles formulations is a smart way of recycling this environmental dangerous leather derived waste.