Red mud and electroplating sludge as coloring agents of distinct glazes: The influence of heat treatment

The use of red mud (RM) and Cr/Ni electroplating sludge (ES), two hazardous industrial wastes, was studied as possible coloring agents for commercial glazes: transparent (TR), bright white (BR) and matte (MT). The influence that a heat treatment produced on the color development/stability was analyzed by comparing, separately, RM and ES non-calcined and calcined at 1200 degrees C. RM and ES yielded glazes with red/brown and grey/green hues, respectively. The calcination enhanced the powders coloring strength. ES (non-calcined and calcined) provides a fairly stable coloration when added to BR and MT, and RM (non-calcined and calcined) when added to TP and BR, upon firing at 1100 +/- 15 degrees C. So, depending on the type of glaze, when using RM and ES as coloring agents their previous heat treatment can be avoid leading to meaningful environmental and economic benefits. (C) 2018 Elsevier B.V. All rights reserved.