Galvanic sludges: Effectiveness of red clay ceramics in the retention of heavy metals and effects on their technical properties

Tiles of red clay mixed with 5% by weight of galvanic sludge were obtained by dry pressing, enameling in the line of production, and sintering in a semi-industrial roller kiln. In the process, a 30-minute firing cycle was employed at a temperature of 1170 degrees C, with heating-cooling ramps between 47 degrees C and 197 degrees C. In order to estimate the effects of the addition of galvanic sludge on the finished product, the technical properties of the material were evaluated: loss by calcination, water absorption, linear shrinkage, three-point flexural strength, color, and spectroscopy characterization via IFTR, UV-Vis-NIR, and RAMAN, and ceramic-mount microstructure and crystal structure via XRD. The effectiveness of the ceramic for the retention of Cu, Ni and Cr was determined from the leaching test, in order to characterize the toxicity (TCLP) of the finished and ground samples according to EPA 1311. As a result, it was determined that the addition of sludge to the clay modified the color of the finished product, decreased the flexural strength, and increased the shrinkage and the total porosity. Therefore, the sintered product acted satisfactorily as an encapsulating agent. (C) 2019 Elsevier B.V. All rights reserved.