Evaluation of industrial shaping processes and firing cycles for the encapsulation of galvanic sludge in ceramics

This study aimed to scale the process of encapsulation in clay of the heavy metals Ni, Cr, and Cu, traditionally carried out at the laboratory level, up to industrial conditions. For this purpose, sludge from the galvanic industry, considered highly polluting, was mixed with the clay used to make traditional ceramics. The sludge concentrations were 2%, 5%, and 8% by weight. Two shaping processes traditionally used in the ceramic industry were used: extrusion and dry pressing, and the sintering was carried out in industrial gas kilns at 2 firing cycles: fast, lasting 34 min in a roller gas kiln, and slow, lasting 42 h in a tunnel gas kiln. The specimens thus obtained were characterized in terms of mechanical and esthetic properties. In the first case, the following characteristics were evaluated: flexural strength at three points, shrinkage, calcination losses, and water absorption. In the second, the color change obtained in the finished product generated by the presence of sludge was evaluated. Additionally, by means of the toxicity characteristic leaching procedure (TCLP) method, the impact that the finished product would have on the environment by leaching was determined. The results showed that the two processes of forming and sintering are viable for the treatment of galvanic sludge contaminant.(c) 2022 Published by Elsevier Espa n similar to a, S.L.U. on behalf of SECV. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/

Automated summary

This study aimed to scale up the encapsulation process of heavy metals in clay from laboratory to industrial conditions. Sludge from the galvanic industry, considered highly polluting, was mixed with clay used in traditional ceramics. Two shaping processes, extrusion and dry pressing, were used, followed by sintering in industrial gas kilns. The specimens were characterized for mechanical and esthetic properties, and the impact on the environment was determined using the toxicity characteristic leaching procedure (TCLP) method.