Abstract
Circular economy promotes the use of waste materials into new production processes as a key factor for resource efficiency. The construction sector, and specifically the fired clay industry, is able to assimilate large amounts of waste in their processes, without significantly altering the technical properties of products. The introduction of different waste in ceramic products at the laboratory level has been extensively studied in the literature, but most of these studies have not yet been scaled-up to industrial production. Differences in processing with respect to laboratory conditions introduces uncertainty in relation to the expected properties of the final products. This paper uses a Self-Organizing Map (SOM)-based methodology for analysing and assessing the incorporation of industrial waste, Waelz slag (WS) and foundry sand dust (FSD), in ceramic products obtained sequentially at laboratory, semi-industrial and industrial level, over technological properties and metals release. As a result, from the SOM analysis, a clustered map of the samples developed is obtained that highlights the most important parameters affecting the technological and environmental properties to be the type of clay and therefore, the firing temperature; secondly, the Waelz slag content, being independent of the foundry sand addition; and finally, the type and level of processing (laboratory-pressing, semi-industrial extruder, industrial extruder).
Highlights
The implementation of the circular economy through the incorporation of residual raw materials into material cycles is a high priority for the Green Deal (Circular EconomyAction Plan adopted by the European Commission on 11 March 2020)
Laboratory ceramic pieces obtained by pressing at a wide range of raw materials composition and firing temperature (Figure 1) were analysed for their technological properties of bulk density (D), water absorption capacity (WA), open porosity (OP), flexural strength (MOR), linear firing shrinkage (LFS) and weight loss during firing (WL), as well as for As, Ba, Cd, Cr, Cu, Mo, Ni, and Zn in equilibrium leaching tests at L/S = 10 (Table S2) (Supplementary material)
The data set results of the 14 variables obtained in the 30 samples of laboratory pieces can be grouped in a Self-Organizing Map (SOM) trained map (Figure 3a) based on “range” data normalisation resulting in a 6 x 5 (30 neurons) map, similar to the size of the 27-unit map proposed by the algorithm [59], with Quantization Error (QE) = 0.519 and Topographic Error (TE) = 0
Summary
The implementation of the circular economy through the incorporation of residual raw materials into material cycles is a high priority for the Green Deal (Circular EconomyAction Plan adopted by the European Commission on 11 March 2020). Clay brick and tile industries are showing innovative solutions to add to the circular economy in Europe, regulatory and technical barriers still exist to scale up current initiatives or to start new ones. Some of them are the differentiated interpretations of end-of-waste and by-products status among Member States, the lack of a well-functioning European market for secondary raw materials, as well as the need for an efficient system for collection, sorting and separation of waste that includes the adaptation of technical requirements of installations [4]. Dondi et al [6], shows the conflict between resource efficiency and market trends in the ceramic tile industry, and how it reflects on the supply chain raw materials.
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