Study of Heavy Metal Encapsulation in Geopolymerized Industrial Waste by Sequential Extraction

The valorization of industrial waste is a part of the circular economy strategy of the European Union. The study of the potential mobility of heavy metals has been performed by the BCR sequential procedure. Additionally, the same procedure was applied to the obtained geopolymers to study the level of heavy metal encapsulation in the geopolymer matrix and, correspondingly, the environmental footprint of the newly obtained materials. For verification of the sequential extraction, the BCR procedure and CRM BCR 701 were chosen. In this study, the BCR procedure was modified by lowering the weight of the sample but maintaining the solid-to-liquid ratio, as well as applying different procedures for supernatant separation. ICP-OES measurement was used for determination of Zn, Pb, Cu, Ni, Cd, and Cr in the leachates. The amount of extracted metals in the sequential procedure agreed with the certified values; however, some discrepancies in individual steps were observed. The BCR procedure was applied to fly ash, mine tailings, and geopolymer samples. Different indices were calculated from the BCR data to assess the environmental footprint of the studied materials. A high efficiency of encapsulation in the geopolymer matrix was observed for Cr, Ni, Pb, and Zn. Copper showed increased mobility in the geopolymer samples.