Environmental implications and recovery potential of rare earth elements in solid residues from the incineration of sewage sludge

Abstract

Abstract The presented research aimed to contribute new insights into the chemical composition of solid waste generated during the incineration of sewage sludge, with a particular focus on the occurrence and behaviour of rare earth elements (REEs). In this study, the total content as well as the mobility of rare earth elements (REE) were determined in disposed fluidized beds (FB), sewage sludge ash (SSA), and air pollution control residues (APC) samples obtained from three Polish facilities engaged in thermal sewage sludge treatment. The mobility of REE was assessed using the BCR sequential extraction procedure. Each type of tested material was characterized by different content of REE (SSA > FB > APC). Moreover, statistically significant differences were observed in the REE content in individual waste fractions depending on the sampling places. The mobility of REE in SSA and FB was determined as very low (approx. 98.5% of Sc and > 99% of other REE in the immobile fraction). Based on the results, it can be concluded that the recovery potential of REE from each fraction of the tested waste is negligible. Because of the very low mobility of REE, these elements should not be considered hazardous during FB and SSA management.