Rare earth element patterns in sewage sludge and its incineration ash in Sapporo city

Abstract

There are still many unknowns regarding the causes of anomalies in lanthanum (La) patterns among rare earth elements in the environment. In this study, we analyzed the rare earth element patterns in sewage sludge and its incineration ash from Sapporo City. Samples of incineration ash and dewatered sludge were collected from two sludge incineration plants in Sapporo City and subjected to sequential extraction and decomposition to measure the rare earth elements. The results showed that while there were no La anomalies in the residues, other components exhibited significant positive La anomalies. The concentration of rare earth elements in the incineration ash was an order of magnitude higher than in the dewatered sludge, and the concentration of rare earth elements in the initial acetic acid extract was an order of magnitude lower than in the citric acid or hydrochloric acid extracts. The absence of La anomalies in the residues ruled out the possibility of it being caused by La-containing zeolites. It was concluded that the La anomalies were due to lanthanum carbonate tablets (such as Fosrenol), a phosphate binder administered to patients with renal failure and undergoing dialysis. Additionally, this study suggests that the use of lanthanum carbonate has the potential to disrupt the natural patterns of rare earth elements.