Variability of rare earth elements content in ash and slag deposited at a landfill site

Abstract

The article presents the results of investigations into the chemical composition, contents of selected rare earth elements and the reaction of eluates obtained from the waste (ash and slag) produced in the process of hard coal combustion in a pulverized-fuel boiler. Samples for tests were taken from the ash and slag landfill from three 10-metre vertical profiles. The total content of REEs in the examined ash-slags ranges from 295 to 366 mg/kg. The average concentration of rare earth elements is 330 mg/kg, with a standard deviation of 19 mg/kg. Among the examined 16 rare earth elements, the highest average contents in ash-slags, ranging from several dozen to more than 100 mg/kg, have been noted for: cerium (~113 mg/kg), lanthanum (~60 mg/kg), neodymium (~48 mg/kg), scandium (~33 mg/kg) and yttrium (~31 mg/kg). The contents of the remaining elements are much lower and, only praseodymium slightly exceeds the value of 10 mg/kg. The variability of REEs content depending on the storage time (vertical profile of landfill) was analyzed.