A characterization of rare earth elements in coal ash generated during the utilization of Australian coals

Abstract

ABSTRACT Establishing an alternative resource of rare earth elements (REEs) in coal by-products has been a topic of high interest for the past decade. Despite this, research that characterizes REEs in such materials produced in Australia is lacking. This paper focuses on the concentration and occurrence of REEs in power station coal ashes that represent a suite of major economic coal basins in Australia. The concentration of REEs in coal ash samples was determined by Inductively Coupled Plasma Mass Spectroscopy (ICP-MS). Fly ash and bottom ash generated at power stations that utilize coals from the Collie Basin in Western Australia contained elevated REE concentrations. A REE-rich fly ash containing 0.21% total rare earth oxides (REO) was subject to further analysis by Scanning Electron Microscopy with Energy Dispersive X-rays (SEM-EDX) and TESCAN Integrated Mineral Analysis (TIMA). Fine (avg. <5 μm) monazite grains were observed in the fly ash which were typically bound to Al/Si-rich phases. A substantial increase in the aqua regia-extractable fraction of REEs occurred when fly ash samples were milled to an ultrafine particle size. The current investigation has demonstrated that Australian coal ash may represent a promising resource of REEs as the demand for these metals increases.