Microwave-Assisted Acid Digestion of Malaysian Monazite for Determination of REEs Using ICP-MS

Abstract

The objective of this study to investigate microwave-assisted digestion as a rapid sample preparation method for the determination of REEs in Malaysian monazite using Inductively Coupled plasma-mass spectrometry (ICP-MS). Finely powdered monazite (D90 < 75μm) was the raw material for the digestion and fusion procedures. In the Li-borate fusion method, the digestion was achieved by lithium tetraborate: metaborate flux (Li2B4O7: LiBO2) flux fusion followed by acid attack, using nitric acid (HNO3). The second method, the microwave-assisted digestion method, involved digestion of the monazite in a mixture of H2SO4, HNO3, and HF, followed by neutralization of the insoluble fluorides and complexation of residual HF. The concentrations of REEs, measured by both the methods, were in agreement with each other, except for the values of P and Si, which were slightly apart. Both the sample dissolution methods offer feasible means of quantifying REEs in the monazite sample, but only a combined microwave digestion-fusion technique yields complete quantitative data for monazite-type samples.