Analysis of iron-rich hydrochloric acid solutions for uranium, thorium, rare-earth elements and other heavy metals

Abstract

A simple solvent extraction method is described for the separation of trace elements including uranium (U), thorium (Th) and rare-earth elements (REEs) from industrially processed iron-rich hydrochloric acid solutions. Iron (Fe) causes severe spectral interference during the analysis of trace elements using inductively coupled plasma optical emission spectrometer (ICP-OES) and U by light-emitting diode (LED)-based fluorimeter (LEDF). The spectral interferences of Fe on trace elements are studied and documented. Sequential solvent extractions using methyl isobutyl ketone (MIBK) effectively removed the highly interfering Fe from these processed acid solutions, thereby enabling accurate and sensitive determination of Cd, Zn, Pb, Co, Ni, Cr, V, Cu, Sr, Zr, Ti, REEs including radioactive elements like U and Th. Solvent extraction parameters like the number of extractions, aqueous-organic ratio and acidity have been optimized for removal of Fe. The accuracy of the method has been established by analyzing synthetically prepared hydrochloric acid solutions by spiking-recovery method. Ion exchange separation of REEs using Dowex 50 × 8 cation exchange resin has been also studied and reported. The precision obtained has been well within ± 10% RSD for elements having concentration above 10 mg L−1 and ± 15% for elements having concentration below 10 mg L−1 for replicate (n = 5) measurements.