A new approach for sample preparation to determine the multi-element composition of cobalt-rich crust samples by wavelength dispersive X-ray fluorescence spectrometry

Rough surface of the pellet and the particle size effect limit better application of pressed pellet sample preparation to wavelength dispersive X-ray fluorescence spectrometry (WDXRF) for determination of multi-element composition in cobalt-rich crust samples. This paper explored the technique for preparing ultrafine powder of cobalt-rich crust samples by wet grinding, and an ultrahigh-pressure system was used to prepare pellets for WDXRF. Ultrafine cobalt-rich crust samples having 99% of the particle size < 4 μm (D₉₉ < 4 µm) with narrow size distribution were successfully prepared. The advantages of the new approach were investigated and the developed WDXRF method was validated. Results showed that the detection limit and precision of the proposed method for major components were improved. The detection limit of the method was within the interval from 7.0 to 1704 μg/g, and the results of precision test showed that the relative standard deviation of the measured values of components was improved to between 0.2% and 1.6%. The present method was applied to determine major, trace and rare earth components in cobalt-rich crust samples, a good agreement was achieved between the reference and measured values with relative percentage difference not more than 6.7%.