Method Development and Optimisation of Sodium Peroxide Sintering for Geological Samples

Abstract

This work provides a measurement procedure for the complete digestion of rock samples containing refractory minerals such as zircon and chromite. Their dissolution by wet acid digestion is often incomplete but, although providing complete digestions, alkali fusion techniques can result in solutions with a high blank and total dissolved solid content. It was established by the systematic study with reference material trachyandesite MTA‐1 that a 1:6 sample to sodium peroxide (Na2O2) ratio is conservative for the complete digestion and recovery of all the analytes especially those contained in zircon. The sample decomposition time was 120 min for the zircon‐bearing rhyolite reference material MRH‐1. Complete digestion of chromite was obtained in the harzburgite RM MUH‐1. The sample solutions were stable for at least 1 year. Accurate measurements of SiO2, Al2O3, TiO2, P2O5 and K2O could be made with ICP‐MS by not discarding the supernatant of the sinter solution and by using geological reference materials for external calibration. HF digestions are slow, not universal, and may form new mineral/phases that are insoluble under high temperature conditions. The validated sample decomposition procedure combined with ICP‐MS presents an alternative to the use of HF in routine analysis of difficult to digest geological materials.

The hydrothermal alteration of carbonatite in the Fen Complex, Norway: mineralogy, geochemistry, and implications for rare-earth element resource formation

“…Initial digestions of rock powder by conventional multi-acid (HNO 3 , HCl, HF) methods in Teflon vials at 220°C left insoluble material in the vast majority of the samples. Therefore, solutions were obtained by sodium peroxide sintering digestion according to Bokhari and Meisel (2016): 100 mg of sample was mixed with ~600 mg of Na 2 O 2 (finely ground Merck analytical-grade granular sodium peroxide) in high-purity nickel crucibles and heated for 60 min at 480°C in a conventional muffle oven. The resulting sinter cake was dissolved in 90°C ultrapure water (Elga Purelab flex, >18.2 MΩ cm), centrifuged, and the clear solution decanted.…”

A general strategy for the voltammetric trace determination of tellurium in geochemical and environmental matrices after arsenic coprecipitation and critical assessment of digestion schemes

“…Total digestions of silicates are also possible by fusing the sample with NaOH in Ag crucibles (Heinrichs and Herrmann 1990), or by fusing or sintering with Na 2 O 2 in Ni, Zr or glassy carbon crucibles (Meisel et al 2002;Bokhari and Meisel 2017). These alkaline and oxidative fluxes were included because they allow for a complete digestion at much lower temperatures than that of LiBO 2 , which makes volatilisation losses of Te appear less likely.…”

“…The apparent Te content of this reagent rose to 6.2 AE 0.6 (N ¼ 3) ppb on sintering in a Zr crucible (Alfa-Aesar), but to only 2.2 AE 0.2 (N ¼ 11) ppb when a glassy carbon crucible (Sigradur, Germany) was substituted for Zr. Digestions with Na 2 O 2 were therefore conducted exclusively using this method (Bokhari and Meisel 2017). The mass of flux used in each digestion was accurately weighed and a blank Te value subtracted from the determination.…”

Rapid Determination of Trace Element Compositions in Peridotites by LA‐ICP‐MS Using an Albite Fusion Method

“…) or fusion or sintering rock powders with alkalis before dissolution (e.g., Bayon et al . , Bokhari and Meisel ).…”