Microwave digestion of carbonate rock samples for chemical analysis

Abstract

The use of a microwave oven has permitted rapid and complete digestion of powdered carbonate rock samples, replacing the classical methods of dissolution which involved lengthy multi-step processes. The procedure includes the initial open heating of the powdered rock samples with 0.5 M ethanoic acid to inhibit the subsequent formation of calcium fluoride, and a two-acid closed system, heated in the microwave oven. Boric acid is then added before further heating of the closed system. This ensures that the silica remains in solution, thereby allowing complete analysis of the major components, by atomic absorption spectrometry, to be carried out on a single solution. The results compare favourably with three previous analyses obtained by a variety of lengthy, classical methods. The advantages of the microwave digestion of carbonate rock include its accuracy, safety and rapidity, permitting the digestion and analysis of 12 rock samples within a working day. The detection limit of SiO₂ with this method was 0.20%.