Determination of W, Mo, Cu and Zn in Tungsten-Molybdenum Ores by Inductively Coupled Plasma-Optical Emission Spectrometry after Microwave Digestion with Nitric Acid-Hydrofluoric Acid

Tungsten-molybdenum ore represents a crucial and valuable mineral resource in China, characterized by its abundant associated elements. Accurate and rapid analysis of key elements (W, Mo) and associated elements (Cu, Zn) holds significant importance for the exploitation and sustainable development of tungsten-molybdenum ore deposits. In acidic environments, W and Mo are prone to hydrolysis. Current national and industry standard analytical methods for tungsten-molybdenum ores predominantly employ alkali fusion for sample pretreatment. While alkali fusion effectively suppresses hydrolysis, it introduces alkali metal matrices that may interfere with the analytical instrument’s precision and potentially elevate the lower detection limit. In this paper, a microwave digestion method was developed using a mixed acid system of nitric acid and hydrofluoric acid. Samples were digested at 180℃ for 45 minutes, and were directly dissolved in a medium containing 2% HF and 1% HNO₃, followed by determination using inductively coupled plasma-optical emission spectrometry (ICP-OES) equipped with an HF-resistant sample introduction system. The precision of the method (RSD) was 1.38%–3.46% (n=11) and the detection limits of this method were 1.91μg/g to 4.40μg/g. Validation using certified reference materials (CRMs) and real-world samples confirmed agreement between measured and certified values for CRMs, as well as consistency with results obtained by national standard methods and closed-vessel acid digestion. This method effectively suppresses the hydrolysis of W and Mo, while circumventing the drawbacks of alkali fusion methods, such as complex matrix interferences and elevated background values caused by the introduction of excessive salts. Moreover, it significantly reduces reagent consumption and experimental duration by eliminating the need for time-consuming steps such as acid evaporation and redissolution. The streamlined protocol is operationally simple and suitable for the determination of batch tungsten-molybdenum ore samples.