Abstract:
BACKGROUND Tungsten-molybdenum ore is generally composed of a variety of minerals with complex composition. It is insoluble in hydrochloric acid, nitric acid and aqua regia, and the alkali melting and mixed acid dissolution method was often selected for sample digestion. However, the matrix effect cause by the alkali melting method seriously affects the accuracy and detection limit of instrument testing; the acid dissolution method has low dissolution efficiency for tungsten, molybdenum and other insoluble elements, and requires a long time and a complex pretreatment process by using a variety of inorganic strong acids such as hydrofluoric acid and aqua regia, which can also cause damage to the analytical and testing instruments.
OBJECTIVES To develop a simple and efficient method for quantitative analysis of tungsten and molybdenum and its associated elements in tungsten-molybdenum ore.
METHODS Based on alkaline melting and acid dissolution, a method was established by inductively coupled plasma-optical emission spectrometry (ICP-OES) with direct sintering and complex extraction of hydrochloric acid-phosphoric acid-citric acid. Seven elements (tungsten, molybdenum, copper, lead, zinc, calcium, and iron) were analyzed in tungsten-molybdenum ore. The tungsten ore standard substances (GBW07240 and GBW07241), molybdenum ore standard substances (GBW07238 and GBW07239) and two actual tungsten-molybdenum ore samples were used to verify the method.
RESULTS Compared with the traditional alkali melting method, the minerals containing the target elements in the samples were converted to acid soluble state by direct high-temperature sintering, and the target elements were transferred to the solution under the complexation of the mixed acid system of hydrochloric acid, phosphoric acid and citric acid, so as to achieve rapid and accurate quantitative determination. The optimal experimental conditions were: sintering at 600°C for 1h, extraction with 5mL mixed acid composed of phosphoric acid and hydrochloric acid (V/V=1:20), complexation with 5mL of citric acid with a concentration of 10g/L, and determination after filtration. The results showed that the contents of the seven target elements were within the standard value range, and the relative error and relative standard deviation (RSD) were within 10%.
CONCLUSIONS The sample pretreatment method combined with direct high-temperature sintering and complex extraction of hydrochloric acid-phosphoric acid-citric acid can be used to effectively avoid the shortcomings of traditional alkali melting and mixed acid dissolution method, and has the advantages of environmental protection and low energy consumption. At the same time, it can effectively reduce the emission of acid gas pollutants in the sample analysis and testing process and has a good application prospect. The results provide basic support for the development and comprehensive utilization of strategic tungsten-molybdenum deposit resources.
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