BACKGROUND Tin is widely distributed in the crust, and more than 20 kinds of tin minerals are known, mainly in the form of cassiterite SnO₂.Cassiterite is insoluble in hydrochloric acid, nitric acid and aqua regia.Even when sulfuric acid is heated for a long time or treated with hydrofluoric acid-sulfuric acid, only a small part of it is dissolved.Therefore, for the analysis of tin ore, the alkali fusion method is usually used for sample pretreatment.The determination methods of tin in ore include polarography, spectrophotometry, hydride generation atomic fluorescence spectrometry, emission spectrometry, inductively coupled plasma-optical emission spectrometry (ICP-OES), and inductively coupled plasma-mass spectrometry (ICP-MS).The selection of these methods mainly depends on the characteristics of the ore itself and the content of tin, but also depends on the operating conditions, the selection of reagents and other objective factors.The ICP-OES has high sensitivity, a wide linear range and low matrix effect, which can not only be used to simultaneously determine the main and secondary elements of tin ore, but also has good precision and reproducibility, and can greatly improve the test efficiency.However, when the elemental contents are determined by ICP-OES, traditional sodium peroxide or other oxidizing fluxes introduce a large amount of salts, and the solution after acidification and extraction needs to be further separated or diluted, which not only affects the accuracy of the analysis and the determination limit of lower content elements, but also causes the signal to decrease and cause damage to the instrument during the long-term determination.Lithiummetaborate is a non-oxidizing flux with high melting point and has strong resolution.Since Ingamells reported in 1964 that lithium metaborate is a good flux, it has been successfully applied in the decomposition of soil, silicate rocks, and even some refractory rock and mineral samples.In this study, the analysis of the elemental contents of tin ores are attempted, which are fused by lithium metaborate and measured by ICP-OES.

OBJECTIVES To develop a method for simultaneous determination of Sn, W, Zn, Cu, Fe and Mn in tin ores which is decomposed by lithium metaborate and determined by ICP-OES.

METHODS Lithium metaborate, a non-oxidizing flux with a high melting point, was used to replace the traditional sodium peroxide and other oxidizing fluxes to melt the sample.After ultrasonic water treatment, Sn, W, Zn, Cu, Fe and Mn of tin ores were determined by ICP-OES.Scanning electron microscopy-energy dispersive X-ray spectrometry (SEM-EDX) was used to observe the morphological characteristics of the sample molten beads under different flux amounts and analyze the elemental content in the molten beads.It was found that the surface structure of molten beads changed from loose and brittle to fine and compact with the proportion of flux to sample from small to large.When the ratio of flux to sample reached 7:1, the surface morphology of the molten bead had no obvious change.When the ratio of flux to sample was 8:1, the Boron element was detected on the surface of the molten bead, indicating that the flux was excessive at this time.In this way the optimal ratio of flux and sample was finally determined.

RESULTS The optimal ratio of flux to sample was 7:1, the sample was melted at 1000℃ and extracted by 5% nitric acid solution.The method precision (RSD) was 1.20%-8.06% by determination of tin ore standard substance GBW07281.The method detection limit was 0.0012%-0.0098%.Each element was compared by this method with classical chemical analysis methods and the relative error was within 7%.

CONCLUSIONS The content of tin, tungsten, zinc, copper, iron and manganese in tin ore is determined by ICP-OES method by means of matrix matching.There is no obvious interference between the elements to be measured.The sample pretreatment is simple, the molten salt extraction is fast, the analysis cost is low, and the environmental pollution is small.The method meets the requirement of content analysis of tin, tungsten, zinc, copper, iron and manganese in tin ore.Compared with the traditional chemical analysis method, this method is more convenient, saves a lot of time and cost, and is easy to master.SEM-EDX is used to observe and analyze the morphology characteristics and composition content of sample residue and bead under different flux amounts, which provides a theoretical basis for determining the optimal ratio of flux and sample.The low result of lead in the experiment may be due to the high melting temperature of lithium metaborate and the low melting point of lead oxide, which can be further studied in future work.The limitations of a single instrument in detection sensitivity, resolution, analysis rate and efficiency can be solved by the combination of a variety of analysis means, to obtain more abundant information and accurate results, which is one of the most important directions in the development of modern instrument technology.