Research Progress on Pretreatment Methods for Analysis of Precious Metal Elements in Geological Samples
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ABSTRACT
BACKGROUNDThis article reviewed the research progress of pretreatment techniques for the analysis of precious metal elements in geological samples in recent years. The fire assay, alkali fusion, acid decomposition and adsorption methods used in the separation and enrichment of samples and absorption, tellurium co-precipitation, ion exchange, solvent extraction, distillation, and biosorption methods commonly used for sample decomposition were reviewed. The characteristics and deficiencies of each method were investigated, and the future development direction of the method is prospected.OBJECTIVESIn order to make the analysis results accurate and reliable, it is necessary to select the appropriate means of sample decomposition and separation and enrichment to ensure complete sample decomposition, effectively eliminate the interference of co-existing ions and matrix effect, enhance the precious metal element test signal, and improve the signal-to-noise ratio.METHODSThe fire assay method used for sample decomposition has been continuously explored and improved by analysts, and has become the best method to decompose precious metals. However, it still has the disadvantages of large reagent consumption, high cost, and long procedure. Although the alkali fusion method can decompose almost all geological samples, the resulted solution contained a large amount of sodium salt, which needed to be further purified. The acid decomposition method was mainly based on the high-pressure sealed Carius tube digestion, but it was limited by the nature of the sample. Different separation and enrichment methods were highly targeted. For example, the adsorption method was mostly used for the enrichment of Au, Pt, and Pd. The distillation method was only suitable for the analysis of Os and Ru.RESULTSPrecious metal elements had features such as strong particle effects, complex and diverse forms, and ultra-trace amounts, so it was necessary to choose a suitable pretreatment method according to the type of samples.CONCLUSIONSBased on the existing precious metal decomposition methods, in combination with the current new experimental equipment and conditions, more efficient and rapid decomposition technologies should be sought and the background of the procedure and pollution problems in each step strictly controlled, realizing multi-technology and multi-method integration and meeting the requirements of precious metal analysis.
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