Determination of rhodium content by the method of Stripping voltammetry in ores and technogenic raw materials

Abstract

Abstract. The method of determination of rhodium by the method of Stripping voltammetry in ores and technogenic raw materials has been developed. Determination of rhodium (III) in solution by Stripping voltammetry method was carried out by peak of selective electrooxidation of bismuth from intermetallic compound Bi2Rh. 1 M KSCN was selected as a background electrolyte. The method of melting of the sample with potassium tetrafluoroborate (KBrF4) at a temperature of 500 was used for the conversion of the rhodium solution.The method of deposition of most ions present in solution of alkali metals was used to separate ions of rhodium (III) from the matrix of the samples. Ions of Pt (IV), Rh (III) and Ir (IV) remain in solution after precipitation. Ions of iridium (IV) and 10-fold excess of platinum (IV) do not interfere with the determination of rhodium (III) against the background of 1 M KSCN. IntroductionThe biggest obstacle to the research of potential natural sources of platinum group metals is extremely poorly developed base of analytical methods for their quantification. The content of rhodium in the technogenic raw materials ranges from 0.001 mg/kg to 10 mg/kg. Advanced instrumental methods of analysis are necessary to determine such low rhodium content. Papers [1][2][3][4] show the capabilities of different analysis methods in determining the rhodium in mineral raw materials. As these papers show all existing methods of analysis require effective methods of sample decomposition and methods for separation of rhodium from the sample matrix.We propose a method of stripping voltammetry (SV) as a method of analysis for determination of rhodium in mineral raw materials. This method is a highly sensitive instrumental method of analysis, which allows determining the elements after their concentration at the electrode surface, followed by sediment electrooxidation. However, determination of rhodium using this method can cause certain difficulties. We cannot detect the process of electroreduction of rhodium ions (III) in the graphite electrode (GE) on the current-voltage curves. It is connected with hydrogen evolution catalytic process that flows in parallel and results in an overlap of rhodium (III) ions electroreduction process. The process of electrooxidation of rhodium precipitate occurs at potentials greater than 1V and is overlapped by the process of oxygen evolution from water.Determination of rhodium (III) ions using SV method is carried out by rhodium IV electrodeposition together with a less noble metal (activator), followed by selective electrooxidation of metal activator. The literature describes methods for SV-determining of rhodium (III) by peaks of selective electrooxidation of bismuth or mercury form intermetallic mercury-rhodium [3] and bismuth-mercury [4] compounds (IMC). ________________________