Highly Sensitive Colorimetric Determination of Os Driven by Electrocatalytic Gaseous Separation

Abstract

Rapid assessment of ore grade is very important for field geological exploration, especially for precious metals. Based on the new electrooxidation gaseous separation (EOGS) idea, this paper reports a simple (colorimetric), fast (∼2 min), and accurate (μg L–1 level) method for the analysis of associated minerals Os in iron ores. The application of highly active coated electrodes has promoted the efficient and quantitative conversion of Os (including trivalent and tetravalent) to gaseous OsO4. Most of the coexisting components remain in the sample digestion solution during electrooxidation, which provides the possibility for ore sample analysis without pre-separation. Further electrochemical tests showed that appropriate catalytic activity (oxygen and chlorine evolution) was the key to both high conversion and anti-interference ability of the RuIr/Ti electrode, while long-term stability and low memory effect offered effective guarantee for practical application. Using the catalytic behavior of OsO4 to the CA-H2O2 reaction, we realized the accurate and rapid analysis of Os at the level of μg L–1 for the first time. Compared with the traditional chemical oxidation generation technology, mild operating conditions (such as not involving high temperature and strong oxidation/corrosive reagents) are the most significant characteristics of the electro-oxidation technology. Under the optimized conditions, the method has the merits of high separation efficiency (>90%), low detection limit (0.01 μg L–1), wide linear range (2–100 μg L–1), and low signal fluctuation (2.7%, n = 11). The aim of this study is to provide not only an economic and sustainable EOGS strategy for the accurate analysis of precious metal elements, but also a simple and effective rapid evaluation method for the ore grade based on the semi-quantitative analysis of color difference observed by the naked eye.