Circular 108—Analysis of rhenium in molybdenites

By L. M. Goebel, 1970, 17 pp., 5 tables, 4 figs.

An improved technique for the analysis of the rhenium content of molybdenite concentrates involves calcining with calcium oxide, leaching with hot aqueous oxidizing solution, and spectrophotometric determination with a-furildioxime. Standard deviations of determinations are substantially lower than those published for other methods. The current procedures for the analysis of rhenium are based on separation methods that do not completely isolate rhenium from interfering elements, especially molybdenum.

Of the many reagents that have been suggested for the spectrophotometric determination of rhenium, the two most widely used are thiocyanate ion and a-furilidioxime. Perhenate ion, on reduction with stannous chloride, yields a reactive complex, ReO2Cl2-3. Perhenate in the presence of stannous chloride with a-furilidioxime, forms solutions that are yellow-orange, orange, or raspberry-red, depending on the quantities of reagents. This suggests the formation of different complexes. The red compound is extractable with organic solvents and the resulting solutions obey Beer's law. The maximum absorption is at 533 microns, with a specific absorbance at 530 microns of 3.39x104.

In this investigation, published procedures for determination of rhenium in molybdenum concentrates were reviewed and compared experimentally, and an improved method was devised. Of several analytical methods studied, calcining with calcium oxide, leaching with a hot aqueous oxidizing solution, and spectrophotometrically determining the concentration of rhenium with a-furilidioxime produces the most reliable results. Using this procedure, a sample of Arizona molybdenite concentrate was shown to contain 320 ppm rhenium with a 95% confidence interval of 10 ppm and a standard deviation of 4.97%; standard deviations as low as 0.79% were obtained on single runs of four of more replicates. Published standard deviations for conventional analyses of the same material average about 20%. Recovery of 90 to 100% of added standards was obtained up to a total rhenium content of 500 ppm for a one gram sample.