UNITED STATES MINERAL RESOURCES 



RHENIUM 



By R. U. King 



CONTENTS 



Abstract of conclusions 557 



Introduction 557 



Uses 557 



Exploitation 558 



Resources 558 



Problems for research 558 



Selected bibliography 559 



ABSTRACT OF CONCLUSIONS 



Rhenium, a rare element that has only recently come into 

 significant industrial use, has properties excellently suited 

 for application as a refractory metal, as an alloying element, 

 in high-temperature thermocouples, in electronic components, 

 and as a catalyst in petroleum refining. Rhenium is ob- 

 tained from molybdenite that is recovered as a byproduct 

 of copper production, and the supply of rhenium, as well as 

 the world resources of rhenium is therefore closely tied in 

 with the world's resources of molybdenum in porphyry copper 

 deposits. 



Identified U.S. resources of rhenium are estimated to be 

 about 10,000 short tons, and world resources on the order of 

 30,000 short tons. Although other sources may exist, they 

 are not known to be significant. 



INTRODUCTION 



Rhenium, one of the rarest and most dispersed of 

 the metallic elements, has been intensively studied 

 since its discovery in 1925. Rhenium metal is silvery 

 gray and has a melting point of about 3,180°C, the 

 second highest of all metals (after tungsten). It 

 has a density of 21 grams per cubic centimeter, the 

 fourth heaviest of the metals ; it is almost as heavy 

 as platinum. It is ductile, extremely hard, and high 

 in tensile strength. Wrought rhenium metal resists 

 oxidation, but rhenium in povi^der form oxidizes 

 readily at the moderate temperature of 150°C. Rhe- 

 nium does not occur in its native or pure state but 

 only in combination with other elements, and no 

 definite rhenium minerals have yet been identified. 



It has been found in significant concentrations only 

 in association with molybdenite. 



Rhenium, atomic number 75, is a heavy transi- 

 tion metal that can form an extensive series of com- 

 pounds that include the widest range of valences of 

 any element, from — 1 to -\-7. Rhenium is placed in 

 column 7B of the periodic table, below manganese 

 and technetium, adjacent to tungsten and the plati- 

 num metals, and diagonally below molybdenum. It 

 has a marked affinity for sulfur, as does molybde- 

 num. The association with molybdenum is marked, 

 but there is evidence of only a slight association 

 with manganese, the platinum metals, and tungsten 

 (Fleischer, 1959). Unique features of rhenium 

 chemistry are the unusually high volatility of the 

 heptoxide and the high solubility of the heptoxide 

 in water and oxygenated solvents. 



Various figures are given in the literature for the 

 abundance of rhenium in the earth's crust, ranging 

 from 0.5 to 10 parts per billion. 



USES 



The principal uses of rhenium are as an alloying 

 element in specialty metals, in high-temperature 

 thermocouples, in filaments of mass spectrographs 

 and ion gages, in electronic and electrical control 

 devices, flash lamp filaments, metallic coatings, heat-, 

 wear-, and corrosion-resistant alloys, and as a cata- 

 lyst in petroleum refining to produce high-octane 

 gasohne (Shimamoto, 1972). Its high melting point 

 and module of elasticity and its heat-stable crystal- 

 line structure make rhenium an excellent refractory 

 metal. 



In view of the current attention being placed 

 upon environmental pollution, pai'ticularly as re- 

 lated to modern gasoline-powered transportation, 

 the beneficial properties of rhenium as a catalyst in 

 the petroleum-refining industry may make it of 

 great national importance in the very near future. 

 High-octane gasoline is produced more economically 



U.S. GEOL. SURVEY PROF. PAPER 820 



