UNITED STATES MINERAL RESOURCES 



SELENIUM 



By H. W. Lakin and D. F. Davidson 



CONTENTS 



Page 



Abstract of conclusions 573 



Introduction 573 



Uses 573 



Geochemical cycle 574 



Crustal abundance 575 



Resources 575 



Selected references 576 



TABLES 



119. 



Selenium resources potentially available in 

 identified resources of copper ores, lead ores, 

 pyrite, and coal of the United States and the 

 rest of the world 



Selenium content of annual coal consumption at 

 five operating and five proposed powerplants 

 in Western United States 



575 



ABSTRACT OF CONCLUSIONS 



The present demand for selenium is less than the amount 

 available as a byproduct from the copper industry. Two 

 factors, however, may result in a severe shortage of selenium 

 in the United States in the future. In situ leaching of copper 

 from its ores leaves the associated selenium undissolved in 

 the waste rock resulting from the process. Thus, as the use 

 of the leaching process increases at the expense of smelting, 

 the supply of selenium will decrease. A second and more im- 

 portant factor is the probable increasing use of selenium as 

 a soil additive to provide enough selenium in the diet of 

 domestic animals to insure good health. It is anticipated 

 that this use will require a minimum of 10 times the present 

 annual production of selenium. 



Identified resources of copper in the United States are 

 estimated to contain about 52 million pounds of recoverable 

 selenium. About seven times the current annual domestic 

 consumption of 1.1 million pounds of selenium is contained 

 in the coal burned per year in the United States. Thus the 

 most promising source for a greatly increased supply of 

 selenium is as a byproduct for coal-burning powerplants. 



INTRODUCTION 



Selenium was discovered in 1817 by J. J. Berzelius 

 and J. G. Gahn in a red sediment found in sulfuric 

 acid prepared from the sulfur recovered from pyrite 

 mined at Fahlun, Sweden. 



It is a nonmetallic element, of atomic number 34 

 and atomic weight 78.96, which exists at normal 

 temperatures in two crystalline forms and two 

 amorphous forms. The metastable monoclinic struc- 

 tural form is red, melts at 144 °C, has a specific gravi- 

 ty of 4.42, and changes to a hexagonal crystal struc- 

 ture when heated. The stable hexagonal form is 

 black, melts at 220°C, has a specific gravity of 4.82, 

 and conducts electricity — the conductivity increases 

 as much as a thousandfold during exposure to light. 

 A black vitreous amorphous form is obtained by 

 quick chilling of molten selenium. The red amorphous 

 form is obtained by reduction of selenious acid to 

 elemental selenium with sulfur dioxide or other re- 

 ductant. It turns black on standing. 



Of the 1.1 million pounds of selenium used in the 

 United States in 1968, about 40 percent was im- 

 ported, principally from Canada. 



USES 



Selenium is commonly marketed as elemental 

 selenium in the form of powder, pellet, and stick in 

 grades varying from 97.00 to 99.99 percent selenium, 

 but it is also available in pellets as very pure seleni- 

 um — 99.999+ percent Se. About 40 percent of the 

 selenium currently consumed in the United States is 

 high-purity grade (99.95-99.9 percent selenium), 

 and it is used in electrostatic printing, rectifiers, 

 exposure meters, photoelectric cells, and optical 

 lenses. 



Nearly 30 percent of the annual consumption goes 

 into the manufacture of glass, in which the selenium 

 is used to eliminate the greenish tinge caused by iron 

 impurities. In larger quantities selenium gives a 



U.S. GEOL. SURVEY PROF. PAPER 820 



573 



