UNITED STATES MINERAL RESOURCES 



CADMIUM 



By Helmuth Wedow, Jr. 



CONTENTS 



Page 



Abstract of conclusions 105 



Introduction 105 



Exploitation 106 



Geologic environment 106 



Geochemistry 106 



Minerals 106 



Ores 107 



Resources 107 



References cited 109 



TABLES 



21. 



Zinc and cadmium Contents and zinc: cadmium 



ratios in selected geologic materials 



Cadmium content of sphalerite from selected 

 U.S. and Canadian mining districts and re- 

 gions 



Estimated identified and undiscovered cadmium 

 resources of the United States and the world- 

 Recoverable identified resources of cadmium in 

 the United States, grouped by major geologic 

 regions and compared with similarly classified 

 zinc resources of these regions 



ABSTRACT OF CONCLUSIONS 



108 



108 



109 



Cadmium, a trace metal similar to zinc in many ways but 

 having a much lower crustal abundance, occurs as an im- 

 purity in zinc-bearing minerals. It is used chiefly in the 

 electroplating of fabricated steel products to obtain superior 

 corrosion resistance; additional uses are in the manufacture 

 of yellow and red pigments, vinyl plastics, phosphors for 

 television picture tubes, and nickel-cadmium batteries. None 

 of the few independent cadmium minerals currently known 

 is sufficiently abundant to be mined as an ore. thus, all 

 cadmium produced has been as a byproduct of zinc refining 

 from sphalerite. World zinc concentrates are estimated to 

 contain an average of about one-fourth of 1 percent cadmium, 

 of which about 75 percent is generally recovered or can be 

 recovered during zinc smelting and refining. 



Estimates of world cadmium resources place recoverable 

 identified resources at more than 1.2 million metric tons, 

 of which about one-fourth is in the United States. Total 

 world recoverable and subeconomic resources, both identified 

 and undiscovered, are estimated to be in excess of 18 million 

 metric tons of contained cadmium. About one-sixth of these 

 resources is in deposits believed to be exploitable under 

 existing economic conditions. 



Many of the deposits containing the world's cadmium re- 

 sources are the conventional zinc-bearing tjrpes, chiefly those 

 known as massive sulfide and strata-bound. However, signi- 

 ficant low-grade resources occur in phosphorites and such 

 black metal-rich shales as the Kupferschiefer of central 

 Europe, in which the Cd:Zn ratio is considerably higher 

 than in the more conventional deposits. 



INTRODUCTION 



Cadmium is a silver-white soft, malleable metal, 

 which with its compounds has a wide range of indus- 

 trial uses. Its relative rarity and consequent high 

 price, however, have prevented more extensive use 

 inasmuch as it is in direct competition with its more 

 abundant less expensive sister element, zinc. Cad- 

 mium metal has a specific gravity of 8.65, and its 

 melting and boiling points are 321°C and 765°C, 

 respectively. The high luster on a freshly cut sur- 

 face dulls rapidly with the formation of a thin, 

 impervious coating of cadmium oxide, which is the 

 most important characteristic of its use as a metal. 

 All new commercial cadmium is obtained as a by- 

 product of zinc production, in which it is recovered 

 from the fumes released by the roasting of zinc sul- 

 fide ores or from sludges generated during the puri- 

 fication of the sulfuric acid leachate of roasted zinc 

 ore. Thus, most zinc producers also market cadmium. 



Cadmium is available in several forms. It can be 

 cast as balls, ingots, slabs, and other shapes, and also 

 can be obtained as sticks, flakes, or sponge. Some 

 producers also convert the molten metal directly to 

 the oxide. For electroplating (see below) as much as 

 0.05 percent lead and 0.033 percent zinc is permitted, 

 whereas for certain other uses the allowable maxi- 



U.S. GEOL. SURVEY PROF. PAPER 820 



105 



