NUCLEAR FUELS 



465 



lb UsOs per ton) (V. E. McKelvey, written commun., 

 1951; J. B. Cathcart, written commun., 1965). 

 Domestic hypothetical paramarginal uranium re- 

 sources in marine phosphorite are estimated at about 

 250,000 short tons of UsOs, and submarginal, about 

 1 million short tons, both mostly in western States. 

 A very small amount of the total resources in phos- 

 phorite can be obtained at moderate cost as a by- 

 product of making fertilizer, but to obtain more 

 uranium would require mining and treating this 

 rock principally for uranium; unit costs would be 

 high and vast quantities of rock would have to be 

 moved to obtain a significant amount of uranium. 



Phosphorite deposits are being mined for phos- 

 phate but their contained uranium is not being re- 

 covered. Uranium in rock that is used to make ele- 

 mental phosphorus by the electric furnace method 

 goes mostly into the silicate slag. A process for re- 

 covering uranium from the slag has not been de- 

 veloped. Most of the uranium in phosphorite that is 

 used to make fertilizer by the wet-process phosphoric 

 acid method stays in the fertilizer and is lost as a 

 resource when the fertilizer is used. Marine phos- 

 phorite from Florida was the source of about 500 

 tons of UaOs recovered between 1953 and 1961 as a 

 minor byproduct from phosphoric acid made by the 

 wet-process method. Recovery was discontinued be- 

 cause of costs uncompetitive with uranium from 

 sandstone ores. Bieniewski, Persse, and Branch 

 (1971) estimated that, if Florida phosphate rock 

 containing 0.012 percent UsOg were treated by the 

 wet-process method at the expected rate of fertilizer 

 production, about 85,000 tons of UgOg could be re- 

 covered between 1971 and 2000 at a cost of slightly 

 more than $10 per pound. 



Residues of copper smelting are also a potential 

 source of byproduct uranium at about the same cost 

 as that from phosphate rock. Bieniewski, Persse, and 

 Brauch (1971) estimated that about 30,000 tons of 

 UaOs could be recovered during the next 30 years by 

 leaching residues containing 0.0001-0.0012 percent 

 UaOs. Although byproduct uranium recovered in 

 manufacturing fertilizer and from smelter residues 

 would help to meet requirements, the amount that 

 could be obtained most economically is limited by the 

 production rate of the principal commodities. 



Marine black shales are a common rock, and they 

 generally contain low concentrations of uranium. Of 

 all the black shale beds of minable thickness that 

 have been sampled in the United States, the Chatta- 

 nooga Shale in eastern Tennessee contains the high- 

 est concentration of uranium, but only 0.007 percent 

 UaOs (0.14 lb UaOg per ton). It represents a sub- 

 marginal resource of about 7 million tons of UsOs, 



but to obtain any significant part of this resource 

 would require mining vast areas by open-cut and 

 underground methods ; unit costs would obviously be 

 high. More than twice as much uranium is present 

 in this formation in other parts of Tennessee and 

 adjacent States, but at concentrations only about 

 half that in eastern Tennessee. Even more uranium 

 is present in the Chattanooga and its correlatives in 

 the midcontinent where they are deeply buried, but 

 the uranium content of these rocks is leaner, and less 

 well defined, than it is in the more restricted areas. 



Most igneous rocks contain a little uranium, repre- 

 senting the order of crustal abundance — 0.0002- 

 0.0004 percent UsOs — but some bodies of igneous 

 rock are appreciably richer and thus might qualify 

 as a potential resource. Of the igneous bodies that 

 have been sampled in the United States, those of 

 syenite and associated pegmatite in the Bearpaw 

 Mountains, Mont., and the Conway Granite in New 

 Hampshire are favorable examples. Those rocks in 

 the Bearpaw Mountains are in relatively small 

 bodies, but they average 0.05 percent UsOg (1 lb per 

 ton), and are estimated to contain a paramarginal 

 resource of about 12,500 tons UaOg. The Conway 

 Granite is exposed over an area of about 300 square 

 miles and contains 0.001-0.003 percent UsOg (0.02- 

 0.06 lb per ton). This body of granite to a depth of 

 1,000 feet (representing almost 50 cubic miles of 

 rock) is estimated to contain about 7I/2 million short 

 tons of UsOg. Hypothetical uranium resources in 

 igneous rocks have not been estimated. 



If bodies of rock like the phosphate deposits, black 

 shales, or igneous rocks are ever seriously consid- 

 ered as possible sources of domestic uranium, it 

 might be possible to develop recovery processes to 

 extract other useful commodities along with urani- 

 um, which might reduce to some extent the unit cost 

 of the uranium recovered. Nevertheless, if signifi- 

 cant quantities of uranium are sought from these 

 sources, vast quantities of rock would have to be 

 mined and treated, which would require much ener- 

 gy and would temporarily disrupt large areas of 

 ground. 



No attempt is made here to evaluate worldwide 

 conditional uranium resources in phosphorites and 

 black shales ; they are known to be very large. 



Hypothetical resource figures are not available for 

 most nations outside the United States. However, in 

 view of the wide occurrence of deposits akin to those 

 in North America, it is postulated that in areas of 

 continental size the uranium resources bear the same 

 relation to the size of the area as the uranium re- 

 sources of North America bear to its area. 



Sea water contains 0.00015-0.0016 ppm uranium. 



