THALLIUM 



635 



Table 131. — World reserves and potential resources of 

 thallium, in short tons 



Reserves: Identified deposits from which minerals 

 profitably with existing technology and under preser 

 tions. 



rces: Identified mineral deposits not profitably recover- 



isting technology and economic conditions, and undis- 



al deposits whether of recoverable or subeconomic grade. 



Specific, identified mineral deposits that may or may 



aluated as to extent and grade, and whose contained minerals 



may not be profitably recoverable with existing technology 



ditions. 



Hypothetical resources: Undiscovered mineral deposits, whether of re- 

 covei-ab'.e or subeconomic grade, that are geologically predictable as 

 existing in known districts . 



Reserves 



Potential 

 able w] 

 covered 



Identified 

 not be < 

 may or 



resources contained in coal ash being 119,000 tons. 

 The coal ash, however, is a highly dispersed source 

 and probably most thallium will continue to be ob- 

 tained as a byproduct from zinc ores. No published 

 data could be found on the recovery factors attained 

 in the processing of thallium from the flue dust and 

 residues of base-metal smelting. Previous authors 

 have inferred the recovery factors to be low. Con- 

 verting the total 1968 U.S. smelter production of 

 zinc to sulfide, calculating the hypothetical thallium 

 amount this sulfide should contain, and then com- 

 paring this value with the estimated amount of 

 thallium actually extracted in 1968, produces a 

 recovery factor of approximately 75 percent. This is 

 considered a realistic value and a minimum if the 

 assumed average thallium content of zinc sulfide 

 at 2.2 ppm is correct. It is certainly not low, as 

 previously stated. 



U.S. recoverable thallium reserves from zinc sul- 

 fides, employing present technology, are estimated 

 at 124 tons, and from all sulfides, 200 tons. At a 

 domestic consumption rate of 3.25 tons annually, 

 the supply is sufficient for 38 and 62 years respec- 

 tively. The present supply of thallium-bearing zinc 

 ores slightly exceeds the requirements for thallium 

 metal, and unprocessed residues containing thallium 



are being stockpiled by the industry. Any unfore- 

 seen increase in the demand for thallium, however, 

 would command that alternative sources other than 

 zinc sulfides be considered. In this respect the vast 

 potential of coal ash and sea floor manganese nodules 

 is important. 



The United States refines approximately 20 per- 

 cent of the world's output of thallium metal to meet 

 domestic requirements. This percentage must surely 

 decrease with continuation of the current trend 

 toward closing of domestic smelters and expansion 

 of zinc-smelting facilities in Canada, Mexico, Aus- 

 tralia, and Japan, together with the capability of 

 extracting thallium as a byproduct. 



Total world reserves of thallium contained in zinc 

 sulfide reserves are estimated at 869 tons, of which 

 650 tons is recoverable with a 75 percent recovery 

 factor. At an estimated world consumption rate of 

 15 tons annually, the supply is sufficient for 43 years. 

 Projected world reserves of thallium from all sul- 

 fide sources, 1,390 tons, will be exhausted in 70 

 years under the same conditions. Total world thal- 

 lium resources contained in coal ash from identified 

 coal resources are estimated at 715,000 tons, and in 

 sea-floor manganese nodules a massive 9.9 million 

 tons. Increased discovery of sulfide deposits will pro- 

 portionately increase thallium reserves, and potential 

 resources are very high, particularly in relatively 

 unexplored areas. In addition, the inclusion as specu- 

 lative resources of the thallium contained in peg- 

 matitic feldspars and micas, which could be recov- 

 ered should the need arise, produces vast potential 

 resources. 



PROBLEMS FOR RESEARCH 



Research is needed to improve our quantitative 

 understanding of thallium distribution in minerals 

 and rocks. Alternate sources for the recovery of 

 thallium metal, such as sea-floor manganese nodules 

 and coal ash, must be delineated to cover anticipated 

 and sudden unforeseen future demands. 



Although thallium is widely distributed in the 

 earth's crust, it is concentrated in, or has an affinity 

 for, certain mineral species. There is evidence to 

 suggest that its concentration in these minerals 

 is temperature and pressure controlled. Thus, its 

 variable abundance in specific index minerals must 

 be studied and modeled over known mineralized 

 deposits and rock suites of genetically different 

 origins. It may then be possible to evaluate the po- 

 tential of mineralized areas for other commodities, 

 on the basis of the distribution and amount of 

 thallium that is present. 



