234 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1923 



iron salts of columbic and tantalic acids. Usually a part of the iron 

 is replaced by manganese, and small amounts of titanium, tin, and 

 tungsten are almost always present. To lesser extent it occurs with 

 rare earths in samarskite and other minerals. 



For the production of metallic tantalum, tantalite is the most 

 desirable ore and should contain at least 60 per cent of the oxide 

 and only a few per cent of columbium oxide. 



The first step involved in the production of metallic tantalum is the 

 extraction of pure compounds of tantalum from the mineral tantalite. 

 This involves the separation of the columbium which may be present. 



There are a number of methods available with which to attack 

 this ore. As the most suitable method for the separation of tantalum 

 from columbium is through the difference in solubility of the potas- 

 sium double fluorides, the method employed should be directed to- 

 ward the easiest method of production of these compounds. The 

 pulverized ore may be fused with potassium bisulphate. On leach- 

 ing this fusion, the acids of tantalum and columbium remain insolu- 

 ble and can be dissolved in hydrofluoric acid and treated with potas- 

 sium fluoride, or the mineral may be fused with acid ammonium 

 fluoride and the tantalum precipitated from the solution of the melt 

 by means of potassium fluoride. 



A method which is more easily carried out on a large scale is the 

 fusion of the finely pulverized ore with potassium hydroxide, which 

 converts the tantalum and columbium into soluble columbates and 

 tantalates. The filtered solution containing these salts may be 

 treated with a mineral acid, preferably nitric or sulphuric acid, 

 which precipitates the insoluble acids of tantalum and columbium. 

 After washing, these are dissolved in hydrofluoric acid and the solu- 

 tion is treated with sufficient potassium fluoride to produce the 

 double fluorides K 2 TaF 7 and K 2 CbOF 5 H 2 0. These two salts are 

 readily separated by crystallization, inasmuch as the columbium salt 

 is about 12 times as soluble as the tantalum double fluoride. 



The oxide of tantalum can be produced from this double fluoride 

 by treating the solution of the salt with ammonia, and precipitating 

 the acid, which can be washed and then ignited to oxide. 



PRODUCTION OF METALLIC TANTALUM 



It is perfectly evident at the present time that the early attempts 

 to produce metallic tantalum, involving such methods as the reduc- 

 tion of the oxide with carbon in an electric furnace, the reduction 

 of tantalum oxide with aluminum by the Thermit process, or the 

 reduction of the oxide by means of misch metal (mixed cerium earth 

 metal), could not have given a product characterized by any degree 

 of purity, and most certainly a metal which could not be subjected 

 to any mechanical working. 



