4 ALUNITE AS A SOUECE OF POTASH. 



The production of potassium sulphate and alum by ignition of 

 alunite and the collection of the evolved oxides of sulphur by ab- 

 sorption in some suitable medium are covered by French patent No. 

 419854. 



In this patent, however, it is stated that the decomposition should 

 not be carried to the end, but that the ignited residue should contain 

 both potash alum and potassium sulphate, a separation of which can 

 be afterwards made by lixiviating the residue and crystallizing the 

 solution thus obtained. Although no reason is given why the decom- 

 position should not be carried to an end, it is probably on account of 

 the residue, which it is claimed after lixiviation is an excellent arti- 

 ficial bauxite. The average price of natural bauxite in 1910, accord- 

 ing to the United States Geological Survey, was $4.89 per ton. 



Unless the alunite used is very pure it is doubtful if the leaching 

 of the potassium sulphate is economical. The experience of the 

 author has been that an enormous volume of hot water is required to 

 free entirely the ignited residue from soluble salts. The subsequent 

 evaporation of this water is both tedious and expensive. Experi- 

 ments with larger samples of alunite indicate that considerable dif- 

 ficulty would be encountered in leaching. A recovery of 83 per cent 

 of the potash present was obtained. 



Pure alunite, according to Dana, has the following composition : l 



Per cent. 



SO 3 38. 60 



AU), 37.00 



K 2 O 11.40 



H 2 O 13.00 



On th.e basis of; this analysis the amount and value of the products 

 obtained from 1 'ton , (2,000 pounds) of pure alunite, would be as 

 follows: - "^ :--', 



Products from -1 ton (2.000 pounds) pure alnnite: 



Potash (K 2 O), 220 pounds, at 4 cents per pound $8. 80 



Sulphuric acid (52B), 1,090 pounds, at $6 per ton 3.27 



Alumina, 740 pounds, at $4.89 per ton 1. 81 



13.88 



From an economic standpoint it would seem more practical to use 

 the ignited alunite (free from soluble aluminum compounds) 

 directly as a fertilizer either alone or in mixed goods, since the ex- 

 pense of separating the soluble salts from the alumina would prob- 

 ably more than counterbalance the value of the alumina obtained. 

 The percentage of potash in the ignited residue is considerably 

 greater than in kainit, our chief source of soluble potash. 



1 See also Schaller's analyses, Bui. 511, U. S. G. S., p. 8. 

 [Clr. 70] 



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