• THE RECOVERY OP POTASH FROM ALUNITE. 7 



The first of these is the use of the material after ignition at 750° to 

 800° C. directly ais a fertilizer without effecting a separation of the 

 soluble potash salt. It has been pointed out by one of the writers ^ 

 that the material after ignition compares very favorably in regard 

 to its potash content with "manure salt" or other low-grade potash 

 carriers heretofore imported from Germany. If produced in the 

 West, however, it is unhkely that such a low-grade product could 

 stand the cost of the long rail haul necessary to bring it to the fer- 

 tilizer market. Moreover, no salable by-product would be obtained, 

 except perhaps sulphuric acid, which would require expensive equip- 

 ment to collect and which under normal conditions has a very restricted 

 market in the West. 



The second scheme ^ is to ignite the material at 800° to 1,000° C. 

 till the sulphate of aluminum is decomposed and then leach the residue 

 with hot water to dissolve out the potassium sulphate, which is 

 later recovered by evaporation of the solution. In the case of the 

 purer alunites the residue consists largely of aluminum oxide suitable 

 for the manufacture of metalhc aluminum. This method has 

 attracted considerable attention, and it is understood that a procedure 

 similar to, if not identical with, it is being practiced in the western 

 alunite fields, DiSiculty in obtaining complete extraction of the 

 potash in the ignited alunite has been experienced both in the labora- 

 tory ^ and on a commercial scale, and it was partly with a view to 

 studying the causes of this incomplete recovery of the potash that 

 the experiments described further on were conducted. 



The third process ^ consists in roasting alunite with hme at 

 1,200° to 1,800° F., producing thereby sulphate of lime (gypsum) 

 and potassium sulphate, and rendering the alumina insoluble. The 

 potassium sulphate is then extracted with water. The main purpose 

 of this process is to produce potassium sulphate without causing the 

 evolution of objectionable or injurious fumes of sulphur dioxide and 

 trioxide. 



The cost of the lime required, the conversion of the sulphuric acid 

 into a relatively valueless form, and finally the difficulty of sepa- 

 rating the resulting gypsmn from both the potash and the alumina, 

 render this process of rather doubtful value. As far as is known 

 this process is not at present being employed for the manufacture 

 of potash from alunite. 



The fourth * process consists in first calcining the alunite to drive 

 off the oxides of sulphur and the water and then increasing the 

 temperature to between 1,100° and 1,600° C, thus volatilizing the 



' Circular 70, nureau of Roils, U. S. Dept. Agr. (1912). 

 J Chappell, U. F., U. 8. Patent No. 1070.324 (1913). 

 ' Morgan, Geo. 8., U. 8. Patent 1101239 ( 191.";). 

 * MacDowell, C. 11., U. 8. Patent No. 113G549 (191S). 



