THE RECOVERY OF POTASH FROM ALUNITE. 7 
The first of these is the use of the material after ignition at 750° to 
800° C. directly as 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 unlikely 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 2 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 metallic 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. Difficulty in obtaining complete extraction of the 
potash in the ignited alunite has been experienced both in the labora- 
tory 1 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 3 consists in roasting alunite with lime 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 gypsum 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 4 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 
i Circular 70, Bureau of Soils, U. S. Dept. Agr. (1912). 
2 Chappell, H. F., U. S. Patent No. 1070324 (1913). 
3 Morgan, Geo. S., U. S. Patent 1161239 (1915). 
* MacDowell, C H., TJ. S. Patent No. 1136549 (1915). 
