THE EECOVEEY OF POTASH FEOM ALUNITE. 9 



author states that this converts the alumina into aluminum fluoride, 

 the potassium remaining as sulphate. The product is then leached, 

 the potassium dissolving as sulphate, and the aluminum remaining 

 in the residue in large part as fluoride. Considerable calcium sul- 

 phate remains with the aluminum fluoride, which might necessitate 

 changes in the standard process for the electrolytic recovery of 

 aluminum. 



TEMPERATURE OF IGNITION AND ITS EFFECT ON THE SUBSEQUENT 

 LEACHING OF ALUNITE. 



Of the methods so far proposed for the production of potash from 

 alunite, those which depend on simple ignition and subsequent ex- 

 traction of the soluble potash with water appear to the writers most 

 attractive. 



The following investigation was conducted for the purpose of de- 

 determining the best conditions under which a complete extraction 

 of the potash could be made from impure as well as the purer grades 

 of alunite, with due regard to the production of a salable by-product. 

 The investigation involved the study of the effect of ignition at vari- 

 ous temperatures, as well as the influence of fineness of division on 

 the solubility, or, more correctly speaking, the ease with which the 

 mineral yields its potash to hot water. 



Chappell/ in discussing the ignition of and subsequent extraction 

 of potash from alunite, states that the temperature may be carried * 

 over 1,000° C. without causing the formation of potassium aluminate, 

 and recommends a temperature of from 800° to 1,000° C. for alunites 

 containing from 1 to 2 per cent of silica. The experience of tlfe 

 writers has been, as shown below, that in igniting alunite containing 

 even small quantities of silica, 800° C. should be the maximum 

 temperature allowed in the furnace. 



Eleven samples of light-colored alunite from the deposits north 

 of Marysvale, Utah, were employed in these experiments. Most of 

 the samples were ground to pass a 100-mesh sieve, though it was later 

 shown that this was probably unnecessary. The material ranged in 

 potash content from 3.48 to 9.61 per cent and in silica from 1.67 to 

 39.93 per cent. 



. The potash content of the samples was determined by the J. Law- 

 rence Smith method,^ and silica and alumina were also determined in 

 all the samples. The results of these analyses are given in Table I. 



> U. 8. Patent No. 1070324 (1913). 



2 In order to avoid an excess of sulphates, the samples after being weighed out were ignited at a bright 

 red heat before mixing with the ammonium chloride-calcium carbonate mixture. 



