50 
The equation for this reaction is:— 
K 2 S0 4 • 3H0AIS0 4 - 3A1 (OH) 3 -f 12NaOH — > K 8 S0 4 + 3Na 2 S0 4 
3Na o Alo0 
2 4 
1 2H a O 
The whole of the products of this reaction are water soluble. The 
results show that alunite is readily dissolved by warm dilute solu- 
tions of caustic alkalis, a process which provides a most satisfactory 
method for getting* the mineral into solution. 
The effective agent in this reaction is the high concentration of 
hydroxyl ion which produces aluminate ion at the expense of the 
basic aluminium salt. 
A. J. Robertson’s experiments on Kalgoorlie nalroalunite, made 
in the Geological Survey Laboratory in 1915, showed that this 
mineral passed wholly into solution on warming for 20 minutes 
with 5 per cent. KOH solution* 
SOLUBILITY IN SODIUM CARBONATE. 
No references were obtained showing the effect of sodium car- 
bonate solutions on alunite. Knowing that caustic alkalis exert a 
very rapid solvent effect, and that sodium carbonate hydrolyses freely 
in water, experiments were carried out with a view to determining 
the solubility of alunite in sodium carbonate. 
The solution used in these experiments contained the same 
amount of sodium as that in the case of the caustic', soda tests. The 
temperature and time of experiment were also the same, so that 
the results as to rate of solubility would be comparable. The material 
also was that used in the caustic soda tests and was treated in ex- 
actly similar manner. 
1,325 per 
cent. Na.,CO 
Solid ion. 
Alunite. 
Sodium in 
Solution. Tempera- 
Time. 
Alunite 
Solution. 
ture. 
dissolved. 
ec. 
o 
/ * 
0 • 5gm. 
0-2875 
50 20° C. 
2 hrs. 
0 13 
0*5gm. 
0-2875 
50 20° C. 
4 hrs. 
0-35 
0* 5gm. 
0-2875 
50 91° C. 
2 hrs. 
43-85 
6.625 per 
cent. Na,C0 3 
Solution. 
0- 5gm. 
1 4375 
50 20° C. 
2 hrs. 
1*09 
0 • 5gm. 
1 4375 
50 91° C. 
2 hrs. 
71*60 
It will be 
noted that Na, 
CO, has very little effect on 
alunite in the 
cold, but 
the attack is < 
c o n si d er a b 1 y increase d 
in warm solutions. 
From tli is 
it is apparent 
the solubility is due 
to the 
hydroxyl ions 
present, the Na 2 00 liydi 
'olysing to form NaO 
11 and 
ILCO,'. The 
reaction may be expresse< 
1 thus : 
Na 2 C0 3 -f- HOH = NaHC0 3 + NaOH = 2Na + + (HC0 3 ) -f (OH)“ 
NaHC0 3 + HOH = NaOH -f H 2 CO a = Na + + (OH) -f- H 2 C0 3 
