RECOVERY OF POTASH IN THE CEMENT INDUSTRY. 1e¢ 
with a view to preparing concentrated potash salts. . The value of the 
dust as a source of cement material is estimated usually at about 75 
cents per ton. The value of potash in the form of sulphate depends 
on the concentration and varies at normal wholesale prices from about 
70 cents per unit for low-grade material to about 90 cents per unit in 
material containing a minimum of 48 per cent potassium sul- 
phate, or to 95 cents in material containing a minimum of 90 per 
cent potassium sulphate. Thus it is seen that a comparatively low 
percentage of potash in flue dust is sufficient to give it more value 
as a source of potash than as cement material. By separating and 
concentrating the potash occurring in flue dust the price thereof per 
unit is increased, the cost of transportation is reduced, the residue 
becomes available for cement manufacture, and if the process of 
separation involves some such treatment as steaming under pressure, 
the percentage of available potash in the dust of some plants at least 
may be increased considerably. Against these advantages incident 
to the separation of the dust must be balanced the relative cost of 
the operation, which will be dependent on the percentage of potash 
in the dust. The best method of disposing of the dust is thus de-_ 
pendent on a number of factors which will vary with conditions, and 
it thus happens that all of the three procedures referred to for utiliz- 
ing the dust are now being given practical application in plants 
where the dust is being collected by electrical precipitation. 
The work so far done on the recovery of potash from cement plants 
apparently has been limited to plants using the dry process. No 
installation for the electrical recovery of the dust has yet been made 
in plants using the wet process, but it is probable that the electrical 
method would prove just as applicable to plants of this kind as to 
those using the dry process. At the temperature at which the gases 
leave the kilns no precipitation of water would take place, and as long 
as the temperature of the gases is maintained above 100° while pass- 
ing through the treater pipes little condensation of moisture should 
occur. The dust in all probability would be precipitated either in a 
dry state or as a mud or slurry. If precipitated in the form of a 
slurry, no electrode hammering system would then be necessary, for 
the precipitated material would flow down the pipes continuously 
and a concentrated solution of salts would thus be obtained directly 
without the necessity of any special treatment. 
RATIO OF POTASH TO SODA IN CEMENT DUST. 
The extent to which the potash salts in flue dust may be concen- 
trated conveniently is dependent in a large measure on the proportion 
of sodium salts also present in the dust. It was, therefore, thought 
advisable to determine the proportion to be expected for a number of 
plants with a view to gaining some idea as to the quantity of soda that 
might be contained in the dust. The results are given in Table V. 
