ae 
RECOVERY OF POTASH IN THE CEMENT INDUSTRY. 9 
this country be now taken in round numbers as 90,000,000 barrels * 
and if the same average conditions be assumed to prevail in the few 
plants from which no samples were received as was found on an 
average for all other plants, then it may be estimated that the total 
potash (K,O) escaping from all the cement plants in this country 
as at present operated amounts to 86,850 tons annually. 
The process at present most generally considered in connection 
with the recovery of the potash that escapes from cement kilns is 
electrical precipitation. The extent to which the dust may be 
recovered in this way is dependent, assuming proper installation, on 
the voltage used and the linear velocity with which the gases pass 
through the treater pipes. The volume of gases treated being con- 
stant, the degree of precipitation of the dust will be dependent on 
the extent of the installation. With present installations a recovery 
of approximately 99 per cent? of the dust has been obtained. It 
happens, however, that the finest portion of the dust escaping from 
any cement plant contains relatively the highest percentage of potash, 
and a 99 per cent recovery of the dust represents a somewhat less 
efficient recovery of the potash. 
In the plant of the Security Cement and Lime Co., where the Cottrell 
process of electrical precipitation has been installed, it is found that 
under normal working conditions, and with a daily output of 2,500 
barrels, the dust collected in the kiln stacks amounts to 16,000 pounds 
and in the treaters 45,000 pounds every 24 hours. The former con- 
tains on an average 4.5 per cent potash, and the latter, as analyzed in 
this laboratory, 11.4 per cent, making a total of 5,850 pounds of 
potash recovered daily. Asshown in Table I, the potash lost from the 
kilns during the same period amounts to 6,525 pounds. On this basis 
of calculation the potash recovery inthis plant amounts to 90 per cent 
of the total. If this value be accepted as the efficiency of recovery of 
the potash in the most economic installations, then the total recover- 
able potash in the cement plants of this country under present work- 
ing conditions amounts to 78,165 tons annually. 
The potassium compounds occurring in cement dust may be 
divided into three groups, as follows: (1) Those which are readily 
soluble in water; (2) those which are slowly soluble; and (8) those 
which are insoluble. 
The insoluble potash represents the combinations occurring in the 
original silicates of the raw mix carried over mechanically in the dust 
before bemg subjected to a sufficiently high temperature to bring 
about decomposition. The form of combination which is slowly 
soluble in water is supposed to be due to a recombination of the vola- 
1 Burchard, E. F. Loc. cit. 
2 Schmidt, W. A., Paper presented at the meeting of the American Institute of Mining Engineers, 
Globe, Ariz., Sept. 21, 1916. 
103837°—17—Bull. 572——2 
