RECOVERY OF POTASH IN THE CEMENT INDUSTRY. 13 



to 1 per cent of the raw mix. The salt is added in the solid state and 

 is brought into intimate mixture with the raw mix and coal by being 

 ground with these materials. The quality of the resulting cement 

 is in no sense impaired by the addition of the salt, for it is found that 

 the total alkalies in the clinker when salt is added to the charge are 

 actually less than when no salt is added, due to the fact that the per- 

 centage of the potash is reduced more than the percentage of the soda 

 is increased. By this treatment the percentage of the potash vola- 

 tilized, which at this plant normally runs about 38 per cent, is in- 

 creased to about 65 per cent. Assuming that this percentage vola- 

 tilization (65 per cent) could be attained by chemical or other means 

 in all plants where a lower volatilization normally prevails, then it may 

 be estimated that the recoverable available potash in the cement 

 plants of this country would be increased from 71,000 tons to 101,000 

 tons annually. In making this calculation it is assumed as before 

 that 90 per cent of the total potash volatilized is recovered, but 

 that the additional recoverable potash is all availaole. 



Other processes that have been proposed for bringing about an 

 increase in the volatilization of the potash involve treatment with 

 such reagents as calcium chloride, 1 calcium fluoride, 2 sulphur dioxide, 3 

 and steam. 3 



The method of increasing the volatilization of the potash by use of 

 calcium fluoride as proposed by Huber and Reath 4 has been tested 

 on a commercial scale and is worthy of special mention. In this 

 process the fluorine compound is first added to the argillaceous com- 

 ponent of the cement material in the form of fluorite and in quantity 

 approximately equivalent to the potassium present. This material 

 is then properly proportioned with limestone to give normal Portland- 

 cement raw mixture and burned in a rotary kiln in the usual way. 

 Volatilization of the potash under these conditions largely takes 

 place in the form of the fluoride, which, as it escapes from the kilns, 

 becomes associated with the salts of calcium carried over mechanic- 

 ally in the dust. It thus happens that when the dust is leached with 

 hot water the potash passes into solution as sulphate or carbonate, 

 while the fluorine remains behind as insoluble calcium fluoride. On 

 using the residue as cement material the same fluorine is fed into the 

 furnace again and may thus be repeatedly used in bringing about 

 increased volatilization of the potash. 



1 Herstein, B., J. Ind. Eng. Chem., 3, 426 (1911); Ross, William H., Circ. No. 71, Bureau of Soils; Brown, 

 H. E., U. S. Patents Nos. 1,123,841 and 1,124,238; Ellis, C, U. S. Patent No. 1,186,522; Spackrnan, H. S., 

 and Conwell, E. L., U. S. Patent No. 1,202,327. 



2 Ellis, C, U. S. Patent No. 1,186,522; Huber, A. W., and Reath, E. F., TJ. S. Patents Nos. 1,194,344 

 and 1,219,315; Spackrnan, H. S., and Conwell, E. L., U. S. Patent No. 1,202,327. 



3 Spackrnan, H. S., and Conwell, E. L., U. S. Patent No. 1,202,327. 



4 Loc. cit. 



