RECOVERY OF POTASH IN THE CEMENT INDUSTRY. 19 



plates take the place of the pipes used in later installations as col- 

 lecting electrodes and the gases flow horizontally between the plates in- 

 stead of vertically as is the case where pipes are used. Two kilns were 

 later added to the equipment of the original plant, and to take care 

 of the gases from these kilns the multiple-pipe system was installed. 



In the case of the plate and wire treater a separation of the dust 

 according to the size of the particles is in a measure effected during 

 the process of precipitation, and it thus happens that the fineness 

 of the dust collected and the percentage of potash present in the 

 precipitated dust increase with the distance of the collecting hoppers 

 from the kilns. In the multiple-pipe treater, however, no separation 

 of the dust takes place other than that brought about by deposition 

 of dust in the flues connecting the treater with the kilns. This dust 

 is coarser and contains a lower percentage of potash than the average 

 of that precipitated. 



In the original method used for taking care of the material pre- 

 cipitated at this plant all of the collected dust was burned in one of 

 the kilns connected with the multiple-pipe treater, and the dust 

 there precipitated separately collected. The dust thus recovered 

 on second precipitation showed a marked concentration of potash, 

 which sometimes ran as high as 20 to 23 per cent. This process of 

 concentrating the potash was abandoned later, as it was found that 

 the potassium sulphate in the treater dust was less readily volatilized 

 than the potash in the original mix, and although a high-grade potash 

 material could be obtained in this way the double treatment actually 

 resulted in a loss of potash, due to the comparatively greater per- 

 centage contained in the final clinker. 



In the method now followed for disposing of the collected material 

 the coarse dust which settles in the long connecting flue of the multiple- 

 pipe treater and in the two rows of hoppers nearest the kilns in the 

 plate and wire treater is returned to the kilns for use as cement 

 material. The dust precipitated in the multiple-pipe treater and 

 in the two remaining rows of the plate and wire treater is separately 

 collected and is either disposed of directly for use as a fertilizer or 

 leached with water at a temperature above 85° for the preparation of 

 concentrated potash salts. 1 By the use of feldspar the potash in the 

 raw mix at this plant has recently been increased considerably above 

 the value given in Table I, with corresponding gains in the quantity 

 of potash volatilized and recovered. 



In the plant of the Security Cement and Lime Co. the multiple- 

 pipe system alone is used. In this installation the original flue 

 stacks are still retained, and each serves as part of the connecting 

 flue which conducts the gases from the corresponding kiln or kilns 

 to the treater with which it is connected. By this indirect method 

 of connecting the kilns with the precipitating system the gases before 



i Huber, F. W., and Reatli, F. F., U. S. Patent No. 1,220,989. 



