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Dust from Cement Works. A.W. STOCKETT (U. S. Bureau of Mines).--The first cement plant to recover potash from the kiln dust was that of the Riverside Portland Cement Company, in California. Owing to litigation with near-by fruit growers who claimed that the fine dust escaping from the kilns was causing damage to the fruit trees, the company was compelled to install an electrical dust-precipitating plant to abate the alleged nuisance. Analysis of the dust thus collected showed that it contained about IO per cent. K20. The dust collector was completed early in 1913 and has been continuously and successfully in use ever since. What was originally considered an additional expense in the manufaeture of cement has proved to be a highly profitable by-product.
Another plant is successfully using the same method at Security, Md., and both electrical precipitation and other methods of collecting dust are being used at different plants. A point in favor of dust collection is that no change in present methods of manufacturing cement is involved, and at one plant the installation has led to a reduction .of IO per cent. in fuel consumption, owing to the more careful attention required in burning the cement.
An investigation recently completed by the Bureau of Soils indicated that the probable maximum amount of potash that might be recovered from all the cement works in the country would be lOO,OOO tons of K20 per year. It is not likely that dust-collecting plants will ever be installed at all cement works, but it seems reasonable to expect that the amount of K20 to be derived from this source should reach 5o,ooo tons a year, or 2o per cent..of the total normal requirements. Probably this amount could be increased somewhat by using, where available, rock containing more K20 in the raw mix.
An objection raised to cement-kiln dust as a source of potash in manufacturing fertilizers is that if used in large quantities the lime content will cause reversion of the soluble phosphoric acid in the phosphate and loss of the ammonia in ammonium sulphate. The K20 content of cement-kiln dust is also too low to permit its use as the only source of potash in a fertilizer that is to contain more than 3 per cent. of K20. However, these objections can easily be overcome, and some potassium sulphate containing 4oper cent. of K2.O is now being marketed by one of the cement works.
Published figures on the cost of production show that, allowing for the amortization and interest on investment, potash can be produced by the cement companies at 3 ยฐ to 5 ยฐ cents a unit of K20, which will enable them to compete successfully with the German salts even at pre-war prices.
Thus the cement industry, especially in view of its geographical situation, seems one of the most p r.omising sources of a permanent American supply of potash, and the Government should offer every possible encouragement to install plants for the recovery of potash, especially in cement works east of the Mississippi, as more than 9 ยฐ per cent of the comm.ercial fertilizer used in the United States is consumed in that area.
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