PHOSPHATE ROCK: UTILIZATION AS FERTILIZER. 15 



practicable to manufacture the product by mixing the phosphate 

 rock with the molten slag as the latter flows from the furnace. The 

 heat of the slag could thus be utilized. 



The fertilizer value of basic (phosphatic) slag is unquestioned, 

 and it would be practicable to produce large quantities of this 

 material by using phosphatic limestone to smelt siliceous iron ores, 

 but it would be very difficult to overcome the prejudice against using 

 a phosphorus-bearing substance in smelting operations when the 

 chief aim is to eliminate phosphorus from the metal product. 



PROCESSES IN WHICH THE PHOSPHORUS OR PHOSPHORIC ACID IS 



VOLATILIZED. 



Processes under this head have been exciting considerable interest 

 in recent years. They are all based on the method long in use for 

 the manufacture of phosphorus and require a high temperature and 

 a furnace which will resist both the temperature and the corrosive 

 effect of the volatile products formed. The main advantage of the 

 processes listed in Table VII is that comparatively pure concentrated 

 phosphoric acid can be obtained from rather impure raw materials. 



The first recorded American process for obtaining phosphoric 

 acid in this way is that of Giles and Shearer. 1 Their process of 

 separating phosphoric acid from its impurities consists in passing a 

 current of steam over the acid heated to redness. The distillate 

 condensed and collected in some suitable vessel consists of relatively 

 pure phosphoric acid. 



In 1907 Landis 2 described a process for producing phosphoric 

 acid and phosphorus from phosphate rock, which consists in mixing 

 phosphate rock, sand, or a silicate and coke with some binding 

 material, and molding the mixture into briquettes. The briquettes 

 are subsequently placed in an electric furnace and heated. The 

 inventor claims that by this method a more even distribution of the 

 heat is obtained, excessive temperatures can be avoided, and less 

 dust and impurities are carried over with the volatilized phosphoric 

 acid. 



The methods of Levi, 3 Washburn, 4 and Haff 5 are three of the more 

 recent processes for the production of phosphoric acid by volatiliza- 

 tion. Described in brief, they are as follows: 



Levi heats a mixture of phosphate rock and silica or silicate in an 

 electric furnace, claiming that the following reaction takes place: 



Ca3(P0 4 ) 2 +3Si0 2 =P 2 6 +3CaSi0 3 . 



The phosphoric anhydride which is volatilized is then absorbed in 

 water, producing phosphoric acid (IT., PC),,), and the fused calcium 



1 Cnlted States Patent No. 3984.28 (1888). < United States Patents Nos. 1047864 (1912); 1100039 (19U). 

 * United Btatei Paten) I o 1907] • I olted Statee Patent No. 1084866(1914). 



•United Htatw Patent No. 984769 (1912). 



