SECTION III. METAL INDUSTRY 

 BY-PRODUCTS 



Blast -Furnace Dust. The iron industry has, in very 

 recent years, provided a valuable by-product containing 

 much potash. Although the percentage of potassium 

 contained in the compounds charged into the blast furnace 

 is comparatively small, yet an important concentration 

 occurs in the process. In the modern blast furnace, iron- 

 stone, limestone and hard coke are charged at intervals, 

 through a closed hopper, into a tall vertical blast furnace. 

 The blast produces such a high temperature that some of the 

 potassium compounds present are volatilized and carried 

 forward into the flues. For the purpose of economizing 

 heat, the waste flue gases are passed through heat-inter- 

 changing ovens for the purpose of heating the blast of air, 

 and then pass on to boilers for raising steam. During the 

 passage of the blast-furnace gases through the tubes in ovens 

 or boilers, a fine dust is deposited, which has been found 

 to contain potash in forms easy to concentrate. The potash 

 content of these flue dusts is very variable, the large amount 

 of black dust deposited in the first dust catcher being compar- 

 atively poor in potash, but the rather reddish dust deposited 

 in the stoves and boilers contains a larger amount, and the 

 very small yield of light-coloured dust at the base of the 

 chimney stacks is the richest of all. The English type of 

 furnace, fed with coke, produces a larger amount of potash 

 than the coal-fed furnaces used in Scotland. When the 

 blast-furnace gases are cooled by washing with water, much 

 potash is lost in the washing waters since nearly all the potash 

 present in these dusts is soluble in water. Owing to the 

 extremely fine division in which the particles of potash 

 occur, attempts have been made to remove the dust either 



