ALKALI WASTE: BLAST-FURNACE SLAG. 



349 



fairly typical analysis * of Leblanc-process waste is given below and 

 will serve to show the composition of this material: 



Lime carbonate (CaCO 3 ) 41 .20 



Lime sulphate (CaSO 4 ) 2 . 53 



Lime hydrate (CaH 2 O 2 ) 8.72 



Lime disulphide (CaS 2 ) 5 . 97 



Lime sulphide (CaS) 25 . 79 



Sodium sulphide (Na 2 S) 1 .44 



Magnesium silicate (MgSiO 3 ) 3 . 63 



Phosphates of iron and alumina 8.91 



This material is obviously unfit for use in the manufacture of Port- 

 land cement. Attempts have been made to recover the sulphur con- 

 tained in the waste, but the removal of this constituent is never suffi- 

 ciently perfect to permit the resulting waste to be of use to the cement 

 manufacturer. 



Ammonia-process waste. The waste from ammonia-process works 

 is, on the contrary, a very pure mass of precipitated lime, mostly in the 

 carbonate form, though some lime hydrate is always present. As pyrite 

 is not used in this process, the sulphur in the waste is commonly well 

 within Portland-cement limits. The magnesia content of the waste may 

 or may not be high, according to the character of the limestone that has 

 been used in the process of soda-manufacture. When a pure limestone 

 low in magnesium carbonate has been used, the waste will be low in 

 magnesia and is then a very satisfactory Portland-cement material. The 

 following analyses are representative of the waste obtained at alkali- 

 plants using the ammonia process. 



TABLE 158. 

 ANALYSES OF ALKALI WASTE, AMMONIA PROCESS. 



The analyses given in the above table are of alkali wastes which 

 have at one time or another been used in the manufacture of Portland: 



* Kingzett, C. T. The Alkali Trade, p. 134. 



