Analyses of marls and clays used iu ccuicnt plants. 



Alkali Waste. 







A very large amount of waste material results from the pro- 

 cess used at alkali works in the manufacture of caustic soda. 

 Tihis waste material is largely a precipitated form of calcium 

 carbonate, and if it is sufficiently free from impurities, it fur- 

 nishes a cheap source of lime for use in Portland cement manu- 

 facture. 



The availability of alkali waste for this purpose depends 

 largely on what process was used at the alkali plant. Leblanc 

 process waste, for example, carries a very large percentage of 

 sulphidies, which prevents its use as a Portland cement material. 

 Waste resulting from the use of the ammonia process, on the 

 other hand, is usually a very pure mass of lime, mostly in the 

 formi of carbonate, though a little lime hydrate is commonly 

 also present. As pyrite is not used in the ammonia process, its 

 waste is usually low enough in sulphur to be used as a cement 

 material. The waste may carry a low or a very high percent- 

 age of magnesia, according to the character of the limestone 

 that has been used. When a low-magnesia limestone has been 

 used, the resulting was te is a very satisfactory Portland' ce- 

 ment material. 



The following analyses are fairly representative of the waste 

 obtained at alkali plants using the ammonia process. 



