Sodium aluminium silicate exchangers

When hard water is passed through a bed consisting of zeolites, which are synthetic material systems composed of complex sodium, aluminium and silicate salts (Na Z), the calcium and magnesium ions are exchanged. The displacing reactions for temporary hardness are ... 

Although many soil scientists had considered the possible mechanisms which soils employ for the retention [fixation] of phosphorus, it remained for Haseman et al. (1950) to demonstrate that phosphorus could — and in experimental situations did — replace the silicon of micas and clay minerals in order to form crystalline hydrous aluminium phosphates of sodium, ammonium and potassium. Prior to experimentation by this group, associated with the laboratories of the Tennessee Valley Authority (TVA), most authors attributed the retention of phosphorus by soils to combination with calcium to produce fairly insoluble minerals to adsorptive, exchangeable combination with silicate minerals and to formation of phosphates of iron... 

Silica-Aluminas. Amorphous. These are generally considered to be cationic exchangers owing to their protonic character. The adsorption character may also vary depending upon whether they were prepared by acid side precipitation (e.g., by adding sodium silicate to aluminium sulphate in which case the alumina tends to precipitate last giving more of an alumina type of surface) or whether conversely if prepared by a base side precipitate (in which case the surface tends towards that of silica). There is no published information that differentiates what effects, if any, this may have. 

This method depends upon the use of zeolite or of base-exchange co,m-plexes. The zeolites are hydrated silicates of sodium and aluminium with a... 

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