Abstract
Before taking up the actual subject of the present work, it is well to point out what is meant by an exchange of ions and to define an ion exchanger. An exchange of ions is a chemical reaction which takes place in a heterogeneous medium; when a solid heteropolar substance is immersed in a liquid, usually aqueous, ions belonging to the solid pass into the liquid in exchange for ions of the same polarity in solution in the liquid, and these dissolved ions thereby become fixed on the solid substance in place of the ions which the latter has just given up. As an example, minerals of the type of zeolite (green sand, harmatome, chabasie, etc.) can exchange their alkaline-earth metal ions, i.e., their cations, for sodium ions in an aqueous solution of sea salt which wets them or penetrates through them, and this phenomenon is reversible. Such a reaction is the basis of the detartarizing purification of industrial waters containing lime. Likewise the heteropolarity of exchangers sometimes renders their anions mobile, i.e., some substances give up their anions to liquids which wet them in exhange for the anions of these liquids, which thereby replace the anions liberated from the solids.
PRODUCTIVITY IMPROVEMENT OF CASTINGS, SWITCHING TO SHELL MOULD PROCESS FROM GREEN SAND MOULD PROCESS
