Regeneration of ion exchangers for removing hardness of water - by treating with sodium chloride soln. then with chelating agent to remove alkaline earth metal ions

摘要

Regeneration of ion exchangers is effected by (a) treating the exchanger with a NaCl soln. to restore it to Na form, and (b) flushing the exchanger with a soln. of a chelating agent (I) to remove any alkaline earth metal ions introduced in step (a). (I) is an alkali metal salt of a carboxylic acid with chelating properties. Pref. step (b) is effected with a soln. contg. 0.2-5 (esp. 0.2-1) wt.% of an alkali metal (esp. Na) salt of nitrilotriacetic acid (NTA) or EDTA. The soln. has a pH above 5. USE/ADVANTAGE - The process may be applied to ion exchangers used for removing hardness ions from water used in heat exchangers and low-pressure steam boilers. The process uses reduced amts. of chemicals compared with processes in which the regeneration soln. is treated to remove alkaline earth metal ion