Method for selectively removing chromates

Abstract

Removal of chromate ions from water containing a large amount of total dissolved solids by contacting the water with an acidified weakly basic anion exchange resin, preferably in .[.microporous.]. .Iadd.macroporous .Iaddend.form, to selectively remove chromates from the water.

I claim as my invention: 
     
       1. The method of selectively removing chromate ions from water containing .[.a large amount.]. .Iadd.at least 1,000 parts per million .Iaddend.of total dissolved solids which comprises .Iadd.adjusting the pH of the water being treated to a value from about 3.0 to about 5.0, .Iaddend.acidifying a weakly basic anion exchange resin .Iadd.in the macroporous form .Iaddend.and thereafter contacting said water with the acidified resin to cause selective removal of chromate ions from said water. .[.2. The method of claim 1 in which said anion exchange resin is in macroporous form..]. .[.3. The method of claim 2 in which said resin has pore diameters in the range from about 10 to 100 Angstroms..]. .[.4. The method of claim 1 in which the pH of the water being treated is adjusted to a value of from 3.0 to 5.0 before contacting the same with said resin..]. .[.5. The method of claim 1 in which the pH of the water being treated is adjusted to a value 
     
     
        of from 3.0 to 3.5..]. 6. The method of claim 1 in which the acidification 
     
     
        of the resin consists in treating said resin with sulfuric acid. 7. The method of claim 1 in which the acidification of the resin consists in 
     
     
        treating said resin with hydrochloric acid. 8. The method of claim 1 in 
     
     
        which said resin is a polystyrene-divinyl benzene amine resin. .Iadd.9.  A method for selectively removing chromate ions from circulating water systems which have been treated with chromate corrosion inhibitors, which comprises: discharging a portion of the water from the system when a level of at least 1,000 parts per million total dissolved solids is present, to obtain a blow-down and adjusting the pH of said blow-down to a value of about 3.0 to about 5.0;   acidifying a macroporous weakly basic anion exchange resin; and   thereafter contacting the blow-down with said resin to selectively remove the chromate from the blow-down to obtain a blow-down substantially free   
     
     
        from chromate ions. .Iaddend. .Iadd.10.  The method of claim 9 wherein the pH of the blow-down is adjusted from about 3.0 to about 3.5. .Iaddend. 
     
     
        .Iadd.11.  The method of claim 9 wherein said resin is treated with a dilute mineral acid to acidify it prior to contact with the blow-down. .Iaddend. .Iadd. 12. The method of claim 11 wherein the dilute mineral acid is sulfuric acid. .Iaddend..Iadd. 13. The method of claim 11 wherein 
     
     
        the dilute mineral acid is hydrochloric acid. .Iaddend. .Iadd.14.  The method of claim 11 further including treating the resin, after contact with the blow-down, with an alkali to regenerate the resin by removing the 
     
     
        chromate ions. .Iaddend. .Iadd.15.  The method of claim 11 in which said resin is a polystyrene-divinyl benzene amine resin. .Iaddend.