Process for selective removal and recovery of chromates from water

Claim 2

The process of claim 1 wherein the rate of upflow of said pH-adjusted water through said bed is maintained in the range of about 1 to 50 gal./min./ft2 of cross-sectional area of said bed.

Claim 3

The process of claim 1 wherein regeneration is effected stepwise by passing said alkaline aqueous solution downwardly through said bed in a plurality of successive operations.

Claim 4

The process of claim 1 wherein regeneration with said alkaline aqueous solution is followed directly by a rinse step wherein an acidic solution at pH in the range of about -1 to 5.5 is fed downwardly through said bed essentially in an amount sufficient to satisfy the acid demand of said resin.

Claim 5

The process of claim 1 wherein said alkaline aqueous solution comprises essentially chromate-free water containing less than about 500 ppm dissolved solids and having a pH in the range of 9 to 11.

Claim 6

The process of claim 1 wherein the water passed upwardly through said bed of resin is passed through another bed of basic anion-exchange resin.

Claim 7

The method of claim 1 wherein said initial leakage of chromate ions is below 2 ppm.

Claim 8

The method of claim 1 wherein the concentration of said regenerant ions in said alkaline aqueous solution is between about 200 and 150,000 ppm.

Claim 9

An improved process for maintaining a recirculating-water system in a substantially corrosion-free condition, comprising: a. treating said system with a chromate-based corrosion-inhibiting compound to maintain a chromate concentration in the range of about 1 to 1,000 ppm; b. maintaining the pH within the range of about 6 to 6.5; c. measuring the buildup of dissolved solids in said system as said system is operated; d. withdrawing a part of said water from said system when said buildup reaches a selected value; e. adjusting the pH of the withdrawn water to a value within the range of about 3 to 5.5; f. passing the pH-adjusted withdrawn water upwardly through a bed of a strongly basic anion-exchange resin to selectively remove chromates therefrom and retain them on said resin to form an essentially chromate-free fraction, said pH-adjusted withdrawn water being passed upwardly at a rate effecting expansion of said bed as a whole, thereby re-distributing resin particles thereof by gravitational settling and establishing from the bottom to the top of said bed a decreasing concentration gradient of chromate; g. discarding part of said essentially chromate-free fraction; h. regenerating the chromate-retaining resin by passing downwardly through said bed an alkaline aqueous solution containing regenerant anions in a concentration between about 200 and 150,000 ppm; i. collecting the chromate removed from the chromate-retaining resin by the regenerating solution; and j. returning the collected chromate to the system for re-use.