Hex Chrome Reduction
Hexavalent Chrome is a contaminant in rinse water that must be reduced to trivalent chrome and removed after precipitation. This reduction can be done 2 ways:
1). While holding the pH at 2.0- 2.5 with sulfuric acid , bisulfite (sodium, calcium or meta) needs to be added to reduce the ORP value by a shift of 50mV. Once this change in ORP value is noted this indicates the reaction is complete. This change happens quickly so the pH of the water should be held tightly so as not to mistake a rise in pH for the completion of the reduction reaction. One this drop in ORP has occurred the color will also change to blue from orange and the pH can then be adjusted up using caustic soda to 8.5-8.8 for best removal of the trivalent chrome. Hubbard-Hall has several products for easy chrome reduction:
2). If you are at a pH > than 2.5 and don’t want to add acid, reduction of hexavalent chrome can be done by the addition of Aquapure™ I-300 wastewater treatment chemicals. Typical additions are 1-3 mls/gallon of rinses contaminated with hexavalent chrome but may require more. Jar testing should be done to determine the best dosing.
In all cases, water needs to meet local, state and federal guidelines for chrome removal.
|Aquapure™ HQ||An excellent, all-purpose reducing agent used in the classic sense to reduce hexavalent chrome to trivalent.|
|Aquapure™ I-300||An inexpensive blended liquid coagulant/ metal precipitant. Will reduce hex chrome as well as other divalent metals.|