Trivalent Chromium Reduction
Q. I am trying to reduce the trivalent chrome in a hexavalent chrome tank. There was a method described in one of the directories a few years ago that I used, and it worked, but now I can't find the book it was in. I used copper rods hung in the tank, but, if I remember correctly, the length and placement of the rods was critical, as was the amount of amps used. A.R.K.
A. You are referring to the standard method of reducing the amount of trivalent chrome in a chromium plating bath. Here is the procedure as given in a classic book on hard chromium plating, the “Handbook of Hard Chromium Plating” by Robert K. Guffie. Copies of this book are available on Amazon, but at a rather hefty price.
“Trivalent chromium can be removed by electrolyzing the solution while using high anode area and low cathode area. Theoretically, an anode to cathode ratio of 27:1 is optimum. I usually try to get at least a 10:1 ratio and electrolyze at 6 V. If the 27:1 ratio can be obtained, 1 ounce per gallon of trivalent chromium can be electrolyzed to trace amounts in about 12 hours at 130°F. At 10:1 ratio and 130°F, it will take about 24 hours to reduce the trivalent chromium to a trace.”
An anion/cation exchange system also can be used to reduce the trivalent chromium.