plating, anodizing, & finishing Q&As since 1989
Electrowinning of Chrome Questions
My company is in the process of developing a novel wastewater treatment system capable of removing and concentrating heavy metals from dilute wastewater streams (less than 1ppm). The process yields equivalent results to ion exchange method but with higher through put and at a fraction of the cost. Our first product is targeted at hex chrome.
Our problem: We would like to be able to electrowin the chrome from our concentrated solution. However, I have not been able to find any literature on a method to do this after searching the current literature and web sites. All I have found are statements claiming that electrowinning is inefficient for hex chrome. I am not too concerned with rates of deposition, more with is it possible and if so what concentrations of chrome are need. Composition of the chromate solution can be controlled through our process (sulfate content, pH, etc.) if this helps. Any information would be nice, but a brief overview of the key features of the process for chrome would be very helpful.Robert W [last name deleted for privacy by Editor]
Worcester MA USA
Well, a typical chrome plating tank is 33 oz/gal as chromic acid. It would plate at less than 1/33 of the same rate at 1 oz per gal. A lot of this can be overcome by extremely close anode to cathode spaceing along with huge anodes and cathodes and high voltage. Flow between the anode and cathode would need to be turbulent to avoid "trees" shorting it out and also to rapidly replace the depleted solution in the "barrier layer". It would not be cost effective in most cases. I think that pH control would be a nightmare since you are well above the hydrogen overvoltage potential and have a very dilute solution.James Watts
- Navarre, Florida
I don't want to discourage you, but I think that you are wasting your time. Chromium is difficult to plate from the hexavalent or trivalent forms in low concentrations. You may have better luck with a trivalent electrolyte, but you would still need a lot of supporting electrolyte and additives to make it work. There are both chloride and sulfate based baths for trivalent chromium and they are somewhat similar to nickel (another metal that is difficult to electrowin) plating baths in operating pH and other characteristics. They use graphite anodes, but, don't make good heavy deposits.
consultant - Cleveland Heights, Ohio
hello . I want the equation of hydrogen over-voltage with current density of hard chromium electroplating . If anyone knows it or knows how can I find it , please say it me !Shayan Sarraf
Extracting Metallurgical Eng. from I.U.S.T - Iran-Tehran