plating, anodizing, & finishing Q&As since 1989
How to plate chrome out of liquefied wood (acid solution)
June 19, 2012
Q. Dear all,
I'm doing research on liquefied wood which contains chrome. Liquefied wood is a solution and I would like to use electrolysis to get the chrome out from this solution. The pH of this solution is about 0,5 and it contains H2SO4. I'm making tests with 0,1L of this solution and I'm using 3V (voltage). Results are not good. I eliminated about 10% of the chrome in 5 days. Can someone please explain to me which conditions should be achieved that I could eliminate chrome?
Best regards, David.
- Ljubljana, Slovenia
A. Hi David.
Unfortunately, I don't know very much about liquified wood, why it has chrome in it in the first place, or why you want to remove the chrome. I don't know what concentration you are starting at, what concentration you want to end at, whether the chrome in solution is in hexavalent vs. trivalent oxidation state, why you feel electroplating is better than chemical treatment, whether heating is practical or not, whether agitation is practical or not, etc., etc. So it is very difficult for me to offer any practical advice.
If you can explain more fully for we readers what your situation is, then I think we can be more helpful. Perhaps you want to recycle CCA pressure treated wood to remove the preservatives and re-use the wood? If so, www.thepineywoods.com/WoodRecycleJy05.htm talks about some success by LSU AgCenter, but reveals zero about what is involved in their process.
About all I can say at this point is that chrome will only deposit from a hexavalent solution when there is an almost exactly correct amount of catalyst, i.e., 1 oz. of H2SO4 for each 100 oz. of hexavalent chrome if you are using sulfuric acid as the catalyst. Good luck.
Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
June 21, 2012
Q. Dear Ted,
Thank you for your reply. You have it right. I would like to recycle CCB treated wood. It is similar to CCA but instead of arsenic there is boron in. One useful method to recycle CCB treated wood is liquefaction. Liquefaction is a method where we are using ethylene glycol (EG) as a reagent and sulphuric acid (H2SO4) as a catalyst. The liquefaction reactions are carried out in thin-walled test tubes which are immersed in an oil bath preheated to 150° C. Liquefied wood can be then used for further application of surface coatings.
My aim is to remove copper and chrome out of liquefied wood (to clean liquefied wood before further application). With the method which I described in my first subscription I eliminated about 95% of copper (copper is not problematic to remove with electrolysis) and only about 10% of chrome. Starting concentration of copper was 458 ppm, concentration after 24 hours 8 ppm. Starting concentration of chrome was 2405 ppm. I would like to get as much as possible of this chrome out of liquefied wood. Chrome is in trivalent oxidation state.
Thank you and best regards.
A. Hi David,
After the wood liquification process, do you wash the wool out prior to the electrolysis?
In what analytical relation stand the H2SO4 to your CrO3 concentration?
- Melbourne, VIC, Australia