Red Sulphuric in cell

[golddigger2]

Has anyone else come across this issue. I have been using steve's de-plating cell for a couple of years and having good results. I was de-plating a mixed batch of pins yesterday and after i finished i poured off the acid and noticed it had turned a dark raspberry red. when i tried to use it again today it was foaming up quite a lot. Is this due to excess copper in the acid? It is a batch of sulphuric i have been recycling for a while. the acid i have been using is chemical grade 98%. I have been using the copper basket off steve's website in fact i bought the copper mesh off him. I think i got it fairly hot yesterday about 50 degrees c. I just need to know if the acid is still ok to use or do i need to get some more acid and responsibly dispose of the red lot.

thanks

 

[mrrdan]

I am having the same issue, and have the same exact question. Any information about this red sulfuric would be greatly appreciated!

 

[butcher]

I have no clue, rhodium will make a red sulfate solution, I wonder if by some odd chance that could be a possibility here.

Many drain cleaners are dark colored (not pure sulfuric acid), this may come from the process in which the acid was made where some metal like iron may be in the acid, or it could be an added inhibitor, or just plain dyed that color.

Pure sulfuric acid is clear liquid, like oil, with the old name oil of vitriol.
Technical grade H2SO4 impure is often colored.

Sulfuric acid sometimes is dyed dark brown during production to alert people to its hazards.

Try taking a few drop of the red sulfuric acid, with a little water in a test tube, add a few drops of the red acid, to dilute it, what is the reaction, same color just diluted? if it was copper the solution should turn a blue copper sulfate solution, an iron nail added would cement out copper metal as iron sulfate was formed in the solution,there are other experiments you could try to see if you can determine what is giving the red color, if it was important enough to you to figure out what the red color id from.

 

[mrrdan]

I don't believe that it is a dye, because i am using rooto and that is a pale yellow to start. The H2SO4 is turning red after running a few batches through the copper anode basket.

also when is a good time to change out the acid, there must be some life expectancy to the acid before it is fully saturated with base metals?

 

[butcher]

Concentrated the acid should not attack base metals, as they passivate in the concentrated acid.

Although keeping it concentrated is the key, concentrated sulfuric acid will suck up moisture from the air, this is why it is recommended to keep it covered when not in use.

Dilute the acid would dissolve base metals, and would not work as well in the cell to remove the gold plating.

 

[jonn]

I would imagine the red color comes from some types of plastic, I ran my cell today and used a tube to siphon off the acid after settling. The tube end oozed out a cranberry colored solution..
Concentrated acid will not attack base metal, my power supply amperage went to 0.11 once the gold was removed. The nickel plated copper was removed from the cell and looked just like nickel plated copper.
The red color coming from the tube may be a colloidal gold mixed with the oils in the tubing. I would avoid the use of any plastics in the cell. 8)

 

[goldsilverpro]

Many times, I've seen sulfuric turn red if any organic materials are present. Several times, I used conc. sulfuric to decompose solder mask and the solution always turned red. The red was from the solder mask, the board itself, or both.

 

[NobleMetalWorks]

I have also had solutions of Sulfuric acid turn red in a stripping cell. I also suspect that this is because of some organic material. However, I have seen the solution turn red when only processing metal pieces that have been incinerated, that I know for a fact have no organic material associated with them.

But there is something else I have noticed while building and testing different designs for a stripping cell.

The copper mesh that is used as the anode basket in a stripping cell often has a coating of oily substance. This is in fact a type of oil used to prevent the copper mesh from oxidizing and creating that green patina we associate with copper that has been exposed to the environment. I believe it's this oil, which is most likely an organic substance, that causes the red color in a sulfuric cell after using it for the first few times. An easy way to prevent this from happening, is to incinerate the copper mesh before using it, thus burning off the oil and preventing the organic material from being dissolved into solution. Since I have started doing this, I don't see the red in my sulfuric acid nearly as much.

Scott