Trying to use iron to settle copper out of AP...

[electrocycle44]

Hello,

Thank you for all the information from the forum, I have learned a lot and just began to figure out how much more I have to learn to get really good at this stuff. I purchased "The Gold Post" and have read a lot about the AP process, and was able to successfully process about two lbs of gold fingers. I would like to wait before doing any more processing and would like to properly dispose of the AP mixture I currently have. From what I have understood the proper process to dispose of AP fluids is to place a piece of iron into the AP mixture and let the acid dissolve the metal, which will push the copper out of solution since it's higher on the chart. After the metal has dissolved and the mixture turned more of a grey color, pour off the fluid, neutralize the acid with baking soda and dispose. Separately let the solid copper (and possibly other metals) from the bottom of your container dry and either keep for further processing or throw away.

The problem that I am having is that even after a week and a half, the piece of iron that I placed in my container is slightly rusted, but the AP solution is still a thick green color. Is it as simple that I need to add more Hcl to make the acid stronger to fully dissolve the iron? The container I am using is open to the air but I do not have an air bubbler setup yet - a couple recent posts seem to indicate that pushing more air into the solution would speed the process along. I want to take a break after my first try is to figure out what I didn't do well and improve the process for next year but do not want to pollute our water in the process.

Thanks for any help, if you need any more information please let me know.

 

[Geo]

Evaporating will concentrate the solution and make it more acidic. The "iron" you placed in solution may be stainless steel which will still dissolve but much slower. Is it galvanized? If it has any coating other than rust, sand it or use a metal brush to remove the coating. WARNING : do not breathe dust from removing galvanized coating. And too, if the solution is too basic, it will cement really slowly. When cementing, like any other process, heating the solution will cause the reaction to speed up.

 

[Pantherlikher]

You do not need air to drop copper. Only to dissolve more "copper" as in the AP process.

Testing the PH is a sure way to know if that is the problem.
Add very little HCL as it should drop PH fast enough and cause it to dissolve steel.
Make sure the steel is clean and is steel with no coating. Steel rusts before your eyes after the coating is removed.

Plan on using allot of baking soda to get the PH high enough...Maybe jump right to raising the PH and drop everything in solution. Unless you want copper for later use.

B.S.

 

[electrocycle44]

Evaporating will concentrate the solution and make it more acidic. The "iron" you placed in solution may be stainless steel which will still dissolve but much slower. Is it galvanized? If it has any coating other than rust, sand it or use a metal brush to remove the coating. WARNING : do not breathe dust from removing galvanized coating. And too, if the solution is too basic, it will cement really slowly. When cementing, like any other process, heating the solution will cause the reaction to speed up.

The iron was a piece of internal computer components, it was a piece of computer internal case that I flattened out. I can grab something else and see if it's a coating or something on the original piece causing the problem.

 

[jason_recliner]

Chassis from a computer will almost certainly be galvanised steel.

 

[g_axelsson]

Take a fresh piece of iron (for example the cover plate from unused expansion slots in a PC, easy to hang over the edge of your vessel) and put it in your green solution. If there is any copper left in solution it should cover the surface with a thin layer of bright copper. If you don't get the copper layer then the green color comes from some other metal in solution, for example iron or nickel.

Zinc plating (galvanizing) on iron is no problem and you don't need to remove it, it will just dissolve before the iron. Rust could protect the surface of iron and should be removed to increase the speed of cementating. A slight acidic solution dissolves some of the rust into soluble iron. Not all but some.

Depending on the source of your solution, the rest of the liquid probably have a lot of other metal ions as zinc, tin, nickel, chromium, lead, aluminum and so on. Treat the leftover solution according to instructions on the forum or leave it in a collection center. Do not pour it into the drain.

Göran

 

[Geo]

I agree galvanized does not stand up good in copper chloride but any coating to slow oxidation will slow the exchange of metal ions if the solution is not acidic enough.

 

[g_axelsson]

But zinc coating is protecting the iron by being dissolved instead of iron, zinc is more reactive so it would only increase the speed of cementation, not hinder it. The zinc will also cement copper from the solution. When the zinc is gone the iron starts to dissolve but not as fast.

If the solution is on the basic side even pure iron would start to get passivated, slowing down the cementation. But before we reach that stage I believe most of the metallic ions would already have been precipitated as metal hydroxides.
Since we are talking about old AP solution that condition is not likely to appear.

There are a lot of chlorides in this solution so towards the end of the cementation we run into another phenomenon. Oxidation of iron chlorides that creates iron oxides and iron hydroxides (or rust). My experience is that if the solution is acidic then most of the iron stays as soluble chlorides, but when allowed to dry out or getting close to neutral (the acid is used up in this process) the iron starts to form undissolvable rust. The chloride acts as a catalyst to transform iron into iron oxide/hydroxide via iron chloride.

Göran

 

[Anonymous]

Chassis from a computer will almost certainly be galvanised steel.

Nah it's primered mild steel mostly.

 

[butcher]

The copper chloride solution can be green or brown.
Iron chloride solution can also be green, brown or even yellow, so do not let the color of your solution confuse you into thinking the iron is not replacing the copper.

If the waste solution is a bit acidic, and you put in a fresh stip of iron into solution, and see no copper plate out to the iron you most likely have most all of the copper out of solution, the green solution is most likely just iron chloride, you could take a small sample and test it by adding a bit of ammonia to see if the solution turns bright blue, from the copper ammonium compound formed in this test, if copper is still present.

 

[electrocycle44]

Thanks for the suggestions everyone, I'm going to test a few things in the next week and see what happens.

 

[patnor1011]

I do use CD/DVD unit metal case, it work fine for me for dropping copper.