Floating gold in AR solution

[tesaygo]

Hello guys please help me.

I try to recover gold plated on some computer parts.
I boil those gold plates in AR solution while boiling it for 3hours, solution tern black color and some gold plated floated. Why AR solution cant dissolve SOME gold plated and make it float? Please see picture attact.

Is my process is wrong?

 

[jimdoc]

Just yesterday you were offering to help people, what's up with that?

Jim

 

[tesaygo]

Just yesterday you were offering to help people, what's up with that?

Jim

Why does some gold is floating and doesnt dissolve in a AR solution?

 

[4metals]

When you have an aqua regia solution that is dark like in your picture do you test to see if it has gold in solution? A common mistake refiners make is they keep adding material to an aqua regia solution and as the material dissolves they add more. The problem is you will get to a point where the gold that is in solution will start to come out as more base metals go in. Essentially, no actually, this is cementation. You can use this to your advantage. You can continue to add to an aqua regia solution until the gold drops, decant the valueless solution and add fresh acid which will redissolve the gold in substantially less acid. Keep testing with stannous. When the acid starts out reacting with gold it will indicate with a stain. Continued additions will get you to the point where testing that same solution that was holding gold earlier is now not holding gold, it is all on the bottom. This is one example of why stannous chloride testing is so important!

I suspect your gold solution is saturated with base metals and it is not able to hold more gold. Be careful because when you get to this point, you are already dropping gold out of solution. Many refiners have lost gold by filtering the solution and tossing the filter paper thinking it is not gold because the gold is in solution. Floating gold that will not dissolve in aqua regia is a sign that your solution is saturated.

 

[autumnwillow]

May I ask how did you make AR?

 

[tesaygo]

When you have an aqua regia solution that is dark like in your picture do you test to see if it has gold in solution? A common mistake refiners make is they keep adding material to an aqua regia solution and as the material dissolves they add more. The problem is you will get to a point where the gold that is in solution will start to come out as more base metals go in. Essentially, no actually, this is cementation. You can use this to your advantage. You can continue to add to an aqua regia solution until the gold drops, decant the valueless solution and add fresh acid which will redissolve the gold in substantially less acid. Keep testing with stannous. When the acid starts out reacting with gold it will indicate with a stain. Continued additions will get you to the point where testing that same solution that was holding gold earlier is now not holding gold, it is all on the bottom. This is one example of why stannous chloride testing is so important!

I suspect your gold solution is saturated with base metals and it is not able to hold more gold. Be careful because when you get to this point, you are already dropping gold out of solution. Many refiners have lost gold by filtering the solution and tossing the filter paper thinking it is not gold because the gold is in solution. Floating gold that will not dissolve in aqua regia is a sign that your solution is saturated.

Thank you very much.

 

[tesaygo]

May I ask how did you make AR?

3:1 ratio HCl:HNO3 how i make AR solution.

 

[4metals]

How much acid did you use and what weight of scrap metal did you put into the acid? It does depend on what metals you are dissolving but a good rule of thumb is 225 to 250 grams of total metal per liter of solution. That is what the acid will hold in solution. As you get close to the upper limit the precious metal values will begin to cement out. Testing will tell you when that actually happens.

 

[tesaygo]

How much acid did you use and what weight of scrap metal did you put into the acid? It does depend on what metals you are dissolving but a good rule of thumb is 225 to 250 grams of total metal per liter of solution. That is what the acid will hold in solution. As you get close to the upper limit the precious metal values will begin to cement out. Testing will tell you when that actually happens.

Thank you to your advise.
By the way what is the best pH level when recovering the gold using SMB in AR solution? Can we add water to lower the pH?

 

[autumnwillow]

Make sure you have neutralized the nitric before proceeding. Dilute it twice the volume using distilled water. Put the container in a bowl then fill the bowl with cold water and ice. This should precipitate most of the silver chloride.
After cooling. Filter the solution. Use the highest grade filter paper you have. The higher the grade the better but takes more time in return with result in a lesser contaminated gold. After filtering. Use the ice bowl water method again and use SMB. As soon as the solution start to clear stop adding smb. Then proceed with the washing process

Sent from my SM-G920F using Tapatalk

 

[geedigity]

I don't ever adjust the pH prior to dropping gold, or at least I don't measure it. Depending on the source material, water would be used to dilute the gold solution to drop out the silver chloride as mentioned by Autumnwillow.

With respect to filtering, I know many like to allow the solution with a cloudy appearance settle over night or over a couple days. What I found to be very effective is simply using a fiberglass plug as my filter. Geo had mentioned using kaowool in a post sometime back.

Take a strip of fiberglass and roll it tightly into cigar shaped piece that will fit snugly into the lower portion of a funnel. Don't use the entire cigar shaped fiberglass plug, just cut about an inch and a half piece and fit that into the bottom of the funnel. Pour the cloudy solution through that, knowing you may need to rerun the solution through the filter several times to get it to run clear.

The only caution is to remember that rinsing the solution out of the filter needs to be done well, since values can get hung up in fiberglass due to the solution taking a preferential pathway as it flows through the fiberglass. Also, save the filter plug to recover any residual values later.

 

[4metals]

Dilute it twice the volume using distilled water.

Using distilled water in this step is just un-necessary, the reason we use distilled or demineralized water is when we want to keep silver in solution as in nitric dissolves. When using aqua regia, there is so much Cl in solution already the use of a diluent with no chlorine is just a waste of money. Plain old tap water works fine, the more chlorinated the better.

 

[4metals]

By the way what is the best pH level when recovering the gold using SMB in AR solution? Can we add water to lower the pH?

I do not know who filled your head with the notion that gold drops at a specific pH from the acid. And adding water to a strong acid like aqua regia does little in the way of raising the pH.

Instead of asking more questions why don't you answer the question asked of you? After all you're the one asking for help here. So earlier I asked you;

How much acid did you use and what weight of scrap metal did you put into the acid?

Your answer here is relevant to the question you asked originally, so let's stick to the topic rather than throwing out more questions please.

 

[Topher_osAUrus]

I do not know who filled your head with the notion that gold drops at a specific pH from the acid..

While he does not say that gold ONLY precipitates from a specific pH, deano does say in his thread, 3rd or 4th post (I believe), that he drops gold at a pH range of 1-2

http://goldrefiningforum.com/~goldrefi/phpBB3/viewtopic.php?f=37&t=21526&hilit=filter

There is another post/thread somewhere, by eagle35? (Maybe), that suggests 1-2.5 i believe (I couldn't find that)

I doubt that is where he got the idea of specific pH for gold reduction though, just thought Id share deano's share

 

[upcyclist]

Make sure you have neutralized the nitric before proceeding.

While we're talking about pH, I want to clarify that Autumnwillow is talking about getting rid of the excess nitrate (denoxxing) the solution here, NOT raising the pH towards 7.

 

[4metals]

I cannot begin to put a number of how many ounces I have precipitated from aqua regia and how many ounces people I have taught to do it have precipitated. It's more than a few. I never worry about the pH of the solution. I make sure there is no free nitric in solution by de-noxing and then I drop the gold.

If you were to measure the pH of aqua regia you wouldn't get an accurate number from a pH meter you would just pin the needle below zero and wait a week for your probe to recover from the shock. And raising the pH by 1 unit of the pH scale still leaves you with a very strongly acidic solution, if you had the means to measure it anyway. Don't worry about the pH of aqua regia, worry about the oxidizer, that needs to be gone, and reduce the gold.

 

[Topher_osAUrus]

I cannot begin to put a number of how many ounces I have precipitated from aqua regia and how many ounces people I have taught to do it have precipitated. It's more than a few. I never worry about the pH of the solution. ..

I believe it!
I never worry about my pH when precipitating either, so long as I have removed the nitric successfully (or, better yet, not overdone it in the first place!)

I was just showing one of the spots where I had seen mention of the specific pH range.

I have no doubts in you and your abilities good sir.

While it had been mentioned earlier how we all start green... In my mind, I always believed that you, lou, gsp (and a couple others) were born with a full and complete knowledge of recovery and refining of precious metals. Because the knowledge you guys posses is immense......and you guys sharing that knowledge, is a beautiful thing.

 

[anachronism]

The pH 1.5 Dean refers to is the pH whereby the SMB is its most selective. Does the solution need to be at this pH? As 4metals says no not at all, but Dean has dropped 3 nines gold from dirty solutions using this method. I've not perfected it myself yet. You pH control the solution using Urea which has the added benefit of cooling the solution to the point where silver chloride drops out, then filter and then drop using SMB.

Give it a try Toph. At the very least it's a great experiment.

Jon

 

[Geo]

The only time I adjust PH is when I'm cementing copper from solution. There's a difference between neutralizing and diluting. You can dilute the solution but the acid is still there and available. I tend to heat my solutions after the drop to ensure that all the gold is dropped and settled. At first I did it to reduce the volume of solution going into my stock pot. Seeing the gold powder residue after heating led me to doing this after every drop. If I did that without neutralizing the excess free nitric before the precipitation, that extra amount of gold would stay in solution because a heated solution is more reactive even if it is highly diluted. Pick a chemical that neutralizes free nitric acid and learn how to use it well. Only experiment to find out which one works for you. After you make up your mind, use it exclusively.

I have read on the forum of members that only use copper to drop their gold. No need to neutralize, no need for any other chemical. The refinery pays on content of the assay, so purity is a non issue. Many of us like to show off so cementation is not an option in that case.

 

[goldsilverpro]

During the 50 years I've been doing this, there are very few things I have not refined and I have developed my own techniques in each for making the refining processes go fast, safe, smooth, and efficient. In all cases, I can't remember ever having a need to adjust the pH.