huggybear
Active member
Thank you. It's good to understand the reason why things happen the way they do.
When In Doubt, Cement It Out
- Thread starter FrugalRefiner
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I would just add that air is also quite beneficial from other point of view - it helps to dissolve the surface layer of copper in combination with HCL. This allow the cemented metals to more easily shed off the surface of copper, reviving fresh surface for further cementation to proceed. This is espetially crucial for PGM cementation, as the formed cement tend to adhere to the surface of copper, blocking the access of more PGM ions to the Cu.
Manual stirring function is also very helpful in removing the cement, and it is nice synergy working for you in terms to obtain cemented values quicker. Altough, in exchange for more copper dissolved.
Very similar to issue of cementing copper out on iron. If you leave bucket uncovered, copper chloride will synproportionate with copper metal cemented, creating CuCl in solution, which in turn gets oxidized back to CuCl2 - slowly ruining your effort to get the copper out of solution - because in the end, only iron is spent and copper will stay as "oxidation" carrier.
It is always very useful to understand theoretic principles. With deeper understanding, you can much more easily solve the problems which arise along the way, be prepared that some things may happen and how to solve the possible issues
Scaled refining is quite complicated inorganic chemistry, and as you add more and more elements, you can get very strange reactions, shifted equilibriums, stalled cementations, strange complexes formation (mainly PGM chemistry) which refuse to react with anything (like cementing Pt with zinc going on for 4 days and still not complete...), delayed autocatalytic runaway reactions (like adding fresh nitric acid to hot nitric depleted AR, creating eruption of desorbed NOx gasses)... All sorts of "not so nice" things
With theory, you can predict quite a bit of them, making your life much easier. And with theory, you can use the observations and findings more easily, as you rationalize them much more efficiently.It is time consuming to go into detailed chemistry, oxidation potentials, solubilities and stuff, but if you intend to refine for more than few weekends in your life, it is well worth your time.
Why would I get a bunch of blue crystals when cementing silver from silver nitrate with copper busbar?
Cu, Ni, Zn, Ag and likely some Pb and Co present. I let it bubble for a couple an extended period of time. Silver nitrate bearing liquor was diluted by 4x as much water as acid.
The crystals are minimally soluble in water, but are soluble in HCl, and make a beautiful green solution.
Cu, Ni, Zn, Ag and likely some Pb and Co present. I let it bubble for a couple an extended period of time. Silver nitrate bearing liquor was diluted by 4x as much water as acid.
The crystals are minimally soluble in water, but are soluble in HCl, and make a beautiful green solution.
@snoman701
Are you rinsing your silver crystals with hot distilled water? This can take several rinses, until the rinse water is clear on a white background, a sheet of paper works well for this. If you have some test tubes, you can keep a bit of each rinse water to see the color change as well. Rinse will be light blue then fade to eventually a clear wash. This will remove any copper nitrate solution which may be on the crystals, causing it to cement out as copper nitrate when the crystals are dried.
To further purify your silver crystal, you would want to run in through a silver cell.
Elemental
Are you rinsing your silver crystals with hot distilled water? This can take several rinses, until the rinse water is clear on a white background, a sheet of paper works well for this. If you have some test tubes, you can keep a bit of each rinse water to see the color change as well. Rinse will be light blue then fade to eventually a clear wash. This will remove any copper nitrate solution which may be on the crystals, causing it to cement out as copper nitrate when the crystals are dried.
To further purify your silver crystal, you would want to run in through a silver cell.
Elemental
This is very strange since practically all nitrates are perfectly soluble in water.
One thing that comes to my mind is to check the pH to the end of the process. Some metal salts, bonded with anions from relatively weak acids (like nitric) could undergo partial or full hydrolysis, if pH isn´t kept below certain value. Maybe you accidentally created this enviroment and produced some hydroxy-nitrate copper salts (??), which maybe does not have good solubility in water, but dissolve nicely in HCL since you reacidify them and make soluble.
Last edited:
NobleMetalsRecovery
Well-known member
My earlier question should have been, Does FrugalRefiner have a "book" for sale?
NobleMetalsRecovery
Well-known member
Thank you.
huggybear
Active member
Is a magnetic stirrer with a beaker a decent "substitute" for this set-up? I understand it may not be as effective but I am looking to cement out a one-off batch of PGMs in solution.
Thanks,
HuggyBear
Thanks,
HuggyBear
It’s hard to know what you mean with “this set-up” without rereading the whole thread, but I assume you mean cementing on copper.
For cementing PGMs the most important is vigorous stirring.
Air bubbling or stirring will do that.
The important part is that there is plenty turbulent flow around the copper bar, dislodging the cemented metal to expose fresh copper.
huggybear
Active member
Sorry, I should be more specific. I meant the copper cementing set-up described by FrugalRefiner in the original thread.
Thanks for your response. I will try cementing using my magnetic stirrer and copper powder.
Thanks for your response. I will try cementing using my magnetic stirrer and copper powder.
I saw now. That is a very nice set up, but is not very good for copper powders.
For powders a very strong stirring will be neccessary and adding air bubbling to the same will probably increase efficiency.
Turbulence is your friend when cementing PGMs
I have a question or 2.
First thanks for the time you took on that post. It was beyond simple information on cementation. It was well put together to say the least and I thank you.
1. How long would say a half gallon or full gallon of solution take for cementation to be thoroughly finished? Approximately of course.
2. Actually only one question! I found the answer to the other.
First thanks for the time you took on that post. It was beyond simple information on cementation. It was well put together to say the least and I thank you.
1. How long would say a half gallon or full gallon of solution take for cementation to be thoroughly finished? Approximately of course.
2. Actually only one question! I found the answer to the other.
Cementation of PGMs on copper is better done with that bubbling. That´s because PGM cement form thick layer on the surface of copper which does not permeate new solution to the surface of the copper. Air helps to dissolve surface copper into the solution and allow the PGMs to flake off the copper bar.
If you have decent quantity of PGMs in solution, I would cement them on iron for the sake of time and efficiency. Use just a tiny bit - copper also come out of solution, but if you use just a little iron, little copper came out vith VAST SURFACE AREA - which will then exchange for PGMs and precipitate them from the solution
Now, the magnetic stirrer comes handy not exactly scientific approach, but it works and saves time. If you are only using it to concentrate PGMs from larger quantity of liquid. Because the cement from Fe nor Cu won´t be nowhere nice and clean, there would be plenty of base metals present as copper and also iron flake off with PGM cement. Just to be prepared that this isn´t exactly rafination method, just a recovery method.kurtak
Well-known member
Yes - if you only have a small amount of solution (couple liters) & stirrer hot plate & copper powder (& of course beaker) there is absolutely no reason why you can't do it this way instead of with hanging a copper bar & running a bubbler
You just need to make sure the solution is just "a bit" to the hot side of warm & that each time you add copper powder you let it stir for a while to insure the copper fully dissolves as the PGMs cement out
Leave plenty of room in the beaker for foaming up of the solution when you add the copper powder - when the foaming dies down let it stir for a couple/few minutes before adding more copper powder (to insure the copper is fully dissolved)
As you near the end (of doing copper powder addition) it starts taking longer for the copper powder to fully dissolve - so you want to let it stir longer between copper addition to insure the copper powder fully dissolves
The down side of this method is knowing when to stop with the copper powder additions (when all the PGMs are cemented out) so that you are not adding copper that does not dissolve any longer & you end up contaminating the cemented PGMs with copper
So stannous testing is important especially as you near the end
For small amounts of solution this is actually my preferred method over that of copper bar & bubbler
Please ALL of this tread ------
https://goldrefiningforum.com/threads/fuzz-button-interconnects-need-some-advice.22203/#p232030
On page 2 you will see a post of the results of my first time using the copper powder method (& I have used it many times since then)
That said - it will serve you well to read the whole thread
Kurt
kurtak
Well-known member
That depends entirely on a few things ----
1) how diluted - or - how concentrated the solution is
2) how much free acid is in the solution - if there is a lot of free acid in the solution the acid need to work at dissolving copper before it actually starts cementing the precious metals
3) though not as much of a factor of the above - temp of the solution also plays "some" roll in the time
So depending on the above it could take anywhere from a few hours to 3 days
Example of 3 days = VERY dilute + free acid + plus cold
Kurt
kurtak
Well-known member
And for what it is worth (side note) --------
Stirring & copper powder works better on concentrated solutions
Copper bar & bubbling works better on diluted solutions
Kurt
Stirring & copper powder works better on concentrated solutions
Copper bar & bubbling works better on diluted solutions
Kurt
