# Red Foreign precipitate after dropping Ag with Cu



## ZiegenSauger (Dec 15, 2020)

Howdy!

I have been recovering Ag from Sterling, .800, and plated items. I separate my batches per weight: I process ~250g of "raw material" per batch (consisting of 85% Sterling, 5% .800, and 10% plated total weight).

After dissolving in Nitric Acid/Distilled Water and filtering clean, I precipitate Ag with 99% Cu stripes:



After separating the cement Ag, I take the filtered solution back to a beaker with 99% Cu stripes, and set aside for a week (extra 1g usually drops):



After this week, I filter the solution again and bottle it, storing in my processed solution storage (I try to match 1:1 => each bunch yields 2L filtered solution and I store in 2L bottles, I do not add any of the wash liquids on this). I add a virgin 99% Cu stripe in each bottle and keep it until it is time to take to City Waste Management (every other month).

Question: every couple of batches, I noticed a *Red deposit at the bottom*. I tried to process it in the past but I messed up with everything else. Now I have filtered and washed this Red deposit and have it on a coffee filter paper:



Based on this short description and Image03 above, is it possible to have any clue about what this might be? The waste filtered solution is crystal clear (as per Image02), I have removed over 99% of Ag and there is only the Nitric Acid only solution with whatever leftovers from the Silver items (100% kitchen, flatware, tea sets) dissolved with Cu in the beaker. Even so this Red powder comes down.

Is there any idea? Since I got to my limit in terms of experience and have not found similar case after same steps, I ask help to the masters.

Thank you

ZZ


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## butcher (Dec 15, 2020)

Iron also known as rust.


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## ZiegenSauger (Dec 15, 2020)

Thank you Butcher.

I had no idea this was possible when using metal Cu to separate Ag.
Appreciate it, big time.

ZZ


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## Lino1406 (Dec 15, 2020)

Additional option Cu2O


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## ZiegenSauger (Dec 15, 2020)

Thank you Lino1406! That was my conclusion but I would not bet my penny for the color. I could not confirm if the scenario would yield any form of Cu precipitate. Thank you very much indeed for your response.


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## g_axelsson (Dec 16, 2020)

If you get iron into solution (springs and hinges in jewelry, plated items or alloying of copper) it will sit in solution until the pH increases enough. Then it will precipitate as a hydroxide. The pH will go up as the excess nitric acid is used up by dissolving copper.

/Göran


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## Lino1406 (Dec 17, 2020)

According to wikipedia, this red precipitate may still contain silver -
Red plague is caused by normally occurring electrode potential difference between the copper and silver, leading to galvanic corrosion occurring in pits or breaks in the silver plating. It develops in the presence of moisture and oxygen when the porosity of the silver layer allows them to come in contact with the copper-silver interface. It is an electrochemical corrosion—a copper-silver galvanic cell forms and the copper acts as sacrificial anode.


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## ZiegenSauger (Dec 24, 2020)

Thank you Lino and Axelsson.

One way or the other, I usually dry this "red goo" and accumulate until there is a vial worth for me to reprocess again. So far, never got any further Ag and Stannous got negative.

(Nowadays I have constantly renewed Stannous test flasks "everywhere", so there are no excuses wherever I am in the cycle to make my tests)


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## Lou (Dec 24, 2020)

It may also be selenium!


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