About to attempt a Formic Acid purification, advice appreciated.

[Elemental]

I'm getting back into refining sterling silver junk into fine Silver. In the past, I was using copper to drop the silver out of solution, then refining via a silver cell. I've found that I still have copper that carries over when I use copper wire to drop the silver. So, to try something a bit new, I'm going to go the silver chloride and formic acid route to drop the silver then filter, hoping to get cleaner silver out of the process.

Here is the Lab Instructions I have created for this new process. Any advise or sharpshooting is appreciated.

Lab Instructions: Refining Sterling Silver into Fine Silver Using Formic Acid​

This guide describes how to refine sterling silver (92.5% silver and 7.5% other metals) into fine silver (99.9%) using formic acid to reduce silver chloride into metallic silver.

---

Materials and Reagents​

Reagents:​

1. Sterling silver (weighed amount)
2. Concentrated nitric acid (HNO₃, 68%)
3. Distilled water
4. Hydrochloric acid (HCl, 37%)
5. Formic acid (HCOOH, 95%)
6. Sodium hydroxide (NaOH)

Equipment:​

1. Beaker (500 mL or larger)
2. Glass stirring rod
3. Fume hood or well-ventilated workspace
4. Hot plate
5. Filter paper and funnel
6. Crucible
7. Tongs
8. Scale (to weigh reagents)
9. pH meter or pH paper
10. Protective gloves, goggles, and lab coat

---

Step-by-Step Instructions​

Step 1: Dissolving the Sterling Silver​

1. Weigh the Sterling Silver:
   • Record the mass of sterling silver (m_{ss}).
2. Dissolve the Silver in Nitric Acid:
   • Place the sterling silver in a beaker.
   • Under a fume hood, add concentrated nitric acid to the beaker. Use approximately 4 mL of HNO₃ per gram of sterling silver.
   • Observe the reaction, which produces brown nitrogen dioxide (NO₂) gas.
   • Once the silver is completely dissolved, a blue-green solution will form due to dissolved copper.
3. Dilute the Solution:
   • Add distilled water to dilute the solution (1 part acid solution to 3 parts water).

---

Step 2: Precipitating Silver Chloride​

1. Add Hydrochloric Acid or Salt Solution:
   • Slowly add hydrochloric acid (HCl) or a saturated salt solution to the silver nitrate solution while stirring.
   • A white, curdy precipitate of silver chloride (AgCl) will form.
2. Test for Complete Precipitation:
   • Add a few additional drops of HCl. If no new precipitate forms, all silver has been precipitated.
3. Filter the Precipitate:
   • Filter the silver chloride using filter paper and a funnel.
   • Rinse the precipitate several times with distilled water to remove impurities.

---

Step 3: Reducing Silver Chloride to Metallic Silver​

1. Prepare the Reduction Solution:
   • Place the washed silver chloride in a clean beaker.
   • Add enough sodium hydroxide solution (NaOH) to cover the silver chloride completely and make the solution strongly alkaline (pH > 12).
2. Add Formic Acid:
   • Slowly add 95% formic acid (HCOOH) to the alkaline solution while stirring.
   • The reaction will produce metallic silver as a fine gray powder:2AgCl+HCOOH→2Ag+CO2+2HCl
   • Continue adding formic acid in small increments until all the silver chloride has reacted.
3. Confirm Completion:
   • Stir thoroughly and allow the reaction to finish. The solution should no longer contain visible white AgCl.

---

Step 4: Collecting and Washing the Silver​

1. Filter the Metallic Silver:
   • Filter the silver powder from the solution using filter paper and a funnel.
2. Wash the Silver:
   • Rinse the powder thoroughly with distilled water to remove any remaining salts or impurities.
   • Optionally, wash with dilute ammonia to remove traces of silver chloride, followed by distilled water.

---

Step 5: Drying and Melting the Silver​

1. Dry the Silver Powder:
   • Spread the silver powder on a clean surface or in a crucible.
   • Allow it to air-dry, or heat gently on a hot plate at low temperature to remove moisture.
2. Melt the Silver:
   • Place the dry silver powder in a crucible and heat with a torch or furnace until molten.
   • Pour the molten silver into a mold to form an ingot or let it cool in the crucible.

---

Safety Notes​

1. Perform all steps involving acids and formic acid in a fume hood or well-ventilated area.
2. Wear protective gloves, goggles, and a lab coat.
3. Neutralize all waste solutions with sodium carbonate or sodium hydroxide before disposal.
4. Dispose of all chemicals and waste according to local regulations.

---

This method is efficient for refining sterling silver into fine silver with minimal equipment and reagent waste. It produces high-purity metallic silver suitable for industrial or artistic applications.

 

[Yggdrasil]

I'm getting back into refining sterling silver junk into fine Silver. In the past, I was using copper to drop the silver out of solution, then refining via a silver cell. I've found that I still have copper that carries over when I use copper wire to drop the silver. So, to try something a bit new, I'm going to go the silver chloride and formic acid route to drop the silver then filter, hoping to get cleaner silver out of the process.

Here is the Lab Instructions I have created for this new process. Any advise or sharpshooting is appreciated.

Lab Instructions: Refining Sterling Silver into Fine Silver Using Formic Acid​

This guide describes how to refine sterling silver (92.5% silver and 7.5% other metals) into fine silver (99.9%) using formic acid to reduce silver chloride into metallic silver.

---

Materials and Reagents​

Reagents:​

1. Sterling silver (weighed amount)
2. Concentrated nitric acid (HNO₃, 68%)
3. Distilled water
4. Hydrochloric acid (HCl, 37%)
5. Formic acid (HCOOH, 95%)
6. Sodium hydroxide (NaOH)

Equipment:​

1. Beaker (500 mL or larger)
2. Glass stirring rod
3. Fume hood or well-ventilated workspace
4. Hot plate
5. Filter paper and funnel
6. Crucible
7. Tongs
8. Scale (to weigh reagents)
9. pH meter or pH paper
10. Protective gloves, goggles, and lab coat

---

Step-by-Step Instructions​

Step 1: Dissolving the Sterling Silver​

1. Weigh the Sterling Silver:
   • Record the mass of sterling silver (m_{ss}).
2. Dissolve the Silver in Nitric Acid:
   • Place the sterling silver in a beaker.
   • Under a fume hood, add concentrated nitric acid to the beaker. Use approximately 4 mL of HNO₃ per gram of sterling silver.
   • Observe the reaction, which produces brown nitrogen dioxide (NO₂) gas.
   • Once the silver is completely dissolved, a blue-green solution will form due to dissolved copper.
3. Dilute the Solution:
   • Add distilled water to dilute the solution (1 part acid solution to 3 parts water).

---

Step 2: Precipitating Silver Chloride​

1. Add Hydrochloric Acid or Salt Solution:
   • Slowly add hydrochloric acid (HCl) or a saturated salt solution to the silver nitrate solution while stirring.
   • A white, curdy precipitate of silver chloride (AgCl) will form.
2. Test for Complete Precipitation:
   • Add a few additional drops of HCl. If no new precipitate forms, all silver has been precipitated.
3. Filter the Precipitate:
   • Filter the silver chloride using filter paper and a funnel.
   • Rinse the precipitate several times with distilled water to remove impurities.

---

Step 3: Reducing Silver Chloride to Metallic Silver​

1. Prepare the Reduction Solution:
   • Place the washed silver chloride in a clean beaker.
   • Add enough sodium hydroxide solution (NaOH) to cover the silver chloride completely and make the solution strongly alkaline (pH > 12).
2. Add Formic Acid:
   • Slowly add 95% formic acid (HCOOH) to the alkaline solution while stirring.
   • The reaction will produce metallic silver as a fine gray powder:2AgCl+HCOOH→2Ag+CO2+2HCl
   • Continue adding formic acid in small increments until all the silver chloride has reacted.
3. Confirm Completion:
   • Stir thoroughly and allow the reaction to finish. The solution should no longer contain visible white AgCl.

---

Step 4: Collecting and Washing the Silver​

1. Filter the Metallic Silver:
   • Filter the silver powder from the solution using filter paper and a funnel.
2. Wash the Silver:
   • Rinse the powder thoroughly with distilled water to remove any remaining salts or impurities.
   • Optionally, wash with dilute ammonia to remove traces of silver chloride, followed by distilled water.

---

Step 5: Drying and Melting the Silver​

1. Dry the Silver Powder:
   • Spread the silver powder on a clean surface or in a crucible.
   • Allow it to air-dry, or heat gently on a hot plate at low temperature to remove moisture.
2. Melt the Silver:
   • Place the dry silver powder in a crucible and heat with a torch or furnace until molten.
   • Pour the molten silver into a mold to form an ingot or let it cool in the crucible.

---

Safety Notes​

1. Perform all steps involving acids and formic acid in a fume hood or well-ventilated area.
2. Wear protective gloves, goggles, and a lab coat.
3. Neutralize all waste solutions with sodium carbonate or sodium hydroxide before disposal.
4. Dispose of all chemicals and waste according to local regulations.

---

This method is efficient for refining sterling silver into fine silver with minimal equipment and reagent waste. It produces high-purity metallic silver suitable for industrial or artistic applications.

Why are you using Copper wire.
Thick soilid Copper is adviced.
And if you stop Cementing before it is completed, you get very pure Silver.

 

[Elemental]

I was using 6 AWG copper grounding wire, as it was easily available and I was able to form it into whatever shape required for my reaction vessel. My issue was if I didn't dilute the solution, it would form a crust on the outside of the wire and then carry bits of the copper over, thus defeating my attempts to get fine silver prior to electrolysis. Regardless, I'm looking for any input or advise on the Formic Acid method, as I'm experimenting with other refining methods.

Hoping that someone who has done it before can give any insights on it or issues they see with it. I'm also curious to see how treatment of the waste stream changes with this reaction as I won't have to deal with a lot of copper nitrate.

 

[Yggdrasil]

I was using 6 AWG copper grounding wire, as it was easily available and I was able to form it into whatever shape required for my reaction vessel. My issue was if I didn't dilute the solution, it would form a crust on the outside of the wire and then carry bits of the copper over, thus defeating my attempts to get fine silver prior to electrolysis. Regardless, I'm looking for any input or advise on the Formic Acid method, as I'm experimenting with other refining methods.

Hoping that someone who has done it before can give any insights on it or issues they see with it. I'm also curious to see how treatment of the waste stream changes with this reaction as I won't have to deal with a lot of copper nitrate.

Thick solid Copper will not flake off like thin sheet or wire.
You can actually get close to 3 nines fine if you stop the cementing just short of complete.
Or use atomized powder with hefty stirring.

 

[Elemental]

Thank you for the advice. I will try that the next time I cement with copper.

 

[4metals]

This was the first post I ever made on this forum. It may help.