Pyrometallurgy: Roasting, Smelting, Refining & Electrowinning

Pyrometallurgy: Roasting, Smelting, Refining & Electrowinning 2017-03-23T09:55:18+00:00
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Silver Recovery from Acid Solution (14 replies)

Sachin Prakash
1 year ago
Sachin Prakash 1 year ago

We prepare our gold concentrate, which contains about 8ppm Ag, for smelt through treatment with nitric acid? This silver is not seen in the final bullion because I suppose it is dissolved in the nitric acid as silver nitrate. I want to recover this silver using sodium chloride to precipitate the silver. I tried it once on a lab scale but couldn't get any precipitate. Now, does anyone know why the silver couldn't be precipitated in my experiment? Could it be the silver concentration was too low? Or is there a more efficient process I could use to achieve my goal?

Sandeep Bisht
1 year ago
Sandeep Bisht 1 year ago

Will you please tell about the process of smelting first? Because in smelting, reagents have different redox power, their quantity is maintained according to the concentration of metals to recover. 8ppm is too low concentration to appear as precipitate. It would be effective if lead button is prepared because it can recover even 1ppm of Ag and Au from the sample.

Sachin Prakash
1 year ago
Sachin Prakash 1 year ago

Our smelting is done in an electric furnace using only Borax (sodium borate) as an additive. Tell me more of the lead button process.

Marshal Meru
1 year ago
Marshal Meru 1 year ago

You may have added too much salt water in your experiment. Silver chloride is soluble in salt water hence you should add it slowly until precipitation is complete, and do not use more that is needed to completely remove the silver from solution.

Tarun Karakoti
1 year ago
Tarun Karakoti 1 year ago

I suggest following steps:

Ensure the sanctity of analysis which says no Ag is with Au bullion. Method of analysis should be of ICP.
If the nitric solution is having 8 ppm Silver, you need to convert to its chloride by adding HCL followed by caustic lie and dextrose treatment.
Add Zinc dust to get some precipitate which can be filtered and smelted for getting Silver.

Tony Verdeschi
1 year ago
Tony Verdeschi 1 year ago

You can precipitate Silver with metallic copper also, you can enter two copper wires in the solution, if you want a faster reaction, add electric current (5-10 V) you can use alkaline commercial batteries or a cellphone feeder, copper will be coated silver.

Standartenfurer
1 year ago
Standartenfurer 1 year ago

Your gold concentrate is 8ppm Ag but we don't know the concentration of your Ag solution after dissolving with HNO3. If Ag + in your nitric leach is lower than 1.6 ppm you do not see any precipitate because this is the solubility of ClAg at 20 centigrade.

If the concentration is higher than 1.6 ppm and you don't see any precipitate you are re-dissolving the precipitate because you are adding an excess of Cl-

Confirm that Ag+ in your nitric leach is higher than 1.6 ppm, add (drop by drop) dilute solution of ClNa (calculate Cl- necessary to precipitate all Ag in solution before adding and don't add a big excess)

Sachin Prakash
1 year ago
Sachin Prakash 1 year ago

I must admit I added quite a lot of NaCl at temps above 30degrees. My Ag concentration in nitric solution was 4ppm.

Marshal Meru
1 year ago
Marshal Meru 1 year ago

While working in Ecuador I recovered more than a kilo of silver that had been dissolved by using too much salt water in a process tank by adding silver nitrate solution to eliminate the excess Cl- ions.

I do not recommend it, but lead nitrate or mercury nitrate would also work to remove the excess Cl- ions to recover the silver from solution. The silver chloride will co-precipitate from solution, but will be contaminated with lead chloride or mercury chloride.

Zander Barcalow
1 year ago
Zander Barcalow 1 year ago

You could try immersion plating (cementing) the silver on a less noble metal that also forms stable inter-metallic compounds with silver. I used this trick to recover traces of palladium in the presents of tin ions using aluminum metal.

Maya Rothman
1 year ago
Maya Rothman 1 year ago

What are you dissolving with the nitric acid?

OberstGruppen
1 year ago
OberstGruppen 1 year ago

Where is the Ag in the gold concentrate? The stated 8 ppm may indicate the Ag is in solid solution. The nitric acid will not dissolve the silver in this case. Why are you concerned about removing the Ag? Produce a dore bar and ship to a refinery.

Subhash-Kumar-Roy
1 year ago

How bad do you need the answer? It's very much possible to reverse the reaction equilibrium. Have you tried playing around with the pH of the solution? Perhaps removing the nitrate as nitrogen from the solution would allow the sodium chloride to precipitate. I have done chemistry all my life and I do remember some stuff.

Sachin Prakash
1 year ago
Sachin Prakash 1 year ago

I am not trying to precipitate NaCl but rather AgCl.

Bill Rico
1 year ago
Bill Rico 1 year ago

Addition of the Chloride has to be such that the [Cl-] is kept in exact stoichiometric balance to the silver molarity, too little silver nitrate will remain room much and soluble silver di Chloride complex will form.

Hence precipitating AgCl in a process is generally much harder than on the lab bench as on line analysis of the chloride is impractical in a general mineral process plant regime.

The exchange from Nitrate complex to chloride complex is also a slow reaction in nitric liquors, and slows in alkaline nitrate liquor. A dew idea; other Silver precipitants! A NO3 destruction process!

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