Silver baths: strike and analysis of silver
We electrodeposit silver on decorative Ni-coated pieces.
We work with a silver strike bath (we chose 6 g/l AgCN, 60 g/l KCN, no filtration, approx. 1.5 A/dm2 for 15 minutes), followed by the silver bath at the conditions our provider gave us.
* We want to check two things:
- Are we doing it right about the strike bath?
- Our analysis method (from the provider) to determine the g/l silver: adding acids, boil it and using "alumbre ferrico" (spanish term) to see a colour change via titration to a "melon" colour. This colour change seems difficult to determine. The sample to titrate has already a melon colour.
I'm looking for alternative methods for silver analysis (also via titration, we do not have other equipment here). I don't know if they exist, but if they do, please tell me.
- Queretaro, Mexico
A. The way I do it is as follows:
5.0 ml plating bath is combined with about 20 ml water in a 500 ml Erlenmayer flask, and about 3 ml 30% hydrogen peroxide added. Next, WAIT. In 10 - 15 minutes, there will be a very obvious reaction in which most of the cyanide is destroyed, leaving a gray black precipitate of silver metal/hydroxide.
Now, IN A FUME HOOD, add about 15 ml sulfuric acid and about 10 ml nitric acid,(cyanide gas will be evolved) and heat. First you'll see brown fumes, then the characteristic white fume of refluxing sulfuric. Heat it at this point until a clear solution is obtained. There is sometimes a little solid matter that will not dissolve. Let it cool.
Then, lastly, carefully add about 150 ml water, and about 1 ml of 5% ferric ammonium sulfate solution. Titrate to an orange-red endpoint with 0.1 N potassium thiocyanate solution.
ml titrated x 0.288 = Silver in oz/gal (avoir)
Consultant - The Bronx, New York
A. Why not use atomic absorption spectrophotometry? in a 100 ml volumetric flask, dilute your sample 10:100, then add 1 ml to each flask, marked a, b,c....in flask b spike with 1 ml of 100 ppm silver reference, in flask b spike with 2 mls 100 ppm silver reference solution, run on AA with silver lamp and proper wavelength and slit; you will record the results of each flask (a, b, and c) I'm afraid I do not have the calculations with me offhand for the results, but they are available from perkin-elmer.
Jason A. Brown
Sanmina-sci, USA - Athens, Pennsylvania, USA
A. Concentration of silver strike should be 1.5 g/k AgCN + 100 g/l KCN.
15 minutes is too long!
chemical process supplier
Q. Nowadays we lowered the current density to about 0.05 A/dm2 (in a barrel of 13 kg of little pieces, bath of 200 l).
Is 15 min then still too long?
- Queretaro, Mexico
December 23, 2017
Q. I have a problem analyzing silver from a silver cyanide bath. This bath is a 6 oz/gal bath and my readings are not constant. I dilute the sample 0.1 ml solution to 100 mls DI water and my ICP results vary from 45 ppm to 60 ppm. I am using a Varian 710 ICP. Anybody has another method or probably I am missing a step in my sample preparation?sergio lopez
electroplating company - fullerton ca, USA
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