paladium and silver chloride

[ciki]

Hello everybody, I am new here and I have one question for began. I have from telephonic relay points: copper, paladium and silver disolved in hno3 50%, 15 liters of solution with: about 2 kilo of ag, maybe 100 grams of paladium, and 1 kilo of copper. How many grams of kitchen salt(nacl) can I use for silver chloride? 350 grams nacl is enought for 1 kilo of pure silver(from solution)?
Thank in advance!

 

[Oz]

Since you already have everything in solution but are not sure “exactly” how much silver is there, I would suggest you forget the math.

Using a saturated NaCl solution or HCl, start adding until no more cloudiness occurs with an addition. Stirring will be necessary as the silver chloride you will be forming will “hold” some of your solution that needs to be exposed to your Cl additions.

 

[Sucho]

i would use HCl to precipitate AgCl to minimize metal cations addition into a solution.
then filter your AgCl and wash thoroughly with HCl.

next step is a Pd extraction.evaporating your sol at cca 80 degrees Celsius with addition of HCl in a quite large shape to get rid of nitrate anions and to depress volume is a good way how you can extract palladium.you have to concentrate your sol a lot.you have about 1 kilo of Cu and a 0.1 kilo of Pd in your sol after AgCl precip. in my opinion you can end with 2-3 litres of concentrated sol, maybe less.
then use a standard process to precipitate Pd complex using NH4Cl and Chlorine gas or NaClO

 

[ciki]

oz & sucho,
thanks for your answers and advices!
ciki

 

[Harold_V]

Were that my project, I'd cement the silver and palladium using copper, then part the silver in a silver cell to recover the palladium.

Harold

 

[Sucho]

i have bad experience with cementing Pd on copper from a nitrate sol.it takes a lot of time to cement it out on copper and a significant ammount of Pd stays in sol due to palladium adsorption on copper and Pd crust formation. dont know why it is happening yet.electrochemical potential is almost same as el.potential of silver.
i have observed that cementation on copper from a chloride sol works much better. Pd deposit is much more integral and falls off easily..

Harold, i will be pleased if you will post some hints or an explanation

thanks

 

[freechemist]

Hello ciki,

As far as I understand, you're dealing with 15 liters of a solution containing 2 kilograms Ag, 1 kilogram Cu and probably about 100 g Pd. Given this rather big volume (even for an experienced lab worker) and the fact that there is roughly the tenfold amount of copper and a twentyfold amount of silver dissolved, compared to the palladium, I recommend to precipitate the Pd with dimethylglyoxime (H2DMG) as Pd(HDMG)2, collect the precipitate by filtration, wash and dry it and burn it down carefully and slowly to raw Pd-metal in an oven at a final temperature of about 800oC. The thus obtained raw metal may be contaminated with some PdO and can be dissolved and refined by known methods. To precipitate Pd(HDMG)2 you can use the solution of 250 g dimethylglyoxime and 175 g NaOH in about 4.5 liters of water. First dissolve NaOH, add solid H2DMG and stir until completely dissolved. The quantities given are based on the assumed amount of 100 g of Pd. This amount of dissolved Pd represents today a value of about 2'200 to 2'500 SFr., roughly the same value like the 2 kg Ag. 250 g dimethylglyoxime will cost you 282.- SFr. (3 packages with 100 g each from Fluka, a Sigma-Aldrich company in Switzerland).

Two additional hints: Use HCl/H2O2 or HCl/NaClO3 to dissolve the raw Pd. Do not use aqua regia, because dissolution of finely divided Pd-metal in HCl/HNO3 is a bitch of a reaction, easily getting out of control spontaneously, leading to extended cleansing actions (reaction vessel, fume hood, installations etc.) and losses of Pd.
Be careful using ammonium salts together with chlorine or NaOCl and HCl in Pd-precipitation in the refining step. There is a known risk of forming explosive byproducts. To refine Pd for this reason I always have used KCl, even if K2PdCl6 is a little bit more soluble than the ammonium salt.

Good luck, freechemist

 

[Harold_V]

Harold, i will be pleased if you will post some hints or an explanation

thanks

That the palladium comes down slowly didn't escape me. I had the same results---and with platinum as well. I processed a lot of dental material through the years, so it was an ongoing experience.

When I'd cement silver, I'd use a lot of copper. Pounds of copper, in fact. I was known to melt small pieces, casting them in a 100 ounce silver mold. I'd use no fewer than two of them, or assorted pieces of buss bar to recover the values. I can't recall even one instance where everything of value wasn't cemented in no more than 24 hours.

I wasn't concerned about what little may have remained on the copper bars, for they were used exclusively for silver recover, which, in turn, was processed in a silver cell. I didn't have to account for any of the platinum group, so in the end all of it reported in the slimes of the silver cell, which was my objective.

When cementing, my experience indicated that the platinum metals came down only after silver was depleted. It was obvious by the shift in color of the cement silver, to a dark gray color. Solutions were tested until they showed no values, but a visual inspection usually sufficed. As long as there was platinum or palladium included in the solution, it would display a green color, which shifted to a nice blue color when the values were down.

Harold

 

[Sucho]

DMG for Pd works great but you will need vacuum filtration apparatus definitely. you will have to filter entire volume of your solution because Pd(HDMG)2 is very fluffy and wont settle as AgCl.

Harold, thanks for reply!
my Ag/Pd nitrate solutions with copper have never changed colour to blue.they always stays green with a significant ammount od PD in sol although i let it precipitate for a week...

 

[Harold_V]

my Ag/Pd nitrate solutions with copper have never changed colour to blue.they always stays green with a significant ammount od PD in sol although i let it precipitate for a week...

I have to wonder if, maybe, there's too much palladium present as compared to the amount of copper. My thinking is that you may be forming a covering of palladium that eventually stops the cementation process. Also, a little free nitric does wonders. A few drops may be all it takes.

Harold