Undissolved Mystery Metal in AR

[cbarney522]

I'm a newbie but I've been researching PM refining for about two years. I started refining about a month ago using AR. So far, so good. I'm stumped, however, by one of my batches. There is a thick layer of blackish/gray silt at the bottom that will not go into AR solution. It's about a half-inch thick, and 3 inches in diameter, so it's a substantial amount if it's PM. The gold was electrostripped from 25 lbs of gold-plated metalware, and I'm assuming that there was a mix of copper, stainless steel, zinc and nickel in the stripped feed stock. I used 32% HCl as step 1 to eat away zinc, nickel and stainless steel, and then nitric to eat away the copper. I then filtered and dried the precipitate and placed it into AR. No reaction. I tried stirring it, letting it sit in the sun all day to warm up (South Florida), and after 5 days, nothing. What could this be? I was thinking that it might be carbon, given that stainless steel has a very small percentage (<0.5%) of carbon. But this silt looks grayer than I would expect carbon to look like.

 

[JHS]

how did you mix your ar

 

[santiago]

Try warming your AR, it might help. Chromium sometimes gets passivated, and even if your platinum group metals are alloyed with base metals they may need to be heated in AR to get them to dissolve.

 

[cnbarr]

I used 32% HCl as step 1 to eat away zinc, nickel and stainless steel, and then nitric to eat away the copper. I then filtered and dried the precipitate and placed it into AR. No reaction.

I would say if you had gold from your cell slimes, you dissolved it before it ever made it to AR. Did you incinerate your powders in between your HCl wash and Nitric wash, otherwise you dissolved your gold during the nitric bath.

Have you tested any of your solutions with Stannous?

 

[Charles Connor]

Im having a problem with a solution too, i let it settle for a week i think and there is a layer that looks like copper, the solution has a black color and other solution i filtered has a blue color, wich are not the yellowish green of gold in AR, the problem here is that they are swepings from polishing machines wich should have gold because i have got gold from that kind of scrap... I still dont know whats in solution, already did the stannous test and marks the false positive of gold and a light blue color too, i added some NaCl to it and there was no AgCl2...

 

[mitchd]

I would take a very small bit of the gray powder and try to melt it into a metal bead. It might be AgCl or a mix of Ag, Sn, and Au or many other things with out know all that went into the lot it is hard to say what you have. Testing AgCl with salt will do nothing it is allrealy AgCl.
There might be a lot of smoke so be careful and a small bit of backing soda and borax might help. If you can get a bead from the powder
then you can test the metal to see if it is silver.

Mitch.

 

[santiago]

mitchd is right, if the part that didnt dissolve is already silver chloride, you can also try to filter or decant the solution, then add some strong ammonia to the residue, if its AgCl, once the pH rises high enough it will dissolve, then add some HCl to the filtrate and if it was silver chloride, thats the time you will see the white silver chloride precipitate appear.