nitric turned a dark rust color

[DAVEEDO]

well i ran into a problem. i was desolving gold filled and gold plated and it was going fine. the last batch i soaked in half nitric half distilled water turned dark orange didnt desolve all the base metal and my coffee pot is filled with a sludge like substance. i dont know what i did wrong. the nitric did not disolve all the metal and i dont know what to do now. i started to filter it off. it sat over night and the next day the solution was a dark blue color and it had a brown powder in the bottom of the container i filtered into. any pointers as to what i can do with this? thanks

 

[glondor]

My guess is you need more fresh acid. perhaps there was some iron in your mix and it cemented out the copper.

 

[DAVEEDO]

i added some pics to show the resulting mess i am in. has anyone ever see this before?

 

[butcher]

Did you test the gold fill and gold plated material with a magnet?
It looks like you tried to dissolve a lot of iron.
from the pictures above I do not see copper.

 

[DAVEEDO]

no i didnt run a magnet over the items i was working with. tomorrow i will check with a magnet. i have quite a bit more to process. what should i do with this batch though?

 

[glondor]

It does look like cement copper to me. a small addition of nitric should put you right. Cement copper will go back into solution very fast. Add the nitric slowly. I think I would split that batch and do it in 2 pots as you are very close to the top and a vigorous reaction will have your solution everywhere.

Here is how I think it happens. Your nitric puts all the lesser metals in to solution first. Then the iron. If the nitric is low the iron will push the copper out as there is not enough nitric to keep the copper in solution. Add a bit of nitric and the copper will go back into solution. Works for me 8)

 

[DAVEEDO]

well ive run a magnet over the material i am going to process and a lot of it is magnetic can i still process this with nitric?

 

[butcher]

I would consider a different process like the concentrated sulfuric stripping cell.

 

[Dr. Poe]

I remember having this problem myself when I was a newbie (32 years ago). In that respect, I'd like to take a shot at this: Try first more 50/50 nitric acid/distilled water. Heat it to 68C for an hour. Let it cool and settle to room temperature. Carefully decant the solution and save it for silver recovery. Repeat this process with concentrated nitric acid. Save the solution for possible palladium. To what's left, heat with aqua regia. Process this AR solution for gold and the platinum group metals (PGM's). The next time, start with a sulfuric stripping cell instead. You should know that copper consumes twice the nitric acid as the first molecule oxidizes the copper (releasing NO gases) and the second dissolves the copper oxide forming copper nitrate. It's just less profitable to start with nitric. The stripping cell will reduce the mass to a smaller volume. Then You might actually make a profit. :mrgreen: Dr. Poe

 

[DAVEEDO]

I remember having this problem myself when I was a newbie (32 years ago). In that respect, I'd like to take a shot at this: Try first more 50/50 nitric acid/distilled water. Heat it to 68C for an hour. Let it cool and settle to room temperature. Carefully decant the solution and save it for silver recovery. Repeat this process with concentrated nitric acid. Save the solution for possible palladium. To what's left, heat with aqua regia. Process this AR solution for gold and the platinum group metals (PGM's). The next time, start with a sulfuric stripping cell instead. You should know that copper consumes twice the nitric acid as the first molecule oxidizes the copper (releasing NO gases) and the second dissolves the copper oxide forming copper nitrate. It's just less profitable to start with nitric. The stripping cell will reduce the mass to a smaller volume. Then You might actually make a profit. :mrgreen: Dr. Poe

you are a godsend with the knowledge you've provided. i would be completely lost trying to solve this problem by myself. thank you very much. i do have some studying to do on the sulfuric cell. i am not to familiar with it. any pointers would be highly appreciated. thank you again

 

[Harold_V]

I'd have a slightly different approach to the problem. The pictures indicate to me that you have a substantial amount of iron involved. Because there's still base metal remaining (I'm assuming there is), I wouldn't add any nitric. Instead, I'd allow the solution to settle well. Any silver or palladium that may be present will have long ago cemented, so the solution should be barren. At some point it should be eliminated, and I can't think of a better time than when it's barren. Test with stannous chloride to ensure it doesn't contain palladium, and with a drop of HCl, or a crystal of salt, for silver.

Dealing with iron isn't in your best interest. You may be well served to incinerate the solids, then give them a prolonged digest in dilute sulfuric, which will eliminate the iron. Once it's gone, you can then proceed with eliminating the balance of the base metals and recovering any silver that may be present. Otherwise, you'll just have a repeat of the same conditions that exist now.

You should have learned a valuable lesson form this experience. Keep iron, aluminum and tin out of your processing to the best of your ability. If, by chance, you find you have iron present, as is the case now, you may wish to consider using the material in the stock pot, where the iron will be gradually eliminated, all the while collecting values. Not a bad idea if the values contained within the existing material are not all that great to begin with.

Alternately, you may wish to do the digest with HCl instead of sulfuric. If that's your decision, be certain to incinerate after that digest, before attempting to use nitric.
Harold

 

[philddreamer]

Harold wrote:
"You may be well served to incinerate the solids, then give them a prolonged digest in dilute sulfuric, which will eliminate the iron."

Harold, this "dilute sulfuric", is it the same dilute sulfuric as the 10% sulfuric for dissolving the borax after a melt, or what % of "dilute" would this be?

Thank you!

Phil

 

[Geo]

for some reason (and im sure some of our chemist can explain why) concentrated sulfuric and diluted sulfuric tends to act like two different acids. where concentrated sulfuric will hardly attack iron diluted sulfuric for some reason will attack iron strongly. the normal percentage of battery acid should work for diluted sulfuric purposes as thats what i use to clean my melting dishes.

 

[Harold_V]

Harold, this "dilute sulfuric", is it the same dilute sulfuric as the 10% sulfuric for dissolving the borax after a melt, or what % of "dilute" would this be?

I'd have to agree with Geo on this one! 8)

Harold

 

[DAVEEDO]

i was going to ask what is the best way to clean my crucible between meltings. diluted sulfuric will work for this? how should i approach this task? thanks

 

[butcher]

The first I have heard of using dilute sulfuric to clean a melting dish was a post by Phil dreamer, he reported good results with his process (and I trust his view on this although I never heard of it before), (search cleaning melting dish or crucible using author Phildreamer), if trying this procedure my concern would be adding liquid to dish and drying and driving out moisture slowly bringing up heat till red hot, so as not to break dish would be important, and also if melting silver later in this dish driving out any sulfates would also be important in my mind (getting dish red hot should also help here).

Normally I will just add a little sodium carbonate (soda ash) (some time’s a little bit more borax depending on conditions), and heat a with a torch to melt metals in dish to a small bead,(flux also picking up oxidized metals), heating dish well red hot, stirring beads with torch pushing them into button and cleaning sides of dish, picking up dish with tongs in one hand and pouring bead, and flux into small carbon sooted, or oiled warmed iron cone mold, forcing the molten flux (used to clean dish) out of dish with the action of the torches blue cone flame, the sodium carbonate will dissolve a thin layer of the dish cleaning it, (just a note: too much sodium carbonate and heat and you can also dissolve a hole right through the bottom of your dish).

Degrade your dirty dishes to use for dirty melts, keep new or clean dishes for high purity melts (well refined gold should not be contaminated by melting it in a dirty dish adding metals from dish to the pure gold you worked so hard to get, dishes are not that expensive, contaminating your gold can get costly)

Search for cleaning the melting dish using Harold as author for better details.

 

[Smack]

i was going to ask what is the best way to clean my crucible between meltings. diluted sulfuric will work for this? how should i approach this task? thanks

Crucible or melting dish? My crucibles are clay graphite and only get scraped clean while still hot. My little melting dishes like the silica ones I use soda ash to clean them, never had to bust out the Sulfuric on any of them.

 

[philddreamer]

Back on Jan 15, 2011 we talked about how to clean melting dishes:
http://goldrefiningforum.com/phpBB3/viewtopic.php?f=53&t=5689&p=83853&hilit=cleaning+melting+dish#p83853

but I never got to it, even though I bought all the "ingredients".
After doing many melts of scrap jewelry since, I had a few precious stones, mainly diamonds, that I wanted to recover. So I tried adding borax & soda ash but it was too slow. I had some diluted sulphuric that I had used the day before for cleaning the borax off a small ingot I was shipping, so :idea: I said to my self, what if I boil the melting dish, will I get rid of the borax & free the diamonds? :roll: So having extra melting dishes, & not minding losing that dish, I gave it a shot. Well, it got rid of most of the borax; the diamonds, gold & other stones were freed & I had fun removing them with tweezers. I tested the clear stones & was surprised at how many I had.

Learning here that is not safe to suddenly heat a dish or mold & allowed the dish to sit for several days before trying to melt in it. When the time came, I applied little heat for a few minutes, I let it cool a bit, then added my scrap & proceeded to melt. I had no problems. I have done about a dozen melts & the dish is sound.

For more insight:
http://goldrefiningforum.com/phpBB3/viewtopic.php?f=49&t=12291&p=121229&hilit=cleaning+melting+dish#p121225

Take care & be safe!

Phil

 

[Geo]

if you heat too long with an oxy/acet torch, the borax will turn grey. it doesn't have to have any contamination in the dish. this i learned first hand trying to melt out excess borax from a dish that i had used before i knew what i was doing, i was melting silver and really loaded the borax up in this dish thinking most of it would come out with the silver. i was wrong. it had about a quarter of an inch of borax glass in the bottom when i finished, thinking i could remelt the borax and pour it out, i heated the dish and poured on the heat. i did remove quite a bit of the excess but what was left was grey and very nasty looking. i set it aside untill i found that i could remove the borax with battery acid.

 

[Harold_V]

I gotta say, that's a pretty slick method of removing the old slag. I used the soda ash and borax system with success, but it's hard on the dish. I salute you for your contribution to the board. I'd have sworn the sulfuric wash would have been destructive.

Harold