is it necessary to dilute AR before precipitation
- Thread starter diverwild
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When you burn the sweeps and crush them, any oversize that doesn't pass through a 40 mesh screen is usually metallic gold from filings. This material needs to be inquarted with silver and parted in nitric in order to recover the gold. 16% silver is too high to completely digest the gold in aqua regia without hanging up gold in the silver chlorides, so for the oversize, inquart.
At 16% and the fine particle size you crush to, a nitric / distilled water leach should get a good percentage of the silver out. Filter out the insolubles and recover the silver from the acid. (Cementation or as a chloride, your choice)
You do not have to worry about any nitric that may remain in the solids because you are going to make aqua regia anyway, so another incineration isn't needed. Just add the hydrochloric acid and the nitric to dissolve the gold. Heat for the dissolve will help as well. When everything is reacted and filtered, I always like to take a small spoonful of the filtered and rinsed solids and add them to a small beaker of aqua regia, then test with stannous to see if any gold was dissolved.
I never mix up aqua regia the same strength for sweeps as for karat scrap, I usually start at 8:1. By testing the processed solids in a small beaker if aqua regia you will learn what ratio of acid works best for your material.
At 16% and the fine particle size you crush to, a nitric / distilled water leach should get a good percentage of the silver out. Filter out the insolubles and recover the silver from the acid. (Cementation or as a chloride, your choice)
You do not have to worry about any nitric that may remain in the solids because you are going to make aqua regia anyway, so another incineration isn't needed. Just add the hydrochloric acid and the nitric to dissolve the gold. Heat for the dissolve will help as well. When everything is reacted and filtered, I always like to take a small spoonful of the filtered and rinsed solids and add them to a small beaker of aqua regia, then test with stannous to see if any gold was dissolved.
I never mix up aqua regia the same strength for sweeps as for karat scrap, I usually start at 8:1. By testing the processed solids in a small beaker if aqua regia you will learn what ratio of acid works best for your material.
4metals said:
I will try what you have suggested then I will reply، BTW there are no oversized pieces in the polishing bags، when I sieve the incinerated ashes I cant see any gold particles at all they are very very small and mixed with ash
since we opened this topic I have one concern which is iron or stainless steel I use a magnet after sieving، but lets say some amount of iron went to AR what problems could occure ?
because I dont make the first step washing with HCL I made it once and the solution took long time for me to settle and decant
Topher_osAUrus
Well-known member
What concentration of nitric did you use on your half hour nitric boil?
Did you test the green nitric leach with stannous or dmg to see if any palladium was in the solution?
If the solution got any sunlight, the black is probably silver chloride.
Did you test the green nitric leach with stannous or dmg to see if any palladium was in the solution?
If the solution got any sunlight, the black is probably silver chloride.
Did you dilute that at all, or did you boil it at 68%?diverwild said:
Concentrated acid has little "room" left for metal ions. When we use nitric to leach silver, palladium, or base metals, we usually dilute concentrated nitric acid with an equal amount of distilled water. The silver (or palladium, copper, etc.) nitrate is soluble in the water used for dilution.
Dave
The reason you use distilled water and nitric is to allow the silver to leach out of the alloy. Granted at the ratio of gold to silver this may be difficult you did 2 things that did not help the situation. First you used full concentrated nitric acid and Dave explained the problem with that, and second you added tap water which provided a source of chlorine to form a film of silver chloride on the gold.
Before you give up on leaching out the silver, try doing it properly by diluting the concentrated nitric with an equal volume of distilled water.
At 18% silver you aren't getting all of the gold with aqua regia either so try to leach it properly so as to eliminate any possibility of premature chloride formation. Rinse it well with distilled water, and then try aqua regia. If you can successfully lower the silver content the gold dissolution will be more complete.
Before you give up on leaching out the silver, try doing it properly by diluting the concentrated nitric with an equal volume of distilled water.
At 18% silver you aren't getting all of the gold with aqua regia either so try to leach it properly so as to eliminate any possibility of premature chloride formation. Rinse it well with distilled water, and then try aqua regia. If you can successfully lower the silver content the gold dissolution will be more complete.
upcyclist
Well-known member
The more likely scenario is that the chlorine in your tap water reacted with the silver nitrate to form silver chloride. The silver chloride crust then prevented the nitric from getting to the silver and the AR from getting to the gold.diverwild said:
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Diver- you need to look at the chemistry of AR, because when you do and learn it you'll not be asking if some Chlorine in Nitric will dissolve gold. I mean that kindly- it's the basis of most of what is done with gold refining (apart from cyanide leaching) on this forum. 8)
I'm not entirely sure what search term would be best could someone help me out?
Jon
I'm not entirely sure what search term would be best could someone help me out?
Jon
upcyclist
Well-known member
I'm thinking some Hoke reading is in order before he even attempts the forum searching.anachronism said:
Diverwild, check out Dave/FrugalRefiner's signature block--he posted the second reply to your OP. Click on one of the Hoke links and read up--then you'll have a much better knowledge base from which to start querying the forum and its members.
upcyclist
Well-known member
You are absolutely right--but it didn't react with the nitric acid to act like an oxidant. AgNO3 + Cl- = AgCl + NO3-diverwild said:
anachronism said:
well my friend، I am realy surprised it actually had gold،
yesterday a friend of mine gave me old japanese solder senju 1976، to prepare stannous chloride (which I never used before)، I made the test solution، and I had to test its efficiency، I had only that nitric solution which I used in the first wash، it gave light purple color، which made me skeptical، I evaporated the solution with maximum heat untill the solution became very green I put some HCL، let cool، filtered، SMB precipitation، I recovered 0.4 gram of gold، then the solution became pale blue، with stannous test it gave yellow color، I was very happy with this experiment
but how nitric digested some gold along with tap water.
