Black sediment when dissolving sterling silver

I have refined some gold jewelry two times now, and have saved the HNO3 solution. For the first time, I used some to refine some sterling. I added some distilled water and the silver jewelry, then heat. I needed to add a little nitric acid twice, and some distilled water. When complete, I had my solution and some small scraps at the bottom that didn't dissolve, so I knew the solution was saturated with metals. However, I also have a black sediment at the bottom and cannot find what that might be. I have searched, but nothing on "black" sediments. I have attached a picture and was hoping someone could shed some light on this. I filtered it out and need to know if I toss the filter, or if it has value.
By the way, the filter in the picture is one of two. I had to double my filter and do it again as there was still some that got past the first filter.

Probably gold.

When I used to refine substantial sterling, it would show up at about 3-6 ounces/10,000 ounces of sterling.

Some things, like old Mexican coinage had enough to be worth your while!

Well, I got two filters like this one, with that much or more sediment. I could try rinsing really good, then adding some HCL, and see what happens. If nothing, I will drop in HNO3 and see if I get my orange AR.
Worth a try? Alternatively, I could just rinse it into my silver stock pot. What's the best way to handle it?

Have you tried just adding some fresh nitric to it? Sometimes a dissolution stalls because the acid becomes very dilute. If it were mine, I would take a small sample and add a bit of fresh nitric and distilled water. If nothing more dissolves, add some HCl and test it with stannous.

Dave

Lou said:

Probably gold.

When I used to refine substantial sterling, it would show up at about 3-6 ounces/10,000 ounces of sterling.

Some things, like old Mexican coinage had enough to be worth your while!

Click to expand...

Aye either that or higher PGMs.

Thanks all. Good info. I think I will try the nitric first, with some distilled water (which will already be the case since that is how I will "flush" the filters). If I get digestion, it will let it complete and add to my other (unused) nitric/metals solution. If nothing happens, I will add some HCL (while it is cool) and see if i get the orange. Also test with Stannous.
Not sure when I will get to this, but I will update the post when I do!

Watch the color after nitric addition. Is it white?

Well, I cut a small piece of the filter with the thickest of this sediment. I added about 20ml of distilled water to a small beaker, then added my piece of filter with the "dirt" on it and about 3 drops of Nitric Acid. Swirled and watched, but nothing. After a minute or so, I added about 4ml of HCL. It warmed a little, but still NO color change at all. I waited several minutes. I guess this is just some sort of dirty residue that came out of the old sterling pieces I digested.
Thanks for the input everyone! My silver cement is drying out now and I am excited to melt it down and see the results of my first silver precipitate!

renkenbw said:

I added about 20ml of distilled water to a small beaker, then added my piece of filter with the "dirt" on it and about 3 drops of Nitric Acid. Swirled and watched, but nothing. After a minute or so, I added about 4ml of HCL.

Click to expand...

3 drops of nitric in 20 ml of distilled water is incredibly dilute. I wouldn't expect it to do anything. We usually use equal parts nitric acid and distilled water.

Likewise, 20 ml distilled water, 4 ml HCl, and 3 drops of nitric isn't going to do much. Aqua regia is traditionally about 3 to 5 parts HCl to 1 part nitric, with the nitric being added in increments. But all the water dilutes it so much...

Dave

Thought I might still get a little color, without using too much. I will try it again tonight with just 3-5 drops of distilled water and nitric. Then, about the 2 ml of HCL if no color. I will post my result.

FrugalRefiner said:

renkenbw said:

I added about 20ml of distilled water to a small beaker, then added my piece of filter with the "dirt" on it and about 3 drops of Nitric Acid. Swirled and watched, but nothing. After a minute or so, I added about 4ml of HCL.

Click to expand...

3 drops of nitric in 20 ml of distilled water is incredibly dilute. I wouldn't expect it to do anything. We usually use equal parts nitric acid and distilled water.

Likewise, 20 ml distilled water, 4 ml HCl, and 3 drops of nitric isn't going to do much. Aqua regia is traditionally about 3 to 5 parts HCl to 1 part nitric, with the nitric being added in increments. But all the water dilutes it so much...

Dave

Click to expand...

Whilst I agree with Dave's principle here that your solutions are too weak, I don't subscribe to the "we do things" in a particular way theory. Every task requires something different. There are no hard and fast rules as years of contributions on this forum have amply demonstrated.

Many sterling silver items are weighted with epoxy, clay's, cement, or other types of fillers, for example, the weight in the base of candlestick holders, fillers inside the knife handles.

Silver surface oxidization as a sulfide.

Solders or platings.

Less likely gold or PGM's in the silver

I agree Richard.

My PGM comment was based upon plating.

Jon

Another alternative to adding more acids is to heat your solution and see if you get any reaction before adding anything anything else.

butcher said:

Many sterling silver items are weighted with epoxy, clay's, cement, or other types of fillers, for example, the weight in the base of candlestick holders, fillers inside the knife handles.

Click to expand...

As well the oils & waxes on jewelry - jewelry can & often is VERY dirty (body oils & waxes from make up)

Did you take a torch to it to burn off oils, waxes &/or fillers (as pointed out by butcher)

If you did not torch it - the crap will result in a black (dirt) residue/sediment

if you did torch it - carbon/ash will result in a black residue/sediment

Kurt

Nothing precious, just “dirt”. I did incinerate first, but I know there was dirty and tarnished silver. No worries, I’ve learned some new things, and know how to test moving forward. Thanks all!

New here and I may be off.

Did you incinerate the silver before dissolving? Or did you melt it into flakes first?
On the first part I have had the experience of silver cleaner that some people use that goes black in solution. The second part could be nothing more than borax, although it usually turns white for me in solution,

renkenbw said:

Nothing precious, just “dirt”. I did incinerate first, but I know there was dirty and tarnished silver. No worries, I’ve learned some new things, and know how to test moving forward. Thanks all!

Click to expand...

Save ALL of your filters. I've gotten several grams of gold from my silver silvers. Put them up until you've got a pile then burn them to a fine ash. I made a video that shows how to process silver filters. Silver is a carrier of platinum group metals and gold. But you've got to concentrate the values. One filter won't give any kind of yield. But 30 or 40 will give you several grams of pure gold!

Here is the link to my YouTube video that shows the whole process start to finish;

https://youtu.be/GYDGOSDPTxc

Respectfully,
kadriver (sreetips)