# Should I treat my cemented silver with dilute HCl?



## kadriver (Nov 17, 2010)

I am recovering some silver (about 3 troy ounces) from a batch of inquarted gold that I just completed. The silver dissolved into a nearly clear solution, but had some fine dark powder in it so I filtered that off.

The silver is cememnting out nicely with coils of 10 gauge clean copper wire suspended in the silver nitrate solution with string.

I have stirred the silver nitrate vigorously then filtered the nice new silver powder out and placed it in a corningware casserole to start drying.

Hoke, page 79, describes a process for ridding cemented silver of excess zinc. The zinc is from a DIFFERENT process than the one I am using.

Hoke says to mix up 1 part HCl to 15 parts water, and pour it over the cemented silver powder and watch for bubbles. When the bubbles stop on stirring, then wash well with clean hot water and allow the silver powder to dry.

Here is my question:

Can I, or should I, use this process on my cemented silver powder to further reduce any contamination of my cemented silver powder?

Is there any value to doing this, or is it just a wasted step?

Is there some other, more effective process to use to rid the silver powder of any contaminates?

I am just trying to get the purest silver I can with the method I am using (copper cementing).

I know the eltrolytic cell is the best way to get real pure silver - that is on my plate for the near future.

Thanks to all - kadriver


----------



## Oz (Nov 18, 2010)

If your silver had zinc in it for some odd reason the zinc would indeed go into a nitric solution along with your silver. However you cemented this solution on copper to recover your silver. The zinc will not cement on copper but will stay in solution. Proper washing techniques are all that is needed at this point to be free from zinc contamination. Even if zinc was present in your original feedstock drag down from your solution in your cement silver would be minimal.


----------



## Harold_V (Nov 18, 2010)

kadriver said:


> I am recovering some silver (about 3 troy ounces) from a batch of inquarted gold that I just completed. The silver dissolved into a nearly clear solution, but had some fine dark powder in it so I filtered that off.


That may be gold, and the reason I suggest you not crush inquarted gold when dissolving with dilute nitric. If you have done your work properly, there is no need, as the acid will penetrate fully, leaving the inquarted items intact. Once you crush, you liberate particles, as fine as colloidal gold and larger. It adds considerable time to the process because you must allow the fine gold to settle, otherwise it is poured off with the solution. 

Harold


----------



## nickvc (Nov 18, 2010)

The dark powder maybe gold so save it and process it with your next batch and your cemented silver can always be used in your next inquartation until you have an excess of silver for your needs from the silver in the karat scrap. A point I learnt from Oz is that if you have pgms in your scrap the silver collects it and comes out with it on cementation.


----------



## kadriver (Nov 18, 2010)

I filtered off the dark powder and saved the filter paper.

I knew it was odd. I will not crush the inquarted gold next time.

Thank you - kadriver


----------



## metatp (Nov 18, 2010)

If I dissolve silver/tungsten contacts in nitric acid, I often either wash the cement in HCL or refine one more time. A lot of the cntaminates seem to come out when I melt with borax, but I would like to remove them sooner.


----------



## kadriver (Nov 18, 2010)

I am learning a great deal as I go here.

I re-refined a batch of silver one time because when I tried to dry it, the silver clumped together and would not dry properly.

I assumed that something had contaminated the batch so I sent it back through the whole proess - and it came out lovely.

Can anyone explain why the silver clumped and would not dry properly.

I suspect it was due to improper washing.

Can someone give me a good wash process?

Here is what I am doing now:

Currently, I filter off the cemented silver with the blue liquid going into one filter flask. I save the blue liquid for further processing, or for addition to my waste tank once no more silver will cement out.

I use another filter flask and run boiling distilled water over the silver in the filter until the water runs clear and clean, then I run 2 more boiling water washes and put the sivler powder in a large casserole to dry.

So far this has been working, even though I still get a clumpy batch every now and then.

Is this sufficient - is there a better process?

Thank you for looking,

kadriver


----------



## Harold_V (Nov 18, 2010)

I didn't waste much time, nor effort, on cemented silver, the only exception being that which came from tungsten contacts. In that case, the cemented silver was washed with HCl.

I rarely re-used cemented silver, due in part to the loading of platinum and palladium. As has been stated, silver becomes a carrier for these metals, which are recovered from the slimes from a silver parting cell. 

I generally did my cementing in small plastic buckets (5 quart ice cream buckets are a good size). When the silver was down, the entire lot got a vigorous stirring, then allowed to sit longer. Often, after cementing, stirring exposes silver nitrate that gets dragged down and is trapped by the cemented silver. A vigorous stirring exposes the traces of silver nitrate to copper, where it is finally cemented. It is wise to test the siphoned solution by adding a drop of HCl, or a small amount of salt. If a white cloud forms, the solution should be treated with salt or HCl to recover traces of silver as silver chloride

Note that when you have platinum group metals present, your solution will be green, not blue. If, after cementing the silver, the color is not brilliant blue, test with stannous chloride. If the test yields positive results, allow the entire lot to sit longer, insuring that you have an abundance of copper present. The platinum metals are slow to cement, coming down last. They yield a black deposit, and discolor the silver accordingly. 

My procedure was when all of the metal was down, I'd simply remove the copper, then add tap water, stirring well. When the values had settled, I'd siphon off the solution, and repeat the process until the rinse was clear of color. At that point I'd get the cemented silver in a Buchner funnel, tamping it down well using the butt end of a (large) pestle. A final rinsing with tap water after the silver was well tamped yielded clear water. 

After removing the vast majority of the water, I then transferred the cement silver to a large Coors evaporating dish, which was then placed on a burner at low heat to dry the silver. It was heated to well past the boiling point of water, at which time it was common for traces of nitric to fume off. In spite of careful rinsing, some is still present, if not consumed totally. 

The dried cement silver was melted, then a small amount of borax added to the molten silver, which removes oxides that are present. The molten silver is then poured to a cone mold, so the flux can be separated easily. The resulting button was then re-melted, along with others, and poured to an anode for the silver cell. 

There is no need to wash your cement silver with distilled water. The traces of chlorine that are present do no harm unless your objective is to dissolve the recovered silver in nitric before it is melted. 

Harold


----------



## kadriver (Nov 18, 2010)

Got it - Thank you

kadriver


----------

