Silver Sweeps Dissolving Extremely Slow

[SilverMac18]

So I’m pretty new to this and have been watching a ton of Screetips videos. To the point of my eyes crossing So here is my question. I’ve been trying to process 50 ozts of silver sweeps. I screened out all the large material first. Then incinerated the material. Then I added distilled water and nitric acid and heated. But it is taking a lot longer to dissolve then if I had formed shot with it first. So I’m assuming it’s because with the silver sweeps which is like fine dust has less surface area. So how would I go about melting this into shot first with all the dirt that is still present in the sweeps. In order to save on the nitric acid. As I’m making my own concentrated nitric which takes all day just to get 1 liter. I’ve dissolved 900 grams of pure silver for the electrolyte and it only took a day as I made shot with it and also it used way less nitric. I’m currently on day 4 with the silver sweeps and still have about half of this left. Very frustrating. Any ideas would be greatly appreciated. Thanks in advance ! Or Am I just being extremely impatient lol

 

[Lou]

It isn't all silver or it would have dissolved, and quite violently.

One thing I always do is wash any sweeps with DI water extensively after incineration, if I'm going to part with nitric. Typically I just add more silver and melt the sweeps that way, in which case I would mix in silver powder or shot with flux (2 parts borax: 1 part soda ash: 1 part silica) and the sweeps (2 parts flux, 1 parts silver, 1 part sweeps) and bring to a solid 2000 F with good stirring.

That generally parts just fine leaving the gold and most of the platinum. The Pt/Pd/Ag can then be worked up any particular way.

 

[kurtak]

I have to agree with Lou - when dealing with sweeps you are better served smelting them first so you can deal with refining "metal" - rather the trying to leach a fine (dust) metal from a bunch of powder that has a bunch of non-metal crap in it

SilverMac18

How deep are the sweep powders in the bottom of your beaker ? - and are you stirring the powders up during the process of dissolving ?

I ask because "in theory" powders have MORE surface area then solid metal (like shot) so "in theory" powders should dissolve faster (much faster) then shot

The problem is - that if you don't KEEP the powder "stirred up" the acid does not get fully in contact with the metal to dissolve it

in other words - with shot - there is a lot of space between the pieces of shot - so the acid is able to "flow" in & out between those spaces thereby keeping fresh acid contacting the shot by the "motion" of the acid from the reaction of the acid it's self

What happens with powders - if they are not stirred continually &/or "often" - is because the powder is so fine it will settle & pack in tight - so - although you have some acid "in" the powder - it will dissolve "some" metal but then - once the acid "in" the powder is used up the reaction "in" the powder stops --- at that point the acid is only working on the top surface of the powder in the bottom of your beaker

In other words because the acid is only working on the surface of the powder it's kind of like trying to dissolve a sold Kilo bar of silver - it's going to take MUCH longer to dissolve a solid kilo bar then dissolving a kilo of silver poured to shot

The other problem with trying to leach incinerated "sweep powders" is the "dirt" (ash/fine grit etc.)

Depending on how much "dirt" you have the dirt at the very least is going to be a filtering problem & can end up being a nightmare - even with a vacuum filter

Smelting the sweeps (as suggested by Lou) will "slag off" most if not all that dirt leaving you with just metal to dissolve/refine

So - IF - you have a furnace I recommend first smelting the sweeps (add silver as a collector) - pour the smelt to a cone mold - knock the slag off - re-melt the metal cone - pour it to shot - refine the shot --- or pour to silver (anode) bars & run it in a silver cell

Some people run silver shot in their silver cells - I prefer running anode bars because IMO you get more complete parting in the cell with bars instead of with shot

Be careful when dissolving powders (with stirring) they will foam up MUCH more then dissolving shot

Kurt