Converting .925 Scrap Silver to shot for my Anode Basket

[Yggdrasil]

Hey Kurt, curious as to why it’s not advisable to do the sugar conversion immediately after the lye conversion without a wash in between the two. I have noticed the amount of heat generated is far greater when skipping that intermediate wash. Thanks in advance.

Do not double post, he will answer when he sees it.

 

[kurtak]

Hey Kurt, curious as to why it’s not advisable to skip washes in between the lye and sugar conversions. I have done it both ways, with washes in between and without washes after converting to silver oxide then going straight to adding sugar to get the elemental silver. I will say the amount of heat generated is higher with skipping the wash after the lye conversion. Thanks in advance.

I have posted about this a few times before - here is one place where I posted about the problem of "mixing" the lye & sugar together when converting the AgCl

https://goldrefiningforum.com/threa...ing-the-use-of-salt-vs-hcl.30504/#post-319679
So - copied from that thread/post ----------

For what it is worth --- some people suggest first dissolving there lye & sugar together then adding the lye/sugar to the AgCl thereby doing the conversion & reduction in one step & that's fine if you are doing "small" batches (a few ozt) --- however - if you are working with larger batches (pounds) I do not recommend doing so

Why ?

Because your lye/sugar waste is going to be HIGH Ph (like Ph 13 - 14) --- high Ph waste is considered hazardous waste & so needs to be adjusted to a Ph between 6 - 8 to be considered safe for disposal

The problem of adjusting the lye/sugar solution down in Ph is that around Ph 11 you start precipitating the sugar out of the lye --- it precipitates out as a VERY thick/heavy sugar foam that does not dissipate (foam does not go down) & does not separate (foam on top - liquid on bottom) the foam makes it impossible to filter --- before you reach Ph 8 (the high end of your target Ph adjustment) you will have a sugar foam so thick you can't stir it to finish adjustment & due to the foaming have 3 -4 times the volume you started with

It's one thing to dump a gallon or two of lye/sugar down the drain (without adjusting Ph) - its another thing doing it with larger volumes

Because of the above - the lye/sugar waste can not be used for adjusting the Ph of other acid waste solutions

So if you convert you AgCl to AgO with lye only - then wash the lye out - you can use that lye to adjust Ph of other acid waste --- then when you use the sugar only (the lye has been washed out) to reduce your AgO to Ag & you wash the sugar out you have only sugar water which can go down the drain

End copy from other thread
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I added the bold print in the above copy to highlight why I do not recommend mixing the lye/sugar together when doing the AgCl conversion

In other words - if you first use just lye - then wash the lye out --- you can then use that lye solution for treating other acidic waste products from other refining processes

If you combine the sugar with the lye you can not use it to treat other acidic waste because it will make one hell of a mess

Kurt

 

[kurtak]

In a solution as concentrated as a Silver cell electrolyte, there can be ounces per gallon of Silver to be cemented. I prefer to add a slab of copper which is pretty smooth so it has no ridges or grooves to trap any cement Silver and when the reaction slows, meaning it is still displacing Silver but at a reduced rate, remove the copper slab. You have not recovered all of the Silver yet but you have the lions share. Next filter and rinse the cemented Silver. Rinse it well, mix it and rinse some more. This Silver will be about as pure as you will get it. And I have seen 999+ this way.

4metals nailed it - one of the keys to cementing silver with copper & getting 999 (plus) silver is stopping the cementing process just a bit short of completely cementing out all of the silver --- the SMALL amount of silver remaining (after stopping the cement process short) can then be recovered in a second cementing process (stock pot recovery) or dropped out as AgCl - this "second" recovery (of the SMALL remaining silver) is of course done after being sure ALL the copper nitrate & SMALL amount of silver (nitrate) has been washed out of that "first" cementing

Also - GOOD agitation is required here so that as the silver is cementing the silver stays stirring up in the solution so that the silver does not settle/build up in the bottom of the cementing vessel/tank as copper oxide coming off the copper during cementing can become entrapped in the silver cement if it is allowed to build up in the bottom of the vessel/tank

Remember - in my last post I said it is not the copper nitrate that is a problem of contaminating the silver (as the silver nitrate can be COMPLETELY washed out) rather - it is bits of actual copper &/or copper oxide that come off the copper that cause contamination - which then gets trapped in the silver cement if it is allowed to settle in the bottom of the vessel --- copper/copper oxide that gets trapped in the cement silver can not be washed out --- so when the cementing silver is kept stirred up in the solution it allows the copper to complete go into solution (as copper nitrate) rather then the "possibility" of forming copper oxides

Also - make sure the copper is completely submerged - if you hang the copper so that the top of the copper is above the solution it will form copper oxide on the exposed copper & that copper oxide will fall into your silver cement & contaminate it

Per the bold print in the above quote (by 4metals) I prefer to add a slab of copper --- I prefer to use fine copper powder - at least 100 mesh copper powder or finer (200 - 300 mesh)

The concept is the same - you still want to stop the cementing process "a bit" short of the cementing process & you still need GOOD stirring/agitation

I first learned about this (producing 999 plus silver by cementing with fine copper powder) when a member posted about it here on the forum quite a few years ago

He was doing this on a relatively LARGE scale - he was doing it in LARGE stainless steel tanks with SS stirring paddles on SS stir rods --- he was turning out several thousand ozt of 999 plus silver every day

You want to add the copper powder in several addition - giving a bit of time (10 - 15 minutes) between additions of copper powder to insure all copper powder goes into solution as the silver cements out & of course testing between additions - & then stopping "just short" of cementing out all of the silver

One way of judging just how effectively the cementation is proceeding is to have a length of solid copper wire and some steel wool. Polish the end of the wire so it shines with the steel wool. If you dip the copper wire in the electrolyte when the reaction is at peak, you will see how quickly it accumulates. Every time you re-dip the wire it needs to be polished with the wool. When you think it's time to stop, dip in the polished wire and when it discolors slightly it's time to pull the big slab. This is a modification of Harold's end of reaction test when you have no stannous chloride, but it is quite effective on Silver Nitrate.

That is certainly one way to test & it certainly works - personally I preferred to test with HCl

Put 10 - 15 ml solution (silver/copper nitrate) in a 25 mil beaker - add HCl - when you get just a thin cloud of AgCl (instead of actual AgCl precipitate &/or heavy cloud) you know you have hit the point to stop the cementing process in order to get your 999 plus silver (after of course washing all the copper nitrate out of the silver cement)

You can do the same thing with all of the precious metals - whether it is silver - gold - or PGMS --- you can in fact cement them out - with copper - & have them cement out at 999 plus - the trick is simply stopping the cementing process "just short" of complete cementing

This is of course assuming the solution you are cementing only has one PM in it - if the solution has more then one PM in it then all the PMs will come down

I learned many years ago - that cementing with copper can often be a refiners best friend

It is a refiners best friend when -----------

1) when you have VERY dirty solutions (lots of base metals) such as leaching ceramic CPU &/or ceramic IC chips &/or leaching IC chip bond wire concentrates - in these cases - chemical precipitation can & often will drag down traces of base meals - on the other hand - once you learn to cement with copper & do it right - you can get your PMs back as 997 if not 999

2) in cases (like the above) where you NEED to use an excess of nitric (or other oxidizer) to insure all PMs (along with base metals) go into solution --- in those situations - the copper uses up the free oxidizer as well as giving you back you PM - all in one step

I call the above - going down & dirty

And don't get me wrong - when dealing with clean product to start with (like gold foils etc.) & where you have better control over the oxidizer - chemical precipitation is the way to go

But when you have to go down & dirty & need to use excess oxidizers - cementing with copper can be & often is the refiners best friend

In my years of refining for a living I cemented A LOT of PM with copper - & had those PM come back very pure

For what it is worth

Kurt

 

[4metals]

The situation I have encountered most with Silver Chloride was processing the chlorides after aqua regia refining of karat gold or chemical stone removal. In that situation the chlorides are always holding Gold so they need to be refined, typically by a Silver cell in house or at an outside refiner. Often the Gold assay can approach 1%. Not something a refiner is wanting to give away for free to his refiner! Generally larger refiners have a minimum assay below which they do not pay on Gold in Silver bars. And they have a minimum return on Gold contained, often 1 ounce. The minimum payable assay is typically 0.0003 (ironically that is what sterling typically holds in Gold so that number was not derived by accident). For this reason, a lot of medium sized refiners venture into Silver refining. Especially refiners who deal with jewelers where they can sell their electrolytically refined Silver.

Back to chlorides. In the scenario above, the Silver is already in the chloride form so reduction to metal is needed. It is rarely melted, occasionally tumbled in dilute sulfuric with iron, and most often reduced with caustic and dextrose. In consideration of what the resultant bars will contain the process is conducted with as little rinsing as possible and a result of 98% Silver plus any contained Gold is acceptable. This is possibly where the misnomer that the caustic dextrose method often results in 98% purity gets its origin. Take it from the GRF, that is fake news!!!!!

But for a small shop, it is a viable option and the important consideration of eliminating the caustic snot made by caustic and sugar should not be overlooked. Rinsing the Silver oxide of the caustic and re-using the rinse water to neutralize other wastes is viable. And the rinse step after the sugar reduction produces a waste that requires no special treatment and many utilize the "porcelain goddess" to handle that sweet waste!

 

[cejohnsonsr1]

Here’s some more weirdness. One of the comments that I was typing a couple of days ago that disappeared before I finished just showed up here at the end of this thread. 2 degrees in computer science and I’ve never seen anything quite like this before. Lol.