assay result/silver crystal, advice needed.

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Lightspeed

Well-known member
Joined
Jul 29, 2017
Messages
80
Location
Western Australia
Hi all,
help is needed from experienced members please. My assay result shows I have some trace elements which I am struggling to quantify in my assay report.

This assay is on crystal silver from stainless steel silver cell runs.

Loose description of my process:
1:Clean glassware with Bar keepers friend, triple rinse with distilled water.
2:Digest clean scrap in 50/50 nitric &/DW(source is small amount of jewellery, sterling pre decimal junk silver coins, hallmarked sterling in various forms mostly antique)
3:Filter; either vacuum or gravity
4:precipitate with clean 110 grade copper slab
5:Rinse,rinse,rinse,rinse, you get the picture,test samples separately for Ag nitrate & ammonia Cu test etc and rinse, rinse, rinse etc
6:Vacuum filter rinse
7:Dry
8:Melt in Morgan salamander clay graphite crucible, no flux in LPG fired furnace
9:Shot into iced tap water
10:Rinse shot and dry on hotplate

Electrolytic cell
1: Electrolyte composition; Silver crystal from previous run or silver shot, electrolyte test for palladium with DMG. Electrolyte colour is either colourless or slight tint of yellow. Electrolyte is heated down to nil active nitric on remaining silver digest. Ag concentration of 200g pl minimum x 4L
2:Vacuum filter electrolyte with Whatman No 5 paper twice through same paper.
3:Clean inside of 300series SS bowl and rinse with DW x3
4:Rinse all cell running equipment in contact with electrolyte several times in DW, Muslin filter in dilute nitric and DW wash and x3 rinse
5:RUN cell 4-5 Amp @3-4V
(note** at worst electrolyte condition after 2 kilo run is slightly tinted greenish, certainly not enough colour to indicate possible co deposition issues)

Crystal
1:Harvest and rinse, you know the drill, rinse and rinse and rinse, test sample for silver nitrate with hcl and rinse as needed, dry crystal and store or re-run according to needs.

Well as a rough in you get the picture, I may have missed a few small details but that's pretty much me for silver runs.

So obviously I need help with my contaminants, and where and at what steps and points where i must apply extra work, or extra processes, i already spend a small fortune on rinsing alone, and I don't know where I am getting Calcium and Potassium from. I am obviously still learning from all my experiences to this point and have a way to go yet.
My DW is not homemade and is store bought deionization process, I do not get Ag chloride from its use at any stage.

There is much room for improvement with my process management, I hope the ones who shoot for 4N silver can help.
By the way, this Ag shoots 99.99 on two bullion dealers handheld XRF's, its not good enough for me 99.95 is not where its at for me, I need 4N, because its my goal and my standard I set for myself.

My results are listed below from 2 separate samples to the right of BATCH-00 corresponding to the elements and listed in ppb.

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edit due to formatting.
 
Sorry brother i have been away.
Have you checked your nitric as a source of contaminates?
The silver cell is not a guarantee of 4-9 silver in a one step process when all you need is 999 and you coming out the mud hole so to speak with the feed stock. It can be but according to the feed stock. If you run it a 2nd time though a cell i can't imagine you not getting 4-9. I have a cell set up next to my first cell. Take two bowls and run them off of the same 10 amp power supply. As the crystals come out the first bowl run them through the second bowl. Just lightly rinse them to cut down on cross contamination between cell from drag out. You can run crystals through the 2nd bowl for what seems like forever before you have to change the solution. Of course you have contaminates now, but each step you take it further up the ladder the less they get. The best tweaks are downstream of your upstream process. What is your feed stock? Do you use a chloride conversion in your feed stock process or do you use a feed stock process from cementation? Sodium Formate reduction? Their are lot of ways contaminates can get into your process stream and travel upstream to give you headaches. I call it the Eco system of processing! :mrgreen: :mrgreen:
 
I see above you said copper. After a couple of water washes of the cemented silver to remove the copper nitrate solution do you do a rinse with Hcl then the water washes?
 
After you cement the silver on copper are you washing the cemented silver with Distilled water? You can use chlorinated water at this step.

I keep my wash water separate in my operation and it directed to water evaporators to condense my waste exposure and cut down on the large volume of water it requires. For a small guy a simple water evaporator can be an open top plastic drum with a $10 box fan on top.
 
This one is optional. In your fist step of dissolving the feed stock you use distilled water. When processing in volume i use straight tap water. Any chlorides that might be created will be trapped in the filtering process and recovered downstream anyways. I offer 98% accountability and this falls with that range by far. In that filter you may also find gold from time to time. Palladium will follow either the nitric in solution or it will follow the silver as a complex. Either way the copper will drag it down. The platinum, if any will be as a solid in the filter, or as a complex which will carry over with the silver and be dragged down by the copper cementation. Later it will be separated out in the cell basket.The palladium can be found in the cell basket or if the ph of your cell solution is high it will dissolve and be found in you cell solution. According to your feed stock sometimes you have to adjust you cell ph by adding nitric acid to boost or low the ph for certain reasons.
 
When you sent the sample in did you send crystals or melted samples?
I wouldn't trust these kind of analytics to a hand held xrf when you get into this territory tolerances get real tight.
 
I have used tap water for rinse after cementing once, the chlorides were kept and processed after accumulation of enough to warrant it. I have since stopped the practice as I absolutely hate processing silver chlorides, chloride process is reserved for me as a when I must do only when I accumulate enough to bother. So SOP is DW rinse at all stages regardless, our local water authority in all their wisdom injects chloramine gas into our tap water.I have not used Hcl as a rinse, although now I can see the benefit of such a step with my listed contaminates, it will eradicate some of my issues. The Hcl rinse at approx 20% dilution? I imagine I would use this rinse before the Buchner filter step to avoid unwanted metal precipitates being held up in the paper i have been using Whatman 42 for cement final few rinses. I have no idea where I have picked up potassium, the only source I figure possibly could be the nitric? It does not have a technical readout on the bottles. I do have technical grade Hcl made by Merck, it has a technical readout on the label. I always get a fair amount of gold after initial digest into nitric the source is usually the antique silver as one of my main sources as previously mentioned, it's either in flakes or dark brown red residues caught on the filter paper. I generally keep my cell around ph of 2, there are many recommended ph levels for cells in my readings. My feedstock is 99% copper cement, I hate chlorides. No I don't trust handheld XRF at all this is why the ICP assay, my sample was boiled and rinsed in DW and sent in a clean but not sterile glass vial. I am getting through your list of questions Ralph, bear with me if I get overlap
 
I was sort of happy with my residual copper on the assay, yes it can be improved but as a major secondary metal In my source I was happy with the ppb result, the other metals not so much, the Tellurium, Lead etc bothers me, there are 500000ppb I need to eradicate. Can pouring shot into tap water carry over Calcium pre cell run?
 
But did they go through two separate processes in two separate cells or just through the same cell twice?
Or are you talking about you sent two samples from two different cell runs where the materials only went through the cell in a one single pass process?
 
Two entirely separate cell runs, separate electrolyte for each batch new electrolyte in both batch runs. Sadly both were run twice, in same electrolyte due to visual lack of copper contamination and neg test on DMG for palladium, each electrolyte was topped up with 200g of silver to bring up cell electrolyte silver concentration.
 
Lightspeed said:
I was sort of happy with my residual copper on the assay, yes it can be improved but as a major secondary metal In my source I was happy with the ppb result, the other metals not so much, the Tellurium, Lead etc bothers me, there are 500000ppb I need to eradicate. Can pouring shot into tap water carry over Calcium pre cell run?


Don’t trust your labs and what do the crystals look like?
 
My head is a little screwy, and I've never ran a silver cell...so take these comments with a grain of salt.

Barkeepers friend is a mixture of oxalic acid and feldspar. Feldspar is composed of K, Ca, Na...and is not water soluble. Any possibility your stainless bowl is not electropolished and harboring small amounts of feldspar in the cracks/surface abrasions that are then picked up in the crystal when you harvest?

I only ask this because I don't see a quantity of crystal ran. If you are only processing a couple ounces and getting wonky assay results...I can see this being significant. If you are processing a few kg, then sampling, not as much.

Same question with how you wash your muslin.
 
silver crystal from batch 1 pics

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silver crystal from batch 2 pics


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Lou, although I live in a mining state here in Western Australia, assay is not cheap, its $200 Aud to run 2 samples, the lab I chose is also the lab which other assay labs (I.A.L.) send their samples to for umpiring. I am not saying my lab is the ducks nuts but I did do my research before settling on a lab to do the work. With that being said it does give me cause for concern over some elements being so high which were not expected, are they cleaning out their spec well enough before running other samples, honestly I thought that is what the top line in the report represents, a datum line if you like of a base reading before running the sample. I am no lab tech and I have never had assay like this done for me before, its a far, far cry from my prospecting days of bottle rolls or fire assay.



Snoman,
the muslin is washed in a dilute Nitric and DW soak and wash then rinsed with DW not with Barkeepers. Your point regarding the microscratches on the SS bowl surface is valid, although in addition to the 3x DW rinses after ward it also gets a wash with dilute Nitric and DW as well, hey anything at this point is on the table for review. I like to process approx. 2 kilo runs which is a reasonable capacity for the 4 litre cell in a single run, I can do this as there is little discolouration to the electrolyte to give me warning of possible co deposition issues.

Lou,
Of note in regard to the crystal, on the first run it has a more.... well.... silvery appearance, second run this characteristic changes and the crystal takes on a more pale white look. I do wish I had a trinocular metallurgical microscope to visually analyse the crystal.

In my research here on the forum there are a few using Hcl washes, some incinerating the cement before this step and some not, some boiling in Hcl and some not I have also seen sulphuric rinses mentioned somewhere also dilute nitric rinse.
 
Lightspeed,

This may be a dumb question because judging from what you have done and described so far you seem to be an intelligent guy, but do you realize just how small one part per billion is? In keeping with Lou's statement, the lab needs to be as scrupulous with it's cleaning and preparations as you do, are they? Again one part per billion is not a standard you make up with a pipette and volumetric flask, so to split hairs that fine really takes you to another level.

That being said, we sit here evaluating everything you put into your solution, but lets for a moment consider what you have a hard time removing from the silver you have refined. First consider the fact that water isn't called a universal solvent for no reason. It has the capacity to dissolve a lot of different elements, especially at the levels you are talking, parts per billion. It also has a property we call surface tension, or in other terms, the ability for it (the water filled with parts per billion of so many elements) to cling to your refined silver. True multiple rinses make it better but it is tough to rinse it all without some help.

Years ago I would never had thought this an issue because all silver before the cell was nitric parted and the purity of the silver going into the cell was high. So the electrolyte remained clean for a long time and commercially, the goal was .999 fine. Then along came Sterling Silver, Silver high enough for it to work in a cell but the trade off was a rapidly increasing level of copper in the cell. The purity a Silver cell can produce remains high but the rinsed (and rinsed and rinsed and rinsed) product, when dried, may be contaminated. This means that the electrolyte, or what remains of un rinsed, or poorly rinsed electrolyte on the surface can contaminate your clean silver.

To the rescue comes a spin drier! I have installed many stainless steel basket spin driers after the rinse cycles to physically remove the last of the rinse water. The effect of the spinning removing that last of the last few drops of water and preventing it from drying on the Silver is dramatic. This tells me, from a good number of years of personal experience, that the contamination may very well be from the rinse water (spelled universal solvent!) that is dried on to the Silver from your cell.

But spin driers are costly, and stainless steel spin driers even more so. And while a small stainless spin drier is made which holds 6" baskets, it still is over the top expensive for a small refiner. I have taught some clients how to make a small silver cell, very likely much like your cell Lightspeed, to make high grade silver for their assays. The trick I use to get the last of the rinses off is from the salad section of your local cooking supply store, a salad spinner.
salad spinner.jpeg

I have them line the spinner with a fine polypropylene mesh screen to retain the silver needles and rinse their silver when harvested and then spin it dry, or close to dry before using heat to dry it.

I think your issue may well be impurities dried on to your silver rather than impurities in your silver.
 
Thanks 4Metals, I know right, here's me little nobody home refiner trying to squeeze 4N from a home project, posting here whining about how to improve on my already fine silver.

I do not know much about the assay lab https://www.labwest.net/
but they are the only lab in my state capital which run the type of assay I need, I did do the ring around. I cannot speak for their cleanliness and prep, but I will give them the benefit of the doubt as I am a home nobody getting by with a shed/backyard lab so for the time being I am inclined to self reflect on my own cleanliness and procedural steps before I blame the so called pro's.
I am not saying that labs are a source of infallibility regarding assay, hey when you are dealing with ppb the microscopic contaminants make a huge influence on the final result.

There are many members here on the forum who I hold in high esteem, I have never met them, never even had a computer aided conversation with most of them, they have no idea of the regard that I have for them, due to the fact of their amazing achievements using their garage (except for Kevin, I have lab envy)and locally sourced materials, their ability to get by on ingenuity( I love it) and dedication is simply commendable, not even working in a pressurized room yet they all achieve a fine result and is highly respected by many.

So yes I am being a bit picky for something made in a mixing bowl, and it is that fact of being picky which gets those who strive for excellence to where we want to be, to share our experience so that maybe others like in dedication may learn and apply our experiences and in turn strive themselves.

Yes it is another level, but it has been reached by some members and I demand that level of myself, it cannot be given, it cannot be shown, only by researching, doing, making mistakes and learning will I achieve my goal, I just need some pointers and nudging in the right direction. I am proud of what I have achieved but at the same time disappointed I did not reach the mark set for myself.

My crystal after a single run has a beautiful almost schiller moonstone effect crystal pattern when poured, when I first poured this sample bar I had no idea what i was looking at, I thought it was contamination, I re poured that bar every which way I could trying to get rid of it for hours...literally, bahahaha hindsight eh!!! I laughed when Ralph told me what it was!!

"We chose to do these things, not because they are easy.......but because they are hard"

A salad spinner it is then lets use a centrifuge to spin it out, cant hurt and its worth a shot, thanks for the tip 4metals.
 
here's me little nobody home refiner trying to squeeze 4N from a home project

To the contrary, it is because of you and members like you, that this forum has become what it is. The fact that there are so many educational, technical, and working backgrounds represented here helps us come to solutions from an amazing number of various perspectives. Add in the economic factor of refiners wanting to do this economically because they either cannot afford a big setup or when they are refining in some poorer countries and it just isn't available and you get what we have here.

The reason I asked about the realization of just how small a part per billion is, is because it is unimaginably small. When e-scrap is sent to large smelters or refiners, the result is often expressed in PPM, parts per million. That is one gram of the precious metal in question to one metric ton of material. Not exactly a huge quantity. Well one PPB, part per billion, is one thousandth of one gram per metric ton. Makes a needle in a haystack look substantial. People always have trouble with both excessively large and excessively small numbers which is why scientists try to break them down into easier units. Personally I hate billions because here in the US the politicians just throw those numbers in the billions around like nothing. I would prefer it for budget reasons if it were said as one thousand million dollars instead of one billion dollars! But I digress, falling towards that slippery slope of politics, my apology. Suffice it to say a part per billion ain't much.
 
I'm quite confused on what you're saying vs the analysis results. Like 4metals said, a ppb is a very small amount. If your silver were 99.99% pure, there would be 1 part contaminant per 9,999 parts of silver. That little 1 part/10,000 parts, total weight, would be the equivalent of 100 parts per million or 100,000 parts per billion, total contaminants. Unless I missed something in your readout, I came up with the total contaminants about 18,000 ppb, or 18 ppm, with over half (10 ppm) of this being an innocuous amount of sulfur. Tarnish is composed of silver sulfide. You might of picked up that tiny amount of sulfur just from exposing the sample to the air. If anyone is burning coal or wood or trash or any other sulfur containing material in the area, there will be sulfur in the air. At the tiny amount of 10ppm S, that tarnish would most likely not be visible.

If that analysis were true, which is questionable, your silver would be about 99.9982% pure - nearly 5 nines. If you believe that analysis, you've exceeded your goal. That purity is getting into (or, already is into) clean-room conditions. If my tarnish idea is correct and the actual sulfur were,say, 100 ppb, you would have 99.9992% Ag. The only other big? contaminant is the 5 ppm Iron. Maybe that came from the stainless. Maybe from the nitric. Maybe from the copper. Who knows?

Sometimes, labors of love are expensive.
 
It is over 4N to be sure. The crystals are inconsistent with lower purity product.

The fact that there’s 38 ppm tellurium (which you missed, Chris) and no selenium should be cause for concern.

There are a variety of things that ICP-MS is useful for but there are interferences. Context in assays!

To be honest, I think the assay may be half right at best.
 
well thanks for the confidence Lou and Goldsilverpro.

Lou and Goldsilverpro, the numbers I have:

Batch 1: 498409.91ppb total impurity or 999501590.09ppb purity or 999502ppm or 99.95%

Batch 2: 408162.87ppb total impurity or 999591837.13ppb purity or 999592ppm or 99.96%

The impurity calculation has not included the minimum reading range of some elements, but the Ca alone is in the hundred thousand ppb.

derived from online conversion=https://www.convert-me.com/en/convert/percent/uppb.html?u=uppb&v=999%2C591%2C837

I really do wish I had 4N Goldsilverpro, can you enlighten me how you arrived at over 4N? where have I mis calculated?


edit: there are a few elements I question eg: so I have Cr with Fe lets say from the stainless steel but with low Mo but no Ni also considering the presence of Vanadium points to the SS bowl
Te is just a guess but one of my main sources being pre decimal Australian 925 silver coins, if it was Australian silver used in the minting process and our ores being telluride based this is a possible source. But I am not full bottle on elemental associations. Having said that, Te is also used in Stainless steel manufacture for machine ability, also added to copper for the same reasons.

The cost of analysis is appreciable but I may need to find an umpire at this stage.
Has anyone else run ICP on their silver crystal, surely I cant be the only one??
 
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