assay result/silver crystal, advice needed.

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GSP, you are reading the wrong line in the printout. I did the same thing at first. The first line of numbers are detection limits. The samples are the last two lines.

I'm surprised to find calcium as a contaminant in your silver. Calcium reacts quickly with water to form calcium hydroxide so even if it could be deposited in a silver cell it should go into solution immediately.
So the calcium should be present as a compound and probably not in the metal. What do you use for rinsing? If your water supply is contaminated with calcium (dust particles? Any limestone in your area?) then it might get concentrated and mechanically trapped in the silver crystals.

I might have missed it, going back over the thread, but do you wash the silver on a filter or in a beaker? What do you use, tap water or distilled water?

Silver crystals have a huge surface area compared to it's mass and if you are drying quite moist silver anything contained in that water will dry out and form a crust. By the same process, slow rinsing and letting the silver dry out in between might deposit more contaminants with each rinse - dry - rinse cycle.

Take some of the water you use for rinsing and let it dry in a glass. Then you will find out how much contaminants that comes from the water.

I wonder if you melt the silver crystals with a bit of flux if the contamination goes away. My gut feeling is that most calcium would combine with the slag and be captured by the flux.

I hope you will find the culprit and report back. Good luck!

Göran
 
I must admit if it were me I would melt a sample and have that analysised and see if much of what you are seeing will simply go away, I’d be tempted to add a little flux and clean the button well and dry using paper towels.
 
Sorry about that.

The highest metals are Te, Fe, and Cr. The Tellurium is a mystery. Is it a coincidence that the Fe and Cr are 2 of the 3 main constituents of the 300 series stainless bowl?

I agree that assaying a sample that has been melted would be much more meaningful than assaying the crystal.
 
I do not think I'm adding anything useful to this conversation, but just reinforcing the obvious for my own selfish pleasure: In any 99.9999% pure metal bar of any metal, the right-most three nines are, by far, the most interesting and difficult to obtain, and the left-most three nines are, by far, the most profitable. :shock:
 
the right-most three nines are, by far, the most interesting and difficult to obtain, and the left-most three nines are, by far, the most profitable.

Unless you are selling to an end user who pays a premium for purity, the rates don't get any better than what you get for 99.0 purity. So what you said is very true. Most metals are refined at the major refineries to high purity in a first refine and it is the second refine that brings the purity up to the 4 nines purity that they sell. If you can clean up your metal (in quantity of course) to the purity they get with their first refine your metal can enter their production refine schedule at the last step and that is where you will get the best rates.

But I completely understand, as a chemist, the desire to achieve the highest purity at least once. Even if you loose your shirt when you sell it!
 
Attached a pic of my DW label used at every stage from digestion, all rinses and electrolyte.

DSC_0125.JPG



At this point I am going to change from generic 68% Nitric like the pic to RCI labscan Nitric which at least comes with a technical analysis on the label.
With the DW I will go to my lab supply and use their deionized water, it would seem when chasing the fourth 9 these constituents may be critical. Of interest though the DW msds of the product I am using states 100%water.
Regarding Limestone, we are coastal and Calcium carbonates abound so airborne particles of Ca do indeed exist, in addition to this the manufacturer of the DW water is also coastal in my capital and believe that they will be using groundwater for their product before deionizing. So there are many sources for possible Ca contamination, I must stress again that my process from beginning to end uses DW as per the pic below.
It simply means I will have to do more work to delineate my contaminants.
The Te has got me scratching my head, apart from the source metal, I could point the finger at the lab, I so wish analysis were more economical, I could simply do a process of elimination and breakdown at process points to see where I am picking the elements up.

I will ask again,

Can Ca be carried over from the shot stage by pouring into tap water?

Has anyone else here done ICP on their silver crystal or bars from silver crystal?

Does running the cell contaminate the crystal with Cr and Fe, and can these be limited if indeed are from the 300 series SS by raising PH, I would like to compare these elements with another home refiners results.

Believe it or not, there is only one refinery here in Western Australia, to be honest I dislike them with passion, I have dealt with them for decades but no more. Regardless if you refine to 999 they still will charge you the full refine fee, they are profit mongering pigs. Even if I inquart my gold they still charge full refining fees, so unless you have a 15 ounces of Au to process in one parcel the $550 refining charge eats your margin, same goes with Ag but worse, now you need a kilo of sterling just to lodge your parcel as the charge is nearly a kilo of scrap, if I don't refine to 999 they get the gold and whatever palladium and still charge the $550 refine fee. So you're damned if you do and damned if you don't, so now I just wont.

Thanks for your feedback and comments Mods, Palladium and other interested parties.
 
I used to routinely do ICP-OES on silver when I produced it, that's why I'm saying I wouldn't take your assay to the bank--certain things about it do not make sense to me. I still do for Au/Pt/Pd but these days, just titration and x-ray for what little silver I'm buying.

I used CP2 titanium as the cathode in my cells, so I didn't experience any stainless carry over phenomena, and none of the ASTM/ISO tests for refined silver call out for titanium. I took down my Thum cells (been trying to sell them/give them away for some time now) but we did use a stainless push/scraper thing to push the crystal to either end of the 5' long cell box. None of that was contaminated.They were Chris's design more or less and worked phenomenally. Our Ag output was consistently 99,992 99,993, etc. after melting. I also obtained a much sandier silver powder, which is what we wanted because it scooped and handled easier (your type of crystals, though beautiful, suck when you're loading them by the shovel into a 1000 C furnace with the lid open. If you're really starting with 99%+ Ag as a feed, you're probably more in the 5N territory so long as your anode bag isn't leaking into the crystal.

As for the Ca, it can contaminate the crystal but usually an issue if evaporated onto the surface. It should slag off if melted.

If you want, you can send a sample of your silver to me in the USA and I'll run it by difference on the ICP-OES and see if you're 4 N or not per ISO/ASTM standards for refined Ag.

In lieu of an ICP, you can make your silver into silver nitrate using reagent grade nitric, then evaporate all the water and acid until the silver nitrate melts. Hold it at 250 C in a porcelain container for a few hours, well covered. Let it cool and add pure water. Any black crap is a transition metal oxide.Silver nitrate stays stable well above 250 C. Any copper or lead or even palladium will form a precipitate and you won't have a colorless turbidity-free solution.
 
4metals said:
the right-most three nines are, by far, the most interesting and difficult to obtain, and the left-most three nines are, by far, the most profitable.

Unless you are selling to an end user who pays a premium for purity, the rates don't get any better than what you get for 99.0 purity. So what you said is very true. Most metals are refined at the major refineries to high purity in a first refine and it is the second refine that brings the purity up to the 4 nines purity that they sell. If you can clean up your metal (in quantity of course) to the purity they get with their first refine your metal can enter their production refine schedule at the last step and that is where you will get the best rates.

But I completely understand, as a chemist, the desire to achieve the highest purity at least once. Even if you loose your shirt when you sell it!
Indeed 4metals. No experience is wasted. We are in this life for many different reasons, and through arts and crafts we can discover many things even about ourselves. My fixation with precious metals and money showed me that I was borderline OCD or some disorder of a kind or another. One day I had this realization, after much time dedicated to this precious metals obsession. I wish I had discovered it sooner, but you only live once, and now I realize that time is better spent with friends, family, and people you love. Since this forum members provided much of the avenue for my self-discovery, I decided to share this, very personal insight, right here and right now, for others to either ignore or use in their own hopefully blissful lives. :G
 
Its been a while since I posted in regards to this topic.

I have tried no less than 5 other brands of distilled water, some which is locally available from supermarkets, another produced specifically for our wine production labs local to our area, and another for laboratory purposes 4 of the 5 brands failed the basic boil down test leaving substantial carbonate residues after evaporation of 250ml in a clean beaker.

During this time I also purchased a distiller unit made for alcohol distillation purposes to try and improve on the available D/W I had tried which failed my test, after distillation and evaporation whist the water improved in its carbonate residue it was not substantial enough to warrant the additional cost of this method to re purify.

I ended up ordering a 20 litre drum of water from my lab supply source and tested the same size sample by evaporation with a result I was impressed by, leaving almost no residue of carbonates after the 250ml evaporation.
Also have my technical grade Nitric, and a new 304 SS bowl to use as a cathode.

I searched Australia wide to find a fabricator who could make me a Ti cathode bowl, not a single Ti specialist workshop I spoke to in Australia would take on the job, either the Ti was too thin to weld or the if I increased its gauge it was too thick to form so back to SS it was.

Well since this started Silver spot has dropped its guts to $20aud tr oz. No longer inclined to process and back to stockpiling, I don't see any short term recovery of the silver market spot any time soon, so will use the down time to further analyse and improve my process.

Short of running a true moebius cell with a Ti cathode plate I will pursue my current changes. As for the definition of stupidity "doing the same thing, expecting a different result" I will see where the small changes take me first.
 
While I am in no way at the level of you guys, I have changed distilled water brands three times in my effort to make 4 nines to meet my current buyers requirement. The first change made it worse the second got better while the third seems to be holding up quite well. It is clear to me that not all distilled water is the same. I wish I had thought to evaporate some dry instead of using them separately in processing, then having the material tested to find the results. I also had not realized that you could get distilled water from a chemical supplier (?).
 
What about just buying a small RO system with mixed bed DI.

It should say 0 ppm on the TDS and have very low conductivity.
 
Hi all, am resurrecting this old thread as i am at it again. In between my last posts and topic discussion my in my life has changed, life events etc.
Suffice to say i am now having another crack at 4N. I have added some new equipment as regards my water source and now am using a 5 stage RO/DI filter system, no tap water whatsoever comes into contact with my metal at any stage in my process and is 0 ppm TDS exclusively.

Feedstock has not really changed apart from there is no sterling flatware product.

A small modification after initial cementation and filtration is to roast the cement after getting a nil indicator from ammonia on filtrate, i can never get this 100% clean as the ammonia addition makes the filtrate sample cloudy and very hard to tell for me regarding a bluish indicator but i do my best and use copious amounts of water in my vacuum filtration stage.
After the filtration and roasting, i then add the cement back into a beaker, after the cement cools i add enough 0 TDS water to cover the rec overed values with around 20-30 mm high in a 5000ml beaker.
To this i add approx 20-30 ml of 98% technical grade Sulphuric acid, the result is astounding, the water immediately turns bluish as the remaining copper held in the cement is converted to Copper sulphate and goes straight into solution, many cold water 0 TDS rinses are now done again with the cement until the blue tint has disappeared then Boiling rinses are done with 0 TDS water. I will state i have done a chloride test after the sulphuric addition and have never detected disolved values with this procedure.

After the boiling 0 TDS water addition the cement now changes to a very lumpy weird texture, far different from what is usual with boiling water rinses, coagulated and lumpy wierd consistency, and back into the vacuum filter it goes, it must be stated that the cement though now lumpy seems to pass water unbeleivably well as the structure of the cement though coagulated seems to be more porous between the grains of cement powder, it takes very few rinses to get this clean and free of any bluish tint. Then its just back to the pyroceram for a final evap and dry.

The result is that after this modification in procedure, when making electrolyte from the shot made from this cement and even after running the entire batch through the cell (2kg) there is absolutely no greenish or bluish tint in the electrolyte as impurities go into suspension. I am hoping to be able to use the same electrolyte from beginning to 4N end but i have never had an issue with Copper co-deposition anyway as per my posted ICP results.

My goal is not to grow pretty crystals of size, it is purely a parting and recovery of the cleanest product in my pursuit of 4N by icp oes assay. I could not care less what the crystals look like.

First pic is my readout of Nitric 70% technical, second is readout of 90% Sulphuric technical, then my new water filtration system and 0 TDS output. Previously was just using industrial grade 68%, this has no technical readout, its amazing at just how little of the technical grade Nitric is needed for digestion in comparison, utilising this i am hopeful of omitting some contaminants.

With these small changes in chemicals, process, water filtration system and application of the advice given i will see if i can attain my desired 4N product, so far am running the shot then crystal through the cell and may just repeat this for a few times before icp assay. Unfortunately though i am not over the moon at the stainless steel contaminating the crystal with certain elements.
After the first two runs i will change to a different SS cathode and see where that takes me, i am reluctant at this stage to make large changes in the existing equipment setup so i can see and trace the current effect of the simple changes made.

Hope you are all well. There are a great many things that have changed in our world.
 

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