What might be the blue sediment after AR treatment

[Alentia]

I have processed unknown test batch of karat jewellery. I did not go into rigourous test of testing jewellery to the full extent as it was not the concern, nor it is now either.

All is good. I did several washes after HNO3 treatment and obviously have bit of silver chloride, which usually is not an issue after siphoning and filtering AR.

However in this batch, i am left with alot of blue sediment (like light navy blue color). The sediment resembles AgCl, but I do not think it is it. As well, it is partially passing through medium filter paper. Most likely some kind of chloride of the metal un-reactive to HNO3.

I will see if I have a patience to discover what it is, even though may seem as waste of time and post the results, if no one had the same experience before.

 

[Alentia]

Here is the picture. The particles are very tiny, easily bypass 3 layers of medium filters. Settles down - does not seem to be colloid. There is a very little chance Sn was present.

H2SO4 has no affect on it.
Dissolves in ammonia and turns violet color.

It does not look like Co or V chlorides as both are soluble in water, this one is not.

 

[Alentia]

Considering it dissolves in ammonia, I left 5% of undecanted solution to drop gold and than to wash it in Ammonia. If that works it should not be a big threat.

 

[butcher]

When we take a gold solution and add stannous chloride we make a violet color of colloidal gold, the stannous chloride reduced the gold back to metal, in very fine flakes that repel each other keeping the gold from settling and the reflected light it looks purple (purple of Cassius) colloidal gold in tin hydrate.

What I am going to say next needs to be understood, that it is dangerous, would serve no purpose in a procedure, I state it as something I have read and made notes of, I do not understand all of the reaction, but thought it of interest. I do see where this reaction could easily form an explosive mix.

Here is what I have read, I also do not know all of the details.
Purple of Cassius is soluble in ammonia solution, and in dilute caustic potash solution, forming reddish liquids, these solutions when cold remain clear for a long time, and can even be boiled without decomposition, as the solution concentrates a flocculent precipitate is formed which is soluble in excess ammonia.
The brown coloration can be seen if 0.3 mg gold is dissolved in 100ml of the solution, if less than 0.3mg is present only a yellowish color is observed.

I would not try this, for the simple reason that gold or silver solutions in ammonia are deadly and dangerous, because explosives are made with ammonia and gold solution (fulminates), these fulminates could also be yellow in color which can explode on warming or drying and even very small amounts could blow up a beaker in your hand or your face.

I would keep ammonia away form your gold solution or even your silver, except in the certain instances as a final gold wash where we always re-acidify the powders or solution afterwards or for dissolving silver chloride where we re-acidify it after wards to precipitate silver, were we also understand the process, and Know we can perform the reaction safely, and have a good understanding and how to treat the waste (never add ammonia waste solutions to your other waste solutions).

 

[Alentia]

It is definitely not Purple of Cassius, but some type of metal chloride.

1. It is sticky (even sticks to the glass) - colloids are to remain in the solution
2. It is a sediments, while colloids are not
3. It is blue, gold colloids are violet

Unless I am wrong on colloids physical properties.

 

[butcher]

I sometimes have other things on my my mind and when I am tired I may not understand what I was reading well, I seen you mentioning chlorides and colloids and I guess I had colloids on the brain sorry.

I may be misunderstanding some points, I know you used nitric acid, and then mention having chlorides involved (silver chloride and you suspect this to be a chloride blue salt), was this treated with HCl or aqua regia or other to form chlorides? or for some reason is your nitric contaminated with chlorides, water used...

Most metals would dissolve in the nitric acid, if you used enough to dissolve the metals, and had enough water involved, you should not have many metals left, which would not dissolve, as you know Valuable metals like gold and PGM would not dissolve, there are very few other metals unreactive to nitric, we also know silver, copper, nickel... are soluble in nitrate solutions (unless maybe a chloride where involved where we could have silver precipitate as a chloride), also as we but there are also metals resistant to nitric acid stainless steel, titanium,, also the strength of the nitric acid can also determine if a metal will dissolve or react with nitric acid chromium, Iron, Aluminum which will dissolve in dilute HNO3, but are oxidized so strongly in concentrated nitric the passivate and will not dissolve in concentrated nitric acid.

If chloride were involved most metals are soluble as chlorides, except silver, mercury or lead.

Lead Chloride becomes soluble in boiling water, when allowed to cool will again form white crystals needle like if allowed to grow without disturbing, silver chloride is not soluble in hot water.

Silver chloride in acidic solution is a white insoluble powder, if diluted or rinsed of most of the acid and exposed to light it decomposes to a darker color of violet to gray or black (light converting silver chloride back to silver metal), silver chloride is not soluble in boiling water as lead chloride is, silver metal (or portion the silver chloride exposed to light) will not dissolve in ammonia, or ammonium solution, silver chloride will dissolve in an ammonia solution forming a silver clear solution of silver amine complex which can be explosive if dried Ag(NH3)2, (if copper or nickel in may have blue color), the silver will precipitate from this solution as a white powder with additions of HCl ,the ammonia solution needs acidified for safety, and should be treated as waste separate from your other waste solutions .

nickel and copper are also soluble in excess ammonia solutions, nickel gives a more violet color, copper gives a dark blue color amines.

nickel is easy to identify in solution with DMG giving a pink red precipitate, palladium in solution gives a yellow precipitant with DMG, cobalt can give brown.



(You said H2SO4 had no effect on this) most sulfates are soluble except strontium, barium, and lead, silver is just barely soluble as a sulfate.

Salts or solutions of metals can give colors from other metal or salts in solution, some metals have strong colors that can easily color a solution, or salt even if only involved in small amounts.

Also powders can be metals that were not soluble in the acids used (like noble metals, PGM's not attacked by acids used), these depending on what you are working on can also be mixed with other insoluble salts of metals or insoluble substances that would not dissolve in the acid used (silica ...), so an insoluble colored material or salt can be a combination of several metals and salts, even in solution we can get colors from several metals in solution at the same time, or one metal (like copper) which colors a solution strongly giving color to a solution of dissolved metal which is colorless (like silver nitrate) .

Colors can be indicators of what something may contain, but these are just clues, metal salts and solutions can be many colors, and colors can fool you easily, some metals in solutions can change colors very easily in solution depending on condition, some metals can look just like another metal in solution, so you really cannot determine what something is just by color alone.

 

[solar_plasma]

butcher, you would have been my favorite chemistry teacher!

so you really cannot determine what something is just by color alone.

Would a simple chromatography help? - When I put a drop on filter paper, I always watch it again, when the colours are devided, because I believe, I have more informations to interprete then.

 

[butcher]

solar_plasma,
thank you for the compliment, that is honoring especially coming from you. but I really do not know that much about chemistry, but it is a compliment I appreciate, when I finished high school I could barely read, very few subjects in school did I learn much of anything, but I do love to learn, somehow though no matter how hard they tried you would not be able to teach me anything, but if I find something interesting I will search the end of the world looking for the answer, I just wish they would have taught me how to find the answers to my own questions, instead of making up all of those stupid questions and trying to make me find the answer to them.

 

[FrugalRefiner]

In all my years in school, I learned the most from my high school chemistry teacher. On the first day of his class he told everyone that all of his quizzes and tests would be open book. We were free to use whatever books, periodic tables, notes we had made that we wished. He explained that it wasn't important that we memorize atomic weights or formulas. What was important was that we learned where to find the information and how to use it. butcher, you would have liked Mr. Cotton.

Dave

 

[Palladium]

Try adding some hcl to it and a drop or two of nitric, heat, test with stannous cl. I've had gold that fine that drops from a weak dirty solution. Even with a packed filter bed the stuff still makes it's way through.

 

[solar_plasma]

Butcher wrote:

I really do not know that much about chemistry

cmon now, that's understatement! :lol: You're an engineer, - you guys can calculate like hell and the best of it: you understand, why those cryptic formulas work. Math has always been a subject of hate for me. Unfortunately those hated mathmatics often stand between me and the answers to my questions. At time I learn much about redox potential and why this ORP-electrode (should be called halfcell instead of electrode - YOU made me getting that insight :lol: ) does what it does and especially how this is related to a practical application like iodine- or thiosulfate leaching. And that's something school often isn't good enough to: the practical application. Maybe people should first work in real life, before they become teachers.

 

[butcher]

I am a building engineer, I work maintaining buildings, boiler man, electrician, plumber, steamfitter, electronics, and general repair, basically a mechanic, I have learned to do some math related to my work, but it is always a problem then I find the formula and plug in the numbers to get the answer.

In school they give you a formula you have no clue what it is for, or how to really use it, they give you the numbers, and expect you to do the math a certain way, in school I must of done thousands of problems of that kind of math (I call it dead math), when I got out of school and wanted to fix or make something I had ways to do the problem without math, or to get around it, latter I learned how to solve the problem with math, take Pi for instance I must have done hundreds of problems with Pi 3.1416, but I had no clue of what a useful tool it was to figure out real problems, later after I got out of school I learned what it was, and how to use it, how simple it really was to take a string or a tape measure and stretch it across the circle, the string will go around the outside of the circle a little more than three times, wow that is all I needed, a real world problem, a simple way to measure and to know what or where to find the formula, then just plug in the numbers to get the answer, I did not learn much in school having math problems that did not apply to anything, trying to memorize formulas I had no idea what they were good for, coming up with a number that had no use except may to not get another failing grade.

I have got licenses in many of my skills boiler, electrician, HVAC, licenses and others, most of these I had to go to school to get, but I had years of experience doing these jobs before I got the licenses, so the school was easy for me I knew most of the subjects many times better than the teachers doing the teaching, and I learned a few things that I was missing, I also went to these schools with others who did not have experience, they could memorize and pass the tests, but they really did not learn much from the school, too many things to remember, not real experience behind the book learning, they passed the tests and got the license, but still did not know much more than before, so yes I believe a man should work and learn a job or a skill before he goes to school to learn about it.

 

[Alentia]

Try adding some hcl to it and a drop or two of nitric, heat, test with stannous cl. I've had gold that fine that drops from a weak dirty solution. Even with a packed filter bed the stuff still makes it's way through.

Metal was very clean from the start. Jewellery was simmered in NAOH solution prior to inquartation.
The sediment came after AR treatment. It does not react with: HCl, HNO3 and/or H2SO4, H2O, H2O2, but ammonia.

I can think of some piece was not gold, but gold filled, as I had removed some GF objects from the whole batch, but one, possibly slipped through.

 

[solar_plasma]

For me it looks loke a metal, the way it is lingering to the flask bottom.

butcher wrote:

not real experience behind the book learning

I agree. Look at me, in fact once I "learned" all this stuff, much of that I teach by myself, but I teach only the first 10 schoolyears. Thereafter the students go for 3 years to another school that may be a little equal to your senior high. So, I teach it, but not to the depth. I know how to calculate a redox process, nernst equation, an acid-base equilibrium or soluability products, but I ain't had a clue, how to use this in real. Now, I learn this step by step and get some wow-experiences. I am sure, I will be able to use this in school, in order to fill some learning items with a bit more life.

 

[butcher]

Solar, if you use what you learn, and get excited about, and inspire that excitement for learning, inspire that search for answers, and interest in your students, provide them with the tools to find the answer, and fill in the places they are yearning for an answer, but just are not sure how to get it, then you will be the best teacher these students ever had, you will make a difference in their young lives, even a small difference that can set them on a rich road for their future, I feel a great teacher does not make you learn, he just inspires an interest, helps to provide the tools needed to find the answers, and provides guidance when walls are encountered, the student with a desire to find the answer and who knows how to use the tools, will go on with many of his own questions, knowing how to find the answers now he is put on a trail of a journey and a quest to continue in his own education.

Just as you are now with your new interest in this fascinating field of recovery and refining of metals, your interest and excitement to find an answer to a question leads you to ten more questions, while you work towards the goal of finding that answer, and each answer you find to your questions builds not only on your education but also on your practical skills not only in recovery and and refining but also your skills of educating yourself further.

A baby learns mostly on his own, you cannot really force him to learn, but you can help in his interest, and natural curiosity in the world around him, everything around them they absorb like a sponge, you cannot teach them to walk, but when they are ready they will walk and talk and in only a few years it is really astonishing of how much they are educated of the life and world around them.

 

[bswartzwelder]

Butcher,

In a response above, you said: In school they give you a formula you have no clue what it is for, or how to really use it, they give you the numbers, and expect you to do the math a certain way, in school I must of done thousands of problems of that kind of math (I call it dead math),

I had a teacher high school or college (so many years ago I can't remember which), but one thing he taught us I do still remember. He said we use equations. Formula is something we give to babies. Made me smile and brought back some memories when I read your statement. You chemistry background may not be much from high school or college classes, but what you have acquired with your work with precious metals is astounding. Do not ever sell yourself short. You have the admiration of many of the people on this forum. And please don't take my comment about formula in any negative context.

 

[Alentia]

My apologies for not so clear statement at the beginning:

1. Base metals (inquarted with Silver) were removed by Nitric acid
2. Blue sediment appeared after AR treatment (I usually do a bit of excess HCl, keeping ratio at around 5:1)

The gold is already washed and dried. Will undergo second refining soon. I keep a bit of this sediment. Maybe someday I will figure out what it is.

Interesting that no one has seen it before.

 

[butcher]

I have a place just for this type of material, when working with dental gold I will end up with some metals or powders that do not dissolve well, I consider them goodies that I will save up in their own jar, if the material is only suspected to having a small amount of value, it will go to the stock pot or the plastic coffee can of chips and filters, if there is value I will get it later.

 

[lazersteve]

What you are seeing is tungsten. Tungsten is slightly soluble in highly acid solutions, when the solution is diluted the tungsten precipitates. Depending on the valence and pH of the tungsten it can change from a liquid (orange-brown) color to yellow with a tint of green when oxidized:

Tungsten Oxides

and when the solution or the tungsten oxides are exposed to a reducing agent, they turn a dark cornflower blue or olive drab:

The above photo is of the yellow tungsten oxide powder with a few drops of stannous chloride added.

If you have a bucket or beaker that has developed a bright yellow stain on the wall, this is tungsten oxide.

I have mentioned this over and over again, but no one seems to listen. Do not process your ceramic CPUs with gold plated copper-tungsten alloy heat spreader tops directly in AR. If you do, you will have tungsten sneak into your precipitates, prolong melting, foul your beakers, and fool your stannous chloride. The notion that all ceramic cpus get processed together is another refiners myth that has been perpetuated across the internet, even on 'respected' web sites. It seems people will use the term GIGO (Garbage In Garbage Out) but they do not understand it as they promote adding all types of ceramic cpus together in AR (Aqua Regia). Forget what you have learned about processing ceramic cpus if this is the manner in which you were taught to run them.

To avoid the types of problems the OP is seeing you must not toss all of your ceramic CPUs into a mix of AR. Sort the various types by grade and construction. Each type gets processed differently. When 'gold topped' ceramic cpus are properly processed, the tungsten heat spreaders slide off in one piece and the tungsten can easily be collected without any problems.


Properly removed tungsten plates from gold topped ceramic cpus:

It's obvious from this thread that tungsten chemistry is not understood by most refiners here. Perhaps I'll do video dedicated to tungsten to let you guys in on a few 'secrets' of tungsten. Even if I don't, I'm sure someone will after seeing this post. Prove it to yourself by collecting some of that yellow powder you have left after processing ceramic gold topped cpus. Place some in a spot plate or on a cotton swab and add a few drops of stannous... it will change to cornflower blue as seen in the second post above and my photos. If you have a beaker with a yellow ring around it add some diluted sodium hydroxide solution and watch it miraculously vanish. If you want to see how tungsten can fool you into thinking you have gold, place a piece of a tungsten plate in a beaker and heat with concentrated AR. You'll see a lot of bubbles and the solution readily will turn orange-brown. Decant the solution and dilute it with twice it's volume of water and watch the tungsten reappear as a fine yellow powder. Now imagine if you had gold in the solution with the tungsten and filtered it while it is concentrated. After filtering clear you add some water and wonder why a precipitate is forming, it's tungsten in your AR. If you do not add tungsten to your reactions you will not have to deal with it in your gold.

Tungsten can be found in some jewelry as well. It is possible that you could boil the batch of jewelry in 30%+ peroxide followed by diluted sodium hydroxide before processing to remove the bulk of the tungsten.

AR has it's merits and is a great tool for refining, but it's misuse reminds me of a Confucius quote:

One must not use an ax to remove a fly from a friends forehead.

It amazes me how much misinformation on the use of AR can be found on the internet.

Sorry for the long post, but the subject of tungsten is an important one that has been largely ignored here. I know the OP is processing karat, but it's obvious to me he has made a tungsten compound. I figured this is as good a place as any to rant about tungsten.

Steve

 

[Alentia]

Steve,

As a matter of fact, I do remove tangsten heatspreaders before processing CPU in AR, otherwise the delay in process and chemicals wasted are to great. I agree introducing additional element to AR complicates the precipitation.

I do not believe I had tangsten in the jewellery batch. My residue appeared after AR treatment when AR settled overnight, while are saying:

and when the solution or the tungsten oxides are exposed to a reducing agent, they turn a dark cornflower blue or olive drab

It happened prior any reducing agent was applied. The blue residue slowly dissolves in ammonia coloring it violet-purple.

The reason I have returned to this tread, is that traces of that residue after 1st refining now posing serious issue for 2 refining with Oxalic acid. Where gold is not sticking to each other, but remains as very fine gold (sparkling) powder. Sounds like a colloidal issue, but not sure if it is. As treatment with Ammonia should create white precipitate:

Aqueous Ammonia:

Aqueous ammonia precipitates white Sn(OH)2 and white Sn(OH)4 with tin(II) and tin(IV), respectively.

[SnCl4]2-(aq) + 2NH3(aq) + 2H2O(l) <==> Sn(OH)2(s) + 2NH4+(aq) + 4Cl-(aq)
[SnCl6]2-(aq) + 4NH3(aq) + 4H2O(l) <==> Sn(OH)4(s) + 4NH4+(aq) + 6Cl-(aq)

While I am getting violet-purple liquid when "blue residue" reacts with Ammonia and being dissolved.

While I tried to google what Chloride will dissolve in Ammonia giving violet-purple color, I found no answer.

What what I had gathered so far, it could be Vanadium, Titanium or Cobalt, but I can not validate as such. The behavior of the metal is somewhat strange.