# Platinum-iridium alloy - need help with affinage



## vovanius (Nov 2, 2016)

Alloy contains 97% Pt and 3% Ir. Melted it with zinc, dissolved zinc with HCl, remaining PM powder was treated in AR for quite long, and everything dissolved. Then denox, and drop Pt with ammonium chloride. But, Ir also goes down at the same time. I read, that there is delay for about an hour between platinum and iridium salts precipitation, and ammoniun chloroplatinate, which drops immediately, can be filtered out while iridium is still in solution. What am I doing wrong? Thanks.


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## Lou (Nov 2, 2016)

Need more information.

What is the volume and concentration of the platinum iridium solution. Did you destroy the excess nitrates prior to refining the metal?


There are several options. I would consider 97% Pt, 3% Ir to be a good refining material.


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## vovanius (Nov 3, 2016)

The batch is approx. 15 grams of alloy. No other metals in alloy, just Pt and Ir. And yes, I did denox very thoroughly, then add water to 100 ml volume. In fact, I was working by the C.W. Ammen's "Recovery and Refining of Precious Metals" book, but something goes wrong...


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## Lou (Nov 3, 2016)

in that case, I would heat to a boil and add 12% w/v (fresh) sodium hypochlorite bleach very slowly until a pH of 7.5 is achieved and all the Ir is thrown down as Ir(OH)4. That can be filtered off and then be rinsed with freshly boiled pH 7 water to remove platinum stuck on the iridium hydroxide. 


In the library section you can also find Gilchrist's procedure which will more or less give the same result.


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## vovanius (Nov 3, 2016)

Ok, i'll give it a try. After filtration I can lower pH with HCl and drop Pt with NH4Cl, right? And, I can burn out filter paper from Ir(OH)4, and then reduce it to metal in hydrogen tube furnace?
And more questions:
Can this bleach technique be used on a regular basis for Pt-Ir separation or this is just a workaround for my situation?
How critical sodium hypochlorite overdosage can be? I mean, do I have to use precise pH-meter to control things or indicator paper and visual observation is enough?
With next batch, do I have to denox before sodium hypochlorite addition?


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## goldsilverpro (Nov 3, 2016)

I've been doing this for 50 years and have never heard of the word "affinage." I had to look it up. It means either the refining of metal or the aging of cheese. According to Merriam-Webster, its usage for refining metals is obsolete. I have worked in 34 different refineries and have never seen or heard it used in the PM refining industry, ever. I know this sounds trite and picky but its usage on this forum is a very pretentious and undesirable one, in my opinion, especially since it is obsolete. I assume you won't use it again unless you're discussing the aging of cheese.


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## Lou (Nov 3, 2016)

https://fr.m.wikipedia.org/wiki/Affinage_des_métaux

Everything sounds pretentious in French :mrgreen: 

"To make fine"


I don't think the poster's first language is English


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## Platdigger (Nov 3, 2016)

"in that case, I would heat to a boil and add 12% w/v (fresh) sodium hypochlorite bleach very slowly until a pH of 7.5 is achieved and all the Ir is thrown down as Ir(OH)4. That can be filtered off and then be rinsed with freshly boiled pH 7 water to remove platinum stuck on the iridium hydroxide."

As usual, way cool Lou. 8)


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## g_axelsson (Nov 3, 2016)

I have run into one goldsmith and one refiner here in Sweden that uses the term "affining" (or at least with Swedish spelling "Affinering"). Maybe it is a term still used in Europe... or maybe only in Sweden.

Göran


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## vovanius (Nov 4, 2016)

goldsilverpro said:


> I've been doing this for 50 years and have never heard of the word "affinage." I assume you won't use it again unless you're discussing the aging of cheese.


I'm Ukrainian, English is not my native language. I think, word "affinage" is not a problem for anyone on the board but for you :lol: Everyone understood what the topic is about. So, aside from aging of cheese, do you have to say something useful on the topic?


vovanius said:


> How critical sodium hypochlorite overdosage can be? I mean, do I have to use precise pH-meter to control things or indicator paper and visual observation is enough?
> With next batch, do I have to denox before sodium hypochlorite addition?


These questions are still actual...


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## Platdigger (Nov 4, 2016)

I'd be careful addressing GSP in such a manner vovanius.
goldsilverpro is highly regarded here, and rightfully so.


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## anachronism (Nov 4, 2016)

It's a simple misunderstanding between languages and translations. Nothing more. I'm sure everyone can move on from this and help each other as intended.


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## g_axelsson (Nov 5, 2016)

As often happens when a thread makes a turn, maybe it isn't useful for the original poster but at least I thought it was an interesting turn and learned something new from GSP's response.  

And the original platinum iridium discussion was also good information.

Göran


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## butcher (Nov 5, 2016)

:lol: 
When I first saw affinage my mind thought appendage.


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## vovanius (Nov 6, 2016)

Did not want to be rude to Goldsilverpro, maybe my not perfect English let you think so. So, peace to all and let's get down to business.


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## zachy (Jan 14, 2017)

There was no answer of the subject, the only thing I wanted to know is if the sodium hypochlorite is the same one used for cleaning floors and in the kitchen, and if I need a lot of volume to reach the proper pH and precipitate the Iridium.


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## aga (Jan 15, 2017)

Sodium hypochlorite (NaClO) is the active ingredient in household bleach.
https://en.wikipedia.org/wiki/Sodium_hypochlorite

Usually the cheapest un-perfumed bleach brand will be purer than the more expensive brands, as it costs money to put in the perfumes, colour, foaming agents etc.

Whichever brand you get, it is normally very dilute, around 3 to 10%.

How much hypochlorite is present can be measured with an iodine back-titration :
http://www.ausetute.com.au/redoxbleach.html

If you're lucky, it can be bought in 30% concentration as a bulk pool chlorine additive.

NaClO decomposes spontaneously into table salt and sodium chlorate, so it cannot be stored forever.

It is a highly reactive oxidiser that can release lots of toxic chlorine gas, and should be treated with the same respect as nitric acid.


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## butcher (Jan 15, 2017)

Many manufacturers of cleaners, may have added additives or buffers to their products, check your MSDS sheet.


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