Recovery of Iridum from iridium coated Titanium Mesh - APC Forum

Interesting problem. What is your use for the iridium? And what's the need to extract it from these electrodes? Do you need iridium or are you extracting it for profit or for interest?

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If these are standard MMO electrodes such as used in pools and chlorate cells, the coating contains more than iridium, at least some titanium dioxide is present, along with other noble metal oxides - manufacturer-dependent. 

It sounds like your current experiment has dissolved away the titanium dioxide in the hot HCl which destroyed the structural integrity of the coating, letting the noble oxide fall to the bottom. This may be your best option for recovering only the noble metal, as you can filter this powder and then dissolve it separately in boiling aqua regia.  

If you have to dissolve the whole coating off, I think your best bet would be hot aqua regia. Which would dissolve the iridium oxide, but would also dissolve the titanium dioxide, and may also dissolve the other oxides (although not platinum). Maybe this is a problem, but may not be depending on your use case.

Titanium (substrate) is said to be resistant to aqua regia, but it may be attacked when hot. Titanium is an extremely reactive metal, but the oxide coating is so strong that it behaves highly as a highly unreactive metal in normal conditions (once the oxide forms). The oxide is what makes it resistant though, any compound able to destroy the oxide coating should also be able to destroy the much less resistant metal beneath. 

You may have to just dissolve everything and then separate out the desired compound/s with further processing. 

Firstly, Ir is not soluble in AR. This is how it was discovered in fact, as a black redue left from natural Pt dissolved in AR.

Secondly, the Ir you get from MMO is in very small amounts. You probably need around 50-100 kg of mesh to reclaim one gram of Ir.

Thirdly, Ir is not very saleable. You will likely be paid 50% from the spot value and you need lots of grams to even start thinking about a transaction. The buyers are not numerous like in the case of gold.

And finally, you'd better sell the MMO as it is. You surely make way more this way.

Iridium and Ruthenium are each several dollars per gram when pure, BUT how much do you have at 5 and 3 percent, percent of how much. Given a kilo of your tested powder 8% is valuable and 8% of a kilo is 80 grams - it's worth the work. If you have 1 gram of powder then 8% is only 80 milligrams so recovery is probably a waste of time -keep it til you have more.

DO you have a precious metal recovery company in your country? Someone who would take your Black waste powder and recover the PGMs for you and give you a price for the metals. It's likely cheaper to engage a contractor than too learn and practice the whole chemistry  of PGM recovery buying all the reagents.

Should you engage in chemistry with PGMs read carefully any noted hazards in the literature, some PGMs have catalytic properties and some PGM compounds are powerful irritants to skin.

Remember that your test gun will tell you percentages, BUT only you know what that's a percentage of. 

Sreetips has pulled some interesting metals out of old jewelery.

There are a few papers/ forum posts indicating decent solubility of the oxide in hot AR, so I do think it’s a viable route. Although as a_bab said the metal itself, not already oxidised, cannot be oxidised by AR and is highly resistant to attack. AR is really the only route available to you.

You have to get the coating into solution somehow to process it further, but the exact steps you need to take we cannot tell you. It depends what contaminants you have, what scale you’re working at, and what chemicals you have access to. People here also are not experts in these subjects, you need to speak to someone in the field of precious metal refining. 

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