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Noble metals dissolved without aqua regia[*]:
A common way of extracting noble metals from other materials is by dissolving that material in solution. However, dissolving noble metals remains a big challenge due to their low reactivity, and effective recycling of noble metals requires high dissolution rates and controllable selectivity.
'Noble metals can be dissolved using different hydrometallurgical methods. Unfortunately, all of them have drawbacks,' explains Serhiy Cherevko, who studies noble metal dissolution on a fundamental level at the Helmholtz Institute Erlangen-Nürnberg for Renewable Energy but was not involved in this research. 'The most common approach is to use hydrochloric acid as a complexing agent and nitric acid, chlorine, or hydrogen peroxide as an oxidant.'
A mixture of hydrochloric acid and nitric acid is also known as aqua regia, from the Latin for royal water, and is frequently used to dissolve gold and platinum in industry. However, it is a potentially dangerous mixture and there are environmental concerns related to its use. Because of this, there is a significant drive to find alternatives.
[...] Binnemans' team prepared a very concentrated mixture of hydrated AlCl3 and Al(NO3)3 to use as their solvent. They tested it on metal wires and spent automotive catalysts.
In the case of palladium, nitrate ions in the solution oxidised the metal. A chloropalladate (II) complex between the oxidised metal and chloride anions formed and was stable at the low pH. In a matter of hours, the palladium had fully dissolved in solution, and the palladium metal was then recovered via reductive precipitation using ascorbic acid.
'Platinum can also be dissolved but it just requires longer,' notes Riaño. 'Rhodium remains practically intact, but this is also the situation when you use aqua regia; it's just too inert and you require higher temperatures and pressures to digest it.'
While the aluminium salt solutions cannot be reused, they can be disposed of safely and are much less noxious than aqua regia. However, further work is needed to optimise yields and achieve high purities of the recovered metals.
[*] Aqua regia on Wikipedia.
Journal Reference:
Proton magnetic resonance chemical shifts and the hydrogen bond in concentrated aqueous electrolyte solutions, (DOI: 10.1021/j100634a011)
(Score: 2) by driverless on Friday September 04 2020, @08:28AM (2 children)
Or at least no-one's ever proven that it doesn't, there was no trace of gold left in the crater afterwards.
(Score: 3, Informative) by c0lo on Friday September 04 2020, @08:52AM (1 child)
Well, maybe ClF5 [wikipedia.org] then.
I mean, only noble gases, nitrogen, oxygen and fluorine won't react with it.
https://www.youtube.com/watch?v=aoFiw2jMy-0
(Score: 2) by hendrikboom on Friday September 04 2020, @06:29PM
I remember that someone once managed to produce crystals of Xenon fluoride.
(Score: 2) by FatPhil on Friday September 04 2020, @08:40AM (1 child)
This new mix give you chloride ions and nitrate ions in solution.
Sounds like they've created hydrated sameoldium sameoldiate.
Great minds discuss ideas; average minds discuss events; small minds discuss people; the smallest discuss themselves
(Score: 4, Informative) by c0lo on Friday September 04 2020, @09:08AM
You seem to forget the presence of the aluminium in the solution (so this one is hydrated sameoldium choloroaluminate).
Which will trap some of the noble metals**, but offers the interesting development of generating some interesting zeolites if you involve some silicic acid on the way - it may result in some aerogels with heaps of noble metals active centers and maybe some interesting catalytic activity.
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**see that "further work is needed to optimise yields"? That's a sign the aluminium hydroxide won't let those complexed metals go that easy.
https://www.youtube.com/watch?v=aoFiw2jMy-0
(Score: 5, Funny) by Bot on Friday September 04 2020, @09:52AM (1 child)
the list of things that dissolve gold, order by ascending efficiency.
1. this thing
2. acqua regia
3. girlfriend
4. wife
5. ex wife
Account abandoned.
(Score: 0) by Anonymous Coward on Friday September 04 2020, @02:10PM
Bad solution.
Should've try diamonds.
(Score: 0) by Anonymous Coward on Saturday September 05 2020, @04:46AM
I always used potassium iodide/iodine solution from sigma-aldrich.