[COFF] Re: Typical Fate of Older Hardware

[segaloco via COFF <coff@tuhs.org>]

> My understanding is the extraction of the gold from the contacts is more
> often than not, more expensive to do then to mine new gold. If I recall
> the details correctly, there are not a lot of ways to do that with gold
> because it doesn't react with a lot of other elements so it ends up
> being hard to reduce.
> Brad Spencer

Pardon the length, caught the chemist in me interested.

Gold is famously difficult to attack with acids, which actually is a benefit moreso than a detriment.  One strategy to free native gold from a substrate is to instead attack that substrate.  The main acidic mixture which will actually attack gold is "aqua regia" which is typically a 1:1 nitric/hydrochloric mix, and is "regia" in that it can attack "regal" metals like gold and platinum.  Nitric on its own is a very effective acid and oxidizer, and can be used to knock out all sorts of other metals, up to and including silver.  However, nitric alone won't make a significant impact on the gold without the HCl there too.  One of the problems with HNO3 alone (can't recall if this is why gold is unresponsive) is that its strong oxidizing potential can, in some circumstances, actually prevent its acidic reactions by fully oxidizing the exposed surface area of a metal before the acid can dissociate it.  This can be observed with copper and anhydrous nitric: the copper will immediately oxidize on the surface and no further reaction occurs.  Add water to facilitate the dissolution of the iron nitrate being formed and the reaction goes apoplectic.  Still, this doesn't come into play as much simply in that anhydrous nitric is very uncommon, and it's hygroscopic so it'll sponge up enough water from the atmosphere if left to do so and then overcome the otherwise insoluble oxidation.

Long story short, you can extract all sorts of metals *from* gold given they present surface area to react with, while leaving much of the gold intact, by successive baths in individual strong acids, taking care to not have HNO3 and HCl in contact with the metal at the same time.  This isn't 100%; platinum, for instance, will also survive this process I'm pretty sure, as well as some minerals and other complexes, but its a good place to start.  You can then take what's left and dissolve it in aqua regia, yielding a solution containing gold, possibly platinum, but hopefully little if any other metals.  At that point, either electrolysis or precipitation reactions can be used to further purify, either by depositing the gold or at least eliminating remaining impurities.  Similar processes are used for preparing radioactive isotopes for analysis: several stages of precipitation reactions to eliminate unwanted isotopes and then a final precip of the target species onto a planchet for alpha spectrometry or beta emission counting.  For the curious, gamma is a different beast entirely, so this doesn't apply to particularly high potency radioisotopes.

That said, this all has to take into account the cost of the acids, safe handling vessels for actually performing the separation, disposal (or further refinement) of the secondary metals from the process, etc.  My hunch based on experiences in the environmental market, is that these sorts of costs are more often than not the barrier than any amount of technical difficulty.  Mining operations have the game figured out on how to balance production and environmental stuff (note balance doesn't necessarily mean accept and value, industrial ops often budget for compliance violations and smaller fines.)  Metal recycling operations likely have a lot more eyes on them, ironically, than extractive measures, and that is a newer industry.

So much of it too is informed by market volatility.  When gold peeks above a certain threshold, suddenly reclamation outweighs the costs, but then it dips again and you're bleeding money on a formal operation.  Mining, sadly, has more history behind it, so will probably continue to be the most supported avenue for pursuing resources until either the chemical and disposal costs involved in reclamation come down or we run so low on resources the tacit, implied violence towards the communities these resources are extracted from escalates into full blown war.

Of course, the other option is the steady march towards new horizons in semiconductor research, quantum computing, all of these attempts to get away from the current entrenched norms of IC implementation.

One of the possible solutions to these issues, now that I've thought about my chemistry and tech stuff in the same breath, is perhaps designing newer substrates from which gold can be more easily reclaimed.  If planned obsolescence is already a thing, those same engineers could at the very least design these frequently disposable devices with high turnover to have a recycling potential higher than what we have currently.  In other words, if things are going to be made cheaply and to be discarded every couple of years to keep a revolving customer base, at the very least, engineer processes to easily put those discarded resources right back into the pool, not into landfills.  Granted, I could go on for hours about that sort of humanistic engineering...

- Matt G.

P.S. You really awakend the chemist in me.  Not often I get to dredge some of those memories up talking tech.  There's a metallurgist living somewhere deep in my mind that enjoyed thinking about this at length.