Tuesday, 23 July 2013

Gold in them thar mobiles

I'm continuing to mine the rich lode of information from my hoard of back-issues of Nature.  In the 14 Mar 2013 issue there is a mini-feature on Gold, including another article by the redoubtable Brian Owens.  He had one in the following issue as well that I mentioned yesterday.  Something is wrong with the system if they haven't taken this guy onto the permanent payroll by now.  The subtitle of his article is "High gold prices are making it worthwhile to look for gold in some unusual places".  In teaching Environmental Chemistry at The Institute earlier in the year, I turned up some interesting stuff about the economics of the element lithium which was really close to home and I'll catch you-all up with this later in the year.

I liked the piece by Owens because it had some data that I could get my molars round.  I remember when I was a nipper watching a film about the gold rush in Klondike (or was it Ballarat, or Sutter's Mill?).  Some whiskery and whiskey-whiffey Old Timer bursts into the Saloon crying "Thar's ounces to the ton".  It struck me then as a poor return and a helluva lot of dirt that had to be processed for a thimbleful of gold.  Gold is dense (19.3 g/cu.cm) so a couple of  ounces would fill 3 ml.  But ounces to the ton is HUGE, because the average sort of yield from open cast gold mines like the horrendous Serra Pelada is 1g per tonne - 1 part per million. Owens points out that mobile phones in contrast contain as much as 350g/tonne and you don't have to go to some yellow-fever infested jungle to get it.  Other circuit-boards might have as much as 250 ppm.

My phone weighs 3.25oz which is close to 100g.  The price of gold was $56/g at its insane peak in October last year and has tanked to $42/g and some folks have lost their shirts.  Note: when converting gold from price per ounce to price per gram, be sure to use the troy ounce of 31g, not the avoirdupois ounce of 28g unless you don't care about a 10% difference.  Current price of gold is $1300/oz.  So if my phone was pure gold (rather than a tedious pain in the neck), I'd be taking a foreign holiday.  As it's only 350ppm gold, there's about $1.50 worth of gold in it.  But it scales up even though you have to get it out.  The recipe is:
  • shred a 40ft shipping-containerful of old phones
  • melt it down and boil it up at 1250oC
  • the valuable metals (mainly copper) sink to the bottom while a noxious slag floats
  • cool and grind metals to powder
  • add sulphuric acid to dissolve the copper
  • do some cleverer chemistry to separate the Au, Ag, Pt, Pd
  • form into ingots
  • process lead, cadmium and other byproducts from the slag
  • buy yacht
The maths:  my humble not-very-smart phone is about 50cc. A 40 ft container (2.4m x 2.4m x 12m) is 70cu.m,  enough to hold a million phones at $1.50 a go.   It is the owner of the processing plant by the Hwang-Ho who buys the yacht, of course, not the poor jokers who do all the work in a miasma of heavy metal fumes.  Nevertheless, the working conditions are much better getting gold from ground phones than getting it from the ground itself.  There cyanide (HCN, Prussic acid, smells of bitter almonds) and/or Mercury is used to separate the gold from the ore.  Both of these are considerable poisons (although nothing like Polonium or botulinum toxin) both to the workers and to the fish down-stream.  There is, and always has been, an insatiable desire for gold; would it were otherwise.

You can't do better than send your old phone to The Jack and Jill Foundation who will recycle it efficiently.  Like OU and RNLI, the  J&JF is great because it helps people find the heroic in themselves.

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