Xref: utzoo sci.astro:13834 sci.space:31760 Newsgroups: sci.astro,sci.space Path: utzoo!utgpu!news-server.csri.toronto.edu!rpi!think.com!snorkelwacker.mit.edu!world!webber From: webber@world.std.com (Robert D Webber) Subject: Re: Platinum-group metal concentrations in earth-crossing objects Message-ID: <1991Jun16.000359.10311@world.std.com> Keywords: gold Organization: The World @ Software Tool & Die References: <5248@dirac.physics.purdue.edu> <1991Jun12.073415.12543@sequent.com> Date: Sun, 16 Jun 1991 00:03:59 GMT Lines: 106 In article <1991Jun12.073415.12543@sequent.com> szabo@sequent.com writes: > >The best data we have come from the asteroid samples fallen to Earth, >meteorites, many of which contain metal or metal grains from core >material. The best platinum-group concentrations have been >found in the metal grains of LL-type chondrites, as follows: > [...numbers in the tens of ppm deleted...] > >As an aside, they also contain 1-15 ppm gallium, 200 ppm germanium, and >1.2 ppm arsenic. Space Industries Inc. is currently working on a >wake shield to produce large volumes of very high vacuum, which can >be used with microgravity to create GaAs and other semiconductors >with much greater purity than in Earthside semiconductor fabs. Back in semiconductor fabrication class they always told us the biggest contamination problem came from the container, and that the high vapour pressure of arsenic led to a need for either As pressurization or some kind of complete encapsulation for the melt. In the absence of a container the composition of the GaAs crystal comes out wrong, so I don't see how the "very high vacuum" will help fabrication operations for the materials used to make devices. >Back to platinum: we have a total of 55 ppm platinum group, about 5 >times better than the best Earth ore. This still wouldn't be that >good, given the high costs of launching mining equipment, except >that there exists a process which, taking advantage of the large >amounts of solar-thermal power available in space, could make >extracting the platinum economical. > >First, we should find grains with the above concentrations or better >in a high-metal regolith (a task for space exploration). We >extract the metal grains with a magnetic rake. Next, we process >the metal regolith with the gaseous carbonyl process, as follows: You will need to break the hunk of rock down in size quite a bit, first. On the ground this is generally accomplished by crushing in rather large, heavy machines, then grinding in a mill where balls or rods are raised from and dropped back onto the material to be ground. Obviously the term "dropped" implies the machine's presence in a gravity field. I suppose that some other accelerating field could be substituted. Anyway, the grinding medium in a conventional process needs to be dense so that the individual grinding elements have a lot of kinetic energy for a small surface area: this allows a lot of K.E. to be transformed into the energy of new surfaces during the grinding process in a short period of time. What are you proposing as an alternative to this very much earthbound, heavyweight technology? You definitely need something to get the mineral particles down to liberation size in the process you describe. > >First phase: > >Treat the regolith with CO at c. 5 atm pressure, 100 degrees >C. This forms a vapor of gaseous carbonyl compounds. [...some details of carbonyl processing deleted...] >The water and CO are again recycled. So how much does it cost to get the carbon monoxide and water up there in the first place? I would guess that you can ship up oxygen and make the monoxide on the spot, once you ship up or build the requisite process equipment, but shipping water around seems like a somewhat bad idea. Incidentally, you will need a fair bit of material for the carbonyl process fixtures as well. The units I saw on a tour of the Inco facilities in Sudbury were pretty massive, though I'll grant you that a space facility can be less concerned about accidental carbonyl releases than an earth-based one. One other point: you get metals back out of the carbonyl state by plating them out on metallic seeds. If your particles are all down to liberation size, I'd be willing to bet real money that a lot of platinide dust will end up blowing around in the carbonyl tank and getting trapped by nickel/ cobalt/iron shell growth on a seed. >This technique, called the gaseous carbonyl process, is currently >used at the Sudbury mine in Ontario, primarily to extract the nickel, >and secondarily to extract the c. 5 ppm platinum. By some accounts >the Sudbury ore is actually the remains of an impacted asteroid, >but I won't get into _that_ broohaha. :-) There are several operators and a number of mines and mills in the Sudbury, Ontario area. The carbonyl plant is located (if my memory of my visit hasn't spoiled since it's been defrosted) at one of Inco's facilities, as noted above. However, precious metals are typically recovered from anode slime which collects at the bottoms of electrolytic cells during electrowinning, having precipitated out of molten sulphide as very fine metallic particles. Further separation of gold and platinides is carried out by additional electrochemical processing. The last I heard, the theory was that the high-grade sulphide ore being mined at Sudbury was formed by an upwelling in crustal cracks after a meteor strike. The actual material involved in the meteor seems unlikely to have produced the millions of tons of material which have been mined in the Sudbury area. >If we want to get the pure elements additional processing is >required. No kidding?! I've often wondered whether any of the people who figure that metallurgical operations in space would be simple have ever visited an earthside metals extraction plant. It ain't simple down here, guys, and the size and cost of even crude equipment is pretty staggering for somebody used to stuff like computers. Our state of knowledge for most extraction processes, and for the systems from which we're extracting values, is pretty poor, too: we've come a long way from Agricola, but not as far as it is to what you want to do, and in nowhere nearly as little time.