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Moon Mining is not Minor

A lot of talk on what, but exactly how?

Mining the moon, but how?

There has been a lot of talk and many articles written about the riches to be found in mining the moon.  But very little on the actual how, and by this I mean how to physically dig and extract the minerals.  This may not be as simple as many assume.

First off, you are probably not going to fins many secondary minerals and mineral deposits, but mostly primary igneous and perhaps some metamorphic deposits.  This will limit what minerals are found and how they are associated.   For Rare Earth Minerals this will probably mean more bastnasite and less xenotime, and monazite.   Similar conditions should exist for other minerals too.

Then we get to mining methods, and this is where it starts getting expensive.  Mining equipment is generally LARGE and HEAVY.  Getting it to the moon (beyond some prospecting sizes) will take a lot of energy.  Then it will need to be assembled.  For similar levels of effort look at the work being done and costs of seabed mining equipment.  An example is simple excavating,  much of the work expended is based on the force that a dozer or shovel can exert in a 1 g field, on the moon it will be much less.  So to accomplish the same amount of effort, the equipment will need to be proportionately larger (and thus more expensive).

Now we get to processing.  I seriously doubt that we will find pure mineral deposits, but rather minerals mixed with gangue as we do here on earth.  While some talk has been made on direct smelting, this takes energy, and then further separation.   Separating the two, at least to a level that further processing is economical, will need to be done.   Most extractive technology used today is in an aqueous form, and using water for this on the moon will be problematic (water is scarcer there then in the deep deserts here).  Gravity separation (as in mining) makes use of the gravity field which is much less (83.3% (or 5/6) less) .  The use of induced gravity (centrifuges) or magnetic or electrostatic processes is possible, but this will require size reduction (comminution) which also relies on gravity.

None of this is insurmountable, but does need some serious thought and planning besides saying we are going to mine the moon.

 

Flyrock in orbit!

In a recent post (Mining the moon, but how? (https://www.linkedin.com/pulse/mining-moon-how-mike-albrecht-p-e-)) I raised some thoughts on mining on the moon and how we made need to look at the physical side of doing it more. 

This got me thinking about blasting, and in particular flyrock.  Flyrock is the rock propelled beyond the blast area.

Anyone with experience in surface mining has experienced flyrock issues.  And of course seeing a piece of broken drill still sticking out of a roof a long way from a blast can be disquieting.  Or finding a small chunk of rock on a roof or in a yard miles away happens all too frequently.

But on the moon another issue might occur without adequate safety concerns.  Some numbers:

      Lunar escape velocity   2,400 m/s

      Anfo Explosion velocity 3,200 m/s

So not just locale concerns for flyrock, but the potential for putting debris in orbit around the moon.   Okay this is a pretty far fetched thought, but it could happen.  If we are going, let's make that When we are mining on the moon many of the methods used on earth will need a major rethinking.

Getting to the moon has been accomplished, supporting operations there can be solved (if we can support FIFO operations in the Altoplano or Outback we can do it on the moon).  But like deep sea mining, the actual mining technology will likely be the stumbling block.

 

Producing Steel in Zero Gravity – How now brown cow?

Mining in space and on the moon or mars, is not impossible, but it will need thought.  And after the mining, we will need to convert the material into a usable form. 

A commonly proposed method of producing the steels and other metals that will be needed in space and on the moon is by direct reduction or smelting of the (for lack of a better term) “ore”.  Most often the proposed “ore” are high iron meteors and asteroids.  One small problem is that iron meteors and asteroids make up under 10% of the total, and of these high metal content are the rarest.

Iron meteorites, also called "irons", are usually just one big blob of iron-nickel (Fe-Ni) metal, as if it came from a industrial refinery without shaping. The alloy ranges from 5% to 62% nickel from meteorite to meteorite, with an average of 10% nickel. Cobalt averages about 0.5%, and other metals such as the platinum group metals, gallium, and germanium are dissolved in the Fe-Ni metal. (Fe is the chemical symbol for iron.) While most "irons" are pure or nearly pure metal, the technical definition of an "iron" includes metal meteorites with up to 30% mineral inclusions such as sulfides, metal oxides and silicates. The irons represent the cores of former planetoids.

"Stony irons" consist of mixtures of Fe-Ni metal of between 30% and 70% along with mixtures of various silicates and other minerals. The Fe-Ni metal can be present as chunks, pebbles and granules. Stony irons resemble the outer cores or mantles of planetoids or else a mix of materials due to a collision.

This means that most will need some processing to be able to use the metal.  The most likely method will be (or at least include) a method of smelting. 

Smelting is achieved by heating the ore in the presence of slag-forming fluxes, at temperatures in excess of the melting point of an the components. This smelt temperature is maintained for a period of time to ensure complete separation of the impurities into the slag. The metals are heavier than the slag and hence sinks to the bottom of the smelting crucible. The metals are then cast into bars by pouring the molten charge out into molds.

Oops, getting the slag to float let alone the metal to pour requires some force to make the heavier components move in one direction faster than the lighter ones.  In space this could be a problem, and even on the moon it will take around 7 times longer than on earth.   

Another problem will be the removal of any gases formed during the smelting to prevent voids and inclusions. 

Again, none of this is insolvable, but we better have some thinking done before we get there.