NEEP602 - Lecture 23

NEEP602 Course Notes (Fall 1997)
Resources from Space

Extraction Techniques for Minerals in Space

Mining on Earth
Mining in Space - General
Mining in Space - The Lunar regolith

Begin with a review of Mining on Earth

Requirements for a mine:

3-D workplace that must be: safe, well drained and ventilated with necessary power and transportation
also must be able to produce ore at steady rate and quality

Extraction Methods:
Orebody shape is function of its mode of formation (and subsequent history):

2-D sheetlike or tabular bodies
linear or rod-like bodies
irregular 3-D masses

Mining depends on:

thickness, attitude, depth, strength of ore and host materials

Blasting:

an individual explosion removes cone of material
more explosives lead to smaller rock but not more excavation
amount of breakage should be controlled or keyed to requirements of subsequent treatment
timed blasting:
- to remove material from an open pit bench
- to advance a face underground

Open Pit/ Quarry

f(overburden thickness, topography, nature of ore)
pit wall angle: 45 deg for rock; 30 deg for unconsolidated material
- f(gravity)
pit vs underground: f(geometry of ore body; grade of the ore)
pits may lead up to underground operations (or the reverse) over time
- originally too expensive, now infrastructure in place and paid for
- postpone the ecological day of reckoning
Surface mines are likely scenario on the moon.

Underground Operations

details depend strongly on geometry and grade of ore and the nature of the gangue
usually need to leave ore behind as pillars
gravity is commonly used to help reduce handling
must start with access system of drifts and shafts (usually in footwall)
extraction done in rooms (stopes) connected by drifts, raises
artificial supports commonly needed

What is a major advantage of underground mining on the moon?

Here are some traditional underground methods:

[1] Shrinkage Stope method takes advantage of the fact that

Broken ore occupies 30-50% more volume than parent material
keep minimum headroom by drawing down the muck pile

[2] Cut and Fill: fill mined area with waste rock or cemented tailings

very versatile, commonly used
development costs relatively low
pillars can be recovered
takes care of some of the waste disposal problem

Both Shrinkage Stoping and Cut and Fill work well on vertical, tabular ores which are not likely to be found on the moon.

[3] Sublevel or Block Caving

used in weak ore which may not be safe to mine in other ways
low cost
LOTS of premining development needed
problems with ore dilution and surface disturbance
Ex: Questa Moly mine in New Mexico

[4] Mining either by advancing from or retreating to the point of access

advance more common because quicker return on investment
retreat common in some coal mines
may lead to surface subsidence

[5] In-situ recovery: possible for oil shale (burn front)
[6] Heap Leaching as The Cheapest Way

Milling: "bust it up and classify it"

breaking method depends on tensile and compressional strengths
classifying depends on size, shape, density, magnetic properties, ...
various types of crushers: gyratory, cone, jaw, ball/rod mill
sorters: grizzlies, screens, cyclones, flotation, settling velocity, shaker table
hydrometallurgy, pyrometallurgy

Resource Recovery in Space

Unconsolidated material at the Surface: Ex: Lunar regolith

Mobile Slusher
- able to move from site to site as needed
Stationary Slusher
- simpler, lighter
- would need help getting around
Both are 3-drum cable tools which can reach any area defined by the location of the power unit and the 2 anchor pylons
Scraper fills because of combination of in-haul forces and weight of the scraper
Looks like a simple operation but at present this would probably have to be run by people either on site or by teleoperation. We still couldn't automate even this simple process.
Ability to change from scraper to rake to ripper to plow.
- Lower levels of regolith will probably need to be broken up.
- Explosives? Design of ripper or plow?

Before going any further consider weight, mass, inertia, friction, traction

Inertia not weight is the real problem with moving things and, as this is a function of mass not weight, the lack of gravity is not a real bonus
Fracturing and evacuation equipment on Earth uses gravity as the hold-down mechanism. Something else will have to take its place.
On Earth, loading equipment operates near its traction limit
Reduced gravity creates a less favorable inertia: traction ratio
Can increase traction by increasing mass (which makes for inertia problems)
Once anchored, the slusher fills basically in response to the in-haul force which is traction independent. The bucket will have to be more massive but this may be accomplished by using onsite rocks.
Fracturing provides initial velocity to rock particles/pieces. On Earth these pieces rapidly lose their V and accumulate; at zero gravity you have an out-of-control 3-D billiard game.

Specific Lunar Examples: Ti, Fe, Al, Ca

Where do these elements come from on Earth?

Titanium recovered from rutile TiO2 or ilmenite FeTiO3 - both primary igneous minerals.
Iron recovered from simple oxides or carbonates or sulfides - both sedimentary and igneous sources
Aluminum recovered from oxides and hydroxides - deep weathering, or possibly from the pre-weathering igneous rock
Calcium (for cement) recovered from sedimentary limestone

Let's take a quick look at some slides from ore deposits on Earth that bear on this subject.

Now let's look at some of the figures from Lecture 21, not in the context of recovering oxygen but instead from the standpoint of 'the rest of the story'.

The lunar soil composition pie chart (Fig. 5) shows what is most available.
Fig. 7 pointed out that O2 could be recovered from all the different lunar rock types and thus we might be processing any of these
The metal-oxygen bond strength graphic (Fig. 8) applies whether you are trying to recover oxygen or the metals
Fig. 9 schematically shows production on TiO2 from ilmenite - next stop, Ti?
Figures 15, 16, and 17 show variations on melting lunar source materials and generating either ceramics (=bricks?) or metals by electrolysis
Other possibilities:
- platinum group elements from the meteoritic component of the regolith
- native iron from old mature regolith

Asteroidal Mining:

Probably start with a near-earth Amor, Apollo, or Aten asteroid
Some asteroidal material is very easily crushed and may be processed easily
Long lead time increases expenses
- long duration manned mission
- automated or teleoperated mission
- slow long low DeltaV equipment arrival combined with faster high DeltaV manned portion
Problems with manned mission:
- long exposure to zero gravity
- solar radiation
- life support
- manned deep space vehicle

Problems with automation or teleoperation

slow progress on doing this on Earth
so many unknowns which might require a human touch to overcome
time lag of teleoperation may make it impossible to respond soon enough to keep disaster at bay

Possible solution to low gravity problems:

Cable the mining equipment to the small asteroid.
The cable holds both the fracturing/removal equipment and the collecting `bag' to the surface of the asteroid. The bag maintains its shape because the asteroid is spinning; this spinning also helps collect the broken material into the bag.
Material needs to be boosted with enough energy to pass the synchronous orbit limit so that centripetal force collects it into the bag.
Blasting could be an alternative but would have to be done very carefully.

Extraterrestrial Mining Problems for Research:

How should mechanical equipment be modified for operation in reduced gravity? (excavation, loading, moving)
Remote and automated mining. What progress has been made on Earth?
Environmental effects: extremes of heat and cold
Applicability of terrestrial techniques to low gravity, no atmosphere situations.
Rock drilling:
- conventional drilling: drilling mud? friction?
- melting and vaporization; chemical reaction; heat induced spalling; mechanical stress; spark cratering
Changes in traction and how to compensate:
traction is function of gravity and friction
Changing role of blasting in low gravity settings; vacuum will also affect blast
Wear resistant materials
Particle size reduction in low gravity settings
- design of crushers; substitute for wet grinding and separating?
- classifiers

References:

W. H. Dennen and B. Moore (1986) Geology and Engineering

W. H. Dennen (1989) Mineral Resources: Geology, Exploration, and Development

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Extraction Techniques for Minerals in Space