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
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
- 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
- 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.
- 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:
 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
 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.
 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
 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
 In-situ recovery: possible for oil shale (burn front)
 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
- 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?
W. H. Dennen and B. Moore (1986) Geology and Engineering
W. H. Dennen (1989) Mineral Resources: Geology, Exploration, and Development
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