Unit 25
Future Mining
Unit 25
Future Mining
This unit covers several possible future mining
methods which are being planned today. Mining
technology is an ever evolving field which
pushes the limits of engineering and
technological advances.
As traditional earth bound resources are
depleted, other sources will need to be
developed in order to provide the standards we
have become accustomed to.
In this unit we will look at the feasibility of future
proposed mining techniques. These include :
Ocean Mining
Asteroid Mining
Gold from the Sea
Helium-3 Mining
Deep Seabed Nodules
Moon Mining
Biological Leaching
Oxygen Mining
Nuclear Blasting
Bacterial Leaching
Ocean Diamonds
... in the ocean depths, there
are mines of zinc, iron, silver
and gold which would be quite
easy to exploit."
Jules Verne (1870)
Ocean Mining
There are about 140 sites of
presently or recently active
hydrothermal venting on the
sea floor and more are being
found every year by marine
geologists, geophysicists and
biologists conducting basic
research on a fundamental
Earth process.
Ocean Mining
This is one important way that
heat is ventilated from the
interior. The vented hot water,
at temperatures as high as
420
°
C but more commonly
350
°
C, carries dissolved in it
high concentrations of metals,
reduced sulfur and other
elements that are precipitated
when it encounters the 2
°
C
bottom water.
Ocean Mining
Next in size appear to be the mounds at
the Middle Valley site off the west coast of
Canada totaling about 25 million metric
tons. These mounds are growing in thick
sediments and have some attributes to
deposits on land. Recent drilling by the
Ocean Drilling Program, of which Canada
is a member has shown that one of
mounds contains 220 metres of stacked
sulfide lenses and intervening feeders
from which 8 representative samples gave
average values of 3.3% Cu, 19.6% Zn and
0.1% Pb. Beneath is a "Deep Copper Zone"
that is about 40 metres thick and is
returning copper assays of >10%.
Ocean Mining
The environmental consequences of ocean mining may
be less deleterious than land mining. There will be no
acid mine waters to contend with because sea water,
being alkaline, would neutralize any acids that may form
and submarine weathering is a very slow process in any
case. There will be no gaping holes on the sea bed and
no huge rock piles; the deposits are sitting on the sea
floor uncovered.
Besides, it would be technically difficult and very
expensive to excavate in lavas compared with
extracting rather crumbly, poorly consolidated
polymetallic sulfides. Some fauna are bound to be killed
but a competent biological assessment prior to mining
can determine whether or not this would lead to species
extinction.
Ocean Mining
The technology for extracting
bulk samples from the sea floor
does not yet exist in total but
some engineering can be
borrowed from the ill fated
manganese nodule programs of
the 1970s. The Japanese are
developing an ocean miner
which is said could be used
both for manganese nodules
and polymetallic sulfides
Ocean Mining
Manganese nodules were first
discovered on the ocean floor in
1803. After the Second World War, a
comprehensive investigation of the
Ocean World started, and new data
were obtained on a wide
distribution of manganese nodules,
that made scientists consider
modules as one of the major
characteristics of the deep oceanic
zone.
Since the 1960's manganese
nodules have been recognized as a
potential ore source, investigation
of which is stimulated by the
progressive depletion of land-based
mineral resources.
Ocean Mining - Seabed Nodules
About the sources of ore material
supply to the ocean, there were once
three major presumptions:
(1) Main ore material supply to
the ocean comes from
terrigenous and volcanic, and
also hydrothermal material.
(2) Volcanic material is the major
source of the supply of ore
matter to the ocean.
(3) Terrigenous is the major
source of the supply of ore
matter to the ocean.
Ocean Mining - Seabed
Nodules
Goldshmidt was the first to
open the problem of balance
for discussion. In 1954, he
pointed out that absolute
masses of some metals in the
ocean exceed their supply from
continental rock weathering
over geological time. This
problem has risen a great
interest in geochemistry. It is
sustained by the problem of
manganese nodule origin and
also by the problem of
hydrothermal matter supply to
the ocean.
Ocean Mining - Seabed Nodules
In 1966, Scientists computed the
balance of some elements in the
ocean. Their computations revealed
an actual excess of manganese over
its supply from continental sources.
The computation result also revealed
that elements such as chlorine,
sulfur, bromine, iodine, molybdenum
were "excessive." According to the
calculating result of Elderfield
(1976), dissolved manganese supply
to the ocean from various sources is
2.2-4.0 million tons annually; 0.7-7.4
million tons of manganese sink to
the ocean bottom annually; 0.5-10
million tons of hydrothermal
manganese are supplied to the
ocean annually.
Ocean Mining - Seabed Nodules
But according to different estimates, the supply of labile
and dissolved manganese to the ocean is :
0.2 - 0.4 million tons yearly through river
discharge;
0.05 - 0.3 million tons yearly by atmospheric
material;
1 - 10 million tons by hydrothermal material;
and
0.4 - 4 million tons yearly by diagenetic flow.
So, the amplitude of minimum-maximum summary
estimates is 1.2 - 14.7 million tons per year. These are the
general profiles of the accumulation of manganese
nodules. The accumulation rate of manganese should be
studied in individual oceanic regions.
Ocean Mining - Seabed Nodules
Depending on the major ore elements (manganese, iron
and base metals) the nodules contain, three major types
were distinguished:
(1)
hydrogenous
, i.e., formed due to slow
deposition of metals out of sea water and
characterized by a high concentration of base
metals and varying Mn/Fe rations (from 0.5-5)
(2)
hydrothermal
, i.e., rich in iron and depleted of
other metals, and turns out to be having an
extremely wide range of Mn/Fe rations
(3)
diagenetic
, i.e., characterized by high Mn/Fe
ratios and relatively low concentration of base
metals.
Ocean Mining - Seabed Nodules
In 1928, Butkevich first reported the discovery of some
specific iron bacteria in manganese nodules from the
Arctic basin bottom.
Later, in manganese nodules, other species of
microorganisms were found which were capable of
accumulating iron and manganese. Although the function
of microorganisms in manganese and the mechanism of
oxidation are still under debate, it is believed that the
biogenic factor determines to a considerable extent the
manganese destiny on its ways to the ocean.
Ocean Mining - Hydrothermal Vents
High temperature hot springs in the
deep ocean, also known as "black
smokers" because they look like a
dirty industrial process, produce a
cloud of fine particulate matter near
the ocean floor that can be traced for
kilometres down current from the
source. Fallout of particles from the
plume raises the trace metal content
of the underlying seafloor sediment
Seabed Mining
The substances which can be
mined from the sea might be
divided into two classes:
first, fossil fuels, chiefly
oil and gas; and
second, all others,
chiefly minerals.
With the increase in the price of oil
and gas in the 1970's, the
commercial exploitation of oil and
gas deposits beneath shallow
continental waters became an
economic possibility. This is a
technology which is now routine
and is the only case of fully
developed seabed industry.
Seabed Mining
Seabed resources of oil and gas
are estimated to be about 20%
of total world resources and
presently earn about that share
of worldwide oil and gas
revenues. It is not presently
possible to recover oil and gas
from the abyssal depths of the
ocean and it may never be
commercially feasible to do so. .
Seabed Mining
Of the more than 25 possible
materials which are known to occur
in significant quantities on the
seabed only four are presently
exploited. Sand and gravel for
landfill purposes is taken from
shallow water chiefly in Japan and
Western Europe. The industry
constitutes only one percent of the
worldwide activity and is
considered unlikely to grow.
Seabed Mining
A small operation off the coast
of Louisiana recovers less than
one percent of the world's
production of sulphur but it is
unlikely that this operation can
survive as sulphur extraction
from pollution control
equipment is increased in the
next few years in an effort to
limit atmospheric pollution.
Seabed Mining
A full 14 percent of
the world's tin is
obtained by offshore
dredging in the "tin
belt" of southeast
Asia. This activity
along the Malay
peninsula and
Borneo has been in
operation for over a
century.
Seabed Mining
Other materials which could become
important in the future can be categorized
in three broad classes.
1) The first is "
mineral placers
" or
deposits. The tin deposits are of this type
but also such important metals as
titanium, chromium, gold and silver are
known to exist.
A very interesting case is titanium for
which the seabed resources are thought to
comprise one half of the world's supply.
Seabed Mining
2) Even more interesting is the second category of
"
nodules and crusts
". These are unique seabed minerals
that are rich in platinum, cobalt, nickel, manganese and
copper. In the case of cobalt and nickel this may be much
larger than the dry land resource.
Unfortunately, they occur mostly at the abyssal depths
and there is not even a start on the technology to
recover them. It is not considered to be an economic
prospect in the foreseeable future
Seabed Mining
Finally, the recent discovery of the
thermal vents
on the
ocean floor has added a new class of minerals. These
hot water plumes bring up metallic sulfides from the
earth's interior and in contact with the cold surrounding
water deposit the sulfides in large quantities. These are
huge potential sources of copper, zinc and lead but
again are at abyssal depths.
Law of the Sea Treaty
In the beginning...
1494 the Pope divided the oceans between Spain and
Portugal
by 1600's, since the oceans were limitless, everyone
agreed that Freedom of the Seas should apply
3 mile strip of territorial sea along coasts
1930 League of Nations tried to codify further
Post WW II...
Truman claimed resources on shelves out to depth of
200 m
1st LOS Conference in 1958:
agreed on "innocent passage" but couldn't agree on
width
outlawed slavery, piracy; allowed hot pursuit, over
flight, fishing
allowed exploitation out to a depth of 200 m
Law of the Sea Treaty
Fishing
Exclusive rights out to 12 or 50 or 200 miles
Iceland went in a few years from 4-12-50-200 miles, only
for fish
Peru & Chile claim 200 miles even though there is
essentially no continental shelf
Lead to cod, tuna, shrimp wars
1960's: Resources started to be known
manganese nodules seemed most likely possibility
only the industrialized countries had ability to exploit
"common heritage of Mankind"
U.N. resolution on "common heritage"
U.N. moratorium resolution on production
1982 Law of the Sea Treaty
"common heritage of mankind"
International Seabed Authority
Royalties of 5-12% of gross or 2-4% of gross plus 35-70%
tax on net profits
45 LDC's have ratified, 60 needed to make law, unlikely
U.S. Exclusive Economic Zone: 3-200 miles offshore
(large area)
Additional Features
Territorial sea limits: 12 or 200 miles
right of transit, innocent passage
archipelago nations?
resources within 200 miles belong to coastal states
Deep Sea: "common heritage" zone
Moon Mining
More than 4.5 billion years ago, the
surface of the Moon was a liquid
magma ocean. Scientists think that
one component of lunar rocks,
KREEP
(K-potassium, Rare Earth
Elements, and P-phosphorous),
represents the last chemical
remnant of that magma ocean.
KREEP is actually a composite of
what scientists term "incompatible
elements": those which cannot fit
into a crystal structure and thus
were left behind, floating to the
surface of the magma.
For researchers, KREEP is a convenient tracer, useful
for reporting the story of the volcanic history of the
lunar crust and chronicling the frequency of impacts by
comets and other celestial bodies.
Moon Mining Primary elements:
The lunar crust is composed of a
variety of
primary elements
, including
uranium, thorium, potassium, oxygen,
silicon, magnesium, iron, titanium,
calcium, aluminum and hydrogen.
When bombarded by cosmic rays, each
element bounces back into space its
own radiation, in the form of gamma
rays. Some elements, such as uranium,
thorium and potassium, are
radioactive and emit gamma rays on
their own.
However, regardless of what causes them, gamma rays
for each element are all different from one another --
each produces a unique spectral "
signature
," detectable
by an instrument called a spectrometer. A complete
global mapping of the Moon for the abundance of these
elements has never been performed.
Moon Mining
ELEMENT
% BY WEIGHT
Aluminum
7.3
Calcium
8.5
Chromium
0.2
Iron 12.1
Magnesium 4.8
Manganese 0.2
Oxygen
40.8
Potassium
0.1
Silicon
19.6
Sodium
0.3
Titanium
4.5
Moon Mining Treaty
Treaty on principles governing the
activities of states in the exploration and use of outer space,
including the moon and other celestial bodies. Opened for
signature at Moscow, London, and Washington on 27 January
1967
THE STATES PARTIES. TO THIS TREATY,
INSPIRED by the great prospects opening up before mankind
as a result of man's entry into outer space,
RECOGNIZING the common interest of all mankind in the
progress of the exploration and use of outer space for
peaceful purposes,
BELIEVING that the exploration and use of outer space should
be carried on for the benefit of all peoples irrespective of the
degree of their economic or scientific development,
DESIRING to contribute to broad international co-operation in the
scientific as well as the legal aspects of the exploration and use of outer
space for peaceful purposes,
BELIEVING that such co-operation will contribute to the development of
mutual understanding and to the strengthening of friendly relations
between States and peoples,
RECALLING resolution 1962 (XVIII), entitled "Declaration of Legal
Principles Governing the Activities of States in the Exploration and Use
of Outer Space", which was adopted unanimously by the United Nations
General Assembly on 13 December 1963,
RECALLING resolution 1884 (XVIII), calling upon States to refrain from
placing in orbit around the earth any objects carrying nuclear weapons
or any other kinds of weapons of mass destruction or from installing
such weapons on celestial bodies, which was adopted unanimously by
the United Nations General Assembly on 17 October 1963,
TAKING account of United Nations General Assembly resolution 110 (II) of
3 November 1947, which condemned propaganda designed or likely to
provoke or encourage any threat to the peace, breach of the peace or
act of aggression, and considering that the aforementioned resolution is
applicable to outer space,
CONVINCED that a Treaty on Principles Governing the Activities States in
the Exploration and Use of Outer Space, including the Moon and Other
Celestial Bodies, will further the Purposes and Principles of the Charter
of the United Nations,
HAVE AGREED ON THE FOLLOWING:
Article I
The exploration and use of outer space, including the moon and
other celestial bodies, shall be carried out for the benefit and in
the interests of all countries, irrespective of their degree of
economic or scientific development, and shall be the province of
all mankind.
Outer space, including the moon and other celestial bodies, shall
be free for exploration and use by all States without
discrimination of any kind, on a basis of equality and in
accordance with international law, and there shall be free access
to all areas of celestial bodies.
There shall be freedom of scientific investigation in outer space,
including the moon and other celestial bodies, and States shall
facilitate and encourage international co-operation in such
investigation.
Article II
Outer space, including the moon and other celestial
bodies, is not subject to national appropriation by claim
of sovereignty, by means of use or occupation, or by any
other means.
Article III
States Parties to the Treaty shall carry on activities in the
exploration and use of outer space, including the moon
and other celestial bodies, in accordance with
international law, including the Charter of the United
Nations, in the interest of maintaining international
peace and security and promoting international co-
operation and understanding.
Article IV
States Parties to the Treaty undertake not to place in orbit
around the earth any objects carrying nuclear weapons or any
other kinds of weapons of mass destruction, instalL such
weapons on celestial bodies, or station such weapons in outer
space in any other manner.
The moon and other celestial bodies shall be used by all States
Parties to the Treaty exclusively for peaceful purposes. The
establishment of military bases, installations and fortifications,
the testing of any type of weapons and the conduct of military
maneuvers on celestial bodies shall be forbidden. The use of
military personnel for scientific research or for any other
peaceful purposes shall not be prohibited. The use of any
equipment or facility necessary for peaceful exploration of the
moon and other celestial bodies shall also not be prohibited.
Article V
States Parties to the Treaty shall regard astronauts as envoys of
mankind in outer space and shall render to them all possible
assistance in the event of accident, distress, or emergency
landing on the territory of another State Party or on the high
seas. When astronauts make such a landing, they shall be
safely and promptly returned to the State of registry of their
space vehicle.
In carrying on activities in outer space and on celestial bodies,
the astronauts of one State Party shall render all possible
assistance to the astronauts of other States Parties.
States Parties to the Treaty shall immediately inform the other
States Parties to the Treaty or the Secretary-General of the
United Nations of any phenomena they discover in outer space,
including the moon and other celestial bodies, which could
constitute a danger to the life or health of astronauts.
Moon Mining - Helium-3
Identification of the potential of lunar
helium-3 as a fuel for 21st Century
commercial fusion power has sparked
increasing interest in the extraction of
solar wind volatiles from the lunar
regolith.
Extraction of one metric tonne of helium-3, that
necessary to provide about 1/25 of the annual U.S.
electricity consumption or 10 GWe-yr, will require the
mining of about 11 km
2
of the lunar surface to a depth of
three meters, assuming a recoverable grade . The
regolith mining, beneficiation, and processing concept
ultimately chosen to accomplish this task will clearly
influence the final economics of volatile extraction and
the architecture of lunar bases and settlements.
Moon Mining
Rectilinear mining concepts, with mining,
beneficiation, and volatile extraction
systems integrated into a single, self
contained mobile unit, have received
important attention. Such concepts
envision interim storage of extracted
volatiles in pressurized tanks which
would then be picked up and transported
to a central processing location at a
permanent lunar base. Long duration,
full service, and permanently emplaced
support facilities appear to be required
to support such concepts. Once mining
operations reach the practical limits of
transportation support, an entirely new
base and transportation network must
be established at another location in the
resource region.
Moon Mining - Spiral Mininq Concept
Spiral mining, extending outward from a
periodically mobile central station ,
represents an alternative concept for
comparison with more traditional mining
schemes. With spiral mining, the mobile
mining machine would be attached to the
central station by a telescoping support
arm. The miner would extract regolith
fines in an outward spiral away from the
central station. Using solar thermal
energy collected at and beamed from the
central station, the miner's internal
systems would then beneficiate the
fines, extract solar wind volatiles, and
recover waste heat. Cooled, spent fines
would be deposited at the rear of the
miner. In these particulars, the spiral
mobile miner and the rectilinear miner
are comparable.
Moon Mining - Mobile Miner
During normal operations, the mobile miner of a spiral
mining system would mine its way through the upper
three meters or so of the lunar regolith, supplementing
its mass with the regolith moving within its systems and
possibly with extra regolith as ballast.
A look-ahead radar system should make it possible to
either avoid or excavate boulders too large to deal with
normally. Blocky craters as well as major boulder
concentrations would be avoided by extending and
contracting the telescoping support arm.
Moon Mining
Continuous processing of the mined regolith would take
place within the miner (see Sviatoslavsky and Jacobs,
1988), including separation of fines and rejection of
coarse material, beneficiation of fines, heating of fines to
extract volatiles, and recovery of waste heat prior to
disposal of spent fines.
Thermal energy for the continuous extraction of volatiles
from regolith fines initially could be collected by
appropriately placed solar collectors on the top of the
central station. This thermal energy, or thermal energy
from any other potential source, would be transmitted by
reflectors or the support arm to the miner and directed
into the extraction heat exchangers.
Moon Mining
The mobile miner may be fully automated or operated tele-
robotically from the central station. Design should provide,
however, both for human inspection and maintenance and for
temporary human operation in the event that automated or
tele-robotic systems require extensive down time for repair.
The central station of a spiral mining system, in addition to
providing support facilities for its inhabitants, would supply
electrical and solar thermal power to the mobile miner. The
station also would perform command and control functions for
teleoperation of routine mining. Extracted raw volatiles,
pumped from the miner, would be processed and tanked for
export or storage. Refined and liquefied helium-3 and other
volatiles would be launched to Earth or space from a launch
and landing platform (LP), placed along the support road from
the main lunar base so as to serve two of more central station
sites. Other liquefied volatiles, in excess of those needed to
operate the station or for export to space based users, would
be stored in radiatively cooled cavities within the insulating
regolith and beneath the central station.
Some considerations suggest that the standard operating
duty cycle for each station would be daytime mining,
beneficiation, and volatile extraction and nighttime volatile
refining. Such a cycle would take maximum advantage of
sunlight for mining and volatile extraction and of the deep
space cold sink during volatile refining. Electrical power could
be generated by hydrogen-oxygen engines and/or fuel cells
with a very small net utilization of the extracted volatiles.
This duty cycle also would provide convenient work cycles for
the station's crews in multiples of two weeks, such as six
weeks on and two weeks off.
The basic architecture of a spiral mining central station might
have a cylindrical plan. A central core area could house the
power subsystem (PS). Habitat sections (HS) and other crew
occupied areas could be arranged around the power
subsystem core. Finally, the outer cylinder could include
volatile refining subsystems (GP), feeding directly into the
mobile miner support arm. This configuration, along with
appropriately located regolith fill in the station's outer walls,
also would provide radiation shielding for the crew.
Wheel assemblies, motors, gear boxes, and other
components of the station's mobility subsystem could be
located in four internally accessible compartments beneath
either the habitat or the volatile refining cylinders.
Preplanning of the station's actual mining track should make
it possible to center each mining spiral over an
appropriately sized crater that can then be configured to
contain the cryogenic storage subsystems for excess
volatiles. The insulating cover placed over storage vessels
could then be used as a prepared area for storage, vehicle
parking, and routine vehicle maintenance and repair.
Oxygen Mining
By weight, moon rocks are about
40% oxygen. By heating the top
meter of 1 acre of moon dust to
1300 degrees Celsius, we get
3000 to 3500 tons of oxygen.
Every ton of extracted oxygen
requires 450 kilocalories of
energy.
If we increase the temperature
(and the amount of energy) just
a bit... to 1500 degrees Celsius,
we get a lot more than just
oxygen.
Nuclear Mining
The first completely
contained nuclear
explosion, of 1.7 kiloton
energy release (TNT
equivalent) was fired on
Sept. 19,1957. Although
one of the prime
purposes of this blast
was to test the depth of
solid rock necessary to
contain a nuclear
explosion, the rock
breakage, seismic
waves generated and
local effects of the rock
were also of vital
interest.
Nuclear Mining
The initial temperature in the
room which contained the
nuclear device was calculated
to be 1,000,000 K and the
pressure 7,000,000 atm. The
rock melted a 15 ft. chamber
and crushed the rock out to a
150 ft. radius. The top of the
cavity collapsed to form a
chimney ultimately 400 ft.
high. About 200,000 tons of
rock was fragmented.
Nuclear Mining
The Sedan Crater was
formed in a series of tests
called Project 'Plowshare'
This was conducted by the
Dept of Energy to see the
effects of using Atomic
weapons for construction
purposes and so the words
'peaceful' tests were
evolved. Sedan is currently
'one' of the largest craters
in the NTS and was
conducted on Yucca Flat
Proving Ground
Nuclear Mining
A nuclear explosion could easily excavate a large area,
facilitating the building of canals and roads, improving
mining techniques, or simply excavating a large amount
of rock and soil. Unfortunately, the radiation proved too
omnipresent and the program was abandoned. The
device was thermonuclear; 70% fusion, 30% fission with
a yield of 100 kilotons. The crater is 653 feet deep,
1280 feet in diameter. The weight of the material lifted
was 12 million tons.
Asteroid Mining
There are estimated to be about 200,000
sizeable Apollo, Amor and Aten asteroids, and
millions of Main Belt asteroids.
The vast majority of Near Earth asteroids are
thought to have originated in two ways:
asteroids
from the Main Belt (between
Mars and Jupiter) which dropped down to
lower orbits due to gravitational
perturbations by Jupiter followed by Mars
or inner planets, or occasionally due to a
collision with another asteroid in the Main
Belt.
comets
from the outer reaches of the
solar system that were captured when they
passed close to a planet or planets in the
inner solar system. These would probably
be volatile rich.
Asteroid Mining - Processing the Material
Asteroidal material is exceptionally good ore requiring a
minimum of processing.
Only basic ore processing need occur at the asteroid,
producing free metal and volatiles (usually stored as
ices), and perhaps selected minerals, glasses and
ceramics. The required equipment is quite simple.
At the input chute, the ore will be ground up and sieved
into different sizes as the first step of a basic ore
processing system. Most asteroids probably offer far
more crumbly material than we could consume in one
mining expedition
Asteroid Mining - Processing the Material
Simple mechanical grinders, using a rocking jaw
arrangement for coarse crushing and a series of rollers
for fine crushing, are arranged in a slowly rotating
housing to provide centrifugal movement of the material.
Vibrating screens are used to sift the grains for directing
them to the proper sized grinders.
The streams of material are put thru magnetic fields to
separate the nickel-iron metal granules from the silicate
grains. Alternatively, the streams can be dropped onto
magnetic drums, whereby the silicates and weakly
magnetic material deflect off the drum whereas the
magnetic granules and pebbles stick to the magnetic
drum until the scrape off point. Repeated cycling thru the
magnetic field gives highly pure bags of free nickel iron
metal.
Asteroid Mining - Processing the Material
An optional additional piece of equipment is an "impact
grinder" or "centrifugal grinder" whereby a very rapidly
spinning wheel accelerates the material down its spokes and
flings it against an impact block. Any silicate impurities still
attached to the free metal are shattered off. It's feasible to
have drum speeds sufficient to flatten the metal granules by
impact. A centrifugal grinder may be used after mechanical
grinding and sieving, and before further magnetic separation.
In fact, most of the shattered silicate will be small particles
which could be sieved out.
The nonmagnetic material is channelled into a solar oven
where the volatiles are cooked out. In zero gravity and
windless space, the oven mirrors can be huge and made of
aluminum foil. The gas stream is piped to tanks located in a
cold shadow of space. The tanks are put in series so that the
furthest one away is coldest. This way, water condenses more
in the first one, carbon dioxide and other vapors in the tanks
downstream.
Asteroid Mining - Processing the Material
Rocket fuel for the delivery trip to Earth orbit can be produced
by separating oxygen and hydrogen gases from the mix, or by
electrolysis of water. Alternatively, the hydrogen could be
chemically bonded with carbon to produce methane fuel.
Thin, relatively lightweight spherical tanks could be sent to
store the frozen volatiles. Ultimately, tanks for storing frozen
volatiles for sending to Earth orbit can be manufactured by
some of the nickel iron metal, by use of a solar oven for
melting the nickel iron metal. A cast can be made from sand or
glass-ceramic material from melted leftover ore.
Some silicate material from the asteroid will also be shipped
back to Earth orbit to be used for making glass, fiberglass,
ceramics, "astercrete", dirt to grow things in, and radiation
shielding for habitats and sensitive silicon electronics.
Asteroid Mining - Processing the Material
Processing of glasses, ceramics, "astercrete" and the like is not
discussed here, because it is discussed in the chapters on lunar
material utilization and space manufacturing. If we were to not
use lunar materials but use only asteroidal materials,
processing asteroidal material to make glasses, ceramics and
astercrete is analogous to the discussion on processing lunar
materials for the same feedstocks and products.
Undesired material can be put in a big wastebag container, or
"sandbags", or cast into bricks by a solar oven, used for
shielding the habitat from space radiation, creating more cold
shadows, or just removed from the mining operation's space. (If
waste were simply ejected at escape velocity, it would not
significantly increase the number of meteors in interplanetary
space. However, it's cheaper to skip the ejector equipment and
power supply and just bag it all.)
Asteroid Mining - Equipment Redeployment
After the asteroid is entirely consumed, the equipment can be moved to
the next asteroid to mine. Overall, the equipment is capable of
producing at least several hundred times its own mass, and perhaps
thousands of times its own mass, per year.
A few on-site general purpose engineers will almost surely be needed at
the asteroid to help set up the equipment, teleoperate equipment
without a time delay (being that communications from Earth experience
a time delay of minutes due to distance and the speed of light), and
handle any repairs and glitches. The workers would likely live in
artificial gravity produced by connecting habitats by cable and spinning
the barbell. One-tenth to one-third Earth gravity is probably healthy for
a long stay. All the chemicals necessary for breathing and drinking are
abundant on asteroids, but a reserve of air and water, and getaway fuel,
would always be kept on hand in case of an emergency.
The equipment will be sent to the asteroid in advance of the people, on
a slower and more fuel-efficient trajectory. Once in place with all vital
systems appearing OK, the humans will be sent. Their first task will be
to set up camp in a radiation-protected environment.
Bacterial Leaching
Heap leaching is also used in
recovering metals from their
ores. Bacterial leaching is first
used to oxidize sulphide
minerals. Cyanide solution is
then used to leach the metals
from the mineral heap.
Removal of materials by
dissolving them away from
solids is called leaching. The
chemical process industries use
leaching but the process is
usually called extraction, and
organic solvents are often used.
Basic concept
The theory and practice of
leaching are well-developed
because for many years leaching
has been used to separate metals
from their ores and to extract
sugar from sugar beets.
Environmental engineers have
become concerned with leaching
more recently because of the
multitude of dumps and landfills
that contain hazardous and toxic
wastes. Sometimes the natural
breakdown of a toxic chemical
results in another chemical that is
even more toxic. Rain that passes
through these materials enters
ground water, lakes, streams,
wells, ponds, and the like.
Bacterial Leaching
Although many toxic materials have low solubility in water, the
concentrations that are deemed hazardous are also very low.
Furthermore, many toxic compounds are accumulated by living
cells and can be more concentrated inside than outside a cell.
This is why long-term exposure is a serious problem;
encountering a low concentration of a toxic material a few
times may not be dangerous, but having it in your drinking
water day after day and year after year can be deadly.
The main theory of leaching neglects mechanisms for holding
the material on the solid. Although adsorption and ion exchange
can bind materials tightly to solids, we will simplify the analysis
and consider only dissolving a soluble constituent away from an
insoluble solid. An example is removing salt from sand by
extraction with water.
Bacterial Leaching
Countercurrent stagewise processes are frequently used in
industrial leaching because they can deliver the highest possible
concentration in the extract and can minimize the amount of
solvent needed. The solvent phase becomes concentrated as it
contacts in a stagewise fashion the increasingy solute-rich solid.
The raffinate becomes less concentrated in soluble material as it
moves toward the fresh solvent stage.
'Heap leaching' is a countercurrent process where the solid is in
a stationary heap and the solvent percolates through the solid.
An example is a dump or landfill. This leaching is essentially
countercurrent. In industrial leaching, solvent and solid are
mixed, allowed to approach equilibrium, and the two phases are
separated. Liquid and solids move countercurrently to the
adjacent stages. The solvent phase, called the extract, becomes
more concentrated as it contacts in stagewise fashion the
increasingly solute-rich solid. The raffinate becomes less
concentrated in soluble material as it moves toward the fresh
solvent phase.
Deep Sea Muds
"Metal-Bearing mud has been
reported thus far only from
the Red Sea, a submarine
volcano off Indonesia, and, in
less concentrated deposits, on
the crest of the East Pacific
Rise. Possibly present also in
other rift or fracture zones, in
parts of the deep trenches, in
volcanic craters, or in other
environments in which rising
hydrothermal solutions may
have been trapped."
Deep Sea Muds
Three pools of brine are known to occur in adjacent local
depressions along the median valley of the Red Sea trench. The
upper surface of the pools is at a depth of 2,000 meters (6,562
feet) below sea level, and the depressions are about 150 metres
(492 feet) in depth, Atlantis II Deep by 5 km (3.1 miles) by 13 km
(7.4 miles). Discovery Deep is 2.5 km (1.5 miles) by 4 km
(2.5miles), and Chain Deep is 2/3 km (0.4 miles) by 3 km (1.9
miles). estimated to be about 50,000,000 tons averaging 29
percent iron, 3.4 percent zinc, 1.3 percent copper, silver 54 parts
per million, and gold 0.05 parts per million; with a value of $2.5
billion exclusive of the value of iron (Mero 1972a, p.22).
The sediments average about 85 percent brine on an 'as is' basis
and contain about $5 per ton of metals, or on a dry-weight, salt
free basis contain about $28 of copper, zinc, and silver per ton. The
highest grade part of the sediments is the sulphide facies and if it
can be mined selectively it should prove to be highly profitable
because it contains over $120 per ton of zinc, copper, and silver.
Because of the gel-like, fine-grained nature of the sediments, they
can be easily fluidized and pumped to the surface but recovery of
the metals is a difficult undertaking (Mero 1972a, p. 22-23).
Methane hydrates
Methane hydrates are a type of
natural formation that contains large
amounts of methane, which is also
known as natural gas, and water, in
the form of ice.
Hydrates are plentiful in nature, both
underwater and under permafrost.
They are a potential source - possibly
a very important source -- of energy
for the future. However, little is
currently known about cost-effective
ways to turn hydrates into an energy
resource.
From a scientist's point of view,
methane hydrates are cages of
water molecules that surround and
trap methane molecules. They are
crystalline solids that form under
moderate pressure (for instance, at
water depths greater than 300
meters) and at temperatures that
are low but above the freezing point
of water. In nature, hydrate
formations are very hard and ice-
like, and they may contain
molecules of substances other than
methane. When hydrates are made
in the laboratory or classroom, they
tend to look more like slush.
Where do methane hydrates form?
Stable methane hydrates are found at the temperature and
pressure conditions that exist near and just beneath the sea
floor where water depths exceed 300 to 500 meters. Hydrate is
also stable in conjunction with permafrost at high latitudes.
How are hydrates formed?
A. There are two processes:
Most natural gas hydrate is formed from biogenic methane, excreted
by bacteria that eat organic matter that has been washed into (or
died in) the ocean. This type of hydrate is concentrated where there is
a rapid accumulation of organic detritus and also where there is a
rapid accumulation of sediments (which protect detritus from
oxidation).
Hydrates also form when faults permit natural gas (or other gases) to
migrate from deeper inside the Earth's crust to the surface of the
seabed at places with appropriate temperature and pressure levels.
These processes can also cause hydrates to form below
permafrost, which acts as a cap to prevent further upward
migration of gas into the atmosphere.
Scientists generally believe that
most natural gas hydrate is
formed from biogenic methane
(produced by bacteria), and that
therefore it is concentrated 1)
where there is a rapid
accumulation of dead organic
material (from which bacteria
generate methane) and 2)
where there is a rapid
accumulation of sediments,
which protect the material from
oxidation.
Geologists tend to believe that deposits formed through underground
venting will prove the easiest to recover because there would seem to
be more potential for biologically produced hydrates to be distributed
relatively evenly over a wide area, while a vent is localized.
Additionally, there appears to be more potential that free methane is
trapped underneath hydrates formed at vents.
This speculation makes sense given the characteristics
of current gas and oil production. Methane, for instance,
one of the most common of earth's molecules, is
produced naturally by bacterial action in swamps,
landfills, rice paddies, and the digestive tracts of cows
and termites. Generally, however, the concentration of
methane in any one place is so low that - with the
exception of a few landfills - we do not attempt to
capture this "resource." Similarly, oil is frequently
dispersed throughout shale formations; but processing
the shale is an energy-intensive activity in itself, thus
raising production costs far above those involving more
porous formations
.
Ocean Diamonds
Industrial diamonds are not yet commercially viable for ocean
mining, but diamond gemstones are being actively hunted and
mined in the alluvial areas offshore the southern tip of Africa,
and in Indonesian waters. It is but a small fraction of the
world's total production of diamonds that find their homes in
jewelry settings. That is why it is so remarkable that at least
ninety percent of diamonds mined offshore are of gem quality.
This is attributable to the fluvial process; only ten percent of
gem quality diamonds eroded by river drainage systems end
up deposited on land.
The other 90 percent are held on the sea floor, where they
were concentrated into diamondiferous gravels through eons
of current and wave action. The stones that survived the
journey to the coast and beyond are generally of superior color
and clarity, and on top of that, they are of the sizes most
desired by consumers in the retail jewelry industry. Most
African offshore diamonds are in the 0.2 to 20 carat size range.
Ocean Diamonds
Because the sea level has fluctuated so
much historically, dropping by some 1640 ft.
(500m) "only" 25 million years ago, alluvial
diamonds are to be found as far as 295 ft.
(90m) above sea level; in very shallow
coastal areas; and on out into deeper
waters. Presently diamondiferous gravels
are being mined in waters as deep as 426 ft.
(130m), but Diamond Fields International is
prospecting Cape Canyon offshore South
Africa in 1,000 ft. (300m) water depths.
Remote technology is being developed to
carry out the harvest, assuming high-grade
gravels are determined to be in these
deeper waters.
Ocean Diamonds
The geology of offshore southern Africa is
too incredibly diamond-rich to be ignored for
long; geologists estimate that ten billion
carats of diamonds were eroded by the
Orange River drainage system over a 100
million year period. They originated from
diamond-bearing geologic features called
kimberlite pipes, which were thrust up
volcanically into the African interior. Three
billion carats are estimated to exist in
mineable deposits along the southern
African coastline, with an economic value
approaching one trillion dollars.
There are two primary methods of mining diamonds from the
ocean floor: bucket line dredging and air lift dredging. The
methods will vary depending on available equipment, water
depth, and operator expertise. The nature of the gravel deposit
can influence the dredging technique, with proprietary methods
and technologies often being deployed.
A typical small air lift dredging operation will place a diver on
the sea floor with a suction hose. The hose is located at the
mine face, suction is effected, and alluvial gravels are
vacuumed to the surface where they are processed. Diver
operations are typically limited to 92 ft. (28m) using an 8" lift
pipe.
Once the vacuuming starts, the diver is working in zero-
visibility, for all practical purposes, due to water turbidity.
Boulder-sized rocks must frequently be pried loose and placed
away from the mine face. As the diver works the air lift, he must
be cautious that no loose rocks ‚ weighing up to a ton ‚ fall
inward toward the pump nozzle, potentially causing injury to or
trapping the diver. As an added hassle, kelp is often around to
clog up the suction nozzle.
Ocean Diamonds
The bucket line dredge consists of a vessel with a
conveyor-type of assembly lowered to the seafloor, in
which a rotating line of "buckets" carries bite after bite
of alluvial gravels to the surface for processing.
Topside, the gravels are tumbled and screened. The
resulting finer gravels are then "jigged," typically using a
vibrating pan or similar system that takes advantage of
the diamonds' higher specific gravity to segregate them.
On smaller operations these functions take place on
crude hand-tool level machinery, whereas the more
sophisticated operators have automated most functions.
Gold from the Sea
Gold ores worldwide in 1974 averaged 0.15 ounces troy per ton.
By 1986 that average had dropped to 0.05 ounces per ton. As
the concentration of these minable continental ores continues
to diminish, the seas have increasingly become the object of
exploration and research into gold reserves. Significant
quantities of gold have been mined from ocean beach placers,
and mid-oceanic ridges have yielded rich gold ore samples, but
the greatest accessible reserve is the ocean itself. Seawater
contains vast quantities of dissolved gold, perhaps as much as
10 trillion dollars (US) worth, though in dilute concentrations.
Recent evidence suggests that much of the earths continental
gold deposits have biological origins. Certain bacteria are
believed to have been involved in the precipitation of gold out
of dilute hydrothermal solutions. A possible avenue for
commercially viable gold recovery from seawater might involve
such a bacterium, or a specifically engineered microbe.
Gold from the Sea
Seawater contains gold in solution. When considering
only the data gathered since 1980, reported values for
the concentration of gold in seawater have ranged
from 5 to 50 ppt , with the average concentration at
about 13 ppt. Some of the highest concentrations
recently reported have come from seawater samples
taken from the Bering Sea at 50 ppt (Pashkova 1988).
Much about the process of precipitation of gold and
other metals from these solutions is unknown,
however, it is believed that some sulfur-oxidizing
bacteria of the genera Beggiatoa, Thiothrix or
Thiovulum play an active role in this precipitation
.
These chemosynthetic bacteria derive energy unlike
their surface dwelling relatives (assuming that they are
related). Instead of deriving energy from the oxidation
of organic mater, or from photosyntheses, they oxidize
sulfide compounds directly from the scorching hot
hydrothermal liquids.
How these bacteria can live and even thrive at 200o C is
a matter of much discussion and investigation, but
evidence suggest that these bacteria can efficiently
remove gold, silver, copper, and other metals and
minerals from dilute aqueous solutions. Proposed
methods for this deposition vary. One such method
involves the increase in pH in the micro-environment of
the microbial mats that line these vent chimneys. These
metals are less soluble at the higher pH's and precipitate
out of solution and are then stored within the cell walls .
The possibility that certain bacteria can concentrate
gold in amounts sufficient to comprise a major share of
the Earth's gold ores suggest that with the right
application, these or similar bacteria may be employed
in the extraction of gold from low grade deposits or
solutions. Already, there are commercial applications of
bacteria in the mining of gold. Specifically, the bacteria
Bacillus cereus is being used by the Canadian Genprobe
Company to increase the yield of gold from pyrite ores .
In this case the bacteria are after the pyrite matrix that
binds the gold and prevents economic recovery
otherwise. Bacterial processing of these pyrite ores is
relatively inexpensive and has increased yields from an
average of about 65% to as much as 96% . Given the
affinity that some bacteria have for the concentration of
gold, the question arises as to whether it might be
feasible to employ such a bacterium, or one specifically
engineered for the task, to scavenge gold directly from
the dilute concentrations present in sea water.
Introduction to Mine Engineering