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OCR for page 56
3
Role of Science and Technology in
Minerals and Metals
Competitiveness Issues
To be truly competitive in the nonrenewable resource sector, a firm or
industry must locate new economic raw material sources and also maintain,
update, and replace its production and processing facilities as costs, tech-
nologies, and regulatory requirements change. In the minerals and metals
industry in particular, exploration accomplishes the former function, while
mining and process research and development (R&D) fulfill the latter. In
financially difficult times these functions require corporate commitment,
maintenance of an effective infrastructure, and the availability of money on
a sustained basis.
A technology-based competitive strategy cannot be developed without a
long-term commitment of intellectual and financial resources. Creative in-
terdisciplinary thinking and experimentation by well-trained scientists and
engineers, using modern equipment in well-equipped laboratories and pilot-
plant facilities, can lead to both evolutionary and revolutionary technologies.
if companies, universities, and governmental organizations commit to this
strategy over the long term by supporting research and implementing its
most promising products, U.S. firms will be competitive producers of min-
erals and metals, adapting relatively easily to changing economic and envi-
ronmental conditions and requirements.
Evolutionary developments incrementally improve the efficiency of an
existing technology. For instance, a larger truck to haul larger loads is an
evolutionary enhancement, since the principles of the truck remain unchanged.
Revolutionary research transforms a system. The advent of in situ extraction
56
OCR for page 57
ROLE OF SCIENCE AND TECHNOLOGY
57
is an example of a revolutionary advance, since it rendered many of the
basic extraction techniques obsolete.
This chapter identifies the technological developments that will be required
to strengthen the competitiveness of the U.S. minerals and metals industry.
The commodities it examines are the base metals, iron and steel, aluminum,
and the precious metals. Coal and the industrial minerals are also included,
since the technologies serving them may also have applications to the min-
erals and metals considered in this report. The chapter is divided into the
four components of the mining industry: exploration, mining, minerals
processing, and metals extraction. Within each of these four sections the
state-of-the-art techniques and the research efforts of the U.S. minerals and
metals industry are reviewed. The research strategies (both evolutionary
and revolutionary) with the greatest potential impact on the competitiveness
of the U.S. minerals and metals industry are also identified.
BACKGROUND
Although mining's origins can be traced back through five or six millen-
nia, its modern structure is about 200 years old. The explosive growth in
mechanics during the nineteenth century greatly improved the primitive
devices for size reduction and gravity concentration that had been in use for
over 500 years. Dynamite, compressed-air-driven tools, and most of the
crushing and grinding machinery in use today were all developed before
1900. Meanwhile, gravity concentration was vastly improved by the
mechanization of older devices and the invention of shaking tables. By the
end of the nineteenth century, gravity's preeminence was challenged first
by magnetic and electrostatic methods for mineral separation and then by
the development of flotation.
Goals for developing new technology in mineral processing were identi-
fied at least as early as 1866 (Hues, 18661:
. . . to reduce the intervention of the worker by extension of mechanical treat-
ment . . . to reduce [waste] . . . by continually improving equipment . . . and to
replace the intelligent attention of the workers by mechanical precision . . .
More recently, Revnivtsev (1988) wrote:
. . . although five years ago the use of the word revolution in mineral processing
might have been questioned, today the word should be underlined; starting
with comminution, this technology is facing the necessity of creating and
implementing new principles of ore breakage on a large scale.
These forecasts have come not from the industry but from its service sector.
the research and consulting development arm. Industry itself has been far
less enthusiastic with respect to the introduction of new technology. As
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58
COMPETITIVENESS OF THE U.S. MINERALS AND METALS INDUSTRY
noted by the Office of Technology Assessment (OTA), there have been few
revolutionary advances in mining technology since the 1950s:
Witness a 1983 U.S. Bureau of Mines report on Technological Innovation in
the Copper Industry . . . that had to stretch its time frame to the last 30 to 50
years to develop a list of innovations. Instead, incremental improvements in
existing methods, and adaptations of other types of technology to mining
(e.g., computers, conveyor systems) have gradually reduced costs and increased
productivity (OTA, 1988, p. 1 191.
The conclusion to be drawn is that meaningful dialogue is often lacking be-
tween the engineers who operate mines and plants and those engaged in R&D,
both in companies and in service organizations. In too many cases both the
targets for innovation and the efforts to address them have been defined by the
service sector; but the industry's resistance to adopting anything significantly
new ranges from formidable to insurmountable. Few companies have taken
positive roles in developing new technologies, and these have been primarily
in extractive metallurgy, particularly in the development of new or substan-
tially modified smelting or leaching processes. Much of this technology has
come from abroad or was first tested by smaller domestic companies. Among
the best-known examples are Outokumpu's and Inco's flash smelting, initially
developed in the 1940s and 1950s and very slowly adopted by U.S. firms.
Some of the same companies that exhibit strong resistance to accepting
new technology from the outside, however, are heavily involved in develop-
ing new technology internally when compelling needs are recognized by
management or forced on it by new regulations. This contradictory attitude
raises important questions about the conduct of mining and minerals R&D:
· What are the areas of major importance?
· What opportunities exist for incremental or evolutionary improvements
in technology to contribute to competitiveness?
.
What are the most promising areas for revolutionary improvements in
technology for the mining and metals industry?
EXPLORATION TECHNOLOGIES
Exploration techniques are used to locate and evaluate minerals deposits
for potential mining and metal extraction. U.S. mineral exploration has
been largely commodity specific over the past 50 years. Certain materials
have been in great demand during specific periods, as with the uranium
"rush" of the 1950s and early 1970s and the porphyry copper boom of the
1960s. Although precious metals currently command the majority of explo-
ration budgets, there is increasing activity in copper (particularly oxide
copper), other base metals, strategic metals (e.g., the platinum group met-
als), rare earths, beryllium, germanium
, gallium, manganese, and titanium.
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ROLE OF SCIENCE AND TECHNOLOGY
59
Exploration Geology
Computers and selectively sensitive sensors have greatly affected explo-
ration geology in recent years. Reconnaissance data can now be obtained
through a personal computer using time-share services such as GEOREF to
collect bibliographical references. The U.S. Geological Survey's Mineral
Resources Data System and the Bureau of Mines' Mineral Availability System
provide site-specific mineral deposits and occurrence data and site maps.
Models have also become increasingly important to exploration; many are
based on new information related to regional and plate tectonics. At least
one computer program, Prospector, has incorporated such data and permits
the user to identify a particular model for a region depending on the geological
information input. The program's projection can be used to enhance and
refine subsequent detailed explorations.
Mapping and Surveying
The basic data collection stage of exploration programs has been greatly
enhanced in recent years by the increased availability of aerial and satellite
photo coverage. Base maps can now be prepared quickly and cheaply. The
availability of high-quality color and infrared photos are a great aid to
geologic mapping and interpretation. At the engineering stage the current
generation of electronic distance-measuring instruments has enhanced speed
and accuracy in establishing benchmarks, triangulation stations, property
boundaries, drill hole locations, geophysical stations, and other data for
which accurate topographic control is required. Finally, a great deal of
geographic and topographic data can be entered and retrieved from computer
data bases. The various computer-aided drafting programs can readily pro-
duce maps and sections at any scale required and can be color coded as
desired.
Geophysics
Geophysical activities and surveys have not advanced as rapidly in the
past 10 years as previously Magnetics, electromagnetics, induced polarization,
and, to a lesser degree, gravity and seismic probes are still widely used,
both ground based and airborne. Some variations are now also being exploited,
such as "radiometry and controlled-source magnetotellurics. The most im-
portant results of recent research have been improvements in reliability and
reductions in the weight of solid-state instrumentation. Ultrasensitive gravimeters,
particularly gravity-time-variation detectors, offer a powerful new geophysical
tool. From the standpoint of regional airborne studies, electronic position-
ing systems such as Ranger or Loran can provide positional data within 5
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COMPETITIVENESS OF THE U.S. MINERALS AND METALS INDUSTRY
meters. The ability to record digital data allows further data manipulation,
filtering, and enhancement for better interpretation.
One technique widely accepted in both the minerals and petroleum in-
dustries is bore-hole logging. Probes now available include acoustic velocity,
natural gamma, self-potential, resistivity, caliper, fluid resistivity and high-
resolution temperature, bore-hole azimuth and inclination, dip meter, gamma-
gamma density, neutron, induced polarization, and spectral gamma. These
sensors can be used alone or in various combinations. Many of these functions
provide information useful in both mining and geotechnical engineering.
Geochemistry
The use of geochemistry as an exploration tool at both the regional and
the site-specific scales has increased greatly over the past 20 years. A
scientific basis for sampling has been developed to identify geologic anomalies
despite errors in sampling and sample preparation. Some of the more exciting
developments in geochemistry have been advances in the technology of
sampling through the transported overburden. In addition to improved lightweight
drills and augers, some new techniques require no physical penetration of
the overburden. Biogeochemistry, in particular sampling of plants with deep
root systems, has shown very encouraging results. A recently developed
technique that is still largely experimental involves the detection and quan-
titative determination of specific bacteria that are known to have an affinity
for certain metals. This technology may have widespread applications in
the future. Another technique being researched and used to some extent is
soil gas geochemistry as a means of locating minerals not visible on the
surface without the expense and time required for drilling and testing core
samples.
Analytical techniques have also improved in recent years, particularly in
the field of trace element determination. Although a fire assay is still
considered the final answer for precious metals, the accuracy and precision
of atomic absorption analyses have been improved. Also, resonance-enhanced
multiphoton ionization (REMPI) and laser-induced fluorescence have made
element-specific trace analysis possible at far lower concentration levels.
Techniques such as induction coupled plasma (ICP) provide multielement
trace element data at a fraction of the cost of individual element analyses.
Likewise, neutron activation analysis (NAA) shows great promise in high-
precision multielement determinations. Portable field analyzers based on
variations of x-ray fluorescence technology are becoming widely used, particularly
in operating mines where element concentrations are in ore-grade ranges;
these instruments are quite useful in rapid scanning of drill core, working
faces, and outcrops.
Computer statistical and graphic techniques are widely used in the inter-
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ROLE OF SCIENCE AND TECHNOLOGY
61
pretation and presentation of survey results. Some of the more sophisti-
cated multivariate statistical methods have proven successful in the detection
of subtle anomalies, particularly in regional surveys. Computer surface modeling
and geostatistics are widely used in early-stage interpretation and evalua-
tion of deposits.
Drilling Technology
Core drilling is still widely used in mineral exploration, although rotary
and percussion methods enjoy a high popularity, particularly in precious
metals exploration. The improvements in core drilling in recent years have
been in the areas of hydraulics, instrumentation, and mechanical systems.
New bit designs and improved mud and chemical additives have helped
improve core recovery. More attention has been given in recent years to
sample collection and preparation. Numerous sample collection devices are
now on the market that collect multiple representative samples of drill cut-
tings or other crushed material. Directional control of small-diameter drill
holes has also improved. In addition to the old photographic methods,
gyroscopic and laser systems are available.
Directions for Future R&D
It is an adage within the minerals industry that discovering a good new
deposit is better than trying to improve the yield from a poor one with the
use of advanced mining and processing technologies. If it is assumed that
undiscovered rich ore bodies are still extant within the United States, the
evolutionary improvement of exploratory technologies could enhance the
competitiveness of the U.S. minerals and metals industry by allowing the
discovery of new viable deposits. Evolutionary improvements in exploratory
technologies include
· spatial and spectral image resolution to penetrate foliage and surface
cover;
· digital geophysical coverage of the United States magnetically, gray
tationally~ radiometrically, and spectrally to a scale of one-half mile;
~ . ~ . .
· improved drilling/sampling techniques and analytical methods to increase
basic geophysical knowledge; and
· deep drilling of epithermal zones (15,000 to 25,000 feet).
Improvements in data bases and increased availability of information
would allow smaller aggressive companies to perform effective exploration
without prohibitive expense. Another research advance that could revolutionize
the industry would be a more complete general theory of ore genesis and
deposition, which would not only improve the probability of discovering
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COMPETITIVENESS OF THE U.S. MINERALS AND METALS INDUSTRY
new deposits but also aid in the development of new mines and the selec-
tion of more efficient extraction methodologies.
MINING TECHNOLOGIES
Current Mining Technologies
Mining technologies are those required to expose and remove ores and
minerals from their natural deposits. The development of current mining
technologies reflects the following factors:
· Cost of labor (both wages and benefits) rose rapidly after World War
II. forcing a relentless drive for higher productivity,
· Demand for mineral products and energy increased with World War II.
the Korean 'war, and the postwar reconstruction in Europe and elsewhere,
· Concern for the natural environment heightened in recent decades,
evolving into a major responsibility for the U.S. mining industry but affect-
ing most foreign competitors to a lesser degree,
· It was realized that the safety and health standards of the prewar
period were no longer acceptable. While this has been most serious for
coal, it has also affected metal mining costs.
As a result of these factors, present mining technologies (with a few
exceptions) are designed to achieve high labor productivity and to handle
large volumes of rock or ore. Mining machines, especially those used in
surface mines, have huge capacities but very high unit capital costs. This
mining technology was developed and implemented mainly in the United
States for metal and surface coal mining. Mass production technology for
i: :~_ —_
A continuous miner that, together with the Longwall system, represents the forefront
of mechanization in underground coal mining. (Courtesy M.D.G. Salamon, Colo-
rado School of Mines.)
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ROLE OF SCIENCE AND TECHNOLOGY
63
underground coat mining (i.e., room and pillar mining) was also initially
developed in the United States. Longwall technology, which is regarded by
many as the most effective underground coal mining method and which will
form most of the basis of future development, was imported from Europe.
Limitations of Present Mining Technology
Virtually every mechanized mining system used today was in use by the
late 1950s. Recent advances have been limited to increasing the size of the
equipment and to a few improvements to achieve higher labor productivity.
This approach provided only limited opportunities for continued improvement.
This policy of evolutionary equipment development has resulted in a situa-
tion where most foreign companies use technology identical to that used by
their U.S. counterparts, placing the U.S. companies at a disadvantage because
of lower ore grades and higher environmental protection costs and unit
labor costs, which although improved, may still be higher than those of
competitors.
The Case for New Technology
The recent return to profitability by many mining companies resulted
from their own cost-cutting efforts and from rises in the prices of many
mineral commodities. This improvement has created a favorable opportu-
nity to invest in the future of the industry through development of new
technologies. The present evolution of mining equipment may be leading to
a dead end; if real progress is to be made, the mining industry must embark
on a new research program that will result in mining systems that will
reduce demands placed on the abilities of operators, remove operators as far
as possible from dangerous environments, and exploit opportunities created
by minimizing the need for humans in mines.
Since many of the ground support systems and environmental measures
used in the mining industry are designed primarily to protect human beings,
the absence of workers would create opportunities for redesigning mining
processes. In other words, new technologies (e.g., robotics and automation)
should not merely reduce the labor force but also exploit the opportunities
presented by an operator-free working environment.
Directions for Future R&D
By its nature, mining involves intimate interaction with the rock mass.
Unfortunately, geological conditions are variable and unpredictable by available
means on the scales relevant here. ~4 mining system must therefore have
substantial cognitive abilities to recognize and react to unpredictable varia-
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64
COMPETITIVENESS OF THE U.S. MINERALS AND METALS INDUSTRY
__ ~
~ C:
At San Manuel Copper Mine in Arizona, underground trains are controlled by a
radio dispatcher from the surface. (Courtesy Magma Copper Company.)
lions. Currently, the trained and experienced operator provides all cogni-
tive abilities. If the operator's burden is to be eased and mining automation
is to become a reality, more and more cognitive ability will have to be
imparted to the inanimate part of the system. A number of obstacles ham-
per the development of intelligent mining systems. Some of these are fun-
damental and confront the designers of any automated system that must
operate in unpredictable conditions (e.g., space or battlefield autonomous
vehicles). Others are intimately related to mining (e.g., fragmentation of
rock, prediction of variations in the geological environment, navigation in a
confined underground space). It seems logical to assume that mining research
will have to solve its specific problems, accessing data from other fields by
soliciting the aid of high-technology companies with related experience.
Four areas of research can be identified that address the problems to be
overcome if a new generation of mining systems is to be realized:
· Geosensing, or the ability to (1) predict variation in the ore body, (2)
sense the closeness of geological disturbances (e.g., faults), and (~) obtain
in situ measurements of grade variations, would improve the likelihood of
discovering new deposits and contribute to the design of more effective
mining equipment. The feasibility of automated mining relies on this data
for the navigation and control of an intelligent system. Although clearly
related to aspects of geophysics and geochemistry, this research area must
aim for resolution and accuracy that has not hitherto been attempted.
Nonexplosive rock fragmentation would be a great advantage to the
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ROLE OF SCIENCE AND TECHNOLOGY
65
mining industry and is a basic component of automated mining systems.
Considerable advances have been made in recent decades in the mechanical
extraction of softer rocks, especially in the area of hydraulic mining. Nonexplosive
extraction offers enhanced safety through better control and continuity of
operations, leading to improved production capacities.
· Intelligent mining systems incorporating advanced levels of cognitive
ability in inanimate components of the system would allow new approaches
in mining and reduce the exposure of operators to hostile working environ-
ments.
· In situ mining is a potentially revolutionary mining method that could
greatly improve mining economies and allow a human-free working environment,
exploitation of low-grade mineral resources, and retention of waste underground.
1
MINERAL PROCESSING TECHNOLOGIES
Current Mineral Processing Technologies
Mineral processing has a critical role in determining the yield and quality
of concentrates for smelting or other product preparation steps. Most current
mineral processing technologies were invented (if not implemented) in the
nineteenth century (see Table 3-1~. For example, the two crusher types now
in use (jaw and gyratory) were nineteenth-century developments; they have
both increased in size, capacity, and effectiveness since then, but they are
unchanged in principle. The cone crusher, a product of the 1920s, is only a
modification of the gyratory design. The ball mill, brought to this country
from Germany shortly after the turn of the century, has increased substantially
in size, but its basic design and action are unchanged.
Concentration by gravity in its earliest forms involved stratification by
differential settling. New types of gravity washers were introduced in the
nineteenth century and achieved relatively higher efficiencies with improved
designs of many of the older devices. More importantly, mechanization
was added. Dependence on gravity methods alone for concentration was
relieved by the invention of magnetic separators, again in the nineteenth
century, and electrostatic separation, also patented in the nineteenth century
but first applied in 1907. Flotation, with early patents in the late nineteenth
century, had its first use in Australia in 1906 and in the United States in
1911, and almost every reagent type in current use had been established by
1 926.
Directions for Future R&D
The energy inefficiency of the comminution or pulverizing process has
been known for over a century, yet there have been no major developments
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COMPETITIVENESS OF THE U.S. MINERALS AND METALS INDUSTRY
TABLE 3-1 Chronology of Major Innovations in Milling, Nineteenth and
Twentieth Centuries
Comminution
Stamps Described by Agricola and operated then by water
power; mechanized in the nineteenth century, first
by steam and later by electric power.
Roll crusher Invented in England (1806~; introduced to the continent
(1832~.
Jaw crusher Patented in U.S. by Blake (1858~; first use (1861~;
introduced to Europe (before 1866~.
Gyratory First competitive trial versus jaw crusher by Gates
(1883~.
Ball mill Invented by Bruckner in Germany (1876~; earliest on
ores in U.S. 1905.
Autogenous First use Kalgoorlie (1890s); South Africa (19064;
grinding development period North America (1945-1955~.
Classification Mechanical classifier (about 1905~.
and sizing Cyclone (early 1930s).
DSM sieve bend (ca. 1960~.
Concentration
Gravity Wilfley Table (patented 1896~; in wide use (by 1900~.
Heavy medium separation (on ores) (1930s).
Heavy medium cyclone (late 1930s).
Humphreys spiral (first used about 1943~.
Electrical
Magnetic Cleaning apatite by magnetite removal (1853~.
separation Ball-Norton belt separator produced 1,000 tons of
magnetite concentrates (1888~.
High-intensity wet separator (ca. 1960~.
Electrostatic Nonmineral applications ~ 1879~.
separation First successful use on ores: sphalerite-pyrite (1907~.
Flotation First conception: Bessel brothers (1877~.
First use: Australia (1905) of Potter Delprat process,
in the United States (19111.
First use of soluble collectors: Martin (1915~.
Controlled selectivity: Sheridan and Griswold cyanide
(1922~.
Fatty acid collectors: Christensen (1923~.
SOURCE: Arbiter (19641.
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COMPETITIVENESS OF THE U.S. MINERALS AND METALS INDUSTRY
in this technology. Except for blasting and the potential applications of
alternative energy forms, comminution depends entirely on conversion of
electrical energy to motion in crushing or grinding machinery. The low-
head aspects of the tumbling mill, as well as the indirect nature of its
energy transformations, suggest the possible use of other forms of energy
that can be applied more directly for producing ore fragmentation. This is
related to another aspect of fragmentation that has been almost entirely
neglected in conventional comminution theory but that is the starting point
for theories of fracture, namely the existence of flaws (ranging from in situ
structural faults in a mine before blasting, through cracks formed during
blasting, to grain boundaries and lattice defects or dislocations) that influence
subsequent grinding efficiency. Exploitation of these flaws should be a
major goal of comminution research.
There is a marked analogy between problems of improving efficiencies
in comminution and flotation. Both systems involve interaction between
relevant properties of the materials processed and dynamic characteristics
of processing machinery. With both, machine evolution has had the goal of
providing for a number of functions, often with different requirements, in a
single unit. As a result there must be a compromise with less than optimum
execution of all functions. This compromise is evident in the mechanical
flotation cell. The critical requirements are to provide optimum conditions
both for stable particle/bubble attachment and for gravity separation of bubbles
from pulp. A third requirement, related only indirectly to the process itself,
is the necessity of providing sufficient flow velocities to keep all coarse
fractions in suspension within the particle/bubble contacting zones. Flota-
tion can be optimized through developing the most effective device for
maintaining as well as obtaining particle/bubble contact and designing the
optimum phase separator to receive the discharge from the mixer.
Although there have been claims and counterclaims for collectorless flotation
of sulfide minerals as far back as the 1930s, it is only within the past few
years that the phenomenon has moved out of the laboratory and into positive
demonstrations in pilot-plant and full-scale circuits. Results have been
encouraging, but limited scope and proprietary factors do not allow for firm
economic evaluation. Nevertheless, significant benefits are anticipated in
the treatment of porphyry copper ores, which appear to be most readily
amenable to this treatment.
METAL EXTRACTION TECHNOLOGIES
Metal extraction technologies transform ores and mineral concentrates
into salable metal commodities. Virtually all current extraction technologies
are based on pyrometallurgical or hydrometallurgical techniques. A few
exceptions do exist, however, such as the carbonyl process route for nickel.
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ROLE OF SCIENCE AND TECHNOLOGY
Recent Pyrometallurgical Process Developments
Copper
69
The U.S. copper industry has largely replaced traditional reverberatory
smelting methods with flash smelting processes. Reverberatory and electric
furnaces continue to fade under environmental and energy cost pressures,
and only one electric furnace is currently in use in the United States. Sulfur
emissions from smelters are contained as marketable sulfuric acid and liquid
sulfur dioxide (SO21. Foreign companies are relying primarily on flash smelting,
and the flash smelters operating in the United States today are all of foreign
design.
Research has focused on the tuyere injection of concentrates into bath
smelters and elimination of the converter. Alternatives to the converter are
sought that will allow continuous operation and produce constant gas flow
at high SO2 strength. Some significant R&D is being conducted on copper
production technology, but overall funding remains modest. The most notable
projects are the chloride hydrometallurgy-based Cuprex process, the Norddeutsche
Affinerie/Lurgi cyclone smelting process, the Queneau-Schuhmann-Lurgi
(QSL) reactor, the ISASMELT process, flash converting of matte, and con-
tinuing studies of flash smelting reaction thermodynamics and kinetics.` Most
of these innovations were made outside the United States, and all were first
implemented at foreign operations.
Nickel
Flash and electric furnace smelting produce most of the nickel matte
from sulfide concentrates; electric furnaces and leaching dominate lateritic
nickel production. Converting of nickel matte is done pyrometallurgically
in rotary converters. Technological developments in the 1980s on nickel
smelting and refining have focused on increasing energy efficiency and
improving environmental control of existing operations and on adopting
some of the technologies used in other industries to nickel operations.
Z.
nc
Roast-leach-electrowin (RLE) technology has improved steadily since its
invention in 1913, increasing its dominance of the primary zinc smelting
and refining industry in the 1980s. Only about 10 to 15 percent of primary
zinc is still produced pyrometallurgically, primarily by the Imperial Smelt-
ing Process (ISP) and electrothermic process, both of which require thermal
refining to produce special high-grade metal. Environmental pressure on
zinc leach residue and steel-making dust disposal, particularly in the United
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COMPETITIVENESS OF THE U.S. MINERALS AND METALS INDUSTRY
States and Europe, has stimulated development and improvement of pro-
cesses that can produce an environmentally acceptable, disposable residue
and recover zinc and lead. The use of a lead splash condenser in the ISP
has caused that process to come under environmental pressures. Little
R&D on zinc production technology has been undertaken during the 1980s
other than that directed toward environmental issues. No new primary
production processes for zinc have been developed since the l950s, although
some modest work on decreasing energy requirements has led to pilot-scale
trials of a hydrogen anode concept in West Germany.
Lead
Most of the world's primary lead is produced by the sinter-blast furnace-
kettle refining process. Most secondary lead results from blast furnace,
reverberatory furnace, and short rotary furnace smelting of scrap batteries.
No integration of primary and secondary technology has yet occurred on a
significant commercial scale, although the QSL reactor process has such
potential. Environmental pressures (workplace and ambient lead exposure)
led to development of significant new smelting technologies overseas in the
1970s and 1980s, but none of these have been adopted in the United States.
Aluminum
Primary aluminum is produced by the Hall-Heroult process, while sec-
ondary aluminum is generally produced by simple remelting in induction or
Casting lead bullion at Herculaneun lead smelter in Missouri.
Run Company.)
-
-
(Courtesy The Doe
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ROLE OF SCIENCE AND TECHNOLOGY
71
reverberatory furnaces. Recycling of aluminum continues to increase as
more aluminum-containing products are made and incentives for recovering
aluminum-containing products continue. Since current recycling technology
is relatively simple and cost-effective, the committee expects little change
in recycling techniques other than development of better methods for sorting
aluminum alloys to minimize cross-contamination during reprocessing.
Precious Metals
Roasting has been the primary pyrometallurgical process used for precious
metals extraction. A selective roasting technique has been developed at the
E1 Indio mine in Chile for the treatment of arsenic-bearing concentrates,
making these materials salable. New roasting technology will also be used
at several projects under construction in the United States and Canada, with
all gaseous effluents being contained in a cost-effective manner. Circulat-
ing fluid bed roasting for processing refractory gold ore, a process adapted
from alumina calcining technology, is under investigation for a major overseas
project and will be compared to the autoclave processing alternative.
Recent Hydrometallurgical Process Developments
Copper
Major increases in copper production have resulted from the use of sol-
vent extraction/electrowinning processes in the United States and abroad.
New reagents have been developed that permit higher extraction efficiency
and lower solvent losses due to impurity contamination. New equipment is
under development to reduce capital costs and solvent inventory. A tech-
nique for high-intensity electrowinning using permanent stainless steel cathodes
is also being developed, as is a leaching-solvent extraction/electrowinning
process using ferric chloride technology. Ion exchange resins are under
investigation for the removal of copper from dilute mine waters.
Conventional electrolytic refining continues to be the workhorse of high-
purity copper production. Several refineries using permanent cathodes have
now been constructed and more are planned. More refineries are integrat-
ing forward to produce continuous cast copper rod.
Nickel and Cobalt
Nickel refining remains dominated by carbonyl technology and electro-
winning. No significant new developments have occurred in laterite tech-
nology to improve energy efficiency. Concentration technology has not been
improved, and the resulting need to process essentially the entire feed remains
the major hurdle to be overcome in any effort to make laterite processing
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72 COMPETITIVENESS OF THE U.S. MINERALS AND METALS INDUSTRY
Bulldozers working on copper leach piles at San Manuel Copper Mine in Arizona.
(Courtesy Magma Copper Mine.)
Anaconda refinery cathode room, 1902. (Courtesy N. Arbiter.)
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ROLE OF SCIENCE AND TECHNOLOGY
73
Electrowon cathodes being lifted from a cell at San Manuel Copper Mine in Ari-
zona, 1989. (Courtesy Magma Copper Company.)
more competitive with sulfide processing. New reagents have also been
developed to permit high separation efficiencies between nickel and cobalt,
yet no major new facilities have been constructed to utilize these new reagents.
Z.
nc
Improvements have continued in the application of the standard zinc
flowsheet of roasting, leaching, and electrowinning. In addition, pressure
leaching techniques have been introduced to improve recovery and sulfur
management in some plants. A pressure leach has replaced roasting in
several expansion projects, producing sulfur rather than sulfuric acid as a
by-product.
Lead
Significant new developments in primary lead hydrometallurgy are under
way in Italy, and plants treating secondary lead may soon be in operation in
Europe and the United States.
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74
Aluminum
COMPETITIVENESS OF THE U.S. MINERALS AND METALS INDUSTRY
Virtually all the world's primary aluminum is produced via the well-
established and nearly optimized Bayer process for alumina, followed by
the Hall-Heroult process for reduction. Several direct reduction and chlo-
ride-based processes have been developed and evaluated through pilot-plant
scale during the 1970s and 1980s, but none has been reduced to commercial
practice. Alternative feed sources for aluminum have been also evaluated,
but bauxite remains the primary raw material. Significant R&D has contin-
ued into ways to decrease power consumption and improve electrode per-
formance in the existing reduction process and to decrease emissions to the
environment, with some success.
Precious Metals
Pressure oxidation of refractory gold ores appears to be the emerging
technology of choice where roasting cannot be used. Biooxidation is also
being developed. Heap leaching of low-grade ores by cyanide solutions,
with or without agglomeration, continues to expand, with gold-bearing so-
lutions being treated by carbon adsorption/desorption units followed by
electrowinning. The use of ion exchange resins and solvents to replace
. . . . .
carbon Is showing promise In the testing stage.
The primary technology for platinum group metals (PGMs) has become
electric furnace matte smelting of flotation concentrates followed by matte
leaching, chloride-based leaching of matte leach residue, and then separa-
tion and purification of the PGMs by classical solvent extraction, precipita-
tion, and/or ion exchange techniques.
Developments in the field of precious metals also include the installation
of autoclaves for whole ore oxidation in California, Utah, Nevada, and
Brazil. Improvements have been made in the activated carbon process, and
high-capacity contactors have been put into operation. Demonstration plants
for biological oxidation of pyritic and arsenopyritic gold ores have been
constructed in Canada and Africa, and a commercial plant has been built in
the United States.
The search for chemical oxidation agents for refractory gold ores continues,
with attention focusing on chlorine and nitric acid. These latter reagents
appear to offer a major advantage when large quantities of silver are present;
silver recovery is poor in currently used roasting and autoclaving processes.
Directions for Future R&D
The hydrometallurgical and biotechnological techniques associated with
in situ extraction could have a great impact on the minerals and mining
industry. In situ extraction is an interdisciplinary technique bridging min-
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75
ing, mineral processing, and extraction metallurgy that is currently being
used for the production of uranium, copper, salt, potash, and bona. In situ
techniques have also been successfully applied to the extraction of berates.
Further research into advanced reagents or designed organisms capable of
extracting specific metals from underground deposits with a minimum of
earth moving and waste production could revolutionize the minerals and
metals industry. Before these techniques can be properly and universally
applied to in situ extraction methods, however, extensive research is re-
quired in the areas of underground and surface fluid control, containment,
and dewatering techniques.
Residue processing and waste disposal are problems of increasing importance
to the minerals and metals industry. Traditionally, the presence of undesirable
impurities has not been given great weight in assessing the value of a min-
eral deposit. In the United States, however, a significant amount of the
effort currently required to bring a mine into production, or to preserve the
life of an existing operation, is related to the protection of the work force
and the environment. Metallurgists in the domestic industry thus find themselves
with an increasingly difficult task: they must produce the highest-quality
product to compete in world markets but must also contain completely all of
the reagents and effluents and transform any toxic components into useful
by-products or harmless wastes. To address the problems of environmental
quality and waste disposal, R&D should now be focused on a systems approach
to process development. The objective of this approach is to devise processes
that do not simply minimize the cost of recovery of the principal mineral
values from an ore but that also facilitate the required containments and
. . . . .
create harmless wastes at minimum overall cost.
RESEARCH AGENDA
The mining industry is in a state of R&D stagnation. Most of the tech-
nologies currently in use were developed at least 20 years ago. The demise
of many companies and the restructuring of others to survive the recent
decline in commodity prices have made the industry stable for the present,
but it is in danger of ignoring its future. If the minerals and metals industry
is to survive and flourish into the twenty-first century, new technologies
must be developed. The following sections summarize the major conclusions
of this chapter and outline the research agenda that will be required to
enhance the competitive posture of the U.S. minerals and metals industry.
Exploration
Although the methods of exploration currently in use are generally satis-
factory, and considerable strides have been made, even minor further ad-
vancements in technology, improvements in data bases, and increased avail-
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76 COMPETITIVENESS OF THE U.S. MINERALS AND METALS INDUSTRY
-
_
it_
I_
_ . .
The world's first plant to biologically degrade cyanide and strip toxic heavy metals
from wastewater went into operation in 1985. This technology and the mutant
bacteria it uses were developed by Homestake Mining Company. The mine is
located in Lead, S.D. (Courtesy Homestake Mining Company.)
ability of information to more companies could dramatically increase both
the number of deposits discovered and the competitiveness of the U.S. minerals
and metals industry. Evolutionary advances that would improve the current
state of exploration techniques are
· improved spatial and spectral image resolution to penetrate foliage
and surface cover;
· increased digital geophysical coverage of the United States magneti-
cally, gravitationally, radiometrically, and spectrally to one-half mile; and
· improved drilling/sampling techniques and analytical methods to in-
crease basic knowledge.
A research advance that could revolutionize the U.S. minerals and metals
industry would be the elucidation of a more complete general theory of ore
genesis and deposition.
Mining Technologies
The mining industry must strive to develop automated mining, process-
ing, and extraction technologies that can be operated and maintained with
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77
the minimum exposure of people to difficult or hazardous conditions. De-
sign criteria must include the concept of the clean plant, where all equip-
ment is assessed for its spillage potential and where total containment of
harmful residues must be provided. Areas of research needed to address the
problems of developing a new generation of mining systems are
· geosensing, or the ability to predict variations in the ore body or the
coal seam, sense the closeness of geological disturbances, and obtain in situ
measurements of ore grade;
.
nonexplosive rock fragmentation;
· intelligent mining systems incorporating advanced levels of cognitive
ability; and
· in situ mining, a potentially revolutionary mining method that could
greatly improve mining economies and allow a human-free working envi-
ronment.
Minerals Processing
Radical changes, bordering on revolutionary, may be in prospect for mineral
processing:
· in general, through advances in modeling and automation with com-
puter control of operations;
· in comminution, through integration of blasting with crushing, through
taking full advantage of preexisting and process-created structural weak-
nesses, and in the use of energy other than electromechanical; and
· in flotation, through the development of alternative machines that ex-
hibit higher hydraulic and process efficiencies and through advances in the
application of collectorless flotation of sulfide minerals.
Metals Extraction
The discovery of hydrometallurgical and biotechnological techniques for
in situ extraction could greatly influence the minerals and metals industry.
Further research into advanced reagents or designed organisms capable of
extracting specific metals from underground deposits, with a minimum of
earth moving and waste production, could potentially revolutionize the field.
Before in situ extraction methods can be properly and universally applied,
however, extensive research is required in the areas of underground and
surface fluid control, containment, and dewatering techniques.
R&D should address environmental quality and waste disposal issues
through a systems approach as a means of reducing the impact of environmental
regulation on competitiveness. Processes must be developed that minimize
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COMPETITIVENESS OF THE U.S. MINERALS AND METALS INDUSTRY
the cost ot recovering metals while at the same time meeting environmental
standards, maintaining the required containment for harmful materials, and
creating harmless waste at minimum costs.
REFERENCES
Arbiter, N., ed. 1964. Milling Methods in the Americas. New York: Columbia University
Press.
Huet, G. 1866. Preparation Mechanique. Paris.
Office of Technology Assessment (OTA). 1988. Copper: Technology & Competi-
tiveness. OTA-E-368. Washington, D.C.: U.S. Government Printing Office, p.
119.
Revnivtsev, V. I. 1988. We really need revolution in comminution. In Proceedings
of the XVI International Mineral Processing Congress, K. S. E. Forssberg, ed.
Stockholm: Elsevier, pp. 93-1 14.
Representative terms from entire chapter:
precious metals
