METALURGIA

DE
NO METÁLICOS
INDUSTRIAL DIAMOND
 ABRASIVES

DIAMOND,
INDUSTRIAL
CORUMDUN-EMERY
GARNET
 DIAMONDS, INDUSTRIAL.
WORLD DIAMOND PRODUCTION FROM NATURAL
SOURCES (1990).
• Alaska
• Australia 35 %
• Zaire 9%
• Botswana 17 %
• USSR 15 %
• Republic of South Africa 8% (Fig. 1)
• Diamond are also mined in Angola, Namibia, the Ivory Coast, The
Central African Republic, Ghana, Tanzania, Guinea, and other
African countries.
• Since diamonds were first discovered more than 2 000 years ago, only
about 380 t have been mined. In order to obtain 1 g (5 metric carats) of
diamonds, it is necesary to remove and process approximately 25 t of
rock.
• Recovering this small percentage involves a combination of highly
developed techniques in mining and extremely sophisticated
processes in diamond recovery.
DIAMONDS, INDUSTRIAL.
 END USES
Diamond are used for two unrelated end uses:
• Gem diamonds are jewels of great beauty

• Industrial diamonds are essential materials of modern industry.

Synthetic industrial diamonds are now of a quality and size that permit
them to be substituted for natural diamonds in numerous industrial
applications.
 END USES.
Industrial Diamonds
• The diamond is by far the most important industrial abrasive.
• In 1989 the percentage of natural industrial diamonds mined in the
world was 55 %. When synthetic industrial diamonds are added to the
natural industrial diamond figures, this porcentage becomes 87 % of
total world diamond production including gems, near gems, industrial,
and synthetic stones. The many uses responsible for these
significant increases are dependent on the properties of the
diamond, including hardness, cleavage, and parting, optical
characteristics, presence of sharp points and edges, and capacity
for taking and maintaining a high polish.

• As the industrial revolution gained momentum of both sides of the

Atlantic, metal replaced wood and machines replaced people.

• Thus the foundation was laid for precision engineering and the
recognition of diamond as an indispensable tool of industry.
 END USES
• The next major demand for industrial diamonds came after World
War I with the development of cemented carbide cutting tools.
Diamond was found to be the most effective medium for finishing and
grinding the new ultrahard metal. This discovery rapidly increased
the demand for industrial diamonds.

• Since about 1950, the development of ultrahard ceramics,

semiconductor materials, plastics, and exotic metal alloys has
further consolidated the diamond´s position as an indispensable tool
of industry. Only diamond is hard enough to cut these superhard
materials with the precision, speed, and economy that industry
demands today.
 END USES
CLASSIFICATION
Natural industrial diamonds come in many shapes and sizes.

They are generally classified according to use in the following groups:

• Tools and die stones

• Drilling material,

• Grits and powders.

 END USES
Tool and Die Stones.
• The larger diamons of higher quality are called tool and die stones.
• These are used as dressers, turning, boring, and milling tools, and wire-
drawing dies.
• To obtain maximum efficiency from a tool diamond, it is important to
orient it so that the hard direction or the most abrasion-resistant face
bears the work load.
• Orientation is also important in the manufacture of diamond wire-
drawing dies.

Drilling Materials.
• Drilling accounts for 10% of all diamond use.
• Blasthole drill bits are usually made with small crystals of regular shape.
• Mineral exploration bits requiere diamonds ranging in size from 15 to
100 stones per carat.
 END USES
• Masonry and bits make use of smaller diamonds rancing from 50 to
200 concrete stones per carat.
• Oil wellbits require larger sizes, usually 12 stones per carat and
sometimes stones as large as 3/4 carat.
• Drilling material is also used in the manufacture of multiple layer
diamond dressers and rotary form dressers.

Grits and Powders.

• Approximately 75 % of all industrial diamonds-both natural and
synthetic-are used in the form of grit and powder. Diamond grit is
used primarily in grinding wheels and saw blades. There is a specific
diamond grit type, shape, and size for each specific application.
Diamonds abrasive grains are sized by sieving on woven wire mesh or
electroformed screens.
• Diamond grit ranges in size from very coarse material (2.0 to 2.4 mm)
to fine material (38 to 44 micrones).
 END USES
CLASSIFICATION
Industrial diamonds are further classified according to type of material, as
follows:

• INDUSTRIAL STONES (FINE INDUSTRIALS)

• BORT (Boart, boort, bortz, bowr).

• CARBONADO (Carbon, black diamond)

• BALLAS (bort-ballas, short-bort)

 END USES
CLASSIFICATION
Industrial diamonds are further classified according to type of material, as
follows:
• INDUSTRIAL STONES (FINE INDUSTRIALS)
– Stones of large size not suited for gem use because of shape,
mechanical imperfections, or undersirable color.
• BORT (Boart, boort, bortz, bowr).
– Stones whose small size, irregular shape, content of flaws or
inclusiones, or occurrences in finely crystaline aggregates make
them unsuitable for gem use.
– Drlling borts are those stones whose soundness permits their
use in diamond drill bits. The more abundant crystals and crystal
aggregates of lower grade are classed as chushing bort, which is
suitable for being crushed into grit, powder, and dust.
• CARBONADO (Carbon, black diamond)
– Compact, opaque, dark gray to black crystalline material
composed of diamond, graphite, and possibly some amorphous
carbon.
– It has no cleavage and is extremely tough.
– It occurs as rounded masses of average size greater than of gem
stones.
 END USES
• BALLAS (bort-ballas, short-bort)
Dense, globular aggregates of small radially oriented crystals and with
extremely difficult cleavage.
It is both very hard and very tough.

Fig. 2 shows the pattern of industrial diamond consumption for the

United States.

The average persons tends to think that all rough diamonds are of the
octahedron form, but many rough stones are not of this shape (Fig. 3).
 GEOLOGY
GENERAL
• Diamonds are composed of a single element, carbon, crystalized in
cubic form.
• Diamonds range from colorless through faint tinges of blue-white,
yellow, red, brown, green, and gray in gem form; and from yellow-
brown to dark brown and black in industrial form.

• It is the hardest known material, listed at 10 on the Mohs hardness

scale, actually almost five times as hard as corundum listed at 9.

• The specific gravity is high (3.5).

• Index of refraction is very high (2.42).

• Color dispersion is exceptionally strong, producing the characteristic

play of color in the gem.
 GEOLOGY
PROPERTIES OF DIAMONDS
• l.- Chemical composition.
• Diamond is composed of the single element carbon.

– Major impurities:
• Nitrogen, up to 0.2 % in natural Type I diamond.
• Nickel, iron etc. Up to 10 % as inclusions in synthetic diamond
(ppm or less in natural diamond).
• Aluminium, up to 100 ppm in natural Type IIb diamond and 150
ppm in special doped Type IIb synthetic diamond.
• Boron, between 3 and 270 atomic ppm in specially doped
synthetic diamond-now thought to be responsible for
semiconducting properties of Type IIb diamond.
• Others generally < 100 ppm.
• Inclusiones: 22 mineral species have been positively identified.
 GEOLOGY
PROPERTIES OF DIAMONDS
• II.- Classification.
– Type I a diamond:
• Contains nitrogen as an impurity in fairly substancial amounts
(of the order of 0.1 %), and which appears to have segregated
into relatively large sheets or platelets within the crystal. Most
natural diamonds are of this type.
– Type I b diamond:
• Also contains nitrogen as an impurity but in dispersed form.
Almost all synthetic diamonds are of this type.
– Type II a diamond:
• Effectively free of nitrogen impurity. Very rare in nature, these
diamond have enhanced optical and thermal properties.
– Type II b diamond:
• A very pure type diamond which has semiconducting
properties: generally blue in color. Extremely rare in nature.
Semiconducting properties can be imparted to synthetic crystal
by the incorporations of suitable impurities.
 GEOLOGY
PROPERTIES OF DIAMONDS
• III.- Crystal structure
– Unit cell: Cubic, lattice constant aw = between 3.56683 +- 1x10-5 A
and 3.56725 +- 3x10-5 A (25 °C).

• IV.- Density
– Value: Average of 35 diamonds: 3.51524 + - 0.00005 g per cc (25
°C)
 GEOLOGY
PROPERTIES OF DIAMONDS
• MECHANICAL PROPERTIES
– 1.- Hardness
• (a). Scratch harness (Mohs´Scale)
– The Mohs´hardness is a scratch hardness test and is
related to the indentations hardness of the solid. If the
Mohs´number is M, the relation between these quantities is
approximately.

– Log H = 0.2 M + 1.5

• (b). Indentation hardness (Knoop Scale)

 GEOLOGY
PROPERTIES OF DIAMONDS
• MECHANICAL PROPERTIES

– II. Elastic moduli and compressibility

• (a). Elastic Moduli
• (b). Bulk Modulus
• ©. Compressibility

– III. Strength
• (a). Tensile Strength
• (b). Shear Strength
• ©. Compressive Strength
 GEOLOGY
PROPERTIES OF DIAMONDS
• OPTICAL AND ELECTRICAL PROPERTIES
– I. Refractive index
• (a). Plastic Flow
– II. Dielectric constant
– III. Optical tranparency
– IV. Resistivity

• TERMAL PROPERTIES
– I. Termal conductivity
– II. Termal expansion
– III. Specific heat.
 GEOLOGY
PRIMARY OCCURRENCES.
KIMBERLITE:
The main primary source of diamond is a rock called kimberlite or “blue
ground” which occurs in volcanic pipes and dikes. (Table 3)
• The pipes are generally vertical and range in shape from nearly circular
to elliptical.
• They range in size from pipes only a few feet in diameter to pipes
having a surface area of hundreds of acres.

• “Kimberlite is a hybrid, volatile-rich, potassic, ultramafic igneos

rock derived from deep in the earth which occurs near the surface
as small volcanic pipes, dikes, and sills. It is composed principally of
olivine, with lesser amounts of phlogopite, diopside, serpentine,
calcite, garnet, ilmenite, spinel, and/or other minerals; diamond is
only a rare constituent”.
 GEOLOGY
PRIMARY OCCURRENCES.
• The presence of pyrope garnet, ilmenite, chrome dispside, and spinel
serve as indicators for geologists in their search for diamond-bearing
kimberlite occurrences.
 GEOLOGY
PRIMARY OCCURRENCES.
LAMPROITE:
• In 1979 the discovery in Australia of diamonds in a relatively obscure
rock called lamproite led to considerable interst in lamproite as a source
rock for diamonds.

• “Lamproite is an ultrapotassic magnesian igneous rock.

• It is characterized by high K2O/Na2O ratios, typically greater than five.

• Trace element concentrations are extreme with high concentrations of

Cr and Ni, typical of ultrabasic rocks, as well as those more typical of
highly fractionated or acid rocks, e.g., Rb, Sr, Zr, and Ba.

• Generally CO2 appears to be absent.

 GEOLOGY
PRIMARY OCCURRENCES.
LAMPROITE:
• Lamproite contains, as primary phenocrystal and/or groundmass
constituents, variable amounts of leucite and/or glass and usually
one or more of the following minerals are prominent:
– phlogopite,
– clinopyroxene,
– amphibole,
– olivine,
– and sanidine.
• Other primary minerals may include priderite, perovskite, apatite,
wadeite, spinel, and nepheline.
• Other minerals such as carbonate, chlorite, and zeolite, if present, may
not be primary.
• Upper-mantle-derived xenocrysts and xenoliths may or may not be
present”.
 GEOLOGY
ALLUVIAL OCCURRENCES
• Diamond-bearing kimberlite and lamproite in volcanic pipes served as
the main source from which widely distribuited alluvial diamond
deposits were formed. Weathering processes desintegrated these
pipes and other rocks at the earth´s surface.

• Diamonds and other hard, weather-resistant minerals, released

from the disintegrating kimberlite and lamproite, were concentrated
by flowing water and deposited in topographically favorable
localities to form the alluvial deposits found today. Because of high
specific gravity, diamonds tend to be concentrated at the bottom of
alluvial deposits.
 RESERVES.
• World reserves of industrial diamonds can be estimated only very
roughly.

• The estimate in Tabla 4 indicates that reserves apper to be sufficient to

supply industrial stones for only 20 years at the current rates of
consumption of approximately 55 million carats of industrial stones per
year.

• Approximately half of the world´s reserves of industrial diamonds are in

Australia.
 PRODUCING COUNTRIES
• World production (in carats) of natural and synthetic diamonds in 1990
was as follows:

• Total production of natural gem and industrial diamonds: 102 425 000
• Total production of synthetic diamonds: 336 000 000
• TOTAL 438 425 000

• Approximately 55 million carats of the natural diamond production are

industrial diamonds. Adding this figure to the 336 million carats of
synthetic diamonds, total industrial diamond production counts for 90 %
of the total annual diamond production, with gemstones making up the
remaining 10 %. Table 5 lists natural diamond production for the major
producing countries in 1990.
PRODUCING
COUNTRIES
 PRODUCING COUNTRIES
• In 1986 Australia became the world´s largest producer of natural
diamonds, having been unknown as a diamond producer as recently as
1979. The discovery of the significantly economic Argyle lamproite
occurrence in Western Australia in 1979 has led to Australia becoming
the world´s largest diamond producer. The grade of the occurrence is
estimated at 6.8 carats/t.
PRODUCING COUNTRIES
 EXPLORATION
• The first step in diamond exploration is selection of the locality to be
explored. Naturally, favored areas are those where diamonds have
been previosly found in large quantities, such as countries in Africa
where diamond are abundant in both pipe and alluvial deposits
and in South America in alluvial deposits.
• Kimberly and lamproite are frequently intruded alog zones of
structural weakness in the earth´s crust.
• Geophysicl exploration, particularly airborne and ground magnetic
surveying, is adaptable to diamond exploration. The kimberlite
pipes, being ultramafic rock, usually have more magnetite than the
rocks surrounding them, and they have a characteristic magnetic
pattern reflecting their shapes, usually a circular or eliptical magnetic
high.
• Electrical resistivity results reveal that weathered kimberlite is
relatively conductive compared to intruded Precambriam granites in
the Wyoming-Colorado area.
 EXPLORATION
• In areas known to contain kimberlite pipes, their locations can
sometimes be pinpointed by panning alluvial material in streams.
• If characteristic heavy minerals of kimberlites are found, these can be
traced upstream to the source.
• The careful determination of exact composition of pyrope garnets
and ilmenites may help differentiate diamond-bearing from barren
kimberlites.
• In the average commercial deposit, approximately 25 t of rock must be
mined to obtain 1 g of diamond –a high ratio of concentratiion, on the
order of 1: 5 000 000 or higher. Because of this extremely sparce
distribution, bulk sampling methods are best for evaluating both
pipe and placer deposits. Pitting and trenching is better than
drilling. If holes are drilled, their diameter should be as large as
practical to provide representative samples. Holes are frequently drilled
in alluvial deposits merely to determine depths to, and extent of,
diamond-bearing gravels.
 EVALUATION OF DEPOSITS
• Most diamond deposits contain both gem and industrial diamonds.

• Exploration should provide sufficient information to determine the

quantity and quality of diamonds per unit volume, and the total volume
of the deposit.

• Estimates are made of the cost of mining and recovery of the diamonds.

• A feasibility study can then be made to determine whether the deposit

can be mined profitably.
 PREPARATION FOR MARKET
MINING METHODS
• PIPE MINING
• OPEN PIT MINING
• BENCHING
• PLACER MINING
PROCESSING TECHNIQUES
• LODE DEPOSITS
• PLACER DEPOSITS
 PREPARATION FOR MARKET
MINING METHODS.
• During the second half of the 19th century before the diamond-
bearing kimberlite pipes were discovered in South Africa, diamonds
were produced entirely from alluvial deposits in open pit by use of
very primitive tools and techniques. Picks and shovels were
practically the only tools used for mining, and the hand held washing
pan was used for concentration, with hand sorting to recover the
diamond from the washed concentrate.

• The discovery of kimberlite pipes necessitated the development of

completely new methods of mining and recovery. These pipes
eventually have to be mined underground with methods adaptable to
treating large quantities of material.
 PREPARATION FOR MARKET
PROCESSING TECHNIQUES
• LODE DEPOSITS.
– Material form lode deposits is crushed if necessary and
concentrated by washing, winnowing, screening, and hand
shorting, or by combinations of these methods.

– Methods of concentrating diamonds in large-scale operations have

become more mechanized with time. The material, when exposed
to the atmosphere, gradually disintegrated if allowed to remain
exposed in open cuts, or if spread out in nearby areas for as many
as 18 months. Thus no crushing was requiered before processing.
However, as mining has progressed deeper into unweathered blue
ground, the material is crushed in either jaw or giratory crushers or
by corrugated rolls, generally in two or more stages separated by
screening. Fig 5 and 6.
 PREPARATION FOR MARKET
PROCESSING TECHNIQUES
• LODE DEPOSITS.
– Devices used for this purpose include the rotary washing pan, jigs,
heavy media separators, and hydrocylones. Each of these
machines makes use of differences in specific gravity to separate
diamonds and other heavy minerals from the lighter minerals. The
waste is moved off the top into a central rotating weir by rotary
toothed blades. The diamond and other heavy minerals settle to the
bottom and are draw off periodically from the outer rim of the pan.
The concentrate is then classified, and either jigged or
separated by heavy media to produce a rough concentrate
usually amounting to about 1% of the feed from the mine.
Larger, more modern plants have replaced the jigs with heavy media
separators (Fig. 6). In these, a slurry of ferrosilicon powder in water
with a density of 2.7 to 3.1 is used to flot the light particles,
separating them from the heavier minerals, including diamonds,
which sink and are collected as a final gravity concentrate for further
 PREPARATION FOR MARKET
– The final concentrate was formerly processed by separating the
diamonds from the other heavy minerals by hand sorting
– Today most operators use one of several greased surface
methods.

– One type of concentrator is the vibrating grease table, which

consists of a stepped surface made of heavy gage aluminium (Fig.
5)
– The table is vibrated while the diamond-bearing concentrate, mixed
in water, is passed over the steps. The diamond adhere to the
grease; the waste minerals are washed away.
– The diamonds are collected by stopping the process and
scraping them with some of the grease of the surface of the
table. The table is regreased and the process continues.
– The scraping are boiled in water to removed the grease from the
diamonds.
 PREPARATION FOR MARKET
PROCESSING TECHNIQUES
PLACER DEPOSITS
• Diamonds are recovered from loose placer materials and from the
weathered rock of lode deposits by washing, dry winnowing,
screening, panning, jigging, tabling, and hand picking, generally in
some combination.
• The grease belt is the greased-surface concentration method best
adapted to alluvial materials. In fact, it was developed to process
diamond-bearing material from certain alluvial deposits.
• A modification of the normal process was necesary because alluvial
diamond, particularly those from marine terraces, frequently have a film
of mineral salts on their surfaces, which renders them wet table in
water. A wet diamond will not adhere to grease.
• The De Beers Diamond Research Laboratory developed a method
using a soup solution made of corn-acid oil and caustic soda.
Treatment with this solution produces a water-repellent surface on the
diamond but not on the other minerals
 PREPARATION FOR MARKET
PLACER DEPOSITS
• The method also incorporates use of a greased belt, which permits a
continuous rather than a batch process (Fig. 5) Both the soap solution
and the grease are added to the belt surface as the belt is in operation
• Further treatment is required when the grease belt process is used on
finer sizes of alluvial material. In order to clean surfaces and
desintegrate softer materials to slimes, the degreased
concentrates are processed in ball mills. The material is screened,
and the clean coarser diamond particles are futher concentrated by
electrostatic separation.
• Material form alluvial deposits is also concentrated by X-ray
separation. Diamonds tend to luminesce in an X-ray beam, whereas
most of the associated minerals do not. Luminescence excites a
photomultiplier that triggers a gate that diverts the diamonds from the
path of the gravel passing through the machine. Calcite sometimes
luminesces like diamond, but this effects is neutralized by use of a
suitable filter.
 PREPARATION FOR MARKET
FLOWSHEETS – GENERAL
• Many recovery methods are used and methods vary depending on
the location, size and nature of the deposit.
• The methods include production by natives using sinple hand pans to
more complex mechanical means employing:
• washing,
• screening,
• stage crushing,
• clear water and puddle panning,
• heavy media separation,
• jigging,
• atrition and diferential grinding,
• magnetic and/or electro-static separation,
• flotation,
• grease tabling and hand sorting.
 PREPARATION FOR MARKET
FLOWSHEETS – GENERAL
– Certain operations use one or more field plants to supply a
central plant for reconcentration and final sorting.
 PREPARATION FOR MARKET
FLOWSHEET No. 1
• This flowsheet is typical for small to medium tonnages of alluvial feed (
5 to 30 tons per haur). Such material is often cemented and requires
crushing by either jaws or gyratory crushers. In this flowsheet a trommel
screen, with a scrubbing section, is used to break down clay and
cemented fractions, before screening and rejection of the oversize to
waste. The trommel undersize, - 1”, is fed to centrifugal diamond pans
in series.

• Diamond pans were developed in South Africa and have been highly
successful and widely used in the recovery of diamonds. Their use for
the separation of other minerals has been limited and inefficient.
 PREPARATION FOR MARKET
FLOWSHEET No. 1
• A diamond pan is a shallow, flat bottomed circular pan with an inner well
about 0.3 of the pan diameter and several inches lower in height than
the outer pan wall. A vertical shaft is mounted to rotate in the center to
which radial horizontal arms are attached above the pulp level in the
pan. Tines extend downward from the radial arms and are adjustable to
clear the pan bottom. These tines are triangular and so spaced and
mounted on the radial arms to plow material on the pan bottom outward.
The feed entry is tangential to the outer wall while the tailings discharge
is through a weir in the center well. In operation the tangential entry of
the feed combined with the stirring action of the tines causes a vertical
swirl to the mass. The condition created in the pan simulates the heavy
media process in that the lighter materials remain in suspension and are
carried down the vortex to the center discharge weir while the heavier
particles settle through the swirling mass to be plowed outward on the
bottom to a concentrate discharge outlet in the outer wall.
 PREPARATION FOR MARKET
FLOWSHEET No. 1
• Feeds containing a hight amount of clay and fine sands give the most
effective results, however, many pans operate on feeds containing little
or no clay or fines with reduced but still satisfactory recoveries. Capacity
of diamond pans is normally 5 to 6 tons per square foot of effective area
per 24 hours and require 1 to 11/2 horsepower per ton of feed. Ratios of
concentration vary, usaually from 10:1 to 50:1 depending on the
amounts of heavy minerals associated with the diamonds. Recoveries
up to 97% are sometimes possible.
• The diamond pan concentrates is Flowsheet No. 1 are elevated to
trommel screen for sizing to eliminate – 16 mesh undersize and to
produce four size ranges each going to a Duplex Denver Mineral Jig for
further concentration. Denver Mineral Jigs have proven to very efficient
in diamond treatment with recoveries near 100% being reported. The
jigs are equipped with 2 mm bedding screens. No artificial bedding is
added in most operations since the pan concentrates contain sufficient
heavy minerals to form adecuate bedding.
 PREPARATION FOR MARKET
FLOWSHEET No. 1
• A 2 mm concentrate retained on the jigs screens is removed by hand at
intervals as necessary and are hand shorted for recovery of the
diamonds. All phases of concentrate handling are done under
conditions to insure security. All launders, jig compartments and
concentrate collection points are covered, locked or protected to prevent
theft.
 PREPARATION FOR MARKET
FLOWSHEET No. 2
• This flowsheet was developed for diamond recovery from Kimberlite ore
as mined and with properly sized equipment is suitable for tonnages up
to 50 tons per hour. The mined ore is crushed to -3” followed by
screening and secondary crushing to – 1 ½”. A picking belt is
sometimes employed between crushing stages for removal of waste
rock and possible recovery of large diamonds, but this step is generally
considered uneconomical. Few, if any diamonds are broken in the
crushing operations, as they are usually smaller than the crusher
openings, and break free from the matrix without damage. The crushed
ore goes to a bin for storage and for controlled feeding to the recovery
circuit. A trommel screen with scrubbing section is used to break down
any soft portion of the ore before screening. Oversize material is
reduced to -1” with a spring roll crusher and then joins the trommel
undersize to feed a centrifugal diamond pan
 PREPARATION FOR MARKET
FLOWSHEET No. 2
• The flowsheets shows one pan, however, several pans is series are
sometimes found to be effective when the ore containg high
percentages of heavy minerals. The pan tailings are elevated or
dewatered and conveyed to another screening and crushing step to
provide a -3/8” feed to a secondary diamond pan. The tailing from the
secondary pan are elevated and screened to produce a + 1/8” fraction
as a final tailing, and a -1/8” product which passes to a Duplex Denver
Mineral Jig for recovery of any small diamond remaining. The
concentrates from the primary and secondary pans are each separately
fed to two Duplex Denver Mineral Jigs in series for concentration. The
use of Denver mineral Jigs in series on the unclassified eliminates the
necessity of classification or screening to produce sized feed fractions
often necessary when plunger type jigs are used. The ratio of
concentration on jigs in this service ranges from 10:1 upward depending
on the amounts of heavy minerals in the pan concentrates. Feed rates
vary from 200 to 100 pounds per square foot of compartment area per
 PREPARATION FOR MARKET
FLOWSHEET No. 2
• The final recovery of the diamonds from gravity concentrates is
accomplished by several steps of reconcentration which differ in many
cases due to the amount and nature of the associated gangue minerals.
When appreciable amounts of heavy minerals are present the
concentrates are sized to give a – 1/8” fraction which is dried and
paseed through magnetic and/or electrostatic separators to eliminate
affected materials, before being further reconcentrated on grease
tables. The recovery method shown in Flowsheets No. 1 and No. 2 is
frequently used when the gravity concentrates are wet screened to
three or more size ranges as the feed to separate grease tables and to
reject – 16 or – 28 mesh materials.
• The grease tables are of several types being usually either mechanically
or electrically vibrated with the movement normal to direction of flow.
The decks are made both flat and stepped, being adjustable in slope to
give proper flow velocity for the different size ranges of feed. The
stepped decks have from 4 to 8 removable
 PREPARATION FOR MARKET
FLOWSHEET No. 2
compartments or pans each being 8» or more in width by 3 to 4 feet in
length, each pan being mounted in steps down the table. Each step is
coated with +1/2» thickness of a special petroleum grease which is
given a surface covering of about 1/16» of another type grease. In
operation the sized feed is uniformly fed across the table into a flow of
water to carry the material acroos and down the table steps. The
diamonds being non-wettable adhere to the grease while most of the
other minerals are carried off the table by the water and are rejected as
waste. After 45 to 60 minutes of operation the 1/16» surface layer of
grease, together with the diamonds and some other trapped minerals
are scraped from the tables. This grease layer is placed in grease pots
having perforated sides. The pots are covered and placed in boiling
water for removal and recovery of the grease. The diamond
concentrates after degreasing are hand picked and sorted under
diffused light. This final operation is very exacting work and is carried on
under close observation and security conditions.
 PREPARATION FOR MARKET
FLOWSHEET No. 3
• This flowsheet illustrates a more complex diamond recovery method
developed in recent years. With variations it can be used to process 100
to 500 tons per hour of Kimberlite ore and is also arranged to handle
weathered or soft ores. For the hard ore as mined the flowsheet follows
conventional methods of stage crushing and screening to reduce the to
– ½». The weathered ore is intensely scrubbed to break down the soft
fractions and then screened as shown. All the – 1 ½» ore is wet
screened to produce +10 mesh and – 10 mesh sizes. The 1 1/2 «, + 10
mesh fraction goes to a heavy media separator from which the sink
product, after media screening and washing, goes to concentrate
storage. The float product is washed and screened to reject all -3/8» to
waste. The +3/8» size is crushed and screened to – 3/8» to waste. The
+3/8» size is crushed and screened to -3/8», + 10 mesh for retreament
to the heavy media circuit.
 PREPARATION FOR MARKET
FLOWSHEET No. 3
• All – 10 mesh material from the screens ahead of the heavy media
process and from the screen following the scrubber is dewatered and
wet screened to give a – 10 mesh, + 16 mesh size range for treatment
either by heavy media separation through cyclone separators or by
Duplex Denver Mineral Jigs as illustrated.
• In the recovery section a number of reconcentration methods are used.
Attrition grinding using a light grinding charge at near 40% of critical
speed reduces part of the heavy minerals without damage to the
diamonds. The mill discharge is screened to eliminate – 16 mesh or in
some cases – 28 mesh and to split the remaining concentrates at about
7 mesh. These two size ranges being treated separately with the – 7
mesh going to a mill to effect a differential grind to further reduce the
waste materials. This products is wet screened and the oversize is
dried, screene to removed dust before passing through an electro-
static separator. The diamond concentrates are then hand sorted. The
+ 7 mesh concentrates are
 PREPARATION FOR MARKET
FLOWSHEET No. 3
sized, usually to four size ranges, each separately conditioned to
remove any coating from the diamond which interfere with collection on
grease tables or grease belts. Grease belts are a recent development
and require less attention and labor than grease tables. They are
similar to short conveyors and are mounted in a framework so that the
slope can be adjusted for correct flow velocity. The concentrates are
fed to spread a thin layer over the the belt surface down which a
stream of water flows. Grease is continually applied to the belt at the
upper end and is scraped off at the lower end with the diamonds. The
diamonds are degreased and processed by hand sorting.
BATES DIAMOND PAN
JIG
 TRANSPORTATION
Essentially all diamonds are shipped via air, which permits delivery
almost anywhere in the world in a matter of hours. The costs are usually
small compared to the value of the diamond. This favorable
transportation factor also applies to grinding wheels, saws, bits, and
other products.
 FUTURE CONSIDERATIONS AND
TRENDS
DIAMOND SYNTHESIS
• During the 19th century many attempts were made to synthesize
diamond.

• Broadly speaking, three approaches were made.

1. Precipitación from satured solutions at high temperatures and

pressures,
2. Chemical reaction at high temperatures and pressures, and
3. The application of simultaneous heat and pressure to graphite in
a press
• The last of these, subjecting graphite to high temperatures and
pressures in the presence of a catalyst metal is the method now in
commercial use.
 FUTURE CONSIDERATIONS AND
TRENDS
DIAMOND SYNTHESIS
• In the early days of diamond synthesis scientists were only interested
in producing diamonds, hence, little attention was given to the quality
of the product. It was soon realized that improvements in quality were
necesary.
• Research effort for this objetive has continued relentlessly.
• The hydraulic presses in the De Beers synthetic diamond plant are
products of such research.
 FUTURE CONSIDERATIONS AND
TRENDS
DIAMOND SYNTHESIS
• A major difference between natural and synthetic diamonds is the
metal content.
• Synthetic diamond contain significant amounts of the metal solvent used
in synthesis.
• The included metal is believed to exist in three forms, namely:
1. Macroscopic metal inclusions;
2. Small platelike inclusions dominantly on the cleavage planes,
and
3. Substitutional metal atoms in diamonds synthesized from
nickel or nickel-based alloys.
• Synthetic micron-size diamonds are also produced by an
explosive-shock technique. The product is a polycrystalline type of
diamond, which can, at this time, be manufacture only in micron
sizes.
 FUTURE CONSIDERATIONS AND
TRENDS
RECENT DEVELOPMENTS
• Continued research and development have improved the quality and
lowered the cost of synthetic stones.
• Temperatures and pressures required have been lowered.
• Crystals can be made with better shapes.
• Recently, methods have been developed to recrystallize small
synthetic diamonds to form gem-quality diamond of a carat and
larger. However, this has not yet been done profitably.
• Following the successful manufacture of small diamond crystals,
research continued on crystallization of larger stones suitable for
jewelry. (1970 General Electric Laboratories) A few stones of very high
quality were produced, some as large as one carat. However, the
process is so costly that the synthetic diamonds are far more expensive
than natural stones of the same quality.
• Polycrystalline or composite diamond inserts are produced by
sintering together small particles of diamond at temperatures above 1
400 ºC and at pressures on the order of 60 000 atmospheres.
 FUTURE CONSIDERATIONS AND
TRENDS
SUBSTITUTES
• The same technique used in diamond synthetic has been applied to the
synthesis of cubic boron nitride (CBN).
• Today cubic boron nitride is available in several grades with varying
physical properties which, when correctly applied, make it an excellent
abrasive for grinding hardened and difficult-to-grind steels.
• Commercial synthetic rutile is marketed under the name titania.
• A relatively new imitation diamond is yttrium aluminum garnet (YAG).
• YAG was advertised as being only 1.5 less hard than diamond.
• YAG is produced by mixing ingredients in a platinum crucible. The
color, hardness, and freedom from impurities make the stone an
inexpensive substitute for gem diamond.
 STOCKS, PRICES AND
PRODUCTION
GOVERNMENT STOCKPILE
• Crushing bort, dust and powder, and industrial stones have been
stockpiled by the US government since 1946. As of Dec 31, 1989, the
government stockpile contained 22.0 million carats of crushing bort,
dust, and powder, 7.78 million carats of industrial stones, and 25 473
pieces of dies and small pieces.

PRICES AND COSTS

• Prices for industrial diamonds have decreased over the years. From
1954 to 1977 average prices for bort and powder decreased from 3.14
to $2.08 per carat. Average prices for stones for the same period
decreased from 23.13 to $6.20 per carat. This decrease is the result
of greater efficiency developed through large scale production and use
of improved techniques
 STOCKS, PRICES AND
PRODUCTION
US AND WORLD PRODUCTION
• US production, consisting of synthetic bort, powder, and dust, was
90 million carats in 1990. World production of synthetic diamond stones
was 336 million carats. Total world production in 1990 for all synthetic
and natural industrial diamonds was about 391 million carats.
TAXES AND TARIFFS
• No special taxes are placed on the diamond-producing or
diamond-products industries. US companies receive a 14% depletion
allowance for both domestic and foreign production of natural diamonds.
There is no import duty on either natural or synthetic industrial
diamonds.
• Unsorted diamonds, both gem and industrial, can be imported duty
free.
• A tariff rate of 4.9% and valore is in effect, as of Jan.1,1991, for
synthetic diamond stones for industrial use, except for imports from
Canada; the USSR; and free for GSP countries, Israel, and Caribbean
Basin countries.
 SECONDARY SOURCES AND
RECOVERY
– The main sources of recovery for diamonds are the diamond grit
and powders salvaged from industrial wastes by users of diamond
grinding wheels, saws, and lapidary compounds. This amounts to
about 3 million carats annually.

– The other major source is the substantial quantity of stones recovered

from broken or worn diamond tools and drilling bits. These are returned
to the manufacturer for reuse.
 ECOLOGY.
• The diamond industrial, being primarily based in countries out-side the
United States, has been faced with few problems regarding ecologic
restraints, but in recent years concern for environmental protection
has become more widespread in Africa
 FUTURE OF DIAMONDS.
• In 1967, the machining of cast iron and steel was a process virtually
untested. De Beers DXDA-MC, aa metal-clad synthetic, was
specially formulated to grind certain types of steel. Wheel-market
have reported that their customers have had excellent results in grinding
D series tool steels, Ferro-Tic, cast iron, titanium, stainless steels, and
combination steel and carbide dies.

• Scientist at the De Beers Diamond Research Laboratory feel that

research indicates quite convincingly that the characteristic of natural
grit can be altered in way that will permit production of synthetic
materials of virtually any type –hard or friable, octahedron or slivers,
and particles of varying sizes and qualities.

• THE INDICATED FUTURE OF THE INDUSTRIAL

DIAMOND IS INDEED BRIGHT.