Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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~escrigtion
C°om~osition and Method for Agglomerating, Ore
Technical Field
The present invention relates to the recovery of
metal values from ores and, specifically to a process
and composition for agglox~erating ore fines to
enhance the economic recovery of metals in a heap
leaching recovery pr~cess.
.. Bac~C~round Art
The recovery of preci~us metal values by cyanide
solutians, and leeching b~ virtue of the standard
1~ heap l~:ach process are l~cnowin in the a~~. S~g~h process
are descra.bed,, f or examp:l a , in LT o S . Patent No .
3 , ?77 , 00~ , issued D~cem~aer 4 , 1.973 , to ~ankeraan et
al.
It is well redogni~ed that the stag of Nevada
~o has extensive ore deposits of gold and silver. In
these deposits, as well as in deposits in other
states and localities, theme has been found to occur
a~ appreciable amount. of fines, i.e., minus 40 mesh
or finer, in the ore material. Such fires inhibit
~5 the degree of success that has previously been
achieved in connection with recovery of precious
metal values from such ores,. A great deal caf study
has been conducted in connection with the character
of such fines; resembling fine~parti~le clays o~
30 bentonitic type, and the effect of such fines in the
presence of ores undergoing treatment for precious
metal values.
In the prior art, heap leach piles and leaching
solutions have been used with varying degrees of
35 success. Many such processes have not been
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economically successful since tine finE plasterings
over rocks and interstices of heap leach gales have
prevented the advantageous recovery of pregnant
solutions or have allowed leaching fluids to
percolate therethrough. Tn order to economically
heap leach gold and silver ores, it has thus been
found necessary to agglomerate the ores before
leaching can begin, using some type of binder. The
agglomeration prevents migration of ore fines,
swelling of clays, and collapse of the heap.
Migration of fines and swelling of clays can blind
parts ,of the heap making efficient leaching
impossible. Collapse of the heap can seal-up large
areas ~o the leaching solution and channel the
solution around areas where it is needed: ,fit the
present time, high calcium lime and Portland cement
are used as binders. Both of these binders have the
advantage of maintaining the p1i of the leaching
solution in the rangy from about 10-1~ which is
necessary for leaching with a cyanide solution.
Lime, ~Ca(OI~)2, prevents the swelling of clay by
replacing monovalent rations, Na+ and K+, with the
divalent ration, Ca++. The presence of divalent
rations prevents significant swelling of clays in the
recovery process. Also, lime reacts with silica and
alumina in the clays and ore fines giving calcium
silicate and aluminates, hydrates binding the
agglomerates together, thus preventing migration of
fines and heap collapse.
In lPortland cement, calcium silicates and
aluminates are already intimately mixed so that the
hydrates form rapidly, giving good strength to the
agglomerate. If the ore is of low clay content or
the clay has a low pozzolinic activity, i.e., the low
availability of silicates and aluminates, I have
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found that Portland cement will make a higher
strength binder than lime. Portland cement has low
free calcium hydroxide content, however, and
accordingly is not as efficient as lime in preventing
swelling of clays in high clay content ores.
The present invention has as its object the
provision of an economical recovery technigue for
precious metal values from metal ores through the use
of an improved binder composition for agglomerating
the ore fines. The technidue has particular
applicability to the recovery of gold and silver.
Summary of the Invention
The binder composition for agglomerating ore
fines of the invention is a mia~ture of (1) a reactive
calcareous c~mponent, (2) a reactive siliceous and
aluminous Component, and (3) a sulfate comp~und.
Preferably, the binder composition is comprised of 1d7
to 80% by weight lime as the calcareous component, 5
zo to 50% by weight fly ash .as the siliceous~aluminous
companent and 1~ to ~0% by weight sulfate compound
such as gypsum. M~st preferably, the siliceous-
aluminous component is a low carbon content fly ash
having less than about o.5% by weight carbon content.
The preferred lime component of the binder
composition is either a high calcium lime with
greater than about 90% by weight Ca~ content or a
dolomitic lime.
In the process for recovery of metals from ores
having ore fines of the metals, the ore fines are
first agglomerated by adding thereto a binder
composition, the binder composition comprising about
10 to ~0% by weight lime, 10 to 80% by weight sulfate
compound and 5 to 50% by weight silicious-aluminous
material. A leach bed is formed of the agglomerated
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ore and the bed is leached with a leaching agent to
thereby fox°ir:~ a leach lit~uor, The metal values are
recovered from the leach liquor.
Additional objects, features, and advantages
will be apparent in the written description which
follows.
Detailed Description of the Invention
The preferred binder composition of the
1~ invention comprises a mixture of (1) a reactive
calcareous component such as lime (h~.gh calcium or
dolomitic), (2) a reactive siliceous-alumi~ous,
component, and (3) su~:fur or sulfate compound such as
gypsum. The three component mixture of the invention
produces a binder co~posi.tion for ore fine
agglomeration with superior propert~:es to both lime
and Portland cement.
The reactive calcareous component of the binder
composition is an inorganic substance contaaning
2~ calcium mnd/or magnesium oxide or hydroxide or other
form of chemically coaabined calca:um or magnesium
which, under the conditions employed in the steps of
the process, reacts with the siliceous, aluminous and
sulfur components of the composition to form calcium,
25~ aluminous, sulfur, silica hydrates (e. g. ettringite
and tobermorite) . The prefer>"ec~ reactive calcareous
substance is high calcium quicl~ lime. the thigh
calcium quick lime, Ca0 useful in the present
invention has a Ca~ content of greater than about ~0~
30 by weight, preferably greater than about 95~ b~
weight. The reactive calcareous component is
preferably present in the range from about 10 to 80~
by weight ~f the binder composition.
The binder composition also contains a reactive
siliceous-aluminous component which is employed in
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making the calcium silicate, calcium aluminate
hydrate product of the invention. "Such reactive
silica~us-aluminous components include artificial or
natural pozzolans, pulverized fuel ash (fly ash),
granulated slag, pumice dust, ground silica, clays
such aS bentonite or kaolinite, Portland Cement kiln
dust and others, as well as anixtures thereof having a
p~z~olanic character. Sy "pozzolan" is meant a
finely divided material rich in silica or alumina
which, while not necessarily cementitious in itself,
will react at ordinary temperatures with hydrated
., lime in the presence of water to form cementitious.
product CJ s
The preferred siliceous/aluminous component is a
fly ash having a low carbon content. Fiy ash is a
commercially available product whidh will be familiar
to those skilled in the art. In the 192~s, a more
effective method of firine~ power p~:ant boilers came
into use consisting of the pulverizing ~f the coal
into a fane powder, the addlt~.on oft a pra.mary azr,
and the burning of the coal powder substantially in a
suspended state within the furnace. Such coal. is
pulverize, conveyed from the pulverizes with air
into the furnace, and combustion ta~Ces place almost
ix~~tantly while the fine coal particles are in a
suspended state. This method of burning coal has
come into wide use due to its increased efficien;~y of
combustion. The ash content of the coal, which may
' vary from a low of about 4~ t~ a high of about 20~ or
more, is subject to the intense heat of combustion
which may run between 2,000 anc~ 2,800F. Most of the
ash is in the form of fly ash: the discreet sphere-
like par~icles which are converted upwardly with the
flu gases and separated therefrom by electrostatic or
mechanical collectors. A typical fly ash composition
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contains the following constituentse ~1120~, 15-35%:
Si02, 40-55%: Ee2~3, 5-25%: S03, 0-5%: FeSZ, 0-1%:
~igt~, 1-3%: CaO, 1-5%: TiC2, 1°°3%: C, 0°~5%.
The preferred fly ash component useful in the
present invention has less than about 0.5% by weight
carbon by direct carbon analysis. The fly ash
component is present in the range from about 5 to 50%
by weight of the binder composition.
The preferred sulfate compound of the binder
20 composition is gypsum, a readily available mineral
that needs only to be ground fob use in the binder
_. composition. Preferably, the gypsum (CaS~4'2H20)is
ground in the range from about 100%-10 mesh to about
x.00%-200 mesh before making the binder composition.
Other sources of sulfates such as waste wall board or
fossils fuel power plant liras scr'abber sludge can
also be utilized.
The binder composit;.on ~.s itself used in the
range from about 0.100 to 2.000% by weight of ore to
be treated, preferably in the range from about 0.500
to 1.500% by weight of ore.
The mixture of high calcium lime, gypsum and low
carbon content fly ash gives a binder composition for
are fines ac~~lomeration with superior properties to
both lime and Portland cement. Theoretically, this
result can be explained as followse When hydrated, a
reaction occurs between the lime, sulfate, anrl
alumina in the fly ash to form ettringite, a calcium
alumina sulfate hydrate. Microscopically, ettringite
forms an interlocking set of rod-shaged crystals
binding the ore fines together. The result is ore
agglomerates with good strength properties even in
low clay content ores. Calcium from both the lime
component and the gypsum component of the binder
composition can replace monovalent rations in
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swelling clays and prevent swelling. ~s a result,
the binder composition of the invent.on is
particularly well suited for use in high clay content
ores.
.An ore is agglomerated by mixing the granulated
ore with the dry binder composition. mater is then
mixed with the binder composition-ore mixture to
agglomerate the ore. The agglomerate can be air
dried or cured in an oven. If a~.r cured in p~.ace,
to t~ 2~ days, or preferably 7 to 10 days, is required
to develop the desired strength. A Mach bed is then
., formed of the agglomerated ore f fines and the bed is
leached with a leaching accent to form a leach liquor.
The metal values are recovereel from tae leach liquor
in accordance with standard procedure.
The following example is intended t~ be
'.11u '~Jtr~at~.~e of the Ln~ent,LOn s.
Exa~l~[.~la I
T~ test the strength of Ore agglomerates made
with different binders, the -40 mesh fraction of an
ore was separaaed out and port.~ns were mixed with ~%
by weight of the binders to be tested. Enough water
was added to each mixture to form a thick waste and
the pate placed in cube molds. The mixtures were
Y
cured in the molds for twenty-four hours at x.20° F
~to simulate 30 days curing at room temperatures in
to~~ relative humidity atmosphere. The cubs were
then tested to failure to measure unconfined
compressive strength. The binders tested and the
strengths obtained are given in Table T.
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TAELE z
Unconfined Compressive
Strength After Curing
Binder Composition 24 hours at 120° F
Type II Portland Cement 93. Lt p.s.i.
40% Hi°Cal QL, 22.5% Fly .Ash, 97.0 p.s.i.
37.5% Gypsum
40% Hi-Cal QL, 22.5% Clay, 95.0 p.s.i.
37.5% Gypsum
~5 40% Iii°~Gal QL, 22 . 5 % Fly Ash, 92 . 5 p. s ° i .
37 ° 5% Ground Gypsu~a 6~allboard
40% Dolomitic QL, 22.5% Fly Ash, 52.5 p.s.i.
37.5% Gypsum
EF~LE 11
50 pounds of a minus ° inch fraction of a gold
ore was treaded with 0.53 pounds of a birder
c~mpositio~x made up of 4~% lime, 22.5% fly ash and
37,5% gypSUm, all percents being in parts by weight.
The gypsum had boen ground to pass a minus 30 mesh
si~~e before making the binder composition.
Treatynent and agglomeration were carried: ~ut by
placing the sir dry ore in the 55 gallon dsuxn of a
drum roller. The dry binder composition was
sprin7cled on top of the ore and the binder
composition ° ore mixture was rotated in the drum at
1U RQhi fog 1 minute.
Appro~eimately ~., X20 milliliters of water was
then slowly added while rotating the drum for 4
manut~s. The addition of the wetting agent caused
the fans particles of ore to stick together o~ stick
to the coarser particles to form an agglomerated ore.
Total weight of the aggiamerated are was 54.5 paunds.
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Then, 51.5 pounds of the agglomerated ore
mixture was placed in a lPlexiglass column of 5.25
inch internal diamEter, f~rx~ing a column of ~re 62
inches tall with a wet density of 66.3 pounds per
cubic foot. Another 50 pound aliquot of the ore was
agglomerated with 1,770 anilliliters of water in an
identical manner without the binder composition.
51.5 pounds of this ore formed a column 57.75 inches
tall, with a wet density of 71.2 pounds per cubic
foot. The agglomerates curare allowed to cure for 7
days.
.. Both columns were leached at 200 milliliters per
hour (0.006 gallons per minute per square foot) with
a solution of water containing 0.05% sodium cyanide
and 0.09% sodium ~nydrs~xide. The sodium hydroxide was
added t~ bring the initial pH of the water into a
range between~about 11 and 12. During the first 4
hours of leaching, the column containing the ogre
heated with the binder composition of the invent:wn
settled by 3.5 inches (2.4%) gi~ring an ore column
k~eight of 60.5 inches and an ore density of 67.9
pounds per cubic foot> During the same 4 hours, the
untreated ore settled by 7.75 inches (13.4%) to a
coluxan height of 50 inches with an ore density of
82.2 pounds per cultic foot. After 4 hours of
~.eatsh~.ng, n0 further settlement Of th " Ore was
detected.
A third c~lumn was also prepared in an identical
manner using 0.50 pounds of Type 2 Portland cement
and 1,760 milliliters of water for agglomeration.
The initial column height was 62.5 inches giving an
ore density of 65.8 pounds per cubic foot. No
settling of this column was detected during the
leaching.
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It was noted that the leaching solution started
to filter out the bottom of the Portland cement
treated column in about 30 minutes while it took 4e5
hours for solution to begin filtering aut the bottom
of the binder treated and untreated columns. This
indicates ~ solution retention or holding capacity ~f
about 100 milliliters in the Portland cement treated
column and 800-1,000 milliliters in the other two
columns.
7Leaching solution was c~llected and tested for
pH, gold content, and cyanide content several tames
during the leaching period. The values are given in
Table II:
Table II
Leaching Solution Data From C~lumns
Column ~. (N~ Treatment)
2o Leaching NaCN cumulative Gold
Time (hrs.) ~ Concentratian Leached !mo)
!~)
~.0 0.005 1.5:~
27 8.4 0.010 18.8
45 9.3 0.040 22.0
69 Stopped Leaching E~ecause
of Low pH.
C~hamn 2 (Portland C~ment Tr~atment~
Leaching NaCN Cumulative: Gold
Time Lhrs:Z pH Concentration !%) Leached lmr~
2 V 11 . 0 s 02 7 . 1
5
27 11.5 0.02 9.3
45 11.5 0.04 13.2
69 11.5 0.04 17.6
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WO 93/1190 '~ ~~ P~T/U~92/02111
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C~~.umn 3 t~iaader Coa~~~s3.tz~xi)
Leaching NaCN Cu~auZative Gold
Time~hrs.) ~ Concentration (%) Leached tmc)
2 V ~ ~ 0 a 0
. ~
27 11. 0 a 03 ~.9 . 4
5
45 1.1. 0. 04 22 . 9
~
69 1.~.. 0. 04 26. ~
5
Column ~4 t Lime Tr~at~d~nt
Leaching NaCN Cumulative Gold
.. Tine ~hrs.) ~ Concentration (%) heached (ma)
2 tD 11. 5 0 ~ 01 3 4 : 2
1.5 27 ~ ~~ a.J ~ s ~3 1.7 . ~.
~45 llaa 0a0~ 20~g
~~ ~~ s5 ~ s 0~ 23. 3
~t can lbe seen from Table 1I that both the
~~rtland cement and bin~cier composition treatment
keep the pN high enough t~ prevent excessa.ve cyanide
losses. zt is believed that the low gold recoveries
found for the Portland cement treatment are due to
the low amounts of solution held on the ore, i.a~,
~5 the Portland cement does not allow the ore to t~et as
well as the ore treated with the binder composition,
si~wing down or preventing high gold recoveries.
~n invention. has been provided with several
advantages. The improved binder composition of the
invention produces an agglomerated ore with superior
properties> In addition, the binder composition of
the invention is more economical to manufacture than
either Portland cement or lime alone.
While the invention has been shown in only one
of its forms; it is not thus limited but is
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susceptible to various charges and z~~dificatiors
without departing from the spirit thexeofa
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