United States Patent [19]
Litz
[11] Patent Number:
[45] Date of Patent:
4,814,149
Mar. 21, 1989
9 Claims, 1 Drawing Sheet
Primary Examiner-Patrick P. Garvin
Attorney, Agent, or Firm-S. R. La Paglia; T. G. De
Jonghej P. L. McGarrigle
149134 11/1980 Japan 423/55
OTHER PUBLICATIONS
Mellor, A Comprehensive Treatise on Inorganic and Theoretical
Chemistry, vol. XI, p. 595, (1948), pub. by Longmans,
Green & Co., N.Y., N.Y.
The present invention is a process for selectively precipitating
molybdenum in a form that is substantially
free from vanadium impurities. The molybdenum is
precipitated in the form of ammonium octamolybdate
which has a molybdenum to vanadium ratio of about
400:1 in an initial crystallization and a ratio of about
1300:1 in a subsequent recrystallization.
[57] ABSTRACf
[54] PROCESS FOR RECOVERING
MOLYBDENUM FROM SOLUTION IN A
FORM THAT IS SUBSTANTIALLY FREE
FROM VANADIUM
[75] Inventor: John E. Litz, Lakewood, Colo.
[73] Assignee: Chevron Research Company, San
Francisco, Calif.
[21] Appl. No.: 915,306
[22] Filed: Oct. 3, 1986
[51] Int. Cl.4 C01G 39/00; COIG 39/02
[52] U.S. Cl , 423/56; 423/55
[58] Field of Search 423/55, 56
[56] References Cited
U.S. PATENT DOCUMENTS
4,500,495 2/1985 Hubred et aI 423/55 X
FOREIGN PATENT DOCUMENTS
52895 4/1977 Japan 423/55
u.s. Patent Mar. 21, 1989 4,814,149
Mo, V
STRIPPING
MOLYBDENUMI VANADIUM SEPARATION
AND RECOVERY CIRCUIT r------------------.vI
SPENT
CATALYST
NH4 HC0 ~ 3 Mo,V, CO,+Ni ~
ORGANIC .-----'------.
SEPARATION ~
OF Mo +V FROM
Co +Ni
Co, Nil l I
RAFFINATE' T....---:-:OR::'":G:-:"A-:-N='C---J
SUBSEQUENT RECYCLE
TREATMENT
pH 8.0
I. INITIAL TREATMENT TO GET A
MIXED Mo, V STREAM---
n. V PRECIPITATION----m.
Mo CONCENTRATION----~.
AMMONIUM OCTAMOLYBDATE
PRECIPITATION---------
V
I PRECIPITATION
~' NH4 V03 I
AMMONIUM _--.--J I
METAVANADATEJ
-(-AM-V-) r . ,-lIT ----~H~S04 ~O-P'-':H::"2-.5--NH4 OH ...I~
I '-iN AQUEOUS PHASE + 1
I Mo EXTRACTION ORGANIC I
AND PHASE Mo STRIP AND \
II CONCENTRATION CONCENTRATION Org{AQ =1/5 Org/Aq =lOll I
I ORGANIC RECYCLE I J ~~FFINAT~ _ _ _:. ':'_-I':-~
H2S04 TO pH6.5 I
AT 50°C I
• I
S,02 I
HYDROLYSIS I
AND I
REMOVAL I
H2 S04 TO pH :
2.5 AT ao°c I,
AMMONIUM I
OCTAMOLYBDATEI--_-I-JI
PRECIPITATION
(AOM)
t
(NH4)4 MOB 026 '5H20 I
-------------- -----_....:_,
1
4,814,149
2
BRIEF DESCRIPTION OF THE DRAWING
FIG. 1 is a flow chart of the process of the present
invention. Here, the process for recovering molybdenum
(Mo) and vanadium (V) from spent catalysts is
divided up into five sections: the initial treatment; the
vanadium crystallization; the molybdenum concentration;
and the molybdenum precipitation. In the initial
treatment the spent catalyst is leached free of Mo, V,
and other metals and then the Mo and V are extracted.
The next section substantially removes all the V that is
present in the mixed MolY stream. The next step concentrates
the Mo in solution by organic and aqueous
extraction. And, the final section precipitates the Mo as
ammonium octamolybdate (AOM).
SUMMARY OF THE INVENTION
The present invention is a process capable of selectively
recovering a substantially pure molybdenum
precipitate from a solution that has molybdenum and
vanadium values by precipitating molybdenum as ammonium
octamolybdate. All the steps of the process
comprise: crystallizing most of the vanadium from the
initial solution; concentrating the molybdenum that
remains in solution; removing the impurities from the
concentrated solution; then precipitating the molybdenum,
that is in solution, as ammonium octamolybdate.
This last step selectively precipitates molybdenum and
rejects 80% of the vanadium that has not been removed
in the vanadium crystallization. Any vanadium or molybdenum
that remains in solution may be recycled back
to the process for further recovery.
Generally, the present invention is a process capable
of selectively recovering a substantially pure molybdenum
precipitate from a mixed solution comprising molybdenum
and vanadium, by crystallizing vanadium as
ammonium metavanadate and subsequently precipitating
molybdenum as ammonium octamolybdate so that
said precipitated molybdenum is substantially free from
vanadium.
A more specific embodiment of the present invention
involves the process steps of:
(a) crystallizing vanadium from a solution having a
mixture of vanadium and molybdenum;
(b) extracting molybdenum from the remaining solution
of molybdenum with an organic amine;
(c) stripping said extracted molybdenum with aqueous
ammonia;
(d) heating said aqueous solution to boiling;
(e) adjusting the pH of said heated solution to between
5.5 and 8.5 to precipitate impurities; and
(f) adjusting the pH of said heated solution to between
1.5 and 3.0 to precipitate molybdenum;
whereby the molybdenum precipitate is substantially
free of vanadium.
Hubred et al precipitates vanadium then removes
nickel, cobalt, and molybdenum by serial ion exchange.
However, the prior art has not addressed or adequately
solved the problem of vanadium contamination
5 of molybdenum when evaporative crystallization or a
chemical precipitation method is used.
It is an object of this invention to chemically precipitate
molybdenum from a mixed solution of molybdenum
and vanadium. It is a further object of this invention
to precipitate molybdenum while rejecting at least
80% of the associated vanadium.
BACKGROUND OF THE INVENTION
PROCESS FOR RECOVERING MOLYBDENUM
FROM SOLUTION IN A FORM THAT IS
SUBSTANTIALLY FREE FROM VANADIUM
The present invention relates to the recovery of molybdenum
from solution. Here, the more specific use of
the process is to recover molybdenum as ammonium 10
octamolybdate in a form that is substantially free from
vanadium.
Many hydrocarbon feedstocks contain high percentages
of metals as contaminants, e.g., iron, nickel, or
vanadium. Because of the growing shortages of petro- 15
leum in the world refmers are forced to use feedstocks
that contain larger amounts of these metals. Once they
are in the feed, they tend to deposit on the surfaces of
and/or in the interstices between hydroprocessing catalysts
which contain catalytic metals (e.g., cobalt, nickel, 20
molybdenum, or tungsten). When the hydroprocessing
catalysts no longer give the desired conversion rates
(due to plugging of the catalyst pores by coke or the
contaminant metals or due to reactor plugging), they
are replaced and subsequently disposed of (and are 25
called "spent catalysts"). Because of environmental and
economic considerations, it is therefore desirable to
recover the heavy metal values from the spent catalyst,
leaving the catalyst support in an environmentally benign
form. 30
The recovery of metals such as molybdenum and
vanadium from spent catalysts is nothing new of course,
as indicated by U.S. Pat. No. 4,500,495, issued Feb. 19,
1985 to Hubred et al; U.S. Pat. No. 4,554,138, issued
Nov. 19, 1985 to Marcantonio; as well as U.S. Pat. Nos. 35
4,434,140 and 4,434,141, both issued Feb. 28, 1984 to
Hubred et al, just to name a few which are totally incorporated
by reference. However, these patents have
never addressed the separation of molybdenum from
vanadium into a substantially pure form. 40
The recovery of molybdenum from various sources
has been described in the prior art [see U.S. Pat. No.
3,458,277, issued July 29, 1969 to Platzke et al and U.S.
Pat. No. 3,957,946, issued May 18, 1978 to Ronzio et al; 45
and J. Litz, "Solvent Extraction of W, Mo, and V:
Similarities and Contrasts", Extractive Metallurgy of
Refractory Metals, 69-81 (1980)]. See also, U.S. Pat. No.
3,455,677, issued Aug. 1, 1972 and U.S. Pat. No.
3,681,016, issued July 15,1969 to John E. Litz. U.S. Pat. 50
No. 3,455,677 involves evaporative crystallization of
and precipitation molybdenum in a process to recover
copper and molybdenum from ore COncentrates. This
patent describes two methods of forming a molybdenum
compound. The first is by evaporative crystalliza- 55
tion to force molybdenum out of solution at its solubility
limit and the second is a high temperature polymerization
which causes molybdenum precipitation. U.S.
Pat. No. 3,681,016 involves the separation and recovery
of molybdenum and rhenium values from solution. 60
Recovery of vanadium has also been described in the
prior art. See U.S. Pat. No. 4,544,533, issued Oct. 1,
1985 and U.S. Pat. No. 4,551,315, issued Nov. 5, 1985 to
P. J. Marcantonio, and U.S. Pat. No. 4,432,949 to G. L.
Hubred et· al. The patents to Marcantonio involve the 65
recovery of vanadium from an aqueous ammonium
bicarbonate strip solution and a subsequent precipitation.
They are incorporated by reference. The patent to
EXAMPLE
4
concentrations in this aqueous solution (having a pH of
around 9.0) are approximately 1.5-2.0 gil V and
150-200 gil Mo. Because there are some impurities left
in solution (such as the vanadium and silica) the Mo
must be removed in a fourth and fmal step.
Impurities are then taken out by the following procedure.
The concentrated solution (of the previous step) is
heated to between 40· C. and 80· C., more preferably
50· C., and the pH is adjusted to between 5.5 and 9.0,
but more preferably 6.5-8.5 using sulfuric acid (other
mineral acids, Le., HCI, HN03 are also suitable). These
adjustments are made primarily to hydrolyze silica
which precipitates out of solution and the precipitate is
removed by ftltration.
The solution is then contacted with H2S04 (preferably)
to adjust the pH to between 1.5 and 3.5, more preferably
2.5. It is also heated to between 70· C. and 90· C.,
more preferably 80· C., to initiate Mo precipitation as
ammonium octamolybdate (AOM), (NH4)4Mos026.5H20.
The slurry is not cooled. If it is cooled, the
amount of vanadium reporting to the molybdenum precipitate
might increase due to its lower solubility. Also,
the rate of polymerization, of the soluble molybdenum
into the less soluble octamolybdate species, would slow.
Vanadium rejection at this precipitation is approximately
80% (Le., of all V present only 20% precipitates
out with the AOM). The precipitate is then removed by
ftltration and may be subjected to a second recrystallization
procedure to further remove V.
The ftltrate is then recycled back to the V precipitation
step to remove the soluble V and recycle the extra
(NH4hS04 that is formed from the strip ammonia that
reacts with the sulfate. This occurs during the solvent
extraction when sulfuric acid is used to adjust the pH.
This ftltrate solution from the AOM precipitation contains
both ammonium vanadate and molybdate. After
the AOM is crystallized, it is calcined. This decomposes
the AOM into Mo03 by driving off H20 and ammonia.
4,814,149
3
DETAILED DESCRIPTION OF THE
INVENTION
The present invention selectively recovers molybdenum
(Mo) from a mixed molybdenum/vanadium 5
stream. A mixed molybdenum/vanadium stream may
be obtained from many sources such as ore and spent
catalysts. However, this invention discusses the recovery
of molybdenum from spent catalysts.
To recover spent catalyst values, the spent catalyst 10
may be first roasted and then leached with a solution of
ammonia (ammonium hydroxide) and ammonium carbonate.
This removes cobalt, molybdenum, vanadium,
and nickel. Subsequently, molybdenum (Mo) and vanadium
(V) are separated from cobalt and nickel by an 15
organic solvent extraction step. Thereafter, ammonium
bicarbonate (NH4HC03) is used to strip the Mo and V
from the solvent. For a more detailed explanation of
these steps, see the patents to Hubred and Marcantonio
which are hereby incorporated by reference. 20
Vanadium is crystallizated from a solution comprising
molybdenum and vanadium. It is very important to
crystallize as much vanadium as possible before trying
to precipitate the molybdenum. This can be done as
follows. First, the solution is boiled to decompose am- 25
monium bicarbonate and expel C02, NH3, and some
H20. Then ammonium sulfate, (NH4hS04, is added to
the stripped solution and the pH is adjusted to between
7.0-7.5 and then cooled to 30· C. (This heating increases
V precipitation by destroying any vanadium/carbonate 30
complexes). This should crystallize the majority of vanadium
as ammonium metavanadate (AMV), but approximately
30-40 ppm ofV may be left in solution. For
a more detailed explanation, see the patents to Marcantonio
which are incorporated by reference. 35
At this point the solution may contain approximately
3-4 grams per liter (gil) of Mo so that it must be concentrated
prior to precipitation. Thus, the Mo in the
vanadium-free solution is concentrated by an aqueous
and organic extraction. The pH is adjusted between 2.0 40
and 4.0 or more preferably to 2.5 with H2S04 (or an- In this example, Mo was chemically crystallized as
other mineral acid which will not form complexes with AOM. An ammoniacal-ammonium carbonate leach
either vanadium or molybdenum, Le., HCI or HN03) solution, containing nickel, cobalt, vanadium, and moand
the solution is organic extracted with a combination lybdenum values, was fed to a continuous quaternary
of organic solvents, one of which is a tertiary amine 45 ammonium compound solvent extraction step where
(primary and secondary amines may work, but not as the vanadium and molybdenum were extracted by an
well). The solvent may include most of the commercial organic solvent. The solvent comprised 80% Kermac
tertiary amines, such as tricapryl (Alamine 336 [trade- 470B (as diluent), 10% Aliquat 336 (trademark of Genmark
of General Mills, now owned by Henkel] or Ado- eral Mills, now owned by Henkel) (as an extractant),
gen 364 [trademark of Sherex Chemical]. The diluent 50 10% isodecanol (as a modifier). The loaded solvent was
may be a kerosene (Kermac 470B [trademark of Kerr stripped of the vanadium and molybdenum with an
McGee], Standard Odorless Thinner, Escaid [trade- ammonium bicarbonate solution that approached satumark
of Exxon] or something similar) or it can be an ration, i.e., approximately 2.5M. A composite of ammoaromatic,
such as "butylated" xylene (Solvent 150). If nium bicarbonate strip solutions was boiled to evolve
an aromatic diluent is used, there is no need to use an 55 the carbon dioxide, the pH of the solution was adjusted
alcohol modifier. Modifiers other than isodecanol may to 7.0 (with H2S0oi, if necessary), ammonium sulfate
be decanol, trimethyl nonanol, and similar alcohols. was added, and the mixture was cooled under agitation
The actual combination of organic solvents may be: to form a crop of ammonium metavandate crystals. A
10% Adogen 383; 10% isodecanol; and 80% Kermac composite of f1ltrates from the crystallization was ad-
47GB. The volume of this organic phase is approxi- 60 justed to a pH of 2.5 with sulfuric acid and served as
mately 1 part per 5 parts of original aqueous phase so feed to a continuous tertiary amine solvent extraction
that the Mo may be concentrated. The organic phase is where the molybdenum and residual vanadium were
then separated from the aqueous phase and contacted extracted by the solvent. The solvent comprised 10%
with an aqueous strip solution such as NH40H (this Adogen 383, 10% isodecanol and 80% Kermac 470B.
forms an ammonium molybdate strip concentrate solu- 65 The loaded solvent was then stripped of the molybdetion).
The volume of ammonium hydroxide is 1 part per num and vanadium with an ammonium hydroxide solu-
10 parts of organic phase. Both the extraction and strip- tion (120 gil NH3) to form an ammonium molybdate
ping steps are non-selective for either V or Mo, so their strip concentrate.
'The initial precipitates from Batches 1and 2 were consolidated and recrystallized.
Feed MolY Initial Recrystallization
--------------.......;~--- 25
6
whereby the molybdenum precipitate is substantially
free of vanadium.
2. A process for selectivity recovering a substantially
pure molybdenum precipitate from a solution used to
extract molybdenum from spent catalysts comprising
the following steps:
(a) separating molybdenum and vanadium from other
metal values with an organic solvent;
(b) stripping molybdenum and vanadium from said
organic solvent with an aqueous solvent;
(c) heating said aqueous solution containing the molybdenum
and vanadium to boiling;
(d) cooling said boiled solution and adjusting the pH
to between 7.0 and 7.5 to crystallize a majority of
the vanadium that is in said solution;
(e) adjusting the pH of the remaining solution to
between 2.0 and 4.0;
(f) solvent extracting said molybdenum from the solution
of step (b) to increase the molybdenum concentration;
(g) stripping the organic solution having the molybdenum
with an aqueous strip solution to further
increase the molybdenum concentration;
(h) adjusting the pH of the aqueous molybdenum
solution to between 6.5 and 9.0 with sulfuric acid to
hydrolyze impurities;
(i) adjusting the pH of the remaining solution to between
1.5 and 3.5 to precipitate the molybdenum as
ammonium octamolybdate; and
G) recycling the remaining solution to a point immediately
upstream of the vanadium precipitation in
step (e).
3. The process as recited in claim 1 or 2 in which the
ammonium octamolybdate precipitate is washed with
demineralized water.
4. The process of claim 1 or 2 where the ammonium
octamolybdate precipitate is redissolved in pure water
and the process is repeated.
5. The process of claim 1 or 2 where the ammonium
octamolybdate precipitate is calcined to convert the
ammonium octamolybdate to molybdenum trioxide.
6. A process for selectively recovering a substantially
pure molybdenum precipitate from a solution comprising
molybdenum and vanadium values, the process
comprises:
(a) crystallizing vanadium from said solution to form
a substantially vanadium-free mother liquor;
(b) concentrating molybdenum in said vanadium-free
mother liquor to form a molybdenum-rich concentrate;
(c) removing impurities from said molybdenum-rich
concentrate by adjusting the pH of said concentrate
to between 5.0 and 9.0; heating said concentrate
to between 20° C. and 70° C.; allowing said
concentrate to digest for between 0.5 and 2 hours;
and fIltering out said impurities; and
(d) precipitating molybdenum as ammonium octamolybdate
from said concentrate to recover a
substantially vanadium-free molybdenum value.
7. A process a recited in claim 6 wherein the molybdenum
is concentrated according to step (b) by first
extracting an aqueous molybdenum solution with an
organic solvent oflesser volume and then extracting the
molybdenum with an aqueous solvent of lesser volume
than said organic solvent.
8. A process as recited in claim 6, step (d) wherein the
molybdenum is precipitated as ammonium octamolybdate
by adjusting the pH of the solution of step (c) to
4,814,149
) -1300:\'
AOM Precipitate, MolY
463:\
333:\
106:\
58:\
Batch \
Batch 2
Calcium impurities may be avoided by using deminer- 30
alized water for the molybdenum solvent extraction
strip solution. Additionally, silicon does not re-solubilize
if the crystals are dissolved for recrystallization.
Once silicon precipitates, it stays as a precipitate. Also,
nickel cannot be separated from Mo if it goes through 35
the first separation.
The vanadium content of the molybdenum product
can best be controlled by attaining low vanadium levels
in the ammonium metavanadate mother liquor. If this 40
crystallization is operated ideally, less than 50 milligrams
per liter vanadium in the mother liquor, the feed
to the molybdenum recovery will have a molybdenum/
vanadium ratio greater than 200.
Since many modifications and variations of the pres- 45
ent invention are possible within the spirit ofthis disclosure,
it is intended that the embodiments disclosed are
only illustrative and not restrictive. For that reason,
reference is made to the following claims rather than to
the specific description to indicate the scope of this 50
invention.
What is claimed is:
1. A process for recovering molybdenum in a purified
form substantially free from vanadium impurities, said
process comprises: 55
(a) crystallizing vanadium from a solution having a
mixture of vanadium and molybdenum;
(b) extracting molybdenum from the remaining solution
of molybdenum with an organic solvent;
(c) stripping said extracted molybdenum with an 60
aqueous solvent;
(d) heating said aqueous solution from step (c) to
between 40° C. and 80° C.;
(e) adjusting the pH of said heated solution to between
5.5 and 8.5 to precipitate impurities; and 65
(f) adjusting the pH of said heated solution to between
1.5 and 3.0 to precipitate molybdenum as
ammonium octamolybdate;
5
Thereafter, a composite of the ammonium molybdate
strip concentrate was heated to 50° C., the pH was
adjusted to 6.5 with sulfuric acid, and the solution was
allowed to digest for I hour. The hydrolyzed impurities
were removed by fIltration. The purified fIltrate was 5
heated to 80° C., adjusted to 2.5 pH with sulfuric acid
and seeded with ammonium octamolybdate (AOM).
The resulting slurry was digested for 4 to 5 hours, ftltered,
and the chemically precipitated crystals were
washed with a pH 2.5 sulfuric acid solution. The crys- 10
tallization above showed 80% of the initial vanadium to
be separated from the molybdenum product.
The fIltrates from the AOM crystallization were recycled
to the ammonium metavanadate (AMY) crystal- 15
lization as a source of ammonium sulfate and for the
purpose of recycling the contained vanadium and molybdenum.
The molybdenum concentrations in the fIltrates
are in the range from 1.9 to 4.7 grams per liter.
Table I shows the relative concentrations of the metals 20
that have been precipitated.
TABLE I
4,814,149
8
dium values from said solution as a precipitate of ammonium
metavanadate, concentrating the fIltrate of said
solution to assist removal of impurities in the resulting
concentrate by fIltration, and then concentrating the
5 concentrated solution of molybdenum and residual vanadium
values with an acid to precipitate ammonium
octamolybdate therefrom while rejecting greater than
80% of said vanadium values into the extract from such
precipitation of said ammonium octamolybdate.
* * * * *
7
between 2.0 and 5.0 with sulfuric acid; heating the solution
to between 50° C. and 95° C.; allowing the solution
to digest for between 3 and 6 hours; seeding the solution;
removing the precipitated ammonium octamolybdate;
and recycling the remaining solution to the vanadium
crystallization step.
9. A process for selectively recovering a substantially
pure molybdenum precipitate from a solution comprising
a mixture of molybdenum and vanadium values, said
process comprising crystallizing a majority of the vana- 10
15
20
25
30
35
40
45
50
55
60
65
#2hinPA�<-layout-grid-align:none;text-autospace:none'>to conduit 69 and ultimately to cyanide destruction and
disposal site 70.
The vessel 60 may be operated at atmospheric pressure,
or at super-atmospheric pressure, and an oxygen
atmosphere may be provided at the top thereof in either 60
case. Also, the system could be operated so that the
slurry flowed upwardly and the carbon granules flowed
downwardly, if denser carbon were utilized, and/or if
the slurry solids had a lower specific gravity.
FIG. 3 schematically illustrates other exemplary ap- 65
paratus that can be utilized for effectively and efficiently
dissolving the gold and/or silver in the leaching
stage prior to CIP recovery in station 75. Utilizing the
6
apparatus of FIG. 3, the slurried ore in conduit 76 is
mixed with cyanide from conduit 77, and ultimately
mixed with oxygen from conduit 78 in a mixer 79. The
mixer may be any suitable mixer capable of mixing
components of a medium consistency slurry, such as an
MC® mixer sold by Kamyr, Inc, of Glens Falls, N.Y.
Also, as generally disclosed in U.S. Pat. No. 4,501,721;
flocculent and/or fiber can be added to the slurry to
facilitate locking of the particulized ore in a stable network
in the slurry. For instance cellulosic fibers, fiberglass
fibers, or the like are mixed with liquid in tank 80
and then metered to the inlet to mixer 79, while flocculents,
such as synthetic polymers of anionic, cationic, or
nonionic types are mixed with mill water in tanks 81,
and then ultimately passed to conduit 82 prior to introduction
into upflow 83. The leached slurry that is discharged
from the top 84 of vessel 83 will then pass to
the CIP recovery station 75, which can be as illustrated
in FIG. 1 (without the tank 22). The vessel 83 can also
be pressurized, as by utilizing pressure control valve 85,
and a one atmosphere, or super-atmospheric, oxygen
atmosphere maintained therein, or the vessel can be
completely slurry filled.
Utilizing the apparatus heretofore described, according
to the present invention a process of gold and/or
silver recovery from ore and the like may be practiced.
The process comprises the steps of: leaching gold and/
or silver from the ore or the like, to dissolve the gold
and/or silver, utilizing a basic cyanide solution; and (b)
recovering the leached gold and/or silver in solution by
contacting the solution with solid material for adsorbing
the gold and/or silver from the solution; wherein
step (b) is practiced by providing oxygen gas in the
solution in an amount significantly greater than can be
obtained by contacting the solution with air so as to
greatly increase the solution rate of the gold and/or
silver, and by minimizing the amount of carbon dioxide
in the solution so that it is significantly less than would
be obtained by contacting the solution with air, so as to
possibly increase the gold and/or silver adsorption efficiency
of the adsorbing material, and certainly to reduce
the production of CaC03. Preferably step (b) is
practiced by substantially saturating the solution with
oxygen, and preferably by utilizing generally pure oxygen.
The following table I indicates the results achieved
by preparing a gold cyanide solution by leaching a
common gold ore sample (the gold ore sample, as is
typical, also contained a small amount of silver), and
then exposing the solution to carbon adsorption in a
rotating bottle for six hours, with atmospheres of air,
oxygen, and nitrogen, respectively.
TABLE I
Atmosphere
Oxygen Air Nitrogen
Approx. % 02 100 21 0
in atmosphere
Leach solution 4.14 4.14 4.14
assay, Au, mgII
Final solution assay, 0.032 0.041 0.079
Au. mgll
Final carbon assay, 23.4 23.1 23.1
AU,oz/ton
Au adsorption, %1 99.23 99.01 98.10
Leach solution assay, 1.8 1.8 1.8
Ag, mgll
Final solution 0.2 0.2 0.2
assay, Ag, mgII
Final carbon assay, 8.77 8.97 8.36
Test #1 Test #2
Conditions 65
Grind 77.9%-200 77.9%-200
% Solids 27 27
pH: initial/adj. 8.7/10.9 8.7/10.9
In the following table III, further bottletype tests 50
were conducted for a carbon-in-leach cyanidation, confirming
that simultaneous leaching and carbon adsorption
in an oxygenated slurry results in rapid high gold
extraction with low cyanide consumption. The ore
tested in each of the two tests in table III was Gencor's 55
Buffelsfontein ore. With gold extractions of about
91-92%, in six hours, cyanide consumption was only
0.37-0.47 Ibs. per ton. If the pulp density and carbon
concentration was closer to expected plant conditions,
cyanide consumption is expected to be as little as 60
O.19-0.271bs. per ton. The low cyanide consumption is
very unexpected and advantageous.
TABLE III
The following table II indicates the results from a
carbon-in-pulp cyanidation test utilizing three different 10
types of Gencor ore samples from, respectively, Buffeisfontein
(No. 1), Leslie (No.2), and 81. Helena (No.3).
The tests indicate high gold extractions (in the range of
90-95%), and, surprisingly, low cyanide consumption.
All tests were performed in rotated bottles with oxygen 15
atomsphere at the local atmospheric pressure of 12.1
psia. The time in each case (total of 10 hours) was a six
hour cyanide leach plus a four hour elP process.
TABLE II
20 Test #1 Test #2 Test #3
Conditions
Grind 77.9%-200 80%-200 80%-200
% Solids 27 27 27
pH: initial/adj. 8.7/10.9 9.0/10/8 9.0/10.7
NaCN, initial gil 0.3 0.3 0.3 25
Time, hr. 10 10 10
Feed
Weight, g 300.0 300.0 300.0
AU,oz/ton 0.217 0.110 0.186
Reagents added, tola1
CaO,g 0.12 0.12 0.12 30
NaCN, g 0.25 0.25 0.25
Carbon
Mesh size Tyler 6 X 14 6 X 14 6 X 14
Initial wt, g 22.00 22.00 22.00
Final wt, g 22.05 22.11 22.09 35 AU,oz/ton 2.631 0.966 1.779
Sol'n, end of test
NaCN, gil 0.276 0.245 0.264
pH 10.6 10.6 10.4
Filtrate, total
Volume. m1 1414 1453 1399 40
Au, mgll 0.004 0.002 0.003
Residue
Weight, g 298.7 298.6 298.6
Au.oz/ton 0.017 0.004 0.015
0.015 rerun
Reagents consumed 0.16 0.33 0.26 45
NaCN, 1b/ton
Extraction. % 92.0 94.7 89.8
Au
Oxygen Air Nitrogen
8
TABLE III-continued
Test #1 Test #2
NaCN, initial gil 0.3 0.3
Time, hr 61 62
Feed
Weight, g 399.9 399.9
Au? oz/ton 0.217 0.217
Reagents added, total
CaO,g 0.12 0.12
NaCN, g 0.25 0.25
Carbon
Mesh size Tyler 6 X 14 6 X 14
Initial wt, g 22.00 22.00
Final wt, g 22.26 22.07
AU,ozlton 2.684 2.695
Sol'n, end of test 10.5 10.6
pH
Filtrate. total
Volume, mI 1412.67 1417.76
NaCN, gil 0.24 0.22
Residue
Weight, g 298.24 298.48
AU,oz/ton 0.019 0.018
Reagents consumed 0.37 0.47
NaCN, 1b/ton
Extraction, % 91.3 91.7
Au
Calculated heads 0.219 0.217
AU,oz/ton
Ipre-saturated with 02 at ambo press. for 16 hours previous to leach.
2During 6-hr elP leach, purge with 02 at T = 0 ht and T = 1 hr. Also add 11 g
carbon at each of these times.
In conclusion, according to the present invention, a
method and apparatus are provided for the extremely
efficient and effective recovery of gold and/or silver
from ore or the like. While the invention has been
herein shown and described in what is presently conceived
to be the most practical and preferred embodiment
thereof, it will be apparent to those of ordinary
skill in the art that many mddiflcations may be made
thereof within the scope of the invention, which scope
is to be accorded the broadest interpretation of the
appended claims so as to encompass all equivalent process
and apparatus.
What is claimed is:
1. In a leach-adsorpton system for the recovery of
one of gold and silver from ore slurry containing the
same and also a gas containing a substantially higher
proportion of oxygen than is contained in natural air
wherein one of the gold and silver is leached from the
ore and recovered by contacting the slurry with solid
material for adsorbing the one of said sold and silver
from solution, apparatus therefor comprising:
a vessel having an inlet for the introduction of the ore
slurry and an outlet for the ore slurry;
means for controlling the level of slurry within the
vessel;
floating cover means disposed at the top of the slurry
level of the vessel for reducing the transfer of oxygen
out ofthe slurry and the transfer of nitrogen or
carbon dioxide into the slurry; and
a mechanical agitator disposed in said vessel, said
mechanical agitator including a central shaft, and
said floating cover means comprising means defining
an aperture therein for receipt of said shaft so
that said shaft may pass therethrough into the
slurry.
2. Apparatus as recited in claim 1 further comprising
sparger means for sparging oxygen into the slurry adjacent
the bottom of the vessel.
5
4,754,953
88.6 88.6 88.1
Atmosphere
7
TABLE I-continued
Ag,oz/ton
Ag adsorption, %1
'Based on final carbon and final solution.
4,754,953
9
3. Apparatus as recited in claim 2 further comprising
means for introducing activated charcoal particles into
the vessel, means for withdrawing said particles from
the vessel, and screening means at said slurry outlet for
screening the particles out of the slurry passing through 5
said outlet.
4. Apparatus as recited in claim 3 wherein said floating
cover means comprises a bed of floating balls.
5. In a leach-adsorption system for the recovery of 10
one of gold and silver from ore slurry containing the
same and also a gas containing a substantially higher
proportion of oxygen than is contained in natural air
wherein one of the gold and silver is leached from the
ore and recovered by contacting the slurry with solid 15
10
material for adsorbing the one of said gold and silver
from solution, apparatus therefor comprising:
a vessel having an inlet for the introduction of the ore
slurry and an outlet for the ore slurry;
means for controlling the level of slurry within the
vessel; and
floating cover means disposed at the top of the slurry
level of the vessel for reducing the transfer of oxygen
out of the slurry and the transfer of nitrogen or
carbon dioxide into the slurry, said floating cover
means comprising a disc-shaped cover having a top
substantially flat surface, and having a bottom surface
that is substantially concave, said substantially
convcave bottom in contact with the slurry.
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