U.S. patent application number 10/120752 was filed with the patent office on 2003-10-16 for drainage aid for metal heap leaching.
Invention is credited to Burgmayer, Paul.
Application Number | 20030192403 10/120752 |
Document ID | / |
Family ID | 28790160 |
Filed Date | 2003-10-16 |
United States Patent
Application |
20030192403 |
Kind Code |
A1 |
Burgmayer, Paul |
October 16, 2003 |
Drainage aid for metal heap leaching
Abstract
Methods for increasing drainage or percolation of a lixiviant
solution through mineral ore in a heap mining operation. A drainage
aid comprising ethoxylated aliphatic primary alcohols and mixtures
thereof is dripped, sprayed or otherwise brought into contact with
the heaped metal ore aggregate and thereby improves percolation or
drainage of the lixiviant through the heaped metal ore.
Inventors: |
Burgmayer, Paul; (Wayne,
PA) |
Correspondence
Address: |
WEGMAN, HESSLER & VANDERBURG
6055 ROCKSIDE WOODS BOULEVARD
SUITE 200
CLEVELAND
OH
44131
US
|
Family ID: |
28790160 |
Appl. No.: |
10/120752 |
Filed: |
April 11, 2002 |
Current U.S.
Class: |
75/743 ;
75/711 |
Current CPC
Class: |
C22B 11/08 20130101;
C22B 11/04 20130101; Y02P 10/20 20151101; C22B 3/04 20130101; Y02P
10/234 20151101 |
Class at
Publication: |
75/743 ;
75/711 |
International
Class: |
C21B 015/00 |
Claims
What is claimed is:
1. In a method of leaching metals from metal ore in which a
lixiviant solution is placed in contact with said metal ore to
extract said metal therefrom, the improvement comprising contacting
said metal ore with an effective amount of a drainage aid
comprising an ethoxylated aliphatic alcohol.
2. Method as recited in claim 1 wherein said ethoxylated aliphatic
alcohol has the formula HOCH.sub.2CH.sub.2--O.sub.nR wherein R is
C.sub.4-C.sub.20 alkyl or C.sub.4-C.sub.20 alkenyl and n is from
about 2 to about 20.
3. Method as recited in claim 2 wherein R is C.sub.4-C.sub.14 alkyl
or C.sub.4-C.sub.14 alkenyl and n is about 3 to about 8.
4. Method of recited in claim 2 wherein said step of contacting
said metal ore comprises contacting said metal ore with an aqueous
solution containing said drainage aid, said drainage aid being
present in said aqueous solution in an amount of about 1-1,000
ppm.
5. Method as recited in claim 4 wherein said drainage aid is
present in an amount of about 1-500 ppm.
6. Method as recited in claim 4 wherein said drainage aid is
present in an amount of about 1-100 ppm.
7. Method as recited in claim 3 wherein said drainage aid comprises
a mixture of ethoxylated aliphatic alcohols and wherein, in said
mixture, R is about 7.3 alkyl and n is about 4.5.
8. Method as recited in claim 3 wherein said drainage aid comprises
a mixture of ethoxylated aliphatic alcohols and wherein, in said
mixture, R is about 6.7 alkyl and n is about 5.3.
9. Method as recited in claim 3 wherein said drainage aid comprises
a mixture of ethoxylated aliphatic alcohols and wherein, in said
mixture, R is about 10.5 alkyl and n is about 3.5.
10. Method as recited in claim 3 wherein said drainage aid
comprises a mixture of ethoxylated aliphatic alcohols and wherein,
in said mixture, R is about 12.2 alkyl or alkenyl and n is about
4.
11. In a method of leaching gold from a heap of gold metal ore in a
heap leaching operation wherein a cyanide based lixiviant system is
used to contact and remove gold from said gold metal ore, the
improvement comprising contacting said gold metal ore with a
drainage aid comprising an ethoxylated aliphatic alcohol or
mixtures of said ethoxylated aliphatic alcohol.
12. Method as recited in claim 11 wherein said lixiviant system has
a pH of about 9 to about 11.5 and wherein said ethoxylated
aliphatic alcohol is a primary alcohol having a carbon chain length
of about 4 to about 20 carbon atoms and average ethoxylation of
about 2-20 moles of EtO (ethylene oxide) per molecule.
13. Method as recited in claim 12 wherein said ethoxylated
aliphatic primary alcohol is present in an aqueous solution in an
amount of about 1--about 1,000 ppm.
14. Method as recited in claim 13 wherein said ethoxylated
aliphatic primary alcohol is present in an amount of about 1-500
ppm.
15. Method as recited in claim 13 wherein said ethoxylated
aliphatic primary alcohol is present in an amount of about 1-100
ppm.
16. Method as recited in claim 12 wherein said carbon chain length
is from about 4-14 and said average ethoxylation is about 3 to
about 8 moles of EtO per molecule.
17. Method as recited in claim 13 wherein said drainage aid
comprises a mixture of ethoxylated aliphatic primary alcohols.
18. Method as recited in claim 17 wherein said mixture has an
average carbon chain length of about 7.3 and an average of about
4.5 moles of EtO per molecule.
19. Method as recited in claim 17 wherein said mixture has an
average carbon chain length of about 6.7 and an average of about
5.3 moles of EtO per molecule.
20. Method as recited in claim 17 wherein said mixture has an
average carbon chain length of about 10.5 and an average of about
3.5 moles of EtO per molecule.
21. Method as recited in claim 17 wherein said mixture has an
average carbon chain length of about 12.2 and an average of about 4
moles of EtO per molecule.
22. Method as recited in claim 11 wherein said drainage aid
comprises isodecyl alcohol ethoxylate.
23. Method as recited in claim 17 wherein said drainage aid
comprises 2-decylethoxy poly(ethyleneoxy) ethanol.
24. Method as recited in claim 11 wherein said drainage aid
comprises ethoxylated 2-decanol.
25. Method as recited in claim 11 wherein said drainage aid
comprises ethoxylated aliphatic alcohol having a chain length of
about 12.2.
Description
FIELD OF THE INVENTION
[0001] The present application relates to an improved process for
leaching of metal from ore heaps in which a lixiviant solution is
brought into contact with the ore to form a "pregnant" solution,
from which the metal is ultimately separated. The improvement lies
in contacting the metal ore with an ethoxylated aliphatic alcohol
to improve percolation of the lixiviant through the heap.
BACKGROUND OF THE INVENTION
[0002] In recent years, heap leaching has become a cost effective
method for recovering precious metals such as gold or silver from
low grade ores. In the process, a lixiviant system, comprising a
ligant and an oxidant is used to dissolve out the desired precious
metal from the ore. As used herein, the phrases "lixiviant system"
and "lixiviant solution" will be used interchangeably and do not
imply a true chemical solution--only a chemical combination adapted
to extract the mineral value in the ore.
[0003] In heap leaching, the metal bearing ore may be obtained from
an open pit mine or the like and is crushed to produce an aggregate
that is coarse enough to expose the desired mineral values but fine
enough to allow intimate contact of the lixiviant system or
solution therewith. The lixiviant solution may be distributed over
the top of the metal ore heap via sprinklers, wobblers, or other
similar equipment. The barren lixiviant "percolates" through the
heap to perform its desired function with the metal and the
resulting pregnant solution is then collected by an impervious
leach pad or the like located at the bottom of the heap. The
pregnant solution is then subjected to conventional mineral
recovery techniques to obtain the desired precious metal.
[0004] In gold heap mining operations, a lixiviant system
comprising cyanide, air and lime is commonly used under highly
alkaline conditions (pH 9-11.5) to form the pregnant solution,
(i.e., a complex or ligand coordinated with a gold cation). The
gold cation complex or ligand leaches from the ore heap and is
recovered. The gold is then separated from the lixiviant complex
via conventional separation techniques such as the conventional
method of adsorption on an activated carbon column or bed.
[0005] A variety of factors can contribute to poor percolation of
the lixiviant through the heap. For example, high clay ores, the
formation of large rock fragments and the formation of surface muds
or slimes on the heap can be detrimental to the desired percolation
through and contact of the ore with the lixiviant solution.
[0006] It is therefore desirable to provide a treatment that can
enhance the percolation or contact of the ore with lixiviant
solution so as to increase the amount of precious metal recovered
per unit area of the metal ore heap.
[0007] It is especially desirable to provide such a percolation or
drainage aid that does not severely impede the functioning of
desired process parameters such as the ability of the lixiviant
solution to react or complex with the ore, or the ability of the
pregnant lixiviant solution to drain through the heap for
recovery.
SUMMARY OF THE INVENTION
[0008] The present invention is directed to a drainage aid useful
in heap mining operations. More preferably, the invention is
directed toward precious metal heap leaching operations such as
gold heap leaching. The drainage aid can be applied by itself to
the heap or it can be mixed with the lixiviant solution and then
sprayed or dripped onto the ore to thereby contact the ore.
[0009] The drainage aid is preferably applied in an aqueous
solution via drip or spray application and is present in the
aqueous solution in an amount of between about 1-1,000 ppm. The
drainage aid is an ethoxylated aliphatic primary alcohol having a
carbon chain length of from about C.sub.4-C.sub.20 and about 2-20
moles of ethoxylation per molecule.
[0010] The invention will be further described in the following
detailed description and drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0011] FIG. 1 is a graph showing the results of activated carbon
gold uptake tests reported in Example 4; and
[0012] FIG. 2 is a bar graph illustrating the tests reported in
Example 5 showing the uptake of the drainage aids by gold ore.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
[0013] The drainage aids in accordance with the invention are
ethoxylated aliphatic alcohols having the formula
HOCH.sub.2CH.sub.2--O.sub.nR
[0014] wherein R is C.sub.4-C.sub.20 alkyl or C.sub.4-C.sub.20
alkenyl with n being about 2 to 20. More preferably, R is
C.sub.4-C.sub.14 alkyl or C.sub.4-C.sub.14 alkenyl and n is about 3
to 8.
[0015] Preferably, the drainage aid is applied to the metal ore in
the form of an aqueous solution with the drainage aid present in an
amount of about 1-1,000 preferred, about 1-500 ppm active more
preferred, and 1-100 ppm most preferred.
[0016] The ethoxylated aliphatic alcohols are commercially
available from a plurality of suppliers. Based upon presently
available data, the following four commercially available products
appear to be especially effective.
1 McCutcheon Description description Analysis results Ethoxylated
Isodecyl alcohol A heavily branched ethoxylated aliphatic
ethoxylate aliphatic alcohol. The average carbon alcohol chain
length is 7.3 C's/molecule. The average ethoxylation is 4.5 moles/
molecule Ethoxylated 2-decylethoxy a heavily branched ethoxylated
aliphatic aliphatic poly(ethyleneoxy) alcohol. The average carbon
chain alcohol ethanol length is 6.7 C's/molecule. The average
ethoxylation is 5.3 moles/molecule Ethoxylated Ethoxylated a
heavily branched alcohol 1 aliphatic 2-decanol ethoxylated
aliphatic alcohol. The alcohol average carbon chain length is 10.5
C's molecule. The ethoxylation is 3.5 moles/molecule Ethoxylated
Ethoxylated a straight chain ethoxylated aliphatic aliphatic
alcohol alcohol. The average carbon chain alcohol length is 12.2
C's/molecule. The average ethoxylation is 4.0 moles/ molecule
[0017] At present, the most preferred treatment is the
2-decylethoxy poly (ethyleneoxy) ethanol.
EXAMPLES
[0018] The invention will be further explained in conjunction with
the following illustrative examples which should not be construed
as a limitation on the inventive concepts set forth herein
[0019] A drainage aids for heap leaching must have certain
desirable characteristics and not have some undesirable
characteristics. Five tests proving these characteristics have been
developed to determine the suitability of potential drainage aids
for gold heap leach applications. The importance of the ability of
a potential drainage aid to pass each test is described below.
[0020] capillary rise in gold ore--the basic desired outcome for
application of a drainage aid is that it reduce the extent of
capillary rise in a gold ore. Reduction of capillary rise
especially in smaller ore particles is important to promote uniform
movement of lixiviant through the heap. Excessive capillary rise
will lead to so-called "blinding" so that movement of cyanide and
oxygen into and gold cyanide complex out of that portion of the
heap is greatly reduced. A successful drainage aid will have the
maximum possible reduction in capillary rise at a given
concentration.
[0021] goldfilm dissolution inhibition--While it is important that
a drainage aid reduce heap blinding, it is equally important that
the drainage aid not impede gold dissolution from the ore. Gold is
generally present in ore as particles of metallic gold in the rock
matrix. Any coating of the gold metal by the drainage aid could
slow the dissolution process leading to slower recovery of the gold
value, an undesirable outcome. The use of a surface-active agent to
modify capillary rise could reasonably be expected to have an
impact on gold dissolution as any surface film formed by the
surfactant could interfere with the gold dissolution reaction.
Given equal drainage properties, the drainage aid with the least
effect on gold dissolution would be the most successful.
[0022] clear solution cyanide reactivity--Another important
property that a potential drainage aid must possess is an inertness
to cyanide under leaching conditions (pH9-11.5, 7-9 ppm oxygen).
Cyanide concentration is one of the two important parameters (the
other is oxygen concentration) which affect gold dissolution rates.
A drainage aid that reacts with cyanide to reduce cyanide
concentration in the heap will also lead to a slower recovery of
the gold value. Given equal drainage properties, the drainage aid
with the least effect on cyanide concentrations would be the most
successful.
[0023] activated carbon gold uptake--After gold is leached from a
heap, it is passed through a column of activated carbon to strip
the gold cyanide from the lixiviant (so-called carbon-in-column
(CIC) gold recovery). Any drainage aid which prevents the uptake of
gold by the activated carbon would not be desired unless it could
be shown that in actual practice the drainage aid does not reach
the activated carbon column. Again as surface-active agents are
being used, it is a reasonable expectation that gold uptake would
be affected by the film-forming properties of the agent on the
activated carbon.
[0024] uptake of the drainage aid by gold ore--If the drainage aid
had a detrimental effect on activated carbon gold uptake, it is
still possible that a drainage aid could be successfully applied if
it were adsorbed onto the ore in the process of improving drainage.
As is stated in U.S. Pat. No. 5,827,348, proper wetting of the ore
is an important factor in optimizing precious metal recovery.
[0025] A large number of potential drainage aids were initially
tested using a capillary rise experiment to determine if they had
any effect on drainage. Potential drainage aids were selected on
the basis of their stability in high pH (pH 10.5) solutions and a
stated ability (in McCutheon's Emulsifiers and Detergents 1999:
North American Edition, Vol. 1) to impact wetting. Those tested
included fatty acid derivatives (such as those described in AU
application 07/011,659), ethylene oxide/propylene oxide block
copolymers (such as those described by Smith and Craft in Chapter 5
of Heap and Dump Leaching Practice), sulfosuccinate derivates (such
as those described in U.S. Pat. No. 5,827,348), ethoxylated
alkylphenols, betaine derivatives, various phosphate esters,
caprylic and imidazoline amphoterics, sulfonated aromatics,
silicones, 2-ethyl hexyl sulfate, various ethoxylated aromatic
alcohols, branced- and straight-chain aliphatic alcohols, and some
proprietary mixtures of surfactants provided by manufacturers.
Example 1
[0026] Benchtop Capillary Rise Experiments.
[0027] Capillary rise screening tests were performed using an
18.times.30 mesh sieved ore from a mine in Northern Nevada
(Marigold Mine). The ore was prepared by first sieving to this size
fraction. The 18.times.30 fraction was washed extensively with tap
water to remove embedded clays. Material was dried overnight at
105.degree. C. and then stored in an environmental chamber at 50%
humidity and 25 C.
[0028] A 1 cm.times.30 cm plastic tube was prepared with a fine
stainless steel mesh pushed to the bottom of the tube to hold the
ore in place. The tube was filled about 2/3 full with the sieved,
washed, and dried ore and suspended from the bottom weighing hook
of a Mettler analytical balance. A petri dish was filled with a
solution of the surfactant at the desired concentration prepared in
buffer solution. The buffer solution was prepared by dissolving 0.1
gram of calcium oxide per liter of solution along with 400 ppm of
sodium sulfate (expressed as sulfate) adjusted to a pH of 10.5 with
sulfuric acid. The sulfate was added to more closely approximate
the high ionic strength of a typical lixiviant solution. Some
surfactants show reduced activity at his ionic strength, therefore
it was important that test solutions match a typical lixiviant.
[0029] The petri dish was placed under the suspended plastic tube
and raised with a lab jack until the solution just touched the
bottom of the tube and solution began to rise in the tube due to
capillary action. Capillary rise was monitored by the rise in the
liquid level in the tube (easily see as a darkening of the tube
interior) and by the weight gain of the tube.
[0030] The liquid was allowed to enter the tube for seven minutes
after which the petri dish was lowered, the gain in weight of the
tube was measured and then the tube was removed from the hook to
measure the height. In general, weight gain and the rise of liquid
were highly correlated for a given ore so that the two measurements
were used as checks on each other. Height of the wetted column
after seven minutes is reported below.
[0031] Surfactants were run at 5, 20 and 100 ppm. Below the
surfactants are described as one of three classes, those that no
effect or does response (>95% of blank, approximate noise level
of experiment), those that slightly decreased capillary rise with
increasing dose (75% to 95%), and those that had a significant
impact (<75% of blank).
2 height height % Classifi- Type chemical name cm of blank cation
Ethoxylated Ethoxylated 6.8 66% Good effect aliphatic alcohol
2-decanol Proprietary 7.0 68% Good effect fatty acid + sodium
laureth(2) 7.0 68% Good effect amphoteric sulfate Ethoxylated
isodecyl alcohol 7.0 68% Good effect aliphatic alcohol ethoxylate
Ethoxylated Ethoxylated 7.1 69% Good effect aliphatic alcohol
alcohol sulfonate aliphatic sodium dioctyl- 7.3 71% Good effect
sulfosuccinate fatty acid + ammonium lauryl 7.3 71% Good effect
amphoteric sulfate/ ammonium laureth sulfate/ cocoamidopropyl
betaine/ cocamide dea fatty acid + sodium laureth(3) 7.5 73% Good
effect amphoteric sulfate fatty acid + ammonium 7.5 73% Good effect
amphoteric laureth(3) sulfate mixed fatty acid sulfo 7.6 74% Good
effect salt Ethoxylated Ethoxylated 7.7 75% Good effect aliphatic
alcohol 2-decanol Sulfonate sodium dodecyl 7.8 76% Some effect
aromatic diphenyloxide disulfonate sulfonate aliphatic dihexyl
sodium 7.9 77% Some effect sulfosuccinate Ethoxylated Alkoxylated
8.2 80% Some effect aliphatic alcohol isopropanolamide acrylic acid
8.7 85% Some effect Proprietary Modified 8.7 85% Some effect
ethoxylate sulfonate aliphatic tetrasodium 8.7 85% Some effect
N-(1,2 dicarboxyethyl)- octadecyl sulfosuccinate fatty acit +
sodium laureth(1) 8.8 86% Some effect amphoteric sulfate fatty acid
ammonium lauryl 8.8 86% Some effect sulfate Ethoxylated Lauryl
alcohol 9.0 88% Some effect aliphatic alcohol alkoxylate sulfonate
aliphatic di-tridecyl sodium 9.2 90% Some effect sulfosuccinate
sulfonate sodium di- 9.2 90% Some effect aromatic isopropyl
naphalene sulfonate Proprietary 9.3 91% Some effect Ethoxylated
C-12 to C-14 9.5 93% Some effect aliphatic alcohol secondary
alcohol ethoxylate Ethoxylated ethoxylated 9.5 93% Some effect
aromatic alcohol nonylphenol Ethoxylated C-12 to C-14 9.6 94% Some
effect alphatic alcohol secondary alcohol ethoxylate phosphate
ester aromatic based 9.7 95% No effect organic phosphate ester
sulfonate aliphatic dibutyl sodium 9.7 95% No effect sulfosuccinate
Silicone Silicone glycol 9.7 95% No effect copolymers Ethoxylated
ethoxylated 9.8 96% No effect aromatic alcohol nonylphenol
Proprietary 9.9 97% No effect Proprietary 9.9 97% No effect block
copolymer EO/PO 10.0 98% No effect copolymer amphoteric Alkylether
10.0 98% No effect betaine hydroxysultaine Ethoxylated C-12 to C-14
10.0 98% No effect aliphatic alcohol secondary alcohol ethoxylate
amphoteric caprylic 10.1 99% No effect caprylic amphoteric
amphoteric imidazoline 10.1 99% No effect imidazoline sodium salt
sulfonate aliphatic disodium alkoxy 10.1 99% No effect
sulfosuccinate amphoteric sodium salt of 10.2 100% No effect
imidazoline 2-caprylic-1 (ethyl beta oxypropanoic acid) amphoteric
cocoamidopropyl 10.3 100% No effect betaine block copolymer EO/PO
10.4 101% No effect copolymer amphoteric cocoamidopropyl 10.4 101%
No effect betaine sulfobetaine sulfate 2-ethyl hexyl 10.6 103% No
effect sulfate Proprietary 10.7 104% No effect Ethoxylated
Ethoxylated 10.9 106% No effect aromatic alcohol alkylphenol
[0032] Of the surfactants showing a maximum reduction in capillary
rise ("good effect"), it was found that these were of four types, a
sulfosuccinate, ethoxylated aliphatic alcohols, mixtures of fatty
acids and amphoterics, and a sulfo salt of a fatty acid. A fifth
material is described by its manufacturer as a mixture of anionic
and nonionic surfactants. The fatty acid/1 mixtures were found to
be too expensive and were not tested further.
[0033] It is interesting to note that the longer chain ethoxylated
aliphatic secondary alcohols did not show any effect; neither did
the ethoxylated aromatic alcohols. With regard to the
sulfosuccinates, only sodium dioctyl-sulfosuccinate and possibly
dihexyl sodium sulfosuccinate showed an appreciable impact on
capillary rise.
Example 2
[0034] Goldfilm Dissolution Inhibition
[0035] Gold dissolution rates were monitored in the presence and
absence of the candidate drainage aids. The technique used was
similar to that described in U.S. Pat. No. 5,484,470. Gold metal
films sputtered onto 1/4" cm.times.2" plastic film backings were
prepared. The gold film was stripped from the film in the presence
of cyanide at pH 10.5 in a magnetically stirred UV-Vis cuvette.
Gold dissolution was monitored during the stripping using a
Au(CN).sup.-.sub.2 absorption peak at 240 nm. The absorbance at
this wavelength is linearly related to Au(CN).sup.-.sub.2 for
concentrations up to 20 ppm.
[0036] The experiment was run for 15 minutes. Initially, no
surfactant was added to the cuvette. After 1 minute, monitoring of
the rise in the AU(CN).sup.-.sub.2 absorbance peak began at one
minute intervals until 6 minutes. At 7 minutes, 100 ppm of
surfactant was added to the solution using a microliter pipette.
Monitoring the Au(CN).sup.-.sub.2 continued until 15 minutes. The
slope of the increase in absorbance taken from 7 to 10 minutes was
expressed as a percentage of the slope for 1 to 6 minutes.
Typically, the slope for a blank (no surfactant solution) was
slightly (10%) lower than that at the start of the experiment. A
suppression of the gold dissolution by a surfactant was seen as a
further decrease in the ratio (or percentage) of the slopes after
and before surfactant addition.
[0037] Examples of the four top classes of surfactants from the
capillary rise experiments were compared to blank (no surfactant)
solution. The materials included ethoxylated 2-decanol, fatty acid
sulfo salt; LD-450 (Stephan-Proprietary); and sodium dioctyl
sulfosuccinate. Because of claims made in U.S. Pat. No. 4,929,274
about the hydrolyzability of the sodium dioctyl sulfosuccinate,
tests were done using both hydrolyzed (prepared by allowing an
alkaline solution to sit overnight) and unhydrolyzed (freshly
prepared) solutions. The results are shown in the table below:
3 C-3 C-4 Blank X-1 C-1 C-2 (fresh) (aged) Average % of slopes 89%
81% 9% 9% 45% 44% (8 to 15 minutes)/ (1 to 6 minutes) Standard
deviation of 11% 5% 20% 21% of ave % % decrease in dissolution 0%
9% 90% 90% 50% 51% rate from blank {Ave %.sub.sample - Ave
%.sub.blank}/Ave %.sub.blank
[0038] Of the tested materials only X-1 showed acceptable
performance. Both C-1 and C-2 had a dramatic inhibitory effect on
dissolution, reducing the dissolution rate by 90% compared to the
blanks. C-3 reduced the gold dissolution by about 50%. Aged
(hydrolyzed) C-4 had the same effect as fresh C-3. X-1 had no
statistically significant impact on the gold dissolution rate.
[0039] X-1=ethoxylated 2-decanol
[0040] C-1=LD450--Stepan-proprietary
[0041] C-2=fatty acid sulfo salt
[0042] C-3=sodium dioctyl sulfosuccinate
[0043] C-4=hydrolyzed sodium dioctyl sulfosuccinate
Example 3
[0044] Clear Solution Cyanide Reactivity
[0045] Experiments were completed evaluating the effect of the same
four surfactants on cyanide consumption after 1 and 24 hours.
Testing was conducted at 50 and 100 ppm of these surfactants (as
actives) in the presence of 25 ppm cyanide (much higher
surfactant/cyanide ratios than expected in an actual application).
The experiments were done in stock solutions of 1 g/L Ca with 400
ppm of sulfate added, adjusted to pH 10.5.
[0046] Analysis of free CN was done using a LACHAT Flow Injection
Analyzer and an analysis method which converts CN in an alkaline
media to cyanogen chloride, CNCl, by reaction with chloramine-T at
pH<8. The CNCl then forms a red-blue dye by reacting with a
pyridine-barbituric acid reagent. The resulting color is read at
570 nm. The results are shown below:
4 Exposure time, hrs 1 24 surfactant concentration, ppm 50 100 50
100 C-3 96% 96% 95% 96% C-1 100% 96% 96% 98% C-2 96% 96% 95% 96%
X-1 98% 94% 96% 91%
[0047] Within the error of the cyanide analysis methodology
(.+-.10%), none of the surfactants had a negative effect on cyanide
consumption.
Example 4
[0048] Activated Carbon Gold Uptake
[0049] Similar types of experiments have been reported in U.S. Pat.
No. 5,827,348.
[0050] Stock solutions of gold cyanide were prepared by dissolving
0.900 g of KAu(CN).sub.2 and 12.6 g. of NaCN (95%) in DI water to
55 liters. The solution pH was adjusted to pH 10.5. After gold
analysis, the stock solutions were diluted further with DI water to
adjust the gold concentration to 10.25 mL. This gives a test
solution concentration of 10 ppm and approximately 200 ppm NaCN.
Stock solutions of the reagents were prepared to contain 2000 ppm
of active surfactant in a 500 mL solution. The pH was adjusted to
pH 10.5 with lime before final dilution. Surfactants prepared using
this procedure included C-3, X-2, C-5, C-1, X-3, X-1, C-6, C-2,
X-4, C-7, C-8.
[0051] For a test, the specified volume of 10.25 ppm gold stock
solution is placed in a 2.5 liter bottle along with the required
amount of surfactant stock solution to obtain the desired
surfactant concentration (0 ppm, 10 ppm, 50 ppm). Additional DI
water was added to adjust the gold concentration to 10 ppm. The
required amount of preattrited (+20 mesh) Calgon GRC-22 carbon was
added. For each surfactant concentration, five solution to carbon
ratios were tested as shown in the table below. The ratio of gold
solution volume to weight of carbon ("carbon loading") is an
important factor in representing what might happen in a carbon
stripping column. As gold is progressively loaded onto a carbon
column, a profile of loading values is created across the column.
It is important to know if an inhibitor of the gold adsorption
process affects the process at both low and high solution to carbon
ratios.
5 Gold Reagent Total Solution Stock Test Solution to Sol. Carbon
Conc. Volume Carbon Test mL g mg/L mL Ratio 1 1500 0.3 10 1538 5125
2 1000 0.4 10 1025 2563 3 500 0.4 10 513 1281 4 500 0.8 10 513 641
5 450 1.5 10 461 308
[0052] Each bottle was rolled for 48 hours then a sample of the
solution was filtered and analyzed for gold expressed as ppm of
gold in solution. The carbon with loaded gold was fire-assayed for
its gold content expressed as kilograms of gold per metric ton of
carbon. A plot of results (carbon loading vs. solution gold
concentration) is shown in FIG. 1.
[0053] Reference numerals used in FIG. 1 are as follows:
[0054] 20--control
[0055] 22--C-8; di-tridecyl sodium sulfosuccinate
[0056] 24--C-6; dihexyl sodium sulfosuccinate
[0057] 26--C-2; fatty acid sulfo salt
[0058] 28--C-3; sodium dioctyl sulfosuccinate
[0059] 30--C-1; LD 450 Stepan proprietary
[0060] 32--C-5; ammonium lauryl sulfate/ammonium laureth
sulfate/cocoamido propyl betaine/cocamide dea
[0061] 34--X-1; ethoxylated 2-decanol
[0062] 36--X-3; isodecyl alcohol ethoxylate
[0063] The results clearly show that all surfactants (with the
possible exception of C-8, di-tridecyl sodium sulfosuccinate) have
a detrimental effect on carbon loading at 50 ppm. Running the same
experiments at 10 ppm show a decreased but still significant impact
of surfactant on recovery.
Example 5
[0064] Uptake of the Drainage Paid by Gold Ore
[0065] As mentioned above, if the drainage aid had a detrimental
effect on activated carbon gold uptake, it is still possible that a
drainage aid could be successfully applied if it were adsorbed onto
the ore in the process of improving drainage. Tests were conducted
with the four most cost-effective drainage aids to determine their
retention on a representative oxide gold ore from Northern
Nevada.
[0066] As with the capillary rise experiments, the uptake
experiments were done using an 18.times.30 mesh sieved ore. The ore
was prepared by first sieving to this size fraction. The
18.times.30 fraction was washed extensively with tap water to
remove any embedded clays. Material was dried overnight at
105.degree. C. and then stored in environmental chamber at 50%
humidity and 25 C.
[0067] A 1 cm.times.30 cm plastic tube was prepared with a fine
stainless steel mesh pushed to the bottom of the tube to hold the
ore in place. Ore was filed to a height of 10 cm in the tube and 10
ppm surfactant solutions were dripped onto the ore at a pumping
rate (3.24 ml/min) corresponding to a typical heap leach
application rate of 0.005 gpm/ft.sup.2. Buffer solution was the
same as the capillary rise experiments, 0.1 gL Ca with 400 ppm
sulfate added, adjusted to pH 10.5 with sulfuric acid.
[0068] The experiments were run over 66 hours during which a
composite sample of the effluent solution was collected.
[0069] Uptake of surfactant by the ore was measured using total
carbon after acidification with a Shimadzu Model TOC-5000 Carbon
Analyzer calibrated using potassium hydrogen pthalate standards.
Recovery was calculated by the following equation:
(Effluent Total Carbons.sub.surfactant-Influent Total
Carbon).sub.surfactant-(Effluent Total Carbon.sub.blank-Influent
Total Carbon).sub.blank
[0070] Results are shown in the graph shown in FIG. 2.
[0071] Reference numerals used in FIG. 2 are as follows:
6 2 C-3 4 X-2 2-decylethoxy Poly (ethyleneoxy) ethanol 6 C-5 8 C-1
10 X-1 12 C-6 14 C-2 16 X-4 ethoxylated alcohol 18 C-7 sodium
dodecyl diphenyl oxide disulfonate
[0072] Combining the results of all five of the above examples, one
class of compounds successfully meets the desired criteria for a
gold heap leach application. Specific commercial products of this
class (CAS # 61827-42-7) which demonstrated efficacy include the
following:
7 McCutcheon Description description Analysis results Ethoxylated
Isodecyl alcohol A heavily branched ethoxylated aliphatic
ethoxylate aliphatic alcohol. The average carbon alcohol chain
length is 7.3 C's/molecule. The average ethoxylation is 4.5 moles/
molecule (X-3) Ethoxylated 2-decylethoxy a heavily branched
ethoxylated aliphatic aliphatic poly(ethyleneoxy) alcohol. The
average carbon chain alcohol ethanol length is 6.7 C's/molecule.
The average ethoxylation is 5.3 moles/molecule (X-1) Ethoxylated
Ethoxylated a heavily branched alcohol ethoxylated aliphatic
2-decanol aliphatic alcohol. The average carbon alcohol chain
length is 10.5 C's molecule. The ethoxylation is 3.5 moles/molecule
(X-2) Ethoxylated Ethoxylated a straight chain ethoxylated alcohol
aliphatic alcohol aliphatic alcohol. The average carbon alcohol
chain length is 12.2 C's/molecule. The average ethoxylation is 4.0
moles/ molecule (X-4)
[0073] The invention is therefore applicable to enhance drainage or
percolation of lixiviant solutions such as the cyanide based
lixiviant solutions through a heap of mineral ore. The invention
performs particularly well in the leaching of gold from gold ore
with a cyanide/oxygen/lime lixiviation system operated at a pH of
from about 9-11.5 but is also applicable to other heap mining
environments such as precious metal heap mining in general and
copper heap mining.
[0074] While the present invention has been described with respect
to particular embodiments thereof, it is apparent that other forms
and modifications of the invention will be obvious to those skilled
in the art. The appended claims and this invention generally should
be construed to cover all such obvious forms and modifications
which are within the true spirit and scope of the present
invention.
* * * * *