U.S. patent application number 13/992713 was filed with the patent office on 2014-10-23 for electrorecovery of gold and silver from thiosulphate solutions.
The applicant listed for this patent is Alejandro Rafael Alonso Gomez, Ricardo Benavides Perez, Gretchen Terri Lapidus Lavine, Carlos Lara Valenzuela. Invention is credited to Alejandro Rafael Alonso Gomez, Ricardo Benavides Perez, Gretchen Terri Lapidus Lavine, Carlos Lara Valenzuela.
Application Number | 20140311896 13/992713 |
Document ID | / |
Family ID | 45558361 |
Filed Date | 2014-10-23 |
United States Patent
Application |
20140311896 |
Kind Code |
A1 |
Lapidus Lavine; Gretchen Terri ;
et al. |
October 23, 2014 |
ELECTRORECOVERY OF GOLD AND SILVER FROM THIOSULPHATE SOLUTIONS
Abstract
The present invention is related to the mining industry and
treatment of mineral and materials that contain gold and silver.
Specifically, it is related to a process to recover gold and
silver, from copper thiosulfate solutions with a autogenerated
electrolysis process. The advantages of the present invention,
relative to those of the state of the technique, reside in the
increased velocity compared with cementation using copper, without
employing electric current. Our process is characterized by
operating in an electrochemical autogeneration cell, in which the
anode and cathode are connected in short circuit and the anodic and
cathodic compartments are separated by an ion exchange membrane.
Additionally, using a copper anode and the stripped solution as the
anolyte, the levels of soluble copper are maintained stable,
conserving the leaching power of the thiosulfate solutions, whereby
it is possible to recycle them back to the leaching stage.
Inventors: |
Lapidus Lavine; Gretchen Terri;
(Colonia Santa Ursula, MX) ; Alonso Gomez; Alejandro
Rafael; (Colonia Estado De Mexico, MX) ; Benavides
Perez; Ricardo; (Coahuila, MX) ; Lara Valenzuela;
Carlos; (Col. Torreon Residencial, MX) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Lapidus Lavine; Gretchen Terri
Alonso Gomez; Alejandro Rafael
Benavides Perez; Ricardo
Lara Valenzuela; Carlos |
Colonia Santa Ursula
Colonia Estado De Mexico
Coahuila
Col. Torreon Residencial |
|
MX
MX
MX
MX |
|
|
Family ID: |
45558361 |
Appl. No.: |
13/992713 |
Filed: |
December 9, 2011 |
PCT Filed: |
December 9, 2011 |
PCT NO: |
PCT/MX11/00150 |
371 Date: |
November 28, 2013 |
Current U.S.
Class: |
204/252 |
Current CPC
Class: |
C25C 7/06 20130101; Y02P
10/20 20151101; Y02P 10/236 20151101; C25C 7/00 20130101; C25C 1/22
20130101; C25C 1/20 20130101 |
Class at
Publication: |
204/252 |
International
Class: |
C25C 7/06 20060101
C25C007/06; C25C 1/22 20060101 C25C001/22; C25C 1/20 20060101
C25C001/20 |
Foreign Application Data
Date |
Code |
Application Number |
Dec 9, 2010 |
MX |
MX/A/2010/013510 |
Claims
1.-3. (canceled)
4. An autogenerated electrolysis cell for the electrorecovery of
silver from thiosulfate leaching solutions comprising a cathodic
and an anodic compartment separated by a ion exchange membrane, a
copper anode and a titanium cathode, connected in short circuit, a
catholyte consistent in a pregnant leaching solution and an
anolyte, stripped of its gold and silver in the cathodic
compartment.
5. A silver electrorecovery process from thiosulfate leaching
solutions, in an autogenerated electrolysis cell, consisting of the
following: in the first stage, feed the cathodic compartment with a
solution proceeding from the leaching step, feed to the anodic
compartment a synthetic solution similar to the catholyte, but
without dissolved silver, maintain the operation of the
electrolysis cell during a specified time, mechanically recover the
silver deposit by being performed in an autogenerated electrolysis
cell as was stated in the previous claim; the predetermined time
that the cell operates is that which permits the silver
concentration in the catholyte and the copper concentration in the
anolyte to achieve a predetermined level; successive stages follow
the first, in which the anolyte is the catholyte after having been
stripped of silver and the leaching solution is the anolyte after
having been enriched with copper ions.
6. The silver electrorecovery from thiosulfate leach solutions of
claim 5, wherein the predetermined level of the copper
concentration is adequate, on one hand, to maintain the potential
difference necessary from 4 to 7 g/L of dissolved copper for the
autogenerated electrodeposit and, on the other, for silver
leaching.
Description
FIELD OF THE INVENTION
[0001] The present invention is related to the mining industry and
treatment of mineral and materials that contain gold and silver.
Specifically, it is related to a process to recover gold and
silver, from copper thiosulfate solutions with a autogenerated
electrolysis process, in which the metallic values are recovered
from the rich solution in the cathodic compartment. The barren
solution is then used as the anolyte, re-establishing the copper
concentration needed to be recycled back to the leaching stage.
BACKGROUND OF THE INVENTION
[0002] At present, gold and silver are obtained from their
minerals, concentrates and other materials, using different
processes. These processes are in function of the nature of the
gold and silver containing material, as well as their grade.
Accordingly, if it is a high grade material, smelting is employed.
On the other hand, if the material contains only small amounts of
gold and silver, a hydrometallurgical treatment is usually selected
(leaching).
[0003] Since the end of the XIX century, the process based on
cyanide solutions, has been successfully used for leaching gold and
silver from low grade materials. However, cyanide solutions are
highly toxic. Additionally, some materials are refractory towards
this process or contain a high copper concentration, which consumes
large amounts of cyanide during leaching, as the following article
teaches [G. Senanayake, Gold leaching in non-cyanide lixiviant
systems: critical issues on fundamentals and applications, Mineral
Engineering 2004(17)785-201].
[0004] Several alternatives to cyanidation have been proposed,
among them is the method based on thiosulfate. This chemical system
has been utilized, on a pre-industrial scale, since the 1920's
[Fathi Habashi. A Textbook of Hydrometallurgy, 2nd edition (Second
ed). Quebec City, Canada: Metallurgie Extractive Quebec, 1999].
However, the elevated reagent consumption, caused by its oxidation
to tetrathionate and even sulfate by the cupric ions (Cu(II)), has
hindered its large scale implementation.
[0005] Recently, this inconvenience has been solved with additives
that modify the oxidative properties of the cupric ions, [Gretchen
Lapidus-Lavine, Alejandro Rafael Alonso-Gomez, Jose Angel
Cervantes-Escamilla, Patricia Mendoza-Munoz and Mario Francisco
Ortiz-Garcia, "Mejora al Proceso de Lixiviacion de Plata de
Soluciones de Tiosulfato de Cobre (Improvement to the Silver
Leaching Process with Copper Thiosulfate Solutions)"], Mexican
patent granted the 26 Feb. 2008, MX 257151], by limiting
thiosulfate consumption to less than 5% of its initial value
[Alonso-Gomez, A. R. and Lapidus, G. T. (2009), "Inhibition of Lead
Solubilization during the Leaching of Gold and Silver in Ammoniacal
Thiosulfate Solutions (effect of phosphate addition)",
Hydrometallurgy, 99(1-2), 89-96].
[0006] On the other hand, the recovery of values from the
thiosulfate baths has been performed principally by cementation, in
which a reducing agent, usually a metal, is added to generate a
redox reaction which produces gold and silver in their metallic
state. A disadvantage of this technique is that it is not possible
to adequately control the reductive capacity of the agent, which
causes a poor separation efficiency, obtaining gold and silver
contaminated with copper.
[0007] Direct electrodeposition, used as a separation method, is a
viable option, including from solutions with low concentrations of
gold and silver, even when the copper ion concentration is more
than 50 times greater than that of silver and over 100 times that
of gold [Alonso-Gomez, A. R., Lapidus, G. T. and Gonzalez, I.,
"Proceso de Lixiviacion y Recuperacion de Plata y Oro con
Soluciones de Tiosulfato Amoniacales de Cobre, solicitud
PCT/MX2009/000022, fecha 14 Mar. 2008 (WO20097113842, publicada 17
Sep. 2009)]. To attain efficiencies greater than 50%, a rotating
cylinder electrode was employed in a reactor with separate anodic
and cathodic compartments in order prevent the oxidation of the
thiosulfate and the re-oxidation of the deposited gold and silver.
In this type of cell, deposits were obtained with less than 2%
impurities [Alonso, A. R., Lapidus, G. T. and Gonzalez, I. (2008),
"Selective silver electroseparation from ammoniacal thiosulfate
leaching solutions using a Rotating Cylinder Electrode reactor
(RCE)", Hydrometallurgy, 92 (3-4), 115-123].
[0008] Despite the excellent results obtained with this type of
reactor, the relatively low current efficiencies can be considered
a disadvantage due to the high cost of electricity.
[0009] Recently, autogenerated electrolyses have been explored.
These consist of a two electrode cell, in which metal ions are
reduced and deposited on the cathode, differing from a traditional
current-driven electrodeposition, in the fact that the anode is
made of a material whose oxidation potential is less than the
reductive potential of the metal ions and therefore does not
require addition electricity to drive the process. Upon anode
oxidation, an electron flow travels through an electrical conductor
to the cathode, where the electrodeposit occurs. For this reason,
the anodic and cathodic compartment must be separated by an ion
exchange membrane.
[0010] Autogenerated electrolysis shares with cementation the
principle that the oxidation of a metal is used to reduce another
more noble.
[0011] However, in autogenerated electrolysis, the separated anodic
and cathodic compartments allow, on one hand, the election of the
substrate upon which the metal is deposited (similar to a
conventional electrolysis), eliminated the contamination of the
deposit. On the other, because the anode is in contact with a
solution which is different from the one that contains the metallic
ions to be deposited, it is also possible to tailor the anolyte
composition according to the requirement of the process and in this
manner modulate the reductive power of the system.
[0012] This procedure is adequate for gold and silver recovery from
thiosulfate solutions, eliminating the need for electrical energy
through the oxidation of a metallic anode. It is important to
mention that the election of the anode material will depend on the
difference between the redox potentials of the anode and cathode,
as well as the advantages that the dissolution of a certain
material might offer to the process. This should result in lower
process costs.
OBJECTIVES OF THE INVENTION
[0013] One objective of the present invention is to provide a
selective separation process for gold and silver from thiosulfate
solutions, at an increased velocity compared with copper
cementation, without the use of electrical current.
[0014] Another objective is to accomplish the aforementioned task
using the barren solution as the anolyte, conserving in this manner
the level of soluble copper, in order to maintain the composition
of the thiosulfate solution so that it can be recycled back to the
leaching stage.
[0015] Other objectives and advantages that apply the principles
and are derived from the present invention may be apparent from the
study of the following description and diagrams that are included
here for illustrative and not limitative purposes.
BRIEF DESCRIPTION OF THE INVENTION
[0016] The present invention is designed to solve the problem of
gold and silver separation from copper thiosulfate leaching
solutions, providing an improvement over the traditional separation
methods (cementation and external current-driven electrolysis).
This improvement is characterized by the use of a novel
autogenerated electrolysis process, employing a commercial copper
sheet as the anode and a titanium cathode, in a reactor with anodic
and cathodic compartments separated by ion exchange membrane which
prevents the contamination of the thiosulfate solution.
[0017] The membrane achieves the purpose of separating the anodic
and cathodic sections, to prevent the solutions used in each
compartimentsto from mixing. This is important to avoid cementation
of gold and silver on the copper surface, which slows the process
and contaminates the product. On the other hand, it is important to
consider that the rich (pregnant) solution (located in the cathodic
compartment) is poor in copper due to the nature of the leaching
process, and its oxidation power is limited; this allows an
efficient gold and silver deposition because there is little
re-dissolution. By preventing contact of the pregnant solution with
the copper anode, the copper concentration in this solution is kept
low and for this reason the membrane plays a double role.
[0018] In order to better understand the characteristics of the
invention, the following description is accompanied by diagrams and
figures, which form an integral part of the same and are meant to
be illustrative but not limitative and are described in the
following section.
BRIEF DESCRIPTION OF THE DRAWINGS
[0019] FIG. 1 is a schematic diagram of the process for
electrodepositing gold and silver in an electrochemical
autogeneration cell.
[0020] FIG. 2 shows a schematic diagram of the electrochemical
autogeneration cell
[0021] FIG. 3 corresponds to a graph indicating the change in the
silver concentration during the electrolysis performed in Example
1.
[0022] FIG. 4 is a diagram of the recirculation process of lots A
and B of the leaching solution, used in Example 2.
[0023] FIG. 5 shows a graphic representation of the silver
concentration change during the first leach LA1, performed on lot A
(solid lines and markers), as well as during the first
autogenerated electrolysis Ca1 (dotted line, hollow markers).
[0024] FIG. 6 is a series of graphs that compare the quantity of
silver remaining in solution throughout the electrolyses Ca1, Ca3
and Ca5 performed on lot A (markers .smallcircle., .quadrature. and
.DELTA., respectively).
[0025] FIG. 7 shows the lead concentration during the first leach
LA1 performed on lot A.
DETAILED DESCRIPTION OF THE INVENTION
[0026] The process referred to in the present is performed
according to the illustration in FIG. 1: [0027] An ammoniacal
thiosulfate solution pregnant with gold and silver ions,
originating from the leaching stage (100) and after having been
filtered (200), is introduced into the cathodic compartment (310)
of the electrochemical reactor (300). [0028] The electrochemical
reactor possesses and ion exchange membrane (350) that separates
the cathodic (310) and anodic (320) compartments. [0029] A
solution, stripped of the precious metals (360), is introduced into
the anodic compartment of the electrochemical reactor (320). [0030]
The cathode (330) and anode (340) are connected in short circuit
(360) [0031] The solutions in the cathodic and anodic compartments
(310 and 320) are stirred during the entire time of the
electro-deposition process that could range from 1/2 to 4 hours.
[0032] Once the electrodeposition process has finished, the cathode
(330) is removed from the reactor and mechanically scraped to
obtain the gold and silver metals. The solution in the cathodic
compartment is placed in the anodic compartment, ready for the next
electrodeposition cycle (360). [0033] The solution in the anodic
compartment (320), having been enriched with the necessary reagents
(copper ions), is recycled back to the leaching stage (140). [0034]
The leaching reactor is charged with fresh leachable solid material
(160). Fresh solution (150) is only fed to the leaching reactor in
the initial cycle.
[0035] The operation of the electrochemical autogeneration reactor
is represented in FIG. 2: [0036] The reactor consists a single
preferentially rectangular reservoir (400), although it is not
limited to said configuration. [0037] The reactor is divided in at
least two compartments, although it may have more. [0038] The
compartments are divided by a cationic membrane (450) that hinders
the passage of silver-thiosulfate and gold thiosulfate ions from
the cathodic (410) to the anodic (430) compartment. [0039] The
cathode (420) can be a titanium sheet or screen. [0040] The anode
(440) is a copper sheet. [0041] Once the solutions are charged to
the reactor, the electrodes are connected in short circuit (460).
[0042] The solutions are mechanically stirred (470) during the
electrodeposition time. [0043] The cathode should be mechanically
treated to remove the gold and silver deposit. [0044] The anode
should be changed periodically, since it is consumed during the
electrodeposition process.
EXAMPLES
Example 1
[0045] To better understand the invention, one of the many
experiments is detailed as an example, which employs a reactor such
as that schematized in FIG. 2. A 60 cm.sup.2 (exposed geometrical
area) titanium plate was used as the cathode and a copper plate
with the same exposed area was the anode. A synthetic solution,
prepared with the composition that appears in Table 1, which
simulates real solutions after the leaching stage, was introduced
into the cathodic compartment (410).
TABLE-US-00001 TABLE 1 Composition of the solution used in the
cathodic compartment of the autogeneration electrolytic reactor.
Component Composition (mol/L) Ag(I) 1 .times. 10.sup.-3
Na.sub.2S.sub.2O.sub.3 0.2 CuSO.sub.4 0.05 EDTA.sup.4- 0.025
(NH.sub.4).sub.2(HPO.sub.4) 0.1 NH.sub.3 0.6
[0046] A synthetic solution, poor in copper ions, whose composition
is detailed in Table 2, was placed in the anodic compartment
(430).
TABLE-US-00002 TABLE 2 Composition of the solution used in the
anodic compartment of the autogeneration electrolytic reactor
Component Composition (mol/L) Na.sub.2S.sub.2O.sub.3 0.2 CuSO.sub.4
0.025 EDTA.sup.4 0.025 (NH.sub.4).sub.2(HPO.sub.4) 0.1 NH.sub.3
0.6
[0047] The solutions were prepared with analytical grade reagents
and deionized water (1.times.10.sup.10 M.OMEGA.cm.sup.-1). Once the
solutions were placed in their respective compartments, the
electrodes were connected in short circuit. Stirring in both
compartments was maintained during the electrodeposition process.
Samples of the solution were taken every 20 minutes for four hours,
after which time the test was detained. The samples were analyzed
for silver and copper with atomic absorption spectrometry.
[0048] In FIG. 3, a graphic representation is shown of results of
the electrodeposition process, performed in the reactor of FIG. 2.
The decrease in silver concentration is constant from the beginning
of the electrolysis, attaining 50% of its initial value after only
60 minutes. Subsequently, the descent is slower, typical of first
order reaction kinetics in a batch reactor, reaching 4% after 4
hours.
[0049] On the other hand, the copper concentration in the cathodic
compartment remained constant during the electrolysis (data not
shown), indicative of a selective silver deposit.
[0050] In order to determine the leaching power of the recycled
solution, after having stripped the silver ions in the
autogeneration process, experiments were performed with real
leaching solutions, whose results are shown in the following
example.
Example 2
[0051] As was shown in FIG. 1, the recirculation scheme used in the
present invention employs two lots of the thiosulfate leaching
solution, which are alternated in each one of the reactor
compartments (FIG. 2), as was mentioned in the Detailed Description
section. The same reactor was used as in Example 1, with a copper
sheet as the anode and a titanium sheet as the cathode, both with
an exposed geometric area of 60 cm.sup.2.
[0052] To better understand the process, a block diagram is shown
(FIG. 4), in which the passage through the process of lots A and B
of the leaching solution are shown, without the solid streams. By
observing only lot A (solid lines), stream Al enters the first
leach (LA1), and after separating out and discarding the solid
residue, stream A2 (pregnant solution) enters the cathodic
compartment (Ca1) of the electrolytic reactor, where the silver
electrodeposition takes place; only in this stage of the process is
synthetic solution (Stream S1) used in the anodic compartment
(An1).
[0053] Stream A3, stripped of its values, is placed in the anodic
compartment of the reactor (An2), where the first electrodeposit
from the pregnant solution lot B (Ca2) occurs.
[0054] Stream A4 is sent back to a new leaching stage (LA2), where
it is contacted with fresh mineral. The pregnant solution (A5) is
sent to the electrochemical reactor for silver recovery in the
cathodic compartment (Ca3). In this case, the anodic compartment is
occupied by the solution of lot B originating from Ca2.
[0055] Subsequently, the process is repeated, passing the stream A6
to the anodic compartment (An4) during the electrodeposition of B5
(Ca4).
[0056] Finally, stream A7 is again introduced into the leaching
stage with fresh mineral, obtaining a pregnant solution in stream
A8.
[0057] The route that lot B follows is practically the same as lot
A. Table 3 shows the initial composition used in the leaching
solutions for both lots; the volume of each one was 250 mL. Each
leach used 2.5 g of a lead concentrate from Fresnillo mine, whose
silver content is 24 kg/ton with approximately 25% of lead.
TABLE-US-00003 TABLE 3 Composition of the leaching solutions used
in lots A and B. Component Composition (mol/L)
Na.sub.2S.sub.2O.sub.3 0.2 CuSO.sub.4 0.05 EDTA.sup.4 0.025
(NH.sub.4).sub.2(HPO.sub.4) 0.1 NH.sub.3 0.6
[0058] In FIG. 5 the silver concentration during the first leach is
shown (solid lines and markers), as well as the electrodeposition
process in the cathodic compartment Ca1 (dashed line and hollow
markers). It is important to consider that the silver content in
this mineral is very high, explaining the reason for extractions
above 200 ppm, a value close to the solubility limit for this metal
ion in thiosulfate solutions. These high values of silver in
solution are the reason that the silver concentration only
decreases to 50% of its original value in the autogenerated
electrolysis (Ca1). Additionally, because of the high dissolved
lead concentration (200 ppm), there is competition with the silver
in the electrodeposition process. This could represent an enormous
loss in the traditional cyanidation process; however, in this case,
the thiosulfate solution is recycled back to the leaching stage,
the gold and silver remaining in solution are separated in
subsequent cycles.
[0059] In the subsequent leaches performed with lot A, within the
recirculation scheme, extractions similar to that observed in LA1
were achieved (approximately 200 ppm silver ions). The results
obtained in leaches with lot B are very similar, again observing
the solubility limitation of 200 ppm Ag(I). These results are
significant since they show that the thiosulfate solution maintains
its leaching power after three cycles of
leaching-electrodeposition, in which no additional reagent was
added to make-up the solutions.
[0060] Finally, a comparison of the change in silver concentration
during the autogenerated electrolyses for lot A is shown in FIG. 6.
The electrolyses Ca3 and Ca5 present similar behavior to that
registered for Ca1 (first electrolysis of lot A). The quantity of
silver that remains after the electrolyses Ca2 and Ca3 is similar,
indicating that there is no accumulation of silver ions in the
recycling process; in other words, the silver extracted in the
leach is separated in the autogenerated electrolysis stage. The
behavior of lot B during the electrolyses (data not shown here) is
practically the same exhibited by lot A.
[0061] It is important to remember that the mineral leached was a
lead concentrate, the reason for which an important quantity of
this metal dissolved, despite the use of phosphate to inhibit this
process. In FIG. 7, the lead concentration is shown during the
first leach of lot A, where it can be appreciated that the
concentration of Pb(II) is similar to that of silver. Also, in the
corresponding electrolysis, the lead concentration decreases
approximately 35% during the first 20 minutes. This competition
(inexistent in Example 1 with the synthetic solution) could be the
cause that the silver recovery did not exceed 60%. Additionally, it
must be considered that treating such high grade silver minerals
would originate solubility problems during leaching, as well as
electrode saturation in the electrodeposition stage. In these
cases, it is possible to increase the thiosulfate concentration to
increase the solubility of the Ag(S.sub.2O.sub.3).sub.2.sup.3-
complex, even though a larger electroactive area for the cathode
would be required.
[0062] In any event, these examples are evidence that the use of a
autogenerated electrolysis reactor is viable within a
leaching-electroseparation scheme, maintaining the leaching
capacity of the thiosulfate solution.
* * * * *