U.S. patent application number 10/567108 was filed with the patent office on 2007-11-29 for process for gold and silver leaching with thiourea solutions.
Invention is credited to Ita Giron Bautista, Maria Elena Poisot Diaz, Maria Concepcion Lopez Escutia, Mercedes Teresita Oropeza Guzman, Fernando Rodriguez Hernandez, Gretchen Terri Lapidus Lavine, Ignacio Gonzalez Martinez.
Application Number | 20070272055 10/567108 |
Document ID | / |
Family ID | 34374329 |
Filed Date | 2007-11-29 |
United States Patent
Application |
20070272055 |
Kind Code |
A1 |
Lavine; Gretchen Terri Lapidus ;
et al. |
November 29, 2007 |
Process for Gold and Silver Leaching with Thiourea Solutions
Abstract
The present invention concerns the mining and mineral treatment
industry. Specifically, it relates to a solution composition that
permits the use of thiourea. Specifically, the patent refers to a
process to form a solution that improves, on one hand, the velocity
of gold and silver extraction, from minerals and other materials
that contain them, improving the stability of the thiourea in the
leaching solution and, on the other, the direct electrorecovery of
said metals from the aforementioned solution. The invention
consists of the leaching solution that, beforehand or
simultaneously, has been subjected to a controlled
electro-oxidation to produce formamidine disulfide (FADS) which
acts as an oxidizing agent for the mineral phases that contain the
gold and silver. In the preferred mode, the FADS is present as 10
to 30% of the total thiourea contained in the solution and the
electrodeposition of the metals is performed in the same cell
(cathodic compartment) in which the FADS is formed (anodic
compartment).
Inventors: |
Lavine; Gretchen Terri Lapidus;
(Mexico, MX) ; Escutia; Maria Concepcion Lopez;
(San Luis Potosi, MX) ; Guzman; Mercedes Teresita
Oropeza; (Dawrne, CA) ; Martinez; Ignacio
Gonzalez; (Mexico, MX) ; Hernandez; Fernando
Rodriguez; (Mexico, MX) ; Diaz; Maria Elena
Poisot; (Mexico, MX) ; Bautista; Ita Giron;
(Mexico, MX) |
Correspondence
Address: |
CONNOLLY BOVE LODGE & HUTZ LLP
1875 EYE STREET, N.W.
SUITE 1100
WASHINGTON
DC
20036
US
|
Family ID: |
34374329 |
Appl. No.: |
10/567108 |
Filed: |
July 30, 2004 |
PCT Filed: |
July 30, 2004 |
PCT NO: |
PCT/MX04/00054 |
371 Date: |
August 6, 2007 |
Current U.S.
Class: |
75/303 ;
75/392 |
Current CPC
Class: |
Y02P 10/234 20151101;
C22B 3/045 20130101; C22B 11/04 20130101; C25C 1/20 20130101; Y02P
10/20 20151101; C22B 3/1625 20130101 |
Class at
Publication: |
075/303 ;
075/392 |
International
Class: |
C22B 3/16 20060101
C22B003/16 |
Foreign Application Data
Date |
Code |
Application Number |
Aug 4, 2003 |
MX |
PA/A/2003/006955 |
Claims
1. Improvement of the thiourea solutions to leach silver and gold
characterized by containing a quantity of partially
electro-oxidized thiourea.
2. Improvement of the thiourea solutions to leach silver and gold,
such as was demanded in the previous claim, characterized
additionally by a solution which contains formamidine disulfide
(FADS) produced in-situ by a controlled electro-oxidation in a
proportion of 10 to 30% of the total amount of thiourea contained
in the solution.
3. Improvement of the thiourea solutions to leach silver and gold,
such as was demanded in either of the two previous claims,
characterized additionally because the composition of the thiourea
leaching solution is formulated in the same process in which the
leaching solution is placed in contact with the mineral from which
the metallic values are to be leached.
4. Gold and silver leaching and recovery process with partially
oxidized thiourea characterized as consisting of the thiourea
oxidation by the application of an electrical current in a membrane
cell, where the anodic and cathodic compartments are separated,
before sending the product to the leaching stage and that once
concluded the leaching time, the pregnant solution, separated from
the mineral residue (gangue), enters the cathodic compartment of
the same electrolytic cell in which the thiourea was partially
oxidized in the anodic part, where the metals are reduced and
electrodeposited.
Description
FIELD OF THE INVENTION
[0001] The present invention concerns the mining and mineral
treatment industry. Specifically, it relates to a process that uses
thiourea, electro-oxidized under controlled conditions, to form
in-situ an oxidizing agent capable of dissolving gold and silver
from minerals which contain them and the electrolytic recovery of
said metals in the same process.
BACKGROUND OF THE INVENTION
[0002] At present, the processing of gold and silver ores
fundamentally depends on the form in which they are found in the
mineral, using for this flotation, amalgamation and/or leaching. In
this last technique, the solution employed plays an important role
in the efficiency and environmental impact of the process.
[0003] Basically two commercially implemented leaching techniques
exist: cyanidation produces the highest yields in the majority of
cases, however, with the problems of toxic residues and low
efficiency in refractory minerals (those that contain organic
material, arsenic or manganese) or those that contain high
concentrations of silver sulfides. The use of thiourea in acid
media is a solution to the toxic waste problem since this method
does not employ cyanide salts.
[0004] One of the great obstacles for the industrialization of the
thiourea process to extract silver and gold is the instability of
the thiourea solutions themselves. In the presence of strong
oxidizing agents, such as ferric ion or hydrogen peroxide, the
thiourea irreversibly oxidizes to form a species that is not active
for complexing gold and silver.
[0005] Another impediment related to the use of thiourea is that
the methods employed for precious metal recovery from the leaching
solutions results in their contamination, limiting the possibility
of their recycle within the process.
[0006] Additionally, there exists a disequilibrium with respect to
the utilization of electrical energy; on one side of the
electrolytic cell, the thiourea is being partially oxidized while,
on the other side, separated by a membrane, the generated potential
is being wasted on a sacrifice reduction process.
OBJECTIVES OF THE INVENTION
[0007] One objective of the present invention is to avoid the
harmful effects of the external oxidizing agents on the thiourea
solutions.
[0008] Another consists in recovering the gold and silver in their
metallic form, once extracted from the mineral, in such a way that
the electrical energy is employed in an optimal manner, by
oxidizing part of the thiourea to formamidine disulfide in one of
the compartments (anodic) and, in the other (cathodic), reducing
the dissolved gold and silver reducing to their metallic state.
[0009] 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
[0010] In summary, our invention reduces the inconveniences of the
instability of thiourea in the presence of strong oxidants,
permitting at the same time a clean recovery of the metallic
values, and constitutes an improvement of the solution employed for
leaching gold and silver from minerals and other materials that
contain them, employing thiourea. These improvements are
characterized by the controlled electro-oxidation of 10 to 30% of
the thiourea originally in the solution and the simultaneous
electrowinning of the gold and silver from said solution. On the
other hand, it consists of a process which allows the application
of this solution in a process which extracts and recovers the
metallic values from the minerals which contain them.
[0011] For this purpose, the electrochemical cell is formed by the
cathodic and the anodic compartments, separated by a membrane. In
the anodic compartment, the thiourea is partially oxidized, while
in the cathodic compartment, the metals are reduced to their
metallic form.
[0012] In order to better understand the characteristics of the
invention, the following description is accompanied by a diagram,
which forms an integral part of the same and is meant to be
illustrative but not limitative:
BRIEF DESCRIPTION OF THE DIAGRAM
[0013] FIG. 1 illustrates a block diagram of the process, subject
of the present application.
[0014] To better understand the invention, a detailed description
of the process shown in the diagram will be presented, which is
annexed and meant to be illustrative but not limitative
DETAILED DESCRIPTION OF THE INVENTION
[0015] After having performed many experiments, it was found that
the first oxidation product of the thiourea, formamidine disulfide
(FADS), is capable of selectively oxidizing gold and silver
containing minerals, liberating the metals so that they may complex
with the remaining thiourea and dissolve in the leaching
solution.
[0016] Briefly, the process occurs in the following manner,
observing FIG. 1: an acid thiourea solution (1) is introduced into
the electrolytic cell in the anodic compartment (ANODIC), where the
thiourea is partially oxidized by an electrical current, applied
under controlled conditions, to formamidine disulfide (FADS).
[0017] The larger the quantity of thiourea partially oxidized, the
better the performance of the solution. However, considering the
price of thiourea, it is important to point out that the
electro-oxidation should be executed at low voltages and in a
proportion no greater than 30% with respect to the total quantity
of thiourea in solution in order to achieve the reversible
oxidation of the thiourea.
[0018] The partially oxidized solution (2) is sent to the leaching
reactor, where it is mixed with mineral rich in metal values (3),
during a period stipulated for the gold and silver dissolution.
Once the leaching is finished, the mixture of pregnant solution
(rich in precious metals) and the mineral residue (gangue) (4) is
sent to a solid (5)-liquid (6) separation step [L/S]. The solid
residue is discarded in the conventional manner (tailing dam). On
the other hand, the pregnant solution enters into the cathodic
compartment [CATHODIC] of the electrolytic cell, where the metals
are reduced and electrodeposited. The solution, now with a low
metallic ion content, along with a part of the metallic gold and
silver (7) is sent to another solid (8)-liquid (9) separation stage
[L/S] to recover the values. After purging a small quantity of
solution (10), the resulting stream is made-up with reagents (11)
in order to bring the concentrations of the solution up to the
initial conditions of (1).
[0019] To better understand the invention, one of the many
experiments is included as an example, where the adequate
quantities of FADS generated in-situ and gold and silver recovery
from the pregnant solution (after leaching) were determined.
EXAMPLE
[0020] One liter of aqueous solution containing 15.2 grams of
thiourea, with the pH adjusted to 2 with sulfuric acid, was
subjected to a reversible potential of 500 mV for 2 hours in a
membrane cell, where the anodic and cathodic compartments are
separated, to produce in-situ a quantity of FADS, equivalent to the
oxidation of 18% of the initial thiourea. Following this step, the
solution is placed in contact with 10 grams of sulfide concentrate
which contains approximately 8 wt. % silver and 0.08 wt. % gold for
60 hours. After this time, 95% of the original thiourea was intact
and more than 94% of the silver and 65% of the gold contained in
the mineral were leached. The silver extraction was increased 36%
with respect to the amount leached with an equivalent amount of
cyanide. After removal of the solid residue, the pregnant solution
was subjected to an electrolysis in the cathodic compartment of the
same cell, where the thiourea was oxidized. After 2 hours, 98% of
the silver and 92% of the gold present in the solution was
precipitated.
[0021] The variations that the process might have for the
electro-oxidation of the thiourea could be in the FADS
concentration required in the leaching solution and the percentage
of this component with respect to the quantity of mineral to be
treated and the silver and gold concentrations that these may
contain. However, if at any time an electro-oxidizes solution is
employed, the process will be considered within the scope of the
invention described in the present application
[0022] The invention has been sufficiently described so that a
person knowledgeable in the field could reproduce it and obtain the
results that we mentioned in the present invention. Any person
competent in the field of the present invention is capable of
making modifications not described in the present application,
however, if the application of these modifications on any material
or in the manufacturing process of the same require any part of the
process mentioned in the following claims, the material and process
should be considered included within the scope of the
invention.
* * * * *