ES2327202B1 - GOLD RECOVERY THROUGH MEMBRANES IN CONFIGURATION OF FIBER HOLLOW USING REEXTRACTION BY DISPERSION. - Google Patents

Abstract

Gold recovery by membranes in hollow fiber configuration using re-extraction by dispersion.

The present invention relates to a gold recovery procedure using membranes in hollow fiber configuration using reextraction by dispersion in the presence of one or more of the following metals, Zn Ag, Ni, Fe and Cu, in an aqueous medium of cyanide.

Description

Gold recovery by membranes in hollow fiber configuration using re-extraction by dispersion.

Field of the Invention

The present invention relates to a gold recovery procedure using membranes in hollow fiber configuration using scatter reextraction in the presence of one or more of the following metals: Zn, Ag, Ni, Fe and Cu, in an aqueous medium of cyanide.

Background of the invention

Membrane technologies currently play an increasingly important role in resource recovery, pollution prevention, energy production, monitoring Environmental and quality control (1,2). Between these technologies, liquid membranes (LM) have been shown to have certain potential and currently diverse are being investigated LM configurations for different applications. They are also Under study various SLM techniques (supported liquid membrane) with the flat sheet (FSSLM), hollow fiber (HFSLM) and spirally wound (3-5). Fiber modules hollow and spiral wound are the most suitable for provide high surface area proportions with Regarding volume. The use of the HFSLM technique for metal ion extraction from diluted or concentrated solutions has attracted much attention for its potential for recovery of valuable metals or decontamination of wastewater. Although these techniques represent very attractive possibilities, their lack of stability make its large-scale application not frequent (see Table 1). However, they are continually suggesting improvements and modifications for the use of LM techniques in industrial applications for various sectors.

In view of the above, there is a need to find a more stable technique that can use the advantages of LM techniques and be suitable for industrial use. The technique used in the present invention, called the technique of dispersion reextraction based on a pseudo-emulsion (PEHFSD) (12) meets these criteria It can work using a hollow fiber contactor (The proportion of surface area with respect to volume is high) and performs re-extraction in a single module. This could be done by passing a pseudo-emulsion of organic extractant (in diluent) mixed with the solution of re-extraction which facilitates the re-extraction of the metal ion of the organic part in the re-extraction phase in a single module.

Therefore, this technique facilitates the simultaneous extraction and re-extraction in a single module with a good stability (the pores are always filled with extractant organic with a continuous carrier / extractant flow) being able to use for a micro- or macroconcentration (the HFSLM technique is limited to microconcentration due to loss of organic extractant in the later stages) with a yield consistent for low feed flow rates or higher.

Next, Table 1 shows the main differences between the different techniques mentioned.

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TABLE 1 Why the PEHFSD technique is better than the rest of membrane extraction techniques?

one

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In particular, gold has always been the metal precious best considered due to its wide variety of uses in the industry. Therefore, its recovery from different Sources is of great importance. It can be recovered from stock solutions using well known techniques such as Cementation, carbon adsorption and solvent extraction (6). When activated carbon is used, a lack of selectivity in the presence of mixtures of other metal cyanides (7).

The present invention describes a process of recovery of Au (I) in the presence of other metals in a  aqueous cyanide medium using the indicated technique previously (PEHFSD) using a single hollow fiber module for both extraction and re-extraction.

Brief description of the drawings

Figure 1 shows a diagram of the preparation of the pseudo-emulsion phase, where:

one:

Re-extraction agent

2:

Reextraction agent dispersed in LIX-79 / organic solvent; Y

3:

Agitator

Figure 2 shows a schematic view of the PEHFSD technique, where:

4:

Solution Entry feeding

5:

Solution output feeding

6:

Entrance of pseudo-emulsion

7:

Departure from pseudo-emulsion

8:

Pores of hollow fiber filled with organic solvent

9:

Wall hollow fiber

one:

Reextraction Solution

2:

Drops of the reextraction solution dispersed in Lix-79 / organic solvent

10:

Pa (pressure in the tube wall of the hollow fiber module where pass the feed)

eleven:

Po (pressure on the wall of the hollow fiber module cover by where the pseudo-emulsion passes)

and where Pa> Po.

Figure 3 shows the experimental device of the PEHFSD system for the separation of gold from basic metals (transition metals or heavy metals), where:

12:

hollow fiber contactor

13:

feed pump

14:

bomb of pseudo-emulsion (LIX-79 / n-heptane + NaOH)

fifteen:

power reserve; Y

16:

reserve of pseudo-emulsion + re-extraction agent with mixing device

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Summary Description of the Invention

The present invention relates to a gold recovery procedure (Au (I)) by membranes in hollow fiber configuration using re-extraction by dispersion in the presence of one or more of the following metals: Zn, Ag, Ni, Fe and Cu, in an aqueous medium of cyanide.

Description of the invention

The present invention relates to a gold recovery procedure (Au (I)) by membranes in hollow fiber configuration using re-extraction by dispersion in the presence of one or more of the following metals: Zn, Ag, Ni, Fe and Cu, in an aqueous medium of cyanide.

The chemical process that takes place is the next:

Au (I) ions in alkaline cyanide medium  represented as Au (CN) 2 - form a ionic couple type complex with extractant LIX-79 (N, N, -bis (2-ethyl hexyl) guanidine, RH) dissolved in n-heptane. The extraction reaction is expressed as:

(1) R_ {org} + H + {} aq + Au (CN) 2 {} - {{} aq} \ Leftrightarrow [HAu (CN) 2 R] o K_ {ex}

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Next, the organic complex [HAu (CN) 2 R] o is diffused through the hollow fiber pore towards the interface membrane-pseudo-emulsion, where the Au (I) is reextracted in the phase of pseudo-emulsion after coming into contact with NaOH This reaction is fast and instantaneous. This reaction is express as:

(2) [HAu (CN) 2 R] o + NaOH_ {s} \ Leftrightarrow Au (CN) 2 {} - {{} s + R_ {o} + H 2 O + Na +

In preliminary experiments it was observed that the LIX-79 mediated the transport of Au (CN) 2 - to the neutral receptor aqueous phase. This is probably due to the stability of the ionic couple in the pore of the fiber membrane. However, in the presence of sodium hydroxide in the receptor phase (in this case, the phase of pseudo-emulsion), the Au (CN) 2 - is substituted by OH - in the pseudo-emulsion phase, and increases the effectiveness of the transportation process

As can be seen in the tables later showing the results obtained under different experimental conditions, in these transport studies a way to assess the recovery of gold is based on the so-called "separation factor" of each basic metal, which is defined as (taking as an example the Faith):

2

Experimental conditions Reagents

A stock solution of Au (I) was prepared (1 g / l) from solid KAu (CN) 2 (Johnson Mattey Chemicals, Karlsruhe, Germany) dissolved in NaCN (Merck). He Organic solvent used in the study with PEHFSD was n-heptane, which is an available solvent commercially All chemicals were used as and How they were received. LIX-79 was acquired in a manner Free of Henkel Corp., Canada.

Device for PEHFSD

The hollow fiber device for the stage only one was a commercially available unit available in Hoechst Celanese (now known as Celgard GmbH), Charlotte, NC (Liqui-cel contactor, 8 28 cm 5PCG-259).

Partition coefficient of Au (I), equilibrium of density and viscosity extraction and measurements

The procedure adopted to determine the partition coefficient of Au (I), the value of the constant of extraction K_ {ex} for Au (I) and measurements of the density and viscosity are also described in the state of the technique (8-11).

Preparation and general method of PEHFSD (Figures 1, 2 and 3)

The process of scattering by reextraction with hollow fiber comprises a single membrane module for the extraction and re-extraction and a stirred tank with a device mixture for the preparation of the pseudo-emulsion of LIX-79 / n-heptane with NaOH.

The experimental setup to perform the PEHFSD it consisted of two gear pumps capable of providing flow rates of 1 l / min in both phases, driven by a variable speed DC motor. The organic phase immobilized the Porous fiber wall due to its hydrophobic nature. The interface remained in the pore by applying a pressure higher to the aqueous stream (feed) than to the pseudo-emulsion current. The differential of pressure was always kept below the breaking pressure. In the feed in the aqueous phase, the pressure was maintained 0.2 bar above the pseudo-emulsion phase. The PEHFSD operation was performed with LIX-79 at 12% in n-heptane through feed contact of alkaline cyanide containing gold through the side tube and the  pseudo-emulsion of LIX-79 in n-heptane and 0.2 M NaOH through lateral of the housing in countercurrent mode. The stirring speed is kept at 400 rpm. Figure 3 shows the extraction of the membrane based solvent and re-extraction of Au (I) using a single hollow fiber contactor in recirculation mode. The pseudo-emulsion phase is a 2000 solution ml composed of 1000 ml of 12% LIX-79 in n-heptane and 1000 ml of an aqueous solution of NaOH 0.2 M. The aqueous solution of the feed at the concentration of Desired Au (I) was prepared by taking a suitable aliquot of the stock solution The desired feed pH was adjusted by adding 1 M NaOH solution The 0.2 M NaOH re-extraction solution is used to re-extract the Au (I). In a predetermined time during the experimental process, small aliquots of the feed and tank current of pseudo-emulsion and the concentration of metal by atomic absorption spectrometry (AAS) standard.

HFM modules are marketed by Hoechst Celanese (Liqui-Cel) according to following specifications:

100

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Procedure Optimization

To carry out this procedure, studied the influence of different hydrodynamic parameters and chemicals, such as the initial concentration of Au (I) in the feed, the pH of the feed stream, the NaOH concentration in the pseudo-emulsion phase, cyanide concentration in food, the speed of linear feed flow and extractant concentration LIX-79 in n-heptane. It was evaluated with detail the selectivity of Au (I) against cyanide salts metal, such as Fe (I), Cu (I) ions, Ni (II), Zn (II) and Ag (I). This study is from particularly important since all parameters were examined chemicals using an alkaline hydrometallurgical solution synthetic that contained a mixture of gold with other salts of metal cyanides and basic metals. This was done to optimize conditions that are similar to those found for gold recovery of hydrometallurgical leaching solutions containing mixtures of other metal cyanide salts, such as Fe (II), Cu (I), Ni (II), Zn (II) and Ag (I).

Effect of the initial concentration of Au (I) on the feeding

The system was used LIX-79 / n-heptane (12% v / v or 0.375 M) to carry out different experiments in mode countercurrent in the presence of other metal cyanide salts. It should be noted that the Au (I) ions can be transported against its concentration gradient. As the concentration of Au (I) in the feed solution, it He observed that it increased with time in the re-extraction phase. The experiments were carried out using 1000 cm3 of Au (I) 10 mg / l, Fe (II) 30 mg / l, Cu (I) 30 mg / l, Ni (II) 10 mg / l, Zn (II) 5 mg / l and Ag (I) 3 mg / l with a minimum of a solution of NaCN at pH 10.5 in the feed and a feed rate of 20 l / hour (flow rate linear feed of 1.23 cm / s). The pseudo-emulsion was prepared by mixing 1000 cm3 of LIX-79 at 12% in n-heptane and 1000  cm3 of 0.2 M NaOH, stirring at 400 rpm, and passed through the side of the housing. As seen in Table 2, the Au (I) also separated from a mixture of other ions metallic The percentage of transport of other metal ions after 180 minutes it was Fe (II) 3.66%, Cu (II) 0.81%, Ni (II) 1.55%, Zn (II), 4.96% and Ag (I) 1.37%, while the transport of Au (I) in it Time period was over 92%. This shows that the Au (I) can be separated from other metal ions.

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TABLE 2 Recovery of Au (CN) 2 - in presence of other basic metal cyanides using the technique PEHFSD

3

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PH effect

To study the influence of the pH of the feeding, experiments were carried out at various pH, maintaining both the concentration of LIX-79 and the NaOH concentration in the pseudo-emulsion phase constants The results are shown in Table 3. The results showed that the PAu (x 10-5 cm / s) (coefficient of gold permeability) decreased from 21.3 to 3.49 as it increased the pH of the feed from 9.0 to 11.0. These results are similar to those observed previously in studies of liquid membrane supported on flat sheet of extraction Au (I) of medium with alkaline cyanides (with the same feeding composition). Although at slightly basic pH (8-9) you get the best recovery there is the HCN formation problem. This observation is consistent. with the theory that permeability is directly proportional to the concentration of ions [H +] in the phase feeding:

(4) Au (CN) 2 {} - + 2H <+> Au (I) + 2HCN

This equation shows that an increase in Proton concentration in the feed solution will result at increasingly high levels of HCN who is responsible for the decrease in the extraction of Au (I). PH decrease it is also because the LIX79 absorbs CO2 forming acid carbonic and therefore producing protons. With the objective of to maintain the pH at the optimum values it is necessary to go checking feeding and simultaneous addition of NaOH in the feeding.

At a moderately basic pH (greater than 11) the LIX-79 does not dissociate with what the RH + form does not exists at this pH and does not form the complex with Au (CN) 2 -. Therefore the extraction.

The following table 3 summarizes the different recovery values of Au (I) depending on the pH Therefore, the present invention can be carried out in a pH range between 8 and 11, preferably between 9 and 10.5, and even more preferably at a pH of 10.3.

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TABLE 3 Effect of the pH of the feeding phase on the transport of Au (CN) 2 - using the PEHFSD technique

4

Effect of NaOH concentration in the phase of pseudo-emulsion

As seen in Table 4, the effect of the concentration of NaOH in the phase of pseudo-emulsion influenced the separation factor of gold against other salts of metal cyanides. For Fe (III) a maximum recovery was obtained at a 0.2 M NaOH concentration that subsequently decreased to Increase the concentration of NaOH. The same effect is applicable to the separation factors of Ni (II), Zn (II) and Ag (I), although for Cu (II) the separation factor increased as the concentration of NaOH increased. From outstanding way, it should be noted that the permeability of Au (I) It was not affected by an increase in NaOH concentration. By therefore, in the present invention it is considered that the concentration between 0.1 M and 0.3 M is the optimal concentration for NaOH re-extraction agent in the recovery of AU (I) with respect to the rest of metals, a 0.2 M. concentration

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TABLE 4 Separation factors of Au (I) with respect to other metal cyanide salts using Lix-79 / n-heptane countercurrent with a synthetic hydrometallurgical solution depending on the concentration of NaOH in pseudo-emulsion after 3 days of experimentation

5

Effect of cyanide concentration in food

To study the influence of concentration of cyanide in the feeding phase, several experiments at various concentrations of cyanide, maintaining the LIX-79 concentrations in n-heptane and NaOH in the phase of constant pseudo-emulsion. The values of P_ {Au} (10-5 cm / s) obtained were 13.32 and 9.69 for 0 and 100 ppm of NaCN, respectively, while the value of P_ {Au} obtained at 1000 ppm was 1.5 times lower than the value obtained at 0 ppm NaCN. Since it is expected that the actual alkaline solutions containing gold with other metal cyanides contain NaCN in it interval, 1000 ppm of NaCN was selected as the most optimal value. A study was also conducted to observe the effect of concentration of sodium cyanide in the transport of other metals. Table 5 shows that the separation factors of Au (I) against Fe (II), Cu (I), Ni (II), Zn (I) and Ag (I) for 1000 ppm of NaCN are the optimal values. For the therefore, in the present invention the concentration is considered of optimal cyanides is greater than 750 ppm, preferably 1000 ppm.

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TABLE 5 Separation factors of Au (I) with respect to other metal cyanide salts using Lix-79 / n-heptane countercurrent with a synthetic hydrometallurgical solution depending on the cyanide concentration in the feeding phase after 3 h of experimentation by technique PEHFSD

6

Effect of linear feed flow rate

The influence of the linear flow rate of the feed was studied in order to optimize the transfer of gold cyanide in the side tube keeping the flow rate of the pseudo-emulsion constant. In our experiments, by necessity, the interface was maintained at the entrance of the fiber pore. To avoid this problem of contamination of the aqueous feed solution with the emulsion at a higher linear flow rate (11.66 cm3 / s), an optimal linear flow rate of 5.56 cm ^ was selected ^ {3} / s. Table 6 shows that the separation factors reach a maximum at a linear feed flow rate of 4.17 cm3 / s. Although this flow rate produced the greatest gold permeability, 5.56 cm3 / s was considered to be the most optimal value in order to provide a stabilized interface, better performance, good pressure control through of the side tube and the side of the housing and a sufficient separation factor of Au (I) compared to other metal cyanides in order to obtain a better product. When the flow rate was greater than 5.56 cm 3 / s, it was found that the pressure control was better for long-term experiments. Therefore, in the present invention the feed flow rate is preferably between 15 and 31 l / h (4.17 and 8.61 cm 3 / s) and, more preferably 20 l / h
(5.56 cm3 / s)

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TABLE 6 Separation factors of Au (I) with respect to other metal cyanide salts using Lix-79 / n-heptane countercurrent with a synthetic hydrometallurgical solution depending on the linear feed flow rate after 3 h of experimentation using the PEHFSD technique

7

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Effect of extractant concentration LIX-79 in n-heptane

Experimental conditions were established in which the concentrations of LIX-79 in n-heptane were varied with 0.2 M NaOH and the feed concentration of 10 mg / l of Au (I) in 1000 ppm of NaCN in the presence of other salts of basic metal cyanides. Table 7 shows the separation factors of gold with respect to other metals indicating that the separation factors increase as the concentration of LIX-79 increases in the pseudo-emulsion phase. The higher the concentration of LIX-79, the greater the extraction of the Au (CN) 2 - complex,
with the exception of silver where a decrease is observed. Other metal cyanides had lower distribution coefficients and their extraction was lower than that of Au (I).

Therefore, in the present invention considers the range of optimal concentrations of LIX-79 is 12 to 18%, preferably 12%.

TABLE 7 Separation factors of Au (I) with respect to other countercurrent metal cyanide salts with a synthetic hydrometallurgical solution using the PEHFSD technique in  function of the concentration of LIX-79 in the pseudo-emulsion phase after 3 h of experimentation

8

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The separation of gold from copper and  Iron is particularly significant. Since these two metals are normally associated with gold in many minerals, this often causes various problems of pollution in gold refining.

From the Fe (II) ions (30 mg / l), Cu (I) (30 mg / l), Ni (II) (10 mg / l), Zn (II) (5 mg / l) and Ag (I) (3 mg / l) analyzed in the form of a mixture with Au (I) (10 mg / l), the cyanide ions that exist with Au (I) are Ag (CN) 2 - , Cu (CN) 4 3-,
Zn (CN) 4 2-, Ni (CN) 4 2- and Fe (CN) 6 4-. The separation of Au (I) using LIX-79, based on the experimental results obtained, provides the following order of selectivity:

Au (CN) 2 {} - > Zn (CN) 4 {2-2} > Ag (CN) 2 {} - > Ni (CN) 4 {2-2,> Fe (CN) 6 {4 ->> Cu (CN) 4 {3-3

Finally, the factor of concentration, defined as the ratio between concentration final of Au (I) in the re-extraction phase with respect to the initial concentration in the feed solution under conditions similar experimental. In this experiment, the feeding is continuously replaced with new food without changing the pseudo-emulsion. In this way, he let the metal concentrate on the pseudo-emulsion mode of recirculation (in-line flow velocity 0.28 cm / s). In the end of the experiment, the mixing unit was stopped and the Pseudo-emulsion will stabilize for about minutes Finally, the metal concentration in the re-extraction solution. Maximum value was obtained 25 times the initial concentration of the metal in the feed. With similar experiments were obtained values between 10 and 25. Of this The viability of the recovery of Au (I) was demonstrated with PEHFSD using LIX-79.

References

1. Pabby AK., Tailor AM. Hollow fiber supported liquid membrane for the separation / concentration of Gold (I) from aqueous cyanide media: Modeling and mass transfer evaluation. Ind. Eng. Chem. Res . 2000 ; 39: 146-154.

2. Ho WS. Removal and recovery of metals and other materials by supported liquid membranes with strip dispersion. Anals New York Academy of Sciences . 2003 ; 984: 97-122.

3. Shukla JP, Sonawane JV, Pabby AK and Singh RK. Selective transport of Plutonium (IV) from aqueous nitrate solutions across a supported liquid membrane containing Aliquat-336 as a mobile carrier. Radiochimica Acta . 1996 ; 72: 189-193.

4. Sheriff FJ, Delgado AL, Alonso M. and Sastre AM. The phosphine oxides Cyanex-921 and Cyanex-923 as carriers for facilitated transport of Chromium (VI) -chloride aqueous solutions. Chemosphere 2004 ; 57: 813-819.

5. B. Hu Shih-Yao and Wiencek JM. Emulsion liquid membrane extraction of copper using a hollow-fiber contactor. AIChE Journal . 1998 ; 44 (3): 570-580.

6. Yannopoulos JC. The extractive metallurgy of gold . New York: Van Nostrand Reinhold, 1991 .

7. Curtain JL, Meinhardt E, Roijals O. Marti V. Modification and preparation of polymeric adsorbents for precious-metal extraction in hydrometallurgical processes. React. Polym 1998 ; 36: 149.

8. A. Kumar , R. Haddad , AM Tailor . Integrated membrane process for recovery of gold cyanide with LIX-79 from hydrometallurgical solutions: modeling and performance evaluation, AIChE J. 47 ( 2001 ) 328.

9. A. Kumar , R. Haddad , G. Benzal , R. Ninou , AM Tailor . Use of modified membrane carrier system for recovery of gold cyanide from alkaline cyanide media using hollow fiber supported liquid membranes: feasibility studies and mass transfer modeling, J. Membr. Sci . 174 ( 2000 ) 17.

10. R. Haddad . Metal recovery processes using membranes in hollow fiber configuration: application to the separation / concentration of Aul and Agl of cyanide solutions, Ph. D. Thesis, Polytechnic University of Catalonia, Barcelona, Spain, October 2002.

11. AM Tailor , A. Madi , JL Cortina , FJ Sheriff . Solvent Extraction of Gold by LIX79: Experimental and Equilibrium Study, J. Chem. Technol. Biotechnol 74 ( 1999 ) 310.

12. JV Sonawane , Anil Kumar Pabby and AM Sastre , Au (I) extraction by LIX-79 / n-heptane using pseudo emulsion based hollow fiber strip dispersion (PEHFSD technique), J. Membr. Sci ., 300, 147-155, 2007 .

Claims (6)

1. Gold recovery procedure (Au (I)) in the presence of one or more of the following metals: Zn, Ag, Ni, Fe and Cu, in an aqueous medium of cyanide with a concentration higher than 750 ppm, in which said recovery is made using membranes in hollow fiber configuration with a single module thereof using scatter reextraction, in the pH is between 8 and 11, the extractant is LIX-79 with a concentration between 12 and 18% (v / v) in n-heptane and the re-extraction agent is NaOH with a concentration between 0.1 and 0.3 M. 2. Method according to claim 1, in The concentration of said extractant is 12% (v / v). 3. Procedure according to any of the previous claims wherein the concentration of said re-extraction agent is 0.2 M. 4. Procedure according to any of the previous claims in which said process is carried carried out at a pH between 9 and 10.5, preferably at a pH of 10.3. 5. Procedure according to any of the previous claims wherein the cyanide concentration in the feeding phase it is 1000 ppm. 6. Procedure according to any of the previous claims wherein the flow rate of the feeding is between 15 and 31 l / h, preferably 20 l / h.