WO2020245619A1

WO2020245619A1 - Method for copper and zinc separation from industrial electrolytes including waste industrial electrolytes

Info

Publication number: WO2020245619A1
Application number: PCT/IB2019/000597
Authority: WO
Inventors: Przemyslaw Los; Zoltan VON BERNATH
Original assignee: Individual
Current assignee: Individual
Priority date: 2019-06-06
Filing date: 2019-06-06
Publication date: 2020-12-10
Anticipated expiration: 2021-12-06

Abstract

The object of the invention is the process of copper and zinc separation from industrial electrolytes of very complex composition, including pregnant leach solutions (PLS) which are the products of the ores, flue dusts and solid flotation tailings leaching. The advantage of the electrochemical process of copper and zinc separation according to the invention consists in that the electrolyte solution of copper and zinc ions is carried out under a potentiostatic pulse electrolysis using the cathode potential Eapp1 at stainless steel plate or foil cathode, whereas metallic titanium or PB-alloy is used as an anode and the process is carried out at temperature from 19-60eC, and the electrolysis cycle lasts from 1 to 9 days. Depending on the electrolysis cycle time the product is either a copper cathode or copper powder for shorter electrolysis time. Decopperisation of the PLS solution can be realized in a cascade of electrolysis cells where concentration of copper ions decreases at each cell. When the copper concentration in the PLS solution is lower than 0.050 g/dm3 the stainless-steel cathodes are removed and aluminium cathodes are placed to electrodeposit zinc at Eapp,2, which is according to the Examples below at least 400 mV more negative than the potential of copper deposition Eapp,1. Such high difference of potentials assures almost perfect selectivity of the copper and zinc electrochemical separation. The actual values of the Eapp,1 and Eapp,2 potentials depend on the type of the anode used as it is presented in the Examples. Decrease of the zinc ions concentrations in the PLS solution to the concentrations lower than 0.2 g/dm3, can be realized in a cascade of (a few) electrolysis cells where concentration of zinc ions decreases gradually at each cell. The advantages of the said process is that all operations are carried out in the same electrolysis system without chemical (e.g. additives) or physical modification of the PLS solution, which contributes to the much higher economic effectiveness, lower environmental footprint and technological feasibility of the said method in comparison to the state of the art. The advantage of the said copper and zinc separation process is that it can be used to obtain cathodes, powders or nanopowders of copper and zinc characterised by particle structure and dimension repeatability and purity from 99%+ from waste industrial electrolytes and copper industry PLS solution as well as electroplating plants without additional SX or IE treatment of those solutions.

Description

METHOD FOR COPPER AND ZINC SEPARATION FROM INDUSTRIAL

ELECTROLYTES INCLUDING WASTE IDUSTRIAL ELECTROLYTES

The invention is intended to a method of copper and zinc separation from industrial electrolytes of very complex composition, including pregnant leach solutions (PLS) which are the products of the ores, flue dusts and solid flotation tailings leaching.

Prior Art

Copper and zinc are very widely used in many areas of industry and their production volumes increases considerably. Consequently, there is a need to exploit new secondary resources of those metals apart from the ores and it is very important to develop a new, more effective and environmentally friendly methods of copper and zinc extraction from primary and secondary resources. The most often used method of separation and production of the copper and zinc from their PLS solutions is solvent extraction process (SX) as a main separation stage followed usually by the electrowinning (EW) of the copper and zinc metals. This method is referred in the literature as SX/EW method. According to the data of C. Frias et al, Solvent Extraction Applied to Mixed Copper and Zinc Bearing Materials, Proceedings of Cu 2010, p.1 20% of the world refined copper production is obtained using SX method as part of the hydrometallurgical treatment of the ores. In the latter publication a SX/EW method is proposed for treatment of mixed or polymetallic copper and zinc ores and secondary materials (e.g. flue dusts). The state of the art of copper and zinc separation is described for instance in the paper L.R. Goueva and C.A. Morais, Minerals Engineering, 23 (2010) 492- 497. In this paper it is written, that“Zinc and copper can be separated from sulphuric liquors by cementation or liquid-liquid extraction.” According to this publication cementation is not very effective method of copper precipitation and separation from copper and zinc containing solutions and it is stated that:“The separation of the metals is therefore more appropriate when done through solvent extraction. The solvent extraction technique has become essential to the hydrometallurgical industry due to a growing demand for high purity metals, rigid environmental regulations, the need for lower production costs and diminishing production in high-grade ore reserves. This leads to the necessity of the treatment of ores of lower grade and greater complexity.” In the Goueva and Morais study the organophosphorus extractants and the chelating extractants were investigated for Zn/Cu separation. SX studies of copper and zinc separation from solutions using Versatic 10 acid and Cyanex 272 as solvents have been reported in the paper of Manish K. Sinha, S. K. Sahu, Pratima Meshram, B. D. Pandey, V. Kumar, Solvent Extraction and Separation of Copper and Zinc from a Pickling Solution, International Journal of Metallurgical Engineering 2012, 1 (2): 28-34.

In the Australian patent publication AU 2013388340 B2 titled“Method for bioleaching and solvent extraction with selective recovery of copper and zinc from polymetal concentrates of suldides” the SX/EW process is described for zinc and copper separation. A two-step solvent extraction process is presented for the selective recovery of copper and zinc from the solutions obtained by bioleaching of minerals and sulphide-based concentrates. It is important to note that the whole SX/EW process is complicated by the presence of impurities like e.g. arsenic. Consequently, additional arsenic control step, by forming stable compounds for final disposal is employed. In the US Patent No.: US 10,221 ,493 B2 titled“Method for recovery of copper and zinc” the multistep SX process for the recovery of copper and zinc form an aqueous sulfate and chloride containing solution is presented. The process is rather complex and consists of the following steps:“In the first process step zinc and copper are simultaneous extracting with an extraction solution comprising a liquid chelating cation exchanger and a liquid anion exchanger. The extraction is followed by consecutive stripping stages. First the anionic species are washed from the organic phase with one or more aqueous solutions and finally the copper is stripped with an aqueous acidic solution.” The multistep method of separating copper, chromium and zinc in an acid leaching liquid, with SX as a first stage of the process is described in the Chinese patent CN20131 00821 1 201301 10.

Another multistep method of copper and zinc separation from the PLS solutions is based on the ion exchange or sorption method (IE). In the paper of

OLGA N. KONONOVA, MARINA A. KUZNETSOVA, ALEXEY M. MEL’NIKOV, NATALIYA S. KARPLYAKOVA and YURY S. KONONOV, sorption recovery of copper (II) and zinc (II) from aqueous chloride solutions, J. Serb. Chem. Soc. 79 (8) 1037-1049 (2014) the anion exchangers Purolite S985, Purolite A500 and AM-2B was used for zinc and copper recovery from acidic industrial solutions and wastewater. The patent application number BG20160003488U describes a ion- exchange process is applied for processing and recycling metallurgical waste, including slags, muds, waste sludge and cakes, which contain mainly copper, zinc, gold, silver and precious. A solution to remove copper selectively from a concentrated zinc sulphate solution by ion exchange is described in the patent number WO 2005/045078 A1 titled“A method for the removal of copper from a zinc sulphate solution”, too.

It appears from the above presented prior art processes of zinc and copper separation from PLS solutions that they are based on SX/EW and IE processes, which are characterised by the following disadvantages:

1. They are complex multistep processes, which increases their costs and complicates technological feasibility due to the application of different equipment and apparatus.

2. They require the usage of relatively high cost reagents such as organic solvents or ion exchange substances.

3. They have relatively high environmental impact due to the necessity of manufacturing chemical substances like organic solvents.

4. They are characterised by the increased environmental fingerprint and increased costs due to the necessity of the recovery or recycling of the used solvents, which is not possible to realize as a zero-waste process.

5. The prior art processes are not sufficiently suitable for the widely applied circular economy paradigm and increasingly demanding regulatory requirements. The present invention solves the above problems of the complexity, high environmental impact as well as increasing costs related to e.g. usage and manufacturing of organic solvents and other chemical substances. It has been developed that copper and zinc can be separated from industrial electrolyte solutions including the wastewaters and PLS solutions in a one apparatus system and practically one step, if PLS undergo potentiostatic pulse electrolysis without the current direction change. This was unexpectedly found especially, because as it is explained below the selectivity of electrochemical separation process of copper and zinc cannot be predicted theoretically for such complex electrochemical systems. Similar processes of potentiostatic pulse electrolysis was used for obtaining copper powders and nanopowders from industrial electrolytes as it is described in the Australian patent AU 2010225514 B2 and for copper electrorefining disclosed in patent application WO 2013/075889 A1 . In both described processes where the anode was metallic copper to keep approximately constant copper concentration of copper ions in the solution and for enabling copper anode refining by cathode deposition. Consequently, the methods described in those documents are not useful for separation of copper and zinc.

The current invention considers that the electrochemical separation of zinc and copper by potentiostatic pulse electrolysis or by potential controlled electrolysis (PCE) requires application of electrowinning process where insoluble anode is used, instead of copper anode, and consequently the anode reaction is different. Brief description of the figures

Further details and advantages of the invention emerge from the following description of the accompanying figures, in which a preferred embodiment with the requisite details and individual parts is represented. The figures show in:

Figure 1 : It shows a picture of electrochemical deposition of copper on the electrode the structure and dimensions of deposited powder using a scanning electron microscope for the Example I.

Figure 2: It shows a picture of electrochemical deposition of copper on the electrode the structure and dimensions of deposited powder using a scanning electron microscope for the Example II.

Figure 3: It shows a picture of electrochemical deposition of copper on the electrode the structure and dimensions of deposited powder using a scanning electron microscope for the Example III.

Figura 4: it shows a photographic image of stainless steel cathode with a visible copper powdery layer deposit

DETAILED DESCRIPTION

The process for copper and zinc separation from industrial electrolytes, waste waters and PLS solutions is based on the fact that different metals are in general electrodeposited at different potential applied to the electrolysis system. In general the potential, E_app applied to the pair anode - cathode consists of the following components:

E_app = E_Nernst + h + i R where,

E_Nernst - is Nernst equilibrium potential;

h - overpotential is a potential related to the electrochemical processes kinetics during the flow of the electrolysis current;

iR - is an uncompensated ohmic drop due to electrolyte and other parts (e.g. cables, connections of electrodes) of the electrical resistance.

The electrochemical separation is based on the observation that Nernst potentials of different electrochemical processes are different as well as overpotentials related to the electrochemical kinetics are different. Consequently, different metals are in general can be electrodeposited at different E_app potentials. In the case of copper and zinc separation the following simplified cathode reactions occur:

1 . Cu⁺² + 2e = Cu° at potential E_{app, 1}

2. Zn²⁺ + 2e = Zn° at potential E_{app, 2}

When solid insoluble or inert anode (e.g. inert Pb-alloy anode) is used the anode process is the following:

3. H₂O = 0.5O₂ + 2H⁺ + 2e The exact value of E_app cannot be calculated theoretically for the above electrochemical system, especially when concentrate and complex matrix PLS electrolyte is used. Additionally, it is assumed that no chemical modification of PLS solutions are applied. Consequently, the E_app potentials of copper and zinc deposition from PLS solutions cannot be modified. The standard electrode potentials, E° are known for copper and zinc and they are equal to +0.34 V and - 0.23 V, for reaction 1 and 2 respectively. Even when the difference of standard potentials is relatively high the selectivity of the separation of copper and zinc in actual conditions cannot be theoretically predicted because the values of overpotentials are often in the range of a few hundred mV and standard electrode potentials are just part of the Nernst potential equation. For instance, according to the W.G. Davenport et at, Extractive Metallurgy of Copper, Elsevier Science 2002 Fourth Edition p. 328, the oxygen evolution reaction overpotential at industrial Pb-alloy anode is approximately 0.5 V.

The advantage of the electrochemical process of copper and zinc separation according consists in that the electrolyte solution of copper and zinc ions is carried out under potentiostatic pulse electrolysis using the cathode potential E_app,i at stainless steel plate or foil cathode, whereas metallic titanium or PB-alloy is used as an anode and the process is carried out at temperature from

, and the electrolysis cycle lasts from 1 to 9 days. Depending on the electrolysis cycle time the product is either a copper cathode or copper powder for shorter electrolysis time. Decopperisation of the PLS solution can be realized in a cascade of electrolysis cells where concentration of copper ions decreases gradually at each cell. When the copper concentration in the PLS solution is lower than 0.050 g/dm³ the stainless-steel cathodes are removed and aluminium cathodes are placed to electrodeposit zinc at E_{app, 2}, which is according to the Examples below at least 400 mV more negative than the potential of copper deposition E_{app, 1}. Such high difference of potentials assures almost perfect selectivity of the copper and zinc electrochemical separation. The actual values of the E_{app, 1} and E_{app, 2} potentials depend on the type of the anode used as it is presented in the Examples. Decrease of the zinc ions concentrations in the PLS solution to the concentrations lower than 0.2 g/dm³, can be realized in a cascade of (a few) electrolysis cells too, where concentration of zinc ions decreases gradually at each cell.

The advantage of the process according to the current invention consists in that, that the PLS solution is carried out under a potentiostatic electrolysis in which:

- A pulse in cathodic potential E_{app, 1} in the range from -2.0 V ÷ -2.1 V, in reference to Pb-alloy electrode/anode or in the range from -0.9 V to -1 .0 V in reference to titanium anode, in time t_k,1 from 1 to 9 days, i.e. until the copper concentration is not lower than 0.050 g/dm³,

- Subsequently, a pulse in cathodic potential E_{app, 2} in the range from -2.5 V - -2.8 V, in reference to Pb-alloy electrode or in the range from -1 .4 V to -1 .7 V in reference to titanium anode, in time t_k,1 from 1 to 9 days, in time t_k,2 from 1 to 9 days, i.e. until the zinc concentration is not lower than 0.2 g/dm³.

When stainless steel cathodes are used the time they remain in the electrolyte is equal to the duration of one electrolysis cycle. After each cycle an electrode is removed from the solution and a copper is removed from the cathode and new electrode is immersed in the electrolyte solution.

The electrolysis product, i.e. zinc or copper cathodes, powders or nanopowders can be removed from an electrode surface mechanically using e.g. a sharp-edged gathering device. The advantages of this is that all operations are carried out in the same electrolysis system without chemical or physical modification of the PLS solution, which contributes to the much higher economic effectiveness, lower environmental footprint and technological feasibility of the invention in comparison to the state of the art.

The advantage of the copper and zinc separation process is that it can be used to obtain cathodes, powders or nanopowders of copper and zinc characterised by particle structure and dimension repeatability and purity from 99%+ from waste industrial electrolytes and copper industry PLS solution as well as electroplating plants without additional SX or IE treatment of those solutions. Although, copper can be obtained by the current invention from electrochemical copper and zinc separation process even at the highest Cu-CATH-1 purity, zinc purity and quality obtained by electrowinning process is very sensitive to the presence of different impurities in PLS solutions as it is explained in Michael L. Free, Hydrometallurgy, Fundamentals and Applications, John Wiley&Sons Inc., New Jersey 2013, p 226.

Copper and zinc separation from PLS solutions using in the invention is shown in the Examples. Example I.

A stainless-steel plate working electrode of surface area from 10 cm² to 25 cm² serving as a cathode and the anode (a reference and auxiliary) electrode in the form of a titanium plate (Good Fellow, Great Britain), the surface area of which was approximately 25 cm² are placed in an electrochemical cell thermostated up to

The Pb-alloy electrode is used to establish as additional reference electrode, too. The cell is filled with PLS industrial solution, used in copper electrowinning process, composed of 3-25 g/dm³ Cu, Zn 0.8-25 g/dm³, 12-200 g/dm³ H₂SO₄, As 0.05-20 g/dm³, Fe (>1 000 mg/dm³), Ni, Cd, Co, Bi, Ca, Mg, Pb, Sb (from 1 mg/dm³ to 1000 mg/dm³), Ag, Li, Mn (<10 mg/dm³) and 1 -20 g/dm³ chloride ions. The electrodes are connected to measuring device— Autolab GSTST30 potentiostat working on-line with a personal computer (PC) with GPES software by Eco Chemie with the aid of a BNC connector.

Parameters of the process have been as follows:

E_{app, 1} = -0.9 V, in reference to titanium anode (or -2.0 V in reference to PB-alloy electrode), t_k,1 = 300 s

E_{app, 2} = -1 .4 V, t_k,2 = 1800 s

After electrochemical deposition of copper on the electrode the structure and dimensions of deposited powder have been studied using a scanning electron microscope and it has been observed that the obtained deposit is in the shape of powders for shorter electrolysis time and layers/foils for longer electrolysis time. On the basis of the analysis of energy dispersion spectrum (EDS) it has been established that only lines characteristic of copper are present which shows the purity of the obtained product. Electrodeposition of zinc is carried out on a fresh stainless-steel cathode at potential E_app,2. On the basis of the analysis of energy dispersion spectrum (EDS) it has been established that zinc is the main product of the cathode deposit and the main impurity is copper when its concentration in PLS solution is higher than 0.2 g/dm³.

Copper deposit obtained at the cathode using the following conditions: E_app = - 0.9 V; t_k,1 = 300 s, room temperature (approx. 25°C) - EDS results indicates copper lines and SEM images present copper powder of 170 nm to 400 nm in size shown in figure 1 .

Example II.

The Pb-alloy electrode is used to establish as additional reference electrode, too. The cell is filled with PLS industrial solution, used in copper electrowinning process, composed of 3-25 g dm^-3 Cu, Zn 0.8-25 g dm^-3, 12-200 g dm^-3 H₂SO₄, As 0.05-20 g dm^-3, Fe (>1000 mg/dm³), Ni, Cd, Co, Bi, Ca, Mg, Pb, Sb (from 1 mg/dm³ to 1000 mg/dm³), Ag, Li, Mn (<10 mg/dm³) and 1 -20 g dm^-3 chloride ions. The electrodes are connected to measuring device— Autolab GSTST30 potentiostat working on-line with a personal computer (PC) with GPES software by Eco Chemie with the aid of a BNC connector. Parameters of the process have been as follows:

E_{app, 1} = -1.0 V, in reference to titanium anode (or -2.1 V in reference to PB-alloy electrode), t_k,1 = 120 s

E_{app, 2} = -1.6 V, t_k,2 = 1800 s

After electrochemical deposition of copper on the electrode the structure and dimensions of deposited powder have been studied using a scanning electron microscope and it has been observed that the obtained deposit is in the shape of powders for shorter electrolysis time and layers/foils for longer electrolysis time. On the basis of the analysis of energy dispersion spectrum (EDS) it has been established that only lines characteristic of copper are present which shows the purity of the obtained product. Electrodeposition of zinc is carried out on a fresh stainless-steel cathode at potential E_{app, 2}. On the basis of the analysis of energy dispersion spectrum (EDS) it has been established that zinc is the main product of the cathode deposit and the main impurity is copper when its concentration in PLS solution is higher than 0.050 g/dm³.

Copper deposit obtained at the cathode using the following conditions: E_app = - 1.0 V; t_k,1 = 120 s, room temperature (approx. 25°C) - E DS results indicates only copper lines and SEM images present copper powder of 280 nm to 400 nm in size shown in figure 2.

Example III. A stainless-steel plate working electrode of surface area from 10 cm² to 25 cm² serving as a cathode and the anode (a reference and auxiliary) electrode in the form of a titanium plate (Good Fellow, Great Britain), the surface area of which was approximately 25 cm² are placed in an electrochemical cell thermostated up to . The Pb-alloy electrode is used to establish as additional reference electrode, too. The cell is filled with PLS industrial solution, used in copper electrowinning process, composed of 3-25 g/dm³ Cu, Zn 0.8-25 g/dm³, 12-200 g/dm³ H₂SO₄, As 0.05-20 g/dm³, Fe (>1 000 mg/dm³), Ni, Cd, Co, Bi, Ca, Mg, Pb, Sb (from 1 mg/dm³ to 1000 mg/dm³), Ag, Li, Mn (<10 mg/dm³) and 1 -20 g/dm³ chloride ions. The electrodes are connected to measuring device— Autolab GSTST30 potentiostat working on-line with a personal computer (PC) with GPES software by Eco Chemie with the aid of a BNC connector.

Parameters of the process have been as follows:

E_{app, 1} = -1 .0 V, in reference to titanium anode (or -2.1 V in reference to PB-alloy electrode), t_k,1 = 1200 s

E_{app, 2} = -1 .7 V, t_k,2 = 1800 s

After electrochemical deposition of copper on the electrode the structure and dimensions of deposited powder have been studied using a scanning electron microscope and it has been observed that the obtained deposit is in the shape of powders for shorter electrolysis time and layers/foils for longer electrolysis time. The photographic images of the powdery layer of copper at the cathode have been taken, too. On the basis of the analysis of energy dispersion spectrum (EDS) it has been established that only lines characteristic of copper are present which shows the purity of the obtained product. Electrodeposition of zinc is carried out on a fresh stainless-steel cathode at potential E_app,2. On the basis of the analysis of energy dispersion spectrum (EDS) it has been established that zinc is the main product of the cathode deposit and the main impurity is copper when its concentration in PLS solution is higher than 0.050 g/dm³.

Copper deposit obtained at the cathode using the following conditions: E_app = - 1.0 V; t_k,1 = 1200 s, room temperature (approx. 25°C) - EDS results indicates only copper lines and SEM images present copper powder of 350 nm to 650 nm in size.

SEM/EDS results of the copper powder presented at Figure 3.

A photographic image of stainless steel cathode with a visible copper powdery layer deposit it shown in figure 4.

Claims

1. Electrochemical process for copper and zinc separation from industrial electrolytes including waste and PLS industrial electrolytes through selective electrochemical deposition of copper and zinc on a cathode, characterised because it is carried out under a pulse electrolysis using the cathode potential E_{app, 1} at stainless steel plate or foil cathode, whereas metallic titanium or PB-alloy is used as an anode and the process is carried out at temperature from

, and the electrolysis cycle lasts from 1 to 9 days and when the copper concentration in the PLS solution is lower than 0.050 g/dm³ said stainless-steel cathodes are removed and aluminium cathodes are placed to electrodeposit zinc at the cathode potential value E_{app, 2}

2. Electrochemical process for copper and zinc separation from industrial electrolytes including waste and PLS industrial electrolytes according claim 1 , characterised because decopperisation of the PLS solution is realized in a cascade of electrolysis cells where concentration of copper ions decreases gradually at each cell.

3. Electrochemical process for copper and zinc separation from industrial electrolytes including waste and PLS industrial electrolytes according claim 1 , characterised because the zinc ions concentrations in the PLS solution is decreased to the concentrations lower than 0.2 g/dm³ and it is realized in a cascade of (a few) electrolysis cells.

4. Electrochemical process for copper and zinc separation from industrial electrolytes including waste and PLS industrial electrolytes according claim 1 , characterised because that the electrolyte solution of copper and zinc ion concentrations is higher than 0.05 g/dm³ is carried out under a potentiostatic pulse electrolysis without the current direction change, using a cathode potential value E_app,i ranging from -0.9 V to -1 V.

5. Electrochemical process for copper and zinc separation from industrial electrolytes including waste and PLS industrial electrolytes according claim 4, characterised because when the copper concentration is lower than 0.050 g/dm³ said stainless-steel cathodes are removed and aluminium cathodes are placed to electrodeposit zinc the cathode potential value E_{app, 2} ranging is -1.4 V to -1.7 V until the zinc concentration is lower than 0.2 g/dm³.

6. Electrochemical process for copper and zinc separation from industrial electrolytes including waste and PLS industrial electrolytes according to Claim 1 , characterised because a Pb-alloy anode is used.

7. Electrochemical process for copper and zinc separation from industrial electrolytes including waste and PLS industrial electrolytes according claim to Claims 1 , 4 - 6, characterised because the electrolyte solution is carried out under a potentiostatic electrolysis in which:

- a pulse in cathodic potential E_{app, 1} in the range from -2.0 V ÷ -2.1 V, in reference to Pb-alloy electrode/anode or in the range from -0.9 V to -1.0 V in reference to titanium anode, in time t_k,1 from 1 to 9 days; - subsequently, a pulse in cathodic potential E_{app, 2} in the range from -2.5 V ÷ -2.8 V, in reference to Pb-alloy electrode or in the range from -1 .4 V to -1 .7 V in reference to titanium anode, in time t_k,1 from 1 s to 9 days, in time t_k,2 from 1 s to 9 days.