An electrolyte purification process for copper refineries

Abstract

According to the present invention there is provided use of a lead electrode in a method for removing one or more impurities from a copper refinery electrolyte. Preferably, the method is a single-stage electrolyte purification / liberation (EPP) method. More preferably, the one or more impurities comprise arsenic. Also provided is a lead cathode, per se, for use in such a method. Preferably, the method comprises the steps of: providing an electrolyte having a concentration of arsenic that is sufficiently elevated as to affect the purity of the final copper cathode product; providing a cell adapted for performing a single- stage electrolyte purification / liberation (EPP) method; providing to the EPP cell a cathode comprised of about 90 to about 100 wt.% lead; performing the EPP method for a predetermined period, thereby to effect a copper / arsenic reduction step; and obtaining the resultant cupric arsenide deposit in a sludge layer at the bottom of the EPP cell.

Description

AN ELECTROLYTE PURIFICATION PROCESS FOR COPPER REFINERIESRelated Application

[0001] The present invention claims convention priority to Australian provisional patent application AU 2024902635, filed on 23 August 2024. The content of AU’635 is incorporated by reference herein in its entirety.Field of the Invention

[0002] The present invention relates generally to the field of extractive metallurgy.

[0003] The present invention relates to an impurity removal process for copper refinery electrolyte.

[0004] More particularly, the present invention relates to the use of an inert lead cathode in EPP cells, giving rise to a sludge-only product.

[0005] Although the present invention will be described hereinafter with reference to its preferred embodiment, it will be appreciated by those skilled in the art that the spirit and scope of the invention may be embodied in many other forms.Background of the Invention

[0006] Any discussion of the prior art throughout the specification should in no way be considered as an admission that such prior art is widely known or forms part of common general knowledge in the field.

[0007] Electrorefining is one of the most common methods by which high quality copper cathode (99.99 wt.%) is produced. In this technique, impure copper cast anodes (about 98.5 wt.%) electrochemically dissolves / oxidises in sulfuric acid electrolyte causing copper ions to be selectively reduced / electrodeposited on the stainless steel cathode blanks as substantially pure metal.

[0008] During copper electrorefining, two types of impurities are continuously released from the solid anodes, either as insoluble phases (z.e., slimes), which fall to the bottom of the cell, or as dissolved species in the electrolyte.

[0009] Under standard electrorefining conditions, insoluble (or more noble than copper) elements such as Au, Ag, Os, Ru, Ir, Rh, Pd, Pt, Pb, Te, Se and Sn will be not electrodeposited onto the stainless cathode blank and will report to the anodic slimes.

[0010] On the other hand, less noble elements such as As, Sb, Bi, S, Fe, Co and Ni will dissolve and gradually accumulate in the electrolyte. Failure to control accumulation of these impurities causes high energy consumption and reduces the quality of the final copper product.

[0011] To maintain final product purity, these insoluble impurities must be continuously removed from the copper electrorefining electrolyte. Historically, As and Sb have been recognised as two of the most challenging impurities to remove.

[0012] In electrorefining, blister copper is remelted and poured into a sheet. These sheets act as the anode of the cell, which dissolves as the final copper cathode product and eventually re-plates. Most of the impurities in the copper anode form insoluble “sludge” on the electrode surface or fall to the bottom of the cell.

[0013] However, some impurities, particularly As, Sb and Bi, dissolve into the acidic copper electrolyte and may be incorporated into the cathode by a variety of mechanisms. These impurities deteriorate the cathode quality, leading to unfavourable downstream processing (e.g., drawing copper wire). Because of the significant economic impact of electrolyte impurities, copper manufacturers go to great lengths to mitigate any factors that negatively impact operating costs and / or final product quality.

[0014] A common strategy to ensure high purity product is to control the concentration of these unwanted metals in the electrolyte, which increases rapidly over time if not suppressed. Typically, the concentration in the acid electrolyte is maintained at 0.3-0.5 g / L (e.g., Sb and Bi), but when the concentration reaches a critical limit, the electrolyte stream is vented, treated, and eventually returned to the cell.

[0015] Several methods of removing the above-mentioned impurity metals have been studied. Among the various methods available for removing As, Sb and Bi, one option is ion exchange. However, the high reagent consumption in this process makes it an expensive and inefficient option. Another option involves the precipitation of unwanted metals. However, such treatments require varying various characteristics of the solution (e.g., acid concentration). This requires additional reagents, and the resulting solution cannot be returned to the electrorefining process due to changes in the solution properties (e.g., too acidic). It may also be desirable to recover the copper values prior to treatment by precipitation. Other options also include electrolytic extraction of impurities.However, this method typically requires that the copper be extracted electrolytically from the effluent stream and sent back for reprocessing before any other contaminants can beremoved from the solution.

[0016] Across many copper refineries, a three-stage electrolyte purification method (primary, secondary and tertiary liberation) is used. The primary liberator stage aims to produce saleable electrowon copper by targeting relatively high Cu in the cell outlet. Secondary liberators reduce the copper concentration further by plating Cu to make low grade (non-saleable) cathode. Finally, tertiary liberators reduce Cu further and remove As, Sb and Bi by co-depositing them on the cathode as mixture of adhesive but crumbly deposit and loose sludge product. Some of the deposit adheres to the cathode substrate and some falls to the bottom of the cell as sludge.

[0017] The conventional three-stage electrolyte purification process utilises lead alloy electrodes as electropositive anodes and copper-coated stainless steel plates or scrap copper anodes as the electronegative cathode substrate.

[0018] Another common configuration for electrolyte purification cells is a cascading system, wherein electrolyte flows in series from one cell to the next, progressively reducing the copper concentration as electrolyte passes through each cell. The first cells in the cascade produce a largely cohesive cathode deposit consisting mainly of copper. The middle and final cells in the cascade produce a mixture of copper / arsenic deposit on the cathode and non-adherent sludge. In general, the amount of As, Sb and Bi electroplated from the electrolyte increases with each cell pass. The proportion of sludge to solid cathode deposit also increases.

[0019] The Applicant’s recently conducted trials have successfully demonstrated that secondary and tertiary liberation steps can be effectively combined into one, the single- stage electrolyte purification / liberation (EPP) step.

[0020] In the single-stage liberation step, copper refinery electrolyte is recirculated through a single set of cells (one stage), at high flowrate such that copper levels and the copper to arsenic (Cu: As) ratio in the electrolyte are controlled at their optimum levels for plating arsenic. Thus, the arsenic removal rate is maximised and the risk of producing toxic arsine gas is minimised. Since arsenic removal can be carried out in a single decopperising step, this eliminates the “dirty” copper that is normally produced in secondary liberators, and which requires costly remelting / anode recasting steps. Primary liberators can also run more efficiently and produce better quality (saleable) copper since they can run in parallel with the single-stage EPP liberators instead of in series, allowing them to run at much higher flowrates targeting higher Cu concentration at the cell outlet.

[0021] Although the single-stage liberation process has demonstrated to be an effective and efficient method for Cu / As removal, electrodeposited material does come in two physical forms - a larger portion as a solid deposit still attached to the cathode surface and as a sludge accumulated at the cell bottom.

[0022] From a material handling and processing perspective, producing only one rather than two separate products is highly preferable. Since single-stage liberation trials were unable to produce a solid-only deposit, the Inventors’ focus was shifted toward the sludge-only production pathway.

[0023] It is an object of the present invention to overcome or ameliorate at least one of the disadvantages of the prior art, or to provide a useful alternative.

[0024] It is an object of a particularly preferred form of the present invention to provide an improved impurity removal process for copper refinery electrolyte.

[0025] Although the invention will be described with reference to specific examples it will be appreciated by those skilled in the art that the invention may be embodied in many other forms.Definitions

[0026] In describing and claiming the present invention, the following terminology will be used in accordance with the definitions set out below. It is also to be understood that the terminology used herein is for the purpose of describing particular embodiments of the invention only and is not intended to be limiting. Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one having ordinary skill in the art to which the invention pertains.

[0027] The term “lead” cathode / electrode would be understood by one of ordinary skill in the art to typically mean ~98 wt.% lead alloyed with elements such as Sn, Ca, Sb, etc.

[0028] The term “sludge” in the context of an EPP cell should be understood to consist predominantly of Cu and As, with small amounts of Sb, Bi and Pb which come from the anodes / cathodes.

[0029] Unless the context clearly requires otherwise, throughout the description and the claims, the words “comprise”, “comprising”, and the like are to be construed in an inclusive sense as opposed to an exclusive or exhaustive sense; that is to say, in the sense of “including, but not limited to”.

[0030] As used herein, the phrase “consisting of’ excludes any element, step, or ingredient not specified in the claim. When the phrase “consists of’ (or variations thereof) appears in a clause of the body of a claim, rather than immediately following the preamble, it limits only the element set forth in that clause; other elements are not excluded from the claim as a whole. As used herein, the phrase “consisting essentially of’ limits the scope of a claim to the specified elements or method steps, plus those that do not materially affect the basis and novel characte stic(s) of the claimed subject matter.

[0031] With respect to the terms “comprising”, “consisting of’, and “consisting essentially of’, where one of these three terms is used herein, the presently disclosed and claimed subject matter may include the use of either of the other two terms. Thus, in some embodiments not otherwise explicitly recited, any instance of “comprising” may be replaced by “consisting of’ or, alternatively, by “consisting essentially of’.

[0032] Other than in the operating examples, or where otherwise indicated, all numbers expressing quantities of ingredients or reaction conditions used herein are to be understood as modified in all instances by the term “about”, having regard to normal tolerances in the art. The examples are not intended to limit the scope of the invention. In what follows, or where otherwise indicated, “%” will mean “weight %”, “ratio” will mean “weight ratio” and “parts” will mean “weight parts”.

[0033] Units and measures are provided according to the metric system, with the exception being pressure, which is quoted in atmospheres (atm).

[0034] The term “substantially” as used herein shall mean comprising more than 50% by weight, where relevant, unless otherwise indicated.

[0035] The term “about” should be construed by the skilled addressee having regard to normal tolerances in the relevant art.

[0036] The recitation of a numerical range using endpoints includes all numbers subsumed within that range (e.g., 1 to 5 includes 1, 1.5, 2, 2.75, 3, 3.80, 4, 5, etc. .

[0037] The terms “preferred” and “preferably” refer to embodiments of the invention that may afford certain benefits, under certain circumstances. However, other embodiments may also be preferred, under the same or other circumstances. Furthermore, the recitation of one or more preferred embodiments does not imply that other embodiments are not useful and is not intended to exclude other embodiments from the scope of the invention.

[0038] It must also be noted that, as used in the specification and the appendedclaims, the singular forms “a”, “an” and “the” include plural referents unless the context clearly dictates otherwise.

[0039] The prior art referred to herein is fully incorporated herein by reference unless specifically disclaimed.

[0040] Although example embodiments of the disclosed technology are explained in detail herein, it is to be understood that other embodiments are contemplated. Accordingly, it is not intended that the disclosed technology be limited in its scope to the details of construction and arrangement of components set forth in the following description or illustrated in the drawings. The disclosed technology is capable of other embodiments and of being practiced or carried out in various ways.

[0041] This specification is prepared having regard to the principles of general application. As such, where the specification discloses a principle of general application, the claims may be drafted in correspondingly general terms (Biogen v Medeva

[1997] RPC 1 at 48). A “principle of general application” is a general principle that can be practically applied in making a class of products, or in working a process, including where the claims define the products or process(es) in terms of the result to be achieved.

[0042] A feature in the claims stated in general terms will represent a principle of general application, where it is reasonable to expect (reasonable to predict) that the claimed invention will work with anything that falls within the general term. Such a feature defined in general terms may be a major part of the claim, or it may be a simple descriptive word. In either case, a feature in the claims expressed in general terms will be sufficiently enabled if the disclosure enables at least one form of, or one application of, a general principle in respect of the feature, and the person skilled in the art would reasonably expect the invention to work with anything that falls within the general term. (Kirin-Amgen Inc. v Hoechst Marion Roussel Ltd

[2005] RPC 9 at

[0112] ).

[0043] Where the claims are more broadly drafted they may be considered enabled if, prima facie: a) the disclosure teaches a principle that the person skilled in the art would need to follow in order to achieve each and every embodiment falling within a claim; and b) the specification discloses at least one application of the principle and provides sufficient information for the person skilled in the art to perform alternative applications of the principle in a way that, while not explicitly disclosed, would nevertheless be obvious to the person skilled in the art (T484 / 92).Brief Description of the Drawings

[0044] A preferred embodiment of the present invention will now be described with reference to the accompanying drawings, in which:

[0045] Figure 1 shows photographs of the scrap copper anode EPP process. Figure 1(a) shows a rack of single use cathodes and Figure 1(b) is a close-up image of the crumbly cupric arsenide deposit, which also reports to the loose sludge at the bottom of the cell. As noted, this process embodies a high environmental impact and attendant health and safety risk factors.

[0046] Figure 2 shows photographs of the copper coated stainless steel cathode process. Figure 2(a) is a close-up image of the crumbly cupric arsenide deposit, which also reports to the loose sludge at the bottom of the cell. Figure 2(b) shows a stack of spent cathode plates. As noted, this process embodies a high environmental impact and attendant health and safety risk factors.

[0047] Figure 3 shows the lead cathode of the present invention. Figure 3(a) shows a rack of inert lead cathodes positioned above an EPP cell. Figure 3(b) shows the cupric arsenide-containing sludge reporting to the bottom of the EPP cell. Overall, the present invention gives rise to a less labour-intensive process resulting in a single product (z.e., the sludge only), reduced environmental, health and safety risks such that the EPP sludge can be briquetted (see, Figure 3(c)) and sealed - and finally, a low product volume (the EPP sludge only; the lead cathodes are reusable).Summary of the Invention

[0048] Based on the Inventors’ industrial experience and observation that copper nucleation on a lead-based surface is relatively poor, the idea of substituting standard stainless steel or copper cathodes with chemically inert lead anodes was contemplated.

[0049] Conception and trialling of single-stage liberation with an all-lead electrode has successfully demonstrated the production of a non-adhesive, sludge-only material.

[0050] During the trials, the lead cathode provided sufficient electrical conductivity for the copper / arsenic reduction step, but an insufficient deposit-to-substrate bond. Weak adhesion between the cupric arsenide deposit and lead oxide substrate proved too weak to support accumulative weight of the electrodeposited material, which resulted in continuous sludge dislodgment / sliding off from lead cathode surface.

[0051] Merging the inventive all-lead electrode concept with a single-stage liberation step can be highly beneficial to copper refining electrolyte purification plants. Notable benefits of substituting the traditional copper-coated stainless steel cathodes and copper scrap anode with all-lead electrodes include:

[0052] a) A sludge-only product. Because the Cu / As deposit bonds poorly onto a lead substrate the all-lead electrode process will produce a sludge-only material. Accordingly, the all-lead electrode process stands to improve, reduce or eliminate a number of tasks associated with traditional EPP processes:

[0053] i) Elimination of single-use scrap copper anodes as EPP cathodes. Traditionally, the EPP copper scrap anodes need to be uniform and straight and are therefore about 7-10% thicker than standard scrap anodes. On top of the extra 7-10% thickness, remelting or additional handling steps such as anode manual washing, transportation, sorting, spacing, cell loading / harvesting, bundling, strapping and storing, etc., would be eliminated.

[0054] ii) Elimination of copper-coated stainless steel electrodes as EPP cathodes. Some copper refinery plants use copper pre-coated stainless steel electrodes as the EPP cathode. This method utilises / sacrifices commercial -grade 3-day copper deposit as the EPP plating substrate. Like the above-mentioned scrap anode method, these cathodes need to be manually stripped, bundled, strapped, stored and remelted.

[0055] iii) EPP plant CAPEX reduction. The traditional EPP cathode options require a significant amount of specialised equipment. The need for various storage racks, cathode washing and stacking equipment, product transportation containers and specifically designed crane lifting equipment will be substantially reduced.

[0056] iv) EPP product transport cost reduction. Compared to the traditional EPP cathode options, the inventive all-lead electrode concept stands to reduce the weight and volume of product by approximately 50 to 60%.

[0057] v) Environmental impact reduction. Cell sludge can be contained, handled and transported far more easily than a crumbly, solid deposit. Activities such as bundle loading, transporting and off-loading can easily disturb and spill arsenic-loaded deposit resulting in environmental contamination and a costly remediation process. The sludge can be packed in sealable drums or other sealable containers for disposal or storage.

[0058] vi) Health and safety impact reduction. The first two options (scrap anode or copper-coated stainless steel cathode) require a significant amount of manual handling.This exposes workers to high potential for injuries and exposure to arsenic airborne contaminants. The sludge of the inventive EPP cells would be primarily handled in a wet form by a series of tanks, pumps and filters which would significantly reduce human exposure to injuries and airborne contaminants.

[0059] b) Improved EPP time efficiency. Since both sets of lead electrodes (z.e., anodes and cathodes) would be of substantially identical size and shape, only one type of electrode lifting / handling equipment would be needed. A single crane bale with correctly spaced hooks could be utilised to pick up both types of electrodes at once which would speed up cell emptying / cleaning process significantly.

[0060] c) Electrode polarity alternation. Since both electrodes are formed of the same material and are of substantially identical size, electrical polarity alternation (electrode rotation) can be easily applied. The ability to alternate electrode polarity can be beneficial not only to the in-situ electrode cleaning process but is also advantageous in terms of electrode wearing and sludge dislodgement when the DC rectifier pulse reverse current method (PRC) is applied.

[0061] According to a first aspect of the present invention there is provided use of a lead electrode in a method for removing one or more impurities from a copper refinery electrolyte.

[0062] In an embodiment, the method for removing one or more impurities from a copper refinery electrolyte is a single-stage electrolyte purification / liberation (EPP) method.

[0063] In an embodiment, the one or more impurities comprise arsenic. In other embodiments, the one or more impurities comprise arsenic, antimony and / or bismuth.

[0064] Under standard electrorefining conditions, elements that are insoluble / more noble than copper, such as Au, Ag, Os, Ru, Ir, Rh, Pd, Pt, Pb, Te, Se and Sn will be not electrodeposit onto the stainless cathode blank and will report to the anodic slimes. However, less noble elements such as As, Sb, Bi, S, Fe, Co and Ni will dissolve and gradually accumulate in the electrolyte. Failure to control accumulation of these impurities causes high energy consumption and reduces the final copper product quality.

[0065] In an embodiment, the lead electrode is a cathode. During the electrorefining of copper, oxidation occurs at the cathode and as such, the plating surface of the lead cathode will comprise lead oxide.

[0066] In an embodiment, the lead electrode is comprised of about 90 to about 100wt.% lead. Preferably, the lead electrode is comprised of about 90, 90.5, 91, 91.5, 92, 92.5, 93, 93.5, 94, 94.5, 95, 95.5, 96, 96.5, 97, 97.5, 98, 98.5, 99, 99.5, or about 100 wt.% lead. The term “lead” cathode / el ectrode is defined in paragraph

[0026] , above.

[0067] In an embodiment, the lead electrode provides sufficient electrical conductivity to facilitate a copper / arsenic reduction step, but insufficient adhesion between the resultant cupric arsenide deposit and lead (lead oxide) substrate to facilitate plating. It will be appreciated that these qualities are key to the present invention as it enables the cupric arsenide to be advantageously extracted in a single form (z.e., in the sludge).

[0068] In an embodiment, the cupric arsenide deposit subsequently reports to a sludge layer at the bottom of the EPP cell.

[0069] In an embodiment, prior to deployment of the EPP method, the copper refinery electrolyte has an initial concentration of arsenic of about 0.1 g / L to about 30 g / L. In other embodiments, the copper refinery electrolyte has an initial concentration of arsenic of about 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, or about 30 g / L.

[0070] According to a second aspect of the present invention there is provided a lead electrode for use in a method of removing one or more impurities from a copper refinery electrolyte.

[0071] In an embodiment, the method for removing one or more impurities from a copper refinery electrolyte is a single-stage electrolyte purification / liberation (EPP) method.

[0072] In an embodiment, the one or more impurities comprise arsenic. In other embodiments, the one or more impurities comprise arsenic, antimony, bismuth, sulfur, iron, cobalt and / or nickel.

[0073] In an embodiment, the lead electrode is a cathode. During the electrorefining of copper, oxidation occurs at the cathode and as such, the plating surface of the lead cathode will comprise lead oxide.

[0074] In an embodiment, the lead electrode is comprised of about 90 to about 100 wt.% lead. Preferably, the lead electrode is comprised of about 90, 90.5, 91, 91.5, 92, 92.5, 93, 93.5, 94, 94.5, 95, 95.5, 96, 96.5, 97, 97.5, 98, 98.5, 99, 99.5, or about 100 wt.% lead. The term “lead” cathode / el ectrode is defined in paragraph

[0026] , above.

[0075] In an embodiment, the lead electrode provides sufficient electricalconductivity to facilitate a copper / arsenic reduction step, but insufficient adhesion between the resultant cupric arsenide deposit and lead substrate to facilitate plating. It will be appreciated that these qualities are key to the present invention as it enables the cupric arsenide to be advantageously extracted in a single form (z.e., in the sludge).

[0076] In an embodiment, the cupric arsenide deposit subsequently reports to a sludge layer at the bottom of the EPP cell. The term “sludge” is defined in paragraph

[0027] , above.

[0077] In an embodiment, prior to deployment of the EPP method, the copper refinery electrolyte has a concentration of arsenic of about 0.1 g / L to about 30 g / L. In other embodiments, the copper refinery electrolyte has an initial concentration of arsenic of about 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, or about 30 g / L.

[0078] According to a third aspect of the present invention there is provided a method for removing one or more impurities from a copper refinery electrolyte, the method comprising the steps of:

[0079] providing an electrolyte having a concentration of arsenic that is sufficiently elevated as to affect the purity of the final copper cathode product;

[0080] providing a cell adapted for performing a single-stage electrolyte purification / liberation (EPP) method;

[0081] providing to the EPP cell a cathode comprised of about 90 to about 100 wt.% lead;

[0082] performing the EPP method for a predetermined period, thereby to effect a copper / arsenic reduction step; and

[0083] obtaining the resultant cupric arsenide deposit in a sludge layer at the bottom of the EPP cell.

[0084] In an embodiment, the lead electrode is comprised of about 90, 90.5, 91, 91.5, 92, 92.5, 93, 93.5, 94, 94.5, 95, 95.5, 96, 96.5, 97, 97.5, 98, 98.5, 99, 99.5, or about 100 wt.% lead. The term “lead” cathode / electrode is defined in paragraph

[0026] , above.

[0085] In an embodiment, the copper / arsenic reduction step is performed from about 1% substantially to completion. In other embodiments, the copper / arsenic reduction step is performed to about 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49, 50, 51, 52, 53, 54, 55, 56, 57, 58, 59, 60, 61, 62, 63, 64, 65, 66, 67, 68, 69,70, 71, 72, 73, 74, 75, 76, 77, 78, 79, 80, 81, 82, 83, 84, 85, 86, 87, 88, 89, 90, 91, 92, 93, 94, 95, 96, 97, 98, 99 or about 100% completion.

[0086] In an embodiment, the method further comprises the step of removing the sludge from the electrolyte, thereby providing a dearsenified (purified) electrolyte.

[0087] In an embodiment, the method further comprises the step of returning the dearsenified (purified) electrolyte to the copper refinery cell or to downstream processing.

[0088] In an embodiment, the method comprises a plurality of EPP cells arranged in series or in parallel.

[0089] In an embodiment, the ratio of copper to arsenic (Cu: As) is maintained at optimum levels for plating arsenic. In general, the continuous deposition of arsenic from the electrolyte requires copper in solution (< 10 g / L Cu(II)) to form copper arsenides.

[0090] According to a fourth aspect of the present invention there is provided a purified (dearsenified) copper refinery electrolyte, when so purified by a method according to the third aspect of the present invention.

[0091] According to a fifth aspect of the present invention there is provided a sludge comprising cupric arsenide, when formed by a method according to the third aspect of the present invention.

[0092] According to a sixth aspect of the present invention there is provided a cell for removing one or more impurities comprising arsenic from a copper refinery electrolyte in a single-stage electrolyte purification / liberation (EPP) method, the cell comprising:

[0093] means for circulating a flow of the electrolyte between an anode and a cathode, wherein the cathode is comprised of about 90 to about 100 wt.% lead;

[0094] means for providing an electrical circuit between the anode and the cathode, thereby to facilitate a copper / arsenic reduction step; and

[0095] a bottom portion comprising a sludge to which cupric arsenide formed from the reduction step reports.

[0096] In an embodiment, the lead electrode is comprised of about 90, 90.5, 91, 91.5, 92, 92.5, 93, 93.5, 94, 94.5, 95, 95.5, 96, 96.5, 97, 97.5, 98, 98.5, 99, 99.5, or about 100 wt.% lead.

[0097] In an embodiment, the cell further comprises means for extracting the cupric arsenide-containing sludge from the bottom portion of the cell. Exemplary means includepumping the sludge, or one or more exit ports to facilitate gravity flow of the sludge from the cell.

[0098] In an embodiment, the cell further comprises means for reintroducing the resultant cleansed electrolyte to the copper refinery cell.

[0099] According to a seventh aspect of the present invention there is provided a system for removing one or more impurities comprising arsenic from a copper refinery electrolyte in a single-stage electrolyte purification / liberation (EPP) method, the system comprising a plurality of cells as defined according to the sixth aspect of the present invention, arranged in series or in parallel.

[0100] In an embodiment, the plurality of cells are arranged in parallel.

[0101] It will be appreciated that the present invention facilitates the removal of arsenic from copper refinery electrolyte in a single form (z.e., reporting to the sludge) rather than some of the cupric arsenide depositing on the cathode. This lends itself to material handling and productivity benefits.Detailed Description of a Preferred Embodiment

[0102] A preferred embodiment of the present invention relates to a method for removing one or more impurities from a copper refinery electrolyte, the method comprising the steps of:

[0103] i) providing an electrolyte having a concentration of arsenic that is sufficiently elevated as to affect the purity of the final copper cathode product;

[0104] In practice, the contaminated electrolyte may have a concentration of arsenic of about 0.1 g / L to about 30 g / L.

[0105] ii) providing a cell adapted for performing a single-stage electrolyte purification / liberation (EPP) method;

[0106] Such a cell is known in the art and described at paragraphs

[0019] through

[0021] , above.

[0107] iii) providing to the EPP cell a cathode comprised of about 90 to about 100 wt.% lead;

[0108] The cathode does not need to be pure lead; it may be an alloy or the like. The critical factor is that the cathode provides for sufficient electrical conductivity to facilitate a copper / arsenic reduction step, but insufficient adhesion between the resultant cupric arsenide deposit and lead substrate to facilitate plating.

[0109] iv) performing the EPP method for a predetermined period, thereby to effect a copper / arsenic reduction step;

[0110] The copper / arsenic reduction step may be performed from about 1% substantially to completion, or anywhere from about 1 to about 99% completion.

[0111] v) obtaining the resultant cupric arsenide deposit in a sludge layer at the bottom of the EPP cell.

[0112] Because none of the cupric arsenide deposits on the cathode, it reports exclusively to the sludge layer at the bottom of the cell, thereby facilitating more ready removal with fewer safety and environmental implications.

[0113] The inventive method may further include the step of removing the sludge from the electrolyte, thereby providing a dearsenified electrolyte and / or may further include the step of returning the dearsenified electrolyte to the copper refinery cell or further downstream processing.

[0114] To facilitate performing the inventive method on an industrial scale, a plurality of EPP cells may be arranged in series or in parallel. Preferably, the cells are arranged in parallel as this enables a greater throughput.

[0115] Significantly, throughout the process, the ratio of copper to arsenic (Cu:As) is maintained at optimum levels for plating arsenic. In general, the continuous deposition of arsenic from the electrolyte requires copper in solution (< 10 g / L Cu(II)) to form copper arsenides.Economic and Environmental Implications

[0116] The present invention embodies significant economic and environmental benefits. For example, improved impurity removal from a copper refinery electrolyte leads to less downtime due to cleaning, greater copper output and quality, etc.

[0117] The cell sludge formed from the inventive method is contained, handled and transported far more easily than a crumbly, solid deposit. Activities such as bundle loading, transporting and off-loading can easily disturb and spill arsenic-loaded deposit resulting in environmental contamination and a costly remediation process. The sludge can be packed in sealable drums or other sealable containers for disposal or storage.Industrial Applicability

[0118] The inventive method has clear utility in a coppery refinery producing highquality copper cathode (99.99 wt.%). Global supply of such cathode is about 30 million metric tons per annum, making it a highly significant industrial process.

[0119] Although the invention has been described with reference to specific examples it will be appreciated by those skilled in the art that the invention may be embodied in many other forms.

Claims

THE CLAIMS DEFINING THE INVENTION ARE AS FOLLOWS:-1. Use of a lead electrode in a method for removing one or more impurities from a copper refinery electrolyte.

2. Use according to claim 1, wherein the method for removing one or more impurities from a copper refinery electrolyte is a single-stage electrolyte purification / liberation (EPP) method.

3. Use according to claim 1 or claim 2, wherein the one or more impurities comprise arsenic.

4. Use according to any one of the preceding claims, wherein the lead electrode is a cathode.

5. Use according to any one of the preceding claims, wherein the lead electrode is comprised of about 90 to about 100 wt.% lead.

6. Use according to any one of claims 3 to 5, wherein the lead electrode provides sufficient electrical conductivity to facilitate a copper / arsenic reduction step, but insufficient adhesion between the resultant cupric arsenide deposit and lead substrate to facilitate plating.

7. Use according to claim 6, wherein the cupric arsenide deposit subsequently reports to a sludge layer at the bottom of the EPP cell.

8. Use according to any one of claims 2 to 7, wherein prior to deployment of the EPP method, the copper refinery electrolyte has a concentration of arsenic of about 0.1 g / L to about 30 g / L.

9. A lead electrode for use in a method of removing one or more impurities from a copper refinery electrolyte.

10. An electrode according to claim 9, wherein the method for removing one or more impurities from a copper refinery electrolyte is a single-stage electrolyte purification / liberation (EPP) method.

11. An electrode according to claim 9 or claim 10, wherein the one or more impurities comprise arsenic.

12. An electrode according to any one of claims 9 to 11, wherein the lead electrode is a cathode.

13. An electrode according to any one of claims 9 to 12, wherein the lead electrode is comprised of about 90 to about 100 wt.% lead.

14. An electrode according to any one of claims 11 to 13, wherein the lead electrode provides sufficient electrical conductivity to facilitate a copper / arsenic reduction step, but insufficient adhesion between the resultant cupric arsenide deposit and lead substrate to facilitate plating.

15. An electrode according to claim 14, wherein the cupric arsenide deposit subsequently reports to a sludge layer at the bottom of the EPP cell.

16. An electrode according to any one of claims 10 to 15, wherein prior to deployment of the EPP method, the copper refinery electrolyte has a concentration of arsenic of about 0.1 g / L to about 30 g / L.

17. A method for removing one or more impurities from a copper refinery electrolyte, the method comprising the steps of: providing an electrolyte having a concentration of arsenic that is sufficiently elevated as to affect the purity of the final copper cathode product; providing a cell adapted for performing a single-stage electrolyte purification / liberation (EPP) method; providing to the EPP cell a cathode comprised of about 90 to about 100 wt.% lead;performing the EPP method for a predetermined period, thereby to effect a copper / arsenic reduction step; and obtaining the resultant cupric arsenide deposit in a sludge layer at the bottom of the EPP cell.

18. A method according to claim 17, wherein the copper / arsenic reduction step is performed from about 1% substantially to completion.

19. A method according to claim 17 or claim 18, further comprising the step of removing the sludge from the electrolyte, thereby providing a dearsenified electrolyte.

20. A method according to claim 19, further comprising the step of returning the dearsenified electrolyte to the copper refinery cell or downstream processing.

21. A method according to any one of claims 17 to 20, comprising a plurality of EPP cells arranged in series or in parallel.

22. A method according to any one of claims 17 to 21, wherein the ratio of copper to arsenic (Cu: As) is maintained at optimum levels for plating arsenic.

23. A purified copper refinery electrolyte, when so purified by a method according to any one of claims 17 to 22.

24. A sludge comprising cupric arsenide, when formed by a method according to any one of claims 17 to 22.

25. A cell for removing one or more impurities comprising arsenic from a copper refinery electrolyte in a single-stage electrolyte purification / liberation (EPP) method, the cell comprising: means for circulating a flow of the electrolyte between an anode and a cathode, wherein the cathode is comprised of about 90 to about 100 wt.% lead; means for providing an electrical circuit between the anode and the cathode,thereby to facilitate a copper / arsenic reduction step; and a bottom portion comprising a sludge to which cupric arsenide formed from the reduction step reports.

26. A cell according to claim 25, further comprising means for extracting the cupric arsenide-containing sludge from the bottom portion of the cell.

27. A cell according to claim 25 or claim 26, further comprising means for reintroducing the resultant cleansed electrolyte to the copper refinery cell or downstream processing.

28. A system for removing one or more impurities comprising arsenic from a copper refinery electrolyte in a single-stage electrolyte purification / liberation (EPP) method, the system comprising a plurality of cells as defined according to any one of claims 25 to 27, arranged in series or in parallel.

29. A system according to claim 28, wherein the plurality of cells are arranged in parallel.

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