Acid mist suppressant for metal electrowinning

Abstract

The invention relates to an aqueous electrolyte solution, comprising: - non-ferrous metal ions; - at least one acid; and - at least one surfactant of formula X-(RO)n-Y where RO is a propyleneoxy group or a propyleneoxy / ethyleneoxy group, n being an integer from 3 to 35, X is selected from H, H2N, H2NCH2, HO, (R'O)(R'O)OP, or (R'O)(R'O)OPO, and their salts, where R' is H or a C1-C3 hydrocarbon chain, Y is selected from H, a linear alkyl chain of C1-C3, CH2CH2NH2, CH2CH(CH3)NH2, PO(OR')(OR'), CH2CH2PO(OR')(OR'), CH2CH(CH3)PO(OR')(OR'), and their salts, where R' is H or a C1-C3 hydrocarbon chain. It also relates to an electrowinning system comprising said aqueous electrolyte solution and to a method of reducing acid mist generation in metal electrowinning applications comprising said surfactant.

Description

ACID MIST SUPPRESSANT FOR METAL ELECTROWINNINGTECHNICAL FIELD

[0001] The invention generally relates to the extraction and recovery of metals from ores, especially non-ferrous metals such as copper for example, particularly via electrowinning or electroplating processes. The invention relates more specifically to an aqueous electrolyte solution comprising, inter alia, at least one aqueous-soluble surfactant, to an electrowinning system comprising a cell containing the aqueous electrolyte solution, and to the method of reducing acid mist generation in metal electrowinning applications using said aqueous-soluble surfactant. The use of said surfactant as an acid mist suppressant in non-ferrous metal electrowinning and nonferrous metal electroplating are also specific objects of the invention.BACKGROUND

[0002] The production of non-ferrous metals from ores can be achieved by hydrometallurgical processing using leaching and electrowinning (EW) steps. The metal is extracted from ores through leaching, where the ore may be first subjected to comminution and then contacted with the leaching reagent (such as dilute sulfuric acid) which dissolves the metal from the ore, transferring it to the aqueous phase. The metal in the leach solution may be refined using techniques such as solvent extraction and / or ion exchange. In solvent extraction, the leach solution is mixed with an immiscible organic phase containing an extractant that selectively transfers metal. The organic phase is composed of one or more extractants such as hydroxy oxime extractants, used in the refining of copper and nickel, or organophosphorous extractants, used in the refining of cobalt, nickel, and zinc. The extractant is dissolved in a kerosene diluent. Modifying reagents may also be added to the solvent extraction organic phase to alter the metallurgical and / or physical performance of the solvent extraction system. Metal is transferred from the solvent extraction organic into a second aqueous phase in a stripping reaction, resulting in a concentrated and purified solution. When copper is the non-ferrous metal, a high acid (120-240 g / L H2SO4) high metal (25-45 g / L) solutionknown as lean or spent electrolyte (LE) is used to strip. The metal is recovered from the electrolyte electrolytically in an electrochemical cell.

[0003] Taking the example of copper as the non-ferrous metal, the production of copper by electrowinning involves plating copper in an electrochemical cell. The electrolyte following stripping, known as the rich electrolyte (RE), is enriched in metal and depleted in acid. The rich electrolyte is mixed with lean electrolyte prior to entering the electrowinning cell where metal is recovered electrolytically. The electrolyte entering the electrowinning cell has a composition of 30-60 g / L metal, 100-220 g / L H2SO4 and a temperature of 25-65 °C. Copper is reduced at the cathode according to Equation 1 :Equation 1 : Cu2++ 2e’ CuOxygen is evolved at the anode according to Equation 2:Equation 2: H2O i O2 + 2 H++ 2e’

[0004] During the electrowinning process, the electrolyte solution is pumped into cells containing several anode and cathode pairs. The anodes are primarily lead-based alloys or titanium mesh coated with mixed metal oxides (MMO) while the cathodes can be copper starter sheets or stainless-steel blanks. An electric current (current density 150- 400 A / m2) is applied to the electrowinning cells resulting in high purity copper metal being deposited onto the surface of the cathode. Typical plating cycles are 1-20 days. Oxygen is evolved at the surface of the anode. The oxygen bubbles rise to the surface of the electrolyte and burst, dispersing the acidic electrolyte in small droplets forming an acid mist. The presence of sulfuric acid mist in the air presents a safety concern to all individuals required to work in the electrowinning tankhouse. The health and safety implications of suspended sulfuric acid droplets in the air are the primary driver in mitigating the formation of acid mist.

[0005] The acid mist creates health and safety issues as well as possible corrosion issues in the electrowinning tankhouse. Various mechanisms thus have been proposed for the suppression of acid mist using surfactants, including the control of the acid mist bubble size and modification of the bubble burst mechanism.

[0006] In order to reduce acid mist generation, several different approaches have been implemented which include mechanical and chemical methods. Two of the most common mechanical methods used in industry include dispersing round plastic balls across the EW cell, referred to as acid mist balls, which act as a barrier keeping the acid mist near the electrolyte surface. Secondly, most electrowinning tankhouses are designed to allow fresh air to pass freely through the tankhouse, allowing for enhanced ventilation. Hoods can also be installed over the cells to provide direct ventilation, however, they can limit access to the cathode for harvesting and their high installation cost can be prohibitive. Both of these methods are often used in conjunction with a chemical method due to the fact that the plastic round balls and open-air ventilation do not provide a suitable amount of acid mist suppression to be a standalone solution. Chemical methods involve the addition of surfactants to the electrolyte solution.

[0007] Acid mist is generated during the electrodeposition of other metals such as zinc, chromium, or nickel. Similar mechanical and physical methods for acid mist suppression during copper electrowinning may also be applied to these metals.

[0008] Several surfactants have been used for acid mist suppression in metal electrowinning applications through the creation of a stable foam layer on the electrolyte surface, however the presence of the foam presents a safety hazard in the electrowinning process. The electrolyte following solvent extraction often contains organics that originate from imperfect phase separation in the solvent extraction process. A large percentage of the organic is a kerosene-based liquid, and when combined with a foaming surfactant in an electrowinning tankhouse can present a considerable fire hazard. Several saponins, which are naturally occurring substances, tend to be foaming surfactants which include MISTOP and licorice. For example, one can refer to document US 2023 / 0110076 which proposes to add licorice extract to the acidic electrolyte, thereby forming a layer of foam which, according to this document, could mitigate acid mist production. Dosing of the surfactant may be controlled to reduce the tendency for foaming; however, the electrowinning operation may be limited to lower current densities.

[0009] Fluorosurfactants have proven to be very effective and widely used. Document US 4484990 discloses a process for recovery of metal values by liquid solventextraction of said metal values via electrowinning. The electrolyte contains a fluoroaliphatic surfactant to provide mist-inhibiting foam on the surface of the electrolyte. However, fluorosurfactants are not environmentally safe chemicals to produce and use. Some fluorosurfactants are known to be persistent environmental pollutants and may bioaccumulate in complex organisms causing long-term health impacts.SUMMARY

[0010] In view of the foregoing, an object of the invention is to provide an aqueous electrolyte solution having acid mist suppressor or inhibitor properties, which may be used in electrowinning applications or electroplating applications.

[0011] In one aspect, the invention relates to an aqueous electrolyte solution, comprising: non-ferrous metal ions; at least one acid; and at least one surfactant of formula X-(R0)n-Y whereinRO is a propyleneoxy group or a propyl eneoxy / ethyleneoxy group, n being an integer from 3 to 35,X is H, H2N, H2NCH2, HO, (R’O)(R’O)OP, or (R’O)(R’O)OPO, and their salts, where R’ is H or a C1-C3 hydrocarbon chain,Y is H, a linear alkyl chain of C1-C3, CH2CH2NH2, CH2CH(CH3)NH2, PO(OR’)(OR’), CH2CH2PO(OR’)(OR’), CH2CH(CH3)PO(OR’)(OR’), and their salts, where R’ is H or a C1-C3 hydrocarbon chain.

[0012] The surfactant of formula X-(R0)n-Y acts as an acid mist suppressor in the electrolyte solution, thereby reducing or suppressing the mist generally observed during electrowinning when the oxygen formed on the anode rises to the electrolyte surface in the form of bubbles which then burst at the air / electrolyte interface and disperse the acidic electrolyte in small droplets.

[0013] From a practical point of view, and this aspect will be described in more details in the following, the surfactant is mixed with a metal-containing electrolyte prior to the electrowinning process.

[0014] Without being bound to any theory, the inventors have discovered that the specific formula X-(R0)n-Y of the surfactant described above, with specific groups X and Y, and short alkyl chains of one to three carbon atoms, lead to good mist suppression performance, and yields better solvent extraction physical and metallurgical performance (including parameters such as kinetics, phase disengagement, and solubility) than that seen with known surfactants, without the formation of a foam. Put another way, the aqueous electrolyte solution does not rely on the formation of a stable foam layer to inhibit acid mist suppression, as opposed to products such as DOWFROTH™ 250 and saponins / licorice for example or other biobased structures.

[0015] Another advantage is that the surfactant of formula X-(R0)n-Y is not a perfluorinated surfactant or a structure containing perfluorinated alkyl groups (PF AS), thereby avoiding negative environmental and health risks and impacts, while showing at least similar mist suppression performance.

[0016] Thanks to the surfactant of formula X-(R0)n-Y, the aqueous electrolyte solution containing the latter: exhibits acid mist suppression performance equal to or greater than other commercially available acid mist suppressants at an economical cost for the customer; is compatible with adjacent solvent extraction unit operations, in particular with respect to kinetics, phase separation, and solubility; is compatible with conventional copper electrowinning operations and does not exhibit negative impacts to metal cathode quality; is chemically stable in the electrowinning process; does not generate a persistent foam layer during electrowinning or electroplating.

[0017] For clarification purposes, the compounds of formula X-(R0)n-Y are polymers. In particular, in formula X-(R0)n-Y, the terms “RO is a propyleneoxy group or a propyl eneoxy / ethyleneoxy group” means that RO may be a propyleneoxy group, or can comprise both a propyleneoxy group and an ethyleneoxy group. In the present invention, when RO comprises both a propyleneoxy group and an ethyleneoxy group, the at least one surfactant is in the form of a copolymer.

[0018] In this same formula X-(RO)n-Y, in relation to the X group, the terms “where R’ is H or a C1-C3 hydrocarbon chain” means, when there are two R’ in the molecule, that one of the R’ may be H and the other may be a C1-C3 hydrocarbon chain, or that both R’ may be H, or that both R’ may be a C1-C3 hydrocarbon chain and, if applicable, the same C1-C3 hydrocarbon chain or different C1-C3 hydrocarbon chains.

[0019] In order to clarify what is meant by the terms “electrowinning” and “electroplating”, the electroplating process uses electrodeposition to coat an object in a layer of metal(s), said object may be an electrode such as a cathode. As explained previously, in electrowinning, an electrical current is passed from an inert anode through an electrolyte solution containing the dissolved metal ions so that the metal is recovered as it is deposited in an electroplating process onto the cathode. Electroplating is thus part of an electrowinning process, but it can also be carried out in a separate process.

[0020] Electrowinning and electroplating thus are both electrochemical processes that use an electric current to deposit metal (contained in an electrolyte) onto a cathode. Electrowinning produces solid metal as the final product. Electroplating coats the surface of an object with a thin layer of metal.

[0021] According to other optional features of the aqueous electrolyte solution of the invention: in formula X-(R0)n-Y of the at least one surfactant, X is H2N and Y is CH2CH(CH3)NH2; in formula X-(R0)n-Y of the at least one surfactant, X is HO and Y is H; in formula X-(R0)n-Y of the at least one surfactant, when Y is a linear alkyl chain of C1-C3, X is different from H or HO;The non-ferrous metal ions are selected from the group consisting of copper, zinc, cobalt, nickel, manganese, chromium, cadmium, tin, lead, gallium, germanium, indium gold, silver, platinum group metals, and their alloys. Platinum Group Metals usable according to the invention (acronym PGM) include in particular ruthenium, rhodium, palladium, osmium, iridium, platinum. More preferably, the non-ferrousmetal ions are selected from the group consisting of copper, zinc, cobalt, nickel. Even more preferably, the non-ferrous metal ions are copper;The acid is sulfuric acid;The at least one surfactant is present in an amount sufficient to reduce acid mist generation from the aqueous electrolyte solution when O2 is generated within the aqueous electrolyte solution;At least one surfactant is present in the aqueous electrolyte solution in an amount ranging from 1 to 100 ppm;- the non-ferrous metal ion is present in an amount ranging from 30 to 60 g / L;The at least one acid is present in an amount ranging from 100 to 220 g / L;The at least one surfactant is present in an amount insufficient to produce a stable foam in the aqueous electrolyte solution;- the molecular weight of the surfactant is inferior or equal to 2500 g / mol;- the aqueous electrolyte solution does not contain a fluorinated surfactant;

[0022] Another object of the invention is an electrowinning system, comprising: a cell containing the aqueous electrolyte solution as described above, a cathode and anode immersed within the aqueous electrolyte solution; and a rectifier for providing an electrical current between the cathode and anode, thereby resulting in the deposition of the non-ferrous metal on the cathode.

[0023] Preferably, the electrowinning system comprises, within a tank house, a plurality of the cells containing the aqueous electrolyte solution, each cell having the cathode and the anode immersed in the aqueous electrolyte solution, a rectifier for providing an electrical current between the cathode and anode, thereby resulting in the deposition of the non-ferrous metal on the cathode.

[0024] Another object of the invention is a method of reducing acid mist generation in metal electrowinning applications, comprising: adding at least one surfactant of formula X-(R0)n-Y to an aqueous electrolyte solution comprising at least one non-ferrous metal ion species and an acid; and conducting an electrowinning process on the aqueous electrolyte solution,wherein in the formula X-(RO)n-Y,RO is a propyleneoxy group or a propyleneoxy / ethyleneoxy group, n being an integer from 3 to 35,X is H, H2N, H2NCH2, HO, (R’O)(R’O)OP, or (R’O)(R’O)OPO, and their salts, where R’ is H or a C1-C3 hydrocarbon chain,Y is H, a linear alkyl chain of C1-C3, CH2CH2NH2, CH2CH(CH3)NH2, PO(OR’XOR’), CH2CH2PO(OR’)(OR’), CH2CH(CH3)PO(OR’)(OR’), and their salts, where R’ is H or a C1-C3 hydrocarbon chain.

[0025] According to other optional features of the method of the invention:The aqueous surfactant is added in an amount of between 1 ppm to 100 ppm;The method further comprises: controlling the addition of the at least one surfactant to maintain the concentration of the at least one surfactant in the aqueous electrolyte solution;The electrowinning process extends for a period of time ranging from 1-20 days.

[0026] The invention also relates to a use of at least one surfactant of formula X-(R0)n- Y as described above as an acid mist suppressant in a non-ferrous metal electrowinning process.

[0027] Other aspects and advantages of the claimed subject matter will be apparent from the following description and the appended claims.BRIEF DESCRIPTION OF DRAWINGS

[0028] FIG. 1 shows an exemplary schematic of the acid mist suppression testing apparatus in one or more embodiments of the present disclosure.

[0029] FIG. 2 shows an exemplary plot of electrolyte solution vs. DI water pH in one or more embodiments of the present disclosure compared to embodiments of the prior art.DETAILED DESCRIPTION

[0030] One or more embodiments provides an aqueous electrolyte solution for use in electrowinning systems and methods to reduce acid mist generation therein. Inparticular, the aqueous electrolyte solution may include a soluble surfactant that inhibits or at least reduces acid mist generation.

[0031] AQUEOUS ELECTROLYTE SOLUTION

[0032] Embodiments disclosed herein are directed to an aqueous electrolyte solution that may advantageously reduce acid mist generation in metal electrowinning applications or electroplating applications. In one or more embodiments, the aqueous electrolyte solution includes non-ferrous metal ions, at least one acid, and at least one surfactant.

[0033] Therefore, in one aspect, the invention relates to an aqueous electrolyte solution, comprising: non-ferrous metal ions; at least one acid; and at least one surfactant of formula X-(R0)n-Y whereRO is a propyleneoxy group or a propyl eneoxy / ethyleneoxy group, n being an integer from 3 to 35, preferably from 5 to 25,X is selected from H, H2N, H2NCH2, HO, (R’O)(R’O)OP, or (R’O)(R’O)OPO, and their salts, where R’ is H or a C1-C3 hydrocarbon chain,Y is selected from H, a linear alkyl chain of C1-C3, CH2CH2NH2, CH2CH(CH?)NH2, PO(OR’XOR’), CH2CH2PO(OR’)(OR’), CH2CH(CH3)PO(OR’)(OR’), and their salts, where R’ is H or a C1-C3 hydrocarbon chain.

[0034] As electrowinning operations seek the electrodeposition of a non-ferrous metal ion from a solution, the non-ferrous metal ions may include any metal ions that have been leached from their ores and / or secondary materials (scrap, e-waste, batteries) for eventual recovery as a bulk metal. For example, in one or more embodiments, the nonferrous metal ions may include but are not limited to copper, zinc, cobalt, nickel, manganese, chromium, cadmium, tin, lead, gallium, germanium, indium, gold, silver, platinum group metals, and their alloys. Platinum Group Metals usable according to the invention (acronym PGM) include in particular ruthenium, rhodium, palladium, osmium, iridium, platinum. More preferably, the non-ferrous metal ions are selected from the group consisting of copper, zinc, cobalt, nickel. Even more preferably, the non-ferrous metal ions are copper.

[0035] The non-ferrous metal ion in one or more embodiments may be present in an amount ranging from about 30 to about 60 g / L. The amount may have a lower limit of one of 30, 35 or 40 g / L and an upper limit of 45, 50, 55 and 60 g / L, where any lower limit may be combined with any mathematically compatible upper limit.

[0036] The solution from which the metal ions are to be deposited contains sulfuric acid. Such acid may be present in the solution entering the electrowinning cell, for example, in a concentration ranging from about 100 to about 220 g / L.

[0037] The concentration of acid may have a lower limit of 100 g / L, preferably 110 g / L, preferably 120 g / L, preferably 130 g / L, preferably 140 g / L, more preferably 150 g / L, and even more preferably 160 g / L.

[0038] The concentration of acid may have an upper limit of 170 g / L, preferably 180 g / L, preferably 190 g / L, preferably 200 g / L, more preferably 210 g / L, and even more preferably 220 g / L. For example, the concentration of acid is from 120 to 220 g / L.

[0039] In one or more embodiments, the acid may be sulfuric acid, hydrochloric acid, nitric acid, phosphoric acid, methanesulfonic acid. Preferably, the acid is sulfuric acid.

[0040] As noted above, the present disclosure is directed to the incorporation of a surfactant in the electrolyte solution to reduce acid mist generation therefrom during electrowinning. In one or more embodiments, the surfactant may be a glycol ether or a mixture of glycol ethers. The glycol may be represented by the formula X-(RO)n-Y.

[0041] In the formula, X is selected from H, H2N, H2NCH2, HO, (R’O)(R’O)OP, or (R’O)(R’O)OPO, and their salts, where R’ is H or a C1-C3 hydrocarbon chain.

[0042] In one embodiment, X is selected from H, H2N, H2NCH2 or HO, and their salts.

[0043] In the formula, Y is selected from H, a linear alkyl chain of C1-C3, CH2CH2NH2,CH2CH(CH3)NH2, PO(OR’XOR’), CH2CH2PO(OR’)(OR’),CH2CH(CH3)PO(OR’)(OR’), and their salts, where R’ is H or a C1-C3 hydrocarbon chain.

[0044] In one embodiment, Y is selected from H, a linear alkyl chain of C1-C3, CH2CH2NH2, or CH2CH(CH3)NH2, and their salts.

[0045] In the formula, RO is a propyleneoxy group or a propyl eneoxy / ethyleneoxy group, n being an integer from 3 to 35. For example, n may have a lower limit of any of 3, 4 or 5 and an upper limit of any of 15, 20, or 25, where any lower limit can be used in combination with any upper limit. In a preferred embodiment, n is an integer from 5 to 25.

[0046] In one or more embodiments, RO in the formula may comprise both an ethyleneoxy group and a propyleneoxy group. Preferably, RO in the formula comprises an amount of propyleneoxy group from 5 to 99 mol%, preferably from 25 to 99 mol%, more preferably from 50 to 99 mol%, for example from 55 to 95 mol% relative to the total number of propyleneoxy group and ethyleneoxy group in the formula.

[0047] In one preferred embodiment, in the formula, X is H2N and Y is CH2CH(CH3)NH2. In another preferred embodiment, in the formula, X is OH and Y is H.

[0048] Preferably, in the formula, when Y is a linear alkyl chain of C1-C3, X is different from H or HO. This means, for example, that when Y is a linear alkyl chain of C1-C3, X is not H or HO but may be any other group mentioned as X in the formula, in particular an amino or phosphonate group.

[0049] In one or more embodiments, at least one surfactant may be present in an amount sufficient to reduce acid mist generation from the aqueous electrolyte solution when O2 is generated within the aqueous electrolyte solution. In one or more embodiments, the surfactant in the present disclosure may be present in an amount insufficient to produce a stable foam in the aqueous electrolyte solution. It is known by a person skilled in the art that the generation of O2 in an aqueous electrolyte solution can lead to the formation of acid mist and foam. Thus, the at least one surfactant according to the invention can reduce acid mist generation when O2 is generated, while not producing a stable foam in the aqueous electrolyte solution, as shown in the examples.

[0050] For example, in one or more embodiments, the at least one surfactant may be present in an amount ranging from about 1 ppm to about 100 ppm of the electrolyte solution. The amount may have a lower limit of one of 1, 5, 10, 15, 20, 25, 30, 35, 40or 45 ppm and an upper limit of 50, 55, 60, 65, 70, 75, 80, 85, 90, 95 and 100 ppm, where any lower limit may be combined with any mathematically compatible upper limit. For example, the at least one surfactant is present in an amount ranging from about 1 ppm to about 50 ppm.

[0051] In one or more embodiments, the molecular weight Mn of the at least one surfactant is inferior or equal to 2500 g / mol. In one or more embodiments, the molecular weight Mn of the at least one surfactant is greater than 250 g / mol.

[0052] In one or more embodiments, the aqueous electrolyte solution does not contain a fluorinated surfactant.

[0053] ELECTROWINNNING SYSTEM

[0054] As mentioned above, the aqueous electrolyte solution may be used in an electrowinning system and process.

[0055] Therefore, another object of the invention is an electrowinning system, comprising: a cell containing the aqueous electrolyte solution as described above, a cathode and anode immersed within the aqueous electrolyte solution; and a rectifier for providing an electrical current between the cathode and anode, thereby resulting in the deposition of the non-ferrous metal on the cathode.

[0056] Thus, one or more embodiments of the present disclosure is directed to an electrowinning system in which the electrolyte solution is used. The electrowinning system of the present disclosure may contain a cell, a cathode and anode, and a rectifier for providing an electrical current between the cathode and anode, thereby resulting in the deposition of the non-ferrous metal on the cathode.

[0057] The electrowinning system of the present disclosure may be within a tank house having a specified volume. The tank house may include a plurality of cells, each containing the aqueous electrolyte solution. Each cell may contain the cathode and the anode immersed in the aqueous electrolyte solution.

[0058] In one preferred embodiment, the electrowinning system comprises, within a tank house,a plurality of the cells containing the aqueous electrolyte solution, each cell having the cathode and the anode immersed in the aqueous electrolyte solution, a rectifier for providing an electrical current between the cathode and anode, thereby resulting in the deposition of the non-ferrous metal on the cathode.

[0059] Moreover, it is common practice in solvent extraction and electrowinning operations to filter the electrolyte to remove solid particles from the electrolyte and to also have an electrolyte bleed that is designed to remove and maintain a targeted level of soluble contaminants. Due to the presence of the electrolyte bleed and the filter media, it is envisioned that the surfactant may be periodically or consistently added to the electrolyte solution in order to maintain the target concentration of the surfactant in the electrolyte.

[0060] METHOD OF REDUCING ACID MIST GENERATION IN METAL ELETROWINNING APPLICATIONS

[0061] As mentioned above, the present disclosure provides an aqueous soluble surfactant within the electrolyte solution that inhibits tiny bubbles from bursting at the surface of the electrolyte solution, thus reducing acid mist generation. To achieve the reduction of acid mist generation in the electrowinning process the present invention is added to the electrolyte in quantities between about 1 ppm and 100 ppm, such as for example, between about 5 ppm and 60 ppm before the electrowinning process.

[0062] One or more embodiments of the present disclosure includes a method of reducing acid mist generation in metal electrowinning applications. The method includes adding at least one surfactant to an aqueous electrolyte solution comprising at least one non-ferrous metal ion species and an acid and conducting an electrowinning process through the aqueous electrolyte solution. By mixing the surfactant into the aqueous electrolyte solution, in one or more embodiments the surface tension of the electrolyte may be reduced.

[0063] Therefore, another object of the invention is a method of reducing acid mist generation in metal electrowinning applications, comprising: adding at least one surfactant of formula X-(R0)n-Y to an aqueous electrolyte solution comprising at least one non-ferrous metal ion species and an acid; andconducting an electrowinning process on the aqueous electrolyte solution, wherein in the formula X-(RO)n-Y,RO is a propyleneoxy group or a propyleneoxy / ethyleneoxy group, n being an integer from 3 to 35, preferably from 5 to 25,X is H, H2N, H2NCH2, HO, (R’O)(R’O)OP, or (R’O)(R’O)OPO, and their salts, where R’ is H or a C1-C3 hydrocarbon chain,Y is H, a linear alkyl chain of C1-C3, CH2CH2NH2, CH2CH(CH3)NH2, PO(OR’)(OR’), CH2CH2PO(OR’)(OR’), CH2CH(CH3)PO(OR’)(OR’), and their salts, where R’ is H or a C1-C3 hydrocarbon chain.

[0064] In one or more embodiments of the present disclosure, the method may include adding the aqueous surfactant to the electrolyte solution in an amount of between about 1 ppm to about 100 ppm. The amount may have a lower limit of one of 1, 5, 10, 15, 20, 25, 30, 35, 40 or 45 ppm and an upper limit of 50, 55, 60, 65, 70, 75, 80, 85, 90, 95 and 100 ppm, where any lower limit may be combined with any mathematically compatible upper limit.

[0065] In one or more embodiments, the method may further comprise controlling the addition of the at least one surfactant to maintain the concentration of the at least one surfactant to the aqueous electrolyte solution.

[0066] As previously mentioned, the surfactant in accordance with one or more embodiments of the present disclosure may be represented by the formula X-(RO)n-Y in which RO is a propyleneoxy group or a propyleneoxy / ethyleneoxy group, n being an integer from 3 to 35, X is H, H2N, H2NCH2, HO, (R’O)(R’O)OP, or (R’O)(R’O)OPO, and their salts, where R’ is H or a C1-C3 hydrocarbon chain, Y is H, a linear alkyl chain of C1-C3, CH2CH2NH2, CH2CH(CH3)NH2, PO(OR’XOR’), CH2CH2PO(OR’)(OR’), CH2CH(CH3)PO(OR’)(OR’), and their salts, where R’ is H or a C1-C3 hydrocarbon chain. The surfactant in the present disclosure may be present in an amount insufficient to produce a stable foam in the aqueous electrolyte solution.

[0067] In one or more embodiments of the present disclosure, the electrowinning process may extend for a period of time ranging from about 1 to about 20 days. The time period may have a lower limit of one of 1, 2, 3, 4, 5, 6, 7, 8, or 9 days and an upperlimit of 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, and 20 days, where any lower limit may be combined with any mathematically compatible upper limit.

[0068] The invention also relates to a use of at least one surfactant of formula X-(RO)n-Y as described above as an acid mist suppressant in a non-ferrous metal electrowinning process.

[0069] The features concerning formula X-(RO)n-Y, especially the possible choices for group X, group Y, group RO, and integer n, apply to all the objects of the present invention detailed above, whether they are composition, process, or use. The full description of the formula may not be recast for every object in the present text to simplify said text.

[0070] EXAMPLES

[0071] The following examples are given for a better understanding of the present invention and should not be construed as limiting to the scope and objects of same.

[0072] Materials

[0073] Commercial surfactants and surfactants according to the invention are tested. The commercial surfactant is FC-1100 (fluorinated surfactant) and was obtained from 3M Company. The commercial surfactants Tergitol™ TMN-6 and Tergitol™ TMN-10 were comparative examples and were purchased from Sigma Aldrich. The surfactants according to the invention are the following: polypropylene oxide), i.e. polypropylene glycol, polypropylene glycol)poly(ethylene glycol) copolymers as both monoamines and diamines and polypropylene glycol) diamine.

[0074] Measuring acid mist suppression

[0075] Acid mist suppression behavior of each reagent was screened using the schematic shown in FIG. 1.

[0076] A synthetic electrolyte solution containing 30 g / L Cu and 150 g / L H2SO4 acid was used for initial testing. The desired dosage of acid mist suppressant was added to 1000 mL of synthetic electrolyte solution in a 1000 mL flask. A rubber hose was inserted into the flask with an air stone at one end submerged in the electrolyte solution. The other end of the rubber hose was attached to an air pump to simulate the oxygenevolution that occurs at the surface of the anode. A piece of filter paper 102 was placed on top of the flask 104 to collect any acid mist that was generated during the test. The test was run at a constant setting on the air pump 106 for 120 minutes. Evidence of foaming on the electrolyte surface was monitored visually. Following the test, a beaker was filled with 50 mL of deionized water and the pH of the water was measured. The filter paper was submerged in the water and mixed for 5 minutes and then removed. The pH of the water was measured again and recorded.

[0077] FIG. 2 shows the results from the acid mist screening test of the surfactants. Baseline in FIG. 2 refers to an electrolyte solution without a surfactant and FC-1100 refers to a comparative sample where the electrolyte solution is made from the commercially available FC- 1100 surfactant.

[0078] With respect to the surfactants of the invention, the results from the acid mist screening test can be found in Table 1.Table 1 : Acid mist generation and reduction results

[0079] According to Table 1, the pH of the water at the end of the test is much higher for the surfactants of the invention than for the baseline, implying that the water is much less acidic. The surfactants of the invention thus strongly reduce the acid mist. Although the ability of a surfactant to reduce acid mist is influenced by multiple parameters such as the selection of X and Y endcaps, molecular weight, and mol% polypropylene glycol), acid mist is more strongly reduced as the mol% polypropylene glycol) and the molecular weight of the surfactant increases. Surfactants of the invention did not generate a stable foam on the electrolyte surface. Avoiding stable foam on the electrolyte surface is crucial to ensure process safety because a stable foam can result in a fire hazard when combined with organics from the solvent extraction process. Moreover, by comparing the results of Table 1 with FIG. 2, we see that the efficacy of the surfactants of the invention is at least similar to that of commercial products such as FC-1100. In Table 1, and in the rest of the text, Mn is the number average molecular weight of the polymers. Molecular weight of polymers may be determined by suitable method known in the art, for example by liquid chromatography-mass spectrometry (LC-MS).

[0080] Dosing

[0081] A similar setup to the acid mist screening test described above was used to estimate the minimum mist suppressant dosage in the LE required to suppress acid mist. A synthetic electrolyte solution containing 30 g / L Cu and 150 g / L H2SO4 acid was dosed with varying concentrations of mist suppressant. 1000 mL of synthetic LE solution dosed with mist suppressant was added to a 1000 mL flask. A rubber hose was inserted into the flask with an air stone at one end submerged in the electrolyte solution. The other end of the rubber hose was attached to an air pump to simulate the oxygen evolution that occurs at the surface of the anode. A piece of filter paper was placed on top of the flask to collect any acid mist that was generated during the test. The test was run at a constant setting on the air pump for 120 minutes. Following the test, a beaker was filled with 50 mL of deionized water and the pH of the water was measured. The filter paper was submerged in the water and mixed for 5 minutes and then removed. The pH of the water was measured again and recorded.

[0082] The results are summarized in Table 2.Table 2: Minimum mist suppressant dosage

[0083] The results show that more surfactant leads to better efficacy. The optimal concentration of surfactant depends on the chemical nature of the surfactant. For polypropylene oxide) Mn= 425, a dosage of at least 10 mg / L leads to great mist suppression, while polypropylene glycol) diamine Mn= 400 a dosage of at least 40 ppm is optimal. Still, reduction of the acid mist is observed when the concentration of these surfactants is lower than their optimal concentration.

[0084] Solvent Extraction Compatibility

[0085] The electrolyte solution is commonly shared between a solvent extraction step and electrowinning; therefore, any acid mist suppressants must be screened for solvent extraction compatibility.

[0086] A synthetic electrolyte solution consisting of 30 g / L Cu and 150 g / L H2SO4 acid is mixed with an organic solution containing 10vol% ACORGA® M5910, a commercial copper extractant, diluted in Orfom SX12, was used to evaluate SX strip compatibility. The organic material was loaded using a loading solution and filtered. The filtered organic material was mixed with the synthetic electrolyte solution in a vessel with samples taken at 15 and 900 seconds. The electrolyte solution is added second in order to maintain organic continuity. The samples are analyzed for copper concentration and the results are shown in Table 3.Table 3: Copper strip kinetics

[0087] Using the existing organic from the strip kinetics testing, phase disengagement testing was completed. The synthetic electrolyte and organic were added to the vessel and mixed for 3 minutes. The time was recorded when the interface passed numbered marks on the vessel and a final time was taken when the solutions were completely separated. This test was repeated 4 more times, with fresh electrolyte added each time. The final contact was completed under aqueous continuity. The results are shown in Table 4.Table 4: Strip phase disengagement

[0088] Advantageously, use of the described surfactant in an electrolyte solution provides a non-fluorinated solution to address acid mist mitigation in metal electrowinning processes. The present disclosure does not negatively impact the solvent extraction process or exhibit any negative impact to metal cathode quality. Additionally, the presentdisclosure does not act as a foaming surfactant while providing similar performance to other acid mist suppressants and delivering the results at a competitive cost.

[0089] Although only a few example embodiments have been described in detail above, those skilled in the art will readily appreciate that many modifications are possible in the example embodiments without materially departing from this invention. Accordingly, all such modifications are intended to be included within the scope of this disclosure as defined in the following claims.

Claims

CLAIMS1. An aqueous electrolyte solution, comprising: non-ferrous metal ions; at least one acid; and at least one surfactant of formula X-(RO)n-Y whereRO is a propyleneoxy group or a propyleneoxy / ethyleneoxy group, n being an integer from 3 to 35, preferably from 5 to 25,X is selected from H, H2N, H2NCH2, HO, (R’O)(R’O)OP, or (R’O)(R’O)OPO, and their salts, where R’ is H or a C1-C3 hydrocarbon chain,Y is selected from H, a linear alkyl chain of C1-C3, CH2CH2NH2, CH2CH(CH?)NH2, PO(OR’XOR’), CH2CH2PO(OR’)(OR’), CH2CH(CH3)PO(OR’)(OR’), and their salts, where R’ is H or a C1-C3 hydrocarbon chain.

2. The aqueous electrolyte solution according to claim 1, wherein RO is a propyleneoxy / ethyleneoxy group comprising an amount of propyleneoxy group from 5 to 99 mol%, preferably from 25 to 99 mol%, more preferably from 50 to 99 mol%, for example from 55 to 95 mol%, relative to the total number of propyleneoxy group and ethyleneoxy group in the formula.

3. The aqueous electrolyte solution according to claim 1 or 2, wherein, in formula X-(RO)n-Y of the at least one surfactant, X is H2N and Y is CH2CH(CH3)NH2.

4. The aqueous electrolyte solution according to claim 1 or 2, wherein, in formula X-(RO)n-Y of the at least one surfactant, X is OH and Y is H.

5. The aqueous electrolyte solution according to claim 1 or 2, wherein in formula X-(RO)n-Y of the at least one surfactant, when Y is a linear alkyl chain of C1-C3, X is different from H or HO.

6. The aqueous electrolyte solution according to any one of claims 1 to 5, wherein the nonferrous metal ions are selected from the group consisting of copper, zinc, cobalt, nickel,manganese, chromium, cadmium, tin, lead, gallium, germanium, indium, gold, silver, platinum group metals, and their alloys.

7. The aqueous electrolyte solution according to any one of claims 1 to 6, wherein the nonferrous metal ions are copper.

8. The aqueous electrolyte solution according to any one of claims 1 to 7, wherein the acid is sulfuric acid.

9. The aqueous electrolyte solution according to any one of claims 1 to 8, wherein the at least one surfactant is present in an amount sufficient to reduce acid mist generation from the aqueous electrolyte solution when O2 is generated within the aqueous electrolyte solution.

10. The aqueous electrolyte solution according to any one of claims 1 to 9, wherein at least one surfactant is present in the aqueous electrolyte solution in an amount ranging from 1 to 100 ppm.

11. The aqueous electrolyte solution according to any one of claims 1 to 10, wherein the nonferrous metal ion is present in an amount ranging from 30 to 60 g / L.

12. The aqueous electrolyte solution according to any one of claims 1 to 11, wherein the at least one acid is present in an amount ranging from 100 to 220 g / L.

13. The aqueous electrolyte solution according to any one of claims 1 to 12, wherein the at least one surfactant is present in an amount insufficient to produce a stable foam in the aqueous electrolyte solution.

14. An electrowinning system, comprising: a cell containing the aqueous electrolyte solution of any of claims 1 to 13; a cathode and anode immersed within the aqueous electrolyte solution; and a rectifier for providing an electrical current between the cathode and anode, thereby resulting in the deposition of the non-ferrous metal on the cathode.

15. The electrowinning system according to claim 14, wherein the electrowinning system comprises, within a tank house, a plurality of the cells containing the aqueous electrolyte solution; each cell having the cathode and the anode immersed in the aqueous electrolyte solution, a rectifier for providing an electrical current between the cathode and anode, thereby resulting in the deposition of the non-ferrous metal on the cathode.

16. A method of reducing acid mist generation in metal electrowinning applications, comprising: adding at least one surfactant of formula X-(RO)n-Y to an aqueous electrolyte solution comprising at least one non-ferrous metal ion species and an acid; and conducting an electrowinning process through the aqueous electrolyte solution, wherein in the formula X-(RO)n-Y,RO is a propyleneoxy group or a propyleneoxy / ethyleneoxy group, n being an integer from 3 to 35, preferably 5 to 25,X is selected from H, H2N, H2NCH2, HO, (R’O)(R’O)OP, or (R’O)(R’O)OPO, and their salts, where R’ is H or a C1-C3 hydrocarbon chain,Y is selected from H, a linear alkyl chain of C1-C3, CH2CH2NH2, CH2CH(CH?)NH2, PO(OR’)(OR’), CH2CH2PO(OR’)(OR’), CH2CH(CH3)PO(OR’)(OR’), and their salts, where R’ is H or a C1-C3 hydrocarbon chain.

17. The method according to claim 16, wherein the aqueous surfactant is added in an amount of between 1 ppm to 100 ppm.

18. The method according to claim 16 or 17, further comprising: controlling the addition of the at least one surfactant to maintain the concentration of the at least one surfactant to the aqueous electrolyte solution.

19. The method according to any one of claims 16 to 18, wherein the electrowinning process extends for a period of time ranging from 1-20 days.

0. Use of at least one surfactant of formula X-(RO)n-Y as an acid mist suppressant in a nonferrous metal electrowinning process, wherein in the formula X-(RO)n-Y,RO is a propyleneoxy group or a propyleneoxy / ethyleneoxy group, n being an integer from 3-35,X is selected from H, H2N, H2NCH2, HO, (R’O)(R’O)OP, or (R’O)(R’O)OPO, and their salts, where R’ is H or a C1-C3 hydrocarbon chain,Y is selected from H, a linear alkyl chain of C1-C3, CH2CH2NH2, CH2CH(CH?)NH2, PO(OR’XOR’), CH2CH2PO(OR’)(OR’), CH2CH(CH3)PO(OR’)(OR’), and their salts, where R’ is H or a C1-C3 hydrocarbon chain.

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