Processes, Compositions and Kits for Acid Mist Suppression in Electrolytic Metal Refining Processes

Abstract

Processes, compositions and kits are provided for suppressing generation of acid mist in an electrowinning process. The processes include the step of adding a powder of lignosulfonate or a derivative thereof or an aqueous solution comprising lignosulfonate or a derivative thereof to an electrolytic solution of the electrowinning process in an amount sufficient to suppress generation of acid mist without formation of foam at an upper surface of the electrolytic solution. The kits include instructions for carrying out the processes.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application, filed under 35 U.S.C. § 111 (a), is a continuation of PCT Application No. PCT / CA2024 / 051201, filed on Sep. 12, 2024, which claims the benefit of priority to U.S. Provisional Patent Application No. 63 / 538,337, filed on Sep. 14, 2023. The above-referenced patent applications are each incorporated herein by reference in entirety.TECHNICAL FIELD

[0002] The technology relates generally to the field of electrolytic recovery of metals and more particularly to compositions for reducing the extent of hazardous acid mist formation which occurs during electrowinning processes.BACKGROUND

[0003] Electrowinning is a process by which metals, such as copper or nickel, are recovered from aqueous electrolyte solutions resulting from the extraction of the metal ion from an acidic or basic leach solution. Metal-bearing aqueous solution is obtained by dissolving from an ore, the desired metal in aqueous leach liquor, in a process known as leaching. The leached solution is mixed with water-immiscible organic solvent(s) containing a water-insoluble ion exchange composition that has selective affinity for the desired metal(s), to form a metal-extractant complex / chelate that is separated from the metal-depleted aqueous phase in, e.g., a settling tank. The aqueous and organic phases are separated. The desired metal ions are removed from the organic phase with a highly acidic strip solution containing strong acid such as sulfuric, phosphoric, or perchloric acid, which breaks apart the complex, dissolving the metal ions into another aqueous solution that following another phase separation from the now-metal-depleted organic phase. The desired metal ions are present in the aqueous strip solution, and the resulting metal-enriched strip solution is usually referred to as “electrolyte” or “pregnant electrolyte” which is customarily forwarded to an electrowinning “tankhouse.” In the tankhouse, the metal ions are deposited on cathode plates by electrodeposition and then recovered from the cathode plates. Other processes may be employed with other metals, such as nickel, zinc, among others, to produce an electrolyte from which their respective metals are obtained.

[0004] During the electrowinning (electrodeposition) stage, elemental metal is plated out at the electrowinning cathode and oxygen evolves at an insoluble anode. The evolution of oxygen gas forms bubbles which entrain strong acid electrolyte, carrying it into the air above the electrowinning tank in the form of a fine mist or spray when the bubbles break. An acidic mist is generated above the electrolyte (strip aqueous phase). This mist or spray then spreads throughout the electrowinning tankhouse. The acidic mist is corrosive and a health hazard which can cause extreme discomfort to the skin, eyes, and respiratory systems of tankhouse workers, especially during hot weather conditions.

[0005] U.S. Pat. No. 4,484,990, incorporated herein by reference in its entirety, discloses the use of cationic or amphoteric fluoroaliphatic surfactants as anti-misting agents in the electrowinning of metals in an acidic electrolyte, wherein all of these agents contain perfluoroalkyl chains and at least one linking group such as a carboxyl group, a sulfonyl group, a sulfate group, a phosphate group a biphosphate group or an ammonium group. Functionalized perfluoroalkyl compounds, however, have come under increased scrutiny by the EPA due to their impact on human health and the environment.

[0006] U.S. Pat. No. 7,384,533, incorporated herein by reference in its entirely, primarily describes and claims a class of additives of a class relating to 4,6-dihydroxypyrimidine, for reduction of electrical potential requirements and for reducing gas formation as well as a single example of lignosulfonate investigated for this purpose which resulted in a conclusion that addition of 0.084 g of lignosulfonate to a functioning 50 mL electrowinning cell has no effect on reducing evolution of O2 gas which forms acid mist, in contrast to other additives including ethanol, methanol, ethylene glycol, urea, glucose sucrose, glycerol, 2-amino-2-thiazoline, and 1,4-diazabicyclo[2.2.2]octane, all of which showed moderate to significant reductions in acid mist evolution.

[0007] U.S. Pat. No. 3,578,651, incorporated herein by reference in its entirety, describes a process for acylation of lignosulfonate.

[0008] Chinese Patent application CN 105271886A, incorporated herein by reference in its entirety, describes a modified lignosulfonate superplasticizer for use as an additive to reduce water usage in processes for preparing concrete.

[0009] A review of the use of chitosan films in food applications is provided in Melro et al., Polymers, 2021, 13 (1) (PMID 33374920 Published online 2020 Dec. 22), incorporated herein by reference in its entirety.

[0010] Ruwoldt et al., Colloids and Surfaces A, 2020, 606, 125478, incorporated herein by reference in its entirety, describes viscoelastic properties of interfacial lignosulfonate films and the effect of added electrolytes.

[0011] The use of various classes of synthetic non-ionic surfactants as acid mist suppression agents is described in US Patent Publication No. 20080264799, incorporated herein by reference in its entirety.

[0012] There remains need for improved acid mist suppression agents for electrolysis and electrodeposition, particularly for such agents which are free of fluoroalkyl components.SUMMARY

[0013] One aspect of the technology is a process for suppressing generation of acid mist in an electrowinning process. The process includes the step of adding a powder of a lignosulfonate or a derivative thereof or an aqueous solution comprising the lignosulfonate or the derivative thereof to an electrolytic solution of the electrowinning process in an amount sufficient to suppress generation of acid mist. In some embodiments of the process, the amount of the lignosulfonate or the derivative thereof added to the electrolytic solution provides a concentration of the lignosulfonate or the derivative thereof in the electrolytic solution of about 15 ppm to about 100 ppm, about 20 ppm to about 80 ppm, or about 30 ppm to about 70 ppm.

[0014] In some embodiments of the process, the lignosulfonate or the derivative thereof is in the form of a salt with a cation selected from the group consisting of sodium, potassium, ammonium and calcium.

[0015] In some embodiments of the process, the lignosulfonate or the derivative thereof is selected from a preparation of the lignosulfonate which produces a pH between about 2.0 to about 12.0 when dissolved in water.

[0016] In some embodiments of the process, the lignosulfonate or the derivative thereof has an average molecular weight of up to about 10,000 g / mol.

[0017] In some embodiments of the process, the lignosulfonate or the derivative thereof comprises at least about 1.2 mmol carboxyl groups per gram of the lignosulfonate or the derivative thereof.

[0018] In some embodiments of the process, the aqueous solution of the lignosulfonate or the derivative thereof further comprises a C2 to C6 organic acid.

[0019] In some embodiments of the process, the organic acid and the lignosulfonate or the derivative thereof are provided in the aqueous solution in a mass ratio ranging from about 0.05 parts organic acid:1 part of the lignosulfonate or the derivative thereof to about 3 parts organic acid:1 part of the lignosulfonate or the derivative thereof.

[0020] In some embodiments of the process, the C2 to C6 organic acid has at least one carboxylic acid group with a pKa value of between about 3.8 to about 5.5.

[0021] In some embodiments of the process, the C2 to C6 organic acid is selected from the group consisting of acetic acid, lactic acid, citric acid, ascorbic acid, benzoic acid, oxalic acid, and propanoic acid.

[0022] In some embodiments of the process, the aqueous solution of the lignosulfonate or the derivative thereof further comprises a diphenyl oxide disulfonate compound.

[0023] In some embodiments of the process, the aqueous solution of the lignosulfonate or the derivative thereof further comprises a polyaminosaccharide.

[0024] Another aspect of the technology is a kit for use in suppressing generation of acid mist in an electrowinning process. The kit includes: a powder of lignosulfonate or a derivative thereof or an aqueous solution comprising the lignosulfonate or the derivative thereof.

[0025] In some embodiments, the kit further includes instructions to provide the lignosulfonate or the derivative thereof in an amount sufficient to provide a lignosulfonate concentration in the electrolytic solution which is sufficient to suppress generation of acid mist.

[0026] In some embodiments of the kit, the instructions specify to provide the lignosulfonate or the derivative thereof in the electrolytic solution at a concentration of between about 15 ppm to about 100 ppm, between about 20 ppm to about 80 ppm, or between about 30 ppm to about 70 ppm.

[0027] In some embodiments of the kit, the lignosulfonate or the derivative thereof is in the form of a salt with a cation selected from the group consisting of sodium, potassium, ammonium and calcium.

[0028] In some embodiments of the kit, the lignosulfonate or the derivative thereof is selected from a preparation of the lignosulfonate or the derivative thereof which produces a pH between about 2.0 to about 12.0 when dissolved in water.

[0029] In some embodiments of the kit, the lignosulfonate or the derivative thereof has an average molecular weight of up to about 10,000 g / mol.

[0030] In some embodiments of the kit, the lignosulfonate or the derivative thereof comprises at least about 1.2 mmol carboxyl groups per gram of lignosulfonate.

[0031] In some embodiments of the kit, the aqueous solution of the lignosulfonate or the derivative thereof further comprises a C2 to C6 organic acid.

[0032] In some embodiments of the kit, the organic acid and the lignosulfonate or derivative thereof are provided in the aqueous solution in a mass ratio ranging from about 0.05 parts organic acid:1 part of the lignosulfonate or the derivative thereof to about 3 parts organic acid:1 part of the lignosulfonate or the derivative thereof.

[0033] In some embodiments of the kit, the C2 to C6 organic acid has at least one carboxylic acid group with a pKa value of between about 3.8 to about 5.5.

[0034] In some embodiments of the kit, the C2 to C6 organic acid is selected from the group consisting of acetic acid, lactic acid, citric acid, ascorbic acid, benzoic acid, oxalic acid, and propanoic acid.

[0035] In some embodiments of the kit, the aqueous solution of the lignosulfonate or the derivative thereof further comprises a diphenyl oxide disulfonate compound.

[0036] In some embodiments of the kit, the aqueous solution of the lignosulfonate further comprises a polyaminosaccharide.

[0037] According to another aspect of the technology, there is provided a composition for suppressing generation of acid mist in an electrowinning process. The composition includes about 1.5% to about 30% (m / m) of a C2 to C6 organic acid; about 40% to about 60% (m / m) of a diphenyl oxide disulfonate compound; and about 5% to about 30% (m / m) of a lignosulfonate or a derivative thereof.

[0038] The composition may further include up to about 2% of a polyaminosaccharide, which may be chitosan, or a derivative thereof. In some embodiments, the polyaminosaccharide is cross-linked with the lignosulfonate or the derivative thereof.

[0039] In some embodiments, the organic acid and the lignosulfonate or derivative thereof are provided in a mass ratio ranging from about 0.05 parts organic acid:1 part lignosulfonate or derivative thereof to about 3 parts organic acid:1 part lignosulfonate. The organic acid may have at least one carboxylic acid group with a pKa value of between about 3.8 to about 5.5. The C2 to C6 organic acid may be selected from the group consisting of acetic acid, lactic acid, citric acid, ascorbic acid, benzoic acid, oxalic acid, and propanoic acid.

[0040] In some embodiments, the diphenyl oxide disulfonate compound is an acid or salt form of the general structure of:wherein R is a linear or branched C6 to C16 alkyl group.In some embodiments, R is a linear or branched C12 alkyl group.

[0042] In some embodiments, the compound is:

[0043] The lignosulfonate may be provided in the form of a salt with a cation selected from the group consisting of sodium, potassium, ammonium and calcium. In some embodiments, the lignosulfonate is selected from a sample which produces a pH between about 4.0 to about 11.5 when dissolved in water. In some embodiments, the lignosulfonate is selected from a sample having sugar content from 0% to about 21%.

[0044] Also provided is a method for reducing generation of acid mist in an electrowinning process, the method comprising adding a composition as recited herein to an electrowinning solution to provide the composition at a concentration of about 5 ppm to about 30 ppm (v / v).

[0045] Also provided is a method for preparing a composition for suppressing generation of acid mist in an electrowinning process, the method includes the steps of mixing an aqueous solution of a C2 to C6 organic acid with a diphenyl oxide disulfonate compound to provide a first mixture; adding a lignosulfonate or a derivative thereof to the first mixture with agitation to generate a second mixture at a temperature between about 30° C. to about 40° C.; and cooling the second mixture to a temperature between about 20° C. to about 25° C., thereby providing the composition. The first mixture may be formed with about a 2:1 ratio of the diphenyl oxide sulfonate compound relative to the C2 to C6 organic acid. The second mixture may be formed with the organic acid and the lignosulfonate or derivative thereof provided in a mass ratio ranging from about 0.05 parts organic acid:1 part lignosulfonate to about 3 parts organic acid:1 part lignosulfonate.BRIEF DESCRIPTION OF THE DRAWINGS

[0046] Various objects, features and advantages of the compositions and processes described herein will be apparent from the following description of particular embodiments, as illustrated in the accompanying drawings.

[0047] FIG. 1A is a process flow diagram indicating addition of lignosulfonate in powder form to an electrowinning solution to obtain acid mist suppression.

[0048] FIG. 1B is a process flow diagram indicating addition of lignosulfonate in an aqueous solution to an electrowinning solution to obtain acid mist suppression.

[0049] FIG. 2 is a process flow diagram illustrating preparation of one embodiment of the acid mist suppressing composition.

[0050] FIG. 3 is a process flow diagram illustrating preparation of another embodiment of the acid mist suppressing composition.DETAILED DESCRIPTIONIntroduction and Rationale

[0051] Various additives have been investigated as agents for reduction of acid mist in electrowinning processes. The use of lignosulfonates as acid mist suppression additives has not been significantly investigated. To the best of the inventors' knowledge, there is only a single example of lignosulfonate having been tested as an acid mist-suppressing agent in an electrowinning process, with the result indicating failure to detect any acid-mist suppression. Although this published result likely informed others to not consider pursuing any further investigations of lignosulfonate as an acid mist suppression additive, the inventors decided to undertake such an investigation and surprisingly found that lignosulfonate is effective for this purpose.

[0052] Lignosulfonates are water-soluble anionic polyelectrolyte polymers: they are by-products from the production of wood pulp using sulfite pulping. Most delignification in sulfite pulping involves acidic cleavage of ether bonds, which connect many of the constituents of lignin, a class of complex organic polymers forming key structures in support tissues of plants, such as cell walls. Lignosulfonates are polydisperse, exhibiting heterogeneity of sizes of molecules or particles in a mixture with broad ranges of molecular masses.

[0053] Lignosulfonates have been employed as bio-based surfactants in industrial applications, such as plasticizers, dispersants stabilizers in various chemical formulations.

[0054] As noted briefly in the background section, U.S. Pat. No. 7,384,533, incorporated herein by reference in its entirety, primarily describes a class of additives of a class relating to 4,6-dihydroxypyrimidine, for reduction of electrical potential requirements and for reducing gas formation. In this patent document, there is a single example of a lignosulfonate being investigated as an additive for reducing formation of O2 bubbles leading to spreading of acid mist in a tank house during electrolytic processes. The experiment of this example used 0.084 g of an unspecified lignosulfonate to an experimental electrolyte volume of 50 mL, representing a lignosulfonate concentration of about 1.68 g / L (which is equivalent to 1680 ppm). The reported result indicated that there was no change in the extent of O2 gas evolution. The applicability of lignosulfonate as an additive to suppress formation of acid mist was not investigated further. Since no additional investigations of using lignosulfonate as an acid mist suppressing agent have been reported, it is concluded that this published result had the effect of discouraging further investigations of lignosulfonate as and acid mist-suppressing agent.

[0055] The present inventors, who have been engaged in developing safer alternative processes, compositions and kits for acid mist suppression in electrowinning processes using non-toxic compounds, decided to investigate lignosulfonates for this purpose. The inventors surprisingly found that when lignosulfonates are added to an electrolytic solution within an appropriate concentration range, they provide useful and effective acid mist suppression.

[0056] The inventors postulated that the sulfonates and carboxyl groups of lignosulfonates contribute to the suppression of evolution of acid mist during electrowinning processes. The inventors further postulated that selection of lignosulfonate having an appropriate average molecular weight range will improve the acid mist suppression properties of lignosulfonate. In processes for separating lignin from natural sources the industrial standard for extraction uses a sulfur-free process with an organic acid as the solvent. The solvent can also be alcohol / water / organic acid combination. This extraction process is carried out with a temperature of 80° C. to 200° C. The temperature employed in the extraction is based on choice of reaction time as well as the control on the distribution of the molecular weight of the lignin extracted. While it is believed that most preparations of lignosulfonates will provide some extent of acid mist suppression when added to electrowinning solutions, the inventors further postulated that lignosulfonates prepared from lignin having increased quantities of carboxyl groups will be more effective at acid mist suppression. It has been previously determined that the carboxyl content of lignosulfonates produced from conventional processes ranges from about 0.6 to about 3.0 mmol / g of lignosulfonate. Therefore, the inventors postulate that carboxyl content of at least about 1.2 mmol / g of lignosulfonate will provide enhanced acid mist-suppression properties. Such preferred carboxyl content may be determined using conventional processes.

[0057] Preparations of lignosulfonates have average molecular weight ranging from about 1,000 g / mol to about 400,000 g / mol. Acid hydrolysis of such preparations may produce lignosulfonates with molecular weights of 1,500 to 50,000 g / mol and a product known as “organosolv lignin” has an average molecular weight of 500-5,000 g / mol (Vishtal et al., BioResources, 2011, 6, 3547-3568, incorporated herein by reference in its entirety). It is postulated by the inventors that an average molecular weight less than 10,000 g / mol, which includes organosolv lignosulfonate, will provide suitable acid mist suppression in electrowinning processes. It is therefore considered appropriate to select a lignosulfonate manufacturing process and reaction time to produce such a desirable molecular distribution within this range.

[0058] In considering the functionality of lignosulfonate in acid mist suppression, the inventors postulated that the main function of lignosulfonate would be to act as a surfactant to lower the surface tension between the air-liquid interface in the electrowinning cell. Surfactant properties of lignosulfonates have been investigated (see for example, Askvik et al., Colloids Surfaces A: Physicochem. Eng. Aspects, 1999, 159 (1), 89-1101; Yang et al., J. Dispers. Sci. Technol., 2008, 29, 1296-1303; and Rana et al., Colloid Polym. Sci. 2002, 280, 775-778, each incorporated herein by reference in its entirety). Other technical papers have described aggregation and agglomeration process of lignin under various pH and temperature conditions (see for example, Ruwoldt et al., Colloids Surfaces A: Physicochem. Eng. Aspects, 2020, 606, 125478; and Deng et al., Bioresources, 2012, 7, 1145-1156, each incorporated herein by reference in its entirety). However, the main desirable property is reduction of surface tension between the air-acid liquid interface. One interesting and important aspect of these technical discussions is that the lignosulfonate molecules form mono layers or multi-layers on the liquid phase.

[0059] The choice of lignosulfonate with a lower average molecular weight range has been found to display a tendency to induce a larger change of interfacial tension whereas another report indicated that increasing molecular weight increases the surface tension (Yan et al, Colloids Surfaces A: Physicochem. Eng. Aspects, 2010, 371, 50-58, incorporated herein by reference in its entirety). The reduction of surface or interfacial tension can further be enhanced by increasing ionic strength or by reducing the pH (Yan & Yang, J. Braz. Chem. Soc., 2015, 26 (3), 555-561; Ström & Stenius, Colloids Surfaces, 1981, 2 (4), 357-371; and Fredheim & Christensen, Biomacromolecules, 2003, 4 (2), 232-239, each incorporated herein by reference in its entirety).

[0060] The inventors postulate that the performance of lignosulfonate as an acid mist suppressing reagent also relies on the effectiveness of its dispersion on the surface of the electrowinning cell. The interactions of lignosulfonate with other surfactants and polymers are determined by the presence of ionic functional groups. The inventors postulated that synergistic effects of adding another anionic surfactant may promote the dispersion. The additional surfactant should be stable in a harsh operating environment such as the combination of elevated temperatures and acidic conditions. Examples of such surfactants are described herein.

[0061] An early study revealed that interactions between lignosulfonate and cationic polyelectrolytes can lead to soluble complexes, colloids, and macroscopic precipitates (Ström & Stenius, Colloids Surfaces, 1981, 2 (4), 357-371, incorporated herein by reference in its entirety). With organsolv lignosulfonates which have an average molecular weight of 500 to 5,000 g / mol, the lignin formed in higher temperature with organic acid is expected to be in colloidal form with a small fraction of the formulation in macroscopic precipitates. Fredheim et al. further described the interactions between lignosulfonate and chitosan (Fredheim & Christensen, Biomacromolecules, 2003, 4 (2), 232-239, incorporated herein by reference in its entirety). This association led to the formation of insoluble complexes with a sulfonate / amino ratio close to 1.0, from which it was deduced that essentially all sulfonate groups are accessible for interactions with chitosan (Ouyang et al., Biomacromolecules, 2011, 12 (9), 3313-3320; and Luo et al., Mater. Sci. Eng. C, 2012, 32, 2001-2006, each incorporated herein by reference in its entirety). With the addition of chitosan as an optional component in an acid mist suppressing composition, and its interaction with the lignosulfonate, it is expected that a multilayer of lignosulfonate will develop at the air-liquid interface of the electrowinning cell. Experiments described herein have determined that addition of a polyaminosaccharide such as chitosan to a lignosulfonate-based acid mist suppressing composition further improves the acid mist suppressing properties of the composition.

[0062] One embodiment of the present technology is based on the aforementioned surprising discovery that addition of lignosulfonate to an electrowinning solution in an effective amount provides suppression of acid mist formation. Accordingly, one embodiment of the technology is a process for reducing acid mist formation in an electrowinning process which includes addition of lignosulfonate to the electrolytic solution of the electrowinning process. The lignosulfonate may be added in a powder form directly to the electrowinning solution or in an aqueous solution to the electrowinning solution to provide a concentration of lignosulfonate in the electrowinning solution ranging from about 15 ppm to about 100 ppm to provide effective acid mist suppression.

[0063] The inventors of the present application have also surprisingly discovered that a slurry of a lignosulfonate in a powder form can be prepared when mixed into an aqueous solution of a nonionic surfactant and an organic acid. The combination of organic acid and nonionic surfactant assists the dispersion of the soluble fraction of the lignosulfonate when introduced into the copper electrowinning apparatus and provides effective suppression of acid mist at low concentrations without generating adverse conditions such as excessive foaming and / or interference with the electrowinning process. It is reasonably predicted that certain alternative organic acids and nonionic surfactants of the same class of diphenyl oxide disulfonate, as well as cross-linking agents such as polyaminosaccharides will provide alternative embodiments of the acid mist suppressing composition.DESCRIPTION OF EMBODIMENTS

[0064] An example of a general process for addition of lignosulfonate powder to an electrowinning solution to obtain acid mist suppression is outlined in FIG. 1A. An example of a general process for addition of an aqueous solution of lignosulfonate to an electrowinning solution to obtain acid mist suppression is outlined in FIG. 1B.

[0065] An example of a general process for preparing an acid mist suppressing composition appropriate for use in an electrowinning process is outlined in FIG. 2. A first mixture which includes an organic acid and a diphenyl oxide disulfonate surfactant is prepared at ambient temperature of about 23° C. and then heated to about 50° C. with agitation until the components are dispersed. Then lignosulfonate is added as a powder to the second mixture and the temperature is increased to about 50° C. again, with additional agitation. When a uniform mixture is obtained, it is permitted to cool to ambient temperature again, thereby providing the acid mist suppressing composition.

[0066] Another process embodiment is illustrated in FIG. 3, where the acid mist suppressing composition includes a polyaminosaccharide such as chitosan, which is added to the composition after the lignosulfonate is added and prior to cooling. Cross-linkages between chitosan and lignosulfonate polymers occur following this step. While a detailed analysis of the characteristics of the cross-linked composition has not yet been undertaken, it has been experimentally confirmed that compositions containing chitosan enhance the acid mist suppressing properties of the lignosulfonate compositions.

[0067] Lignosulfonates are water-soluble anionic polyelectrolyte polymers: they are by-products from the production of wood pulp using sulfite pulping. Most delignification in sulfite pulping involves acidic cleavage of ether bonds, which connect many of the constituents of lignin, a class of complex organic polymers forming key structures in support tissues of plants, such as cell walls.

[0068] The lignosulfonates of the compositions described herein may be modified or derivatized. Examples of lignosulfonate derivatives are described in U.S. Pat. No. 4,219,471A, incorporated herein by reference in its entirety. Advantageously, such lignosulfonate derivatives may exclude modifications which confer any type of toxicity to the lignosulfonate, in keeping with the objective of developing alternative anti-mist agents which are not harmful to the environment. Any reference to “a lignosulfonate or a derivative thereof” encompasses any chemical modification of a lignosulfonate preparation which does not reduce the acid mist-suppressing properties of the lignosulfonate preparation and which is compatible with electrowinning processes.

[0069] A suitable diluent for lignosulfonates is pure water, or aqueous solutions including simple or complex saccharides.

[0070] As established herein, lignosulfonates are effective at providing acid mist suppression when added as a powder form or as an aqueous solution to electrowinning solutions. It is also established that providing partial digestion of the lignosulfonates by mixing with a solution of a C2 to C6 organic acid improves the acid mist suppression properties of the lignosulfonates. Further it is established that preparing compositions that include lignosulfonate, a C2 to C6 organic acid and a non-ionic surfactant further enhances the acid mist suppression properties of the lignosulfonates. A further optional component is a polyaminosaccharide such as chitosan.

[0071] Embodiments of the acid mist suppressing compositions are effective in quantities ranging from about 2 to about 100 ppm, preferably from about 2 to about 30 ppm, and most preferably from about 5 to about 25 ppm, in terms of the volume of the of the composition added to the volume of the electrowinning solution. In an electrowinning application, they are added to the metal-containing electrolyte / strip aqueous phase in the electrowinning tankhouse.

[0072] The effectiveness of using a combination of the lignosulfonate and nonionic surfactant arises from three main factors: (1) as the mass fraction of solubilized lignosulfonate increases, its degradation in the electrowinning process will decrease; (2) the surfactant employed in this formulated mixture must be both acid and temperature tolerant in order to achieve the desirable dispersing and suppressing effects when employed as a mist suppressant in the copper electrowinning tank; and (3) increasing the solubilization of the lignosulfonate provides a more stable and effective acid mist suppression composition. In some embodiments, the form of lignosulfonate includes salt forms of ionizable groups including, but not limited to, sulfonate groups, phenolic hydroxyl groups and carboxyl groups.

[0073] The composition includes an organic acid to assist the process step of dispersing the lignosulfonate into the water phase. It is expected that this process will result in partial digestion of the lignosulfonate. The organic acid may be a C2 to C6 organic acid. In some embodiments, the organic acid has at least one carboxylic acid group having a pKa value ranging between about 3.8 to about 5.5. Examples of such C2 to C6 organic acids include, but are not limited to: acetic acid, lactic acid, citric acid, ascorbic acid, benzoic acid, oxalic acid, and propanoic acid.

[0074] The mass ratio organic acid with respect to the lignosulfonate which is expected to produce a useful acid mist suppressing composition is in a mass ratio ranging from about 0.05 parts organic acid:1 part lignosulfonate to about 3 parts organic acid:1 part lignosulfonate. This range of mass ratios includes any fractional mass ratio value therebetween, for example 0.5, 1.0, 1.5, 2.0, 2.5 and 3.0 parts organic acid: 1 part lignosulfonate.

[0075] The selection of diphenyl oxide disulfonate compounds as appropriate surfactants for the composition was made taking into consideration the solubility and stability of these compounds in concentrated electrolytes, together with resistance to oxidative and thermal degradation under strongly acidic conditions, for example strong acid concentrations of 100 to 200 grams per liter. In some embodiments, the diphenyl oxide disulfonate compound is an acid or salt form of the general structure of:wherein R is a linear or branched C6 to C16 alkyl group. In some preferred embodiments, R is a linear or branched C12 alkyl group. In one preferred embodiment, the diphenyl oxide disulfonate compound is a compound formerly marketed by Dow Chemical as DOWFAX™ 2A0 (now discontinued), which has the following structure:In some embodiments, the aqueous solution containing the organic acid further includes a polysaccharide, to increase the viscosity and promote formation of a gelatinized composition with enhanced stability, which also quickly disperses into an electrowinning solution. In some embodiments, the polysaccharide is a polyaminosaccharide, which may be any polymer of any monosaccharide in which a single hydroxyl group is replaced by an amino group. In some embodiments, the polyaminosaccharide is chitosan, a straight chain polyaminosaccharide composed of randomly distributed β-(1→4)-linked D-glucosamine (deacetylated unit) and N-acetyl-D-glucosamine (acetylated unit). It is made by treating the chitin shells of shrimp and other crustaceans with an alkaline substance, such as sodium hydroxide for partial deacetylation to enhance solubility in water.In certain embodiments acetic acid is added to chitosan to generate fully protonated chitosan which is more reactive with the cation component of lignosulfonate in preparation of the acid mist suppression composition. Chitosan is reactive with acetic acid, nitric acid, hydrochloric acid, perchloric acid and phosphoric acids in the deacetylation step but is not expected to be reactive with sulfuric acid. This is an advantageous property for the acid mist suppressing composition.

[0078] In certain embodiments, for the addition of chitosan into a composition comprising an organic acid, a diphenyl oxide disulfonate compound and lignosulfonate, the mixing temperature is between 45 to 50° C. In certain embodiments, chitosan is added to provide a ratio of chitosan to lignosulfonate at about 1:125 minimum and about 1:15 maximum. It is to be understood that this range of ratios encompasses about 1:120, about, about 1:110 1:100, about 1:90, about 1:80, about 1:70, about 1:60, about 1:50, about 1:40, about 1:30 and about 1:120 and any ratio value therebetween.

[0079] The chitosan content is provided to reduce free water content in the composition. In some embodiments, the free water content is less than 20 percent and the desired viscosity of the composition including chitosan is between about 100 CPI to about 120 CPI. Therefore, it is advantageous to employ a high torque mixer since the initial viscosity of the mixture from about 700 CPI to about 1000 CPI until the chitosan is fully acidified. Addition of chitosan is the final step following addition of the other components of the composition.

[0080] In mixing chitosan with a composition comprising an organic acid, a diphenyl oxide disulfonate compound and lignosulfonate, cross-linking between the chitosan and the lignosulfonate occurs and this cross-linking enhances the acid mist suppression properties of the composition, as indicated in the examples below.

[0081] Chitosan derivatives such as glycerylated chitosan, hydroxyethyl chitosan, hydroxypropyl chitosan, hydroxybutyl chitosan, hydroxybutyl hydroxypropyl chitosan, carboxymethyl chitosan and succinyl chitosan may be used. In other embodiments, other polyaminosaccharides such as alkylsulfonated polyaminosaccharides and glycosamino glycans may be used.

[0082] It is preferable that the acid mist suppressing properties provided by the composition embodiments are sufficient for the composition to be effective at concentrations in the electrowinning solution within ranges of lignosulfonate concentrations of about 2 to about 100 ppm, preferably from 2 to 30 ppm, and most preferably from about 5 ppm to about 25 ppm, in terms of the volume of the of the composition added to the volume of the electrowinning solution. In an electrowinning solution, they may be added to the metal-containing electrolyte / strip aqueous phase in the electrowinning tankhouse.EXAMPLESExample 1: Investigation of Lignosulfonate as an Acid Mist Suppression Additive

[0083] Laboratory copper plating experiments with laboratory made tankhouse electrolyte were conducted using a small-scale electrowinning cell constructed of clear glass, 14.3 cm long by 14.3 cm wide by 14.3 cm deep covered with a clear polyvinyl chloride plastic cover with 1 hole (about 1.5 inch from the cell top) about midway up anode and cathode. The cell included one lead anode and one stainless steel cathode, with each electrode being 9 cm high by 13.5 cm wide. Experiments were run under static conditions. The electrolyte liquid height was maintained at a level about 1 cm below the top of the electrodes during operation of the test cell. Electrolyte temperature was adjusted to 46° C. by pre-warming the electrolyte solution. The electrowinning cell was kept in a laboratory water bath and electrolyte temperature was monitored during each experiment using a thermometer hung in the cell away from the electrodes. The power supply used was direct current, with a current range of 1 to 6 amps.

[0084] The tankhouse electrolyte was prepared by mixing 155 g CuSO4·5H2O with 195 g concentrated (95-98%) H2SO4 per liter of electrolyte solution. Calgary tap water was used and a total of 2.0 liters of electrolyte solution was prepared for each test. The acid mist suppression provided by lignosulfonate was investigated at two different lignosulfonate concentrations. The test cell was filled with 2.0 L of the electrolyte with acid mist suppressing composition. A vacuum-pump was connected to a 0.50-inch internal diameter clear vinyl tube which was connected to a 500 mL Kimax Flask Filtering Erlenmeyer containing 200 mL of deionized water. The flask was closed with a rubber stopper containing one hole. Through the hole, a 0.17-inch glass tube was inserted into the flask stopping at 0.25-inch from the bottom of the flask. A 0.17-inch inner diameter polyethylene tube was connected from the glass tube to the hole on top of the electrowinning cell. Each test was operated for 40 minutes. The vacuum pump was started 10 minutes after the commencement of each test to allow for equilibrium conditions to be established, with the vacuum pump operating at a 5.0 liter per minute air flow rate. The pH of the water was measured at the beginning and at the end of each test.

[0085] To demonstrate the acid mist suppression characteristics of the lignosulfonate additive, a series of blank tests without any acid mist suppressing composition was added were tested in the copper electrowinning cell. The amount of acid mist generation was measured, repeated, and a standard deviation was established. Once the acid mist generation without mist suppressant was established, new tests were conducted with two different concentrations of lignosulfonate and the new values of mist generation were compared to the baseline in order to evaluate the effectiveness of mist suppression under laboratory conditions.

[0086] A sample of calcium lignosulfonate in powder form (LignoBond DD, Borregaard Lignotech) was used to prepare a 15% (m / m) solution of calcium lignosulfonate in water. This aqueous solution was added to the electrolyte solution to provide the ppm concentrations indicated in Table 1, which refer to the corresponding mass of dry powder of calcium lignosulfonate. A baseline of acid mist is provided by a pair of blank measurements (no calcium lignosulfonate added).TABLE 1Comparison of Acid Mist Suppression Providedby Lignosulfonate at 40 ppm and 10 ppmCalciumLignosulfonateAcid MistMist Sup-ConcentrationMeasurementpression(ppm)(mg H3O+ / m3)(%)0144.0—0161.5—4016.5389.16%4014.4090.56%10157.85−3.51%10147.323.39%

[0087] The acid mist suppression data presented in Table 1 indicates that calcium lignosulfonate provides effective acid mist suppression at 40 ppm but not at 10 ppm. Based on this result, it is reasonably predicted that a range of about 15 ppm to about 100 ppm lignosulfonate in an industrial electrolytic solution will provide similar useful acid mist suppression. The upper limit of acceptable lignosulfonate concentration will likely depend upon other factors such as its influence on the generation of foam, which presents a fire hazard due to trapping of oxygen bubbles. This is expected to be confirmed by future experiments where it may be determined that some minimal amount of foam will be acceptable but excessive foam will not be acceptable.Example 2: Characteristics of Lignosulfonate Samples

[0088] The inventors obtained a series of lignosulfonate powder preparations obtained from Borregard Lignotech, a commercial supplier of lignin biopolymers. The different lignosulfonate preparations have various counterions including sodium, calcium, and ammonium, various molecular weight ranges from 1,000 to 140,000, varying sugar content ranging from less than 1% to 21%, as determined by HPLC, varying sulfur content ranging from 3.4% to 10.4% and providing pH ranges between 4 and 11.5, when the lignosulfonate powder sample is dissolved in water.

[0089] Table 2 below summarizes the characteristics of the lignosulfonate preparations used in the tests described in subsequent examples.TABLE 2Characteristics of Lignosulfonate SamplesHPLCMolecularProductSugarsWeightSulfurNumberCationNa+Ca2+NH4+pH%Range*%NCB 223Sodium9.000.60—8.31.0Intermediate7.0NCB 222Calcium0.308.70—7.03.0Low5.2NCB 211Sodium6.800.50—6.02.1Low5.0NCB 367Calcium0.404.40—4.017.9Low5.8NCB 251Sodium19.600.10—11.50.0Low3.6NCB 257Sodium7.000.05—8.71.0High5.0NCB 319Sodium12.500.10—9.50.0Intermediate10.4NCB 463Ammonia—0.104.005.521.0Intermediate6.8NCB 210Ammonia——5.005.06.0Intermediate5.0*Estimated ranges: low: up to about 40,000 Da; intermediate: from about 40,000 Da to about 90,000 Da; High: from about 90,000 Da to about 140,000 Da.Example 3: Comparison of Acid Mist Suppression by Lignosulfonate and Acid Digested Lignosulfonate

[0090] In this series of experiments, acid mist suppression by selected samples of lignosulfonates described in Example 2 added to an electrowinning solution described in Example 1, to provide 40 ppm of lignosulfonate in the electrowinning solution are compared with the results obtained from same lignosulfonate samples mixed with a C2 to C6 organic acid for the purpose of partially digesting the lignosulfonate prior to addition of the mixture to the electrowinning solution. The resulting mixture containing 25% lignosulfonate and 75% of a 50% aqueous solution of acetic acid was incubated at 50° C. for 2 hours. This partially digested mixture was added to the experimental electrowinning solution to provide 40 ppm lignosulfonate in the electrowinning solution. This experiment was conducted for three different samples of lignosulfonate as follows; lignosulfonate 210 which includes ammonium as the counter ion and has intermediate average molecular weight (about 40,000 Da to about 90,000 Da), intermediate sugar content as measured by HPLC, and generally acidic pH; lignosulfonate 222 which includes calcium as the counter ion and has low molecular weight (about 40,000 Da to about 90,000 Da), low sugar content as measured by HPLC and generally neutral pH; and lignosulfonate 223, which includes sodium as the counter ion, intermediate molecular weight and generally alkaline pH. The results are shown in Table 3 below.TABLE 3Comparison of Acid Mist Suppression by Lignosulfonateand Acid Digested LignosulfonateLignosulfonateAcid MistMist Sup-ConcentrationMeasurementpressionSample(ppm)Cation(mg H3O+ / m3)(%)Blank0—144—Blank0—161.5—Lignosulfonate40Ammonia3775.7%210Lignosulfonate40Ammonia41.5272.8%210Lignosulfonate40Calcium65.856.8%222Lignosulfonate40Calcium58.6561.5%222Lignosulfonate40Sodium38.7574.6%223Lignosulfonate40Sodium43.4871.5%223Digested40Ammonia23.3584.7%lignosulfonate210Digested40Ammonia25.683.2%lignosulfonate210Digested40Calcium20.8186.3%lignosulfonate222Digested40Calcium23.8984.3%lignosulfonate222Digested40Sodium31.579.3%lignosulfonate223Digested40Sodium29.3980.7%lignosulfonate223

[0091] These results indicate that providing partial digestion of the lignosulfonate samples using a C2 to C6 organic acid such as acetic acid provides a mixture which has improved acid mist suppression properties relative to undigested lignosulfonate. Some of this effect may arise from dispersion of the soluble fraction of the lignosulfonate when introduced into the copper electrowinning apparatus. The average increase in acid mist suppression using the acid treated samples over the six measurements is an increase of 14.3%. In terms of the mist suppression values for the different lignosulfonate samples, lignosulfonate 222, which includes calcium as the counter ion and which has a low average molecular weight is the best performing lignosulfonate among the three lignosulfonate samples investigated.Example 4: Lignosulfonate Compositions Including C2 to C6 Organic Acid and Surfactant

[0092] This example describes two embodiments of a process for preparing acid mist suppressing compositions at laboratory scale to test for acid mist suppressing properties with an aim to improvement of the acid mist suppression provided by lignosulfonate alone. The compositions include a first composition which includes lignosulfonate, acetic acid, a diphenyl oxide sulfonate compound functioning as a surfactant. A second composition contains lignosulfonate, acetic acid, a diphenyl oxide sulfonate compound functioning as a surfactant and chitosan. Alternative embodiments may use different organic acids, different diphenyl oxide sulfonate compounds and polyaminosaccharides other than chitosan.

[0093] Composition 1: In this example, 50 g of a 50% aqueous solution of acetic acid (viscosity 1.04 CPS) was mixed with 100 g of a diphenyl oxide disulfonate compound of the structure:

[0094] This diphenyl oxide disulfonate compound itself has a viscosity of 35 CPS. The mixture was prepared at ambient temperature of about 23° C. and agitated using an overhead mixer at 200 RMP for about 20 to 30 minutes to achieve uniform mixing and a temperature of about 50° C. Then a mass of the sample of the lignosulfonate powder selected from the samples listed in Table 2 was added. This addition resulted in lowering of the temperature of the mixture to about 30 to 40° C. The mixture was then heated again to about 50° C. for about 10 minutes. At that stage, the mixture was cooled slowly over three hours to about 23° C. to provide a final composition. The resulting composition includes 12.5% (m / m) acetic acid, 12.5% (m / m) water, 50% (m / m) of the diphenyl oxide disulfonate compound, and 25% (m / m) lignosulfonate. This composition was investigated for mist suppression properties, as outlined in Example 5.

[0095] Composition 2—This composition was prepared in a process identical to Composition 1 with the exception that following addition of lignosulfonate and agitation, an aqueous solution of chitosan was added, prior to cooling the mixture to ambient temperature of about 23 to provide a final composition. The resulting composition includes 12.5% (m / m) acetic acid, 12.5% (m / m) water, 50% (m / m) of the diphenyl oxide disulfonate compound, 24.5% (m / m) lignosulfonate and 0.5% (m / m) chitosan. This composition was investigated for mist suppression properties, as outlined in Example 5.Example 5: Investigation of Acid Mist Suppression Properties of Acid-Mist Suppressing Compositions

[0096] Laboratory copper plating experiments were conducted using the laboratory made tankhouse electrolyte and small-scale electrowinning cell described in Example 1, except that air flow of 3.5 liters / min was used.

[0097] The acid mist suppression compositions described in Example 4 were investigated at different concentrations using the same experimental process outlined in Example 1.

[0098] To demonstrate the acid mist suppression characteristics of the two compositions, a series of blank tests without any acid mist suppressing composition tested in the copper electrowinning cell. The amount of acid mist generation was measured, repeated, and a standard deviation was established. Once the acid mist generation in the absence of an acid mist suppressing composition was established, new tests were conducted with different concentrations of the two acid mist suppression compositions and the new values of mist generation were compared to the baseline to evaluate the effectiveness of mist suppression under laboratory conditions. The two acid mist suppressing compositions were found to have acceptable solubility in the electrowinning solution in each case. Table 4 lists a series of acid mist suppression measurements and calculated mist suppression percentages for a sample of sodium lignosulfonate having a medium molecular weight distribution and low sugar content. The composition concentration refers to the volume of the composition added to the volume of electrowinning solution.TABLE 4Acid Mist Suppression by the Compositions of Example 4CompositionAcid MistMist Sup-ConcentrationMeasurementpressionSample(ppm)(mg H3O+ / m3)(%)Blank0225.5—Blank0258.9—Composition 11515.693.5%Composition 11521.591.1%Composition 11522.690.7%Composition 11089.862.8%Composition 21029.787.7%Composition 21024.789.8%Composition 21020.191.7%Composition 21023.190.5%

[0099] The results of Table 4 indicate that composition 1, which does not include chitosan, provides effective acid mist suppression properties at a concentration of 15 ppm of the composition but at 10 ppm the effectiveness is significantly decreased. In contrast, sample composition 2, which includes chitosan cross-linked with lignosulfonate provides a better acid mist suppression effect at 10 ppm of the composition. This data set indicates that while the composition without chitosan is effective, the addition of chitosan increases the acid mist suppressing properties, permitting lower concentrations of lignosulfonate to be employed. It is highly desirable to keep concentrations of acid mist suppression additives low, in order to minimize generation of foam which can trap oxygen bubbles and increase the risk of a fire.Example 6: Comparison of Acid Mist Suppression for a Range of Lignosulfonate Samples

[0100] In another series of experiments, acid mist suppressing compositions corresponding to composition 2 of Example 4 (including chitosan) using the individual lignosulfonate samples listed in Table 2 of Example 2 were tested for acid mist suppression using the test method described in Example 3. Each sample was tested in duplicate. The acid mist suppressing composition corresponding to the last four entries labelled “calcium lignosulfonate” is a 15% (m / m) solution in water of a calcium lignosulfonate without any other additives, which was originally presented in Table 1 of Example 1 and included here for a comparison. As noted above, the ppm concentrations for the calcium lignosulfonate sample refers to the corresponding mass of dry powder of calcium lignosulfonate.TABLE 5Comparison of Acid Mist Suppressionfor a Range of Lignosulfonate SamplesLignosulfonateEquivalentAcid MistMist Sup-ConcentrationMeasurementpressionSample(ppm)(mg H3O+ / m3)(%)Blank0144.0—Blank0161.5—NCB 2101047.768.74%NCB 2101037.075.73%NCB 2111024.483.97%NCB 2111033.078.37%NCB 2221044.570.83%NCB 2221062.858.79%NCB 2231020.886.35%NCB 2231026.882.42%NCB 2511088.841.79%NCB 2511082.845.67%NCB 2571036.276.29%NCB 2571042.572.14%NCB 3191049.967.27%NCB 3191032.278.87%NCB 3671072.252.68%NCB 3671057.362.42%NCB 4631061.459.73%NCB 4631057.362.42%NCB 251400.1099.93%NCB 251400.1499.91%calcium4016.5389.16%lignosulfonatecalcium4014.4090.56%lignosulfonatecalcium10157.85−3.51%lignosulfonatecalcium10147.323.39%lignosulfonate

[0101] A ranking of the acid mist suppression provided by compositions including the different lignosulfonate samples is provided in Table 5, based on the average of the two determinations for each sample listed in Table 6. Table 5 also enables a comparison of the lowest ranked sample, NCB 251 with the calcium lignosulfonate sample composition without surfactant, organic acid and chitosan at 40 ppm of lignosulfonate. This comparison between NCB 251 and calcium lignosulfonate at 40 ppm indicates that the absence of the other composition additives provides about 10% less effective composition for acid mist suppression. The calcium lignosulfonate sample without chitosan organic acid and diphenyl oxide disulfonate surfactant was also tested at 10 ppm lignosulfonate (last two entries in Table 5). The measurements indicate that lignosulfonate without chitosan at 10 ppm has essentially no acid mist suppression effect. Collectively, the data show that the diphenyl oxide surfactant and organic acid are important components of the composition to provide improvements in acid mist suppression. Compositions without chitosan are also effective at acid mist suppression but are enhanced when chitosan is included in the composition, indicating that inclusion of a polyaminosaccharide such as chitosan to provide cross-linking is useful but may not be required in all cases.TABLE 6Ranking of Lignosulfonate Samples for Acid Mist SuppressionAvg. MistMistMolecularSuppressionSuppressionSugarWeightSulfurSample%RankCationpH%Range%NCB 22384.41sodium8.31.0Medium7NCB 21181.22sodium6.02.1Low5NCB 25774.23sodium8.71.0High5NCB 31973.14sodium9.50.0Medium10.4NCB 21072.25ammonia5.06.0Medium5NCB 22264.86calcium7.03.0Low5.2NCB 46361.17ammonia5.521.0Medium6.8NCB 36757.68calcium4.017.9Low5.8NCB 25143.79sodium11.50.0Low3.6

[0102] In Table 6, nine samples of lignosulfonates with different properties are ranked according to the average of duplicate determinations of the acid mist suppression data of Table 5. Sugar content may have an effect, with lower sugar content being more favorable. The lignosulfonate samples with sodium counter ion have the highest ranking with the exception of NCB 251, which is ranked last. Low to medium molecular weight lignosulfonate appears to generally provide a better mist suppressing effect. There is no clear trend observable for sulfur content. The pH of the lignosulfonate powder samples when dissolved in water may have an effect on acid mist suppression at the extremes since the lowest ranked lignosulfonate samples provide pH values of 4.0 and 11.5 when dissolved in water. Otherwise, it appears that lignosulfonate powders producing pH values between 5.0 to 9.5 provide good acid mist suppression in the compositions. Therefore, it may be advantageous to select lignosulfonate samples with low to medium average molecular weights, sodium as a counter ion, relatively low sugar content of about 6% or lower, and producing pH values between about 5.0 to about 9.5 when the lignosulfonate powder is dissolved in water.

[0103] When employed at industrial scale, it is expected that levels of 100 ppm or higher of lignosulfonate would promote generation of significantly greater volumes of foam which can trap oxygen bubbles formed in the electrowinning process, creating a fire hazard. It is reasonably predicted that the extent of foam formation in scaled up electrowinning solutions treated with the acid mist suppression composition described herein where the lignosulfonate concentrations are significantly lower, will provide effective acid mist suppression without generation of dangerous volumes of foam.Example 7: Treatment of Industrial Electrowinning Solutions with Lignosulfonates and Compositions Containing Lignosulfonates with Other Additives

[0104] It is to be understood that the data presented herein were obtained using an experimental laboratory electrowinning apparatus and an experimental electrowinning solution which permit reasonable and sound predictions to be made regarding acid mist suppression in scaled up industrial electrowinning processes. However, it remains possible that such scaled up processes may produce varying degrees of foam when treated with the lignosulfonates and compositions thereof.

[0105] It is expected that industrial electrowinning processes will generally benefit from treatment with a minimal number of additives to reduce the complexity of the electrowinning solution and to reduce costs in efforts to suppress acid mist formation. Therefore, if a given lignosulfonate sample provides sufficient acid mist suppression without excessive foam at a suitable concentration, such as between about 15 ppm to about 100 ppm, as evidenced by data presented herein, it may not be necessary to combine the lignosulfonate with any of the other additives described herein. However, various electrowinning solutions used to produce different metal products may have different physicochemical characteristics and different mixing parameters which may lead to excessive foam production. In such cases, it may be appropriate to combine the lignosulfonate with a C2 to C6 organic acid to obtain some improvement in acid mist suppression. At this stage, additional experimentation may be warranted, if desired by the operators of the industrial process. For example, if this combination is found to be insufficient in reducing foam production during the electrowinning process, a composition comprising lignosulfonate, a C2 to C6 organic acid, and a diphenyl oxide disulfonate compound may be preferred. Further, if this combination is found to be insufficient in reducing foam production during the electrowinning process, the composition may be supplemented with a polyaminosaccharide which has been established to improve the acid mist suppression characteristics of the composition. Other operators may be willing to absorb the increased cost of the most effective composition and not engage in experimentation to determine the effectiveness of lignosulfonate itself or in any of the combinations with the additives described herein.EQUIVALENTS AND SCOPE

[0106] Other than described herein, or unless otherwise expressly specified, all of the numerical ranges, amounts, values and percentages, such as those for amounts of materials, elemental contents, times and current rate, ratios of amounts, and others, in the following portion of the specification and attached claims may be read as if prefaced by the word “about” even though the term “about” may not expressly appear with the value, amount, or range. Accordingly, unless indicated to the contrary, the numerical parameters set forth in the following specification and attached claims are approximations that may vary depending upon the desired properties sought to be obtained. At the very least, each numerical parameter should at least be construed in light of the number of reported significant digits and by applying ordinary rounding techniques.

[0107] The terms “approximately,”“about,”“substantially,” and similar terms are intended to have a broad meaning in harmony with the common and accepted usage by those of ordinary skill in the art to which the subject matter of this disclosure pertains. It should be understood by those of skill in the art that these terms are intended to allow a description of certain features described and claimed without restricting the scope of these features to the precise numeral ranges provided. Accordingly, these terms should be interpreted as indicating that insubstantial or inconsequential modifications or alterations of the subject matter described and are considered to be within the scope of the disclosure.

[0108] The articles “the”, “a” and “an” are not necessarily limited to mean only one, but rather are inclusive and open ended so as to include, optionally, multiple such elements.

[0109] “At least one,” in reference to a list of one or more entities should be understood to mean at least one entity selected from any one or more of the entities in the list of entities, but not necessarily including at least one of each and every entity specifically listed within the list of entities and not excluding any combinations of entities in the list of entities. This definition also allows that entities may optionally be present other than the entities specifically identified within the list of entities to which the phrase “at least one” refers, whether related or unrelated to those entities specifically identified. Thus, as a non-limiting example, “at least one of A and B” (or, equivalently, “at least one of A or B,” or, equivalently “at least one of A and / or B”) may refer, to at least one, optionally including more than one, A, with no B present (and optionally including entities other than B); to at least one, optionally including more than one, B, with no A present (and optionally including entities other than A); to at least one, optionally including more than one, A, and at least one, optionally including more than one, B (and optionally including other entities). In other words, the phrases “at least one,”“one or more,” and “and / or” are open-ended expressions that are both conjunctive and disjunctive in operation. For example, each of the expressions “at least one of A, B and C,”“at least one of A, B, or C,”“one or more of A, B, and C,”“one or more of A, B, or C” and “A, B, and / or C” may mean A alone, B alone, C alone, A and B together, A and C together, B and C together, A, B and C together, and optionally any of the above in combination with at least one other entity.

[0110] Where two or more ranges are used, such as but not limited to 1 to 5 or 2 to 4, any number between or inclusive of these ranges is implied.

[0111] As used herein, the phrase, “for example,” the phrase, “as an example,” and / or simply the term “example,” when used with reference to one or more components, features, details, structures, and / or methods according to the present disclosure, are intended to convey that the described component, feature, detail, structure, and / or method is an illustrative, non-exclusive example of components, features, details, structures, and / or methods according to the present disclosure. Thus, the described component, feature, detail, structure, and / or method is not intended to be limiting, required, or exclusive / exhaustive; and other components, features, details, structures, and / or methods, including structurally and / or functionally similar and / or equivalent components, features, details, structures, and / or methods, are also within the scope of the present disclosure.

[0112] The term “comprising” is intended to be open and permits but does not require the inclusion of additional elements or steps. When the term “comprising” is used herein, the term “consisting of” is thus also encompassed and disclosed. Where ranges are given, endpoints are included. Furthermore, it is to be understood that unless otherwise indicated or otherwise evident from the context and understanding of one of ordinary skill in the art, values that are expressed as ranges can assume any specific value or subrange within the stated ranges in different embodiments, to the tenth of the unit of the lower limit of the range, unless the context clearly dictates otherwise. Where the term “about” is used, it is understood to reflect + / −10% of the recited value. In addition, it is to be understood that any particular embodiment that falls within the prior art may be explicitly excluded from any one or more of the claims. Since such embodiments are deemed to be known to one of ordinary skill in the art, they may be excluded even if the exclusion is not set forth explicitly herein.

[0113] In addition, it is to be understood that any particular embodiment of the present disclosure that falls within the prior art may be explicitly excluded from any one or more of the claims. Since such embodiments are deemed to be known to those of ordinary skill in the art, they may be excluded even if the exclusion is not set forth explicitly herein. Any particular embodiments of compositions disclosed herein can be excluded from any one or more claims, for any reason, whether or not related to the existence of prior art.

[0114] All cited sources, for example, references, publications, databases, database entries, and art cited herein, are incorporated into this application by reference, even if not expressly stated in the citation. In case of conflicting statements of a cited source and the instant application, the statement in the instant application shall control.

Claims

1. A process for suppressing generation of acid mist in an electrowinning process, the process comprising:adding a powder of a lignosulfonate or a derivative thereof or an aqueous solution comprising the lignosulfonate or the derivative thereof to an electrolytic solution of the electrowinning process in an amount sufficient to suppress generation of acid mist.

2. The process of claim 1, wherein the amount of the lignosulfonate or the derivative thereof added to the electrolytic solution provides a concentration of the lignosulfonate or the derivative thereof in the electrolytic solution of about 15 ppm to about 100 ppm.

3. The process of claim 1, wherein the amount of the lignosulfonate or the derivative thereof added to the electrolytic solution provides a concentration of the lignosulfonate or the derivative thereof in the electrolytic solution of about 20 ppm to about 80 ppm.

4. The process of claim 1, wherein the amount of the lignosulfonate or the derivative thereof added to the electrolytic solution provides a concentration of the lignosulfonate or the derivative thereof in the electrolytic solution of about 30 ppm to about 70 ppm.

5. The process of claim 1, wherein the aqueous solution of the lignosulfonate or the derivative thereof further comprises a C2 to C6 organic acid.

6. The process of claim 5, wherein the organic acid and the lignosulfonate or the derivative thereof are provided in the aqueous solution in a mass ratio ranging from about 0.05 parts organic acid:1 part of the lignosulfonate or the derivative thereof to about 3 parts organic acid:1 part of the lignosulfonate or the derivative thereof.

7. The process of claim 5, wherein the C2 to C6 organic acid is selected from the group consisting of acetic acid, lactic acid, citric acid, ascorbic acid, benzoic acid, oxalic acid, and propanoic acid.

8. The process of claim 1, wherein the aqueous solution of the lignosulfonate or the derivative thereof further comprises a diphenyl oxide disulfonate compound.

9. The process of claim 1, wherein the aqueous solution of the lignosulfonate or the derivative thereof further comprises a polyaminosaccharide.

10. A kit for use in suppressing generation of acid mist in an electrowinning process, the kit comprising:a powder of lignosulfonate or a derivative thereof or an aqueous solution comprising the lignosulfonate or the derivative thereof.

11. The kit of claim 10, further comprising instructions to provide the lignosulfonate or the derivative thereof in an amount sufficient to provide a lignosulfonate concentration in the electrolytic solution which is sufficient to suppress generation of acid mist.

12. The kit of claim 11, wherein the instructions specify to provide the lignosulfonate or the derivative thereof in the electrolytic solution at a concentration of between about 15 ppm to about 100 ppm.

13. The kit of claim 11, wherein the instructions specify to provide the lignosulfonate or the derivative thereof in the electrolytic solution at a concentration of between about 20 ppm to about 80 ppm.

14. The kit of claim 11, wherein the instructions specify to provide the lignosulfonate or the derivative thereof in the electrolytic solution at a concentration of between about 30 ppm to about 70 ppm.

15. The kit of claim 10, wherein the aqueous solution of the lignosulfonate or the derivative thereof further comprises a C2 to C6 organic acid.

16. The kit of claim 15, wherein the organic acid and the lignosulfonate or derivative thereof are provided in the aqueous solution in a mass ratio ranging from about 0.05 parts organic acid:1 part of the lignosulfonate or the derivative thereof to about 3 parts organic acid:1 part of the lignosulfonate or the derivative thereof.

17. The kit of claim 15, wherein the C2 to C6 organic acid is selected from the group consisting of acetic acid, lactic acid, citric acid, ascorbic acid, benzoic acid, oxalic acid, and propanoic acid.

18. The kit of claim 10, wherein the aqueous solution of the lignosulfonate or the derivative thereof further comprises a diphenyl oxide disulfonate compound.

19. The kit of claim 10, wherein the aqueous solution of the lignosulfonate further comprises a polyaminosaccharide.

20. A composition for suppressing generation of acid mist in an electrowinning process, the composition comprising:about 1.5% to about 30% (m / m) of a C2 to C6 organic acid;about 40% to about 60% (m / m) of a diphenyl oxide disulfonate compound; andabout 5% to about 30% (m / m) of a lignosulfonate or a derivative thereof.

Images