TECHNICAL FIELD

[0001] The invention 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

[0002] 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.

[0003] It is 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 can cause extreme discomfort to the skin, eyes, and respiratory systems of tankhouse workers, especially during hot weather conditions.

[0004] U.S. Patent 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.

[0005] Saponins have been investigated as replacements for fluoroalkyl components in acid mist suppression agents (see for example, Cheng et al. Hydrometallurgy, 2004, 73, 133-145 and San Martin et al., Hydrometallurgy, 2005, 77, 163-170, both incorporated herein by reference in entirety).

[0006] 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.

[0007] Combinations of reconstituted licorice root extracts and surfactants are investigated as acid mist suppression agents in PCT Publication No. WO 2003059872, incorporated herein by reference in its entirety.

[0008] There remains a need for improved anti-misting agents for electrolysis/electrodeposition, particularly for products which do not include fluoroalkyl components.

SUMMARY

[0009] In accordance with one aspect of this technology, there is provided an aqueous composition for suppressing generation of acid mist in an electrowinning process. This composition includes about 1.5% to about 20% (m/m) of a C2 to Ce organic acid; about 15% to about 35% (m/m) of a diphenyl oxide disulfonate or diphenyl oxide disulfonic acid compound; and about 20% to about 30% (m/m) of a plant root extract containing a triterpenoid saponin.

[0010] In some embodiments, the triterpenoid saponin is present in the plant root extract in an amount between about 4% to about 15% (m/m).

[0011] The organic acid and the triterpenoid saponin may be provided in a mass ratio ranging from about 0.05 parts organic acid:1 part triterpenoid saponin to about 0.65 parts organic acid:1 part triterpenoid saponin.

[0012] In some embodiments, the C2 to Ce organic acid has at least one carboxylic acid group with a pKa value of between about 3.8 to about 5.5.

[0013] In some embodiments, the C2 to Ce organic acid is a C2 to C4 organic acid. The C2 to C4 organic acid may be selected from the group consisting of acetic acid, lactic acid, oxalic acid, malic acid, taratic acid, butanoic acid and propanoic acid.

[0014] The diphenyl oxide disulfonate or diphenyl oxide disulfonic acid compound may be an acid or salt form of the general structure of: wherein R is a linear or branched Ce to C16 alkyl group. In some embodiments, R is a linear or branched C12 alkyl group. In some embodiments, the compound is:

[0015] The triterpenoid saponin may be a pentacyclic triterpenoid saponin or a tetracyclic triterpenoid saponin.

[0016] The pentacyclic triterpenoid saponin may be an enoxolone, a hederagenin, a hopane, a lupane, a maslinic acid, an oleanane, an ursane, or a taraxasterane.

[0017] In some embodiments, the enoxolone is glycyrrhizin.

[0018] In some embodiments, the tetracyclic triterpenoid saponin is a saponin of Quillaja saponaria.

[0019] In some embodiments, composition may have a viscosity of about 740 to about 880 CPS.

[0020] According to another aspect of the technology described herein, there is provided a method for reducing generation of acid mist in an electrowinning process. This method includes adding a composition as described herein, to an electrowinning solution to provide a composition concentration of about 5 to about 30 ppm in the electrowinning solution.

[0021] According to another aspect of the technology described herein, there is provided a method for preparing a product for suppressing generation of acid mist in an electrowinning process. The method includes the steps of mixing an aqueous solution of a C2 to Ce organic acid with a diphenyl oxide disulfonate or diphenyl sulfonic acid compound to provide a first mixture; adding a triterpenoid saponin to the first mixture with agitation to generate a second mixture having an initial viscosity of about 1500 CPS to about 1900 CPS 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 reducing the viscosity of the second mixture to a range between about 740 CPS to about 880 CPS, thereby providing the product.

[0022] In some embodiments of the method for preparing the product, the first mixture is formed with about a 2:1 ratio of the diphenyl oxide sulfonate compound relative to the C2 to Ce organic acid.

[0023] In some embodiments of the method for preparing the product, the second mixture is formed with the organic acid and the triterpenoid saponin provided in a mass ratio ranging from about 0.05 parts organic acid:1 part triterpenoid saponin to about 0.65 parts organic acid:1 part triterpenoid saponin.

[0024] In some embodiments of the method for preparing the product, the C2 to Ce organic acid is a C2 to C4 organic acid.

[0025] In some embodiments of the method for preparing the product, the C2 toC4 organic acid is selected from the group consisting of acetic acid, lactic acid, oxalic acid, malic acid, taratic acid, butanoic acid and propanoic acid.

[0026] In some embodiments of the method for preparing the product, the diphenyl oxide disulfonate or diphenyl oxide disulfonic acid compound is an acid or salt form of the general structure of: wherein R = a linear or branched Ce to C16 alkyl group. In some embodiments, R = a linear or branched C12 alkyl group. In some embodiments, the compound is:

[0027] In some embodiments of the method for preparing the product, the triterpenoid saponin is a pentacyclic triterpenoid saponin or a tetracyclic triterpenoid saponin.

[0028] In some embodiments of the method for preparing the product, the pentacyclic triterpenoid saponin is an enoxolone, a hederagenin, a hopane, a lupane, a maslinic acid, an oleanane, an ursane, or a taraxasterane.

[0029] In some embodiments of the method for preparing the product, the enoxolone is glycyrrhizin.

[0030] In some embodiments of the method for preparing the product, the tetracyclic triterpenoid saponin is a saponin of Quillaja Saponaria.

[0031] In some embodiments of the method for preparing the product, the product has a viscosity of about 740 to about 880 CPS.

BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Various objects, features and advantages of the compositions and processes described herein will be apparent from the following description of particular embodiments of the invention, as illustrated in the accompanying drawing.

Figure 1 is a process flow diagram illustrating preparation of the acid mist suppressing product. DETAILED DESCRIPTION

Introduction and Rationale

[0033] While the use of saponins or surfactant as acid mist suppression additives is generally known in the art to indicate some potential for reduction of acid mist in electrowinning processes, the more promising results have been observed for low density current electrowinning processes. Addition of saponins or surfactant have not provided satisfactory results for high density current electrowinning processes such as the processes used for copper electrowinning. Improved compositions for providing acid mist suppression in these processes are needed.

[0034] The inventors of the present application have surprisingly discovered that a composition of a plant root extract containing a triterpenoid saponin such as glycyrrhizin (the main saponin compound of licorice root (Glycyrrhiza glabra)) in a powder form can be prepared when mixed into an aqueous solution containing a surfactant and an organic acid. As used herein, the term “plant root extract” refers to any preparation of a plant root suitable for use in formulating a composition. One convenient preparation is in the form of a powder prepared by spray drying, for example. Preparation of a mixture of an organic acid such as acetic acid and a nonionic surfactant assists the dispersion of the soluble fraction of the triterpenoid saponin when the composition is introduced into the electrolyte solution in a 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 C2 to Ce organic acids and nonionic surfactants of the same general class, as well as alternative triterpenoid saponins present in alternative plant root extracts will provide alternative embodiments of the acid mist suppressing composition. Without being bound by any particular theory, it is believed that the C2 to Ce organic acid hydrolyzes biomolecular components of the licorice root powder such as polysaccharides such as lignins, for example. When applied to licorice root powder solutions, this process liberates glycyrrhizin from its biological matrix to increase the amounts of solubilized glycyrrhizin available to function as an acid mist suppressant. It is believed that C2 to C4 organic acids, being of a smaller size, may be more effective in penetrating the root powder matrix and more effective in liberating the triterpenoid saponins from root powder matrices. Furthermore, mixing of an aqueous solution of the surfactant with an aqueous solution of the organic acid to provide a first mixture prior to addition of the licorice root powder provides first mixture with viscosity suitable to interact well with the licorice root powder to promote liberation of glycyrrhizin from the biological matrix. It is reasonably predicted that this process may be applied to prepare alternative composition embodiments from different plant root extracts which include different triterpenoid saponins.

[0035] An example of a general process for preparing an acid mist suppressing composition appropriate for use in an electrowinning process is outlined in Figure 1. A first mixture which includes an organic acid and a diphenyl oxide disulfonate or diphenyl oxide sulfonic acid 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 a plant root powder containing a triterpenoid saponin is added 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 product.

[0036] Saponins are a diverse group of amphipathic glycosides having one or more hydrophilic glycoside moieties combined with a lipophilic triterpene (triterpenoid saponins) or steroid aglycone (steroidal saponins or steroid glycosides) backbone called a sapogenin. The saponins are a subclass of terpenoids, the largest class of plant extracts. The amphipathic nature of saponins provides them with properties similar to those of synthetic surfactants. Triterpenoid saponins include, without limitation, tetracyclic triterpenoid saponins and pentacyclic triterpenoid saponins. Non-limiting examples of tetracyclic triterpenoid saponins include cucurbitanes, cycloartanes, cycloartenols, dammaranes, euphanes, lanostanes and tirucallanes. Non-limiting examples of pentacyclic triterpenoid saponins include enoxolones, hederagenins, hopanes, lupanes, maslinic acids, oleananes, ursanes, and taraxasteranes. Non-limiting examples of steroidal saponins include diosgenins, eleutherosides, ginsenosides, sarsasapogenins, and yamogenins. Soap bark tree (Quillaja saponaria), fenugreek (Trigonella foenum- graceum), alfalfa (Medicago sativa), horse chestnut (Aesculus hippocastanum), licorice (Glycyrrhiza species such as Glycyrrhiza glabra), soapwort (Saponaria officinaux), Mojave yucca (Yucca schidigera), gypsophila genus (such as Gypsophila paniculata), sarsaparilla (Smilax regelii and other closely related species of Smilax genus) and ginseng (Panax genus) are the main plant sources of saponins used in health and industrial applications. Additional examples of saponins are described in Guglu-llstundag; and Mazza, Saponins: Properties, Applications and Processing. 2007 Crit. Rev. Food Sci. Nutr. 47(3): 231-58 (2007), incorporated herein by reference in its entirety.

[0037] The effectiveness of using a combination of the triterpenoid saponin and nonionic surfactant arises from three main factors: (1) as the fraction of solubilized triterpenoid saponin 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 triterpenoid saponin provides a more stable and effective acid mist suppression composition.

[0038] The composition includes an organic acid to assist the process step of releasing the triterpenoid saponin into the aqueous phase. The organic acid may be a C2 to Ge 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. In other embodiments, the organic acid may be a C2 to C4 organic acid. Examples of such C2 to C4 organic acids include, but are not limited to: acetic acid, lactic acid, oxalic acid, malic acid, tartaric acid, butanoic acid and propanoic acid.

[0039] The mass ratio organic acid with respect to the plant root extract containing a triterpenoid saponin 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 plant root extract to about 0.65 parts organic acid:1 part plant root extract. This range of mass ratios includes any fractional mass ratio value therebetween, for example 0.1 , 0.15, 0.2, 0.25, 0.3, 0.35, 0.4, 0.45, 0.5, 0.55, and 0.6 parts organic acid:1 part plant root extract.

[0040] The total mass percentage of the organic acid in the aqueous composition may be between about 2% to about 20% (m/m), between about 3% to about 20% (m/m), between about 4% to about 20% (m/m), between about 5% to about 20% (m/m), between about 6% to about 20% (m/m), between about 7% to about 20% (m/m), between about 8% to about 20% (m/m), between about 9% to about 20% (m/m), between about 10% to about 20% (m/m), between about 11 % to about 20% (m/m), between about 12% to about 20% (m/m), between about 13% to about 20% (m/m), between about 14% to about 20% (m/m), or between about 15% to about 20% (m/m). The total mass percentage of the organic acid in the composition may also be provided in narrower ranges, for example, between about 8% to about 16% (m/m), between about 9% to about 15% (m/m), between about 10% to about 14% (m/m) and between about 11% to about 13% (m/m).

[0041] It is preferable that the plant root extract used to prepare the composition includes a triterpenoid saponin at a suitable mass percentage to provide sufficient amounts of the triterpenoid saponin in the aqueous composition. In some embodiments, the plant root extract includes at least about 4% (m/m), at least about 5% (m/m), at least about 6% (m/m), at least about 7% (m/m), at least about 8% (m/m), at least about 9% (m/m), at least about 10% (m/m), at least about 11% (m/m), at least about 12% (m/m), at least about 13% (m/m), at least about 14% (m/m), or at least about 15% (m/m) of triterpenoid saponin. In other embodiments, the plant root extract includes between about 4% to about 15% (m/m), between about 4% and about 12%, between about 4% and about 10%, between about 4% and about 8%, or between about 5% to about 7% (m/m) of triterpenoid saponin.

[0042] The selection of diphenyl oxide disulfonate salts or diphenyl oxide disulfonic acid 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. In some embodiments, the diphenyl oxide disulfonate or diphenyl oxide disulfonic acid compound is an acid or salt form of the general structure of: wherein R is a linear or branched Ce to C16 alkyl group. In some preferred embodiments, R is a linear or branched C12 alkyl group. In one embodiment, the diphenyl oxide disulfonic acid compound has the following general structure:

[0043] In one preferred embodiment, the diphenyl oxide disulfonic acid compound used to prepare the aqueous composition is a compound formerly marketed by Dow Chemical as DOWFAX™ 2A0, which has the following structure:

[0044] In some embodiments, the aqueous solution containing the organic acid further includes a polysaccharide, to increase the viscosity and promote formation of a gelatinized product with enhanced stability, which also quickly disperses into an electrowinning solution.

[0045] It is preferable that the acid mist suppressing properties provided by the composition are sufficient for the composition to be effective at concentrations in the electrowinning solution within ranges of about 2 ppm to about 100 ppm of the composition, preferably from about 2 ppm to about 30 ppm of the composition, and most preferably from about 5 ppm to about 25 ppm of the composition. In an electrowinning solution, they may be added to the metal-containing electrolyte/strip aqueous phase in the electrowinning tankhouse.

Examples

Example 1 : An Acid Mist Suppressing Composition

[0046] This example describes one embodiment of a process for preparing an acid mist suppressing aqueous composition at laboratory scale to test for acid mist suppressing properties. Alternative embodiments may use different organic acids, different diphenyl oxide sulfonate or diphenyl oxide disulfonic acid compounds and different plant root extracts containing different triterpenoid saponins. In this example, 50 g of a 50% aqueous solution of acetic acid (viscosity 1.04 CPS) was mixed with 100 g of a 48% aqueous solution of a diphenyl oxide disulfonic acid compound of the structure:

[0047] This aqueous solution of the diphenyl oxide disulfonic acid compound 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 RPM for about 20 to 30 minutes to achieve uniform mixing and a temperature of about 50 °C. Then 50 g of licorice root powder containing about 6.48% (m/m) of glycyrrhizin was added without a wetting agent. This addition resulted in a solution viscosity of 1700 CPS and lowering of the temperature of the mixture to about 30 to 40 °C. Viscosity measurements were made using a Brookfield Meter LVF spindle #1. The mixture was then heated again to about 50 °C for about 10 minutes, thereby reducing the viscosity to about 1250 CPS. At that stage, the mixture was cooled slowly over three hours to about 23 °C to provide a final product with a viscosity of about 820 CPS. The resulting composition includes about 12.5% (m/m) acetic acid, about 38.5% water, about 24% of dodecyl diphenyl oxide disulfonic acid, and about 25% of licorice root powder containing about 6.48% (m/m) glycyrrhizin relative to the total mass of the licorice root powder (which provides glycyrrhizin in the aqueous composition equivalent to about 1 .6% (m/m) glycyrrhizin). This product included about 47.5% to about 51.0% total precipitated solids. This product was investigated for mist suppression properties, as outlined in Example 2.

[0048] Test results indicating the effectiveness of the composition described above in acid mist suppression are described in the subsequent examples. On the basis of the test results, it is reasonably predicted that alternative aqueous compositions (where water is included and understood to account for missing mass percentages of the total mass of the composition) may be prepared having the following ranges of components: about 1 .5% to about 20% (m/m) of a C2 to Ce organic acid, about 15% to about 35% of a diphenyl oxide disulfonate or diphenyl oxide disulfonic acid compound and about 20% to about 30% of a plant root extract containing a triterpenoid saponin.

Example 2: Investigation of Acid Mist Suppression Properties

[0049] 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 from the 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 0 to 6 amps.

[0050] For each experiment, the tankhouse electrolyte was prepared by mixing 155 g CUSO4'5H ₂ O 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 composition described in Example 1 was investigated at 25 ppm, 15 ppm and 10 ppm of the composition in 2.0 L of the tankhouse electrolyte solution. 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 7.0 liter per minute air flow rate. The pH of the water was measured at the beginning and at the end of each test.

[0051] To demonstrate the acid mist suppression characteristics of the aqueous composition of Example 1 , 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 different concentrations of the aqueous composition of Example 1 expressed in Table 1 as the mass equivalent of licorice root extract (where 25 ppm of the composition provides 6.25 ppm of licorice root extract, 15 ppm of the composition provides 3.75 ppm of licorice root extract and 10 ppm of the composition provides 2.50 ppm of the licorice root extract). The data representing mist generation were compared to the baseline in order to evaluate the effectiveness of mist suppression under laboratory conditions. The results of the anti-misting tests are shown in Table 1. The acid mist suppressing composition was found to have acceptable solubility in the tankhouse electrolyte solution in each case.

Table 1 : Acid Mist Suppression by the Composition of Example 1 r 10 I 2.50 I 19.3 I 84.31 |

[0052] The results of Table 1 indicate that highly effective acid mist suppression begins to be observed at 3.75 ppm of licorice root extract and improves significantly to greater than 99% acid mist suppression at 6.25 ppm licorice root extract, when provided to the electrowinning solution as 15 ppm and 25 ppm, respectively, of the acid mist suppression composition of Example 1 . Still, quite effective acid mist suppression above an average of 80% is observed with the 10 ppm of the composition added to provide 2.5 ppm licorice root extract. It is reasonably predicted that the mass ratio of organic acid to licorice root extract may be varied from about 0.05 to 1 to about 0.5 to 1 , while retaining the properties useful for a stable solution providing useful acid mist suppression.

[0053] In contrast to the results shown in Table 1 , an investigation of the acid mist suppression properties of higher concentrations of licorice root extract alone (without organic acid and diphenyl oxide sulfonate) under similar conditions, indicated that significantly higher concentrations of 75 ppm licorice root extract were required to obtain acid mist suppression in a range of about 71% to about 80% (see Table 2).

Table 2: Acid Mist Suppression Using Licorice Root Powder Alone

[0054] When employed at industrial scale, these higher concentration levels of licorice root powder of 75 ppm or higher are expected to 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 concentrations of licorice root powder are significantly lower, will provide effective acid mist suppression without generation of dangerous volumes of foam.

[0055] This example confirms that the acid mist suppressing composition of Example 1 is significantly more effective at suppressing acid mist under simulated electrowinning conditions than licorice root extract alone.

Example 3: Comparative Investigation of Acid Mist Suppression Properties of Alternative Combinations of Additives

[0056] Combinations of reconstituted licorice extracts with surfactants for acid mist suppression in copper electrowinning are described in PCT publication No. WO2023059872, which is incorporated herein by reference in its entirety. In one of the described combinations, a powdered licorice extract having 8% to 15% wt% glycyrrhizin was reconstituted in water and added to an electrowinning electrolyte solution to provide a concentration of 13 ppm of powdered licorice extract. In addition, VANMIST 210 which includes sodium dodecyl diphenyl oxide disulfonate (CAS No. 25167-32-2; trade names CALFAX® DB-45 from Pilot Chemical or under the trade name DOWFAX® 2A1 from Dow Chemical) and the fluoroaliphatic surfactant C4FgSO2N(C2H4COOH)C3H6N(CH3)2 was also added to the electrowinning electrolyte solution to a concentration of 2 ppm, to provide a total active component concentration of 15 ppm in the electrowinning electrolyte solution. In another one of the combinations described in PCT publication No. WO2023059872, the same powdered licorice extract was added to the electrowinning electrolyte solution to a concentration of 13 ppm of powdered licorice extract. In addition, sodium C9-C22 alkyl secondary sulfonate (CAS No. 68188-18-1 ; MERSOLAT® H95 from LANXESS Corporation, Pittsburg, PA) was added to the electrowinning electrolyte solution to a concentration of 2 ppm, to provide a total active component concentration of 15 ppm in the electrowinning electrolyte solution. The last two entries of Table 3 of PCT publication No. WO2023059872, indicate that the two combinations described above are more effective at acid mist suppression than licorice extracts alone and more effective at acid mist suppression than the fluoroaliphatic surfactant FC-1100 (C ₄ F9SO2N(C2H ₄ COOH)C3H6N(CH3)2) alone (see Table 2 of PCT publication No. WO2023059872). [0057] It was deemed desirable to compare combinations similar to the combinations of PCT publication No. WO2023059872 with the composition outlined in Example 1 herein, using the experimental acid mist measurement system described in Example 2 herein. As noted above, the composition of Example 1 includes about 12.5% (m/m) acetic acid, about 38.5% water, about 24% of dodecyl diphenyl oxide disulfonic acid, and about 25% of licorice root powder containing about 6.48% (m/m) glycyrrhizin relative to the total mass of the licorice root powder (which provides glycyrrhizin in the aqueous composition equivalent to about 1.6% (m/m) glycyrrhizin in the aqueous composition).

[0058] To investigate two combinations of additives similar to the additives outlined above in PCT publication No. WO2023059872, the same test conditions outlined in Example 2 were used, with separate additions to the test electrolyte solution of a 17.2% (m/m) aqueous solution of the same licorice root powder used in Example 2 mixed with demineralized water for 45 minutes, to provide 13 ppm licorice root powder in the test electrolyte solution.

[0059] In a first test electrolyte combination containing 13 ppm licorice root powder, the surfactant CALFAX® DB-45 was added neat using a micropipette to provide 2 ppm CALFAX® DB-45 (hereinafter designated as the “CALFAX- licorice combination”).

[0060] In a second test electrolyte combination containing 13 ppm licorice root powder, the surfactant MERSOLAT® H95 was added as a 1 % (m/m) aqueous solution of dry flakes prepared in demineralized water with mixing for 10 minutes to generate a solution to provide 2 ppm surfactant based on the dry mass of MERSOLAT® H95 (hereinafter designated as the “MERSOLAT- licorice combination”).

[0061] It was decided to not investigate the fluoroaliphatic surfactant C4F9SO2N(C2H ₄ COOH)C3H ₆ N(CH3)2 (which is included in the VANMIST 210 formulation described in PCT publication No. WO2023059872) because such fluoroaliphatic surfactants are deemed environmentally unsuitable for continued use.

[0062] The results of the experiments determining the acid mist suppression provided by the two combinations described above using the experimental conditions outlined in Example 2, are outlined in Table 3 below, with acid mist data expressed as mass of H2SO4/m ³ as in Tables 1 and 2.

Table 3: Acid Mist Suppression of the CALFAX-licorice and MERSOLAT- licorice Combinations

[0063] The average acid mist suppression provided by the CALFAX-licorice combination is 53.57%. In contrast, the composition of Example 1 provided to the test electrolyte solution at a concentration equivalent of 15 ppm to provide 3.75 ppm of licorice root extract provides average acid mist suppression of 89.76%. Likewise, the composition of Example 1 provided to the test electrolyte solution at a concentration equivalent of 10 ppm to provide 2.50 ppm of licorice root extract provides average acid mist suppression of 80.56%. Therefore, at significantly lower equivalent concentrations of licorice root extract, the composition of Example 1 is significantly more effective at suppressing acid mist than the CALFAX-licorice combination.

[0064] The average acid mist suppression provided by the MERSOLAT-licorice combination is 44.85%. In contrast, the composition of Example 1 provided to the test electrolyte solution at a concentration equivalent of 15 ppm to provide 3.75 ppm of licorice root extract provides average acid mist suppression of 89.76%. Likewise, the composition of Example 1 provided to the test electrolyte solution at a concentration equivalent of 10 ppm to provide 2.50 ppm of licorice root extract provides average acid mist suppression of 80.56%. Therefore, at significantly lower equivalent concentrations of licorice root extract, the composition of Example 1 is significantly more effective at suppressing acid mist than the the MERSOLAT-licorice combination.

[0065] The composition described herein is significantly more effective than the two additive combinations described in PCT publication No. WO2023059872, even when provided to the electrolyte solution at lower concentrations with respect to the mass of licorice root powder. It is advantageous to provide acid mist suppression compositions at lower concentrations of licorice root powder to avoid excessive foaming, which can complicate electrowinning processes.

[0066] It is believed that the organic acid component of the composition described herein promotes liberation of the triterpenoid saponin from the licorice root powder matrix to the aqueous solution via one or more mechanisms which may include hydrolysis of structural biomolecules such as polysaccharides and that this liberation of the saponin component from the powder matrix provides more effective acid mist suppression. It is believed that the selected surfactant for the composition, which in a disulfonic acid form is responsible for the enhanced synergistic acid mist suppression activity. Surfactants which are chemically similar in either acid or salt form and falling within the scope of the general structures described above are also expected to be effective in alternative composition embodiments.

Equivalents and Scope

[0067] 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. [0068] 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.

[0069] 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.

[0070] “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 nonlimiting 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.

[0071] 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. [0072] 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.

[0073] 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.

[0074] 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. [0075] 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.