WO2020190822A1 - Methods of reducing nitration of extractants in solvent extraction systems - Google Patents

Abstract

Disclosed are methods of reducing nitration of extractants in metal solvent extraction systems. The methods include at least one of adding a sacrificial compound to the leaching solution or contacting the leaching solution with a gas.

Description

METHODS OF REDUCING NITRATION OF EXTRACTANTS

IN SOLVENT EXTRACTION SYSTEMS

FIELD

[0001] Disclosed herein are methods for reducing nitration of extractants in metal solvent extraction systems.

BACKGROUND

[0002] Copper, copper alloys and numerous other valuable metals have been used for various purposes over thousands of years. Because of the importance of such metals, there is continuous research into increasing the efficiency and productivity of procuring these metals. In particular, it is critical for mines to maximize efficiency when extracting metals from ore.

[0003] Copper-containing ores are typically classified into two categories - oxidic and sulfidic ores. Oxidic ores (e.g., cuprite, malachite, and azurite) are found near the surface as they are oxidation products of the deeper secondary and primary sulfidic ores (e.g., chalcopyrite, bomite, and chalcocite). Due to the chemical nature of copper oxides and secondary sulfides, mines typically treat the ore with hydrometallurgical processes - i.e., heap leaching, solvent extraction, and electro winning. Approximately 20% of the world’s annual copper production is obtained through hydrometallurgical processes.

[0004] During hydrometallurgical processes, metal is extracted when the metal-containing material is leached in one of several ways. Leaching is typically accomplished by applying a lixiviant to a collection of ore. The most common lixiviant used in the mining industry is sulfuric acid (“H2SO4”) because it provides efficient and cost effective liberation of the metal from the ore. The leaching process can be a heap, dump, percolation or agitation leaching process. The lixiviant dissolves salts of the metals (e.g., copper) in the ore and results in an aqueous and acidic pregnant leaching solution containing dissolved metal ions.

[0005] Following the leaching process, the pregnant leaching solution is fed to a solvent extraction system where it is contacted with an organic solution. The organic solution contains dissolved extractants that selectively form metal-extractant complexes with one or more metal ions (e.g., copper ions) in preference to other metal ions. During the solvent extraction process, the metal values are transferred from an aqueous phase to an organic phase and are subsequently recovered, typically through stripping and electrowinning processes. [0006] Reagents (e.g., aldoximes, ketoximes) used in solvent extraction processes generally have favorable characteristics relating to phase separation, reagent stability and rate of reaction. However, under some conditions, oxime reagents can experience nitration resulting from the presence of NxOy species (i.e., NO, N02⁺, N2O, HNO2, HN03, N2O5 and NO3 ) in the leaching solution or in the solvent extraction system. The chemistry in a solvent extraction system can be complicated and is dependent on the composition of the pregnant leaching solution, which varies from plant to plant, and on the extractants dissolved in the organic phase. The cause of nitration of an oxime reagent in a solvent extraction system is not always straight-forward to ascertain, but it is important to reduce or eliminate such nitration. Nitration of oxime extractants can form nitro-oxime compounds that bind too strongly to copper and while nitrated oximes may be able to extract metal (e.g., copper) effectively, the metal cannot be stripped effectively under standard stripping conditions. Nitration problems can worsen if not addressed because the byproducts of nitration reactions can enhance degradation of the oxime reagents. In a plant having the potential for N_xO_y species to enter the leaching solution, it is essential to select an appropriate organic extractant and/or to mitigate the effects of N_xO_y species buildup.

BRIEF SUMMARY

[0007] A method of reducing nitration of an extractant in a solvent extraction system, comprising: adding at least one sacrificial compound to a leaching solution of the solvent extraction system, wherein the sacrificial compound has preferential nitration to nitration of the extractant.

[0008] A method of reducing nitration of an extractant in a solvent extraction system, comprising: introducing a gas into an aqueous leaching solution supplied to the solvent extraction system, wherein the aqueous leaching solution comprises an amount of at least one NxOy compound, and wherein the gas reduces the amount of the at least one N_xO_y compound within the aqueous leaching solution.

[0009] A method of reducing nitration of an extractant in a solvent extraction system, comprising: adding a sacrificial compound to a leaching solution of the solvent extraction system, wherein the sacrificial compound has preferential nitration to nitration of the extractant; and introducing a gas into an aqueous leaching solution supplied to the solvent extraction system, wherein the aqueous leaching solution comprises at least one N_xO_y compound, and wherein the gas reduces a concentration of the at least one N_xO_y compound within the aqueous leaching solution. [0010] The above summary provides a basic understanding of the disclosure. This summary is not an extensive overview of all contemplated aspects, and is not intended to identify all key or critical elements or to delineate the scope of any or all aspects of the disclosure. Its sole purpose is to present one or more aspects in a summary form as a prelude to the more detailed description that follows and the features described and particularly pointed out in the claims.

BRIEF DESCRIPTION OF THE DRAWINGS

[0011] The present disclosure is illustrated by way of example, and not by way of limitation, in the figures of the accompanying drawings in which like references indicate similar elements.

[0012] FIG. 1 is a flow diagram for a solvent extraction process according to embodiments herein.

DETAILED DESCRIPTION

[0013] Embodiments are described herein in the context of methods of reducing or eliminating nitration of reagents in solvent extraction systems. Those of ordinary skill in the art will recognize that the following description is illustrative only and is not intended to be in any way limiting. Other aspects will readily suggest themselves to those of ordinary skill in the art having the benefit of this disclosure. Reference will now be made in detail to implementations of the example aspects as illustrated in the accompanying drawings. The same reference indicators will be used to the extent possible throughout the drawings and the following description to refer to the same or like items.

Definitions

[0014] Reference throughout the disclosure to terms such as“one embodiment,”“certain embodiments,”“one or more embodiments,”“various embodiments,”“an embodiment” and so forth mean that a particular feature, structure, material, or characteristic described in connection with the embodiment is included in at least one embodiment. Thus, such terms throughout the disclosure are not necessarily referring to the same embodiment.

Furthermore, the particular features, structures, materials, or characteristics may be combined in any suitable manner in one or more embodiments. [0015] As used herein, the singular forms“a,”“an,” and“the” include plural references unless the context clearly indicates otherwise. Thus, for example, reference to“a metal” includes a single metal as well as two or more different metals.

[0016] As used herein, the term“about” in connection with a measured quantity, refers to the normal variations in that measured quantity, as expected by one of ordinary skill in the art in making the measurement and exercising a level of care commensurate with the objective of measurement and the precision of the measuring equipment. In certain embodiments, the term“about” includes the recited number ±10%, such that“about 10” would include from 9 to 11.

[0017] The term“at least about” in connection with a measured quantity refers to the normal variations in the measured quantity, as expected by one of ordinary skill in the art in making the measurement and exercising a level of care commensurate with the objective of measurement and precisions of the measuring equipment and any quantities higher than that. In certain embodiments, the term“at least about” includes the recited number minus 10% and any quantity that is higher such that“at least about 10” would include 9 and anything higher than 9. This term can also be expressed as“about 10 or more.” Similarly, the term“less than about” typically includes the recited number plus 10% and any quantity that is lower such that“less than about 10” would include 11 and anything less than 11. This term can also be expressed as“about 10 or less.”

[0018] The term“standard ketoxime” as used herein refers to a compound having a structure represented by:

wherein R¹ is a Ci-22 linear or branched alkyl or alkenyl group, a Ce aryl group or a C7- 22 aralkyl group, R²-R⁴ are each independently hydrogen, halogen, a linear or branched Ce- 12 alkyl group, OR⁶ where R⁶ is a Ci-22 linear or branched alkyl group, a C2-22 linear or branched alkenyl group, a Ce aryl group, or a C7-22 aralkyl group and R⁵ is hydrogen, wherein at least one of R² - R⁴ is not hydrogen. [0019] The term“standard aldoxime” as used herein refers to a compound having a structure represented by:

wherein R¹ is hydrogen and R²-R⁴ are each independently hydrogen, halogen, a linear or branched Ce-u alkyl group, OR⁶ where R⁶ is a Ci-22 linear or branched alkyl group, a C2- 22 linear or branched alkenyl group, a Ce aryl group, or a C7-22 aralkyl group, wherein at least one of R² - R⁴ is not hydrogen.

[0020] The term“NS AO” is used herein interchangeably with 5-nonylsalicylaldoxime, and refers to a compound having the structure:

[0021] The term“HNAO” is herein used interchangeably with 5-nonyl-2- hy dr oxy acetophenone, and refers to a compound having the structure:

[0022] The term“metal recovery” as used herein refers to the amount by mass (e.g., wt%) of metal recovered from a process stream as compared to the total amount (e.g., wt%) of dissolved metal in the process stream. [0023] The term“metal selectivity” as used herein refers to the likelihood that a reagent will complex with a particular metal over another.

[0024] The term“deactivated compound” as used herein refers to Electrophilic Aromatic Substitution reactions and includes aromatic compounds having at least one deactivating group that decreases the rate of reaction relative to hydrogen (H); deactivating groups tend to withdraw electron energy from a ring.

[0025] The term“activated compound” as used herein refers to Electrophilic Aromatic Substitution reactions and includes aromatic compounds having at least one activating group that increases the rate of reaction relative to hydrogen (H); activating groups tend to donate electron density to a ring.

Leaching and Solvent Extraction

[0026] A typical solvent extraction system 100 is depicted in FIG. 1. According to embodiments, a metal ore (e.g., containing copper metal values) is subjected to a leaching process (e.g., a heap leaching process) where an aqueous lixiviant (e.g., sulfuric acid) is sprayed onto a heap of the ore. The lixiviant dissolves at least one metal as it percolates down through the ore and a pregnant leaching solution (PLS) 110 exits the leaching process. The PLS 110 enters a solvent extraction system 115. In the solvent extraction system 115, the PLS 110 comes into contact with a metal-free organic solution (also referred to as an organic phase) 125 that can be supplied by a stripping process 130. In the solvent extraction system 115, the organic solution 125 extracts at least one metal from the PLS 110. The reagent 125 forms complexes with the at least one metal in the PLS 110. A metal-loaded organic solution 135 exits the solvent extraction process 115 and is directed to a stripping process 130. An aqueous raffinate 140, which is a metal-depleted leaching solution, is recycled to the leaching process 105. During the stripping process 130, the metal is stripped from the metal-loaded organic solution 135 and sent to an electrowinning process 145 where the metal is plated as a final product.

[0027] The at least one metal recovered by the solvent extraction process can include, but is not limited to, copper, nickel, cobalt or combinations thereof. In one embodiment, the metal is copper. Other metals that may be present in the pregnant leaching solution include, but are not limited to, bismuth, cadmium, chromium, nickel, antimony, zinc, iron, titanium or zirconium.

[0028] In the solvent extraction system, the metal-containing aqueous solution (i.e., the PLS) is contacted with the organic phase comprising a water immiscible solvent and a reagent composition containing at least one extractant. The resultant metal-pregnant organic phase typically flows to a separator to recover metal values from the metal-pregnant organic phase. The metal-barren aqueous phase can be recycled to the leaching operation. For example, copper from a copper-containing PLS is recovered, which includes contacting the copper- containing PLS with the organic phase comprising the water immiscible solvent and reagent composition comprising a copper extractant.

[0029] The PLS containing dissolved metal values is contacted with the water-immiscible organic solution containing the reagent composition for a period of time sufficient to allow the extractant to form complexes with metal ions. The feedstock can be contacted by the organic solution in any manner that brings the two immiscible phases together for a period of time sufficient to allow the deactivated compound in the reagent composition to form a complex with the metal ions. This includes shaking the two phases together in a separatory funnel or mixing the two phases together in a mix tank as described in U.S. Pat. No.

4,957,714, the entire contents of which are incorporated herein by reference.

Reagent Compositions

[0030] A reagent composition as described herein can include at least one extractant prone to nitration, for example, an organic compound having an aromatic ring and capable of extracting at least one metal from a PLS, dissolved in a water immiscible organic solvent. Suitable water immiscible organic solvents contained in the reagent composition include, but are not limited to, kerosene, benzene, toluene, xylene and combinations thereof. Suitable extractants include, but are not limited to, an oxime, such as a ketoxime, an aldoxime, and mixtures thereof.

[0031] According to embodiments, the reagent composition contains at least one oxime capable of preferentially binding to at least one metal (e.g., copper) in a PLS. A suitable oxime for use as an extractant in the reagent composition has the structure:

wherein R¹ is a H or a linear or branched alkyl or alkenyl group, aryl group or aralkyl group, R²-R⁴ are each independently hydrogen, halogen, a linear or branched alkyl or alkenyl group, OR group, an aryl group, or an aralkyl group.

[0032] In embodiments, for example, copper solvent extraction, the oxime can be a standard ketoxime typically used for copper extraction, or a mixture of oximes containing a standard ketoxime and a standard aldoxime. The standard ketoxime can be a compound having a structure represented by:

wherein R¹ is a Ci-22 linear or branched alkyl or alkenyl group, a Ce aryl group or a C7- 22 aralkyl group, R²-R⁴ are each independently hydrogen, halogen, a linear or branched Ce- 12 alkyl group, OR⁶ where R⁶ is a Ci-22 linear or branched alkyl group, a C2-22 linear or branched alkenyl group, a Ce aryl group, or a C7-22 aralkyl group and R⁵ is hydrogen, wherein at least one of R² - R⁴ is not hydrogen. In embodiments, the standard aldoxime can be a compound having a structure represented by:

wherein R¹ is hydrogen and R²-R⁴ are each independently hydrogen, halogen, a linear or branched Ce-u alkyl group, OR⁶ where R⁶ is a C i-22 linear or branched alkyl group, a C2- 22 linear or branched alkenyl group, a Ce aryl group, or a C7-22 aralkyl group, wherein at least one of R² - R⁴ is not hydrogen.

[0033] Reagent compositions as described herein also can include additives, for example, at least one modifier to increase functionality of the reagent composition. U.S. Pat. Nos.

4,978,788; 6,177,055; 6,231,784; 7,585,475 and 7,993,613, the contents of which are incorporated herein by reference, provide examples of modifiers that can be incorporated into reagent compositions. In embodiments, the use of highly branched chain aliphatic or aliphatic-aromatic C10-C30 esters or C 10-C30 alcohols can be included in a reagent composition as a strip modifier. The reagent composition can include an equilibrium modifier, for example, where the equilibrium modifier is a linear di ester or polyester of an unbranched monocarboxylic acid or unbranched dicarboxylic acid and an unbranched alcohol. A reagent composition can include a thermodynamic modifier and/or a kinetic modifier. Examples of suitable kinetic modifiers include, but are not limited to, dioximes such as 8,9- dioximohexadecane, alpha-bromocarboxylic acids such as alpha-bromolauric acid and/or 5,8- diethyl-7-hydroxydodecan-6-oxime.

[0034] The extractant in the reagent composition can be present in any suitable concentration for metal extraction. For example, in one or more embodiments, the reagent composition contains at least one oxime extractant at a concentration of about 0.01 M to about 2.0 M, or about 0.015 M, to about 1.5 M, or about 0.018 M to 1.1 M. In embodiments, the

concentration of oxime ranges from about 0.018 M to about 0.9 M or 0.018 M to about 0.72 M.

Deactivated Compounds

[0035] In solvent exchange systems determined to have a high potential for nitration of at least one extractant or where nitration of at least one extractant has been observed, the reagent composition can be tailored so that the extractant is a deactivated compound resistant to nitration. In embodiments, the deactivated compound is a deactivated oxime, for example, an oxime having an aromatic group. The deactivated compound includes at least one deactivating group such as a halo group (e.g., F, Cl, Br, I), a carbonyl group, a sulfonyl group, a cyano group, a nitro group, a haloalkyl group (e.g., -CF3) and/or an ammonium group (-NR3). In embodiments, the at least one deactivated compound can be an oxime, such as a ketoxime, for example, 5-nonyl-2-hydroxyacetophenone having the structure:

or an aldoxime, such as, 5-nonylsalicylaldoxime having the structure:

[0036] In embodiments, the reagent composition can contain the deactivated oxime dissolved in a water immiscible organic solvent as described above. The deactivated compound can be present in the reagent composition in an amount of about 0.0001 M to about 0.5 M, or about 0.001 M to about 0.25 M.

Sacrificial Compounds

[0037] As will be described in more detail below, in solvent exchange systems determined to have a high potential for nitration of at least one extractant or where nitration of the extractant has been observed, a sacrificial compound such as an activated compound can be added to the reagent composition in addition to a deactivated compound as described above. The sacrificial compound can be an activated nitration agent, such as an activated aromatic species, to consume any N_xO_y compounds, such as nitronium (NC ⁺), present in the PLS. According to embodiments, the sacrificial compound comprises at least one activating group such as an alkyl group, an alkoxy group, an ester group, a hydroxyl group, an amide group, an alkoxide group and/or an amine group. The sacrificial compound is more prone to nitration than the deactivated compound. According to embodiments, the sacrificial compound can be nonylphenol. The sacrificial compound can be added to the reagent composition in an amount of about 0.01 M to about 2.0 M, or about 0.015 M, to about 1.5 M, or about 0.018 M to 1.1 M.

Methods of Reducing Nitration of an Extractant

[0038] According to embodiments, described herein are methods of reducing nitration of an extractant in a solvent extraction system. As will be described in more detail below, in embodiments, a leaching solution can be quickly measured to determine its nitration aggressiveness and subsequently a sacrificial compound as described above can be added to the reagent. The sacrificial compound is expected to nitrate in preference to the extractant and can help reduce the content of N_xO_y species in the solution. As will be described in more detail below, in embodiments, the leaching solution can be exposed to a gas (e.g., air, carbon dioxide, nitrogen, argon, etc.), which reduces the nitronium concentration in the leaching solution. The use of one or more of the above methods together is also contemplated.

Nitration

[0039] There are a number of different mechanisms for nitration of an aromatic ring. These mechanisms are not infinite due to the laws of chemistry. The benzene ring is electron rich, so it requires that the nitrating agent be a reactive electrophile or radical in nature.

Electrophiles that could be found in a mining solution have a variety of structures; nitric acid mixtures, monodentate metal nitrates, alkyl nitrates, nitronium salts, and metal subnitrates. Radical species can include N2O4 and other N_xO_y and bidentate metal nitrates.

[0040] The mechanism of nitration based on nitronium (N02⁺) for aldoxime and ketoxime extractants having aromatic groups is well understood. Nitration of these extractants diminishes their effectiveness and can cause discoloration (e.g., dark orange / red orange / red) and/or odor of the plant organic in a solvent extraction system. Although nitrated oximes extract metal (e.g., copper) effectively, the metal cannot be stripped effectively under standard stripping conditions (e.g., at a solvent exchange/electro winning plant). In addition, the viscosity of such nitrated extractants is substantially higher than the viscosity of standard aldoxime and ketoximes, which can cause operational problems if the nitration becomes substantial, for example, nitration of the extractants can increase the viscosity of the plant organic.

[0041] Nitration agents typically found in mining solutions (e.g., copper mining solutions) are based on N_xO_y species. These nitration agents can include NO, N02⁺, N2O, HNO2, N2O4, HN03, N2O5, and NO3 . These nitration agents can be dissolved in water where the will eventually form nitric acid and/or nitrate species, which can lead to formation of nitronium (N0₂ ⁺). Nitronium is a linear cation that does not have a low lying lowest unoccupied molecular orbital (LUMO).

[0042] Nitration of aromatic species is typically accomplished via an electrophilic aromatic substitution reaction. Nitronium, however, is not considered a reactive electrophile. Nitration of the aromatic ring of aldoxime and/or ketoxime extractants in the presence of NC ⁺ can be due to polarizability of NC ⁺ by the aromatic p-orbital electrons of the oximes. This requires bending of the linear NC ⁺ molecule and an additional shift of electrons in an N-0 bond to the more electronegative oxygen, thus facilitating the reaction of the aromatic p-electrons with the orbital of the NC ⁺ nitrogen. The bending of the NC ⁺ ion consumes a substantial amount of energy (i.e., about 218 kJ/mol to about 587 kJ/mol). Without being bound by any particular theory, in a solvent extraction process, this series of events can occur at the organic diluent/aqueous interface. If a sacrificial compound is present, nitration of the at least one deactivated compound (i.e., the at least one extractant) by NCh⁺ would be in competition with the sacrificial compound. Under these circumstances, the nitronium species has to exist long enough and in concentrations high enough for a substantial amount of nitration of the oxime extractants to occur before there is a significant effect on the metal solvent extraction system.

[0043] Nitronium is expected to react much faster with reducing agents, such as ferrous ions, than at the organic interface with aromatic species, particularly if the concentration and availability of the reducing reagent in the aqueous is relatively high. The redox potential of NC ⁺ is 1.56 V versus the standard hydrogen electrode (SHE), which would result in spontaneous reaction of N02⁺ with most of the reduced species in the solution of a solvent exchange system. Generally, measurement of oxidation reduction potential (ORP) in mining solutions provides a good indication of the presence of oxidizing and reducing agents, and is dominated by the ferric standard electron potential for metal heap leach systems. Without being bound by any particular theory, for NCh⁺ to be present in the leaching solution, it is expected that the ORP would be very high and in a range where reducing agents have been consumed. In terms of aNemst potential, the concentration of oxidation species in the denominator must be much greater than the reduction species in the numerator;

[0044] In the case of aggressive nitration of an oxime extractant with a low ORP in the aqueous system, an alternate nitration mechanism is unlikely as addition of a reducing agent, such as sulfamic acid, to the aqueous solution would not be expected to appreciably affect the nitration potential. Of particular interest are metal nitrate species used as catalysts for Electrophilic Aromatic Substitution in organic synthesis. Metal nitrates have been used extensively for nitration of aromatic compounds under mild conditions. Nitration in copper heap leach operations containing nitrates is relatively low as long as the ORP is low, so the metal nitrates of concern are expected to be those not typically found in PLS. [0045] In a smelter flue dust leach solution, metals of interest, which are known to be strong nitration agents include, but are not limited to, bismuth, cadmium, chromium, nickel, antimony, and zinc. Of the other metals, bismuth is one of the most commonly used metal nitrates in synthetic chemistry and it functions under a wide spectrum of conditions.

However, nitration of extractants can also be the result of a combination of metal nitrate species. Using bismuth as a model metal nitration agent, the following chemical equation represents nitration of a substituted phenol with a metal nitrate, M(NCb)3:

[0046] Due to the relatively low reduction potential of acids, metal nitrates are typically stable in acid. Metal nitrates facilitate nitration of aromatic phenols by displacing a nitrate moiety. This is possible due to the oxophilicity of bismuth, or the ease with which it makes oxide bonds. The progressive reactions of bismuth nitrate with a phenol result in the production of bismuth subnitrate, [Bΐ6q_c(OH)8-_c(Nq3)io-_c]. The stoichiometry of these reactions in synthetic chemistry typically results in more than one nitration per bismuth nitrate.

[0047] Metal nitrates are not merely a product of the metal ion in a solution containing nitrate ions, that is, they are not salts. Metal nitrates have a polar covalent structure where an oxophilic metal is bonded through an oxygen atom to a nitro moiety. In the case of metals originating from the flue dust of a smelter, it is possible that the dissolved metals are in the presence of sulfuric acid containing some amount of nitric acid. Nitric acid formed in metal (e.g., copper) smelting can result from oxidation of dissolved nitrogen from the air that is hydrolyzed similar to how sulfur is converted to sulfuric acid. The following chemical equation shows the reaction of bismuth with nitric acid and is representative of the formation of other metal nitrates. In the case of bismuth nitrate, the reaction is instantaneous at 65°C.

[0048] Nitration of phenols can occur under mild reaction conditions such as ambient temperature (about 25 °C) and without the presence of a strong acid. Additionally, both sacrificial compounds (e.g., activated aromatic species) and deactivated aromatic compounds can be nitrated. The kinetics for the nitration of sacrificial aromatic compounds can be very fast with the formation of high yields of the nitration product within minutes. Once a metal nitrate is converted to a metal (hydr)oxide by reaction with the aromatic reagent, the active nitration agent can be considered deactivated.

Methods of Measuring Nitration

[0049] Analysis of nitrated species by Gas Chromatography with a Thermoionic Specific Detector (GC-TSD) can be performed due to the sensitivity of the TSD detector for nitrogen atoms. By controlling the temperature ramp of the GC-TSD, it is possible to separate identifying peaks of, for example, nitrated nonylphenol, nitrated aldoxime and the nitrated ketoxime. These compounds can be a mixture of a number of isomeric compounds due to the branching of the alkyl substitution. The nitrated nonylphenol can be completely resolved from the nitrated oximes. For the nitrated oximes, there are outlier peaks that can be used to determine relative ratios of the ketoxime and aldoxime. The relative ratio of outlier peaks can be 3.453 times the area percent for the aldoxime peak versus the ketoxime peak at the same oxime ratio in solution. This can be calculated by comparing data from solutions containing the nitro-aldoxime in solution with nitrated nonylphenol, nitro-ketoxime in solution with nitrated nonylphenol, and a mixture of nitro-aldoxime and nitro-ketoxime in solution with nitrated nonylphenol. The nitrated species may be synthesized and purified for use as standards in these types of analyses.

[0050] Nitration of the aldoxime versus ketoxime can be calculated as a ratio of the nitrated species from the GC-TSD analysis as a function of the relative ratio of aldoxime to ketoxime in the organic solution. A sample from the highest level of hydrolytic degradation can be analyzed. The ratio of aldoxime to ketoxime for the plant sample can be approximately 1.75 to 28.28 % v/v respectively. The relative ratio of the outlier peaks should be 0.212 if the nitration occurs at equal rates for both the aldoxime and ketoxime. However, the relative ratio of the outlier peaks was determined to be 0.649. The area of the nitro-aldoxime outlier peak was 1.54 times the size of the nitro-ketoxime outlier peak where the concentration of the aldoxime reagent was about -1/16 the concentration of the ketoxime peak. Without being bound to any particular theory, this suggests the nitration rate for the aldoxime reagent at this time was ~10 times the nitration rate of the ketoxime.

[0051] According to embodiments, it can be helpful to perform a nitration aggressiveness quick test to evaluate in a qualitative way the aggressiveness of aqueous solutions to nitrate an extractant. According to one or more embodiments, A Nonylphenol solution (1% v/v) in an amount of 0.336 mL can be added to 240 mL of aqueous copper leach solution in a 250 mL sealable bottle. The mixture can be agitated using a magnetic stirrer at approximately 1100 RPM for at least four (4) hours to allow for a sufficient reaction time. The mixture can then be filtered through Whatman 1 PS paper. A 2 pL sample can be taken from the filter paper using a micropipette. The sample then can be eluted using thin layer chromatography (TLC). The eluent is a mixture of toluene: ethanol 10:90 as a v/v solution. The comparison of the stains under a UV lamp versus 1%, 0.1%, and 0.01% nitrated nonylphenol stains can be used to provide a qualitative measure of nitration. This nitration aggressiveness quick test can quickly identify the behavior of different leach solutions at a mining operation. It can be used to identify the exact piles/mineral that cause nitration enabling the plant to take precautionary measures.

Addition of a Sacrificial Compound

[0052] According to embodiments, described herein are methods of reducing nitration of an extractant in a solvent extraction system including adding a sacrificial compound to a leaching solution of the solvent extraction system, wherein the sacrificial compound has preferential nitration to nitration of the extractant. In embodiments, the sacrificial compound can be added to the reagent in an amount of about 0.0001 M to about 0.5 M, or about 0.001 M to about 0.25 M to reduce or eliminate the nitration rate of the extractant. The sacrificial compound can be added to a leaching solution, such as a pregnant leaching solution, to the reagent containing the metal extractant, or a combination thereof.

[0053] According to embodiments, the extractant can be a deactivated compound such as a deactivated oxime. The deactivated oxime can be any oxime comprising a deactivating group as described above. According to embodiments, the deactivated compound is a ketoxime, such as 5-nonyl-2-hydroxyacetophenone oxime, an aldoxime, such as 5- nonylsalicylaldoxime, or a combination thereof. According to embodiments, the sacrificial compound can be an activated aromatic species or aldoxime. The sacrificial compound comprises at least one activating group as described above, such as nonylphenol. [0054] Analysis of the organic solution (i.e., from the solvent extraction system) containing the extractant can be performed to determine the amount of residual sacrificial compounds and the concentration of nitrated extractant (e.g., nitrated oxime). Oxime degradation can be an acid catalyzed hydrolysis of the oxime functionality, which is a ubiquitous degradation mechanism for oximes used in metal (e.g., copper) solvent extraction as shown in the following chemical equation.

[0055] Once the oxime has hydrolyzed, it is no longer able to extract metal (e.g., copper), yet remains in the organic phase which results in an increase in viscosity and an agent competing for the aqueous/organic interface.

Exposure of a Leach Solution to a Gas

[0056] According to embodiments, described herein are methods of reducing nitration of an extractant in a solvent extraction system including introducing a gas into an aqueous leaching solution supplied to the solvent extraction system, wherein the aqueous leaching solution contains an amount of at least one N_xO_y compound, and wherein the gas reduces the amount of the at least one N_xO_y compound within the aqueous leaching solution. According to embodiments, the gas comprises at least one of air, oxygen, carbon dioxide, nitrogen or argon. The aqueous leaching solution can contain sulfuric acid.

[0057] The at least one N_xO_y compound can be selected from at least one of NO, NO2, N02⁺, N2O, HN02, HN03, N2O5 or NO3 . The aqueous leaching solution leaches at least one metal from an ore. The at least one metal comprises at least one of copper, bismuth, cadmium, chromium, nickel, antimony, zinc, iron, titanium or zirconium. The aqueous leaching solution can be a pregnant leaching solution comprising the at least one metal.

[0058] The gas can be introduced into the aqueous leaching solution by various methods including, but not limited to, aerating the gas into the aqueous leaching solution, sparging the gas into the aqueous leaching solution or diffusing the gas into the aqueous leaching solution. The gas can be introduced into the aqueous leaching solution at a flow rate of about 3 mL/min to about 9 mL/min, or about 4 mL/min to about 8 mL/min, or about 5 mL/min to about 7 mL/min, or about 6 mL/min. Without being bound by any particularly theory, it is believed the gas reacts with the at least one N_xO_y compound to reduce concentration of the at least one N_xO_y compound in the aqueous leaching solution. According to embodiments, the aqueous leaching solution can be a pregnant leaching solution containing less than about 0.001 M of the at least one N_xO_y compound.

[0059] Any of the above methods of measuring nitration can be used to evaluate aqueous leach solutions following their exposure to the gas. For example, using the nitration aggressiveness quick test described above, when a gas, such as air, is introduced into the leaching solution one can visibly see the change in color over a period of time. A sample of a leaching solution having a high nitration aggressiveness is typically dark in color and over time, upon exposure to gas (e.g., air or carbon dioxide) becomes visibly lighter in color.

When the nitration aggressiveness quick test is performed again it may be determined that the sample in the leach solution no longer has a nitration potential.

[0060] Applying the above methods to a mining operation involving solvent extraction, in operations where it is determined that the leach solution has a high nitration aggressiveness, air can be added to the leach solution prior to its entry into the solvent extraction system. As discussed above, air can be added to the leach solution by any suitable method known to those of ordinary skill in the art including, but not limited to aeration, sparging, bubbling and/or diffusion. According to embodiments, the air can be added to the pools of leach solution at the plant.

EXAMPLES

[0061] The following examples illustrate the effect of leaching aids according to various example aspects of the disclosure. While the examples described below used copper containing ore, it is to be understood that the examples are illustrative of any metal- containing ore body.

Example 1 Reducing Nitration of an Oxime Reagent in a Copper Leach Solution

[0062] Method for Measuring Nitration: Nonylphenol solution (1% v/v) in an amount of 0.336 mL was added to 240 mL of aqueous copper leach solution in a 250 mL sealable bottle. The mixture was agitated using a magnetic stirrer at approximately 1100 RPM for four (4) hours to allow for a sufficient reaction time. The mixture was then filtered through Whatman 1 PS paper. A 2 pL sample was taken from the filter paper using a micropipette. The sample was then eluted using thin layer chromatography (TLC). The eluent was a mixture of toluene: ethanol 10:90 as a v/v solution. The comparison of the stains under a UV lamp versus 1%, 0.1%, and 0.01% nitrated nonylphenol stains was used to provide a qualitative measure of nitration.

[0063] Copper leach solutions were tested using the Method for Measuring Nitration. In samples where the nitration potential was high, there was strong evidence of nitration. Qualitatively, between 10% and 80% of the nonylphenol was nitrated. Samples identified as having a high nitration potential were exposed to air (i.e., left in unopened containers to allow diffusion of the gas) for two days. These samples were tested again using the Method for Measuring Nitration and all of the high nitration potential samples exposed to air had a nitration of less than 10%. In contrast, samples having a high nitration potential that remained in a sealed bottle (i.e., without exposure to air) demonstrated no loss of nitration capability.

[0064] Bubbling (i.e., aeration/sparging) air and CC into samples having a high potential for nitration resulted in a dramatic reduction or elimination of nitration capability. For the aeration, approximately 0.6 L/min of air was passed through 250 mL of solution for 2 minutes, 16 minutes and 1 hour. After 2 minutes the nitration was approximately 1%. At 16 minutes and 1 hour the nitration was not evident. The experiments were repeated with CO2 and provided the same results. Slow addition of H2O2 without the gas sparging did not reduce nitration in the samples. In all cases of gas sparging, the color of the solution became very apparently lighter.

Example 2 Evaluating Nitration of an Extractant in a Copper Solvent Extraction System

[0065] Methods of Evaluating Plant Organic and Aqueous Solutions from a Solvent Extraction System - Samples of plant organic and aqueous solutions from a solvent extraction system were evaluated. Nonylphenol, 2-hydroxy-5-nonyl acetophenone oxime and 5-nonylsalicylaldoxime standards were obtained from the BASF global mining technical service laboratory in Tucson, Arizona. Concentrated sulfuric acid and reagent grade sodium nitrate were obtained from Sigma- Aldrich Company. Shellsol D70 diluent was obtained from Shell Chemicals. [0066] Organic samples were prepared for analysis by having diluent removed using BASF technical service procedures. The oxime samples were further derivatized with an organosilyl chloride agent in order to mitigate degradation in the injection port.

[0067] The organic samples were analyzed using Gas Chromatography with Flame Ionization Detection (GC-FID) and Thermoionic Specific Detector (TSD). Standards and samples were analyzed using an Agilent 7890 GC-FID with an Agilent DB-5 column (30m x 0.32 mm dia. X 0.25 pm film). GC conditions were as follows: Ramp from 100 °C to 300 °C at a rate of 10 °C/min, Injection port and FID Temp 300 °C, hydrogen flow at 40 mL/min, air flow at 400 mL/min, split ratio of 50: 1, column pressure of 15 psi, and an injection volume of 0.1 pL.

[0068] Inductively Coupled Plasma - Atomic Emission Spectroscopy (ICP-AES) analysis was performed by an external laboratory. Each element concentration was obtained using an individual standard.

[0069] Evaluation of Nitration of an Extractant in a Copper Solvent Extraction System

- A copper solvent extraction plant began experiencing a dramatic increase in nitration of its ketoxime extractant. The ketoximes extractant was 2-hydroxy-5-nonyl acetophenone oxime, which is known to be resistant to nitration by nitronium. A sacrificial compound, nonylphenol, was added to the reagent containing the ketoxime. Nonylphenol is an organic compound that is more easily nitrated than the ketoxime. Nitration of the sacrificial compound helps to reduce the amount of ketoxime extractant consumed.

[0070] Samples of all the aqueous streams at the plant revealed that the overall ORP at the plant was very low. In all cases, the concentration of ferrous ions was too high for nitronium ions to exist in a concentration high enough to explain the increased rate of ketoxime extractant nitration. A chemical analysis of selected aqueous streams by inductively coupled plasma spectroscopy (ICP), indicated the presence of elements in concentrations more consistent with smelter electrolytes, bolded in Table 1. It was determined that a high grade PLS stream from the leaching of a smelter flue dust was being added to the bulk plant PLS. The composition of the bulk PLS and the high grade PLS is illustrated in Table 1. Table 1 - Selected ICP analysis of PLS streams

[0071] High levels of arsenic, bismuth, cadmium, antimony and tin are not typical of copper heap or run of mine (ROM) systems. In this case, the high grade PLS is a relatively small stream from the leaching of smelter flue dust, presumably with acid generated at the smelter. The resulting PLS was shipped to the plant site and added to the top of the heaps. The high grade PLS would then mix with the other PLS streams at the plant to become the bulk PLS feed into the solvent extraction system.

[0072] To determine if the source of the aggressive nitration was due to the high grade PLS, the aqueous solution and solids from the settling of the high grade PLS were contacted with an organic solution containing nonylphenol. Nonylphenol is an“activated” aromatic compound while the ketoxime extractant is a“deactivated” aromatic compound. The relative nitration rate was determined by reacting a more easily nitrated nonylphenol, which is the sacrificial compound in the reagent composition containing the ketoxime extractant, with the nitration agent present in the aqueous solution.

[0073] Five continuously stirring experiments were conducted to determine nitration of the nonylphenol in solution. In the first three reactions, HG1, HG2 and HG3, sodium nitrate was added to the samples to determine if the metal species required the nitrate in solution to either promote nitration or to generate the nitration species. The solids that settled from the high grade PLS were isolated and added to HG2 and HG4 to determine if the nitration species was bound to the solid surfaces. For experiments HG1, HG2 and HG3, a recycle of the organic solution was used to determine if the nitrating power of the aqueous was spent, and if the addition of more sodium nitrate could regenerate the nitration agent. All reactions were allowed to react for eleven days; however, for the recycle experiments, the organic was exchanged for a fresh organic solution and additional sodium nitrate was added to the aqueous. The conditions for each reaction are detailed in Table 2.

Table 2 - Details of experiments for the nitration of nonylphenol

using high grade aqueous stream

Initial Phase Recycle Phase

HG HG Sodium Sodium

solution solids Nitrate Nonylphenol Diluent Nitrate Nonylphenol Diluent Solution (mL) (g) (g) (g) (mL) (g) (g) (mL)

HG1 500 0 0.343 845 200 343 845 200~

HG2 500 1 0.343 8.8 200 3.43 8.8 200

HG3 500 0 0.343 8.8 200 10 8.8 200

HG4 500 1 0 8.8 200 N/A

HG5 500 0 0 8.8 200 N/A

[0074] In all cases, the high grade PLS stream resulted in nitration of nonylphenol. The addition of sodium nitrate dramatically increased the amount of nitration. Because the plant had an abundance of nitrate in solution, it was feared that the nitrating agent could be regenerated in-situ; however, the addition of more nitrate in HG1, HG2 and HG3 to the recycle solution did not result in additional nitration. If sodium nitrate was not added to the solution, the nitration reached a maximum value within one day. The stoichiometry of nitrate added in the initial phase to the nonylphenol was 1: 10. By day five, 40% of the nonylphenol was nitrated as a function of the nitrate quantity. For the recycle reactions, the stoichiometry of the nitrate added to nonylphenol ranged from about 1 : 1 to about 3: 1; however, there was only an additional 0.33%-l% consumption of nonylphenol as a function of the nitrate quantity. Therefore, the nitrating agent(s) have a base nitrating capacity, with additional nitration possible with the presence of nitrate in solution, up to a maximum of approximately 0.004 M reactivity with nonylphenol. Considering that the organic is in a dynamic system where it is contacted continuously with fresh PLS, this can have a dramatic effect.

Example 3 - Evaluating Nitration of Pregnant Leaching Solution from a Copper Mine

[0075] Evaluation of the raw samples - Samples of a pregnant leaching solution (PLS) were received from a copper mine in Chile. The mine was experiencing nitration of its PLS and the samples were evaluated to determine and isolate the component responsible for nitration.

[0076] Samples of the PLS were analyzed using ICP and the results are shown in Table 3.

Table 3 - ICP Results of PLS Samples from the Copper Mine

[0077] The PLS had a redox potential (Eh) of 396 mV and contained 5.935 g/L of nitrate. Copper (Cu), iron (Fe T), iron II (Fe (II)) and iron III (Fe (III)) also were all present in the samples at the concentrations shown in Table 3. The PLS had a pH of 1.90.

[0078] The copper mine previously experienced nitration of its PLS as a result of contamination from the PLS of a nearby smelter operation. The smelter’s PLS is known to contain large amounts of bismuth (Bi). However, the ICP results confirmed that the PLS did not contain significant amounts of bismuth (Bi) (i.e., <3 ppm), which ruled out the presence of the smelter’s PLS. The cause of the nitration was, therefore, a result of something else.

[0079] Isolating NCL from the PLS Samples - To isolate NOx from the copper mine’s PLS samples, nitrogen was bubbled through the PLS and the off gas was captured in a cold finger at -189 °C. After 2 hours, a blue color began to appear in the cold finger. The blue was attributable to the formation of dinitrogen trioxide (N2O3) due to the condensation of NO and NO2 gas. After 4 hours the cold finger was removed. It warmed up and the blue color changed to a brown gas, which is attributable to NO2. The gas was analyzed using Fourier Transform Infrared Spectroscopy (FT-IR), which confirmed that the brown gas was NO2. The FT-IR data indicated that air could force the off-gassing of nitrogen oxide compounds.

[0080] Static Experiments - A Nitration Quick Test was performed on several samples of the PLS from the copper mine. A PLS sample of 200 ml - 500 ml was contacted in a closed bottle (250 ml - 1,000 ml) with an organic solution of 2 ml - 5 ml of nonylphenol (NP) in a kerosene diluent at a concentration of 5 w/v% (Aqueous Organic = 100). The solutions were stirred using a magnetic stirrer for a period of time (h) at 900-1100 rpm. After stirring, the organic was removed and filtered through a Whatman IPS phase separation filter paper. A sample aliquot was then submitted for analysis by FT-IR and HPLC for the concentration (w/v%) of nitrated nonylphenol (NNP). The results are shown in Table 4. Table 4 - Results of Static Nitration Experiment

[0081] Referring to Table 4, samples Blank A and Blank B were as received PLS from the copper mine. The Nitration Quick Test was performed on each of Blank A and Blank B using 500 ml samples of PLS with 5 ml of nonylphenol in a kerosene diluent added to each PLS sample at a concentration of 5 w/v%. Sample Blank A with the NP was mixed for 24 h and sample Blank B with the NP was mixed for 28 h. HPLC and FTIR measurements were subsequently performed on the mixed samples to determine the concentration of nitrated nonylphenonl. For Blank A, HPLC reported a concentration of 0.41 w/v% NNP and FTIR reported a concentration of 0.44 w/v% NNP. For Blank B, HPLC reported a concentration of 0.36 w/v% NNP and FTIR reported a concentration of 0.39 w/v% NNP. The HPLC and FTIR results for the 0.5 L samples measured in Tests 1-4 were compared with the results for Blank A and the HPLC and FTIR results for the 0.5 L samples measured in tests 5, 6 and 8 were compared with the results for Blank B. For each of tests 1-6 and 8, air was sparged through the sample at varying flow rates and times. For example, for Test 1, air was sparged through a 0.5 L sample of the PLS at a flow rate of 0.5 L/min for 2 min with a resulting volume ratio of air to PLS (Vair/VpLs) of 2. The Nitration Quick Test was then performed on the sample with a mixing time of 120 h. The superficial gas velocity of the air in Test 1 was 0.30 cm/s. The mixed sample for Test 1 was then measured using HPLC and FTIR. For Test 1, the air sparged PLS sample with NP added had a NNP concentration of 0.32 w/v% as measured by HPLC and a 0.37 w/v% as measured by FTIR. The percent difference between the HPLC measurement for Test 1 as compared to the HPLC measurement for Blank A is shown in the column entitled % Reduction. The results for Test 1 show that sparging air through the PLS was able to reduce the amount of nitration of the nonylphenol in the PLS sample. The experiments were repeated for tests 2-6 and 8 at varying conditions. As shown in Table 4, an air flow rate of 0.5 L/min was more effective at reducing nitration than an air flow rate of 0.1 L/min. Additionally, longer air sparging times also resulted in less nitration with the samples in Tests 5 and 6 demonstrating no nitration of the nonylphenol.

[0082] Dynamic Experiments: Stirred Vessel - In this experiment, a flotation cell was constructed using a gas (air) piped into the bottom of a 220 ml glass container and a Rushton Turbine (RT) was used to shear gas bubbles of PLS sample within the glass container. The PLS also entered the glass container through the bottom pipe at a flow rate of about 17 ml/min. The air pipe teed into the PLS pipe and combined with the PLS prior to entering the glass container to form an aerated PLS solution. The air was at a flow rate of 500 ml/min. Aerated solution that overflowed from the container was captured in a graduated cylinder for sampling. The results of this dynamic experiment are shown in Table 5.

Table 5 - Results of Dynamic Nitration Experiment in a Stirred Vessel

[0083] The data in Table 5 show that the aeration method used in these dynamic experiments successfully reduced the nitration of the nonylphenol as indicated by the % Reduction in nitration (i.e., the percent difference between the Blank and the Test HPLC and FTIR measurements) as compared to the Blank. The superficial gas velocity reported in the last column, was relatively low. There was a 75-100 % Reduction in nitrated nonylphenol in the test samples.

[0084] Dynamic Experiments: Column Testing - Air was sparged into the bottom of a column at a flow rate of 135-270 ml/min while a sample of PLS from the copper mine was fed into the top of the column at a flow rate of 27-230 ml/min. The aerated PLS overflowed into a hydraulic leg (e.g., a flexible plastic tube) that could be adjusted to the height of the liquid in the column. The overflow was collected in a graduated cylinder and used as a test sample. The maximum gas velocity was 0.5 cm/s; when increased to 0.75 cm/s froth began to overflow from the column. The height of the liquid in the column was about lOx the height of the liquid in the stirred vessel in dynamic experiment and about 3.5x height of the liquid in the cylinder in the static experiments. The results are shown in Table 6. Table 6 - Results of Dynamic Nitration Experiment in a Column

[0085] With reference to Table 6, the HPLC and FTIR results for Tests 1-3 were compared to Blank A, the results for Tests 4-7 were compared to Blank B and the results for Tests 9 and 10 were compared to Blank C. The data in Table 6 show that the cross-flow aeration method used in these dynamic experiments successfully reduced the nitration of the nonylphenol as indicated by the % Reduction in nitration (i.e., percent difference) as compared to the corresponding Blank A, B or C.

[0086] The above experiments showed that contacting the PLS with air resulted in a 75- 100% Reduction in Nitrated Nonylphenol:

Static test (183mm): Vgas/Vpls = 15-25; v _as = 0.3 cm/s

Dynamic test -Stirred vessel (63mm): Vgas/Vpls = 15-30; v _as = 0.25 cm/s

Dynamic test - Column: (648mm): Vgas/Vpls = 6-10 ; v _as = 0.5 cm/s

[0087] Increasing the hydraulic height of the PLS in the vessel reduced the amount of air required (Vg/Vpls). The Nitration Quick Test using FT-IR and HPLC showed consistent results and suggest good repeatability. Reduction in PLS sample nitrating ability was observed over time, especially after mixing all 2L samples into 1 large 25L container.

[0088] Identifying the Nitration Mechanism - Based on the results of the NCR nitration study where nitrogen oxide was isolated by purging gas through the PLS, and the results of the static and dynamic studies where purging gas through the solution significantly or completely reduced the nitration effect, the nitration mechanisms within the PLS could be determined. The following nitration mechanisms were identified: Low ORP Radical Mechanism

[0089] The“High ORP” mechanism requires the existence of nitronium, which cannot be purged by air. If the nitronium mechanism was the primary mechanism, there would not be a reduction in nitration with purging. Without being bound by any particular theory, the fact that purging air works to reduce the nitrating capability of the solution infers that the“Low ORP” mechanism was present to cause this type of nitration.

[0090] The preceding description sets forth numerous specific details such as examples of specific systems, components, methods, and so forth, in order to provide a good understanding of several embodiments of the present invention. It will be apparent to one skilled in the art, however, that at least some embodiments of the present invention may be practiced without these specific details. In other instances, well-known components or methods are not described in detail or are presented in simple block diagram format in order to avoid unnecessarily obscuring the present invention. Thus, the specific details set forth are merely exemplary. Particular implementations may vary from these exemplary details and still be contemplated to be within the scope of the present invention.

[0091] Although the operations of the methods herein are shown and described in a particular order, the order of the operations of each method may be altered so that certain operations may be performed in an inverse order or so that certain operation may be performed, at least in part, concurrently with other operations. In another embodiment, instructions or sub operations of distinct operations may be in an intermittent and/or alternating manner.

[0092] It is to be understood that the above description is intended to be illustrative, and not restrictive. Many other embodiments will be apparent to those of skill in the art upon reading and understanding the above description. The scope of the invention should, therefore, be determined with reference to the appended claims, along with the full scope of equivalents to which such claims are entitled.

Claims

IN THE CLAIMS

1. A method of reducing nitration of an extractant in a solvent extraction system, comprising:

adding at least one sacrificial compound to a leaching solution of the solvent extraction system, wherein the sacrificial compound has preferential nitration to nitration of the extractant.

2. The method of claim 1, wherein the extractant comprises at least one deactivated compound.

3. The method of claim 2, wherein the at least one deactivated compound comprises an oxime comprising at least one deactivating group, or

wherein the at least one deactivated compound comprises (a) a ketoxime, an aldoxime, or a combination thereof and (b) at least one of a halo group, a carbonyl group, a sulfonyl group, a cyano group, a nitro group, a haloalkyl group or an ammonium group.

4. The method of claim 2 or 3, wherein the at least one deactivated compound comprises a ketoxime, an aldoxime or a combination thereof, or

wherein the at least one deactivated compound comprises 5 -nony 1-2- hydroxy acetophenone oxime, 5-nonylsalicylaldoxime, or a combination thereof.

5. The method according to any preceding claim wherein the at least one sacrificial compound comprises at least one activating group, or

wherein the at least one sacrificial compound comprises at least one activating group comprising an alkoxy group, an ester group, a hydroxyl group, an amide group, an alkoxide group, an amine group, or a combination thereof.

6. The method according to any preceding claim, wherein the at least one sacrificial compound comprises an activated compound.

7. The method according to any preceding claim, wherein the at least one sacrificial compound comprises nonylphenol.

8. The method according to any preceding claim, wherein the adding comprises adding the sacrificial compound in an amount of about 0.01 M to about 2.0 M, or about 0.015 M, to about 1.5 M, or about 0.018 M to 1.1 M.

9. The method according to any preceding claim, wherein the sacrificial compound is added to a pregnant leaching solution.

10. A method of reducing nitration of an extractant in a solvent extraction system, comprising:

introducing a gas into an aqueous leaching solution supplied to the solvent extraction system, wherein the aqueous leaching solution comprises an amount of at least one N_xO_y compound, and wherein the gas reduces the amount of the at least one N_xO_y compound within the aqueous leaching solution.

11. The method of claim 10, wherein the gas comprises at least one of air, oxygen, carbon dioxide, nitrogen or argon.

12. The method of claim 10 or 11, wherein the aqueous leaching solution comprises sulfuric acid.

13. The method of any one of claims 10 to 12, wherein the at least one N_xO_y compound comprises at least one of NO, NO2, N02⁺, N2O, HNO2, HNO3, N2O5 or NO3 .

14. The method of any one of claims 10 to 13, wherein the aqueous leaching solution leaches at least one metal from an ore.

15. The method of claim 14, wherein the at least one metal comprises at least one of copper, nickel or cobalt.

16. The method of claim 14 or 15, wherein the aqueous leaching solution is a pregnant leaching solution comprising the at least one metal.

17. The method of any one of claims 10 to 16, wherein the introducing comprises at least one of aerating the gas into the aqueous leaching solution, sparging the gas into the aqueous leaching solution or diffusing the gas into the aqueous leaching solution.

18. The method of any one of claims 10 to 17, wherein the introducing comprises introducing the gas at a flow rate of 3 mL/min to about 9 mL/min, or about 4 mL/min to about 8 mL/min, or about 5 mL/min to about 7 mL/min, or about 6 mL/min.

19. The method of any one of claims 10 to 18, wherein the gas reacts with the at least one NxOy compound to reduce concentration of the at least one N_xO_y compound in the aqueous leaching solution.

20. The method of claim 16, wherein the pregnant leaching solution comprises less than about 0.001 M of the at least one N_xO_y compound.

21. A method of reducing nitration of an extractant in a solvent extraction system, comprising:

adding a sacrificial compound to a leaching solution of the solvent extraction system, wherein the sacrificial compound has preferential nitration to nitration of the extractant; and introducing a gas into an aqueous leaching solution supplied to the solvent extraction system, wherein the aqueous leaching solution comprises at least one N_xO_y compound, and wherein the gas reduces a concentration of the at least one N_xO_y compound within the aqueous leaching solution.