LEACHING AIDS AND METHODS OF PREPARATION AND USE THEREOF FIELD [0001] The disclosure relates generally to the field of mining. More particularly, the disclosure relates to compositions and methods of preparation and use thereof to improve efficiency of leaching aids. BACKGROUND [0002] The leaching of primary and secondary sulfide minerals such as chalcopyrite has been well researched by academia and industry. Heap leaching, in particular, is used to extract precious metals, for example, copper, uranium, and other compounds from ore using a series of chemical reactions that assist in the dissolution of specific minerals. The main objective is to increase the rate and total recovery of a target metal from the ore in a typical heap leaching application at ambient temperature. Additives may be added to the leaching solution to help increase wetting and/or dissolution of the ore ultimately releasing more target metal. There is a need for improved leaching compositions to increase recovery of target metals from ore. BRIEF SUMMARY [0003] Described herein according to one or more embodiments are compositions for leaching a metal-containing material. The compositions include at least one lixiviant, at least one leaching aid and at least one oxidant gas. Suitable leaching aids include, but are not limited to, one or more compound of formula (I): (I) R((AO) _n B) _m ((AO) _n H) _p wherein AO are both alkyleneoxy groups, which are independently selected from; ethyleneoxy, 1,2-propyleneoxy, 1,2-butyleneoxy, and styryleneoxy; each n is independently an integer from 0 to 40; m is an integer from 1 to the total number of OH (alcohol) hydrogens in the R group prior to alkoxylation; p is an integer such that the sum of m plus p equals the number of OH (alcohol) hydrogens in the R group prior to alkoxylation; B is H, R is a group selected from formula (II) to (VIII): (II) R ¹ C(CH2O-)3 wherein R ¹ is H, methyl, ethyl, or propyl; (III) C(CH2O-)4; (IV) O:C(CH2O-)2; (V) N(CH2CH2O-)3; (VI) (R ² )xN(CH2CH2O-)y wherein R ² is a C1 - C4 alkyl, y is 1 – 3 and x + y = 3; (VII) -O(CH2)rO- wherein r is 2 to 6; and (VIII) -O(CH(CH3)CH2)O-. In the at least one leaching aid has the following structure: O O H . In various one composition at a concentration of about 1 mg/L to about 2000 mg/L, or any individual value or sub-range within this range. [0004] In one or more embodiments, the oxidant gas contains air, oxygen, ozone, and/or combinations thereof. The oxidant gas may be in the form of bubbles, nanobubbles, entrained gas, and/or combinations thereof. In one or more embodiments, the bubbles have an average diameter of less than about 1,000 micron, or any individual value or sub-range within this range. In various embodiments, the at least one lixiviant contains sulfuric acid, hydrochloric acid, sodium cyanide, ammonia, ammonium carbonate, ammonium sulfate, ammonium chloride, and/or combinations thereof. [0005] According to further embodiments, disclosed herein are methods of recovering metal values from a metal containing material, including contacting the metal containing material with a composition for leaching a metal-containing material as described above; and increasing the concentration of at least one metal from the metal containing material in the composition. In one or more embodiments, the metal containing material contains copper, gold, silver, nickel, zinc, molybdenum, vanadium, uranium, and/or combinations thereof. In various embodiments, the metal containing material contains ore, smelter mattes, flotation concentrate, leaching residue, tailings, and/or combinations thereof. In some embodiments, the metal containing material contains agglomerated ore. According to one or more embodiments, increasing concentration of at least one metal from the metal containing material includes forming a pregnant leach solution and recovering the at least one metal from the pregnant leach solution. In various embodiments, contacting the composition with the metal containing material includes in-situ leaching, heap leaching, dump leaching, agitation, tank leaching, and/or combinations thereof. In some embodiments, recovering the metal from the pregnant leach solution includes a solvent extraction process. In some embodiments, the at least one lixiviant is sulfuric acid. [0006] According to one or more embodiments, the metal containing material contains copper, and the method of recovering metal values from a metal containing material provides a copper recovery from primary sulfide minerals of about 25 wt% to about 45 wt%, or about 30 wt% to about 40 wt%, or any individual value or sub-range within these ranges when performed under standard temperature and pressure conditions. In one or more embodiments, the metal containing material comprises chalcopyrite. [0007] In yet further embodiments, disclosed herein are methods of preparing a composition as described above. The methods can include combining the at least one lixiviant, the at least one leaching aid and the at least one oxidant gas. In some embodiments, the at least one leaching aid is combined with the at least one lixiviant in a pipe, transfer conduit, holding tank, pond, or combinations thereof to form a solution and the solution is combined with the oxidant gas. According to various embodiments, the oxidant gas is introduced into a solution containing the at least one leaching aid and the at least one lixiviant as nanobubbles to form the composition. In one or more embodiments, the oxidant gas is combined with a solution containing the at least one leaching aid and the at least one lixiviant using an apparatus configured to form nanobubbles of the oxidant gas in the solution. In various embodiments, the apparatus includes an elongate housing having a first end and a second end, the elongate housing defining a liquid inlet, a liquid outlet, and an interior cavity configured to receive the solution of lixiviant and leaching aid. The apparatus can further include a gas-permeable member at least partially disposed within the interior cavity of the housing, the gas-permeable member having an open end configured to receive pressurized oxidant gas from a gas source, a closed end, and a porous sidewall extending between the open and closed ends having a mean pore size no greater than 1.0 micron, the gas-permeable member defining an inner surface, an outer surface, and a lumen. In one or more embodiments, the lixiviant includes sulfuric acid, hydrochloric acid, ammonia, ammonium carbonate, ammonium sulfate, sodium cyanide, ammonium chloride, and/or combinations thereof. In some embodiments, the at least one leaching aid is comprised in a raffinate. BRIEF SUMMARY OF THE DRAWINGS [0008] 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. [0009] FIG. 1 depicts the results of a comparison between a composition according to embodiments herein and a control composition when treating a raffinate sample with nanobubbles. [0010] FIG. 2 depicts the results of a comparison between a composition according to embodiments herein and a control composition when treating a raffinate sample with nanobubbles. [0011] FIG. 3 shows a schematic diagram of an embodiment of a system for preparing and using a composition for leaching metal-sulfide-containing materials according to embodiments herein. [0012] FIG. 4 shows a schematic diagram of an embodiment of a system for preparing and using a composition for leaching metal-sulfide-containing materials according to embodiments herein. [0013] FIG. 5 shows a schematic diagram of an embodiment of a system for preparing and using a composition for leaching metal-sulfide-containing materials according to embodiments herein. [0014] FIG. 6 shows a schematic diagram of an embodiment of a system for preparing and using a composition for leaching metal-sulfide-containing materials according to embodiments herein. [0015] FIG.7 shows a schematic diagram of a leach column setup used in Example 4. [0016] FIG. 8 depicts the results of a comparison between a composition according to embodiments herein and a control composition when leaching a metal-sulfide ore. DETAILED DESCRIPTION [0017] Reference will now be made in detail to the example embodiments of this disclosure, which are illustrated in the accompanying drawings. Wherever possible, the same reference numbers will be used throughout the drawings to refer to the same or like parts throughout the several views. Features of the various embodiments described herein may be combined with each other, unless specifically noted otherwise. The details of one or more embodiments of the invention are set forth in the description below. Other features, objects, and advantages of the invention will be apparent from the description and from the claims. [0018] The present disclosure relates generally to the field of mining and more specifically, to leaching a target metal, such as copper, using a composition containing a leaching aid, and at least one oxidant gas containing air, oxygen, ozone, or combinations thereof. In one or more embodiments, the target metal may be leached from one or more of the following sources of metal sulfide-containing material: (1) metal-sulfide ore, (2) ore concentrate, (3) leaching residue, (4) a matte, and/or (5) tailings produced by upstream processing of ore such as magnetic separation or flotation. [0019] The term “matte” as used herein refers to a crude mixture of molten sulfides formed as an intermediate product of the smelting of sulfide ores of metals, especially copper, nickel, and lead. Instead of being smelted directly to metal, copper ores are usually smelted to matte, for example, containing 40–45 percent copper along with iron and sulfur, which is then treated by converting in a Bessemer-type converter. Air is blown into the molten matte, oxidizing the sulfur to sulfur dioxide and the iron to oxide, which combines with a silica flux to form slag, leaving the copper in the metallic state. Smelting of nickel sulfide ores yields a matte in which nickel and copper make up about 15 percent, iron about 50 percent, and sulfur the remainder; the iron is removed in a converting furnace, and the sulfides of copper and nickel are separated before being reduced to the metals. Smelting of lead sulfide ores produces a liquid layer of copper sulfide matte that can be decanted, along with slag and speiss, from the lead bullion. [0020] Base metal containing ores are typically classified into two categories—oxidic and sulfidic ores. Oxidic ores are generally found near the surface as they are often the oxidation products of the typically deeper primary and secondary sulfidic ores or have formed in areas where metals have leached from the surface in aqueous solution, becoming trapped and concentrated in the host formation. Sulfidic ore deposits typically arise in either igneous rock, formed during the original cooling of the rock from the mantle, or through hydrothermal transformation of metal rich oxidic deposits formed from surface leaching. Sulfidic ores are generally sub-divided into two groups, primary and secondary. Primary sulfidic ores are generally in the initial state whereas secondary sulfidic ores have undergone some subsequent weathering and oxidation processes. [0021] Depending on the chemical nature of metal bearing ore, mines typically process the ore to extract and concentrate the target valuable metal(s) through either a selective flotation or hydrometallurgical process. Selective flotation, most commonly used for sulfidic ores, requires the ore to be finely ground to liberate individual grains of metal containing mineral from the waste (gangue) material. The ground ore is processed as an aqueous slurry, with the addition of surface-active chemicals which facilitate the flotation and separation of the metal containing sulfide minerals from the gangue. The recovered metal sulfide minerals can then be further processed to recover the metal(s), often by pyrometallurgical processing. [0022] In hydrometallurgical processing, the ore is treated with a lixiviant which dissolves the target valuable metal(s) into aqueous solution, leaving the waste (gangue) material in the solid phase. The aqueous solution containing the solubilized metal(s) is collected and separated from the gangue material and the metal(s) can then be recovered in a more concentrated form by one or more processes such as precipitation and/or solvent extraction. The lixiviant used can often be an acid, base or specific ions/salts that enhance the dissolution of the metal(s) from the ore. [0023] The leaching process can be a heap, dump, percolation, or agitation (tank) leaching process. In all cases, the required properties of the lixiviant are the same: 1) can dissolve the ore minerals rapidly enough to make commercial extraction possible and are chemical inert toward gangue minerals because in situations where gangue mineral(s) is(are) also attacked, an excessive amount of the lixiviant is consumed and the leachate liquor fouled with impurities to an undesirable extent; 2) are cheap and readily obtainable in large quantities; and 3) can be regenerated in the subsequent processes following leaching. The underpinning characteristic of leaching is that regardless of the lixiviant used, it interacts with the ore particles in a way that allows for transfer of the desired metal from the ore into the aqueous solution which is collected and separated from the waste. For metals with basic oxides, a common lixiviant is sulfuric acid (H2SO4) because it provides efficient and cost-effective liberation of the metal from the ore. [0024] Heap leaching is a common method of leaching in hydrometallurgical processes where the metal-containing ore is piled into a heap and wetted, for example, with a solution of dilute acid. For the large heaps typically used in mining operations, significant time is required for the solution to percolate down through the heap before it can be collected and supplied to subsequent metal concentrating operations. Although this type of leaching process can require several days to months to extract most of the metal from the ore in the heap, this method has economic advantages as the ore only requires minimal crushing/processing prior to placing the ore into the heap and the leaching process produces only minimal quantities of fluid tailings for disposal. By contrast, selective flotation requires the ore to be ground down to a relatively small particle size, which consumes large amounts of energy, and the waste (gangue) material is in liquid (slurry) form, requiring further processing before disposal. Consequently, the heap leaching method is suitable for recovering metal from low grade ores, where the ratio of metal values to the waste material is low, and more complex processing methods are not economically viable. [0025] However, issues can arise when operating heap leaching, for example when the fine particles in the heap accumulate between larger pieces of ore and decrease the percolation rate of the leaching solution or block the flow altogether in specific regions of the heaped ore. This results in 1) channeling of the leachate (i.e., where the solution follows the path of least resistance through the heap) bypassing some areas and generally inhibiting diffusion of the leaching solution to the surface of the ore; 2) less contact of the leachate with the packed fines; and 3) a lower-than-expected concentration of metal in the resulting pregnant leaching solution (PLS) collected from the heap. These accumulations of fine particles can also lead to pooling of the metal-containing solution and overall, all of these issues can result in a decrease in yield from the ore, as valuable metal remains trapped in the heap. [0026] In the case of copper containing ores, common oxidic ores are cuprite, malachite, and azurite, common primary sulfidic ores are chalcopyrite and bornite, and common secondary sulfidic ores are chalcocite and covellite. Notably, copper sulfide ores such as chalcopyrite are the most abundant naturally occurring copper mineral, estimated to account for about 70% of the copper deposits found in the earth’s crust. [0027] Copper can be extracted from oxidic ore by conventional leaching processes using sulfuric acid as the lixiviant. Historically, most copper sulfidic ores have been concentrated via selective flotation or occasionally tank leach systems utilizing elevated temperatures and pressures, as these ores are difficult to leach with conventional methods at ambient pressures and temperatures. As the grades of available ores decrease, it would be beneficial to the mining and minerals industry if methods were available to enable the efficient extraction of the metal values from these types of minerals and ores using heap leaching and/or other ambient temperature/pressure leaching processes. [0028] Disclosed herein are compositions, methods of preparation and methods of use thereof for leaching metal from ore that can improve the leaching efficiency of the metal. According to various embodiments, described herein are leaching compositions comprising: a leaching aid comprising at least one surface-active wetting compound and, an oxidant. In one or more embodiments, the oxidant is in the form of bubbles, nanobubbles, entrained gas or combinations thereof. The oxidant can be in the form of nanobubbles having an average diameter of less than about 1 µm, or about 1 nm to about 1 µm, or any individual value or sub- range within these ranges. In some embodiments, the oxidant is a gas containing molecular air, oxygen, ozone, or combinations thereof. According to various embodiments, the leaching composition can further include a lixiviant. The lixiviant may be selected from sulfuric acid, hydrochloric acid, sodium cyanide, ammonia, ammonium carbonate, ammonium sulfate, ammonium chloride, or combinations thereof. [0029] Leaching of ore minerals (e.g., metal-sulfide minerals) can be oxygen dependent. For ores that are leachable through oxidation, interaction of the oxidant with the surface of the mineral in the ore can increase the leaching efficiency. Oxidative leaching with Fe ³⁺ (ferric ions) and/or oxygen is more effective at leaching such ores than with an acidic lixiviant alone. Without being bound by any particular theory, it is believed that a large proportion of these leaching reactions are based on oxidation-reduction (redox), which occur when the redox reagent and the aqueous lixiviant component interact with the mineral surface. More particularly, the oxidation can occur directly on the mineral surface, or via the oxidation of a species solvated in the aqueous phase that subsequently oxidizes the mineral surface. The presence of an oxidizing agent, such as hydrogen peroxide, in the composition can improve the rate of recovery of a primary sulfide ore. Oxidation of the mineral ore can be achieved by a chemical oxidant and/or by the presence of oxygen. The oxidation can be direct or through an intermediate oxidant such as Fe ³⁺ . Surface-active wetting components also can improve the kinetic rate of extraction of target metals from ores by increasing the wettability of the ore and material by modifying the surface tension and contact angle of the aqueous lixiviant used in the leaching process. [0030] However, leaching rates of sulfidic ores in conventional leaching compositions such as dilute sulfuric acid tend to be quite slow with low recovery rates observed from predominant target minerals such as chalcopyrite, where only 20-25% of the total available copper may be recovered under normal temperature leaching conditions. This has been shown to be the result of the formation of an iron depleted, copper rich, covellite like layer on the surface of the chalcopyrite which is resistant to chemical oxidation and acts as a passivating film. [0031] The leaching of primary sulfide minerals such as chalcopyrite (CuFeS2) has been well studied and documented in literature. The leaching of copper from sulfide ore bodies occurs naturally, although quite slowly. The reaction kinetics can be improved by reaction with ferric sulfate. These dissolution reactions are as follows: 1. CuFeS2 + 4Fe ³⁺ ^ Cu ²⁺ + 5Fe ²⁺ + 2S ⁰ 2. CuFeS2 + 4Fe ³⁺ + 3O2 + 2H2O ^ Cu ²⁺ + 5Fe ²⁺ + 2H2SO4 [0032] Currently about 75% of leaching of chalcopyrite occurs via Reaction 1. Increasing the availability of oxygen helps more chalcopyrite to leach via Reaction 2, thereby increasing the kinetic rate of copper recovery. Also essential to this leaching process is the regeneration of ferric ion in-situ, which occurs via Reaction 3. 3. 4Fe ²⁺ + 4H ⁺ + O2 → 4Fe ³⁺ + 2H2O [0033] The formation of sulfate is limited by the amount of dissolved oxygen present in the aqueous acidic component. Without being bound by any particular theory, it is theorized that an increased and/or maintained concentration of dissolved oxygen can increase the rate of chalcopyrite dissolution by increasing the rate of sulfate formation in Reaction 2. In addition, the increased oxygen levels can assist in the oxidation of ferrous ions, helping to increase the availability of ferric ions for chalcopyrite dissolution. [0034] Compositions and methods described herein increase the recovery of target metals (e.g. copper) from ores (e.g., primary and/or secondary sulfide ores) through the utilization of an oxidant in combination with a chemical leaching aid. This combination increases the leaching efficiency of the ore at ambient temperature. A further synergistic improvement in the leaching efficiency of the ore minerals can be achieved by introducing bubbles (e.g., nanobubbles) of the oxidant into the leaching solution. In some embodiments, the metal values include copper, and methods as described herein provide a copper recovery from chalcopyrite of about 25 wt% to about 45 wt%, or about 30 wt% to about 40 wt%, or any individual value or sub-range within these ranges, under standard temperature and pressure conditions (e.g., 20-25°C, 1.0 atm). [0035] Compositions according to embodiments herein including a leaching aid and an oxidant (e.g., as nanobubbles) can increase the recovery of metal from primary and/or secondary sulfidic ore. The compositions are suitable for use in heap leaching techniques and traditional flotation processes. In some embodiments, the use of such compositions in heap leaching techniques is preferred because traditional flotation processes can be quite costly due to the requirement to finely grind the ore. In some embodiments, stability of the oxygen (e.g., entrained bubbles, nanobubbles, etc.) in the composition can be improved with the presence of the leaching aid. In some embodiments, use of oxygen in the form of nanobubbles provides the longest life cycle of oxygen in the leaching composition. In some embodiments, the initial dissolved oxidant (e.g., O2) concentration in the aqueous phase of the composition is increased from about 3 mg/L to about 10 mg/L at about (i.e., at ambient conditions: 20°C to about 25°C and 1 atm) to about 35 mg/L to about 45 mg/L at ambient conditions, or any individual value or sub-range within these ranges, through introducing the oxidant (e.g., as nanobubbles) according to embodiments herein and is dependent on the elevation above sea level based on the Ideal Gas Law. In one or more embodiments, the nanobubbles are comprised of air. In other embodiments, the oxidant gas used to form the nanobubbles could be used in combination with SO ₂ , N ₂ , NO, NO ₂ , and/or CO ₂ , or a combination or blend of these gas species. [0036] In one or more embodiments, the nanobubbles may have a mean diameter of less than about 1 micron, less than about 500 nm, less than about 200 nm, or of about 1 nm to about 1 micron, about 10 nm to about 500 nm, about 75 nm to about 200 nm, or any individual mean diameter or sub-range within these ranges. In some embodiments, leaching solutions and/or leaching aids as described herein include nanobubbles that are stable in a liquid carrier for at least one month or for at least three months under ambient pressure and temperature (e.g., 1 atm, 20-25°C). [0037] According to various embodiments, the combination of an oxidant (e.g., in the form of nanobubbles) and a leaching aid in combination yield an improvement in the rate of metal (e.g., copper) recovery. For example, compositions according to embodiments herein can be used for copper leaching, where more than about 90% of the copper minerals are oxidized to improve the rate of recovery. In some embodiments, compositions according to embodiments herein can be used for gold or silver leaching, where the sulfide matrix is oxidized to liberate the target metal. Leaching Compositions [0038] According to various example embodiments, described herein are leaching compositions including leaching aids for improving the rate of recovery and/or the total recovery of metals from ore (e.g., non-agglomerated or agglomerated). The leaching compositions are compatible with a number of mining processes including solvent extraction and electrowinning. [0039] More particularly, according to various example embodiments of the disclosure, the leaching compositions can include a lixiviant and one or more leaching aid having formula (I) as follows: (I) R((AO) _n B) _m ((AO) _n H) _p wherein AO are both alkyleneoxy groups, which are independently selected from; ethyleneoxy (“EO”), 1,2-propyleneoxy, 1,2-butyleneoxy, and styryleneoxy; each n is independently an integer from 0 to 40; m is an integer from 1 to the total number of OH (alcohol) hydrogens in the R group prior to alkoxylation; p is an integer such that the sum of m plus p equals the number of OH (alcohol) hydrogens in the R group prior to alkoxylation; B is H, SO ₃ Y, (CH2)qSO3Y, CH2CHOHCH2SO3Y, or CH2CH(CH3)OSO3Y, wherein q is an integer from 2 to 4 and Y is a cation; R is a group selected from formula (II) to (VIII): (II) R ¹ C(CH2O-)3 wherein R ¹ is H, methyl, ethyl, or propyl; (III) C(CH2O-)4; (IV) O:C(CH2O-)2; (V) N(CH2 CH2O-)3; (VI) (R ² )xN(CH2 CH2O-)y wherein R ² is a C1 - C4 alkyl, y is 1 - 3 and x + y = 3; (VII) -O(CH2)rO- wherein r is 2 to 6; and (VIII) -O(CH(CH3)CH2)O-. [0040] According to various example embodiments, n can be 2 to 30, or 2 to 20, or 2 to 10, or any individual value or sub-range within these ranges, B can be hydrogen (H) and R can have formula (II). For example, the leaching composition can include a leaching aid having a distribution of compounds including the following structure, which leaching aid may be referred to herein as “TMP-7(EO)”: O O O H H . [0041] The process of trimethylolpropane (“TMP”), where the process results in a mixture (i.e., a distribution) of trimethylolpropane compounds having a variety of EO units including: TMP-EO _x,y,z , where x, y and z are independently an integer from 0 to 7, with the proviso that x + y + z = 7. The resulting mixture of compounds includes one of the above TMP-7(EO) structure. [0042] The alkoxylation is preferably catalyzed by strong bases, which are added in the form of an alkali metal alcoholate, alkali metal hydroxide or alkaline earth metal hydroxide, in an amount of about 0.1% to about 1% by weight, or any individual value or sub-range within this range, based on the amount of the alkanol RZiOH. [0043] An acid catalysis of the addition reaction is also possible. In addition to Bronstedt acids, Lewis acids, such as, for example, AlCl3 or BF3 dietherate, BF3, BF3H3PO4, SbCl4 ^2H2O or hydrotalcite are also suitable. Double metal cyanide (DMC) compounds are also suitable as the catalyst. All suitable compounds known to a person of ordinary skill in the art can in principle be used as the DMC compound. [0044] Particularly suitable catalysts for the alkoxylation are double metal cyanide compounds of the general formula (Z): M ¹ a[M ² (CN)b(A)c]d ^h(H2O) ^eL ^kP (Z) where M ¹ is at least one metal ion selected from Zn ²⁺ , Fe ²⁺ , Fe ³⁺ , Co ³⁺ , Ni ²⁺ , Mn ²⁺ , Co ²⁺ , Sn ²⁺ , Pb ²⁺ , Mo ⁴⁺ , Al ³⁺ , V ⁴⁺ , V ⁵⁺ , Sr ²⁺ , W ⁴⁺ , W ⁶⁺ , Cr ²⁺ , Cr ³⁺ , Cd ²⁺ , Hg ²⁺ , Pd ²⁺ , Pt ²⁺ , V ²⁺ , Mg ²⁺ , Ca ²⁺ , Ba ²⁺ , Cu ²⁺ , La ³⁺ , Ce ³⁺ , Eu ³⁺ , Ti ³⁺ , Ti ⁴⁺ , Ag ⁺ , Rh ²⁺ , Rh ³⁺ , Ru ²⁺ and/or Ru ³⁺ ; M ² is at least one metal ion selected from Fe ²⁺ , Fe ³⁺ , Co ²⁺ , Co ³⁺ , Mn ²⁺ , Mn ³⁺ , V ⁴⁺ , V ⁵⁺ , Cr ²⁺ , Cr ³⁺ , Rh ³⁺ , Ru ²⁺ and/or Ir ³⁺ ; A is an anion selected from halide, hydroxide, sulfate, carbonate, cyanide, thiocyanate, isocyanate, cyanate, carboxylate, oxalate, nitrate, nitrosyl, hydrogen sulfate, phosphate, dihydrogen phosphate, hydrogen phosphate and/or bicarbonate; L is a water-miscible ligand selected from alcohols, aldehydes, ketones, ethers, polyethers, esters, polyesters, polycarbonate, ureas, amides, primary, secondary and tertiary amines, ligands comprising pyridine nitrogen, nitriles, sulfides, phosphides, phosphites, phosphanes, phosphonates and/or phosphates; k is a fraction or integer greater than or equal to zero; and P is an organic additive; a, b, c, d, g and n are selected so that the electroneutrality of the compound (I) is ensured, it being possible for c to be 0; e, the number of ligand molecules, is a fraction or integer greater than 0 or is 0; and f and h, independently of one another, are a fraction or integer greater than 0 or are 0. [0045] The organic additive P can include, but is not limited to, polyether, polyester, polycarbonates, polyalkylene glycol sorbitan ester, polyalkylene glycol glycidyl ether, polyacrylamide, poly(acrylamide-co-acrylic acid), polyacrylic acid, poly(acrylamide-co- maleic acid), polyacrylonitrile, polyalkyl acrylates, polyalkyl methacrylates, polyvinyl methyl ether, polyvinyl ethyl ether, polyvinyl acetate, polyvinyl alcohol, poly-N-vinylpyrrolidone, poly(N-vinylpyrrolidone-coacrylic acid), polyvinyl methyl ketone, poly(4-vinylphenol), poly(acrylic acid-co-styrene), oxazoline polymers, polyalkyleneimines, maleic acid and maleic anhydride copolymers, hydroxyethylcellulose, polyacetates, ionic surface-active and interface- active compounds, gallic acid or its salts, esters or amides, carboxylic esters of polyhydric alcohols, glycosides, and/or combinations thereof. [0046] These catalysts may be crystalline or amorphous. Where k is zero, crystalline double metal cyanide compounds are preferred. Where k is greater than zero, crystalline, semicrystalline and substantially amorphous catalysts are preferred. [0047] Preferred embodiment catalysts can be of the formula (A) in which k is greater than zero. The preferred catalyst then comprises at least one double metal cyanide compound, at least one organic ligand and at least one organic additive P. [0048] According to certain example embodiments, k is zero, e is optionally also zero and X is exclusively a carboxylate, preferably formate, acetate and propionate. Such catalysts are described in WO 99/16775, which is incorporated by reference in its entirety. Here, crystalline double metal cyanide catalysts are preferred. Double metal cyanide catalysts as described in WO 00/74845, which is incorporated by reference in its entirety, are crystalline or lamellar and are furthermore preferred. [0049] The preparation of the modified catalysts is affected by combining a metal salt solution with a cyanometallate solution which may optionally comprise both an organic ligand L and an organic additive P. The organic ligand and optionally the organic additive are then added. In a preferred embodiment of the catalyst preparation, an inactive double metal cyanide phase is first prepared and this is then converted into an active double metal cyanide phase by recrystallization, as described in PCT/EP01/01893. [0050] According to other example embodiments of the catalysts, f, e and k are not zero. These are double metal cyanide catalysts which comprise a water-miscible organic ligand (in general in amounts of from 0.5 to 30% by weight) and an organic additive (in general in amounts of from 5 to 80% by weight), as described in WO 98/06312. The catalysts can be prepared either with vigorous stirring (24,000 rpm using a Turrax) or with stirring, as described in US. Pat. No.5,158,922. [0051] Particularly suitable catalysts for the alkoxylation are double metal cyanide compounds which comprise zinc, cobalt or iron or two thereof. For example, Prussian Blue is particularly suitable. [0052] Crystalline DMC compounds are preferably used. In certain embodiments, a crystalline DMC compound of the Zn ₄ Co type, which comprises zinc acetate as a further metal salt component, is used as the catalyst. Such compounds are crystallized with a monoclinic structure and have a lamellar habit. Such compounds are described, for example, in WO 00/74845 or PCT/EP01/01893. [0053] DMC compounds suitable as a catalyst can be prepared in principle by all methods known to the person skilled in the art. For example, the DMC compounds can be prepared by direct precipitation, by the incipient Wetness method or by preparation of a precursor phase and subsequent recrystallization. [0054] The DMC compounds can be used as a powder, paste or suspension or can be shaped to give a molding, introduced into moldings, foams or the like or applied to moldings, foams or the like. [0055] The catalyst concentration used for the alkoxylation, based on the final quantity range, is typically less than about 2000 ppm (i.e. mg of catalyst per kg of product), less than about 1000 ppm, less than about 500 ppm, less than about 100 ppm, less than about 50 ppm, less than about 35 ppm, less than 25 ppm, or any individual value or sub-range within these ranges. [0056] The addition reaction can be carried out at temperatures of about 90 ^C to about 2400 ^C., about 120 ^C to about 1800 ^C., or any individual value or sub-range within these ranges, in a closed vessel. The alkylene oxide or the mixture of different alkylene oxides is added to the mixture of alkanol mixture according to the invention and alkali under the vapor pressure of the alkylene oxide mixture which prevails at the chosen reaction temperature. If desired, the alkylene oxide can be diluted with up to about 30% to 60% of an inert gas. This provides additional safety with regard to prevention of explosive polyaddition of the alkylene oxide. [0057] If an alkylene oxide mixture is used, polyether chains in which the different alkylene oxide building blocks are virtually randomly distributed are formed. Variations in the distribution of the building blocks along the polyether chain are the result of different reaction rates of the components and can also be achieved randomly by continuous feeding of an alkylene oxide mixture of program-controlled composition. If the different alkylene oxides are reacted in succession, polyether chains having a block-like distribution of alkylene oxide building blocks are obtained. [0058] The length of the polyether chains varies randomly within the reaction product about a mean value of the stoichiometric value substantially resulting from the added amount. [0059] Alkoxylate mixtures of the general formula (B) (below) can be obtained by reacting alcohols of the general formula C5H11CH(C3H7)CH2OH with propylene oxide/ethylene oxide in the abovementioned sequence under alkoxylation conditions. Where: R ¹ is at least singly branched C4-22-alkyl or -alkylphenol, R ² is C3-4 –alkyl, R ⁵ is C1-4 –alkyl, R ⁶ is methyl or ethyl, n has a mean value of from 1 to 50, m has a mean value of from 0 to 20, r has a mean value of from 0 to 50, s has a mean value of from 0 to 50, and m being at least 0.5 if R ⁵ is methyl or ethyl or has the value 0. [0060] Suitable alkoxylation conditions are described above. The alkoxylation may be carried out in the presence of basic catalysts, such as KOH, in the absence of a solvent. The alkoxylation can, however, also be carried out with the concomitant use of a solvent. A polymerization of the alkylene oxide is initiated in which a random distribution of homologs inevitably occurs, the mean value of which is specified here with p, n, m and q. [0061] According to various example embodiments of the present disclosure, the leaching solution can include a lixiviant and a mixture of compounds formed by an alkoxylation process of trimethylolpropane with seven equivalents of ethylene oxide TMP-7(EO) as described above. [0062] According to various example embodiments, R3 can be a C10 linear or branched alkyl group and R4, R5 and R6 can be, independently, a C1 to C3 alkyl group. For example, the leaching solution can include a leaching aid having the following structure, which compound may be referred to herein as “MC1000”: . [0063] In accordance with various example embodiments, the leaching solution can include a leaching aid such as an alkyl or alkyl ether sulfate having formula (X) or (XI) as follows: O R ₈ ^O , where s and t are and R8 and R9 are each, independently, a C1 to C20 linear or branched alkyl group. [0064] In various example embodiments, the leaching solution can include a leaching aid having formula (XII) as follows: R10CH2OC(O)C(SO3-)CH2C(O)OCH2R11Na ⁺ (XII), wherein R10 and R11 are each, independently, a C1 to C6 linear or branched alkyl group. [0065] In some embodiments, the leaching aid can have formula (XIII) as follows: wherein n is an integer from 3 to 10,000, 3 to 5,000, 3 to 2,000, 3 to 1,000, 3 to 100, 3 to 10, 3 to 8, or any individual value or sub-range within these ranges. In some embodiments, the leaching aid having formula (XIII) has a molecular weight of about 150 Da to about 10,000 Da, about 150 Da to about 5,000 Da, about 150 Da to about 1,000 Da, about 150 Da to about 450 Da, or any individual value or sub-range within these ranges. [0066] In some embodiments, the leaching aid can have formula (XIV) as follows: wherein n is an integer from 3 3 to 1,000, 3 to 100, 3 to 10, 3 to 8 or any individual value or sub-range within these ranges. In some embodiments, the leaching aid having formula (XIV) has a molecular weight of about 150 Da to about 10,000 Da, about 150 Da to about 5,000 Da, about 150 Da to about 1,000 Da, about 150 Da to about 450 Da, or any individual value or sub-range within these ranges. [0067] Suitable surfactants can include, but are not limited to non-ionic surfactants such as alcohol alkoxylates (e.g., alkoxylated polyols), alkylphenol alkoxylates, alkylpolyglucosides, N-alkylpolyglucosides, N-alkylglucamides, fatty acid alkoxylates, fatty acid polyglycol esters, fatty acid amine alkoxylates, fatty acid amide alkoxylates, fatty acid alkanolamide alkoxylates, N-alkoxypolyhydroxyfatty acid amides, N-aryloxypolyhydroxy-fatty acid amides, block copolymers of ethylene oxide, propylene oxide and/or butylene oxide, polyisobutene alkoxylates, polyisobutene/maleic anhydride derivatives, fatty acid glycerides, sorbitan esters, polyhydroxy-fatty acid derivatives, polyalkoxy-fatty acid derivatives, bisglycerides, t- octylphenoxypolyethoxyethanol, polyethylene glycol sorbitan monolaurate, polyoxyethylenesorbitan monopalmitate, polyethylene glycol sorbitan monostearate, polyoxyethylenesorbitan monooleate or mixtures thereof. In some embodiments, the leaching solutions and/or leaching aids as described herein are free of t-octylphenoxypolyethoxyethanol known commercially as Triton ^® X-100, polyethylene glycol sorbitan monolaurate known commercially as Tween ^® 20, polyoxyethylenesorbitan monopalmitate known commercially as Tween ^® 40, Polyethylene glycol sorbitan monostearate known commercially as Tween ^® 60 and/or polyoxyethylenesorbitan monooleate known commercially as Tween ^® 80. [0068] In some embodiments, the leaching aid and/or leaching solution does not include compounds having thiocarbonyl functional groups. In some embodiments, the leaching aid and/or leaching solution does not include a polysorbate or an alkylphenyl ether of polyethylene glycol. [0069] Additional characteristics of the leaching aids include high water solubility in the aqueous leaching composition to avoid extraction into the organic phase during solvent extraction. Other characteristics of the leaching aids include high critical micelle concentrations and stability at acidic pH. The leaching aids can minimize foaming, and one or more surfactants can decrease the surface tension of the leaching solution. The leaching aids also should have no or minimal impact on any other process related to extraction of the metal (e.g. leaching, solvent extraction, stripping and electrowinning including mixing, phase disengagement, extraction and strip kinetics, copper/iron selectivity or build up in the organic over time). Suitable leaching aids furthermore, should be stable under the acidic conditions of the leaching solution (e.g., sulfuric acid) in an aqueous phase and should be biodegradable. Moreover, suitable leaching aids according to various example embodiments of the disclosure can increase the kinetic rate of metal recovery (e.g., copper recovery) by at least 3%. In certain embodiments, the suitable leaching aids according to the disclosure can increase overall metal recovery by about 0.5% to about 20% or about 1% to about 20%, or about 2% to about 20%, or about 5% to about 20%, or about 0.5% to about 10% or about 2% to about 10% or about 5% to about 10%. [0070] According to various example embodiments of the disclosure, the one or more leaching aids can be added to any leaching composition for any type of leaching technique (e.g., primary and secondary sulfidic ore leaching) where an aqueous solution is used to remove metal from an ore. The one or more leaching aids can be added to the leaching solution at a total concentration of about 1 parts per million (“ppm”) to about 2000 ppm, or about 5 ppm to about 50 ppm, or about 5 ppm to about 100 ppm, or about 15 ppm to about 30 ppm, or about 10 ppm to about 1000 ppm, or about 20 ppm to about 500 ppm, or about 10 ppm to 100 ppm, or about 10 ppm to about 50 ppm, or about 25 ppm to about 50 ppm of the leaching composition, or about 50 ppm to less than the critical micelle concentration of the leaching aid. Critical micelle values can be, for example, about 100 ppm to about 1000 ppm, or any individual value or sub- range within these ranges. For example, the leaching composition can include a leaching aid of formula (I) or (IX) at a total concentration of about 5 ppm to about 50 ppm, or about 5 ppm to about 100 ppm, or about 15 ppm to about 30 ppm, or about 25 ppm, or about 10 ppm to about 100 ppm, or about 25 ppm to about 50 ppm, or any individual value or sub-range within these ranges, of the leaching composition. According to certain example embodiments of the disclosure, the leaching composition can include the TMP-7(EO) leaching aid or the MC1000 leaching aid at a total concentration of about 5 ppm to about 50 ppm, or about 5 ppm to about 100 ppm, or about 15 ppm to about 30 ppm, or about 10 ppm to about 100 ppm, or about 25 ppm to about 50 ppm, or about 25 ppm, or any individual value or sub-range within these ranges, of the leaching composition. [0071] According to various example embodiments of the disclosure, a leaching composition can include a lixiviant and one or more leaching aid of formulas (I) and (IX) – (XIV) described above. For example, the leaching solution can include both the TMP-7(EO) leaching aid and the MC1000 leaching aid. [0072] The lixiviant can be any suitable acid or base for leaching metal values from an ore. For example, the lixiviant can be sulfuric acid, ammonia, ammonium carbonate, ammonium sulfate and/or ammonium chloride. In the case of copper-containing ores, the lixiviant can be, for example, sulfuric acid or ammonia. For certain gold-containing ores, the lixiviant can be, for example, an alkaline sodium cyanide solution. [0073] The metal/metalloid values can be in ionic form and/or in elementary form. The metals/metalloids can be one or more of copper, gold, silver, nickel, zinc, molybdenum, vanadium, uranium, and combinations thereof. In certain example embodiments, the metal can be copper. [0074] The use of the ore leaching aids described herein can reduce the surface tension of the leaching composition and the contact angle of the aqueous phase and ore, thereby providing better wetting of the ore during heap leaching whether or not the ore is agglomerated. Additionally, this reduction in contact angle can improve capillary action in the microscopic crevices of the ore. Quantitative measure of the spreading wetting is the work of spreading (Ws), also referred to as the ‘spreading coefficient’ Ss and is governed by Young’s Equation: ^ _{^ௌ ൌ ^^ௌ ൌ ^^ௌ^ െ} ^{^} _{^^^^ ^ ^^ௌ^} ^{^} Where: ɣLV is the liquid surface free energy, or the interfacial tension between the liquid and air (also known as the surface tension) ɣSV is the solid surface free energy ɣSL is the solid/liquid surface free energy. Sina Ebnesajjad, The Handbook of Adhesives and Surface Preparation, § 3.5 (2011). [0075] The leaching aids according to various example embodiments of the disclosure, are compatible with several processes and process conditions, including, but not limited to, agglomeration, leaching, solvent extraction, and electrowinning. The one or more leaching aids can have no or a limited impact on other processes, such that they are compatible with downstream processes after the one or more leaching aids have been used to recover the metal during leaching. [0076] For example, solvent extraction is a carefully orchestrated balance of various metal and acid concentrations. The foundation of many forms of solvent extraction are built around the hydrogen ion cycle: Vladimir S. Kislik, Solvent Extraction: Classical and Novel Approaches, p.191. [0077] The delicate chemical balance that is inherent to all solvent extraction operations can be negatively affected by the slightest interloper. For example, in a copper solvent extraction process, all of the processes are interconnected and form a symbiotic relationship. Because of this relationship, it is possible that if an additive is meant to amplify one part of the process (e.g., copper leaching) it could easily disrupt another segment (e.g., copper extraction) due to incompatible chemistry. Issues such as these can include: the formation of emulsions, entrainment, introduction of impurities into the tankhouse, manipulation of extraction and/or strip kinetics, degradation or staining of the reagent, or nullification of a particular step of the process. According to various example embodiments of the disclosure, the leaching aids are compatible with leaching, extraction, stripping and electrowinning operations and do not result in the above-mentioned issues. [0078] According to various example embodiments of the disclosure, the leaching aid can be added to a lixiviant solution that is passed through an ore during an extraction process. The ore may be subjected to an agglomeration process prior to leaching with the lixiviant solution. In certain example embodiments, the leaching aid can be added to water and the lixiviant (e.g., sulfuric acid) used in an agglomeration process with no further addition of the leaching aid to the lixiviant solution circulated through the ore to leach the metal (e.g., copper). In yet further example embodiments, the leaching aid can be added to a portion of the lixiviant solution with or without the addition of additional acid for use as an agglomeration aid followed by passing lixiviant through the ore with or without the leaching aid. [0079] The one or more leaching aids used for improving the rate of recovery and/or total recovery of metals from ore, where the ore may or may not have been agglomerated, and which are compatible with numerous mining processes, can have various general characteristics. For example, the leaching aids can be comprised of one or more surfactants or mixtures thereof. In certain example embodiments, the leaching aids can be low-foaming surfactants. In some embodiments, the leaching aids and/or leaching compositions are free of charged surfactants. Methods of Preparation [0080] Further disclosed herein are methods of preparing a leaching composition as described above. The method can include combining at least one lixiviant and at least one leaching aid with an oxidant to form a leaching composition. In one or more embodiments, the oxidant can be introduced into the leaching composition in the form of bubbles. For example, the oxidant can be in gaseous form. [0081] The oxidant can be introduced into the aqueous leaching composition by various methods including, but not limited to, aerating the oxidant into the aqueous leaching composition, sparging the oxidant into the aqueous leaching composition, or diffusing the oxidant into the aqueous leaching composition. The oxidant can be introduced into the aqueous leaching composition at a dose of about 136g/m ³ raffinate to about 1088 g/m ³ , or about 181 g/m ³ to about 362 g/m ³ , or about 227 g/m ³ to about 317 g/m ³ , about 272 g/m ³ , or any individual value or sub-range within these ranges. [0082] FIG.3 shows a schematic diagram of an embodiment of a leaching system 300 suitable for forming and using compositions according to embodiments herein to leach a metal- containing material. As shown in FIG.3, system 300 includes an intake line (not shown) that feeds a pump (not shown) configured to direct fluid to a bubble generator 302. The gas can be introduced into the aqueous leaching composition by various methods including, but not limited to, aeration, sparging and/or diffusion. In some embodiments, a nanobubble generator 302 in combination with a pumping system (not shown), is used to generate and introduce nanobubbles of the gas into the raffinate 320 from a metal extraction process 318. The gas may be added to the raffinate 320 collected in a pond 304. According to various embodiments, the oxidant can be introduced into the leaching aid, or a solution containing inter alia the leaching aid and a lixiviant, using an apparatus for producing a composition that includes nanobubbles dispersed in a liquid carrier. [0083] The nanobubble generator 302 can include (a) an elongate housing comprising a first end and a second end, the housing defining a liquid inlet, a liquid outlet, and an interior cavity adapted for receiving the liquid carrier (e.g., a raffinate leach solution) from a liquid source; and (b) a gas-permeable member at least partially disposed within the interior cavity of the housing. The gas-permeable member includes an open end adapted for receiving a pressurized gas from a gas source, a closed end, and a porous sidewall extending between the open and closed ends having a mean pore size no greater than 1.0 μm. The gas-permeable member defines an inner surface, an outer surface, and a lumen. [0084] The liquid inlet of the housing is arranged to introduce the liquid carrier from the liquid source into the interior cavity of the housing at an angle that is generally orthogonal to the outer surface of the gas permeable member. The housing and gas-permeable member are configured such that pressurized gas introduced into the lumen of the gas-permeable member is forced through the porous sidewall of the gas-permeable member and onto the outer surface of the gas permeable member in the form of nanobubbles as the liquid carrier from the liquid source flows parallel to the outer surface of the gas-permeable member from the liquid inlet to the liquid outlet, forming a composition that includes the liquid carrier and the nanobubbles dispersed therein. In some embodiments, the composition is essentially free of microbubbles when measured 10 minutes after emerging from the liquid outlet. A composition that is “essentially free of microbubbles” is a composition in which microbubbles make up less than 1% of the total bubble volume in the composition. [0085] The nanobubbles from the nanobubble generator 302 may have a mean diameter less than 500 nm, less than 200 nm, ranging from about 10 nm to about 500 nm, from about 75 nm to about 200 nm, or any individual value or sub-range within these ranges. The concentration of nanobubbles in the liquid carrier (e.g., a raffinate leach solution) at the liquid outlet may be at least 1×10 ⁶ nanobubbles/ml, at least 1×10 ⁷ nanobubbles/ml, at least 1×10 ⁸ nanobubbles/ml, or any individual value or sub-range within these ranges. In some embodiments, the composition includes nanobubbles that are stable in the liquid carrier for at least one month, at least three months, or any individual value or sub-range within these ranges, under ambient pressure and temperature. [0086] The gas feed to the nanobubble generator 302 can include, but is not limited to, air, oxygen, carbon dioxide, sulfur dioxide, nitrogen, and combinations thereof. Suitable oxidants include, but are not limited to air, oxygen, ozone, or combinations thereof. In some embodiments, the gas-permeable member may be adapted to receive gas pressurized to at least 5 psi or at least 100 psi. The liquid carrier may include water. In some embodiments, the liquid carrier is free of surfactants. [0087] In some embodiments, the gas-permeable member includes a rigid, ceramic member. The porous sidewall may have a mean pore size ranging from 0.0009 μm to 1 μm. The porous sidewall may include a porous coating. Examples of suitable porous coating include metallic oxides such as alumina, titania, zirconia, manganese, and combinations thereof. The porous coating may be disposed on the inner surface, outer surface, or both surfaces of the gas- permeable member. [0088] In some embodiments, the housing includes a plurality of gas-permeable members. The gas-permeable member may be in the form of a single channel tube, or a multi-channel tube. [0089] The apparatus may include one or more helical members (or helical apparatuses) adapted for enhancing turbulence in the liquid carrier. In some embodiments, the apparatus may further include a jet pump that is integral with the housing. [0090] In various embodiments, there is described an apparatus for producing a composition that includes nanobubbles dispersed in a liquid carrier. The apparatus includes: (a) an elongate housing comprising a first end and a second end, the housing defining a liquid inlet, a liquid outlet, and an interior cavity adapted for receiving the liquid carrier from a liquid source; and (b) a gas-permeable tube disposed within the interior cavity of the housing. The gas-permeable tube includes an open end adapted for receiving a pressurized gas from a gas source, a closed end, an inner surface, an outer surface, and a lumen. At least one of the inner and outer surfaces of the gas-permeable tube includes a porous coating having a mean pore size no greater than 1 μm selected from the group consisting of alumina, titania, zirconia, manganese, and combinations thereof. [0091] The liquid inlet of the housing is arranged to introduce the liquid carrier from the liquid source into the interior cavity of the housing at an angle that is generally orthogonal to the outer surface of the gas-permeable tube. The housing and gas-permeable tube are configured such that pressurized gas introduced into the lumen of the gas-permeable tube is forced through the porous coating of the gas-permeable tube and onto the outer surface of the gas permeable tube in the form of nanobubbles as the liquid carrier from the liquid source flows parallel to the outer surface of the gas-permeable member from the liquid inlet to the liquid outlet, forming a composition that includes the liquid carrier and the nanobubbles dispersed therein. [0092] In one or more embodiments, there is described a method for producing a composition containing nanobubbles dispersed in a liquid carrier using the apparatuses described above. The method includes introducing a liquid carrier (e.g., a solution containing at least one lixiviant and at least one leaching aid) from a liquid source (e.g., a heap leaching operation) into the interior cavity of the housing through the liquid inlet of the housing at a flow rate that creates turbulent flow at the outer surface of the gas-permeable member. The method further includes introducing a pressurized gas (e.g., an oxidant) from a gas source into the lumen of the gas-permeable member at a gas pressure selected such that the pressure within the lumen is greater than the pressure in the interior cavity of the housing, thereby forcing gas through the porous sidewall and forming nanobubbles on the outer surface of the gas-permeable member. The liquid carrier flows parallel to the outer surface of the gas-permeable member from the liquid inlet to the liquid outlet and removes nanobubbles from the outer surface of the gas-permeable member to form a composition that includes the liquid carrier and the nanobubbles dispersed therein (e.g., a leaching composition according to various embodiments described herein). [0093] In some embodiments, nanobubbles are produced by supplying gas under pressure to one side of a ceramic structure, said one side being coated with titanium oxide, aluminum oxide or other metallic oxide and the structure having a pore size of between 0.0009-1.0 μm, so that the gas passes through the ceramic structure and emerges as nanobubbles on the other side thereof, and creating a liquid flow on said other side of the ceramic structure to carry away the nanobubbles as they emerge from said structure, thereby preventing the nanobubbles coalescing to bubbles of a larger size. [0094] In some embodiments, the nanobubble generator includes a porous ceramic structure having a first surface and an opposed second surface, a gas supply system for supplying gas under pressure to said first surface of the ceramic structure so that the gas passes though the ceramic structure and emerges through said second surface and a liquid supply system for supplying liquid under pressure as a stream which flows over said second surface. [0095] The ceramic structure can be in the form of a tube that is closed at one end and has an inlet for gas under pressure at the other end. The nanobubble generator can further include an elongate housing co-axial with said tube having an inlet for liquid at one end and an outlet for liquid at the other end so that liquid flows through the cylindrical channel defined between the tube and the housing. The inlet to the housing can be positioned so that liquid flows into the housing at an angle to the direction of flow through the housing. Projections such as helical members can be provided in said housing for increasing turbulent flow in the channel. [0096] In some embodiments, the nanobubble generator is configured to form nanobubbles using minimal energy, having a bubble diameter of not more than 1000 nm in the solution, in which the nanobubbles remain dispersed in the liquid carrier for one or more months in a stable state under ambient temperature and pressure. High concentrations of nanobubbles in a liquid carrier can be produced. [0097] An advantage of a composition containing gas carried in the nanobubbles is that the nanobubbles can increase the saturation point in a liquid. In one or embodiments, the nanobubbles in leaching compositions as described herein increase the maximum saturated point of the liquid. In some embodiments, it may be desirable to partially “degas” the treated solution (i.e., the leaching composition after it has passed through the nanobubble generator) prior to it reaching drip emitters in irrigation to help remove any “macrobubbles” in the solution that might impact downstream performance. [0098] Referring again to FIG. 3, a treated solution may be returned to a raffinate collection pond 304 before being recycled into the leaching process 308. Bubbles may be introduced into the solution in the collection pond 304 upstream from the leaching process 308. In addition, one or more leaching aids 310 can be added to the solution in the recycle line 312 by use of in- line injection. It is expected that some of the one or more leaching aids 310 would contact a metal-containing material (e.g., a heap of ore) and be present in the pregnant leach solution collection area 314. According to various embodiments, the bubbles may be consumed by the metal-containing material in the leaching process 308, for example, via heap or agitation leach. Pregnant leach solution 316 exiting collection 314 may be directed to a metal extraction process 318 to collect the value metals dissolved therein. The raffinate 320 from the metal extraction process may then be directed to raffinate collection pond 304 and recycled back to the leaching process 308. [0099] FIG. 4 shows a schematic diagram of an embodiment of a system 400 for preparing and using a composition for leaching metal-containing materials. In this embodiment, a bubble generator 402, for example, as described above with reference to 302, can be positioned in the main raffinate return line 413, downstream from in-line injection of the one or more leaching aids 410. As such, the bubbles may be added to the composition containing the one or more leaching aids 410. In this embodiment, raffinate flows from raffinate collection pond 404, through recycle line 412 and out of pump 406 into return line 413. In this embodiment, bubbles are introduced into the composition just upstream of the leaching process 408 (e.g., metal- containing material heap leaching). It is expected that some of the one or more leaching aids 410 would contact a metal-containing material (e.g., a heap of ore) and be present in the pregnant leach solution collection area 414. According to various embodiments, the bubbles may be consumed by the metal-containing material in the leaching process 408, for example, via heap or agitation leach. Pregnant leach solution 416 exiting collection 414 may be directed to a metal extraction process 418 to collect the value metals dissolved therein. The raffinate 420 from the metal extraction process may then be directed to raffinate collection pond 404 and recycled back to the leaching process 408. [0100] FIG.5 shows a schematic diagram of an embodiment of a system 500, a treated solution may be returned to a raffinate collection pond 504 before being recycled into the leaching process 508. Bubbles may be introduced into the solution in the collection pond 504 upstream from the leaching process 508. In addition, one or more leaching aids 510 can be added to the solution in the raffinate leach solution collection pond 504 by use of direct dosing. It is expected that some of the one or more leaching aids 510 would contact a metal-containing material (e.g., a heap of ore) and be present in the pregnant leach solution collection area 514. According to various embodiments, the bubbles may be consumed by the metal-containing material in the leaching process 508, for example, via heap or agitation leach. Pregnant leach solution 516 exiting collection 514 may be directed to a metal extraction process 518 to collect the value metals dissolved therein. The raffinate 520 from the metal extraction process may then be directed to raffinate collection pond 504 and recycled back to the leaching process 508. [0101] FIG. 6 shows a schematic diagram of an embodiment of a system 600 for preparing and using a composition for leaching metal-containing materials according to embodiments herein. In this embodiment, a bubble generator 602, for example, as described above with reference to 302, can be positioned in the raffinate return line 612, upstream from the raffinate pump 606. As such, the bubbles may be added to the composition containing the one or more leaching aids 610. In this embodiment, raffinate flows from raffinate collection pond 604, through raffinate return 612 into the nanobubble generator 602 and out of pump 606 into return line 613. It is expected that some of the one or more leaching aids 610 would contact a metal- containing material (e.g., a heap of ore) and be present in the pregnant leach solution collection area 614. According to various embodiments, the bubbles may be consumed by the metal- containing material in the leaching process 608, for example, via heap or agitation leach. Pregnant leach solution 616 exiting collection 614 may be directed to a metal extraction process 618 to collect the value metals dissolved therein. The raffinate 620 from the metal extraction process may then be directed to raffinate collection pond 604 and recycled back to the leaching process 608. [0102] The one or more leaching aid can be added to the aqueous phase of the composition and adjusted to maintain a concentration of about 0.001 mM to about 67 mM, 0.01 mM to about 0.02 mM, based on the total volume of the composition. [0103] According to various embodiments, the methods can include adding (e.g., from an external source) at least one of an iron oxidizing bacterium (e.g., thiobacillus ferrooxidans, acidithiobacillus ferrooxidans) and/or a sulfur oxidizing bacterium (e.g., sulfobacillus disulfidooxidans) to the composition/raffinate upstream of the leaching process. One or more iron oxidizing bacterium may be added to convert ferrous ions to ferric ion during the leaching process. One or more sulfur oxidizing bacterium may be added to convert elemental sulfur produced during leaching to sulfate in the generation of acid. In some embodiments, an inoculation of the various species listed may be added to assist in the leaching process. [0104] According to various embodiments, the method includes combining a metal-containing material with the leaching composition. The metal-containing material may be in the form of an ore, a plurality of particles, a plurality of agglomerates, a concentrate, a matte, or combinations thereof. In some embodiments, the metal-containing material is a copper-bearing sulfide ore. Suitable copper-bearing sulfide ore includes, but is not limited to, chalcopyrite (CuFeS ₂ ), bornite (Cu ₅ FeS ₄ ), enargite (Cu ₃ AsS ₄ ), tetrahedrite (Cu ₁₂ Sb ₄ S ₁₃ ), tennantite (Cu ₁₂ As ₄ S ₁₃ ), covellite (CuS), chalcocite (Cu ₂ S), carrolite (CuCo ₂ S ₄ ), or combinations thereof. In some embodiments, the metal-sulfide-containing material is a non-copper bearing sulfide ore. Suitable non-copper bearing sulfide ore includes, but is not limited to, one or more of millenite (NiS), pentlandite (Fe ₉ Ni ₉ S ₁₆ ), molybdenite (MoS ₂ ), violarite (FeNi ₂ S ₄ ), cobaltite (CoAsS), pyrite (FeS ₂ ), linnaeite (Co ₃ S ₄ ), sphalerite ((Zn,Fe)S), cattierite (CoS ₂ ), or combinations thereof. [0105] The details of one or more embodiments of the invention are set forth in the description below. Other features, objects, and advantages of the invention will be apparent from the description and from the claims. Methods of Use [0106] In yet further embodiments, disclosed herein are methods of leaching a metal-sulfide- containing material, including contacting the metal-sulfide-containing material with a composition according to embodiments herein; and increasing the dissolved concentration of at least one metal from the metal-sulfide-containing material in the composition. [0107] According to various embodiments, methods of using leaching compositions include contacting the leaching composition with an ore to form a raffinate stream, performing chemical analysis of the raffinate stream and/or visually inspecting the leaching process. In some embodiments, the method includes, generating oxidant nanobubbles in the mine raffinate solution to form a leaching solution, and then contacting the ore with the leaching solution. [0108] In some embodiments, disclosed are methods for increasing the recovery of target metals from ore (e.g., sulfide ores). The method can include contacting the ore with a leaching solution according to embodiments herein. The leaching solution can include an oxidant in combination with a leaching aid. Suitable oxidants include, but are not limited to, air, oxygen, ozone, or combinations thereof. Suitable leaching aids include, but are not limited to, alkoxylated compounds as described herein. EXAMPLES Example 1 – Comparison between a composition according to embodiments herein and a control composition [0109] A nanobubble generator connected to an oxygen cylinder was used to treat thirty gallons of a raffinate leach solution from a copper mine in Arizona. A dissolved oxygen (DO) probe was used to analyze the dissolved oxygen concentration in solution as a function of time. The results are presented in FIG. 1 where the dissolved oxygen concentration is graphed as a function of the time of treatment with oxygen in the nanobubble generator. There was an unexpected synergy observed when charging the system with 30 ppm of leaching aid (TMP- 7EO) according to embodiments herein, which greatly reduced the amount of time required for the system to reach its maximum equilibrium value of about 38 mg/L at about 1,000 m elevation above sea level at about 20-22 degrees Celsius. Sodium dodecyl sulfate was also compared to the leaching aid (i.e., comprising a distribution of ethylene oxide compounds, the bulk compound of which is TMP-7EO) as a standard commercially available surfactant to see if it would also increase the rate of the oxygen dissolution in solution. It demonstrated a similar effect, increasing the rate of oxygen dissolution over time in comparison to the control. Example 2 – Comparison between a composition according to embodiments herein and a control composition [0110] Once the raffinate and the dosed raffinate from Example 1 had reached equilibrium, the nanobubble generator was turned off and the decay rate of dissolved oxygen in solution was monitored as it returned to equilibrium with atmospheric air conditions, approximately 7 mg/L. The results are shown in FIG. 2 where the dissolved oxygen concentration is graphed as a function of the time after treatment with oxygen gas. Interestingly, it was observed that the solution retained dissolved oxygen for significantly longer when the wetting aid was present in solution, which would help to prolong the availability of dissolved oxygen for longer once the solution has been added to a leaching application. Sodium dodecyl sulfate was also compared to the leaching aid (i.e., comprising a distribution of ethylene oxide compounds the bulk compound of which is TMP-7EO) as a standard commercially available surfactant to see if it would increase the longevity of the dissolved oxygen in solution. However, it was found to have a negative synergy, decreasing the retention of dissolved oxygen in solution over time relative to the control and the composition containing leaching aid. Example 3 – Comparison between a composition according to embodiments herein and a control composition [0111] A nanobubble generator connected to an oxygen cylinder was used to treat twenty- five gallons of a raffinate leach solution from a copper mine in Arizona. A “Nanosight NS300” was used to analyze the nanobubble concentration in solution as a function of time. The results are shown in Table 1. It was observed that the concentration and size of nanobubbles in the solution increased following the addition of the leaching aid. There was an unexpected synergy observed when charging the system with 30 ppm of the wetting aid which seemed to greatly increase the concentration and size of the nanobubbles produced from an average of 252,000,000 nanobubbles/mL to 752,000,000 nanobubbles/mL at about 1,000 m elevation above sea level at about 20-22 degrees Celsius. In addition, the average size of these nanobubbles was also increased from 161 nm to 228 nm with the presence of the leaching aid at 30 mg/L (i.e., comprising a distribution of ethylene oxide compounds the bulk compound of which is TMP-7EO) Table 1 – Comparison between a composition according to embodiments herein and a control composition NANOBUBBLE NANOBUBBLE SIZE CONCENTRATION [nanometers] D N Example 4 – Column leaching investigation utilizing a composition according to embodiments herein and control compositions [0112] A raffinate leach solution with the following characteristics: 2.66 g/L Fe, 0.85 g/L H2SO4, ORP of 506mV (1M Ag/AgCl) and a pH of 1.79 was used to leach a sulfide rich ore in column testing in a laboratory. For the testing, the ore used was from a copper mill flotation feed and had a total copper grade of 1.2%, with 96.2% of the copper present as sulfide minerals, and 3.8% as acid soluble minerals. The ore was all <3/4”, with 10.8%wt in the ½”< x < ¾” fraction, 32.7%wt in the ¼” < x < ½” fraction, 28.7%wt in the Tyler 10 Mesh < x < ¼”, and 27.7%wt in the 0 < x < Tyler 10 Mesh Fraction. [0113] The irrigation rate was set at 1 L/hr/m ² and the ore was agglomerated with 26.8 kg/ton sulfuric acid prior to column loading, which equated to 100% acid consumption of the ore.4kg of ore were used per column, and each test was conducted in quadruplicate using the setup described in FIG. 7 and the results averaged. For each sample, the mass, density, pH, and metallurgical data of the PLS were collected and reviewed. The results of this testing are shown in FIG.8. In this testing, the same raffinate was used for each test, with control columns being irrigated with the starting raffinate solution. The leaching aid treated columns were irrigated with the same raffinate described above that had been dosed with 30 mg/L of leaching aid (i.e comprising a distribution of ethylene oxide compounds the bulk compound of which is TMP- 7EO) prior to irrigation starting. The Nanobubble columns were irrigated with a raffinate feed pumped from a tank that was continuously charged for five minutes every hour with oxygen gas nanobubbles produced by the Moleaer XTB Nanobubble Generator. All of these conditions were contrasted relative to a separate nanobubble system, that was used to treat the raffinate solution described above that has also been dosed with 30mg/L leaching aid prior to beginning the test. Over the period of irrigation an elevated rate of copper recovery was observed with the leaching aid treated samples relative to the control, but an unexpected synergy was observed with the leaching aid and nanobubble treated columns, which exhibited a 16.6% total copper recovery (%CuT) relative to a 7.38%CuT seen in the control at the same leach ratio. Oxygen enriched nanobubbles alone without leaching aid had a comparatively lower rate of copper recovery than the control over the period of time these tests were conducted. Definitions [0114] Reference throughout this specification to, for example, “one embodiment,” “certain embodiments,” “one or more embodiments” or “an embodiment” means that a particular feature, structure, material, or characteristic described in connection with the embodiment is included in at least one embodiment of the invention. Thus, the appearances of the phrases such as “in one or more embodiments,” “in certain embodiments,” “in one embodiment” or “in an embodiment” in various places throughout this specification are not necessarily referring to the same embodiment of the invention. Furthermore, the particular features, structures, materials, or characteristics may be combined in any suitable manner in one or more embodiments. [0115] 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 robot arm” includes a single robot arm as well as more than one robot arm. [0116] 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. [0117] 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 greater 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.” [0118] Unless otherwise indicated, all parts and percentages are by weight. Weight percent (wt. %), if not otherwise indicated, is based on an entire composition free of any volatiles, that is, based on dry solids content. [0119] As used herein, the term “nanobubble” refers to a bubble that has a mean diameter of less than about one micron. A “microbubble,” which is larger than a nanobubble, is a bubble that has a mean diameter greater than or equal to one micron and smaller than 50 microns. A “macrobubble” is a bubble that has a mean diameter greater than or equal to 50 microns. [0120] As used herein, the term “combinations thereof” refers to an operable mixture or grouping of any two or more elements preceding the term. For example, “A, B, C, or combinations thereof” refers to “A and B,” “B and C,” “A and C” and “A, B and C.” [0121] The foregoing description discloses example embodiments of the disclosure. Modifications of the above-disclosed assemblies, apparatus, and methods which fall within the scope of the disclosure will be readily apparent to those of ordinary skill in the art. Accordingly, while the present disclosure has been disclosed in connection with example embodiments, it should be understood that other embodiments may fall within the scope of the disclosure, as defined by the following claims.