Abstract:
The present invention relates to flotation of sulfidic copper- molybdenum- and gold-containing minerals. More specifically, the invention relates to sulfoxy reagent-assisted flotation for separating of sulfides of copper, molybdenum and gold from pyrite, marcasite, pyrrhotite, arsenopyrite, and other gangue minerals following aerating by an oxidizing gas and contacting by a sulfoxy reagent. To promote collection and flotation the feed mineral materials are preferably not contacted with an externally generated non-oxidizing gas to lower the dissolved molecular oxygen content prior to flotation.

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     The present application claims the benefits of U.S. Provisional Application Ser. No. 61/266,770, filed Dec. 4, 2009, entitled “Separation of Copper Minerals from Pyrite in Buffered Water Solutions Using Air-Metabisulfite Treatment”, which is incorporated herein by this reference in its entirety. 
    
    
     FIELD 
     The invention relates generally to metal recovery and particularly to recovery of copper, molybdenum and/or gold minerals by flotation in waters with a range of buffering capacities and/or salinities. 
     BACKGROUND 
     The employment of flotation to upgrade valuable minerals from pyrite and other gangue minerals is generally performed at an alkaline pH. Alkalinity is controlled by the addition of lime or other alkaline compounds. Lime is normally employed as it is a relatively inexpensive reagent; however, large amounts of lime and other reagents are required when the water available to the flotation circuit possesses a high buffering capacity. In other words, a large amount of lime is necessary to alter and maintain the pH at the optimal operating conditions. The addition of lime can also depress the flotation of minerals such as chalcopyrite, sphalerite, molybdenite, pyrite, pyrrhotite, and gold and other precious metals via the deposition of calcium on the metal surface. 
     Commonly, in sulfide flotation, the effectiveness of flotation agents is controlled by the level of alkalinity or acidity in the flotation feed or pulp pH regulators such as lime, soda ash and, to a lesser extent, caustic soda, are often employed as the pH controlling agents. Lime is the most commonly used agent because of its cost, availability and ability to maintain pH values of pH 10.5 and above. Adjustment of the pH of the pulp to pH 11.0 is required to depress the gangue sulfide minerals of iron, such as pyrite and pyrrhotite. The costs associated with adding lime can be significant and the effectiveness of lime as a depressant has been shown herein to be reduced in waters containing high levels of dissolved salts or are highly buffered. 
     Other sulfide depressants have been employed to depress pyrite, such as cyanide or sodium hydrosulfide, in conjunction with pH modification. They cannot be used over a wide pH range and require high pH values, so that high lime consumption remains an issue. In addition these depressants may not be sufficiently selective at economic dosages. The use of sulfoxy compounds to improve the recovery of sulfide minerals was described as far back as U.S. Pat. No. 2,154,092 to Hunt. This patent describes a process to treat ores containing carbonaceous or graphitic substances associated with gangue components. These carbonaceous substances may either remain with the valuable ore mineral during flotation and reduce the grade or coat the valuable minerals, thereby reducing their recovery by flotation. To prevent this, sulfur dioxide or any other reducing gas, is added to the pulp, without mixing it with air, to inhibit the flotation of the deleterious gangue and carbon coated minerals. 
     When the sulfur dioxide gas is added, Hunt states that the resulting pH of the pulp water is usually on the acid side (&lt;pH 7). In some cases, depending on the natural alkalinity of both the ore and the milling water, the pulp may remain alkaline. The process can be carried out when the pulp is either acid or alkaline. 
     Hunt teaches that the reducing gas may also be internally generated in the ore pulp itself by the action of one or more suitable chemicals. For example, when sulfuric acid and an alkaline (base) or alkaline earth sulfite, bisulfite, or thiosulfate are added to an ore pulp, sulfur dioxide will be one of the products resulting from the interaction. 
     A number of other patents have employed sulfoxy compounds in sulfide flotation circuits. 
     U.S. Pat. No. 5,171,428 to Beattie, et al., describes a process to separate arsenopyrite from a mixture with pyrite by contacting the mixture with a sulfitic agent providing HSO 3   −  ion. The process is performed at an elevated temperature and a pH below about pH 8 for a period sufficient to impart a selective depression of arsenopyrite. 
     U.S. Pat. Nos. 6,032,805, and 6,092,666 to Clark, et al., disclose a method for reducing the consumption of alkaline pH modifiers by using a sulfoxy radical-containing reagent. Prior to or simultaneously with the introduction of the sulfoxy radical-containing reagent, a non-oxidizing gas (such as an inert or reducing gas) is added in a quantity sufficient to achieve a chemical environment conducive to the flotation separation of minerals. Prior to collector and frother addition but after contact with the non-oxidizing gas, the slurry, only when necessary, is aerated by an oxidizing gas to a particular dissolved oxygen concentration or electrochemical potential suitable for flotation. 
     U.S. Pat. No. 6,041,941 to Newell, et al., presents a similar process to Clark, et al., with the aim of reducing reagent consumption and mineral scale formation in flotation circuits. In the process of Clark, et al., the non-oxidizing gas is added to prevent the oxidation of the sulfoxy radical. The non-oxidizing gas is introduced during the reagent conditioning and flotation stages. At these stages, the dissolved oxygen in the slurry is most likely to degrade the sulfoxy compounds and result in scale formation. 
     There is a need for a process that can separate valuable metal-containing sulfide minerals from other sulfide minerals, particularly sulfidic gangue minerals, while controlling levels of reagent consumption in waters with a significant range of buffering capacities and/or salinities, without the addition of lime or other pH modifiers. 
     SUMMARY 
     These and other needs are addressed by the various embodiments and configurations of the present invention. The invention is directed generally to sulfoxy reagent-assisted flotation separation of valuable metal sulfide minerals from other sulfides, particularly pyrite, marcasite, pyrrhotite, arsenopyrite, and other gangue minerals. 
     In an embodiment, a sulfoxy reagent, preferably an ammonium, hydrogen, alkali metal, and/or alkaline earth metal metabisulfite, is added to an aerated, slurried valuable metal-containing sulfidic feed material prior to flotation. The process is particularly applicable to the flotation separation of copper sulfides, such as chalcocite (Cu 2 S), bornite (Cu 5 FeS 4 ), chalcopyrite (CuFeS 2 ), covellite (CuS), tetrahedrite (Cu 12 Sb 4 S 13 ), tennantite (Cu 12 As 4 S 13 ), and enargite (Cu 3 AsS 4 ) and/or molybdenum sulfide (e.g., as molybdenite (MoS 2 )), on the one hand from pyrite (FeS 2 ), marcasite (FeS 2 ), pyrrhotite (Fe 1-x S), arsenopyrite (FeAsS) on the other. The sulfoxy reagent acts as a depressant of the gangue sulfide minerals. In this manner, a highly selective flotation separation of different sulfide minerals can be realized. 
     Unlike conventional flotation processes which strip molecular oxygen from the slurry prior to sulfoxy reagent addition, the sulfoxy reagent is added to an aerated valuable metal-containing feed material. The aeration step is operated to the extent that a thin layer of surface oxidation is formed on copper sulfide minerals to promote the adsorption of the collector and therefore flotation of the copper minerals. To promote the formation of this layer, the slurried valuable metal-containing feed material is preferably not contacted with an externally generated non-oxidizing gas to lower the dissolved molecular oxygen content, prior to the floating step. 
     In some embodiments, the sulfoxy reagent is introduced after aeration and before pulp conditioning with the collector and frother. 
     In some embodiments, the sulfoxy reagent is introduced not only after aeration but additionally in the primary and/or secondary grinding circuit. While not wishing to be bound by any theory, this enables the sulfoxy reagent to contact freshly exposed and unoxidized mineral sulfide surfaces, thereby enhancing the effectiveness of the reagent. 
     In some embodiments, the flotation process is performed at natural pH and in the substantial absence of pH modification. Stated another way, no acid or base is added to adjust the pH of the slurried feed material at any stage in the comminution and flotation circuits unless pH modification is performed for economic reasons, such as to reduce sulfoxy reagent dosage, reduce any corrosion effect, and/or to avoid a lower pH situation when high sulfoxy reagent dosage is needed. pH modification, however, must be carefully controlled to avoid adversely impacting valuable metal recovery or concentrate grade. 
     The process can use, in pulp formation, any quality of water, whether fresh, brackish, or salt water and regardless of the degree of buffering. 
     The combination of the aeration stage followed by a sulfoxy reagent addition stage, and in the absence of pH adjustment, can result in increased copper sulfide mineral flotation rate and recovery and improved copper sulfide mineral concentrate grade. Although the dissolved molecular oxygen level produced by aeration may, in certain situations, increase sulfoxy reagent consumption, the substantial improvement in kinetics and elimination of lime reagent requirements can more than offset any increase in sulfoxy reagent costs. This process is particularly useful when the water available to form the flotation pulp contains significant buffering capacity and is effective over a broad pulp pH range. In fact, the process can be more cost effective in terms of recovery and reagent consumption than conventional processes using lime addition and cyanide. The process has demonstrated superior performance when used in water containing negligible to significant buffering capacity or salinity. Accordingly, the process is particularly useful for concentrator operations whose only available source of water is sea water or brackish ground water. 
     These and other advantages will be apparent from the disclosure of the invention(s) contained herein. 
     The term “a” or “an” entity refers to one or more of that entity. As such, the terms “a” (or “an”), “one or more” and “at least one” can be used interchangeably herein. It is also to be noted that the terms “comprising”, “including”, and “having” can be used interchangeably. 
     The phrases “at least one”, “one or more”, and “and/or” are open-ended expressions that are both conjunctive and disjunctive in operation. For example, each of the expressions “at least one of A, B and C”, “at least one of A, B, or C”, “one or more of A, B, and C”, “one or more of A, B, or C” and “A, B, and/or C” means A alone, B alone, C alone, A and B together, A and C together, B and C together, or A, B and C together. When each one of A, B, and C in the above expressions refers to an element, such as X, Y, and Z, or class of elements, such as X1-Xn, Y1-Ym, and Z1-Zo, the phrase is intended to refer to a single element selected from X, Y, and Z, a combination of elements selected from the same class (e.g., X1 and X2) as well as a combination of elements selected from two or more classes (e.g., Y1 and Zo). 
     The term “brackish water” refers to water having more salinity than fresh water but not as much as salt water. Typically, brackish water has a salinity ranging from about 0.1 parts per thousand (0.01%) to about 25 parts per thousand (2.5%). 
     The term “buffering capacity” refers to the degree to which a solution can resist the alteration of its pH when external pH modifiers are added. 
     The term “dissolve” and variations thereof refer to is the process by which a solid or liquid enters its aqueous phase (solution). 
     The term “metabisulfite” refers to the oxyanion of sulfur S2O52− or any salt containing this ion. Metabisulfite usually is in the form of a metal and the bisulfite anion (S2O5), usually in the form of an alkali or alkaline earth metal metabisulfite. 
     The term “mineral” and variations thereof refer to any naturally formed chemical substance having a definite chemical composition and characteristic crystal structure. 
     The term “natural pH” refers to the pH of a solution in the substantial absence of intentional pH modification. Intentional pH modification occurs when an acid or base is added to a solution for the purpose of adjusting the pH. An example of unintentional pH modification is when pH is adjusted by aeration, pulp conditioning with a flotation reagent (such as a collector, frother, activator, depressant, dispersant, and the like), or sulfoxy reagent addition. 
     The term “precious metal” refers generally to gold and silver. 
     The term “solution derived therefrom” refers to a solution having at least one common component with the source solution from which the solution is derived, directly or indirectly. For example, a solution having a leaching agent, contaminant, or valuable metal found in the source solution is deemed to be derived therefrom. Thus, a raffinate or barren solution is deemed to be a solution derived from a pregnant leach solution. Likewise, a loaded extractant or electrolyte, which contains the valuable metal, or strip solution are deemed to be derived, directly or indirectly, from the pregnant leach solution. Likewise, a slurried concentrate or tailings is deemed to be derived from the feed material to the flotation stage. 
     The term “sulfide mineral” refers to a mineral containing metal as the cation and sulfide (S2−) as the major anion. 
     The term “sulfoxy reagent” refers to a composition containing an ingredient in which oxygen is directly bonded to S, such as S═O, SO3X, SO4, etc., or which acts as a source for the sulfoxy radical. 
     The term “salt water” refers to water, typically ocean or seawater, having a salinity of about 25 parts per thousand (2.5%) or more, more typically of about 30 parts per thousand (3.0%) or more, and even more typically of about 35 parts per thousand (3.5%) or more. Salt water typically has a total dissolved solids of about 10,000 mg/L or more, even more preferably of about 20,000 mg/L or more, and even more preferably of about 25,000 mg/L or more. Although seawater contains more than 70 elements, most seawater salts are ions of six major elements: chloride, sodium, sulfate, magnesium, calcium, and potassium. 
     The term “salinity” refers to the dissolved salt content of a body of water. It describes the levels of different salts such as sodium chloride, magnesium and calcium sulfates, and bicarbonates. 
     The term “sulfite” are compounds that contain the sulfite ion SO (additive IUPAC name: trioxidosulfate(2−)). The sulfite ion is the conjugate base of sulfurous acid. 
     The term “valuable metal” refers to silver, gold, a nonferrous base metal (nickel, lead, copper, and zinc), cobalt, molybdenum and mixtures thereof, with copper being a common metal in the sulfide matrix. 
     The preceding is a simplified summary of the invention to provide an understanding of some aspects of the invention. This summary is neither an extensive nor exhaustive overview of the invention and its various embodiments. It is intended neither to identify key or critical elements of the invention nor to delineate the scope of the invention but to present selected concepts of the invention in a simplified form as an introduction to the more detailed description presented below. As will be appreciated, other embodiments of the invention are possible utilizing, alone or in combination, one or more of the features set forth above or described in detail below. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The accompanying drawings are incorporated into and form a part of the specification to illustrate several examples of the present invention(s). These drawings, together with the description, explain the principles of the invention(s). The drawings simply illustrate preferred and alternative examples of how the invention(s) can be made and used and are not to be construed as limiting the invention(s) to only the illustrated and described examples. Further features and advantages will become apparent from the following, more detailed, description of the various embodiments of the invention(s), as illustrated by the drawings referenced below. 
         FIG. 1  is a flowchart of a process according to an embodiment; 
         FIGS. 2A-B  are a flowchart of a process according to an embodiment; 
         FIG. 3  is a flowchart of a process according to an embodiment; 
         FIG. 4  is a flowchart of a process according to an embodiment; 
         FIG. 5  is a copper recovery curve for various flotation reagent schemes in tap water and plots copper grade (%) against copper recovery (%); 
         FIG. 6  is a copper recovery curve for various flotation reagent schemes in salt water and plots copper grade (%) against copper recovery (%); 
         FIG. 7  is a copper recovery curve for various flotation reagent schemes in tap water and plots copper grade (%) against copper recovery (%); 
         FIG. 8  is a copper recovery curve for various flotation reagent schemes in salt water and plots copper grade (%) against copper recovery (%); 
         FIG. 9  is a copper recovery curve in salt water and tap water with MBS addition, with and without aeration, and plots copper grade (%) against copper recovery (%); and 
         FIG. 10  is a copper recovery curve in brackish site water and tap water with MBS addition, with and without aeration, and plots copper grade (%) against copper recovery. 
     
    
    
     DETAILED DESCRIPTION 
     The process described herein employs the addition of a sulfoxy reagent, preferably a metabisulfite, to one or more points in a flotation circuit. In one process configuration, the addition of the sulfoxy reagent is preceded by a period of, typically intense, aeration, in which an oxidizing atmosphere and dissolved molecular oxygen is actively promoted, rather than prevented or inhibited. The combination of aeration with sulfoxy reagent addition, without adjustment of the pH of the resulting pulp with a base, such as lime, caustic soda, or soda ash, or an acid, such as sulfuric acid, and in the absence of sulfide depressants, such as cyanide or hydrosulfide, can show a marked improvement over the addition of a sulfoxy reagent without, or in the absence of, the aeration step and can be more cost effective in terms of recovery and reagent consumption than conventional processes that employ base and/or sulfide depressant addition. In addition, the process can have superior performance when used in water containing negligible to a significant amount of salinity. This process can be particularly useful for concentrator operations whose only available source of water is sea water or brackish ground water. In other embodiments, the sulfoxy reagent is introduced not only after aeration but additionally in a grinding circuit, particularly the secondary grinding circuit. 
     Referring to  FIG. 1 , a valuable metal-containing feed material  100  can be any suitable copper- and/or molybdenum containing material, particularly mined ore, tailings, concentrate, or other residue of a metal recovery process. The feed material  100  includes not only one or more copper and/or molybdenum sulfide minerals but also one or more other sulfide minerals (particularly sulfidic gangue minerals) to be separated from the valuable metal sulfide mineral(s)). Typically, the feed material  100  is polymetallic, with some or all of the metals being present as a sulfide. A common feed material  100  includes copper in the form of one or more of chalcopyrite, chalcocite, bornite, covellite, tennantite, enargite, and tetrahedrite and/or molybdenum in the form of molybdenite as the valuable metal sulfide mineral and an iron sulfide mineral that is one or more of pyrite, marcasite, arsenopyrite, and pyrrhotite, as a sulfidic gangue mineral. Gold or silver is typically present. In many applications, iron sulfide is the primary (e.g., more than 50% of the) sulfidic gangue mineral in the feed material  100 . 
     In step  104 , the material  100  is slurried and comminuted in an open or closed milling circuit. The comminuted feed material  108  is forwarded to an aeration step  112  prior to the sulfoxy reagent addition step  114 . 
     The water used in forming the slurry of the material  100  can be fresh water, brackish groundwater, saltwater, or any mixture thereof. The process is surprisingly effective in floating valuable metal sulfide minerals whether or not the water is saline and contains dissolved solids or is fresh water. In one process configuration, for example, the water has a salinity of about 0.1 parts per thousand (0.01%) or more. 
     The optimum liberation size of the material  100  depends on ore type, an understanding of the ore liberation and solution chemistry of the ore, and power and media costs. 
     The comminuted feed material  108  is in the form of a slurry, preferably having a feed pulp density ranging from about 20 to about 45 wt. %. 
     The comminuted feed material  108  is subjected to aeration in step  112  in a suitable vessel to form an aerated feed material  132 . Aeration is typically performed by sparging, under agitation, an oxidizing gas, preferably a molecular oxygen-containing gas (such as air, substantially pure molecular oxygen, and molecular oxygen-enriched air) through the feed material  108 . The oxidizing gas preferably includes at least about 20 vol. % molecular oxygen. Aeration is performed for a time sufficient to allow a thin layer of surface oxidation to form on the surface of the copper and/or molybdenum sulfide minerals  108 . The residence time required to produce the desired oxidized film ranges preferably from about 15 to about 120 minutes and more preferably from about 30 to about 60 minutes. In most applications, the pH is not adjusted during aeration or any steps subsequent to aeration. 
     While not wishing to be bound by any theory, the thin layer of surface oxidation on the copper and/or molybdenum sulfide minerals allows better collector adsorption by the mineral. This is surprising to one of ordinary skill in the art, who would believe that aeration leads to oxidation of the copper and molybdenum sulfide minerals causing reduced floatability and reduced stability of the sulfoxy compound. 
     In step  114 , the sulfoxy reagent  118  is added to the aerated feed material  132  to form a treated feed material  122 . Sulfoxy reagent  118  can be added in any suitable manner. Unlike conventional processes, the sulfoxy reagent  118  is added while the aerated feed material  132  is oxygenated. In other words, dissolved molecular oxygen is not removed from the comminuted feed material prior to sulfoxy reagent  118  addition. The dissolved molecular oxygen level in the aerated feed material  132  during conditioning is preferably at least about 3 ppm, more preferably at least about 5 ppm, and even more preferably at least about 10 ppm. 
     The sulfoxy reagent  118  can be any sulfoxy compound, such as an ammonium, hydrogen, alkali metal, or alkaline earth metal sulfite, bisulfite, metabisulfite, sulfide, polysulfide, thiosulfate, polythionate, or bisulfide, sulfur dioxide, and mixtures and derivatives thereof. The preferred sulfoxy reagent  118  is one or more of an ammonium, hydrogen; alkali metal, or alkaline earth metal sulfite, bisulfite, or metabisulfite, and/or sulfur dioxide, with an ammonium, hydrogen, alkali metal, or alkaline earth metal metabisulfite being even more preferred. While not wishing to be bound by any theory, the sulfoxy reagent  118  is believed to act as a depressant of other sulfide minerals (e.g., iron sulfide gangue minerals, particularly pyrite). As will be appreciated by one of ordinary skill in the art, sulfite ion can be added or formed in situ by a suitable chemical reaction between sulfite ion precursors. 
     There are a number of different process configurations for sulfoxy reagent  118  addition. In one process configuration, a portion of the sulfoxy reagent  118  is added in one stage, optionally during grinding, with additional amounts being added after aeration and before each of the cleaning, recleaning or scavenging flotation stages. In another process configuration, the majority of the sulfoxy reagent  118  is added in one or more stages after aeration, with additional smaller amounts being optionally added before each of the cleaning, recleaning or scavenging flotation stages. In another process configuration, no sulfoxy reagent  118  is added during any grinding stage but only after aeration. The typical cumulative sulfoxy reagent  118  addition rate, for all addition points, is at least about 50 g/t, more typically at least about 100 g/t, more typically more than 200 g/t, and even more typically from more than 200 g/t to about 1,000 g/t. 
     While not wishing to be bound by any theory, it is believed that the sulfoxy reagent and oxidizing gas act synergistically to enhance substantially separation selectively and effectiveness, particularly in highly buffering and/or saline waters. While aeration is believed to oxidize sulfide mineral surfaces, which increases floatability of the valuable metal sulfide mineral, the addition of sulfoxy reagent after aeration is believed to control optimally the depression of the other sulfide mineral to be removed as tailings. The increase in floatability, for example, of copper sulfide minerals with aeration while depressing pyrite with the sulfoxy reagent can allow a much improved flotation selectivity than is possible in the absence of aeration. This synergistic effect is best realized when aeration and sulfoxy reagent addition occur sequentially, with aeration preceding sulfoxy reagent addition. 
     In step  116 , the treated feed material  122  is conditioned to form an aerated and conditioned feed material  134 . Conditioning is performed in a suitable vessel, or pulp conditioning tank, prior to flotation. In flotation, the amount of agitation and consequent dispersion during conditioning are closely associated with the time required for physical and chemical reactions to take place. 
     A number of reagents can be added during conditioning, including a collector  120 , a frother  124 , and other reagents  128 . Any suitable collector  120  and frother  124  may be employed. Other reagents  128  include activators, depressants (such as a carbon depressant to depress the flotation of carbonaceous and/or graphitic material), clay dispersants, modifiers, lime (in limited situations as a low cost dispersant or viscosity modifier as examples), and reagents to control electro potential (Eh) and/or pH. Depending on the type of agitation during conditioning, the level of oxygenation may increase. For a downflow agitator, additional molecular oxygen will likely be entrained in the slurry. Conditioning typically occurs for a period between about 0.5 to about 60 minutes and even more typically between about 2 to about 30 minutes. 
     The aerated and conditioned feed material  134  is floated in step  136 , preferably in the presence of sparged air, to form a concentrate fraction  144  commonly containing about 25% or more, more commonly about 40% or more, and even more commonly more than about 50% of the valuable metal sulfide minerals and a tailings fraction  140  commonly containing about 25% or more, more commonly about 40% or more, and even more commonly more than about 50% of the sulfide mineral(s) to be removed as tailings. In the flotation circuit, the aerated and conditioned feed material  134  is floated in a bank, or series, of flotation machines. The flotation machines can be aerated flotation cells. 
     Flotation may include one or more stages, depending on the application. The number and configuration of roughing, scavenging, and cleaning stages are determined based on criteria known to those skilled in the art. 
     The selection of the collector  120 , frother  124 , and other reagents  128  for a specific feed material as well as the pulp density, addition rates of the reagents, order of reagent addition, rate of air addition during flotation, Eh, and other flotation conditions and parameters are also well known to those of ordinary skill in the art. 
     In one process configuration, the comminution step  104 , aeration step  112 , conditioning step  116 , and flotation step  136  are performed in the substantial or complete absence of pH adjustment by an acid or base (e.g., in the absence of acid or base (e.g., lime, soda ash, and/or caustic soda) addition). In other words, the steps are performed at natural pH, which, for many ores and makeup water, is an alkaline pH of no more than about pH 11, more typically a pH of less than pH 8.5, more typically a pH of no more than about pH 8, and even more typically a pH ranging from about pH 3 to about pH 8. The Eh will typically be greater than about 5 mV and less than about 155 mV and more typically range from about 10 to about 120 mV. 
     In one process configuration, the comminution step  104 , aeration step  112 , conditioning step  116 , and flotation step  136  are performed in the substantial or complete absence of dissolved molecular oxygen reduction by sparging the slurried feed material with a non-oxidizing gas. The non-oxidizing gas has little, if any, oxidant content and is primarily, if not entirely, an inert gas (e.g., nitrogen and argon), a reducing gas (e.g., a reducing gas other than sulfur dioxide such as carbon dioxide, carbon monoxide, methane, ethane, and/or propane), or a mixture thereof. In one process configuration, the added sulfoxy reagent  118  is substantially free of sulfur dioxide gas. By eliminating sparging by the non-oxidizing gas, a relatively high level of dissolved molecular oxygen can be maintained in the slurry before and after aeration. 
     Another process configuration will now be discussed with reference to  FIGS. 2A-B . In this example, the valuable metal sulfide mineral is a copper sulfide and the other sulfide mineral (or sulfidic gangue mineral) is one or more of pyrite, marcasite, pyrrhotite, and arsenopyrite. 
     The valuable metal-containing feed material  100  is comminuted in step  104  to form a comminuted feed material  108 . 
     The comminuted feed material  108  is conditioned in step  116  to form a conditioned feed material  132 . The reagents added during conditioning are the collector  120 , frother  124 , and other reagents  128 . No sulfoxy reagent  118  is added. 
     The conditioned feed material  132  is subjected to rougher flotation in step  200  to form rougher tailings  204  and rougher concentrate  208 . While most of the valuable metal sulfide minerals remain in the rougher concentrate  208 , the rougher tailings  204  contain a significant portion of the sulfide gangue minerals. As can be seen from  FIG. 2A , no sulfoxy reagent  118  has been added prior to rougher flotation. 
     In step  228 , the rougher and scavenger concentrate  208  and  220 , respectively, are combined, pulp density adjusted, and recomminuted, in a closed or open comminution circuit, to form a recomminuted concentrate  232 . As will be appreciated, the floated iron sulfide minerals in the concentrate fraction  208  are more difficult to separate and require further comminution for effective liberation to be realized. 
     Sulfoxy reagent  118  may optionally be added during secondary comminution and after aeration. Addition of the sulfoxy reagent in the mill can allow immediate adsorption of the sulfoxy radical on fresh and unoxidized sulfide mineral surfaces. In one configuration, more sulfoxy reagent  118  is added before cleaner flotation than at any other point during the process. 
     In step  212 , the rougher tailings  204  are further conditioned by the addition of collector  120 , and, in step  216 , the conditioned rougher tailings are subjected to scavenger flotation  216  to produce a scavenger concentrate  220  and scavenger tailings  224 . Slower floating copper sulfide minerals are floated during scavenger flotation. The scavenger concentrate  220  is combined with the rougher concentrate  208  and subjected to secondary comminution. 
     Following secondary comminution step  228 , the recomminuted concentrate  232  is subjected, in step  112 , to aeration to form an aerated concentrate  236 . 
     In optional step  114 , sulfoxy reagent  118  is added to form a treated rougher concentrate  238 . 
     In step  116 , the aerated or treated rougher concentrate  236  (as appropriate) is conditioned to form a conditioned concentrate  240 . Reagents added during conditioning are the collector  120 , frother  124 , and other reagents  128 . Typically, aeration, sulfoxy reagent addition, and conditioning occur in different vessels, and the dissolved molecular oxygen after aeration is not, prior to sulfoxy reagent addition, reduced by introduction of a non-oxidizing gas. 
     In step  248 , the conditioned concentrate  240  is subjected to cleaner flotation to form cleaner tailings  252  and cleaner concentrate  250 . While most of the valuable metal sulfide minerals in the conditioned concentrate  240  remain in the cleaner concentrate  250 , the cleaner tailings  252  contain a portion of the valuable sulfide minerals in the conditioned concentrate  240 . The cleaner tailings contain a significant amount of the gangue sulfide minerals. 
     In optional step  114 , sulfoxy reagent  118  is added to the cleaner tailings to form a treated cleaner tailings  262 . 
     In step  256 , the cleaner tailings  252  or treated cleaner tailings  262  (as the case may be) are conditioned by addition of collector  120  to form conditioned cleaner tailings  260 . The conditioned cleaner tailings  260  are subjected to cleaner scavenger flotation in step  264  to form cleaner scavenger tailings  268  and concentrate  272 . While most of the valuable metal sulfide minerals in the cleaner tailings  252  remain in the cleaner scavenger concentrate  272 , the cleaner scavenger tailings  268  contain a significant portion of the sulfide gangue minerals in the cleaner tailings  252 . The cleaner scavenger concentrate  272  is returned to the secondary comminution step  228 . 
     Returning to the cleaner concentrate  250 , sulfoxy reagent  118  is, in step  114 , optionally added to the cleaner concentrate to form a treated cleaner concentrate  252 . 
     The cleaner concentrate  250  or treated cleaner concentrate  252  (as appropriate) is conditioned in step  274  to form a conditioned cleaner concentrate  276 . During conditioning, collector  120  is added. 
     The conditioned cleaner concentrate  276 , in step  278 , is subjected to first recleaner flotation to form first recleaner tailings  282  and first recleaner concentrate  280 . The first recleaner tailings  282  are returned to the secondary comminution step  228 . 
     In optional step  114 , sulfoxy reagent  118  is added to the first recleaner concentrate  280  to form a treated recleaner concentrate  281 . 
     The first recleaner concentrate  280  or treated recleaner concentrate  281  (as the case may be) is conditioned, in step  284 , to form a conditioned first recleaner concentrate  286 . During conditioning, the first recleaner concentrate  280  collector  120  is added. 
     In step  288 , the conditioned first recleaner concentrate  286  is subjected to second recleaner flotation  288  to form second recleaner tailings  290 , which includes preferably at least most and more preferably about 70% or more of the sulfidic gangue minerals in the valuable metal-containing feed material  100 , and second recleaner concentrate  292 , which includes preferably at least most and more preferably about 70% or more of the valuable metal sulfide minerals in the valuable metal-containing feed material  100 . 
     In the above process, cleaner flotation, cleaner scavenger, and first and second recleaner flotation steps  244 ,  264 ,  278 , and  288 , respectively, are performed at natural pH and ambient temperature. 
     In the above process, it may be desirable to perform an additional aeration step preceding one or more of the sulfoxy reagent addition steps performed downstream of rougher flotation. Whether or not an additional aeration step is performed depends on the oxidation potential of the slurry before further sulfoxy reagent and collector addition. Prior conditioning, aerating, and floating steps will introduce additional dissolved molecular oxygen into the various slurry streams. 
     As will be appreciated, other process configurations may be employed depending on the feed material type and mineralogy. 
     EXPERIMENTAL 
     The following examples are provided to illustrate certain embodiments of the invention and are not to be construed as limitations on the invention, as set forth in the appended claims. All parts and percentages are by weight unless otherwise specified. 
     Example 1 
     Conventional Flotation Methods 
     This example demonstrates the effect that the composition of water employed in the flotation pulp has on the recovery of copper, when various reagents are used to depress pyrite and concentrate copper. As shown in Table 1, the salt water employed has considerably higher total dissolved solids content and conductivity than the tap water. 
     
       
         
               
             
               
               
               
               
               
             
               
               
               
               
               
             
           
               
                 TABLE 1 
               
             
             
               
                   
               
               
                 Composition of Tap and Highly Buffered Site Water 
               
             
          
           
               
                   
                 Parameter 
                 Units 
                 Tap Water 
                 Salt Water 
               
               
                   
                   
               
             
          
           
               
                   
                 pH 
                 pH 
                 7.81 
                 8.48 
               
               
                   
                 Conductivity 
                 μS/cm 
                 0.96 
                 5360 
               
               
                   
                 TDS 
                 mg/L 
                 405 
                 40225 
               
               
                   
                 Sodium 
                 mg/L 
                 191 
                 12060 
               
               
                   
                 Potassium 
                 mg/L 
                 9.3 
                 414 
               
               
                   
                 Calcium 
                 mg/L 
                 332 
                 426 
               
               
                   
                 Magnesium 
                 mg/L 
                 10.4 
                 1297 
               
               
                   
                 Iron 
                 mg/L 
                 0.17 
                 &lt;0.10 
               
               
                   
                 Chloride 
                 mg/L 
                 199 
                 20738 
               
               
                   
                 Bicarbonate 
                 mg/L 
                 120 
                 70 
               
               
                   
                 Sulfate 
                 mg/L 
                 NIL 
                 2890 
               
               
                   
                   
               
             
          
         
       
     
       FIG. 3  is a simplified flow diagram of the kinetics tests conducted in this example. The flow diagram includes comminuted feed material conditioning  300  to form a conditioned feed material  304 , rougher flotation  308  of the conditioned feed material  304  (using five flotation machines) to form rougher tailings  312  and rougher concentrate  316 , secondary comminution  320  of the rougher concentrate  316  to form recomminuted rougher tailings  324 , first cleaner flotation  328  of the recomminuted rougher tailings  324  to form a first cleaner concentrate  332  and first cleaner tailings  336 , second cleaner flotation  344  of the first cleaner concentrate  332  to form second cleaner concentrates  1 , 2   348  and second cleaner tailings  352 , and cleaner scavenger flotation  340  of the first cleaner tailings  336  to form a cleaner scavenger concentrate  356  and cleaner scavenger tailings  360 . 
     The five rougher stages for the kinetics tests described below were performed in a similar manner using two water sources: tap water, and water with a high degree of Total Dissolve Solids (TDS) (Salt Water). All tests were carried out on ore ground to P 80  212 microns for the rougher stages and reground to P 80  20-25 microns for the cleaner scavenger. Other than reagent addition, the tests were carried out using the same conditions. 
     The effect of different reagent additions on sulfide depression and the associated copper grade/recovery was investigated. The reagents employed were none, lime, lime and sodium cyanide, and lime cyanide and Potassium Amyl Xanthate (“PAX”). 
     The composition of the feed (ore) material employed in all the tests is shown in Table 2. The initial feed pulp density was 34%. The experimental conditions are shown below in Table 3. 
     
       
         
               
             
               
               
               
               
             
               
               
               
               
             
           
               
                 TABLE 2 
               
             
             
               
                   
               
               
                 Feed ore employed in flotation tests with tap and salt water 
               
             
          
           
               
                   
                 Parameter 
                 Unit 
                 Assay 
               
               
                   
                   
               
             
          
           
               
                   
                 Copper 
                 % 
                 0.478 
               
               
                   
                 Iron 
                 % 
                 3.66 
               
               
                   
                 Gold 
                 g/t 
                 0.28 
               
               
                   
                 Total Sulfur 
                 % 
                 4.34 
               
               
                   
                 Sulfide Sulfur 
                 % 
                 1.84 
               
               
                   
                   
               
             
          
         
       
     
     
       
         
               
             
               
               
               
               
               
             
               
               
               
               
               
               
               
               
               
               
             
               
               
               
               
               
               
               
               
               
               
               
               
             
               
             
               
               
               
               
               
               
               
               
               
               
               
               
             
               
             
               
               
               
               
               
               
               
               
               
               
               
               
             
           
               
                 TABLE 3 
               
             
             
               
                   
               
               
                 Reagent addition and operating conditions for flotation tests performed with tap and salt water 
               
             
          
           
               
                   
                   
                   
                 Reagent Addition 
                 Float 
               
             
          
           
               
                   
                 pH 
                 Eh mV 
                 A3894 
                 MX950 
                 PAX 
                 NACN 
                 MIBC 
                 Lime 
                 time 
               
             
          
           
               
                 Test Description 
                 rougher 
                 cleaner 
                 rougher 
                 cleaner 
                 (g/t) 
                 (g/t) 
                 (g/t) 
                 (g/t) 
                 drops 
                 (g/t) 
                 (min) 
               
               
                   
               
             
          
           
               
                 Tap Water 
               
             
          
           
               
                 Baseline 
                 7.3 
                 7.2 
                 98 
                 121 
                 9 
                 37 
                   
                 0 
                 16 
                 0 
                 30.5 
               
               
                 Baseline with lime 
                 7.35 
                 10.2 
                 119 
                 −4 
                 9 
                 37 
                   
                 0 
                 7 
                 295 
                 30.5 
               
               
                 Baseline with lime and cyanide 
                 7.4 
                 10.2 
                 127 
                 −27 
                 9 
                 37 
                   
                 20 
                 11 
                 205 
                 30.5 
               
               
                 Baseline with lime, cyanide and PAX 
                 7.5 
                 10.2 
                 105 
                 −27 
                 21 
                   
                 46 
                 20 
                 10 
                 220 
                 30.5 
               
             
          
           
               
                 Salt Water 
               
             
          
           
               
                 Baseline 
                 7.1 
                 7 
                 154 
                 125 
                 9 
                 37 
                   
                 0 
                 16 
                 0 
                 30.5 
               
               
                 Baseline with lime 
                 7.2 
                 10.2 
                 126 
                 7 
                 9 
                 37 
                   
                 0 
                 16 
                 2480 
                 30.5 
               
               
                 Baseline with lime and cyanide 
                 7.4 
                 10.2 
                 96 
                 −21 
                 9 
                 37 
                   
                 20 
                 11 
                 1500 
                 30.5 
               
               
                 Baseline with lime, cyanide and PAX 
                 7.4 
                 10.0* 
                 108 
                 −16 
                 21 
                   
                 46 
                 20 
                 12 
                 1820 
                 30.5 
               
               
                   
               
             
          
         
       
     
       FIGS. 5 and 6  above show the grade recovery curves for the four reagent schemes for tap water and salt water, respectively. For all of the reagent schemes tested, the grade recovery curves for low TDS tap water were better than those achieved with salt water. Tap water with Lime Cyanide and PAX has the best grade recovery curve. Compared to tap water, conventional techniques employed for pyrite depression do not perform as well in salt water. 
     Example 2 
     Aeration/Sulfoxy Reagent Methods 
     Additional tests were conducted using a similar flotation circuit as employed in example 1 with the exception of the addition of 300 g/t before the first stage of cleaner flotation and an additional 300 g/t metabisulfite (MBS) (the sulfoxy reagent) during the secondary grind. In other words and as shown in Table 4 below, a total of 600 g/t MBS has been added in the flotation circuit. 
     The flotation circuit is shown in the flow chart of  FIG. 4 . The flow chart includes conditioning  400  of the comminuted feed material  108  to form conditioned feed material  404 , rougher flotation  408  (using five flotation machines or stages) to form rougher concentrate and tailings fractions  412  and  416 , respectively, secondary comminution  420  of the rougher concentrate  412 , in the presence of sulfoxy reagent  118 , to form a recomminuted rougher concentrate  412 , aeration  112  of the recomminuted rougher concentrate  412  (for 0 (which means no aeration was performed) or 30 minutes) to form aerated recomminuted rougher concentrate  428 , sulfoxy reagent  118  addition prior to cleaner flotation  432 , and cleaner flotation  432  of the aerated recomminuted rougher concentrate  428  to form cleaner concentrate  1 - 6  and cleaner tailings  436  and  440 , respectively. 
     Again, the same two types of water where employed: tap water and salt water with a high degree of TDS (Salt Water). All tests were carried out on feed (ore) material ground to P 80  212 microns for the five rougher stages and reground to P 80  20-25 microns for the cleaner scavenger. Other than reagent addition, the tests were carried out using the same conditions. The initial feed pulp density was about 34%, and the feed (ore) material was the same as that employed in example 1. The experimental conditions are shown below in Table 4. The tests were carried out with and without a 30-minute aeration step after the secondary comminution step, or secondary grind, and prior to the cleaning flotation circuit. The effect of the aeration before MBS addition on sulfide depression and copper grade/recovery was investigated. For reference, the grade recovery curve with lime cyanide and PAX is shown. 
     
       
         
               
             
               
               
               
             
               
               
               
               
               
               
               
               
               
             
               
               
               
               
               
               
               
               
               
               
               
             
               
             
               
               
               
               
               
               
               
               
               
               
               
             
               
             
               
               
               
               
               
               
               
               
               
               
               
             
           
               
                 TABLE 4 
               
             
             
               
                   
               
               
                 Reagent addition and operating conditions for flotation tests performed with 
               
               
                 tap and salt water 
               
             
          
           
               
                   
                 Reagent Addition 
                 Float 
               
             
          
           
               
                   
                 pH 
                 Eh mV 
                 A3894 
                 MX950 
                 MBS 
                 MIBC 
                 Lime 
                 time 
               
             
          
           
               
                 Test Description 
                 rougher 
                 cleaner 
                 rougher 
                 cleaner 
                 (g/t) 
                 (g/t) 
                 (g/t) 
                 drops 
                 (g/t) 
                 (min) 
               
               
                   
               
             
          
           
               
                 Site Water 
               
             
          
           
               
                 MBS with aeration 
                 7.4 
                 5.6 
                 P115 
                 85 
                 9 
                 37 
                 600 
                 13 
                 0 
                 30.5 
               
               
                 MBS with no aeration 
                 7.4 
                 4.8 
                 91 
                 95 
                 9 
                 37 
                 600 
                 12 
                 0 
                 30.5 
               
             
          
           
               
                 Salt Water 
               
             
          
           
               
                 MBS with aeration 
                 7.5 
                 5.2 
                 101 
                 94 
                 9 
                 37 
                 600 
                 12 
                 0 
                 30.5 
               
               
                 MBS with no aeration 
                 7.5 
                 4.9 
                 103 
                 90 
                 9 
                 37 
                 600 
                 14 
                 0 
                 31.5 
               
               
                   
               
             
          
         
       
     
     As can be observed from the grade recovery curves of  FIGS. 7-8 , the use of MBS improves the copper grade recovery curves in both water types. The effect is most pronounced in salt water. However, it is not until aeration is employed that the grade recovery achieved in salt water begins to approximate that observed in the tap water. A graph more clearly comparing the copper grade recovery, with and without aeration, is shown in  FIG. 9 . In salt water, MBS addition improves the copper recovery from 50% to 75% at the same copper grade of 32%. 
     Example 3 
     Aeration/Sulfoxy Reagent Methods 
     Additional tests were conducted using the same flotation circuit of  FIG. 4  as employed in example 2, with the exception that brackish site water was employed. Analysis of the site water is shown in Table 5. The tests were carried out, with and without, a 30-minute aeration step after the secondary grind and prior to the cleaning flotation circuit. The effect of the aeration, after MBS addition, on sulfide depression and copper grade/recovery was investigated. For reference the grade recovery curve with tap water is shown in  FIG. 10 . 
     
       
         
               
             
               
               
               
               
             
               
               
               
               
             
           
               
                 TABLE 5 
               
             
             
               
                   
               
               
                 Composition of Tap and Highly Buffered Site Water 
               
             
          
           
               
                   
                 Parameter 
                 Units 
                 Site Water 
               
               
                   
                   
               
             
          
           
               
                   
                 pH 
                 pH 
                 7.02 
               
               
                   
                 Conductivity 
                 μS/cm 
                 10.38 
               
               
                   
                 TDS 
                 mg/L 
                 7515 
               
               
                   
                 Sodium 
                 mg/L 
                 1940 
               
               
                   
                 Potassium 
                 mg/L 
                 11.2 
               
               
                   
                 Calcium 
                 mg/L 
                 620 
               
               
                   
                 Magnesium 
                 mg/L 
                 84.5 
               
               
                   
                 Iron 
                 mg/L 
                 &lt;0.10 
               
               
                   
                 Chloride 
                 mg/L 
                 2535 
               
               
                   
                 Bicarbonate 
                 mg/L 
                 30 
               
               
                   
                 Sulfate 
                 mg/L 
                 1198 
               
               
                   
                   
               
             
          
         
       
     
     Example 4 
     Locked Cycle Testing 
     Locked cycle tests were performed using differing ore types and a saline and buffered site water to compare flotation performed using sulfoxy reagent addition with that performed using cyanide as a depressant in the absence of aeration and sulfoxy reagent addition. The various ores were copper sulfide ores containing substantial levels of iron sulfides. Actual locked cycle tests using site water are generally deemed to provide more valuable information than open cleaner tests. A summary of the locked cycle tests is presented in Tables 6-7: 
     
       
         
               
             
               
               
               
               
               
               
               
             
               
               
               
               
               
               
               
             
           
               
                 TABLE 6 
               
             
             
               
                   
               
               
                 Locked cycle test results for the drop weight samples using 
               
               
                 the cyanide as a depressant and site water 
               
             
          
           
               
                   
                   
                 % of 
                 Head 
                   
                   
                   
               
               
                 Comp 
                   
                 ore 
                 grade 
                 Conc 
                 Mass 
                 Recovery 
               
               
                 No 
                   
                 deposit 
                 Cu, % 
                 Grade Cu, % 
                 Pull 
                 Cu, % 
               
               
                   
               
             
          
           
               
                 1 
                   
                 5.0 
                 0.59 
                 28.3 
                 1.9 
                 91.7 
               
               
                 2 
                   
                 2.0 
                 0.42 
                 28.2 
                 1.08 
                 72.2 
               
               
                 3 
                   
                 5.0 
                 0.61 
                 32.9 
                 1.51 
                 80.9 
               
               
                 4 
                   
                 3.0 
                 0.51 
                 31.3 
                 1.41 
                 86.1 
               
               
                 5 
                   
                 3.0 
                 0.69 
                 30.5 
                 1.88 
                 83.6 
               
               
                 6 
                   
                 4.0 
                 0.43 
                 33.3 
                 1.14 
                 88.5 
               
               
                 7 
                   
                 6.0 
                 0.36 
                 25.4 
                 1.1 
                 78 
               
               
                 8 
                   
                 5.0 
                 0.67 
                 29.8 
                 2.01 
                 89.5 
               
               
                 9 
                   
                 7.0 
                 0.60 
                 34 
                 1.59 
                 89.9 
               
               
                 10 
                   
                 9.0 
                 0.61 
                 32.2 
                 1.7 
                 90.1 
               
               
                 11 
                   
                 4.0 
                 0.56 
                 29.8 
                 1.66 
                 87.5 
               
               
                 12 
                   
                 11.0 
                 0.51 
                 32.9 
                 1.37 
                 88.8 
               
               
                 13 
                   
                 5.0 
                 0.56 
                 26.7 
                 1.64 
                 81 
               
               
                 14 
                   
                 1.0 
                 0.64 
                 31 
                 1.73 
                 84.5 
               
               
                 15 
                   
                 8.0 
                 0.52 
                 28.7 
                 1.42 
                 78.5 
               
               
                 16 
                   
                 4.0 
                 0.53 
                 30.7 
                 1.49 
                 87.1 
               
               
                   
                 Weighted 
                   
                 0.55 
                 30.59 
                 1.53 
                 85.7 
               
               
                   
                 average 
               
               
                   
               
             
          
         
       
     
     
       
         
               
             
               
               
               
               
               
               
               
             
               
               
               
               
               
               
               
             
           
               
                 TABLE 7 
               
             
             
               
                   
               
               
                 Locked cycle test results for the drop weight samples using the 
               
               
                 Aeration/Metabisulfite Process and site water 
               
             
          
           
               
                   
                   
                 % 
                 Head 
                   
                   
                   
               
               
                 Comp 
                   
                 of ore 
                 grade 
                 Conc 
                 Mass 
                 Recovery 
               
               
                 No 
                   
                 deposit 
                 Cu, % 
                 Grade Cu, % 
                 Pull 
                 Cu, % 
               
               
                   
               
             
          
           
               
                 1 
                   
                 5.0 
                 0.6 
                 33.7 
                 1.66 
                 93.6 
               
               
                 2 
                   
                 2.0 
                 0.44 
                 33.6 
                 1.2 
                 92.1 
               
               
                 3 
                   
                 5.0 
                 0.63 
                 36.6 
                 1.66 
                 92.2 
               
               
                 4 
                   
                 3.0 
                 0.51 
                 34.4 
                 1.38 
                 93.3 
               
               
                 5 
                   
                 3.0 
                 0.7 
                 34 
                 1.98 
                 93.8 
               
               
                 6 
                   
                 4.0 
                 0.44 
                 34.7 
                 1.09 
                 91.3 
               
               
                 7 
                   
                 6.0 
                 0.41 
                 29 
                 1.32 
                 92.6 
               
               
                 8 
                   
                 5.0 
                 0.75 
                 37.6 
                 1.09 
                 87.6 
               
               
                 9 
                   
                 7.0 
                 0.60 
                 37.4 
                 1.49 
                 91 
               
               
                 10 
                   
                 9.0 
                 0.57 
                 33.3 
                 1.65 
                 90.4 
               
               
                 11 
                   
                 4.0 
                 0.6 
                 34.7 
                 1.58 
                 91.7 
               
               
                 12 
                   
                 11.0 
                 0.48 
                 33.2 
                 1.44 
                 92.4 
               
               
                 13 
                   
                 5.0 
                 0.56 
                 24.8 
                 2.11 
                 90.6 
               
               
                 14 
                   
                 1.0 
                 0.6 
                 33.7 
                 1.78 
                 93.5 
               
               
                 15 
                   
                 8.0 
                 0.51 
                 32 
                 1.43 
                 90.3 
               
               
                 16 
                   
                 4.0 
                 0.53 
                 36.8 
                 1.3 
                 90.1 
               
               
                   
                 Weighted 
                   
                 0.55 
                 33.55 
                 1.50 
                 91.42 
               
               
                   
                 average 
               
               
                   
               
             
          
         
       
     
     Both Tables 6-7 show that flotation with aeration followed by ammonium metabisulfite addition yielded significantly better results than flotation using cyanide as an iron sulfide depressant. On average, copper recovery was about 6% higher with about a 3% higher copper concentrate grade for flotation performed with aeration followed by ammonium metabisulfite addition. 
     A number of variations and modifications of the invention can be used. It would be possible to provide for some features of the invention without providing others. 
     For example, the sulfoxy reagent has different modes of operation depending on the mineralogies and slurry conditions (e.g., Eh and pH) involved. Sulfoxy reagent, for example, can act as a depressant and/or activator for the same sulfide mineral under differing slurry conditions or as a depressant for one sulfide mineral and/or activator for a different sulfide mineral under a common set of conditions. For example, under one set of conditions, the sulfoxy reagent activates flotation of copper, lead, and zinc sulfides and under a different set of conditions activates flotation only of copper sulfides and not lead and zinc sulfides. In another example, the sulfoxy reagent depresses flotation of zinc sulfide but not lead sulfide. 
     In other examples, the concentrate and tailings can each include different valuable metal sulfide minerals. The valuable metal in the tailings can later be isolated from any gangue sulfide minerals by subsequent flotation stages. Examples of base metal mixed sulfide ores amenable to the process discussed herein include copper-gold (e.g., as calayerite (AuTe2) or sylvanite (Au,Ag)Te2)), copper-gold-silver (e.g., as acanthite (Ag2S), sylvanite (Au,Ag)Te2), pyrargyrite (Ag3SbS3), and proustite (Ag3AsS3)), lead (e.g., as galena (PbS), altaite (PbTe), bournonite (PbCuSbS3), jamesonite (Pb4FeSb6S14), and cylindrite (Pb3Sn4FeSb2S14))-zinc (e.g., as sphalerite (ZnS))-copper, copper-zinc, and copper-molybdenum. Massive sulfide ores, for instance, usually contain sulfides of three or more valuable metals as well as gangue sulfide minerals, such as pyrite. 
     The present invention, in various embodiments, configurations, or aspects, includes components, methods, processes, systems and/or apparatus substantially as depicted and described herein, including various embodiments, configurations, aspects, subcombinations, and subsets thereof. Those of skill in the art will understand how to make and use the present invention after understanding the present disclosure. The present invention, in various embodiments, configurations, and aspects, includes providing devices and processes in the absence of items not depicted and/or described herein or in various embodiments, configurations, or aspects hereof, including in the absence of such items as may have been used in previous devices or processes, e.g., for improving performance, achieving ease and\or reducing cost of implementation. 
     The foregoing discussion of the invention has been presented for purposes of illustration and description. The foregoing is not intended to limit the invention to the form or forms disclosed herein. In the foregoing Detailed Description for example, various features of the invention are grouped together in one or more embodiments, configurations, or aspects for the purpose of streamlining the disclosure. The features of the embodiments, configurations, or aspects of the invention may be combined in alternate embodiments, configurations, or aspects other than those discussed above. This method of disclosure is not to be interpreted as reflecting an intention that the claimed invention requires more features than are expressly recited in each claim. Rather, as the following claims reflect, inventive aspects lie in less than all features of a single foregoing disclosed embodiment, configuration, or aspect. Thus, the following claims are hereby incorporated into this Detailed Description, with each claim standing on its own as a separate preferred embodiment of the invention. 
     Moreover, though the description of the invention has included description of one or more embodiments, configurations, or aspects and certain variations and modifications, other variations, combinations, and modifications are within the scope of the invention, e.g., as may be within the skill and knowledge of those in the art, after understanding the present disclosure. It is intended to obtain rights which include alternative embodiments, configurations, or aspects to the extent permitted, including alternate, interchangeable and/or equivalent structures, functions, ranges or steps to those claimed, whether or not such alternate, interchangeable and/or equivalent structures, functions, ranges or steps are disclosed herein, and without intending to publicly dedicate any patentable subject matter.