Processes for removing impurity metals from acidic metal sulfate containing streams

Abstract

A process for removing impurity metal ions from an acidic metal sulfate containing stream by adding an effective amount of a reagent, comprising at least one dialkyldithiophosphate compound with the alkyl chain length of C1 to C8 to the acidic metal sulfate containing stream to form impurity metal ion complexes; and separating the impurity metal ion complexes from the acidic metal sulfate stream.

Description

[0001] PROCESSES FOR REMOVING IMPURITY METALS FROM ACIDIC METAL SULFATE CONTAINING STREAMS

[0002] Field of the Invention

[0003] The technological concept disclosed herein generally relates to purification of industrial process streams. More particularly, the concept disclosed herein relates to removing impurity metal ions, especially cadmium, and also arsenic, lead, mercury, chromium, titanium, and copper, from acidic metal sulfate containing streams.

[0004] Background

[0005] During the hydrometallurgical production of cobalt and nickel metals, certain metal impurities, including cadmium, are often present in the solid feed material (e.g. ore, concentrate, electronic waste (e-waste)). Cobalt and nickel metals are extracted from the solid feed material through leaching, that involves transferring a metal of interest from naturally occurring minerals into an aqueous solution, where cobalt and nickel metals may be first subjected to comminution and then contacted with a sulfuric acid leaching reagent which dissolves the metal, transferring it to an aqueous phase as a metal sulfate. Cobalt and nickel, considered “value metals”, and metal impurities are transferred from the solid feed material to the aqueous phase in varying quantities forming an acidic metal sulfate containing stream. Value metals may be recovered from the aqueous solution as saleable products in subsequent product recovery steps by techniques such as precipitation, electrowinning, or crystallization. Metal impurities that transfer to the product are unacceptable above a certain level, depending on the specific metal product and industry specification. Accordingly, metal impurities such as cadmium have to be reduced prior to product recovery. For example, cadmium levels in cobalt sulfate heptahydrate and nickel sulfate hexahydrate, produced for the lithium ion battery industry, may be < 5 mg / kg and < 1 mg / kg respectively. Nickel power may require cadmium levels < 7 mg / kg. Impurity metal ions in the acidic metal sulfate stream must be reduced with high efficiency and with high selectivity relative to value metals. Multiple impurity ions may be present in the acidic metal sulfate stream, therefore several impurity removal techniques may be required to reduce all impurity metal ions to their target levels prior to product recovery. Suitable impurity ion removal processes must not introduce foreign ions, organic species, temperature changes, or acidity changes incompatible with later impurity removal processes or value metal product recovery steps. Major impurities such as iron, aluminum, manganese and / or copper may be removed by conventional methods used in the industrial refining of cobalt and nickel (Crundwell, F.K., Moats, M.S., Ramachandran, V., Robinson, T.G. Davenport, W.G. (2011) “Extractive Metallurgy of Nickel, Cobalt and Platinum- Group Metals”. Elsevier.). Iron, aluminum, manganese, and / or copper present in the initial acidic metal sulfate leach solution are commonly removed using precipitation in a multistage process by the addition of lime (or an alternative base) and an oxidant such as air, sulfur dioxide or their mixture. Copper may be further reduced using conventional methods such as solvent extraction and / or ion exchange. Minor impurity metal ions, especially cadmium, and also arsenic, lead, mercury, chromium, titanium, and copper may require alternative processing steps to reduce their concentration in the acidic metal sulfate- containing streams.

[0006] Several technologies to remove cadmium from metal-containing sulfate streams have been developed, including precipitation, cementation, solvent extraction, ion exchange, and surface adsorption (Rao, K.S., Mohapatra, M., Anand, S., Venkateswarlu, P. (2010). Review on cadmium removal from aqueous solutions. International Journal of Engineering, Science and Technology. 2(7).

[0007] Proposed cadmium removal techniques involve the precipitation of cadmium hydroxides, carbonates, or sulfides. The precipitation of metal hydroxides and carbonates is complicated by poor selectivity resulting in the co-precipitation of value metals. The precipitation of cadmium sulfide involves the use of hazardous sulfide precipitating agents (Na?S, NaHS, EES). Alternative cadmium precipitation methods were proposed by Rickelton (1998) who found a selective method of removing cadmium from zinc, cobalt and nickel by precipitation as its diisobutyldithiophosphinate complex. Dialkyldithiophinates are synthesized using high-pressure phosphine and may be difficult to manufacture industrially. The patent application DE 4040 474 Al (1990) discloses using dithiophosphorous esters of the formula (R-(OC2H4)x-O)2PS2M where R is C9-C18 alkyl or alkenyl compound, x is an integer from 0 to 6 and M is a cation to remove Zn, Cd, Hg, Cu, Ni or As from crude phosphoric acid or from sulfuric acid (for example, during the treatment of lead-acid batteries). Cadmium is removed using precipitation and flotation in the presence of a foaming agent. While potentially simpler to manufacture than dialkyldithiophosphinates, the use of C9 and higher molecular weight dithiophosphorous esters can result in higher treatment costs due to increased dosage requirements relative to lower molecular weight dithiophosphorous compounds.

[0008] Solvent extraction (liquid-liquid) extraction with dithiophosphorous compounds has also been proposed to extract cadmium from phosphoric acid and sulfuric acid based systems. U.S. Patent No. 4,479,924 (1980) proposes a method of extracting metal ions, including cadmium, from an aqueous solution by contact with a reagent mixture including a water insoluble diester of dithiophosphoric acid, a water-insoluble phosphate, and a diluent. Moreover, cadmium removal by ion exchange has also been described previously in, for example, US Patent No. 7,998,441 (2011) where cadmium is selectively removed from a nickel and / or cobalt solution utilizing a thiourea based ion exchange resin. Solvent extraction may require high capital cost equipment, large volumes of organic extractant, and the addition of chemical reagents (acid / base) to facilitate extraction and stripping. Similarly, ion exchange may require high capital cost equipment as well as high operational cost due to the use of chemicals (acid / base) for resin regeneration.

[0009] Thus, while the various reagents and approaches discussed above may have some merits and applicability in sulfuric acid containing streams, new and improved methods are still needed in industry to remove cadmium from acidic metal sulfate containing streams with high efficiency, low capital costs, and low reagent usage.

[0010] Accordingly, the methods presently available for impurity metal removal from acidic metal sulfate streams in the production process require further and / or continuous improvement. Since many factors (e.g., ore type, temperature, agitation, reactor design, acid chemistry, foreign ions, organic species, and viscosity of the acidic metal sulfate medium) can affect the performance of reagents, it is a great challenge to develop high- efficiency reagents useful for removing impurity metals from acidic metal sulfate streams. Successful reagents for removing impurity metals in industrial process streams such as hydrometallurgical production of cobalt, and nickel metals would be a useful advance in the art and could find rapid acceptance in the industry. Summary

[0011] The forgoing and additional objects are attained in accordance with the principles of the invention wherein the inventors detail the discovery of the performance of reagent composition comprising at least one dialkyldithiophosphate compound with the C1-C8 alkyl chain length and optionally at least one surfactant for the selective precipitation of cadmium from an acidic metal sulfate solution containing cobalt and / or nickel, and therefore makes it possible to remove impurity metal ions, especially cadmium, from acidic metal-containing sulfate streams. An effective amount of the at least one dialkyl dithiophosphate compound with the C1-C8 alkyl chain length and optionally at least one surfactant is added to the acidic metal sulfate stream containing cadmium to form an insoluble cadmium complex.

[0012] Formulating the dialkyldithiophosphate compound, with the alkyl chain length of Cl to C8, with a surfactant reduces the effective amount of dialkyldithiophosphate reagent required for cadmium precipitation.

[0013] Accordingly, in one aspect, the present invention provides processes for removing impurity metal ions from a solution containing acidic metal sulfate, said solution containing cobalt and / or nickel metals, by adding an effective amount of a reagent comprising at least one dialkyldithiophosphate compound, with the alkyl chain length of Cl to C8 to the solution to form impurity metal complexes and separating the impurity metal complexes from the solution.

[0014] In the same or additional embodiments, the process can further comprise adding an effective amount of at least one surfactant to the solution containing acidic metal sulfate.

[0015] In the same or additional embodiments, the process can further comprise adding an effective amount of an adsorbent to the solution containing acidic metal sulfate.

[0016] This summary of the invention does not list all necessary characteristics and, therefore, subcombinations of these characteristics or elements may also constitute an invention. Accordingly, these and other objects, features and advantages of this invention will become apparent from the following detailed description of the various aspects of the invention taken in conjunction with the accompanying Examples. Detailed Description

[0017] The present disclosure generally relates to the purification of solutions in industrial process streams. More particularly, embodiments disclosed herein relate to processes for removing and / or recovering impurity metal ions, especially cadmium, from acidic metal sulfate streams containing cobalt and / or nickel metals by adding an effective amount of at least one dialkyldithiophosphate compound with the alkyl chain length of Cl to C8, and optionally at least one surfactant as reagents to form a impurity metal complex, and separating the complex from the solution. The reagents may be added to the acidic metal sulfate containing solution, preferably following the removal of major iron and copper impurities using conventional techniques, or any point prior to the recovery of cobalt and / or nickel products. Afterwards, the impurity metal complex may be separated from the cobalt and / or nickel containing solution. The methods of separation include but are not limited to filtration, centrifugation, sedimentation, flocculation, adsorption, flotation, phase separation, and combinations thereof. The compositions and processes described herein provide improvement and / or an unexpected advantage when compared to compositions and processes of the prior art.

[0018] As employed throughout the present disclosure, the following terms are provided to assist the reader. Unless otherwise defined, all terms of art, notations and other scientific or industrial terms or terminology used herein are intended to have the meanings commonly understood by those of skill in the chemical and / or hydrometallurgical production arts. In some cases, terms with commonly understood meanings are defined herein for clarity and / or for ready reference, and the inclusion of such definitions herein should not necessarily be construed to represent a substantial difference over the definition of the term as generally understood in the art unless otherwise indicated. As used herein and in the appended claims, the singular forms include plural referents unless the context clearly dictates otherwise. Throughout this specification, the terms retain their definitions.

[0019] As used herein with reference to the present invention, the term “impurity metal” or “impurity” shall refer to any elements of the periodic table requiring a reduced concentration in the value metal product relative to the feed solution and an oxidation state higher than 0, (i.e., impurity metal ions). Such impurity metal ions include, for example, one or more of, cadmium, chromium, arsenic, mercury, titanium, copper and lead. In any or all embodiments, cadmium ions are removed from acidic metal sulfate containing streams. In the same or alternate embodiments, arsenic ions are removed from acidic metal sulfate containing streams.

[0020] The concept of a “major” impurity refers to a metal impurity having a concentration greater than 100 mg / L in the acidic metal sulfate solution. A “minor” impurity refers to a metal impurity having a concentration less than 100 mg / L in the acidic metal sulfate solution.

[0021] The concept of “impurity metal complex” refers to compounds formed by reacting impurity metal ions with chelating agents. Impurity metal complexes can be solid, waxy, or oily in the acidic metal sulfate solutions. They can precipitate, float, or suspend in the acidic metal sulfate solutions.

[0022] Those skilled in the art will understand that reference to “acidic metal sulfate containing streams”, or “acidic metal sulfate solutions,” or “solutions containing metal sulfate,” in the context of the invention includes any acidic solution derived from the leaching of a solid feed material with sulfuric acid. Such metal sulfate containing streams are typically obtained from plant streams of hydrometallurgical production of cobalt, and nickel metals.

[0023] “Effective amount” means the dosage of any reagents on an active basis (such as the compositions comprising at least one dialkyldithiophosphate compound with the alkyl chain length of Cl to C8, and optionally at least one surfactant described herein) necessary to provide the desired performance in the acidic metal sulfate system or circuit being treated (such as the formation of impurity metal complexes) when compared to an untreated control system or system using a reagent product of the prior art.

[0024] As used herein, the term “alkyl” is intended to include linear, branched, or cyclic hydrocarbon structures and combinations thereof. Preferred alkyl groups are those of Cs or below. Lower alkyl refers to alkyl groups of from 1 to 4 carbon atoms. Examples of lower alkyl groups include methyl, ethyl, propyl, isopropyl, butyl, s-and t-butyl and the like. Cycloalkyl is a subset of alkyl and includes cyclic hydrocarbon groups having from 3 to 8 carbon atoms. The term "aryl" as used herein refers to cyclic aromatic hydrocarbons that do not contain heteroatoms in the ring. In any or all embodiments, aryl groups contain about 6 to about 8 carbons in the ring portions of the groups. Thus aryl groups include, but are not limited to phenyl. Aryl groups can be unsubstituted or substituted, as defined herein. Representative substituted aryl groups can be mono-substituted or substituted more than once, such as, but not limited to, 2-, 3-, 4-, 5-, or 6-substituted phenyl, which can be substituted with carbon or non-carbon groups such as those known to persons of skill in the art. Aryl groups of Ce-Cs are preferred.

[0025] The term “alkaryl” as used herein is a broad term and is used in its ordinary sense, including, without limitation, to refer to an aryl having at least one aryl hydrogen atom replaced with an alkyl moiety. The term “aralkyl” as used herein is a broad term and is used in its ordinary sense, including, without limitation, to refer to an alkyl having at least one alkyl hydrogen atom replaced with an aryl moiety, such as benzyl, -(CH2)2phenyl, and the like. Particularly preferred are C? and Cs aralkyl groups.

[0026] The terms “comprised of,” “comprising,” or “comprises” as used herein includes embodiments “consisting essentially of’ or “consisting of’ the listed elements, and the terms “including” or “having” in context of describing the invention should be equated with “comprising”.

[0027] Those skilled in the art will appreciate that while preferred embodiments are discussed in more detail below, multiple embodiments of the reagent system and processes described herein are contemplated as being within the scope of the present invention. Thus, it should be noted that any feature described with respect to one aspect or one embodiment of the invention is interchangeable and / or combinable with another aspect or embodiment of the invention unless otherwise stated. It will also be understood by those skilled in the art that any description of the invention, even though described in relation to a specific embodiment or drawing, is applicable to and interchangeable with other embodiments of the invention.

[0028] Furthermore, for purposes of describing the present invention, where an element, component, or feature is said to be included in and / or selected from a list of recited elements, components, or features, those skilled in the art will appreciate that in the related embodiments of the invention described herein, the element, component, or feature can also be any one of the individual recited elements, components, or features, or can also be selected from a group consisting of any two or more of the explicitly listed elements, components, or features. Additionally, any element, component, or feature recited in such a list may also be omitted from such list.

[0029] Those skilled in the art will further understand that any recitation herein of a numerical range by endpoints includes all numbers subsumed within the recited range (including fractions), whether explicitly recited or not, as well as the endpoints of the range and equivalents. The term “et seq.'' is sometimes used to denote the numbers subsumed within the recited range without explicitly reciting all the numbers, and should be considered a full disclosure of all the numbers in the range. Disclosure of a narrower range or more specific group in addition to a broader range or larger group is not a disclaimer of the broader range or larger group.

[0030] Accordingly, in one aspect, the invention embodies processes for removing impurity metal ions from an acidic metal sulfate containing stream, wherein such processes comprise: adding an effective amount of a reagent, comprising at least one dialkyl dithiophosphate compound with the alkyl chain length of Cl to C8 for forming complexes with impurity metal ions as disclosed and embodied herein, to the acidic metal sulfate containing stream to form impurity metal ion complexes, and separating the impurity metal ion complexes from the acidic metal sulfate containing stream.

[0031] In any or all of the embodiments according to the present invention, the reagent can further comprise an effective amount of at least one surfactant to be added to the solution containing acidic metal sulfate.

[0032] In any of the foregoing or additional embodiments, the impurity metal ions that are complexed by the reagent and removed by separation are selected from the group consisting of titanium, chromium, cadmium, arsenic, mercury, copper, lead, and mixtures of any of the foregoing. In the same or other embodiment, said impurity metal ions are selected from the group consisting of cadmium, copper, arsenic, mercury, lead, and mixtures thereof. In a preferred embodiment, the impurity metal ions comprise cadmium and / or arsenic and / or copper. Preferably, the impurity metal ion is cadmium.

[0033] The dialkyldithiophosphate compounds with the alkyl chain length of Cl to C8, described herein for any or all embodiments, comprise dialkyldithiophosphoric acid with the alkyl chain length of Cl to C8 and any salts (e.g., calcium, magnesium, potassium, sodium, ammonium salt with the formula NR1R2R3RC, where Ri, R2, R3, R4 are, equal to or different from each other, independently chosen from hydrogen, alkyl or aryl groups) of any of the foregoing dialkyldithiophosphoric acid with the alkyl chain length of Cl to C8; and mixtures thereof. In some embodiments, the alkyl chain of the dialkyldithiophosphate compound according to the invention is C4 to C8. Preferably, the alkyl chain of the dialkyldithiophosphate compound according to the invention is a C8 alkyl chain.

[0034] In the same or alternate embodiments, the dialkyldithiophosphate compound is selected from the group consisting of any salts of diisobutyl dithiophosphoric acid, di(l ,3- dimethylbutyl) dithiophosphoric acid, di(2-ethylhexyl) dithiophosphoric acid; and mixtures thereof. In a preferred embodiment, dialkyldithiophosphate compound are salts of di(2-ethylhexyl) dithiophosphoric acid; and mixtures thereof. In a more preferred embodiment, the dialkyldithiophosphate compound is ammonium salt of di(2-ethylhexyl) dithiophosphoric acid. In another more preferred embodiment, the dialkyldithiophosphate compound is sodium salt of di(2-ethylhexyl) dithiophosphoric acid.

[0035] In the same or alternate embodiments, the dialkyldithiophosphate compound is selected from the group consisting of diisobutyl dithiophosphate, di( 1,3 -dimethylbutyl) dithiophosphate, di(2-ethylhexyl) dithiophosphate; and mixtures thereof. In a preferred embodiment, dialkyldithiophosphate compound is di(2-ethylhexyl) dithiophosphate; and mixtures thereof. In a more preferred embodiment, the dialkyldithiophosphate compound is ammonium di(2-ethylhexyl) dithiophosphate. In another more preferred embodiment, the dialkyldithiophosphate compound is sodium di(2-ethylhexyl) dithiophosphate.

[0036] In any or all embodiments the surfactant compound can be selected from the group consisting of sulfosuccinates; aryl sulfonates; alkaryl sulfonates; diphenyl sulfonates; olefin sulfonates; sulfonates of ethoxylated alcohols; petroleum sulfonates; sulfosuccinamates; alkoxylated surfactants; ester / amide surfactants; EO / PO block copolymers (ethylene oxide / propylene oxide); and mixtures thereof. In the same or alternate embodiment, the surfactant can be an alkaryl sulfonates. In a preferred embodiment, the surfactant can be an alkyldiphenyloxide disulfonate. Suitable alkyldiphenyloxide disulfonate compounds include, but are not limited to, DOWFAX® 2 Al, DOWFAX® 3B2, DOWFAX® 8390 available from Dow Chemical.

[0037] In the same or alternate embodiment, the surfactant can be a sulfosuccinate. Suitable sulfosuccinate can be sodium dioctylsulfosuccinate. Suitable sodium dioctylsulfosuccinate compounds include, but are not limited to, AEROSOL® OT-70 available from Syensqo S.A.

[0038] In the same or alternate embodiment, the surfactant can be an alkoxylated surfactant. Suitable alkoxylated surfactants can include, but are not limited to, polyethyleneglycol sorbitan monooleate (such as TWEEN® 80 available from Croda), and polyethyleneglycol sorbitol hexaoleate (such as ATLAS® G1086 available from Croda).

[0039] According to one or more embodiments, the dialkyldithiophosphate compound is in a diluted solution when it is added to an acidic metal sulfate containing stream. For example, the diluted solution may include a percent active (of dialkyldithiophosphate compound) having a lower limit of any of greater than 0, 1, 2, 5, or 10% to an upper limit of any of 10, 12, 15, or 20%. The diluted solution may include water.

[0040] According to one or more embodiments, prior to adding a dialkyldithiophosphate compound to an acidic metal sulfate containing stream for forming impurity metal ion complexes, the dialkyldithiophosphate compound may be diluted. Diluting may include 1% to 20% by weight (wt%) of the dialkyldithiophosphate compound added to water to provide a diluted solution. For example, the diluted solution may include a percent active having a lower limit of any of greater than 0, 1, 2, 5, or 10% to an upper limit of any of 10, 12, 15, or 20%. In other embodiments, diluting includes 10% of the dialkyldithiophosphate compound in the diluted solution. It is also envisioned that the dialkyldithiophosphate compound is diluted inline with its addition to an acidic metal sulfate containing stream.

[0041] In any or all embodiments, the at least one dialkyldithiophosphate compound with the alkyl chain length of Cl to C8, and optionally the at least one surfactant may be added to the metal containing solution, preferably following the removal of major iron and copper impurities using conventional techniques, or any point prior to the recovery of cobalt and / or nickel products.

[0042] In any or all embodiments of the invention, the at least one dialkyldithiophosphate compound with the alkyl chain length of Cl to C8, and optionally the at least one surfactant can be added to acidic metal sulfate containing solution, and / or following iron, aluminum, manganese, and / or copper precipitation steps, and / or following copper ion exchange and / or solvent extraction steps, or any point prior to the recovery of cobalt and / or nickel products to complex the impurity metal ions. Afterwards, impurity metal complexes so formed can be separated from the cobalt and / or nickel containing solution. Separation may be carried out via any suitable method known in the art for such separation. In any or all embodiments, the methods of separation include, but are not limited to, filtration, centrifugation, sedimentation, flocculation, adsorption, flotation, phase separation, and combinations thereof.

[0043] In any of the foregoing or additional embodiments of the process, the process can comprise the step of filtering the acidic metal sulfate containing streams prior to adding the reagent.

[0044] In any or all embodiments of the invention, the at least one dialkyldithiophosphate compound with the alkyl chain length of Cl to C8, and optionally the at least one surfactant can be added to the solution containing acidic metal sulfate all in one stage or added in several stages. According to one or more embodiments, the at least one dialkyl dithiophosphate compound with the alkyl chain length of Cl to C8, and the at least one surfactant is added as a blend, or separately in any order such as concurrently together or sequentially. In a preferred embodiment, the at least one dialkyldithiophosphate compound with the alkyl chain length of Cl to C8, and the at least one surfactant is added as a blend.

[0045] According to one or more embodiments, adding the at least one dialkyl dithiophosphate compound with the alkyl chain length of Cl to C8, and optionally the at least one surfactant to the solution containing acidic metal sulfate to form impurity metal ion complexes includes a treatment time. Treatment times in any or all embodiments of the invention can be from a few seconds (z.e., 5 to 10 seconds) to 240 minutes. In those instances where the reagent complexes the impurity metals very rapidly, the preferred treatment times are from about 5 seconds to 5 minutes. Most typically, the treatment times are from 10 seconds to 60 seconds or 120 seconds.

[0046] The dosage of the reagent for complexing impurity metals and removal efficiency for the various impurity metals will depend on the amount of impurity metal impurities present in the acidic metal sulfate containing streams. Generally, the greater number of impurity metals present and the higher their concentrations, the greater will be the overall dosage of the reagent. Those skilled in the art will be able to readily determine and establish the optimum dosage of at least one dialkyldithiophosphate compound with the alkyl chain length of Cl to C8, and optionally the at least one surfactant required using no more than routine experimentation. Generally, the dosages may be in the range of from 1 to 10 mole dialkyldithiophosphate per mole of impurity metal, based on the type of impurity metal ions to be removed. Most typically, the dosages can be from 2 to 4 mole dialkyldithiophosphate per mole of impurity metal ions to be removed. In the case of several metal impurity ions present, the total dose should be the sum of the individual impurity metal dosages. It will be understood by those ordinary skilled in the art that any of the recited dosages (except the lowest dosage point) can also be recited as “less than” a particular dosage, e.g., less than 50 kg; or that any of the recited dosages (except the highest dosage point) can also be recited as “greater than” a particular dosage, e.g., greater than 0.10 kg.

[0047] According to one or more embodiments, the ratio of the at least one dialkyl dithiophosphate compound with the alkyl chain length of Cl to C8 to the at least one surfactant is from 1000: 1 to 5: 1. In a preferred embodiment, the ratio of the at least one dialkyldithiophosphate compound with the alkyl chain length of Cl to C8 to the at least one surfactant is from 100: 1 to 10: 1.

[0048] In any or all embodiments, the solution containing acidic metal sulfates has a pH from 0 to 6, typically from 1 to 6. In a preferred embodiment, the pH of the acidic metal sulfate containing stream is from 3 to 5.

[0049] The compositions and processes described herewith as the present invention can be used over a wide temperature range. In any or all embodiments, for example, the processes according to the invention can be performed at a temperature from 0 °C to 80°C.

[0050] Preferably, the temperature is in the range from 20 °C to 60 °C.

[0051] In any or all of the embodiments according to the present invention, the process can further comprise adding an effective amount of an adsorbent to the solution containing acidic metal sulfate. Such agents are known to be useful in the field. In certain circumstances one or both of these agents can enhance the activity of the reagent including the at least one dialkyldithiophosphate compound with the alkyl chain length of Cl to C8, and optionally the at least one surfactant. In the same or alternate embodiments, the adsorbent agent can be added to the acidic metal sulfate containing streams all in one stage or added in several stages. In the same or other embodiments, the adsorbent agent can be added together as a blend with the reagent including the at least one dialkyldithiophosphate compound with the alkyl chain length of Cl to C8, and optionally the at least one surfactant, or separately in any order with the at least one dialkyldithiophosphate compound with the alkyl chain length of Cl to C8, and optionally the at least one surfactant such as concurrently together or sequentially. While the nature and quantity of the adsorbent agents used depends on the particular composition of the acidic metal sulfate solution, and of the purity specifications, those skilled in the art will be able to determine the optimum dosage range using no more than routine experimentation.

[0052] According to one or more embodiments, adding the at least one dialkyl dithiophosphate compound with the alkyl chain length of Cl to C8, and optionally the at least one surfactant to the solution containing acidic metal sulfate for forming impurity metal ion complexes includes further adding an adsorbing agent. Adsorbent agents can be useful in any or all embodiments according to the invention and include, but are not limited to, active charcoal / carbon, carbon black, ground lignite, adsorbents containing silicate (e.g., synthetic silicic acids, zeolites, calcium silicate, bentonite, perlite, diatomaceous earth, and fluorosilicate), calcium sulfate (including gypsum, hemihydrate, and anhydride), oxides or hydroxides of iron, aluminum, copper or manganese, and mixtures thereof. In the same or other embodiments, the adsorbent is selected from the group consisting of calcium sulfate, fluorosilicate, activated carbon, oxides or hydroxides of iron, aluminum, copper, or manganese and mixtures of any of the foregoing. In any or all embodiments, the adsorbent is present in an amount from 0.05 wt. % to 50 wt. %, and preferably from 0.1 wt. % to 30 wt. %, based on the quantity of impurity metal ions in the solution.

[0053] While various embodiments may have been described herein in singular fashion, those skilled in the art will recognize that any of the embodiments described herein can be combined in the collective. Indeed, the invention may be embodied in many different forms and should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will satisfy applicable legal requirements.

[0054] Examples

[0055] The following examples are provided to assist one skilled in the art to further understand certain embodiments of the present invention. These examples are intended for illustration purposes and are not to be construed as limiting the scope of the various embodiments of the present invention, as defined by the claims.

[0056] The performances of blends of at least one dialkyldithiophosphate compound with the alkyl chain length of Cl to C8, and optionally the at least one surfactant to remove impurity metals and in particular to selectively precipitate cadmium is evaluated with acidic metal sulfate solutions containing zinc, cobalt, and / or nickel. An effective amount of dialkyldithiophosphate reagent is dosed into the acidic metal sulfate solution and mixed. The solution is filtered to remove the insoluble impurity metal complex and afterwards, the filtrate solutions are analyzed with ICP (Inductively Coupled Plasma) to determine the level of impurity metals remaining in the acidic metal sulfate solution. The general procedure for the test and experimental examples are outlined below.

[0057] DOWFAX® 8390, designated as “Surfactant A”, is purchased from Dow Chemical. The dialkyldithiophosphate compounds with various chain lengths were synthesized in Syensqo laboratories. The blend was prepared by combining the dialkyldithiophosphate compounds with various chain lengths, and the surfactant if any.

[0058] The dialkyldithiophosphate compounds with various chain lengths were synthesized as explained in Example 1 below.

[0059] 1-A: Synthesis of di(2-ethylhexyl) dithi ic acid (“C8DTP”)

[0060] To a 250 ml 3-neck round bottom flask equipped with a heating mantle, magnetic stirring, nitrogen flow and vent to a caustic scrubber was added 155.57 g (1.1946 moles) of 2-ethylhexanol (2 mole% excess). After heating to 40 °C, 65.00 g of P2S5 (0.1464 moles) was added in three equal portions over 30 minutes with vigorous stirring. The reaction temperature was then increased to 80 °C where it was held for 4 hours. The reaction product was cooled and filtered to yield a light yellow, low viscosity liquid. (31P NMR 5 85ppm, 85.4%). of di(2-ethylhexyl) dithiophosphoric acid with ammonium hydroxide for ammonium di(2-ethylhexyl)

[0061] (“C8DTP-NH4”)

[0062] To a 250ml 3-neck round bottom flask equipped with a heating mantle, magnetic stirring, and nitrogen flow was added 100.00 g (0.2823 moles) of di(2-ethylhexyl) dithiophosphoric acid, as prepared in Example 1-A above. With vigorous agitation, 18.55 g of 28% aqueous ammonium hydroxide (2 mole% excess) was added to the reactor. An ice bath was raised and the addition rate was controlled to maintain the reaction temperature below 40°C. The reaction product was a light yellow, low viscosity liquid. (31P NMR 5 l l lppm, 93.1%). metal removal from acidic metal sulfate solutions

[0063] 2-A: Process for cadmium from acidic metal sulfate feeds (pH 4) with diluted DTP addition at ambient temperature.

[0064] 100 ml of an acidic metal sulfate feed containing 15.3 mg / L cadmium, 2 g / L cobalt, 2 g / L Mg, and 0.5 g / L at pH 4 zinc is transferred into a 300 ml baffled vessel. Agitation is started with an overhead stirrer and a 4-blade impeller at 600 rpm. An effective amount (as listed as dosage in Table 1) of a reagent of interest diluted to 1% in water is dosed into the acidic metal sulfate sample under ambient temperature without further control. After agitation for 5 minutes, 2 grams of diatomaceous earth is added (as a filter aid) and allowed to mix for an additional 1 minute. The entire sample is then filtered through GF / A filter paper (1.6 pm). This process is repeated two additional times to obtain triplicate filtrate samples for each condition. The filtrate from each test is collected and then submitted for ICP elemental analysis. The ICP results of the remaining Cd in the acidic metal sulfate sample and the corresponding calculated percentage of Cd removed are shown in Table 1. The lower the remaining Cd and the higher the percentage of Cd removed, the better the performance of reagents. From Table 1 it can be seen that C8DTP NF salt was able to remove cadmium from the acidic metal sulfate. Cadmium removal efficiency was improved with the addition of Surfactant A. When the DTP was added in excess (DTP: Cd molar ratio of 3 and 4), cadmium removal was high for both formulations. Table 1.

[0065] Example 2-B: Process for removing cadmium from acidic metal sulfate feeds (pH 4) with neat DTP addition

[0066] 600 ml of an acidic metal sulfate feed containing 15.0 mg / L cadmium, 2 g / L cobalt, 2 g / L Mg and 0.5 g / L zinc at pH 4 is transferred into a 1000 ml baffled vessel. Agitation is started with an overhead stirrer and a rushton turbine impeller at 400 rpm. An effective amount (as listed as dosage in Table 2) of a reagent of interest is dosed into the sulfuric acid sample under ambient temperature without further control. After agitation for 1 minute, a 50 ml sample is collected in a 100 ml beaker and 1 gram of diatomaceous earth is added (as a filter aid) and allowed to mix for an additional 1 minute. This sample is then filtered through GF / A filter paper (1.6 pm). The filtrate from each test is collected and then submitted for ICP elemental analysis. The ICP results of the remaining Cd in the acidic metal sulfate sample and the corresponding calculated percentage of Cd removed are shown in Table 2. The lower the remaining Cd and the higher the percentage of Cd removed, the better the performance of reagents. From Table 2 it can be seen that C4DTP Na salt, C8DTP NF salt and its formulation with surfactant were able to remove cadmium from the acidic metal sulfate sample. The rate of cadmium removal improved as the dosage of DTP was increased.

[0067] Table 2. Various patent and / or scientific literature references have been referred to throughout this application. The disclosures of these publications in their entireties are hereby incorporated by reference as if written herein. However, if a term in the present application contradicts or conflicts with a term in the incorporated reference, the term from the present application takes precedence over the conflicting term from the incorporated reference. In view of the above description and the examples, one of the ordinary skill in the art will be able to practice the disclosure as claimed without undue experimentation.

[0068] While typical embodiments have been set forth for the purpose of illustrating the fundamental novel features of the present invention, the foregoing descriptions should not be deemed to be a limitation on the scope herein. Accordingly, various modifications, adaptations, and alternatives can occur to one skilled in the art without departing from the spirit and scope of the invention described herein, and the scope of the invention should be defined by the appended claims.

Claims

CLAIMS1. A process for removing impurity metal ions from an acidic metal sulfate stream containing cobalt and / or nickel metals, the process comprising: adding an effective amount of a reagent, comprising at least one dialkyldithiophosphate compound with the alkyl chain length of Cl to C8 to the acidic metal sulfate containing stream to form impurity metal ion complexes; and separating the impurity metal ion complexes from the acidic metal sulfate stream.

2. The process according to claim 1, wherein the reagent further comprises an effective amount of at least one surfactant.

3. The process according to claims 1 or 2, wherein the impurity metal ions removed from the acidic metal sulfate stream are selected from the group consisting of titanium, chromium, cadmium, arsenic, mercury, copper, lead, and mixtures thereof.

4. The process according to any one of claims 1 to 3, wherein the impurity metal ions removed from the acidic metal sulfate stream are cadmium.

5. The process according to any one of claims 1 to 4, wherein the dialkyldithiophosphate compound is selected from the group consisting of dialkyldithiophosphoric acid with the alkyl chain length of Cl to C8 and salts of the dialkyldithiophosphoric acid with the alkyl chain length of Cl to C8 in the form of calcium, magnesium, potassium, sodium salt or ammonium salt with the formula NR.1R.2R.3R4 , where Ri, R2, R3, R4 are, equal to or different from each other, independently chosen from hydrogen, alkyl or aryl groups; and mixtures thereof.

6. The process according to any one of claims 1 to 5, wherein said dialkyldithiophosphate compound has an alkyl chain of C4 to C8.

7. The process according to any one of claims 1 to 6, wherein said dialkyldithiophosphate compound has a C8 alkyl chain.

8. The process according to any one of claims 2 to 7, wherein the surfactant compound is selected from the group consisting of sulfosuccinates; aryl sulfonates;alkaryl sulfonates; diphenyl sulfonates; olefin sulfonates; sulfonates of ethoxylated alcohols; petroleum sulfonates; sulfosuccinamates; alkoxylated surfactants; ester / amide surfactants; EO / PO block copolymers (ethylene oxide / propylene oxide); and mixtures thereof.

9. The process according to any one of claims 1 to 8, wherein the dialkyldithiophosphate compound is in a diluted solution.

10. The process according to any one of claims 1 to 9, wherein the process further comprises a step of removal of iron and copper impurities and wherein the reagent is added to the acidic metal sulfate stream following this removal step of iron and copper impurities.

11. The process according to any one of claims 1 to 10, wherein the reagent is added to the acidic metal sulfate stream prior to a recovery step of cobalt and / or nickel products.

12. The process according to any one of claims 1 to 11, wherein the process further comprises filtering the acidic metal sulfate stream prior to adding the reagent.

13. The process according to any one of claims 2 to 12, wherein the ratio of the at least one dialkyldithiophosphate compound with the alkyl chain length of Cl to C8 to the at least one surfactant is from 1000: 1 to 5: 1, preferably from 100: 1 to 10: 1.

14. The process according to any one of claims 1 to 13, wherein the acidic metal sulfate stream has a pH from 0 to 6, preferably from 1 to 6, more preferably from 3 to 5.

15. The process according to any one of claims 1 to 14, wherein the process is performed at a temperature from 0 °C to 80°C, preferably from 20 °C to 60 °C.

16. The process according to any one of claims 1 to 15, wherein the process further comprises adding an adsorbent agent to the acidic metal sulfate stream, wherein the adsorbent agent is selected from the group consisting of calcium sulfate, fluorosilicate, activated carbon, oxides or hydroxides of iron, aluminum, copper, or manganese and mixtures thereof.

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