Methods and uses relating to electrochemical processes

Abstract

The use of one or more additives selected from sulfosuccinate surfactant compounds and α- olefin sulfonate surfactant compounds to reduce acid mist formation in an electrochemical 5 process.

Description

[0001] Methods and uses relating to electrochemical processes

[0002] The present invention relates to electrochemical processes, especially electrowinning processes and improved additives for use therein.

[0003] In hydrometallurgy electrowinning is the final stage of metal production. In this process, target metals are recovered from electrolytes obtained by acidic or basic leaching of metal ores.

[0004] In electrowinning processes in which a current is passed through an electrolyte solution, metals for example copper, nickel or zinc are deposited on the cathode. At the same time oxygen bubbles are released at the anode. These oxygen bubbles rise to the surface of the electrolyte solution where they burst. Because the solution in which the process is carried out is highly acidic (typically having a pH of 1 to 2.5), the bursting of bubbles at the surface of the electrolyte produces an acidic mist. This is water vapour containing acid. This mist is corrosive and hazardous to health.

[0005] To help reduce the formation of this acid mist industrial electrowinning processes typically include a fluorochemical additive (such as a fluoro alkyl acrylate adduct). It is also known to cover the surface of the electrolyte solution with polystyrene beads during the electrowinning process.

[0006] However because the industry standard additive is a fluorochemical this is being phased out due to environmental reasons and regulatory pressure. There is thus an urgent need to find alternative means for reducing acid mist formation in electrowinning processes. One alternative additive is available under the trade mark Mistop® and is believed to be based on saponin compounds. However this material has a negative impact on the performance of the electrowinning step as a whole due to a lower current density being achieved.

[0007] The present inventors have surprisingly found that sulfosuccinate and / or a-olefin sulfonate surfactant compounds can reduce acid mist formation in electrochemical processes and maintain good performance throughout the overall process.

[0008] According to a first aspect of the present invention there is provided the use of one or more additives selected from sulfosuccinate surfactant compounds and a-olefin sulfonate surfactant compounds to reduce acid mist formation in an electrochemical process.

[0009] According to a second aspect of the present invention there is provided a method for recovering a metal from an acidic electrolyte solution comprising ions of the metal, the method comprising:- adding one or more additives selected from sulfosuccinate surfactant compounds and a- olefin sulfonate surfactant compounds to the acidic electrolyte solution; and

[0010] - passing an electric current through the acidic electrolyte solution comprising metal ions;

[0011] wherein the amount of acid mist produced during the method is lower than that produced in an otherwise identical method without the addition of the one or more additives.

[0012] Preferred features of the first and second aspects of the invention will now be defined.

[0013] In the present invention the formation of acid mist is reduced during an electrochemical process.

[0014] The present invention may be used in any electrochemical process involving the use of an acidic electrolyte solution in which an acid mist may form.

[0015] The electrochemical process may be an electroplating, electrowinning, electrochemical deposition or electroforming process.

[0016] Preferably the electrochemical process is electrowinning. Suitably the first aspect of the invention relates to the use of at least one sulfosuccinate surfactant compound to reduce acid mist formation in an electrowinning process.

[0017] In the method and use of the present invention an electric current is passed through the acidic electrolyte solution. As the skilled person will appreciate, an anode and a cathode are immersed in the acidic electrolyte solution and a potential is applied across the electrodes. This leads to flow of current through the acidic electrolyte solution leading to migration of metal cations to the cathode where metal deposition onto the cathode occurs.

[0018] In the use of the first aspect and method of the second aspect one or more additives selected from sulfosuccinate surfactant compounds and a-olefin sulfonate surfactant compounds are added to an acidic electrolyte solution comprising metal ions.

[0019] The method of the second aspect of the invention involves passing an electric current through the electrolyte solution and addition of one or more additives. Preferably the one or more additives is / are added before an electric current is passed through the electrolyte. However further additive may be added during the method as the current continues to be passed through the electrolyte solution.The acidic electrolyte solution suitably has a pH of at least 0.5 and less than 7. Preferably the pH of the acidic electrolyte solution is from 0.5 to 5, preferably from 0.6 to 4, for example from 0.75 to 3, most preferably from 1 to 2.5.

[0020] The electrolyte solution comprises metal cations, hydrogen ions and anions.

[0021] A mixture of anions may be present. These will depend on the acid used.

[0022] Suitable anions include sulfates, phosphates, perchlorates and halides.

[0023] Suitable acids useful for forming the acidic electrolyte solution will depend on the nature of the metal ions and will be known to the person skilled in the art.

[0024] Preferred acids are inorganic acids. Suitable acids include sulfuric, phosphoric, perchloric and hydrochloric acid.

[0025] Preferably the acidic electrolyte solution is a sulfuric acid based solution. Suitably the electrolyte solution comprises sulfate ions. Other anions may also be present, including those from the metal ore.

[0026] The present invention may be used to recover any suitable metal in an electrochemical process. Suitable metals include transition metals, for example copper, zinc, nickel and iron. Preferred metals are copper and zinc.

[0027] In addition to the metal being recovered the electrolyte solution may also comprise one or more further metal cations which are present in the ore, for example manganese, silicon, nickel, cobalt and sodium. Such metals are typically present in only trace amounts.

[0028] In some preferred embodiments the present invention is used to recover copper from an acidic electrolyte solution comprising copper ions, preferably copper (II) ions.

[0029] Preferably the electrolyte solution comprises copper sulfate and sulfuric acid.

[0030] In the present invention one or more additives selected from sulfosuccinate surfactant compounds and a-olefin sulfonate surfactant compounds are used as an additive in an electrochemical process.

[0031] In some embodiments the one or more additives comprise a sulfosuccinate surfactant compound.In some embodiments the one or more additives comprise an a-olefin sulfonate surfactant compound.

[0032] In some embodiments the one or more additives comprise an a-olefin sulfonate surfactant compound and a sulfosuccinate surfactant compound.

[0033] Mixtures of additives can be used in the present invention. Such mixtures may include mixtures of two or more sulfosuccinate surfactant compounds and / or two or more a-olefin sulfonate surfactant compounds.

[0034] In some embodiments one sulfosuccinate surfactant compound is used as an additive. In some embodiments two or more than two sulfosuccinate surfactant compounds are used as an additive.

[0035] Suitable sulfosuccinate surfactant compounds include compounds of formula (I):

[0036]

[0037] wherein one of R1and R2is X and the other is an optionally substituted hydrocarbyl group; or both of R1and R2are optionally substituted hydrocarbyl groups; wherein the or each X is independently selected from hydrogen, a metal ion or an optionally substituted ammonium ion.

[0038] In embodiments in which each of R1and R2is an optionally substituted hydrocarbyl group they may be the same or different. Preferably R1and R2are the same.

[0039] In some embodiments one of R1and R2is an optionally substituted hydrocarbyl group and the other is X. Such surfactants may include mixtures of compounds (II) and (III):

[0040]

[0041] In such compounds each X may be the same or different. Preferably each X is the same.

[0042] In some embodiments each of R1and R2is an optionally substituted hydrocarbyl group.

[0043] In such embodiments R1and R2may be the same or different. Preferably in such embodiments R1and R2are the same.

[0044] Each X is a hydrogen, metal or optionally substituted ammonium ion.

[0045] Suitable metal ions include alkali metal ions, especially sodium or potassium.

[0046] Suitable ammonium ions include alkyl and / or hydroxyalkyl substituted ammonium ions.

[0047] A preferred ammonium ion is NHZ.

[0048] Most preferably the or each X is sodium.

[0049] The additives used in the present invention are preferably provided as alkali metal salts, especially sodium salts. However as the skilled person will appreciate in the acidic solutions in which they are used the compounds may be present in the protonated form as acid moieties.

[0050] Preferred sulfosuccinate surfactant compounds for use in the present invention are sodium sulfosuccinates and disodium sulfosuccinates.

[0051] In the compound of formula (I) R1and / or R2is an optionally substituted hydrocarbyl group.

[0052] R1and / or R2may be selected from an optionally substituted alkyl, alkenyl, aryl, alkaryl or aralkyl group.

[0053] Preferably R1and / or R2may be selected from an optionally substituted alkyl group or an optionally substituted alkenyl group.Preferably R1and / or R2may be selected from an optionally substituted alkyl or alkenyl group having from 1 to 40 carbon atoms, preferably from 2 to 36 carbon atoms, more preferably from 4 to 30 carbon atoms.

[0054] In some embodiments R1and / or R2may be selected from optionally substituted alkenyl groups having from 4 to 24 carbon atoms, for example from 4 to 16 carbon atoms.

[0055] In some embodiments R1and / or R2may be an optionally substituted alkyl group, for example an optionally substituted alkyl group having from 1 to 24 carbon atoms, for example from 2 to 20 carbon atoms, or from 4 to 16 carbon atoms.

[0056] In some embodiments R1and / or R2may be an unsubstituted alkyl group. Preferred alkyl groups have from 1 to 30 carbon atoms, for example from 2 to 24 carbon atoms or from 4 to 18 carbon atoms. In some embodiments R1and / or R2is an alkyl group having from 4 to 10 carbon atoms, for example from 5 to 8 carbon atoms.

[0057] In embodiments in which each of R1and R2is an unsubstituted alkyl group, R1and R2are preferably the same.

[0058] Suitable alkyl and alkenyl groups for use as R1and R2may be straight-chained or branched.

[0059] In some embodiments R1and R2may include a cyclic alkyl group, preferably a branched hexyl group.

[0060] Suitable alkyl groups for use as R1and / or R2include hexyl, cyclohexyl, isodecyl, dimethylbutyl, isopentyl, butyl, pentyl, propyl, octyl, 2-ethylhexyl, nonyl, lauryl, hexadecyl and isomers and mixtures thereof.

[0061] In one preferred embodiment R1and / or R2is a hexyl group. Suitable hexyl groups include straight chain and especially branched hexyl groups.

[0062] Preferably in some embodiments each of R1and R2is a hexyl group.

[0063] Preferred dialkyl sulfosuccinates salts for use herein include salts of dihexyl sulfosuccinate, dicyclohexyl sulfosuccinate, diisodecyl sulfosuccinate, di(dimethylbutyl) sulfosuccinate, diisopentyl sulfosuccinate, dibutyl sulfosuccinate, dipentyl sulfosuccinate, dipropyl sulfosuccinate, dioctyl sulfosuccinate, di(2-ethylhexyl) sulfosuccinate, dinonyl sulfosuccinate, dilauryl sulfosuccinate and dihexadecyl sulfosuccinate.An especially preferred sulfosuccinate compound is sodium dihexyl sulfosuccinate, i.e. the compound of formula (IV):

[0064]

[0065] Preferably in formula (IV) the groups CeHis are branched.

[0066] In some embodiments R1and / or R2may be an alkoxy substituted alkyl or alkenyl group or a poly-alkoxy substituted alkyl or alkenyl group. In preferred such embodiments one of R1and R2is a (poly)alkoxy substituted alkyl or alkenyl group and the other is X. In such embodiments R1or R2may be (CHR3CHR4O)nR5wherein n is at least 1 ; in each moiety CHR3CHR4O one of R3and R4is hydrogen and the other is hydrogen or a methyl group; and R5is a straight chain or branched optionally substituted alkyl or alkenyl group.

[0067] When n is greater than 1 each moiety CHR3CHR4O may be the same or different. Preferably each moiety CHR3CHR4O is the same. Preferably R3is hydrogen and R4is hydrogen.

[0068] Thus R1and R2may be a group of formula (CH2CH2O)nR5.

[0069] n is at least 1. Preferably n is from 1 to 20, preferably from 1 to 16, more preferably from 2 to 10, suitably from 3 to 8, for example about 5.

[0070] R5is an optionally substituted alkyl or alkenyl group, preferably having from 2 to 40 carbon atoms, preferably from 4 to 36 carbon atoms, for example 6 to 24 carbon atoms, preferably 6 to 18 or 8 to 16 carbon atoms.

[0071] Preferably R5is an unsubstituted alkyl or alkenyl group.

[0072] Preferably R5is an unsubstituted alkyl group.

[0073] R5may be straight chain or branched. Preferably R5is straight chain.Preferably R5is an alkyl group, preferably an unsubstituted alkyl group having 1 to 40 carbon atoms, preferably from 4 to 36 carbon atoms, for example 6 to 24 carbon atoms, preferably 6 to 18 or 8 to 16 carbon atoms.

[0074] Preferably R5is (CH2)mCH3 wherein m is from 1 to 40, preferably 2 to 30, suitably 4 to 24, preferably 6 to 18, for example 8 to 12.

[0075] Most preferably m is from 9 to 11.

[0076] One especially preferred sulfosuccinate surfactant compound is the compound of formula (VA) or (VB):

[0077]

[0078] (VA) (VB)

[0079] wherein n is on average 5 and m is 8 to 10.

[0080] As the skilled person will appreciate, mixtures of isomers (VA) and (VB) will typically be present.

[0081] In some embodiments R1and / or R2may be a group of formula (CH2CH2O)n(CH2)mCH3 where n and m are as defined above.

[0082] In some especially preferred embodiments in the compound of formula (I) X is sodium, and each R1and R2is an optionally substituted hydrocarbyl group.

[0083] Preferably each of R1and R2is an optionally substituted alkyl group, preferably an unsubstituted alkyl group.

[0084] Preferably each of R1and R2is an alkyl group, preferably an unsubstituted alkyl group having from 1 to 30 carbon atoms, preferably 2 to 20 carbon atoms, more preferably 4 to 16 carbon atoms, preferably 5 to 10 carbon atoms. R1and R2may be straight chain, cyclic or branched.In some especially preferred embodiments in the compound of formula (I) one of R1and R2is X and the other is an alkoxy substituted alkyl group, preferably a poly alkoxy substituted alkyl group. Suitably each X is sodium.

[0085] Preferably in such embodiments one of R1and R2is (CHR3CHR4O)nR5wherein R3, R4and R5are as defined above.

[0086] Preferably n is from 1 to 12 preferably from 2 to 10, preferably from 4 to 8, suitably from 5 to 7.

[0087] Preferably R3and R4are both hydrogen and R5is an alkyl group having 4 to 40, preferably 4 to 30, more preferably 6 to 20, for example 8 to 16, preferably 10 to 12 carbon atoms.

[0088] In some embodiments the one or more additives used in the present invention comprise an a-olefin sulfonate surfactant compound, a-olefin sulfonate surfactant compounds will be known to the person skilled in the art and include an alkenyl moiety typically having one double bond and a sulfonate head group.

[0089] The term “alpha-olefin sulfonates” is used in the art and in the present disclosure to refer to the products of sulfonation of alpha-olefins followed by neutralisation. Such alpha-olefin sulfonates are typically a mixture comprising alkenyl sulfonates as the major component(s) and also comprising lesser amounts of hydroxyalkane sulfonate, alkenyl disulfonates and hydroxyalkane disulfonates. Said mixtures are referred to herein as “alpha-olefin sulfonates”. For example, the “alpha-olefin sulfonates” used in the present invention may comprise 55 to 75 wt% of alkenyl sulfonates, 25 to 45% of hydroxyalkane sulfonates and 5 to 15% of a mixture of hydroxyalkane disulfonates and alkenyl disulfonates. The sulfonate salts referred to above are preferably sodium salts.

[0090] Preferred a-olefin sulfonates for use herein are linear a-olefin sulfonates.

[0091] Suitable a-olefin sulfonate surfactant compounds for use herein are formula R6SO3'M+wherein R6is an alkenyl group and M+is a hydrogen, metal or ammonium cation.

[0092] R6is preferably an alkenyl group having from 4 to 40 carbon atoms, preferably 6 to 36 carbon atoms, preferably 8 to 30 carbon atoms, preferably 8 to 24 carbon atoms, preferably 10 to 20 carbon atoms.

[0093] R6may be straight chain or branched.

[0094] Preferably R6is straight chain.The skilled person will appreciate that R6may comprise a mixture of isomers and / or a mixture of homologues.

[0095] Suitable a-olefin sulfonate surfactant compounds for use herein include C12 to C14 a-olefin sulfonates, C14 to C16 a-olefin sulfonates, C16 to C18 a-olefin sulfonates and C14 to C18 a-olefin sulfonates.

[0096] Especially preferred a-olefin sulfonate surfactant compounds for use herein are C14 to C16 a-olefin sulfonates.

[0097] Suitably M+is a hydrogen, metal or optionally substituted ammonium ion.

[0098] Suitable metal ions include alkali metal ions, especially sodium or potassium ions.

[0099] Suitable ammonium ions include alkyl and / or hydroxyalkyl substituted ammonium ions.

[0100] A preferred ammonium ion is NHZ.

[0101] Most preferably M+is a sodium ion.

[0102] The present invention involves the use of one or more additives selected from sulfosuccinate surfactant compounds and a-olefin sulfonate surfactant compounds in an electrochemical process, preferably an electrowinning process. In some embodiments the invention may involve the use of two or more additives selected from sulfosuccinate surfactant compounds and a-olefin sulfonate surfactant compounds.

[0103] The present inventors have found that the use of the combination of additives comprising a dialkyl sulfosuccinate surfactant compound and one or more further compounds selected from further sulfosuccinate surfactant compounds and a-olefin sulfonate surfactant compounds is particularly advantageous.

[0104] In some preferred embodiments of the first and second aspects of the present invention the one or more additives comprise:

[0105] (a) a first additive comprising at least one sulfosuccinate surfactant compound of formula (I):

[0106]

[0107] in which both R1and R2are optionally substituted hydrocarbyl groups and X is selected from hydrogen, a metal ion or an optionally substituted ammonium ion; and

[0108] (b) a second additive selected from one or more of:

[0109] (i) a sulfosuccinate surfactant compound of formula (II) and / or (III):

[0110]

[0111] (II) (III)

[0112] in which R1or R2is (CHR3CHR4O)nR5wherein n is at least 1 ; in each moiety CHR3CHR4O one of R3and R4is hydrogen and the other is hydrogen or a methyl group; R5is a straight chain or branched optionally substituted alkyl or alkenyl group; and X is selected from hydrogen, a metal ion or an optionally substituted ammonium ion; and

[0113] (ii) an a-olefin sulfonate surfactant compound.

[0114] According to a third aspect of the invention there is provided an additive composition comprising:

[0115] (a) a first additive comprising at least one sulfosuccinate surfactant compound of formula (I):

[0116]

[0117] in which both R1and R2are optionally substituted hydrocarbyl groups and X is selected from hydrogen, a metal ion or an optionally substituted ammonium ion; and

[0118] (b) a second additive selected from one or more of:

[0119] (i) a sulfosuccinate surfactant compound of formula (II) and / or (III):

[0120]

[0121] (II) (III)

[0122] in which R1or R2is (CHR3CHR4O)nR5wherein n is at least 1 ; in each moiety CHR3CHR4O one of R3and R4is hydrogen and the other is hydrogen or a methyl group; R5is a straight chain or branched optionally substituted alkyl or alkenyl group; and X is selected from hydrogen, a metal ion or an optionally substituted ammonium ion; and

[0123] (ii) an a-olefin sulfonate surfactant compound.

[0124] Further preferred features of the first and second additives are as described in relation to the first and second aspects, as appropriate.

[0125] In some preferred embodiments the first aspect and second aspects of the invention may involve the use of an additive composition of the third aspect.

[0126] In some embodiments the first aspect of the present invention provides the use of an additive composition of the third aspect to reduce acid mist formation in an electrochemical process.

[0127] In some embodiments the second aspect of the present invention provides a method for recovering a metal from an acidic electrolyte solution comprising ions of the metal, the method comprising:

[0128] - adding an additive composition of the third aspect to the acidic electrolyte solution; and - passing an electric current through the acidic electrolyte solution comprising metal ions;

[0129] wherein the amount of acid mist produced during the method is lower than that produced in an otherwise identical method without the addition of the additive composition.Further preferred features of the additive composition of the invention will now be described. These may apply to embodiments of the first and second aspects as appropriate.

[0130] Component (a) of the additive composition of the third aspect of the invention comprises a compound of formula (I) in which each of R1and R2is an optionally substituted hydrocarbyl group. Preferably each of R1and R2is an optionally substituted alkyl group, preferably an unsubstituted alkyl group.

[0131] Component (b) of the additive composition of the third aspect of the invention comprises (b) a second additive selected from one or more of (i) a sulfosuccinate surfactant compound of formula (II) and / or (III) in which R1or R2is (CHR3CHR4O)nR5and X is a hydrogen, metal or ammonium ion and (ii) an a-olefin sulfonate surfactant compound.

[0132] In some embodiments component (b) comprises the sulfosuccinate (i).

[0133] In some embodiments component (b) comprises the a-olefin sulfonate (ii).

[0134] In some embodiments component (b) comprises the a-olefin sulfonate (ii) and the sulfosuccinate (i).

[0135] The a-olefin sulfonate (ii) is preferably a compound of formula R6SO3'M+wherein R6is an alkenyl group and M+is a hydrogen metal or ammonium cation.

[0136] Component (a) preferably comprises a sodium dialkyl sulfosuccinate salt, preferably wherein each alkyl group has 1 to 16 carbon atoms, preferably 2 to 12 or 4 to 8 carbon atoms. Most preferably component (a) comprises sodium dihexyl sulfosuccinate.

[0137] In some embodiments component (b) comprises a polyethylene glycol alkyl ether sulfosuccinate disodium salt preferably having from 1 to 10 ethylene oxide groups, more preferably 3 to 8 ethylene oxide groups, and most preferably 5 ethylene oxide groups.

[0138] In some embodiments component (b) comprises a polyethylene glycol alkyl ether sulfosuccinate disodium salt preferably having a Ci to C24 alkyl group; more preferably a Ce to C16 alkyl group; most preferably a C10 to C12 alkyl group.

[0139] In some embodiments component (b) comprises a polyethylene glycol alkyl ether sulfosuccinate disodium salt preferably having from 1 to 10 ethylene oxide groups, and a Ci to C24 alkyl group; more preferably having from 3 to 8 ethylene oxide groups, and a Ce to C16 alkyl group; most preferably having 5 ethylene oxide groups and a C10 to C12 alkyl group.In some embodiments component (b) comprises an a-olefin sulfonate, preferably a sodium a-olefin sulfonate, preferably a Ce to C30 a-olefin sulfonate, more preferably a C10 to C20 a-olefin sulfonate and most preferably a C14 to C16 a-olefin sulfonate.

[0140] In some embodiments the additive composition of the third aspect comprises:

[0141] (a) a first additive comprising at least one sulfosuccinate surfactant compound of formula (I):

[0142] >

[0143]

[0144] in which X is sodium and both R1and R2are unsubstituted alkyl groups, preferably having 3 to 18, preferably 4 to 12 and most preferably 6 carbon atoms; and

[0145] (b) a second additive comprising:

[0146] (i) a sulfosuccinate surfactant compound of formula (II) or / or (III):

[0147]

[0148] (II) (III)

[0149] in which X is sodium and R1or R2is (CH2CH2O)nR5wherein n is from 1 to 12 preferably from 2 to 10, preferably from 4 to 8, more preferably from 5 to 7 and R5is an alkyl group having 4 to 30, preferably 6 to 20, suitably 8 to 16, preferably 10 to 12 carbon atoms.

[0150] In some embodiments the additive composition of the third aspect comprises:

[0151] (a) a first additive comprising at least one sulfosuccinate surfactant compound of formula (I):

[0152]

[0153] in which X is sodium and both R1and R2are unsubstituted alkyl groups, preferably having 3 to 18, preferably 4 to 12 and most preferably 6 carbon atoms; and

[0154] (b) a second additive comprising:

[0155] (ii) an a-olefin sulfonate surfactant compound of formula R6SO3'M+wherein R6is an alkenyl group having 6 to 36 carbon atoms, preferably 8 to 30 carbon atoms, preferably 8 to 24 carbon atoms, preferably 10 to 20 carbon atoms; and X is sodium.

[0156] The weight ratio of component (a) to component (b) is suitably from 100:1 to 1 :5; preferably from 50:1 to 1 :1. In some embodiments the weight ratio of component (a) to component (b) may be from 30:1 to 1.5:1 ; preferably from 20:1 to 1.5:1 ; for example from 15:1 to 1.5:1.

[0157] The additive composition of the third aspect of the present invention may consist essentially of component (a) and component (b) or it may comprise one or more further components. Suitable further components include water and solvents, especially water miscible solvents.

[0158] Suitable solvents include alcohols and alkoxylated alcohols. Preferred solvents are ethanol, isopropanol and 2-2(butoxyethoxy)ethanol.

[0159] In some embodiments the additive composition comprises a further surfactant. The further surfactant is different to components (a) and (b).

[0160] The further surfactant may be a further anionic surfactant. Suitable further surfactants include sulfates, suitably alkyl sulfates, for example sodium 2 ethyhexyl sulfate.

[0161] In the present invention the one or more additives are added to the acidic electrolyte solution in a total amount of at least 0.1 ppm, preferably at least 0.5 ppm, suitably at least 1 ppm, for example at least 3 ppm or at least 5 ppm. The one or more additives may be added to the acidic electrolyte solution in a total amount of up to 1000 ppm, suitably up to 500 ppm, preferably up to 100 ppm, suitably up to 60 ppm, for example up to 40 ppm or up to 30 ppm.T reat rates of 1 to 100 ppm or 5 to 50 ppm total additives (selected from sulfosuccinate surfactant compounds and a-olefin sulfonate surfactant compounds) and are preferred.

[0162] For the avoidance of doubt in this specification unless otherwise specified ppm refers to parts per million by weight.

[0163] The above amounts refer to the total amount of all active sulfosuccinate surfactant compounds and a-olefin sulfonate surfactant compounds present in the composition. The above amounts refer to the amount of active component present in each case and do not include any diluent, carriers, impurities or residual starting materials.

[0164] The additive composition of the third aspect of the present invention preferably comprises at least 5 wt% component (a), preferably at least 10 wt%, suitably at least 15 wt%.

[0165] The additive composition of the third aspect of the present invention preferably comprises up to 90 wt% component (a), preferably up to 85 wt%, suitably up to 75 wt%.

[0166] In some embodiments the additive composition of the third aspect of the present invention preferably comprises at least 30 wt% component (a), preferably at least 40 wt%, suitably at least 50 wt%.

[0167] In some embodiments the additive composition of the third aspect of the present invention preferably comprises from 15 to 75 wt% component (a), preferably from 40 to 75 wt%, more preferably from 50 to 70 wt%.

[0168] The additive composition of the third aspect of the present invention preferably comprises at least 0.5 wt% component (b), preferably at least 1 wt%, suitably at least 2 wt%.

[0169] The additive composition of the third aspect of the present invention preferably comprises up to 50 wt% component (b), preferably up to 30 wt%, suitably up to 20 wt%.

[0170] Preferably the additive composition of the third aspect of the present invention comprises from 1 to 25 wt% component (b), preferably from 3 to 12 wt%.

[0171] The additive composition of the third aspect of the present invention preferably comprises at least 0.5 wt% component (b)(i), preferably at least 1 wt%, suitably at least 2 wt%.

[0172] The additive composition of the third aspect of the present invention preferably comprises up to 50 wt% component (b)(i), preferably up to 30 wt%, suitably up to 20 wt%.Preferably the additive composition of the third aspect of the present invention comprises from 1 to 25 wt% component (b)(i), preferably from 3 to 8 wt%.

[0173] The additive composition of the third aspect of the present invention preferably comprises at least 0.5 wt% component (b)(ii), preferably at least 1 wt%, suitably at least 2 wt%.

[0174] The additive composition of the third aspect of the present invention preferably comprises up to 50 wt% component (b)(ii), preferably up to 30 wt%, suitably up to 20 wt%.

[0175] Preferably the additive composition of the third aspect of the present invention comprises from 1 to 25 wt% component (b)(ii), preferably from 6 to 12 wt%.

[0176] Suitably component (a) and component (b) together provide from 10 to 90 wt% of the additive composition of the third aspect, preferably from 20 to 75 wt%.

[0177] In some embodiments the additive composition of the third aspect of the present invention may comprise up to 40 wt% of one or more further surfactants, for example up to 30 wt% or up to 20 wt%.

[0178] In some embodiments the additive composition of the third aspect of the present invention preferably comprises from 1 to 40 wt% of a further surfactant, preferably a sulfate, preferably from 15 to 25 wt%.

[0179] The additive composition of the third aspect of the present invention preferably comprises from 30 to 90 wt% total surfactants, preferably from 40 to 80 wt%.

[0180] The additive composition of the third aspect of the present invention preferably comprises at least 1 wt% water, preferably at least 5 wt%, suitably at least 10 wt%.

[0181] The additive composition of the third aspect of the present invention preferably comprises up to 90 wt% water, preferably up to 85 wt%, suitably up to 75 wt%.

[0182] In some embodiments the additive composition of the third aspect of the present invention preferably comprises from 5 to 60 wt% water, preferably from 10 to 50 wt%.

[0183] The additive composition of the third aspect of the present invention preferably comprises at least 0.1 wt% water miscible solvents, preferably at least 0.5 wt%, suitably at least 1 wt%.The additive composition of the third aspect of the present invention preferably comprises up to 30 wt% water miscible solvents, preferably up to 85 wt%, suitably up to 75 wt%.

[0184] In some embodiments the additive composition of the third aspect of the present invention preferably comprises from 1 to 30 wt% water miscible solvents, preferably from 1 to 15 wt%.

[0185] The additive composition of the third aspect of the present invention preferably comprises at least 0.1 wt% alcohols, preferably at least 0.5 wt%, suitably at least 1 wt%.

[0186] The additive composition of the third aspect of the present invention preferably comprises up to 30 wt% alcohols, preferably up to 85 wt%, suitably up to 75 wt%.

[0187] In some embodiments the additive composition of the third aspect of the present invention preferably comprises from 1 to 30 wt% alcohols, preferably from 1 to 15 wt%.

[0188] In one embodiment the additive composition of the third aspect comprises:

[0189] (a) from 10 to 80 wt% of a dialkyl sulfosuccinate, preferably from 15 to 75 wt%;

[0190] (b) from 0.1 to 25 wt% of a polyethylene glycol alkyl ether sulfosuccinate salt or an a- olefin sulfonate surfactant compound, preferably from 1 to 15 wt%;

[0191] (c) from 0.1 to 30 wt% of one or more alcohols, preferably from 1 to 20 wt%; and (d) from 5 to 50 wt% water, preferably 10 to 30 wt%.

[0192] In one embodiment the additive composition of the third aspect comprises:

[0193] (a) from 40 to 80 wt% of a dialkyl sulfosuccinate, preferably from 50 to 75 wt%;

[0194] (b) from 0.1 to 20 wt% of a polyethylene glycol alkyl ether sulfosuccinate salt, preferably from 1 to 10 wt%;

[0195] (c) from 1 to 30 wt% of one or more alcohols, preferably from 5 to 20 wt%; and

[0196] (d) from 5 to 50 wt% water, preferably 10 to 30 wt%.

[0197] In one embodiment the additive composition of the third aspect comprises:

[0198] (a) from 40 to 80 wt% of a dialkyl sulfosuccinate, preferably from 50 to 75 wt%;

[0199] (b) from 1 to 25 wt% of an a-olefin sulfonate surfactant compound, preferably from 5 to 15 wt%;

[0200] (c) from 0.1 to 20 wt% of one or more alcohols, preferably from 1 to 10 wt%; and (d) from 5 to 50 wt% water, preferably 10 to 30 wt%.

[0201] In one embodiment the additive composition of the third aspect comprises:

[0202] (a) from 1 to 50 wt% of a dialkyl sulfosuccinate, preferably from 10 to 30 wt%;(b) from 1 to 25 wt% of an a-olefin sulfonate surfactant compound, preferably from 5 to 15 wt%;

[0203] (c) from 0.1 to 10 wt% of one or more alcohols, preferably from 0.5 to 5 wt%;

[0204] (d) from 5 to 50 wt% water, preferably 10 to 50 wt%; and

[0205] (e) from 1 to 50 wt% of an alkyl sulfate surfactant, preferably from 10 to 30 wt%.

[0206] In one embodiment the additive composition of the third aspect comprises:

[0207] (a) from 40 to 80 wt% of dihexyl sulfosuccinate, preferably from 50 to 75 wt%;

[0208] (b) from 0.1 to 25 wt% of a compound of formula (VA) and / or (VB), preferably from 1 to 15 wt%;

[0209] (c) from 0.1 to 30 wt% of one or more alcohols, preferably from 2 to 20 wt%; and (d) from 5 to 50 wt% water, preferably 10 to 30 wt%.

[0210] In one embodiment the additive composition of the third aspect comprises:

[0211] (a) from 40 to 80 wt% of dihexyl sulfosuccinate, preferably from 50 to 75 wt%;

[0212] (b) from 0.1 to 20 wt% of a compound of formula (VA) and / or (VB), preferably from 1 to 10 wt%;

[0213] (c) from 1 to 30 wt% of one or more alcohols, preferably from 5 to 20 wt%; and (d) from 5 to 50 wt% water, preferably 10 to 30 wt%.

[0214] In one embodiment the additive composition of the third aspect comprises:

[0215] (a) from 40 to 80 wt% of dihexyl sulfosuccinate, preferably from 50 to 75 wt%;

[0216] (b) from 1 to 25 wt% of a CM to Ci6 a-olefin sulfonate salt, preferably from 5 to 15 wt%; (c) from 0.1 to 20 wt% of one or more alcohols, preferably from 1 to 10 wt%; and (d) from 5 to 50 wt% water, preferably 10 to 30 wt%.

[0217] In one embodiment the additive composition of the third aspect comprises:

[0218] (a) from 1 to 50 wt% of dihexyl sulfosuccinate, preferably from 10 to 30 wt%;

[0219] (b) from 1 to 25 wt% of a CM to Ci6 a-olefin sulfonate salt, preferably from 5 to 15 wt%; (c) from 0.1 to 10 wt% of one or more alcohols, preferably from 0.5 to 5 wt%;

[0220] (d) from 5 to 50 wt% water, preferably 10 to 50 wt%; and

[0221] (e) from 1 to 50 wt% of an alkyl sulfate surfactant, preferably from 10 to 30 wt%.

[0222] The present inventors have surprisingly found that the inclusion of at least one sulfosuccinate surfactant compound and / or a-olefin sulfonate surfactant compound in an acidic electrolyte solution can significantly reduce the formation of an acid mist during electrochemical processes such as electrowinning.Preferably the addition of the one or more sulfosuccinate surfactant compounds reduces the formation of acid mist by at least 10%, preferably by at least 20%.

[0223] In some embodiments the formation of the acidic mist may be reduced by more than 50%, for example more than 60%, preferably more than 70%.

[0224] The amount of acid mist which forms during an electrowinning process may be measured by any suitable means. Such means will be known to the person skilled in the art. One suitable method is described in example 2.

[0225] The amount of acid mist produced during an electrochemical process may be determined by dissolving the gases released into the electrochemical chamber in water and measuring the pH of the solution or by titration.

[0226] A particular advantage of the present invention is that it does not involve the use of fluorine containing compounds.

[0227] The additive composition of the third aspect or used in the first and second aspects preferably comprises less that 1 wt% fluorine containing compounds, preferably less than 0.1 wt%, more preferably less than 0.01 wt%, suitably less than 0.001 wt%.

[0228] Preferably the additive composition of or used in the present invention is substantially free of fluorine containing compounds.

[0229] As well as effectively reducing the formation of acid mist it is desirable that any additive used in an electrowinning process does not have a deleterious effect on any of the steps in the ore extraction process.

[0230] A problem that may occur due to inclusion of surfactants in compositions used in these processes is foaming.

[0231] The formation of a foam is highly undesirable as it interferes with subsequent steps. This may increase the time needed to complete the process and may reduce the quality of the deposited metal. In preferred embodiments the method and use of the present invention can achieve high levels of metal recovery and acid mist suppression but not produce a high level of foaming.

[0232] Additionally the additive of the present invention preferably does not inhibit phase separation (of aqueous and non-aqueous phases) in any of the ore extraction steps.Preferably the use of one or more additives selected from sulfosuccinate surfactant compounds and a-olefin sulfonate surfactant compounds according to the present invention does not interfere with phase disengagement. This enables the electrolyte solution to be recycled back into the solvent extraction step after the electrowinning step is completed.

[0233] A further benefit of the present invention is that the inclusion of one or more additives selected from sulfosuccinate surfactant compounds and a-olefin sulfonate surfactant compounds in the electrowinning process allows deposition of the metal to be achieved in high purity and high yield. A smooth metal surface is also provided, with the surface quality being comparable to or superior to that achieved when using the commercial additive of the prior art.

[0234] Preferably metal recovery using the method of the present invention is at least 70%, preferably at least 80%, more preferably at least 90%, for example more than 95%.

[0235] It is common in electrochemical processes to include a smoothening aid as an additive in order to provide a smooth surface on the deposited metal. An additional advantage of the present invention is that a smooth surface is obtained, without the need for a separate smoothening additive.

[0236] However although additional smoothening aids are not needed, the use of these in combination with the additives of the present invention does not lead to any adverse effects.

[0237] The present invention suitably provides an effective and efficient acid mist suppression that does not affect the smoothness of the deposited metal. The present invention suitably does not lead to any nodules, dendrites or other surface abnormalities.

[0238] The invention will now be further described by reference to the following non-limiting examples.

[0239] Example 1

[0240] Additive compositions of the invention were prepared comprising the following components:

[0241]

[0242]

[0243] Comparative compositions were prepared comprising the following components:

[0244] Composition H - the industry standard commercial additive comprising 45 to 55 wt% fluoroalkyl acrylate

[0245] Composition I - commercial product sold under the trade mark Mistop® and comprising 16 to 18 wt% Quillaja saponin extract

[0246] Example 2

[0247] A 20L stock of copper electrolyte solution was prepared comprising 45 g / L Cu in the form of copper sulfate and 180 g / L sulfuric acid. ICP analysis was carried out to confirm the concentration of Cu in the stock solution.

[0248] 350ml of the stock electrolyte solution was charged into an electrochemical cell, connected to an acid mist extraction pump configured to remove gases produced. The cell was heated to 45°C and allowed to stabilize for 30 minutes before the additive was introduced in the amounts specified in table 2:

[0249] Table 2

[0250]

[0251]

[0252] After further stabilisation for 30 minutes at 45°C, the electrodes - a lead anode and a stainless-steel cathode - were immersed in the solution. Electrowinning and the acid mist extraction pump were then started simultaneously. The temperature of the solution was maintained at 45°C throughout the process unless stated otherwise.

[0253] Each electrode had an active surface area of 80x20 mm and a current density of 300 A / m2was used.

[0254] Each test was run for 4h with the acid mist extracted at 1.5 L / min by a pump into a reservoir of deionised water.

[0255] The reservoir of deionised water was collected at the end of the test and a 50 ml sample was titrated with 0.01 M NaOH using a phenolphthalein indicator. The concentration was recorded as acid mist evolved from the process and a percentage of acid mist suppression was calculated by comparison with a blank (identical process mixture additive).

[0256] Once the electrowinning run was finished, the cathode was rinsed in deionised water, and then rinsed with acetone to dry. The amount of Cu deposited or recovered was determined by the difference in the weight of the cathode before and after the test. The cathodes were observed both by the naked eye and under the microscope (KEYENCE VHX 2000) for nodules, dendrites, cracks and for any defects on the quality of the deposit.

[0257] The quality of copper deposition was rated from 1 (lowest quality) to 5 (highest quality) according to the following scale:

[0258] 1 - signs of dendrites, nodules, rough surface

[0259] 2 - nodules, sludge precipitation, rough surface

[0260] 3 - rough surface

[0261] 4 - good deposits with only minor cracks

[0262] 5 - smooth surface

[0263] The foam was visually inspected and assessed during each experiment.

[0264] The results are shown in table 3:Table 3

[0265]

[0266] Example 3

[0267] 5 L of stock of copper electrolyte solution comprising 40 g / L Cu in the form of copper sulfate and 180 g / L sulfuric acid was placed in a polypropylene tank inside an extraction chamber. The electrolyte bath was heated to 40°C and maintained at this temperature for the duration of the test.

[0268] Oxygen was diffused from the bottom of the electrolyte solution at a flow rate of 1.5 L / min, through a gas diffuser that was submerged in the tank. The infused oxygen generated bubbles that travelled through the electrolyte solution and burst at the surface / air interface, releasing droplets of acidic aerosols (acid mist) into the air of the extraction chamber. An exhaust fan located at the top of the chamber pulled the acid mist outward from the electrolyte bath into an open-face sampling cassette equipped with a 37 mm diameter quartz fibre filter, at an air velocity of 2.38 m / s and a flow rate of 0.01929 m3 / s.

[0269] The test was run for 30 minutes to allow vaporized aerosols to be absorbed onto the quartz fibre filter. The filters were then collected, removed from the sampling cassettes, immersed in 50 mL of deionized water and sonicated for 15 minutes to wash the acid from the filter. The collected acidic solution was titrated with an auto titrator to determine the acid concentration.The test was repeated for electrolyte solutions detailed in table 4 below. The mist suppression efficiency for each additive was calculated by comparing the acid concentration obtained from each test with a blank comprising no additive.

[0270] Table 4

[0271]

[0272] Comparative

[0273] The composition of the present invention suppressed acid mist in comparable amounts to the industry standard commercial additive (Composition H)

[0274] Example 4

[0275] A phase disengagement test was carried out to measure the ability of the electrolyte solution to separate from an emulsion. This is important as the electrochemical step is part of a larger ore extraction process. The additives used in the invention must not disrupt a solvent extraction step in another part of the process. This enables the electrolyte to be recycled into the solvent extraction step without any further purification

[0276] An electrolyte stock solution comprising copper sulfate (45g / L) and sulfuric acid (180g / L) was prepared.

[0277] An organic solvent mixture containing 85 v / v% of petroleum distillates (Orfom® SX-12 from Chevron Phillips Chemical Company) and 15 v / v% of a 1 :1 volume blend of 5-nonylsalicylaldoxime and 2-hydroxy-5-nonylacetophenone (LIX®984N-C from BASF) was prepared.

[0278] Organic continuous test200mL of the organic solvent mixture was stirred at room temperature with a magnetic stirrer at maximum stirring speed. 200mL of the electrolyte stock solution was slowly added into the stirred organic solvent to form an emulsion. The emulsion was further stirred for 30 seconds, and the stirring was stopped. Immediately after, the time taken for the emulsion to break was recorded (ie. the time taken to form a clear visual boundary between the organic and aqueous phase).

[0279] Aqueous continuous test

[0280] 200mL of the electrolyte stock solution was stirred at room temperature with a magnetic stirrer at maximum stirring speed. 200mL of the organic solvent mixture was slowly added into the stirred electrolyte stock solution to form an emulsion. The emulsion was further stirred for 30 seconds, and the stirring was stopped. Immediately after, the time taken for the emulsion to break was recorded (ie. the time taken to form a clear visual boundary between the organic and aqueous phase).

[0281] The test was repeated in duplicate for each test electrolyte solution containing the acid mist suppression additives at a treatment rate of 20 ppm additive. The average breaking emulsion times for each test is recorded in Table 5.

[0282] Table 5

[0283]

[0284] Comparative

[0285] Composition D of the invention showed improved performance compared with the commercial additive, composition H.

[0286] Example 5

[0287] The electrowinning method described in Example 2 was repeated using the additives listed in table 6.

[0288] Guar gum and the polyacrylamide MAGNAFLOC® 10 AP are known commercially as smoothening aids.

[0289] Table 6

[0290]

[0291] Microscope images of the surfaces of the copper obtained are shown in figures 1 to 18. Figures 1 to 17 correspond to additive compositions 1 to 17 of table 6 and figure 18 shows the copper surface when no additive was used (blank).

[0292] This test demonstrates that the additive of the present invention can provide a smooth surface whether or not a known smoothening aid is also present. No negative effect is seen when a smoothening aid is also used.

Claims

28Claims1. The use of one or more additives selected from sulfosuccinate surfactant compounds and a-olefin sulfonate surfactant compounds to reduce acid mist formation in an electrochemical process.

2. A method for recovering a metal from an acidic electrolyte solution comprising ions of the metal, the method comprising:- adding one or more additives selected from sulfosuccinate surfactant compounds and a- olefin sulfonate surfactant compounds to the acidic electrolyte solution; andpassing an electric current through the acidic electrolyte solution comprising metal ions;wherein the amount of acid mist produced during the method is lower than that produced in an otherwise identical method without the addition of the one or more additives.

3. A use according to claim 1 wherein the electrochemical process is an electrowinning process.

4. A method according to claim 2 wherein the electrolyte solution comprises a copper salt.

5. A method according to claim 2 or claim 4 wherein the electrolyte solution comprises an acid selected from sulfuric, phosphoric, perchloric and hydrochloric acid.

6. A method according to any of claims 2, 4 and 5 wherein the electrolyte solution comprises copper sulfate and sulfuric acid.

7. A use or method according to any preceding claim wherein the one or more additives comprises a sulfosuccinate surfactant compound of formula (I):wherein one of R1and R2is X and the other is an optionally substituted hydrocarbyl group; or both of R1and R2are optionally substituted hydrocarbyl groups; wherein the or each X is independently selected from hydrogen, a metal ion or an optionally substituted ammonium ion.

8. A use or method according to claim 7 wherein each of R1and R2is an unsubstituted alkyl group, preferably having 4 to 12 carbon atoms.

9. A use or method according to any preceding claim wherein the one or more additives comprises a sulfosuccinate surfactant compound of formula of formula (II) and / or (III):(II) (III)wherein R1or R2is a group of formula (CHR3CHR4O)nR5wherein n is at least 1 ; in each moiety CHR3CHR4O one of R3and R4is hydrogen and the other is hydrogen or a methyl group; and R5is a straight chain or branched optionally substituted alkyl or alkenyl group.

10. A use or method according to claim 9 wherein each of R3and R4is hydrogen, n is from 3 to 8 and R5is an unsubstituted alkyl group having 8 to 16 carbon atoms.

11. A use or method according to any preceding claim wherein the one or more additives comprises an a-olefin sulfonate surfactant compound of formula R6SO3'M+wherein R6is an alkenyl group and M+is a hydrogen, metal or ammonium cation.

12. A use or method according to claim 11 wherein R6is an alkenyl group 8 to 30 carbon preferably 10 to 20 carbon atoms.

13. A use or method according to any preceding claim wherein the one or more additives comprise:(a) a first additive comprising at least one sulfosuccinate surfactant compound of formula (I):(I)in which both R1and R2are optionally substituted hydrocarbyl groups and X is selected from hydrogen, a metal or an optionally substituted ammonium ion; and(b) a second additive selected from one or more of:(i) a sulfosuccinate surfactant compound of formula (II) and / or (III):(II) (III)in which R1or R2is (CHR3CHR4O)nR5wherein n is at least 1 ; in each moiety CHR3CHR4O one of R3and R4is hydrogen and the other is hydrogen or a methyl group; R5is a straight chain or branched optionally substituted alkyl or alkenyl group; and X is selected from hydrogen, a metal or an optionally substituted ammonium ion; and(ii) an a-olefin sulfonate surfactant compound.

14. An additive composition comprising:(a) a first additive comprising at least one sulfosuccinate surfactant compound of formula (I):in which both R1and R2are optionally substituted hydrocarbyl groups and X is selected from hydrogen, a metal or an optionally substituted ammonium ion; and(b) a second additive selected from one or more of:(i) a sulfosuccinate surfactant compound of formula (II) and / or (III):in which R1or R2is (CHR3CHR4O)nR5wherein n is at least 1 ; in each moiety CHR3CHR4O one of R3and R4is hydrogen and the other is hydrogen or a methyl group; R5is a straight chain or branched optionally substituted alkyl or alkenyl group; and X is selected from hydrogen, a metal or an optionally substituted ammonium ion; and(ii) an a-olefin sulfonate surfactant compound.

15. A use or method according to any of claims 1 to 13 wherein the one or more additives are provided in an additive composition according to claim 14.

16. A composition, use or method according to claim 14 or claim 15 wherein the weight ratio of component (a) to component (b) is from 50:1 to 1 :1 , preferably from 20:1 to 1.5:1.

17. A composition, use or method according to any of claims 14 to 16 wherein component (a) comprises at least one sulfosuccinate surfactant compound of formula (I):in which X is sodium and both R1and R2are unsubstituted alkyl groups, preferably having 3 to 18. preferably 4 to 12 and most preferably 6 carbon atoms.

18. A composition, use or method according to any of claims 14 to 17 wherein component (b) comprises:(i) a sulfosuccinate surfactant compound of formula (II) and / or (III):(II) (III)in which X is sodium and R1or R2is (CH2CH2O)nR5wherein n is from 1 to 12 preferably from 2 to 10, preferably from 4 to 8, more preferably from 5 to 7 and R5is an alkyl group having 4 to 30, preferably 6 to 20, suitably 8 to 16, preferably 10 to 12 carbon atoms.

19. A composition, use or method according to any of claims 14 to 18 wherein component (b) comprises:(ii) an a-olefin sulfonate surfactant compound of formula R6SO3'M+wherein R6is an alkenyl group having 6 to 36 carbon atoms, preferably 8 to 30 carbon atoms, preferably 8 to 24 carbon atoms, preferably 10 to 20 carbon atoms; and X is sodium.

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