CA1191812A - Mist suppressant for solvent extraction metal electrowinning - Google Patents

Abstract

ABSTRACT OF THE DISCLOSURE
The invention relates to a process for the recovery of elemental metal values from ores and processing liquids by solvent extraction-eletrowinning.
The process involves extracting metal values by means of an aqueous strip solu-tion containing strong acid such as sulphuric or phosphoric acid. The aqueous strip solution containing the metal values is used as electrolyte in an electro-plating process to electrowin the metal values. A problem which has arisen is that oxygen evolved at the anode during electroplating entrains the strong acid electrolyte, to form a fine mist or spray which is corrosive and constitutes a health hazard. In the present invention, the aqueous strip solution contains from 1 to 200 parts by weight of fluoroaliphatic surfactant, per million parts of strip solution, the surfactant having at least one cationogenic group which is the radical of a base having an ionization constant in water at 25°C of at least 10-6, and containing at least 30 weight percent fluorine in the form of carbon-bonded fluorine in a fluoroaliphatic radical, said fluoroaliphatic radi-cal having at least 4 carbon atoms and at least a terminal perfluoromethyl group.
The invention inhibits or suppresses acidic mist formation above electrowinning tanks.

Description

V~

MIST SUPPRESSANT FOR SOLVENT EXTRACTION METAL ELECTROWINNING

Technical Fleld -This invention relates to the recovery of metal values from a solution thereof by the solvent extraction-electrowinning proce~s. Also, this invention relates tothe recovery of copper by the solven~ extraction-electrowinning process. In addition, this invention relates to a method for inhibiting the ormation of acidic mist above el~ctrowinning tanks.

Background Art The process for recovery of elemental metal values from ores and processing liquids by solvent extraction-electrowinning (hereafter, "SX-EW") is well-known. Briefly, the process is carried out using a metal-bearing aqueous solution. Such metal-bearing solution i8 obtained by dissolving (generally from an ore) the desired metal in an aqueous leach liquor9 or by using a metal-bearlng ~olution such as process ~ffluent. The resulting solutlon of metal values is mixed with a wa~er-immiscible organic solven~ (e.g., kerosene) containing a water-insoluble ion exchange composition having selective affinity for the desired metal values.
The ion axchange composition preerentially extracts the desired metal values from the aquaous solution. The aqueous and organic pha~es are separated. The aqueous solution, now metal-depleted, is usually referred to as "rafEinate". The raEEinate can be recycled as leach liquor (in a l~aching process) or discarde~ (in a process such as recovery of metal from process effluent). The organic phase (which contains ion exchange composition and the extracted metal values) i~ usually referred to as "loaded organic". The de~ired metal values ~re removed ~rom the loaded organic by mixing with an aqueous strip '~

solution containing strong acid such as sulfuric, phosphoric, or perchloric acid, and having lower pH than the above metal-bearing aqueous solution. The aqueous strip solution extract~ the desired metal values into the aqueous phase. After separation of th~ organic and aqueous phases, the desired metal values are present in the aqueous strip solutionl and the re~ul~ing metal-enriched strip solution i3 usually referred to as "electrolyte" or "pregnant electrolyte". The metal-depleted organic phase i~ usually referred to as "spent organic~. Such spent oryanic can be recycled for fresh loading with metal values by mixing with metal-bearing aqueous solution. Metal isolation as described above is generally referred to as "solv~nt extraction"
(h2r~after, ~'SX"). The desired metal is recovered in purified form hy electroplating the metal frQm the electrolyte. Such recovery by electroplating is generally referred to as "electrowinning" (hereafter "EW"). ~fter recovery of the desired metal, the metal-depleted electrolyte is usually referred to as "spentelectrolytel'. Such spent electrolyte can be recycled as aqueous strip solution for fresh loading with metal values by mixing with loaded organic.
The SX-EW process is carried out commercially on a continuous basis and is used for the rPcovery of metals such as copper or nickel~ Industrial use of the SX-EW
process is increasing due to its efficiencyv low energy costs, low pollution levels, and simplified ma~erials handling requirements. The SX EW process is described, for example, in Tuddenham, W. M. and ~ougall, P. A., "Copper", Kirk Othmer Enc~clopedia o~ Chemical Technology, 3rd Ed., Vol. 6, 850-852 (1979), McGarr, H. JO~ "Solvent Extraction Stars in Making Ultrapure CopperU, Chemical Engineering, Vol. 77, No. 17l August 10, 1970, pp. 82-84, and Merigold, C. R. and House, J. E.~ "The Application of Liquid Ion Exchange Technology to the Recovery of Copper~
(a paper presented at the Copper T~chnology Seminar in -3~

Washington, D.C., December 1975). Flow charts showing the SX-~ process are included, for example, in Tuddenham et al, id at 851 and in McGarr, id at 83-84.
During the electrowinning step, elemental metal is plated out at the electrowinning cathode and oxygen evolves at an insoluble anode. The evolution of oxygen gas entrains strong acid electrolyte, carrying it into the air above the electrowinning tank in the form of a fine mist or spray. This mist or spray then spreads throughout the electrowinning tankhouse. The acidic mist is corro-si~e and a health hazard and can cause extreme discomfort to the skin, eyes, and respiratory qystems o~ tankhouse workers, especially during hot weather conditions This has caused high turnover among tankhouse workers.
A similar mis~-formation problem once occurred in the chromium plating industry. Chromium pla-tin~
companies employed extensive ventilation above plating tanks, clothed workers in heavy protective garments, and floated plastic balls on the surface of the electrolyte to reduce mist-formation and problems caused by such mist.
These expedients were cumbersome and insufficiently effective. The use of such expedients was made unnecessary after the discovery and use of certain ~table fluorochemical surfactants which, when added to a chromium plating bath, promoted formation of a foam at the surface oE the plating bath which effectively eliminated chromic acid mist formation. Such fluoroch~mical surfactants are described, for example, in U.S. Patent NosO 2,750t334,

2~750,335, 2,750,336, and 2,750,337.
As described above, the SX-EW process is generally carried out on a continuous basis, with recycling and regeneration of the metal-bearing aqueous solution, the organic phase, and the electrolyteO Thus, after a portion of the desired metal has been plated from the electrolyte, the spent electrolyte is ~ixed with fresh loaded organic. This process subjects the electrolyte to a series o stages in which the electrolyt@ is mixed with loaded organic, phase separa-ted, subjec-ted to electroplating conditions, and recycled. Certain fluorochemical foam-forming surfactants such as those commonly used in the chromium plating indus-try proved -to be unsatisEactory for inhibiting acidic mist formation above electrowinning tanks used in -the SX-EW process. For example, the conventional chrome plating fluorochemical mist suppressan-t C8FL7SO3K gave good ini-tial foam formation and mist suppression above a copper electrowinning tank, but the fluorochemical was rapidly extracted in-to the organic phase during recycling of the electrolyte, and subsequently was extracted in-to the raffinate. In addi-tion, -the fluorochemical surfactant C8F17SO3K was found to interfere wi-th copper recovery and to retard phase separation between organic and aqueous phases when used with ion exchange compounds such as "Acorga P5300"* (commercially available from Imperial Chemical Industries, Ltd.) and "LIX 64N"* (commercially available from ~lenkel Corporation).
In order to suppress acidic mist formation in the electrowinning tank-house, SX-EW metal producers have utilized mist suppression expedients such as those used in the chrome plating industry, before discovery of suitable foam-forming mist suppressing agents. For example, SX-EW producers ernploy extensive ventilation in the electrowinning tankhouse, clothe workers in protective gar-ments, and float plas-tic balls on the surface of the electrowinning electroly-te.
These means are cumbersome and only partially effective, especially during hot weather. Also, electrowinning tanks have been covered with polypropylene tank blankets, and in United States Patent No. 3,948,747 -there is described a mist suppressing technique for copper SX-EW carried out by floating elongated members (such as plastic rods) on the electrowinning electrolyte.
Summary of Invention The present invention provides, in one aspect, a process for recovery of metal values by liquid-liquid solvent extraction of said metal values from *Trade Mark metal-bearing aqueous solution, stripping of said metal values into acidic aqueous solution containing strong acid, and electrowinning of said metal.
values from an electrolytic cell, said cell comprising one or more insoluble anodes, a me-tallic cathode, and electrolyte containing said s-trong acid and said metal values, said process including recycling of said electrolyte, wherein the improvement comprises electrowinning said metal values from elec-trolyte con-tai.ning sufficient fluoroaliphatic surfactant to provide mis-t-inhibi-ting foam on the surface of said electrolyte, said surfactant having at least one ca-tiono-genic group which is the radical of a base having a ionization constant in water at 25 C of at least about 10 , and containing at least about 30 weight percent fluorine in the form of carbon-bonded fluorine in a fluoroaliphatic radical, said fluoroaliphatic radical having at least 4 carbon atoms and a-t least a terminal perfluoromethyl group.
The present inven-tion also provides a process for the recovery of metal values from metal-bearing aqueous solutions, comprising the steps of:
(a) mixing said metal-bearing aqueous solution wi-th water-immiscible organic solvent containing water-insoluble organic ion exchange composition, said compo-sition having selective affinity for said metal values, thereby forming me-tal-bearing organic solution and metal-depleted aqueous solution; (b) separa-ting said metal-bearing organic solution and said metal-depleted aqueous solutioni (c) contacting said metal-bearing organic solution with aqueous strip solution comprising strong acid and 1 to 200 par-ts by weight of fluoroaliphatic surfact-ant per million parts by weight of strip solution, said surfactant having at least one cationogenic group which is the radical of a base having an ionization constant in water at 25 C of at least 10 , and containing at least 30 weight percent fluorine in the form of carbon-bonded fluorine in a fluoroaliphatic radical, said fluoroaliphatic radical having at least 4 carbon atoms and at least a terminal perfluoromethyl group, thereby forming metal-enriched aqueous strip solution and metal-depleted organic solu-tion, said metal-enriched aqueous strip solution having a sur:Eace tension at 25C
which is less than or equal to 35 dynes/cm; (d) separa-ting said metal-depleted organic sol.u-tion and said metal-enriched aqueous strip solution; (e) electroplating said metal values onto a metallic ca-thode using said metal-enriched aqueous s-trip solu-tion as electrolyte in an electrolytic bath, by passing direct electric current between said cathode and an insoluble anode or anodes, wi-th the surface of said electrolytic bath being wholly or partly covered with foam formed from the interaction of said electrolyte (including said surfactant) and a gas selected from the group consisting of oxygen evolved from said electrolyte at said anode or anodes, air and any gas entrained in said electrolyte, said foam suppressing misting of said electrolyte and release of said electrolyte i.nto the atmosphere surrounding said electrolytic bath;
and (E) recycling the resulting metal-depleted electrolyte for use as aqueous strip solution in step (c).
The present invention also provides an el.ectrowinning bath containing foam-forminy mist suppressant comprising fluoro-aliphatic surfactant containing at least one cationogenic groupwhich is the radical of a base having an ionization constant in water at 25C of at least 10 6.

;

33L8~i~

The invention inhibits or suppresses acidic mist formation above electrowinning tank~ at low concentration of surfactant in the electrolytlc bathO Th~ compounds u~ed in this invention do not readily dissolve in the water-immiscible organic solvent and do not seriously interfere with the rate of metal extraction by the ion exchange composition.
An additional advantage of the present invention is that in the process of solvent extrac~ion-electro-winning of copper, copper deposited at the electrowinningcathode from an electrolytic bath containing fluoroaliphatic ~urfactants a~ described in this inventlon generally will be higher quality copper than copper deposited from a similar electrolytic bath which does not contain such surfactants. Such higher quallty deposited copper has a ~ine grained microstructure, a smooth surface, and a reduced level of occluded, partlcula~e impurities, and thus can be more readily drawn int3 small-diameter wire with reducecl chance of breakage compared to lower quality copper containing occluded, particulate impurities. Xt should be noted that certain cationic ~luoroaliphatic surfactants have been reported in U.S. Patent No~ 2,750,335 to give improved plating brightness when added to chromium electroplating baths.
Also, a cationic fluoroaliphatic surfactant has been reported in l'3M Brand Fluorochemical Surfac~ants Technical Information", pp. 36-37 (l963) to provide copper brightening in dip-coating, when used at 0.02 percent concentration of surfactant in the dip bath~

_tailed Description In the practice of the present invention, the electrolyte to be treated with the fluoroaliphatic suractants used in this invention is ordinarily prepared by SX steps using conventional organic SX ~olvents, ion exchange composition~, and aqueous meta~-bearillg and electrolyte solutions, and generally conventional SX-EW

~ ~9~

processing conditions. Such oryanic SX solvents, ion exchange co~positions, aqueous solutions, and processing conditions are well-known to those skilled in the art, and for purposes of brevity will not be described in great detail herein, reference being made to publications describing the SX EW proces~ such as those cited above, Agers et al., Copper Recovery from Acid Solutions U~ing Li~uid Ion Exchan~e, Merigold et al., LIX~64N - The Recovery of Copp~r from Ammoniac~l Leach Solution~, Rordoskyl G. A., Ed., The Chemistry of Metal~ Recovery Using LIX~ R~a~ents/ (the lat~er thre~ public~tions being publications of ~enkel Corporation~ and publications cited therein for further conventional d~tails reg~rding the SX-EW process.
Acidic mi~t formation at ~he EW anode is minimized or eliminated in this inven~ion by use of EW
electrolyte containing a small quantity of certain fluoroaliphatic surfactants. Such surfactants lower the surEace tension of the electrolyte and promote formation of a dense, stable foam at the EW anode. The surfactants used in this invention have low solubility in the organic phase employed in the SX proces~, are not readily extracted from the EW electrolyte, and do not seriously interfere with copper recovery by the ion exchange compo~ition.
Fluoroaliphatic surfactants useEul in this invention are organic molecules containing at least about 30 percent by weight ~luorine in the form of carbon-bonded fluorine in at least one fluoroaliphatic radical Rf and at lea~t one cationogenic group which i~ th~ radical of a base having an ionization constant (the logarithm of the reciprocal of said ionization cons~ant being referred to as pKb) in water at 25~C of at least about 10-6.
Fluoroaliphatic surfactant~ Eor use in this invention can also contain at lea~t one anionogenic group which is the radical of an acid havlng an ionization c~n~tant ~the logarithm of the reciprocal of said ionization constant _9_ being referred to as pKa~ ln water a~ 25C of at least about 10-6. Fluoroaliphatic surfac~ants which contain the above~mentioned cationogenic groups but do no~ contain such anionogenic group~ in the same molecule will be referred to herein as catlonic fluoroallphatic surfactants. Fluoroaliphatic ~urfactant~ which contain such cationogenic and ~uch anionogenic groups in the same molecule will be referred to herein as amphoteric fluoroaliph~tic surfactants. Cationic, amphoteric, or mixtures of cationic and amphoteric fluoroaliphatic surfactants can be used in this invention, with amphoteric fluoroaliphatic surfactant3 and mixtures of cationic and amphoteric fluoroaliphatic surfactants being preferred.
R~ is a fluorinated, monovalent, aliphatic, preferably saturated organlc radic~l containing at lea~t carbon atoms~ The skeletal chain of Rf can be straight~
branched, or, iE sufficiently large, cyclic, and can include divalent oxygen atoms or krivalent nitrogen atoms bonded only to carbon atoms. Preferably, Rf is fully fluorinated, but hydrogen or chlorine atom~ can be present as substituents on the skeletal chain, provided that not more than one atom of either hydrogen or chlorine is present for every two carbon atoms in the skeletal chain, and Rf contains at least a terminal perfluoromethyl group.
While radicale containing a large number of carbon atom~
will function adequately, compounds containing not more than about 20 carbon atoms are preferred since larger radicals usually repre~ent a less ef~icient utilization of fluorine than is possible with ~horter skeletal chains.
Preferably, Rf contains about 5 to 14 carbon atoms.
The cationogenic groups in said cationic and said amphoteric fluoroaliphatic surfactants are radicals of quaternary ammonium salts or radicals of cation-generating amines. Such amine3 can b~ oxygen-free (e.g~ -NH2~ or oxygen-containing ~e.g~ amine oxides).
Such cationogenic groups can have formulas ~uch as -NH2, -(NH3)X, -(NH(R2)2~X, -(N(R2)3)X, or -N(R2)~-~O where X is a co-anion such as halogen, hydroxide, sulfate, bisulfate or carboxylate, R2 is H or Cl_lB and preferably Cl_6 alkyl, and each R2 can be the same as or different from other R2. Preferably R2 is H or unsubs~ituted or substituted hydrocarbyl. ~referably, X is chloride, hydroxide, or bisulfate. Preferably, such ~urfactants contain a cationogenic group which is a quaternary ammonium salt.
The anionogenic groups in said amphoteric fluoroaliphatic surfactants are radicals of anion~ or are radicals which by ionization can become radic~l~ o an1Ons. The anionogenic groups can have formulas such as -COOM, -SO3M, -OSO3M, -PO3H~, or -OPO3HM, where M is H, a metal ion, or N~(Rl)~ where each Rl is independently H or substituted or unsubstituted Cl_6 alkyl. Preferably M i5 Na~ or K~. Preferably such anionogenic groups have the formulas -COOM, -SO~M or ~PO~HM.
Such cationic ~luoroaliphatic surfactants include those cationic fluorochemicals described, for example, in Guenthner and Vietor, I ~ EC Product Res. &
Dev., 1 (3) 165-9 (1962), and U.5. Patent No~. 2,732,398, 2,7S~,60~, 2,764,603, 2,8~3,656, 2,809,990, 3,2S5,131, 4,000,168~ 4~042,522, 4,069,158, 4,069,2~, 4,~090,9~7, 4,161,590 t and 4,161~602.
Such amphoteric fluoroaliphatic ~urfactants include those amphoteri~ fluoroche~icals described, for example, in Guenthner, R. A. and Vietor, M. L., id, Australian Patent Specification No. 432,809, and U.S.
Patent Nos. 2,764,602, 3,147,064, 3r450t755, 4,042,522, 30 4,069,158, 4,090,967, 4,161,590, and 4,161,6~2.
Representative fluoroaliphatic suractants containing the above~men~ioned cationogenic groups (and the above-mentioned anionogenic groups~ if such surfactants are amphoteric) can be repre~ented by ~everal structural formulas, including formulas o~ nonlonized (i.e., neutral) compounds and salts, including internal salts. Such representative sur~actants include those of the formula shown below ~in the for~ of salts):
R3 R3 r ~5 Rf(Q)a~cta(Q)a~zta~Nta(Q)a -N~_R6 [~ ]b R4 _ R7 _ b wherein:
a is independently 0 or 1;
b i~ 1 or 2;
Rf is a flusro~liphatic radical a~ defined above, with the proviso that the molecule con~ains at least about 30 ~eight percent fluorine in the form of carbon-bonded ~luorine in Rf;
Q is independently a polyvalent (e.g., -CH2CHCH~-), generally dival~nt (e.g., -C~2-, -C2~14-~ -C3H6-~ -C6H4-~ -CH2SCH2-, and -CH2OCH2-1, hydrocarbylene linking group of 1 to 12 carbon atoms which can contain catenary oxygen or sulfurl is unsub6tituted or sub~tituted by halogen, hydroxyl, or aryl, and i5 preferably free of aliph~tic un~aturation, with the proviso that at least one Q group is pre~ent in the molecule;
R3 is independently:
R4 wherein R~ is H or alkyl which is unsubstituted or substltuted with halogen, hydroxyl, or aryl and contains no more than a total number of 18 carbon atoms, wlth R4 preferably being ~aturated r unsubstituted Cl_6 alkyl;
(Q1aAM wherein A is -COO~, -SO3-, ~OSO3 , -PO3H-, or -OPO3H-, and M is as de~ined above; or QNR5R6R7 wherein R5 and R6 are independently H, substituted or unsubsti~uted alkyl of 1 to 18 carbon atoms (preferably 1 to 6 carbon atoms), or togethe~ with the N ato~

-~12~

form a cyclic aliphatic or aromatic ring which can contain additional O, S, or N
atoms, and R7 is R~, a quatern~ry a~monium group containing no more than 20 carbon ~toms, or (Q)~jAM;
Z is -CO- or -SO2-; and X is a~ defined above.
Useful subgenera of formula I include compounds of the formula (shown as internail ~alts):
p~ 1~5 R~-SO2-N--~--N+-R6 II

wherein R~ contains about 4 to 8 carbon atoms, Q
is alkylene or hydroxyalkylene, A i~ COO~ or -SO3~, and R5, R6, and R7 ~ire alkyl or hydroxyalkyl; and O~ H R5 R~-Q-C~N-Q-N+-R6 III

~o wherein Rf contains about 4 to 12 car~on atoms, Q is alkylene, R5 and R6 are lower alkyl, and R7 is carboxyalkylene.
Representative cationic fluoroaliphatic surfactants useful in this inventlon include those listed below. Whiile particular structures are shown, in strongly acidic aqueous solution such as electrowlnning electrolyte the cationogenic group of such structures will ~xist primarily in the protonated or ~alt form, and, :~.n neutral or basic solution the cationogenic group of ~ ch structures tends to be in the Eorm of the free ba~e,o such solution-form structure3 are equivalents for purpo~es of the present invention.
C6F13SO2NHc3H6N(c~i3)2y [C6Fl3so2N~lc3H6N+lcH3)3]
C6F13S02NH~3H6~C~3)~ ~

~13--lC6F13502NHC3H6N~(CE~3) 2C2H40H] OH--, C6Fl3so2Nlc2~4(~H)c3H~iN(cH3~ 2, [C6Fl3so2N~2H4oH)c3H6N~(c~3) 2C2H40H] OH
[c6Fl3c2H4so2NE~c3H6N ~(CH3) 3] ~H
tC7F15CONHC3~6N+ ( C~13 ) 2H] Cl--, [C ~Fl 7 S02NHC 3H6N+ ( CE~3 ) 3 ] I~ ~
[C8F17S02NHC3H6N+(CH3) 33 2 S042~', [C8Fl7502NHc3H6N~ ( CH3 ) 3] 03SOCH3--, [C8F17C2E~N~tCH3) 2C2H40H] OH--, 1() [C8Fl7c2H4sc2H~coN~Ic2H~LN~ ( CH3 ) 3] Cl--, C 8 F17 C2H4N ~ I-, ~ N CH2 C8F17C I r \ N - CH2 H
CloFl9oc6H4so2NHc3H6N(cH3)2~
(CF3)2cFoc2F4~oNHc3H6N(cH3~2~ and mixtures thereof.
The cationic fluoroaliphatic surfactants used in this invention can be prepared using methods known in the art, such as those described in the above references relating to cationic Eluorochemicals.
Representative amphoteric fluoroaliphatic surfactants useful in the practlce of this inv~ntion are listed below. While particular structures are shown, in strongly acidic aqueous solution such as electrowinning electrolyte the anionogenic group of such structures may be partly or completely protonated and the cationogenic group of such structur@s will exi3t primarily i.n the protonated or salt form, and, in neutral or basic solution the anionogenic group of such structures tends to be negatively ionized and the ca~ionogenic group of such structures tends to be in the form of the free base; such solution-form structures are equivalen~s for purposes of the presen~ invention. For example, a compound of the Eormula R~SO2N(CH2COONa)C3H6N(CH3)2 will have the Eormula 8~

RfSO2N~CH2COOH)C3H6N~H(CH3)2 HSO4~ aqueous sul:Euric acid solution, and the Eormula R~SO2N(CH2COO-Na~)C3H6N(CH3)~ in aqueous sodium hydroxide sol~tion .

C 4 F 9$02NHC 3H6N~ ( CH3 ) 2CH~COO- ~
C4F9CON ( C3H6S03 ) C3H6N~ ( CH3 ) 2C2E~4COOH' C6Fl3c2H4sc2H4N~( CH3 ) 2CH2COO--, C6F13S02NHC3H6N+(CH3) 2CH2CO~
C6F13SO~NHC3H6N+( CH3 ) 2C~ 4COO--' C6F13S02NHC3H6N~CH3) 2C3~16S03 ~
[~6Fl35o2N(c~2cooNa)c3H6N+(cH3) 3] OH--c6Fl3so2~(c2H~cooNa)c3H6N+(cH3) ~CH2--CH2~.
C~Fl3so2N(c3H~so3Na)c2H4N~ ~

C6Fl3sO2N(c3H6sO3Na)c3H6~(cH3) 2~
C6F13~;02N(C3H6S03--)C3E16N'~(CE13) 2C~H40H, C6F13S02N ( CH2CHOHCH2SO32~a ) C3H6N ( C~3 ) 2 r C6Fl3so2N(cH2cHoHcH2so3 )c3H6N+(cH3~2c2E~4oEl~
[C6Fl3so2N(cH2cHoHcH2so3Na)c3H6N+(cH3) 2C2H4OH] OH-, C6Fl3c2H4so2N(cH3)c2H4N+(cH3)2c2H4coo ' C7Fl5coNHc3H6N+( CH3 ) 2C2H4cOo--~
C7F15CON(CH2COO--)C3H6N~(CH3)3, C7F15CON(C2H,ICoo--)c2H~N-t~, ~C2H4~ ~C2H~OH
C7F15C~ N+
~` C2H4~ C2H4C
C7FlsC2H4SC2H~N+( C~3 ) 2CH2COO
CgF17CH2CH ( COO ) N~ ( CH3 ) 3 ~
C8Fl7so2N~c3H6N+~cH3) 2C3H~SO3-, C8F17S02N~c2El4PO20CH3)--C3H6N+(cH3~3 C8Fl7c2H4coNHc3H6N~(CH3)2C2H4COO
ICF3 ~CF3 C3F60CF`CF20CFCON(C3H6S03 )C3H6N~(~H3)3r (CF ) CFOC F CONHC H4N (CH3)2C2H4COO , CloFlgOC6 4 2 2 3 6 3 mixtures thereof.
The amphoteric fluoroaliphatic surfactants used in this invention can be prepared using methods known in -the axt, such as -those described in the above references relating to amphoteric fluorochemicals.
PreEerred fluoroaliphatic surfactants for use in -this invention are C F SO N(CH CHOHCH S3Na)C3H6N(CH3)2' ~C6Fl3s2N( 2 2 3 3 6 C2H40H]OH , and mixtures thereof, especially in the SX-EW processing of copper.
It should be noted that many of said fluoroaliphatic surfactan-ts use-ful in the practice of this invention are mix-tures of homologous fluorochemical compounds and can also contain fluoroaliphatic precursors and by-products from their preparation. Such mixtures are frequently just as useful as the individ-ual fluorochemical compounds with respect to their surfactant properties. The fluoroaliphatic radical Rf is often such a mixture (see, for example, German patent application No. 2,357,916, published May 22, 1974, to E. I. duPont de Nemours & Co., inventor Donald P. Cords), and a fluoroaliphatic surfactant is frequently described in terms of the Rf radical present in major proportion.
The fluoroaliphatic surfactants used in the present invention are added in amounts sufficient to minimize or suppress mist formation during electrowinning. Preferably, such surfactants have sufficien-t surface activity to provide a surface tension at 25 C which is less than or equal to about 35 dynes/cm at a concentration of less than or equal to 0.02 wt% surfactant in an aqueous solution containing 120 g/liter CuSo4.5H20 and 150 g/liter 18M H2S04~
The amount of surfactant added to the electrowinning electrolyte will generally be between about one to 200 parts by weight of surfactan-t per million par-ts by weight of electrowinning electrolyte. Periodic replenishmen-t of the surfactant will generally be needed in continuous SX-EW processing.

~t The fluoroaliphatic surfactants used in this invention can be added ~o the electroly~ periodically or continuou~ly. Surfactants whlch are in solid form can, if desired, be added in ~olid form or in the form of solutions such as water solution~. Addition of surfactant can take place ln the electrowinning cell or at other SX-EW procesæing location~ such as the electrolyte exchanger, settling tanks, or mixing tanks.
Addltion of the ~luoroaliph~tic surfactants u~ed in this invention to an SX-EW processing stream can increase the time required for thorough phase ~eparation of the organic phase and acid electrolyte. Such time required for thorough phase separation can be reduced by carrying out phase separation at an elevat~d temperature.
For example, in SX-EW processing of copper, if the separa-tion of organic phase and acid electrolyte was carried out at room temperature prior to the use of the pres~nt inven tion, then after addition o fluoroaliphatic surfactant according to the present invention, the organic phase and acid electrolyte can be heated to about 40C to counteract any slowdown in phase separation caused by addition of ~luoroaliphatic surfactant to the acid electrolyte.
The fluorochemical surfactants used in this invention provide stable, long lasting mist suppressing foams at low concentrations, e.g., 10 part~ of surfactant per 1 million parts of electrolyte. 5uch foams are formed by the interaction of electrolyte (containing the surfactant~ used in thi~ invantion) with gas~s entrained in the electrolyte~ Such gases are presen~ due to the evolution of oxygen at the electrowinning ~nod~ and due to air or other gases which may be introduced by injection, mechanical agitation, or other means. The individual foam bubbles have a thin wall of electrolyte surrounding the entrained oxygen, air, or other gases. The foam bubbles rise to the surface of the electrolytic bath, aggregate, and can completely or partly cover the surface of the electrolytic bath.

In the SX-EW procassing of copper, the fluoroaliphatic surfactants used in the presen~ invention can provide improved quality of plated copper at the electrowinning cathode. When copper i~ electrowon according to the process of the present invention, and compared ~o copper which is electrowon under similar process conditions but in the absence of the fluoro-aliphatic surfa~tants used 1n this inventionl the former copper generally will ba smoother, and have a finer graln structure. If particulate matter is present in the electrolyte~ copper which i~ electrowon in the presence of the surfactants used in this invention generally will have a higher level of purity and will be more capable of being drawn into Elne wires without breakag~ than copper which is electrowon without such surfactants. Under op~ical magnification (e.g. 70X), copper which is electrowon ac~ording to the present invention will generally have relatively smooth, regularly structured, sandy-appearing surface grain structure. In contrast, copper which is electrowon under similar process conditions but without the fluoroaliphatic surfactants used in this invention will generally have, at similar magnification, a pebbly or nodular surace grain structure with a coarse, uneven appearance.
Several anionlc and non-ionic fluoroallphatic surfactants were compared to the surfactants used in the present invention. Such anionic and non-ionic fluoro-chemicals failed to perform well in SX-EW processing of copper, as shown below in the comparative examples.
The following examples are oEfered to aid understanding o~ the present invention and are not to be construed as limiting the scope thereof. 5ur~ace tension data in the ~xamples which follow are uncorrected measurements made with a UCenco duNouy'; ten~iome~er. The surface tension values shown above and in the claims are true (i.e corrected) values.
a~ rk EX~MPLE 1 ~n electrolyte solution was prepared from the following ingredients:
Solution_A
1. 120 g CuSO4-5H2O
2. 150 g 18M H2SO4

3. 890 g deionized water

4. 0.050 g mixture of cationic and amphoteric fluoroaliphatic surfactants, in a water ~olutio~ (weight shown is weigh~ of surfactants, no~ weight o water solution).

Total electrolyte solut:Lon volume was 1 liter. The fluoro-aliphatic ~urfactant mixture was prepared by adding 47 g 15 R~SO2NHC3H6N(CH3)2 (where Rf was principally C6F13- and 47 g of the amlne ~tarting material wa~ equivalent to about 0.1 mole) and 60 g C4HgOC2H4OC2H4OH to a 250 ml 3-necked flask equipped with ~hermometer~ agitator, and condenser.
The resulting mixture w~s he~ted to 90~C. To the heat~d 20 mixture wa~ added 15 9 ethylene carbonat~ (0.2 mole~, 3 g water, and O.5 g Na2CO3. This mixture was h~ated to 110C
with agitation for 5 hours. The reaction product wa~
cooled to 80C. Next, 4.2 g solid NaOH (0.1 mole) was added to the reaction ve~sel and the resulting mixture was heated to 100C for 2 hoursO me pr~ssure in ~he reaction ve~sel w~s gr~dually reduced ~nd heating wa~ continued until the pressure over the reaction mixture reached 100 mm Hg and the temperature of the reac~ion mix~ure reached 125C. The reaction mixture was cooled to 9QC, ~ind contained the intermediate [C6~l3so2N(Na)c3H6N+(cH3)2c2H~oH] OH-. Next, 23.1 9 ClCH2CHOHCH2SO3Na (about 90 percen~ pure~ was added to the reaction ve3sel and the r~sulting mixture hea~ed to 110C
for 5 hours. The reaction mixture was cooled to ~0C~
mixed with 120 g water, and cooled to room temperature.
The reaction product was a mixture containing he amphoteric fluoroallphatic surfactant [c6Fl3so2N(cH2c~oHcH~so3Na~c3H6N~cH3)2c2H4o~] OH- as well as unreacted starting material, unre~cted intermediate, and other fluorochemical by-products. Thi~ reaction product was considered to have 30 perc~nt by welght fluoroaliphatic surfactant content.
A 150 g portion oE Solution ~ was added to a 250 ml beaker equipped with a lead anode, a copper cathode having an area of 11.0 cm2 on each slde, and a magnetic stirrer. The ~urface tension of the electrolyte was measured at about 25C and found to be 2~ dyne~/cm.
Electroplating wa~ lniti~ted at a current densi~y of 0.153 ampere/cm2 and a temperature of 22C. Foam quickly formed around the anode and pH paper did not change to reddish (acid) color when held above the el~ctrolyte, lndicating that the air above the electrolyte was essentially free of acidic mist. In a comparison run, the same electrolyte was prepared without addition of fluorochemical, and no foam formed at the anode and p~ paper changed to red in color when held above ~he electroly~er indica~ing that the air above the electrolyte contained acidic mist.
A long-term plating run was then carried out.
The electroplating apparatus was operated for three hours using the fluorochemical-containing electrolyte of Solution A. Hourly additions of ~uSO4 SH2O were made to the electrolyte to replace copper which had been plated out at the cathode. After 3 hours, the foam at th~ anode was still effective as a mist inhibitor, as no change in the color of pH paper was observed when the p~ paper was held above the electrolyte. The electroplating current and stirrer were turned off. ~he surface tension of the electrolyte was measured at abou~ 25C and found to be 25 dynes/cm, indicating that there had been little~ if any, loss of surfactant.
Two solutions were next prepared from the following ingredients, for evaluation of the re~istance of the fluorochemical to extraction into the organic phase during a cyclic SX process:
Solution B
~.
1. 11.8 g CuS0~ 5~20 2. 988.2 g deionized wa~er 3. sufficient 18M H~S0~ to adjust the pH of the solution to 2.2 `.b Solutlo~ C
70 ml l'Acorga P5300" organlc~ monomericJ
hydroxyoxime chelating agent commercially available from Imperial Chemical Xndu~tries, ~td.
2. 930 ml "Kermac 470B" petroleum distillate, commercially available from Rerr-McGee, Inc.
~ 100 ml portion of Solution B was vigorou~ly stirred with a 100 ml portion of 5O1ution C in a separatory funnel Eor 10 minutes~ The organic and aqueous phases were allowed to separate and the aqueous phase then drawn off and discarded. A 100 ml portion of said Solution A (but containing only 0.0035 g of the fluoroaliphatic surfactant mixture instead of the 0.050 g/liter amount recite~ above) was then added to the separatory funnel and vigorously stirred with the organic phase for 10 minutes. T`ne aqueous phase was drawn off, labeled as ~Solution Al~, and subjected to electroplating as described above to de~onstrate that foaming occurred. Electrolysis was then discontinued and Solution Al was set aside. Next,~100 ml of fresh Solution B was added to the organic pha~e remaining in the separator~ funnel, the aqueous ~nd organic phases were vigorously stirred for 10 minltes, ~nd the lower aqueous phase was discarded as be~ore. S~lution Al was added to the separatory funnel, vigorouæly ~tirred for 10 minutes~ and the lo~er aqueous ph~se drawn off and labeled as ~Solution A~". Solution A2 was subjec~ed to electroplatlng as described above. In thi~ fashion7 the electrolyte and organic phase were continually recycled, and successive extracts of electrolyte were labeled c~e ~ark .

~21 "Solution A3", "Solution A~", etc., and ~ubjected to electroplating. ~oaming continued through the sixth testing cycle (Solution A6), and the run was then terminated. The surface tension of Solution A6 was measured at about 25C and found to be 32 dynes/cm, indicating that the ~urfactant was still present in active amount.
This example shows that low concentrations of a mixture of catiollic and amphoteric fluoroaliphaklc surfactants in electrolyte give effective mist suppression at the electrowinnlng anodeg The fluorochemical mixture resis~ed extraction by the organic SX phase and resis~ed plating out at the electrowinning cathode.

EXAMPL2S 2 to 10 _ The long~term plating and cyclic SX procedures of EXAMPLE 1 were repeated using several other cationic or amphoteric fluoroaliphatic surfactants in place of the surfactant mixture used in EXAMPLE 1. Set out below in Table I are results for the long-term plating procedure, including example number, fluorochemical identity, initial weight percent fluorochemical added to the elec~rolyte, number of hours of plating, initial surface tension, and surface tension after the long-term plating procadure was ended. Initial fluorochemical concentration~ were adjusted to give foaming at minimal addition levels.

l~ble I
Surface tension c)~ electro~;yte, dyr~e~/cm 5Example Weight ~ Pla~irlg a~ start at end ~;b. Fluo~h~nical fluorochemical hour3 ~ run of rlm 2 [c6Fl3sc:2~(cH2c~) C3H6N~ 3 ) 33 ~ 0 . 005 2-3 24 36 3 C6F13sO2NE~3H6N~
t CH3 ) 2C~2C~ û . 0075 1 2 21. 5 37 4 C6F13SO2N~IC3H6--N~( C~13 ) 2C2H4~OO- . 005 3+ 23 . 2 23 . 6 C6F1352N(CH2C~
CH2SO3Na)C3H6N(CH3)2 0.005 2~ 25.3 28.5 15 6 C7FlsC(~N~3C3H6Nt--(CH3)2C2H4COO~ 0.005 1--2 32 42 7 C6F13SO2N( C2H4CO~Na )--C3H6~(cH3)2c2H4coo o.oo5 2--3 24 36 8 [C8F17S~C3H~-(CH3)3] I- 0.01 1--2 23 33 9 [C8F175{~2~C3H6--N~(CH3)3] 2 ~042~ o-005 1-2 24 31 [C6F13SO~C3H6--Nt ( CH3 ) ~C2H40H~ OEI O . 05 ~3 25 34 . 5 Set out below in Table II are results for the cyclic SX run, including the example number, fluoro-chemical identity, initial weight percent 1uorochemical added to the electrolyte, number of successful SX cycles (i.e., the number of SX cycl~s through which foaming was ob~erved within 3 minutes of the s~rt of electroplating), initial surface tension, and ~urface tension after SX
cycling had been carried out to th~ point that the electrolyte ~olution would not foam within 3 minutes ater the start of electroplating. A "+" in the column "No. of successEul SX cycl~s" indicates that fo~ming was observed in all run cycles and the run was di~continued after the indisated number of cycles.

Iable II
Surface tension of electrolyte, ~;b. ofd~s/~n ExampleWbight % s~cessf~ at start at end ~ run of run 2 [C6F13S92N(CH2oX~)-C3H6N~(CH3)3]0~r 0.025 4~ 22 25 3 C6F13~~C3H6N~--(C~3) ~ 2C00r 0.01 3 21 38 4 C6F13sOkNHc3H6-N~(cH3)2c2H4cocr 0.005 1 23 30

5 C6Fl3so2N(cH2OE~l~
CH2SO3Na)C3H6N(CH3)2 004 7 26 34

6 C7FlsCONHC3H6N+-(CH3)2c2H4oxr O.005 2 26 37

7 C6F13SO2N~C2~4oX~)-C3H6N~(CH3)2C2H4CCr 0.005 3 23 30 -24~-T~ble II (~cnt.) ..
5urface tension of electrolyte, Mb. of dynes/cm 5 Ex~mple Weight % ~uc~e~f~ at start at end Nb, Fluoro~ al fl~oroch~mical SX cycles of run of run

8 [c8~l7sc2~Hc~l6N~-~CH3)3]~ 0.01 5~ 23 23.5

9 [C8Fl7s02N~3H6-N~(CH3)3~2 S042 0.025 5 ~0 36 [C6F13S022~ 3~6-N~cH3~2c2H4o~oHr 0.004 4 5 32 c~Ar~rlv~ L~
Several anionic and non-ionic fluorochemicals were evaluated for comparison as mist suppressants using the SX procedures of EXAMPLE 1. Set out below in Table III are the resultsr including run number, fluorochemical identity, fluorochemical type (anionic or non-ionic), initial weight percent fluorochemical added to the electro-lyte, number of succes~ful SX cycles, initial ~urfacetension, and surface tension after SX cycling had been carried out to a point at which the electroly~e ~olution would not foam within 3 minutes of the start of electro-plating. Initial fluorochemical oncentrations were adjusted to give fo~ming ~where possible) at minlmal addition levels, ~5 Table III
Surface te~sion of eleetrolyte, Nb. ~f _dynes/em 5 Run ~eight % sueeessful at start at end No. Fluorochemieal Type fluor~hemieal SX eyeles of run of run 1 C8F17S3K anionie 0.05 21 43 2 C2Fs-eyelo-C6F10S3K anionie 0.05 0 28 41 3 C8F17sO2N(c2H5) C2H40S03Na anionic 0~05 0 21 34 4 CgF175O2NHc6H4~
S03Na anionie 0.05 0 22 37 5 C7F17COON~14 anionicno foam 6 C8F17SO2N~CH2-C6H4SO3Na)2 anionicno ~oam 7 CgF17sO2~E~3H6 Po(oH)2 anionie 0.03 0 20 37 8 (cgFl7so2N(c2H5)-C2H~0)2P~2- NH4~ anionie insoluble g C8F17s02Nl C2H5 ) (C2H4O)7CH3 non-ionic 0.03 1 22 45 C8F17S02NtC2~15) -~C2H4O)39CH3 non-ionie 0.03 0 29 46 Various modifica~ions and alterations of this invention will be apparent to those skilled in tne art without departing from the scope and spirit of this invention and the latter should not be restricted to that set Eorth herein for illustrative purposes.

Claims (10)

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. A process for the recovery of metal values from metal-bearing aqueous solutions, comprising the steps of:
(a) mixing said metal-bearing aqueous solution with water-immiscible organic solvent containing water-insoluble organic ion exchange composition, said composition having selective affin-ity for said metal values, thereby forming metal-bearing organic solution and metal-depleted aqueous solution;
(b) separating said metal-bearing organic solution and said metal-depleted aqueous solution;
(c) contacting said metal-bearing organic solution with aqueous strip solution comprising strong acid and 1 to 200 parts by weight of fluoroaliphatic surfactant per million parts by weight of strip solution, said surfactant having at least one cationogenic group which is the radical of a base having an ionization constant in water at 25°C of at least 10-6, and containing at least 30 weight percent fluorine in the form of carbon-bonded fluorine in a fluoroaliphatic radical, said fluoroaliphatic radical having at least 4 carbon atoms and at least a terminal perfluoromethyl group, thereby forming metal-enriched aqueous strip solution and metal-depleted organic solution, said metal-enriched aqueous strip solution having a surface tension at 25°C which is less than or equal to 35 dynes/cm;
(d) separating said metal-depleted organic solution and said metal-enriched aqueous strip solution;
(e) electroplating said metal values onto a metallic cathode using said metal-enriched aqueous strip solution as electrolyte in an electrolytic bath, by passing direct electric current between said cathode and an insoluble anode or anodes, with the surface of said electrolytic bath being wholly or partly covered with foam formed from the interaction of said electrolyte and a gas selected from at least one of the group consisting of oxygen evolved from said electrolyte at said anode or anodes, air and any gas entrained in said electrolyte, said foam suppressing misting of said electrolyte and release of said electrolyte into the atmosphere surrounding said electrolytic bath; and (f) recycling the resulting metal-depleted electrolyte for use as aqueous strip solution in step (c).

2. A process according to claim 1, wherein said surfactant also has at least one anionogenic group which is the radical of an acid having an ionization constant in water at 25°C of at least 10-6.

3. A process according to claim 1, wherein said metal com-prises copper.

4. A process according to claim 1, wherein said surfactant comprises compounds of the formula:

wherein: a is independently 0 or l; b is 1 or 2; Rf is a fluorin-ated, monovalent, aliphatic radical, with the proviso that the molecule contains at least 30 weight percent fluorine in the form of carbon-bonded fluorine in Rf; Q is independently a linking group, with the proviso that at least one Q group is present in the molecule; R3 is independently:

R4 wherein R4 is H or alkyl;
(Q)aAM wherein A is -COO-, -SO3-, -OSO3-, -PO3H-, or -OPO3H-, and M is H+, a metal ion, or N+(Rl)4 where each is independently H or alkyl; or QNR5R6R7 wherein R5 and R6 are independently H, alkyl, or together with the N atom to which R5 and R6 are attached form a cyclic ring, and R7 is R4, a quaternary ammonium group, or (Q)aAM;
Z is -CO- or -SO2-; and X is halogen, hydroxide, sulfate, bisulfate, or carboxylate.

5. A process according to Claim 4, wherein said surfactant comprises compounds of the formula:

wherein Rf contains 4 to 8 carbon atoms, Q is alkylene or hydroxyalkylene, A is -COO- or -SO3-, and R5, R6, and R7 are alkyl or hydroxyalkyl.

6. A process according to Claim 4, wherein said surfactant comprises compounds of the formula:

wherein Rf contains 4 to 12 carbon atoms, Q is alkylene, R5 and R6 are lower alkyl, and R7 is carboxyalkylene.

7. A process according to Claim 2, wherein said surfactant comprises l to 200 parts by weight [C6Fl3SO2N(CH2CHOHCH2SO3Na)C3H6N+(CH3)2C2H4OH]OH- per one million parts by weight of said strip solution.

8. A process according to Claim 2, wherein said surfactant comprises 1 to 200 parts by weight C6F13SO2N(CH2CHOHCH2SO3Na)C3H6N(CH3)2 per one million parts by weight of said strip solution.

9. An electrowinning bath, comprising (a) metal values;
(b) aqueous acid electrolyte; and (c) fluorochemical surfactant having at least one cationogenic group which is the radical of a base having an ionization constant in water at 25°C of at least 10-6 and containing at least 30 weight percent fluorine in the form of carbon-bonded fluorine in a fluoroaliphatic radical, said fluoroaliphatic radical having at least 4 carbon atoms and at least a terminal perfluoromethyl group.

10. A bath according to Claim 9, wherein said surfactant also has at least one anionogenic group which is the radical of an acid having an ionization constant in water at 25°C of at least 10-6.