CA2051097A1 - Ion flotatin with quaternary ammonium cationic surfactants - Google Patents

Abstract

ABSTRACT OF THE DISCLOSURE

A method for ion flotation, especially in the extraction of gold uses as the flotation reagent a cationic surfactant of formula(I), wherein R1 is a C10-C18 alkyl group, R3is a lower alkyl group, or benzene ring optionally substituted with one or more lower alkyl groups and R2 and R4 are lower alkyl groups; or R1, R2 and R4 are methyl groups; R is a benzene ring substituted with a C10-C18 alkoxy group; and X is a halogen atom.

Description

21~9 PCl`/~UgO/00124 20~1097 .

IO~ FLOTATION ~I~II Q-aATE:RN~RY AMMONI~1M
CATIONIC SllRPACMl~TS ;:

Tht~ inventlon relate~ to ion flotatlon reagents and to m~thods for their product~on and use. Tho lnven~lon i partlcularly, but not excluslv~ly concarned with the extractlon o~ gold us~ng lon flotatlon t~chniques.

Partlculate flotatlon iY a physlcochemlcal method of concentrating valuable mlneral from finely-ground ore.
The proces3 ~nvolve~ a selective tre~tment o~ the valuable components to facilltat~ thelr attachment to air bubbles, whlch form a froth concentrate. Ideally, ion flotation i~ a procedure wheraby valuable ions in a .
SIJBSTITUTE SHEE r ~, .. .

.. ..

~ ~/12119 PCT/AU90/001~

- 2 - 2~1097 mixture of charged specles are selectlvely removed by rislng air bubbles. It resembles conventional froth flotatlon in that lt employ~ a collector and slmllar equipment. It differs ln that the substance to be 5 separated is not usually present initially as a solid. The collectors are ~onizable, surface-active orsanic compounds, cationic ~or tha flotatlon of anions, anlonic for the flotatlon of catlons. These addltives perform the dual function of complexing with the ions in solutlon and tra~porting these previously surface-inactive components to the foam phase. Such separation of ions is usually accomplishçd at low gas flow rate~, producln~ a small vo}ume of foam without tall columns or ~olent agltation of th~ llquld phase. Ion flotatlon iR of enormous practlcal slgnlflcance since ions are often successfully floated and con~entrated from lO 7 to lO 4 M solutlons.

[NOTE: Rsferences are collected at the end of this descrlptlon~.

The first of the low gaq-~low rate foam separation technlques wa-~ introduced by Sebba ~n 1959. A surfactant ion of opposlts char~e to the lon to be removed wa~ added in stolchiometric amount~. Se~ba concluded that the collector must bQ lntroduced in such a way that it exlsts a~ simpl~ ions and not mlcelles. The foam produced after sub~ectln~ thls mlxture to air bubble~ then collapsed, thereby concentrating th~ lnorganic lon. Rubi~ et al.
(1966) l~ves~igated oth~r variable~ associated with the technlque, includlng the effect of m~tal lon concentra~ion, pH and temperature, u3ing a soluble copper (I$) lon~ recovered by a sodium lauryl sulphat~ (an~onic) collector. ~erg and Do~ney (1980) studiQd the use of ~5 quaternary ammonlum surfactant- of the type RlN(R2)3Br as collactoss ln th~ lotation of anlonic chlorocomplexes of platlnum group metals.

SllBSTITIITE SUEET

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;

~/12119 PCT/AU~/001 20~1097 The us~ of guaternary ammonlum compound3 as collector~ to remove prerious metals from solution was ~urther studied ~y MiXhailov et al. (1975) and Charewicz and Gendolla (1972~. In both case~ such compounds were S used in the flotatlon of gold cyanide ions. ~he latter paper usad both Au(CN)2 and Ag(CN)2 ions and varlous commerctally avallable quaternary ammonium basQs to determine the relative selectlvity of the bases for one monovalent lon over the other. The former paper claims selectlve gold removal but the exact nature of the quaternary ammonium base used is unclear.

~ ecause of the continuing interest in yold as a preciou~ commodlty, we have investlgated the appllcatlon of lon flotation to a current gold-extractlve technology wlth a view to decreaslng operatlonal costs and delays and lmproving product~vlty. Prtor to 1894, gold was commerclally leached from ores by chlorine but modern-day practlse involves cyanldatlon oE ore materlal to produce 20 ths Au(CN)2 lon. Thls procedure also results in th~ -formatlon of cyanlde complexes of iron, copper, lead, zlnc, cadmlum and sllver. In p~rtlcular we have lnvestlgated the sultablllty of varlous quaternary ammonium bases as collsctors for ~urocyanlds lon~ in alkaline ~olutlon ln ths absenc~ of free cyanlde or competing ion~ and alQo ln mixecl metal cyanide liquors.

We have now found that a class of quaternary ammonium compounds whlch have partlcular characteristlc features are especially su~tabls for us~ as lon flotatlon reagent~ and superlor to the compounds used ln the prlor art.

Acoording to one aspect of the present invention, 3S there i5 provlded a method for ion flotatlon in whtch the flotation reagent employed is a cationic surfactant of formula (I):

. ~ . , . , ~

, . , r~ ~/l2lt9 2 ~ ~1 o 9P~ /AU90/00 3 1 1 X (I) wheratn ~1 is a C}O - C18 alkyl group, R i~ a lower alkyl group, or benzene rlng optionally substituted wlth one or more lower alkyl groups, and R2 and R4 are lower alkyl groups:
or Rl, R2 and R4 are methyl groups;
~3 1~ a benzene ring substituted wlth a C10 C18 alkoxy group:
and X 1~ a halogen atom.

Preferably the long chaln (C10 ~ C18) alkyl or alkoxy group contain3 from 12 to 16 carbon atoms, mo~t preferably 12 carbon atoms.
~`:
~ he term ~lower alkyl", a~ uQed herein, refers to groups which contaln from 1 to 6 carbon atom~, pree~ably 1 to 3 carbons.
Th~ lnven~lon ln a further aspect also provides the us~, a~ an ion flotation rea~ent, of a compound of formula (I), a~ daflned above.
.
Formulaa of some preferred reagents for use ln accordance wlth tha inventlon are ~et out below. All of : these compounds ar~ ~nown r sa. Also shown for compar~son are formulae of some compounds (A,CT~B, and D~AB) which have already been proposed for uYe a~
flotatlon rsagent~. Only A and CTAB have besn used previously for the ion flotatiQn of gold. Compounds B, D
and R are also known ~E se, but have not been sug~ested ¦ SU~STITIJTE SIIEET ¦

` , ` `

` `

~ ` ` `

~ llg PCT/AU90/001~
20~097 prevlou~ly for USQ a~ lon flotatlon reugents.

Some of the remaining compounds of fo~mula (I) a~
def~ned abova are new and the lnventlon also lncludes these compounds E~E se. M~thods for their synthesls of some of these compounds which are described in the literature, have proved unsatlsfactory ~n our hands and the present specificatlon therefore descrlbes new methods for the preparation of these compound-~ a described herelnafter.

.~
f SL STITUTE SU [r .. .. . . - "

::
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~--'0 90/12119 2 0 5 1 o 9}~/AU90/OOt24 ~CH2--~--C,2 H2 A

(A) Beruyldimc~hyldodccylarnmonium bromide ~ ~
CH3 ::

Br(~) (B) Dlme~hyldodccylphcnyl~rnmoniurn br~rrdde H2s C125~ 11(9 _ CH3 D

(D) Tnme~hy~ nunonium bro~d~

~ N(~3_C~2 H2s R
BrG

H3C CH, (R) N,N dime~yl N-dod0cyl-3,~d~ hybnilinium ~rom~e SUBSTlTlgTE SHEET ¦
. .

.
-, .. . .~
. i .. - .... ` . . : .
. . . .. .. ` . . .
.
. , , .. , .. , . .. ~ . : ~:
- , .. - .... .. -. ....

WO 9D~12119 PCI~/AU90/00124 - 7 - ~0~1097 cr3 .
~3C--N--C 16H33 CTAB

(CTAB~ ~tyltri~lammonium brornlde CIHs : ' ~) ~ u~ ~lum bromida ~ ~ ' :` :

j SlJB5Tl'rlJTG SHEIT

`~90/12119 PCT/AU90~001~
- 8 _ 20~1~97 ~ he lnvention, in lts varlou~ aspect~, is further described and illustrated by the followlng non-limlting Examples. (A11 temperature~ are stated in degrees Celsius.) PREPARATION OF FLOTATION REAGENTS

The compounds A, CTAB (cetyltrlmethylammon~um bromlde) and DTAB (dodecyltrlmethylammonlum bromide) were obtained from commercial source3.

ExamDle Cl PreDaration of Compound B

(a) DlmethyldodecYlDhenvlammonium bromlde Dlmethyl anlline (24.2 g, 02 mol), dodecyl bromide (49.8 g, 0.2 mol), acetone (60 ml) water (60 ml) were refluxed togather for 16 hour~, wlth stirrlng. The mixture was then cooled and extracted wlth dlathyl ether ~3 x 50 ml). The aqueou~ layer waQ -ceparated and evaporated on the rotary evaporaltor under reduced pressure (20 mm Hg). The brown gum was dried by addlng ethanol tS0 ml) and azeotroping o~f tha flnal trace~ of water.

The product wh~ch solldiied on cooling to 5C was dissolved ln ethanol, oharcoaled and flnally recrystall~sed from ethanol/aceton~ 4 ratlc), weight was 3.5 g, m.p. 97-98-C.

The reaction had only proceeded to partlal completion and the organic layer from above was evaporated down to remove the ether, treated wlth more watsr (100 ml) and rafluxed wlth stlrrlng for a further 48 hours. After the normal work-up procedure ths welght of rec~ystallised SC.~BSTITUTE S~EET 1 ~_, - . . , . ` `- ` : ~. .

- ~ - .......... . ;: :

...
- . :. . : . ~ ~

~090/12119 PCT/AU90/001~

_ g _ :
product wa9 lO.5 g. Total walght of re ~ ~ d product was 14 g. The MMR and IR spectra were consistent wlth those predic ed for the required product, m.p.
97-98-C.

Exam~le C2 PreDaration of ComDound D

(a) Pre~aration of 4~DodecYloxyaniline To a mixture of 4-hydroxyacetanide (50.4g, 0.3 mol), dodecylbromids (83.lg, 0.33 mol) and absolute ethanol (lOO ml), ln a flask fltted wlth an overhead stlrrer, reflux condanser and dry$ng tube, wa3 added a :
solut~on of sodium matal (7.8g 0.34 mol) l~ absolute ethanol (200 ml). The mixture was stlrred and heated under reflux for 4 hours. The mixture was cooled and the precipitate of sodium bromide flltered. The ethanol was evaporated ~a vacuQ and ths crude product suspended ln a mlxture of wat~r (lOOO ml) cont~inlng conc. HCl (lO ml).
The mlxture was f~ltered and the product washed wlth water. TLC (EtOAc, slllca) showad starting materlal at Rf ~ 0.38 and product at Rf - 0.52, thus lndicating complete conver~lon, wlth no othQr products or starting materlal laft. The 4-dodecyloxyacstamide wa~ stlrred and heated under reflux ln a mlxture of ethanol (500 ml) and 50% pot~sslum hyd~oxlde solutlon t200 ml) for 8 hours.
The mlxtur~ WA~ allowed to cool and extracted wlth ether (4 x 150 ml), dried (K2C03) and evaporated l~ vacuo.
Thi~ gavs 90 g of crude 4-dodecyloxyanllin2. TIc (EtOAc, sil~a) ~howed a product o~ Rf ~ 0.63. A trace o~
startlng materlal wa-~ present along wlth a red impurity.
The product was recrystalllsed ~rom ethanol uslng decolourlsing charcoal and agaln several tlme~ from petroleum-ether bp 40-70-. Almo~t colourle~.~ plates were obtained ~.p. 55-58 ~Llt. 57-60-). Yleld 44.7 g ~49%
overall).

..
SU~STITWE Sl lli[T

' ' ' ~ '" .

' . : ' : :: ` : , , ~90/12119 PCT/AU90/001~
lo- 20~1097 (b) PreDaratlon of 4-dodecYloxYtrlmethvlanlllnlum lodlde 4-Dodecyloxyaniline (27.7 g, lOO mmol) was dissolvsd in dry DMF (65 ml) and cooled ln an ice-bath. In a flask fitted wi~h an overhead stlrr r, refIux condenser, drying tube and pressure equallsln~ additlon funnel, 2,6-Lutadene (purlf~ed by refluxing and dlstilling from KOH, 21.4 g, 23.3 ml, ~OO ml) wa~ added with stlrring, followed by ~low addition of methyl iodide (70.l g, 31 ml, 500 mmol). After the addition, the reaction mixture was allowed to stir at 0' for l hour, allowed to warm up to room temp~raturo and left overnight. Dry acetone (re~luxed and dlstllled from CaCl2, lOO ml) was added to tha solid ma~s and the mixture flltered. The product wa~ re~luxed in dry acetone (500 ml), cooled and filtered, then recrystalllsed twice from methanol, washed with acetone and dried in vacuo. Colourless plates, ~irst crop 28 g, m.p. l63-5- (wlth frot~lng), remelt mp 160-. Second crop 6.3 g, same m.p. 77% yield total.
(c) Anlon exchanae to bromide sal~

~ he iodonlum salt (lO g, 22.4 mmol) was dlssolved in chloroform (75 ml) ~C] ~ 0.299 M and extracted with an aqueous potasslum bromide solutlon contalnlng 204.4 g KBr in H2O (750 ml, ~C~ . 2.99 M), uqlng a fast overhead stirrer ~or hour~ Methanol (lO ml) wa~ added and the layar~ allowed to separate. The lower mllky organ~c layer wa~ separated and a further lO ml of methanol wa~
added. Further standing gavs clear layer~. ~e~ted for lodide ~n the organlc layer by adding a small aliquot to a warm mixture of aqueou3 ~tar~h containlng a few drops of dilut~ HCl and 30% hydrogen peroxlda solution. (A
blu~-black colour lndlcated the pre~ence of I, an orangQ-yellow colour 8r. If a blue-black colour wa~
detected ln the oryanlc layer, the extraction had to be repeated u~lng fresh solutlon).

; SUBSTITUTE SltET

0~097 The organic layer waQ dried over -~lllca gel, flltered and evaporated ln vacuo. A further starch test was applied to the solid to.check if complete exchange had occurred. ThQ bromide salt was recrystallis~d from methanol. Yleld 7 g (78%) colourless plateR m.p. 123-5 (froths). lH and 13C MMR lndicated the correct product.
This procedure was repeated thres tlmes.

ExamDle C3 PreDaration of ComDound R
(a) N - Dodecyl-3, S-Dimethvlanillne A mlxture of water (lO0 ml), 3,5-dlmethylanlllne (lO0 ~) and sodlum bicarbonate (70 g) wa~ heated to 90-95-C. Dodecylbromlde (150 g) wa~ added over l hours, and th~ mixture heated with stirring for a further 8 hour.~. The mlxture was cooled and the organic layer separated to yield the product as a viscous oil (130 g).
lH and 13C NMR. were in agreement wlth the deqlred produat.

(b) Methvlatlon o~ N-Dodecvl-3. ~-Dlmethvlanilina (ComDound R !

N-dodecyl-3, 5-dlmethylanlllne (30 9) wa8 dissolved ln DMF. (60 ml) contalning a ~uspension o~ anhydrous K2C03 (14 g). ~hs mlxture was cool~d in ice and methyliodid~ (60 g) added. ~he mlxture wa~ stirred at 0 ~or 1 hour dur~ng whlch an efferv~gcence occurrsd, 3Q ~ollowed by 48 hour~ at room tempar~ture. The resultant solld was taken up ln hot chloroform and filtered to ramovo insoluble ~I. Chloro~orm was r~moved under reduced pressure and the resldue wa~ washed with ether. ,.
Th~ crud~ iodide Qalt of compound R wa~ colleoted by ~lltratlon, di~olved in chloroform (200 ml~ and stirred with KBr (400 g) in water (lO00 ml) for 3 hours. The chloroform layer was separated and st~rred wlth further _ .
~ ~:

.
:, ~ , .. . . .
.

~ O90/12119 PCT/AU90/00124 2~10~7 KBr (400 g) ln water (l000 ml). Separatlon of the chloro~orm layer and removal of th~ solvent under reduced pressure gave the bromide salt of R as colourless crystals ~20 g). The reaction wa~ repeated and the combined product rerrystallis~d from ethyl acetate to yield compound R a~ colourless crystalc (28 g). lH and 13C NM~ were in agreement with the desired product.
-ION FLOTATION

Reference wlll ba made to ths accompanying drawings in which:

Figure 1 i9 a diagram of thQ experlmental apparatus used:

Figures 2 to l0 are graphs showing the results obtalned.

E~ui~man$

The ~lotation equlpment u~d ln the bench-scale laboratory experlment~ l~ lllusl:rated ln Figure l and consl~ted o~ a modlfied Hallimond tube cell or oolumn 1 of volume approximately lL. A sl~t~red glass fr~t 2 in tha base of th~ column allow~ alr to pa98 through the cQll fsom lnlet 3, metersd by appropriatQ flowmeter~ and regulator-~ (not shown). Sldq port~ 4,5 fltted to the column allow continuous monltoring of pH and/or temperature (4) and removal (5) of small ~ubs~mples of tha llquld contentQ o~ thQ cell. The liquid fe~d to column enters t~rough port 6 and the exit alr ~tream flow~ out through port 7. Thè froth formed during flotation i~ discharged ~rom the overflow lip 9 at the top o~ thQ cell and collected ln anothQr conta~ner (not :' , SUBSTlTt~TE SHEET
:` ~

`` : ~ :
:::
, : , ` . ~: . .: , - 13 _ 20~10 97 shown). Ths column may be completely dr~ined at the end of a batch experim2nt by using th~ talllngs outlet port Procedure A solution containing ~ known concentration of gold (as ths aurocyanlde lon) and a known molar ratio o~ -surfactant to gold was prepared a~d mixed thoroughly.
After ad~ustme~t of the pH to thQ desired level, the feed liquid was in~ected into the ~lotatlon cel~ through port 6 and the air supply connected to lnlet 3. A$r wa3 then lmmedlately bubbled lnto the call and froth began to form at the top o~ the column. When the first drop of froth splll~d over the upper l~p of the cell, a timer was started and at known intervals after thl~ poi~t, sub-sample-R of the liquld content~ of th~ cell were ramoved via the side port and analyzed for thelr gold content by atomlc absorption spectrophotometry. At the completlon of the esperlment (when elther the surfactant 13 exhau~ted or the elapsed tlme reaches ~ certaln value) the alr ~upply was disconnect~d and the collected froth and a sub-sample of the fln~l cell content~ were analyzed for gold. Durlng the test, pH was malntaln~d at a const~nt level by addlng approprlate quantltleQ of acld or ba3e, ~nd thQ lsvel of water ln the cell W83 also rsgulated to a con~tant depth by tha addltion of w~ter through port 6.
, .
Handlin~ of~ esults .. .
Gold recov~ry tmaterial reportlng to froth) as a function of tlme i~ calculated by the formula:

35 R% ~ Ct/CO) x 100 .
where Ct ls the llquld sub-sample gold concentratlon '.

, SU~STITUTE: SHEE'r .
. .. . . . .

'` ~ ' . .. .

' ~90/12119 2 0 ~10 9 7 at tlm~ t, and CO 1~ thQ concentratio~ ln the initlal feed. The ratio Ct/CO represents the fraction of gold from the feed left ln the cell at tlme t.

5Another lmportant parameter in ion flotation studies ls the u~qrade ratlo, calculated by:

UR - Cf/Co 10where Cf ls the concentration of gold in the product froth and CO ~ 5 ths lnltial feed gold concentratlon.

Varying the molar rat~o of surfactant to gold affect~ both the recovery and~the upgrade ratlo ln any experlment. For example, F~gures 2 and 3 show the results obtalned uslng a .
1~

~ . .
, j :
., j . . :
`' ' '.'` ~

WO90/t2119 PCT/AU90/00124 - 15 - 20~097 feed solutlon contalning 50 ppm of gold and CTA~ as the surfactant in various ratlos.

When treatlng mlxed solution3, containing both gold and silver, the upgrade ratio for sllver is also determined. The ratlo of the upgrade ratios o~ gold ~o silver ~URAU/URAg~ has a peak value called the "peak magnltuda~ and is a mea~ure of the ssle~tivity of the reagent. The peak magnltude usually occurs near the lower limit of sur~actant frotha~lllty.

All feed solutlons contalned lOppm each of gold and sllver lon. The respective Figure number, air flow rates, peak upgrade ratios and peak magnitudes are given in ~abl~ 1. Also shown is the suriactant operating concentration range (mole~ -~urfactant~moles of gold present).

¦ SUBSTITUTE SHEET ~
~, b 90/~2119 2 0 ~ 1 ~ 9 7 P~/AU90/00124 -- 16 -- ~
TEST RESU~TS
_ Table l Compound Figure Air Peak un~ ~u Surfactant/Gold No. Flow for gold (~0.2) mole ratio cm31min (~1) range - - -CTAB 4 260 4.~ 2.6 1-10 10DTAB 5 260 9.4 4.2 70-100 DTAB 6 52.532.7 6.8100-120 A 7 260 7.1 2.6 40-70 B 8 260 13.2 3.6 30-?0 D 9 260 12.6 3.S 1-10 15 R 10 260 15.5 1.6 5-10 From th~ above results, lt i.q clear that DTAB i~ a superlor reagent in terms of up~rade ratio and peak magnitude compared to C~AB. However lt take~ a good deal more DTAB than CTAB to ~orm a stable lon flotatlon foam.

The ef~ect of reduclng alr~low (illustrated uslng DTAB) ls to increase upgrade ratio and peak maynitude signlflcantly. The surfactant dose required also increases. Thi~ example ls illustrative for all surfactants.

Compound A is a superior rea~ent in all re~pect~ to CTAB at tha sama airflow. Compound A i5 not as efficient a.~ DT~B in producln~ hl~h upgrade ratios and peak magnitudes. However the dosage of chemi~al required ~or lon flotation with Compound A ls le -~.

Invention compound~ B and D ara superlor to compound A at the same alrflow ln tarm of upgrade ratlo and peak magnltud~. Also, lower do~es of thes~ chemicals are reguired compared to compound A.

Compounds B and D are superior to compound CTAB at 3~ . ' , .

,~090~12119 PCT/AU90/001~
- 17 _ 20alO97 the same airflow, ln term9 of upgrade ratio, peak msgnitudQ and dosage.

Compounds ~ and D are superior to compound DTA8 at S the same airflow, in term~ of upgrade ratio and dosage.
It is possible ~or compound DTAB to achieve slightly hlgher selectiv~ty than the new reagents B and D, however this is not the ma~or consideratlon in thelr use.

Compound R is a superlor reagent to compounds D~A~, CTAB and A at th~ same air~low, ln terms o~ upgrade ratio and dosage. ~swsver, compound R is not ~uperlor to the prlor art in terms of peak magnltude. Compound R 13 superlor to new compounds B and D in terms of upgrade ratlo only.
. .

I SlJBSTlTl.lTE SHEET ~

Claims (8)

1. A method for ion flotation, characterised in that the flotation reagent employed is a cationic surfactant of formula (I):

X (I) wherein Rl is a C10 - C18 alkyl group, R is a lower alkyl group, or benzene ring optionally substituted with one or more lower alkyl groups, and R2 and R4 are lower alkyl groups, or Rl, R2 and R4 are methyl groups;
R3 is a benzene ring substituted with C10 - C18 alkoxy group;

and X is a halogen atom.

2. A method as claimed in Claim 1, characterised in that the long chain alkyl or alkoxy group contains from 12 to 16 carbon atoms.

3. A method as claimed in Claim 2, characterised in that the long chain alkyl or alkoxy group contains 12 carbon atoms.

4. A method as claimed in any one of Claims 1 to 3, characterised in that the lower alkyl group(s) contain from 1 to 3 carbons.

5. A method as claimed in Claim 1, characterised in that the compound of formula (I) is selected from:
Benzyldlmethyldodecylammonium bromide, Dimethyldodecylphenylammonium bromide, Trimethyl-p-dodecyloxyphenylammonium bromide, N,N-dimethyl-N-dodecyl-3,5-dimethylanillnlum bromide, Cetyltrimethylammonium bromide, and Dodecyltrlmethylammonium bromide.

6. A method for the extraction of gold using ion flotation, characterised in that the flotation reagent employed is a cationic surfactant a-q defined in any one of Claims 1 to 5.

7. The use, as an ion flotation reagent, of a compound of formula (I), as defined in any one of the preceding claims.

8. The use as an ion flotation reagent in the ion flotation of gold cyanide, of a cationic surfactant of formula (I), as defined in any one of the preceding claims.