WO1992017614A1

WO1992017614A1 - Copper ion flotation with cationic reagents

Info

Publication number: WO1992017614A1
Application number: PCT/AU1992/000151
Authority: WO
Inventors: Malcolm David Engel; Neville Thomas Moxon; Stuart Kenneth Nicol
Original assignee: The Broken Hill Proprietary Company Limited
Priority date: 1991-04-08
Filing date: 1992-04-07
Publication date: 1992-10-15
Also published as: ZA922544B; ZW5792A1

Abstract

A method for ion flotation of copper ions uses as the flotation reagent a cationic surfactant of formula (I), wherein R1 is a C¿10?-C18 alkyl group, R?3¿ is a lower alkyl group, or benzene ring optionally substituted with one or more lower alkyl groups, and R?2 and R4¿ are lower alkyl groups; or R?1, R2 and R4¿ are methyl groups; R3 is a benzene ring substituted with a C¿10?-C18 alkoxy group; and X is a halogen atom.

Description

- 1 -

COPPER ION FLOTATION WITH CATIONIC REAGENTS

This invention relates to ion flotation reagents and to methods for their production and use. The invention is particularly, but not exclusively concerned with the extraction of copper using ion flotation techniques.

Particulate flotation is a physicochemical method of concentrating valuable, minerals from finely-ground ore. The process involves a selective treatment of the valuable components to facilitate their attachment to air bubbles, which form a froth concentrate. Ideally, ion flotation is a procedure whereby valuable ions in a mixture of charged species are selectively removed by rising air bubbles. It resembles conventional froth flotation in that it employs a collector and similar equipment. It differs in that the substance to be separated is not usually present initially as a solid. The collectors are ionizable, surface- active organic compounds, cationic for the flotation of anions, anionic for the flotation of cations. These additives perform the dual function of complexing with the ions in solution and transporting these previously surface-inactive components to the foam phase. Such separation of ions is usually accomplished at low gas flow rates, producing a small volume of foam wid out tall columns or violent agitation of the liquid phase. Ion flotation is of enormous practical significance since ions are often successfully

-7 -4 floated and concentrated from 10 to 10 M solutions.

[NOTE: References are collected at the end of this description]. - 2 -

The first of the low gas-flow rate foam separation techniques was introduced by Sebba in 1959. A surfactant ion of opposite charge to the ion to be removed was added in stoichiometric amounts. Sebba concluded that the collector must be introduced in such a way that it exists as simple ions and not micelles. The foam produced after subjecting this mixture to air bubbles then collapsed, thereby concentrating the inorganic ion. Rubin et al. (1966) investigated other variables associated witii the technique, including the effect of metal ion concentration, pH and temperature, using soluble copper (II) ions recovered by a sodium lauryl sulphate (anionic) collector. Berg and Downey (1980) studied the use of quaternary ammonium surfactants of the type R._jN(R-2)3Br as collectors in the flotation of anionic chlorocomplexes of platinum group metals.

The use of quaternary ammonium compounds as collectors to remove precious metals from solution was further studied by Mikhailov et al. (1975) and Charewicz and Gendolla (1972). In both cases such compounds were used in the flotation of gold cyanide ions.

Because of the continuing interest in gold as a precious commodity, we have investigated the application of ion flotation to a current gold-extractive technology with a view to decreasing operational costs and delays and improving productivity. Prior to 1894, gold was commercially leached from ores by chlorine but modern-day practise involves cyanidation of ore material to produce the Au(CN)₂ ion. This procedure also results in the formation of cyanide complexes of iron, copper, lead, zinc, cadmium and silver. In particular we have investigated the suitability of various quaternary ammonium bases as collectors for gold ions in alkaline solution from mixed metal cyanide liquors.

In our International Patent Application No PCT/AU90/00124 we showed that a class of quaternary ammonium compounds which have particular characteristic features are especially suitable for use as ion flotation reagents for gold and are superior to d e compounds used in the prior art.

Our process for the ion flotation of gold can be used to selectively float extremely dilute aurocyanide liquors. In principle, ion flotation is also applicable to a wide range of other metal-containing solutions and the market potential of the gold flotation process would be enhanced by the possible combination of the gold recovery capabilities with both cyanide recovery and metal removal. For example, recovery of copper cyanides from a return liquid stream would be a useful means for reducing operating costs and satisfying environmental pressures to treat tailings dams.

We have now found that certain quaternary ammonium components like those described in our International patent application are also especially useful as ion flotation reagents for copper.

According to one aspect of the present invention, there is provided a method for ion flotation of copper ions in which the flotation reagent employed is a cationic surfactant of formula (I): R⁴

R- N^T - R^J X (I)

R²

wherein R is a n - r, alkyl group,

R is a lower alkyl group, or a benzene ring optionally substituted with one or more lower alkyl groups, and

R 2 and R 4 are lower alkyl groups; or R 1 , R2 and R 4 are methyl groups;

3 R is a benzene ring substituted with a C, Q - C, g alkoxy group;

and X is a halogen atom. Preferably the long chain (C_1Q - C_lg) alkyl or alkoxy group contains from 12 to 16 carbon atoms, most preferably 14 carbon atoms.

The term "lower alkyl", as used herein, refers to groups which contain from 1 to 6 carbon atoms, preferably 1 to 3 carbons.

The invention in a further aspect also provides the use, as an ion flotation reagent, of a compound of formula (I), as defined above.

One preferred reagent for use in accordance with the invention is

MTAB, the full name formula of which is set out below. This compound is known pex.se, -Also shown are the names and formulae of some other compounds (A, B, D, R, CTAB and DTAB) which are also known per sa, but have not been suggested for use as ion flotation reagents for copper cyanide.

A = benzyldimethyldodecyl ammonium bromide

B = dimethyldodecylphenylammonium bromide

C = trime hyl-p-dodecyloxyphenylammonium bromide

R = N,N-dimethyl-N-dodecyl-3,5-dimethylanilinium bromide MT.AB = myristyltximethylammomum bromide CTAB = cetylrrimethylammonium bromide DTAB = dodecyltrmethylammonium bromide

- 6 -

The invention, is further described and illustrated by the following non-limiting Examples. (.All temperatures are stated in degrees Celsius.)

IQN FLOTATION

Reference will be made to the accompanying drawings in which:

Figure 1 is a diagram of the experimental apparatus used; .. „.-.—^•— -

Figures 2 to 7 are graphs showing the results obtained, in the various tests, as described below, i.e.

Figure 2. Copper recovery (%) as a function of surfactant dose at two airflow values. Figure 3. Cumulative froth water volume (ml) as a function of surfactant dose at two airflow values.

Figure 4. Copper metal concentrations^~as^" a function of surfactant dose for pulsed additions of various sizes.

Figure 5. Copper metal concentrations as a function of surfactant dose for pulsed additions from different initial surfactant levels.

Figure 6. Copper metal concentrations as a function of surfactant dose for pulsed additions of various sizes.

Figure 7. Copper metal concentrations as a function of surfactant dose for pulsed additions of various sizes.

Equipment

The flotation equipment used in the bench-scale laboratory experiments is illustrated in Figure 1 and consisted of a modified Hallimond tube cell or column 1 of volume approximately IL. A sintered glass frit 2 in the base of the column allows air to pass through the cell from inlet 3, metered by appropriate flowmeters and regulators (not shown). Side ports 4,5 fitted to the column allow continuous monitoring of pH and /or temperature (4) and removal (5) of small subsamples of the liquid contents of the cell. The liquid feed to column enters through port 6 and the exit air stream flows out through port 7. The froth formed during flotation is discharged from the overflow lip 8 at the top of the cell and collected in another container (not shown). The column may be completely drained at the end of a batch experiment by using the tailings ouϋet port 9.

Factors such as the depth of liquid in the cell and hence the depth of froth may be varied readily. Airflow can also be varied at will.

Procedure

A solution containing a known concentration of copper (present with free and bound cyanide ions) and a known amount of surfactant was prepared and mixed thoroughly. The feed liquid was injected into the flotation cell through port 6 and the air supply connected to inlet 3. Air was then immediately bubbled into the cell and froth began to form at the top of the column. When the first drop of froth spilled over the upper lip of the cell, a timer was started^'' and at known intervals after ti is point, sub-samples of the liquid contents of the cell were removed via. the side port and analyzed for their copper content by atomic absorption spectrophotometry or inductively coupled plasma spectrometry. At the completion of the experiment (when either the surfactant is exhausted or the elapsed time reaches a certain value) the air supply was disconnected and the collected froth and a sub-sample of the final cell contents were analyzed for copper.

[The addition of collector can be made in one dose at the commencement of flotation, or by a number of small (pulsed) additions at various intervals thereafter, while the air supply is still connected. For the present work these intervals were fifteen minutes apart.] Handling of Results

Copper recovery (material reporting to froth) as a function of time is calculated by the formula: R % = (1 - C_t/C₀) x 100 - - - where C is the liquid sub-sample copper concentration at time t, and C is the concentration in the initial feed. The ratio ^~ C represents the fraction of copper from the feed left in the cell at time t.

Feed Solution

For the present study, cyanide tailings water from a gold processing plant was sampled for use as an ion flotation feed. Analysis of the cationic constituents of the solution was made using an ARL 3500C Inductively Coupled Plasma (ICP) Emission Spectrometer, while the anions were analysed using a Dionex 20101 Ion Chromatograph. The results are shown in the two parts of Table 1. The metal of interest, copper, had an initial concentration of 940±20ppm: There were no solids present in the feed liquor. The liquor had a pH of 93.

TABLE ! - ~ CHEMICAL COMPOSITION OF FEED SOLUTION

- 9 -

Chemical Reagent

The reagent myristyltrimethylammonium bromide (MTAB) was selected for copper cyanide ion flotation.

This surfactant was added as a clear solution containing 15% isopropanol and 40% active material by weight.

Results. (a) Effect of Airflow

Figure 2 depicts the copper recovery (%) curves as a function of collector dose at two airflow values in laboratory ion flotation experiments using a quaternary ammonium surfactant. The cumulative froth volume curve is shown in Figure 3. At either of the airflow rates the copper recovery eventually approaches 30%, although the higher the airflow, the wetter the froth product becomes and the faster the recovery rate. Such a result implies that the rate of separation of the ion of interest is a function of the rate of bubble formation; this has been demonstrated previously (Engel et al, 1990).

(b) Effect of Collector Dose

A high air flowrate was then selected for copper ion flotation experiments to allow the fastest possible recovery of metal ions. The froth depth chosen for the initial Hallimond tube experiments was 20% of the cell height to promote drainage of excess liquid from the foam product, since entrainment will occur to a greater degree as the airflow rate is increased (Engel et al, 1990). At this froth depth and at a high airflow rate, Figures 4 and 5 depict cell copper metal concentrations as a function of surfactant dose. Pulsed surfactant additions of various sizes in combination with different initial doses have been used. The data for increment size, total froth volume and overall copper recovery (%) appears in Table 2, also. - 10

TABLE 2 ION FLOTATION PERFORMANCE PARAMETERS

Cell Froth Depth 20% Airflow 682cm^J/min

From Figure 4 and Table 2 it is clear that for a decreasing surfactant increment size for pulsed collector addition, the copper recovery actually increases and the copper ions separate into drier product foams. The best flotationVesults were obtained with a threshold (initial) surfactant dose of 0.8 g/1 and the incremental addition of 0.025g/l amounts of surfactant at 15 minute intervals. The overall copper recovery was 45% into a froth product which contained about 10% of the feed flow of water being treated. The "upgrade ratio" (or concentration factor) is therefore approximately four to five. The recycle water to the process plant contains at lowest around 500 ppm of copper, reduced from the inlet level of 940 ppm. "

A lower initial dose of surfactant at 0.7g/l with 0.05g/l increments, (Table 2, Figure 5) did not lead to improved copper recoveries compared to the results obtained with 0.8g/l and 0.05g/l increments. However, as expected the overall water froth volume was less and the metal upgrade was higher.

This result is consistent with previous observations (Engel et al, 1990). At high surfactant doses product foams become very wet and excess volumes of entrained water are removed. (c) Effect of Froth Depth and Collector Dose -^~=-^-^r

The effect of a smaller froth depth (10% of column height) and a high airflow rate on the recovery and upgrade ratio of copper were determined (Table 3, Figures 6 and 7). Clearly small surfactant increments lead to better overall recoveries and smaller froth volumes. The copper recoveries at 10% froth depth are approximately the same as those achieved using a higher froth depth. The advantage is, however, that the consumption of surfactant is markedly less, with a threshold foaming dose of only 0.5 or 0.6g/l. To recover around 35% copper takes a total of 0.85g/l reagent at a cell froth depth of 10% compared with a dose of l.Og/1 required at a frotii depth of 20%. (Table 2). That is, a larger amount of surfactant is required to form a sufficiently strong froth structure over a greater vertical height.

TABLE 3 ION FLOTATION PERFORMANCE PARAMETERS Cell Froth Depth 10%, Airflow 682cm³/min

. .

- 12 -

References -=-==^«

1. Berg, E.W. & Downey, M.D.,

Analytica Chimica Acta, 12Q, 237 (1980) 5 2. Charewicz, W. and Gendolla, T.,

Applied Chemistry, 15, 383 (1972)

3. Davis, B.M. and Sebba, F., 1966, J. Applied Chemistry, 16, 293.

4. Engel, M.D., Moxon, N.T. and Nicol, S.K., 1990, "A Novel Use of Ion Flotation for Recovery of Gold from Extremely Dilute Solutions",

10 Proc. Randol Gold Forum 90, Squaw Valley, California, 13-15

September, p.229-235.

5. Grieves, R.B. and Bhattacharyya, D., 1969, J. Applied Chemistry, 19, 115.

6. Mikhailov, V.N., Glazkov, E.N. and Larionov, E.V. Sb, Nauchn, Tr. 15 Sredneaziat, Nauchno-lssled, Proektn. Iπst, Tsvetn. MetalU (II), 1975,

103-107.

7. Pinfold, T., 1972, "Ion Flotation" from R. Lemich "Adsorptive Bubble Separation Techniques", Academic Press, 331pp.

8. Rubin, AJ., Johnson, J.D., and Lamb, J.C., I. & E.C. Process Design 20 & Development, 5, 368 (1966).

9. Sebba, R, 1959, Naαira, 184, 1062.

10. Sebba, R, 1962, "Ion Flotation", Elsevier, 150 pp.

Claims

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

R⁴

R³ - N⁺ - R¹ X^" (I)

R²

wherein R is a C, Q - C, _g alkyl group,

3 R is a lower alkyl group, or benzene ring optionally substituted with one or more lower alkyl groups, and R 2 and R 4 are lower alkyl groups;

1 A or R , R and R are methyl groups;

3 R is a benzene ring substituted with a C, _Q - C, g alkoxy group;

and X is a halogen atom.

2. A method as claimed in Claim 2, wherein the copper ion is a copper cyanide anion.

~^"3. A method as claimed in Claim 1 or Claim 2, characterised in that the C-^_Q-C-^g alkyl or alkoxy group contains from 12 to 16 carbon atoms.

4. A method as claimed in Claim 3, characterised in that the C^_Q-C^ alkyl or alkoxy group contains 14 carbon atoms.

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

6. A method as claimed in Claim 1, characterised in that the compound of formula (I) is selected from:

Benzyldimethyldodecylammonium bromide, Dimethyldodecylphenylammonium bromide, Trimethyl-p-dodecyloxyphenylammonium bromide,

N,N-dimethyl-N-dodecyl-3,5-dimethylanilinium bromide, Myristyltrimethylammonium bromide Cetyltrimethylammonium bromide, and Dodecyltrimethylammonium bromide.

7. A method for the extraction of copper using ion flotation, characterised in that the flotation reagent employed is a cationic surfactant as defined in any one of Claims 1 to 6.

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

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