Evaluation of flotation column scale-up at Mount Isa mines limited

Minerals Engineering, Vol. 2, No. 3, pp. 369-375, 1989 Printed in Great Britain

0892-6875/89 $3.00 + 0.00 Pergamon Press pie

E V A L U A T I O N OF F L O T A T I O N COLUMN S C A L E - U P AT MOUNT ISA MINES L I M I T E D

R. E S P I N O S A - G O M E Z %, N.W. J O H N S O N % and J.A. FINCH §* %

M i l l i n g Research, Mount Isa Mines Ltd., M o u n t Isa, Queensland, A u s t r a l i a 4825 Dept. of M i n i n g & M e t a l l u r g i c a l Engineering, McGill University, Montreal, P.Q., Canada H3A 2A7 * To w h o m c o r r e s p o n d e n c e should be a d d r e s s e d (Received 31 March 1989)

ABSTRACT In late 1987 Mount Isa Mines commissioned a circuit of 3, 2.5 x 13 m flotation columns to upgrade a bulk Pb/Zn rougher concentrate (low grade middlings). The decision was based on the results of extensive testing in a pilot unit (0.05 x 10 m), involving amenability tests and scale-up parameter estimation. The circuit has performed well and the achieved and expected metallurgy are compared. The pilot column was re-run in parallel with the flotation column circuit. This revealed the importance of operating the pilot and plant columns at similar gas rates for comparative results. The circuit generally exceeded the pilot results; possible reasons are discussed. Kezwords Column flotation; Mount Isa Hines; lead-zinc flotation

INTRODUCTION In 1 9 8 6 M o u n t Isa M i n e s L i m i t e d (MIM) c o n d u c t e d e x t e n s i v e p i l o t c o l u m n t e s t w o r k on a n u m b e r of streams w h i c h p r e s e n t e d process d i f f i c u l t i e s [1,2] ( F i g u r e I). T h e p r o c e s s d i f f i c u l t i e s w e r e in p a r t a s s o c i a t e d w i t h f i n e particles (e.g. 80% l e s s t h a n a b o u t 20 um) w h i c h a r e e n t r a i n e d into the f l o t a t i o n concentrate. F l o t a t i o n columns, therefore, appeared well suited to t r e a t i n g these streams b e c a u s e of their ability to reject e n t r a i n e d particles. The o b j e c t i v e s of the t e s t w o r k were: to c o m p a r e c o l u m n s w i t h the e x i s t i n g m e c h a n i c a l cells (called a m e n a b i l i t y tests); and, to derive scale up data for those streams w h i c h a p p e a r e d amenable. F l o t a t i o n c o l u m n s gave s u p e r i o r m e t a l l u r g y (grade vs. recovery) in all cases [I]. E c o n o m i c c r i t e r i a d i c t a t e d that the first i n s t a l l a t i o n w o u l d be on low grade m i d d l l n g s (LGM, F i g u r e I). Based on the scale-up data and using a scaleup s i m u l a t o r [3] the column circuit was designed. It was c o m m i s s i o n e d in late 1 9 8 7 a n d h a s r u n s u c c e s s f u l l y since then. In 1988 two more column circuits w e r e commissioned, one on the copper r e - t r e a t m e n t c o n c e n t r a t e and the second on the zinc r e - t r e a t m e n t concentrate. This communication r e v i e w s the s c a l e - u p of the L G M c o l u m n s . Some of the o r i g i n a l t e s t w o r k was r e p e a t e d by running the pilot column in parallel w i t h the f u l l - s c a l e columns to provide data on e x a c t l y the same feed material.

PILOT COLUMN SET-UP The column was a 5.08 cm by 1050 cm unit. It was made of Perspex sections for portability a n d to permit visual i n s p e c t i o n of the operation. Feed (from a feed tank), tailings and wash water were c o n t r o l l e d by pumps at p r e d e t e r m i n e d values. Level was c o n t r o l l e d u s u a l l y by m a n i p u l a t i n g the wash water rate. In the case of LGM it was n e c e s s a r y to r e p l e n i s h the feed tank c o n t i n u a l l y w i t h s m a l l (16 L) l o t s to m i n i m i s e o x i d a t i o n w h i c h p r o v e d d e t r i m e n t a l to lead r e c o v e r y in particular. F u r t h e r d e t a i l s are g i v e n in E s p i n o s a - G o m e z et al. 369

[I].

370

R. ESPINOSA-GOMEZet al.

Pb / Zn Plant Heavy medium Heavy medium plant (HMP) plant sinks fines

I ScavengerJ ,bRghr Rougher

II

Zn

I Rougher

•(*)

Pb

Zn ~ Cleaner

Pb !onc. reverse fiotatlon

Rougher ~

Cleaner

~ o/f Zn Clas.I~RetreatmenJ flcatlon I I (R/T) |

T.,,.ll ;u f ~l HMP Slimes Rghr Conc

I

Regrlnd I

1 Zn R/T Conc.

Cu Plant Cu Rougher

~[~1ScavCeUger

, Cu

Cleaner

Tails _] Regrind r I Classlf. and Cu Retreatment (R/T)

T

CuR/TConc.

Fig.1

Flowsheet indicating streams tested by column flotation at Mount Isa Mines (MIM) Ltd. (see also [I]) TEST PROCEDURE

The first step was to conduct amenability tests. This was done by generating g r a d e - r e c o v e r y c u r v e s and c o m p a r i n g w i t h the c i r c u i t grade-recovery. The second step was to determine the two s c a l e - u p p a r a m e t e r s r e q u i r e d by the simulator, namely mineral rate constants and froth carrying capacity [3]. The rate constants were deduced from recovery versus time plots assuming first order kinetics and transport in the pilot column approximated plug flow. Time was the nominal retention time calculated from the volume of the collection z o n e a n d k n o w i n g the t a i l i n g s v o l u m e t r i c flow rate. F e e d d i l u t i o n was sometimes used to keep the operation below the carrying capacity. Carrying capacity was determined by changing the solids feed rate (by altering the percent solids) until the flowrate of concentrate solids reached a maximum [2]. RESULTS AND DISCUSSION Amenability tests F i g u r e 2a gives the L G M test c i r c u i t in m o r e detail. C o l u m n testing was conducted on the feed to the cleaners. The objective was a 47% combined Zn + Pb grade at over 80% Zn recovery across the cleaners. The desired option was to run the c o l u m n s w i t h o u t r e c y c l i n g the t a i l i n g s in part to a v o i d the possibility of overloading the regrind and roughing stages due to the expected large volume of flotation column tail. As a consequence, it was appreciated

Flotation column scale-up

that the available

feed in the p r o p o s e d column circuit for testing in the existing circuit.

371

might

be different

from that

conc. (a)

-t

Regrlnd

1

Tails

Bulk Conc.

(b)

Bulk Rougher I

~-~ Fig.2

Tails

(a) Original low grade middlings circuit at Mount Isa Mines (b) Current column flotation low grade middlings circuit

The comparison of pilot column and e x i s t i n g plant m e t a l l u r g y is shown in Figure 3. It was this favourable result which prompted the decision to proceed with the full-scale design.

'

I

5 40

,

,

I

'

I

otc

i

l 5 50 45 I~4.

I~ 35 ~

30 25

, ,

20 0 Fig.3

40 "6

ExistingP i e n t ~ ~

Amenability

i ie

I

,

I

,

i

20 40 60 80 Recovery of Zn (%)

,

35

10030

test results on low grade middlings

372

R. ESPINOSA-GOMEZ et al.

Scale-up Darameters The parameters derived from the pilot conditions are summarized in Table I.

column

and

the

required

operating

T A B L E 1 D e t e r m i n e d C o l u m n F l o t a t i o n S c a l e - u p P a r a m e t e r s and R e q u i r e d O p e r a t i n g C o n d i t i o n s on L o w G r a d e M i d d l i n g s Circuit, M o u n t Isa M i n e s

original

Solids Rate (t/h Percent Solids Feed: %Zn %Pb Zns Rate Constant, *$ (min -I d80 (~m) ~ C a (g/min/cm z)

(1986)

current

(1988)

30 40 28 13

45 40 20 7

0.08 - 0.13 20 4-5

0.06 35 -

Target M e t a l l u r g y Grade (% Zn + % Pb) R e c o v e r y (% Zn)

>47 >80

The feed to the c o l u m n s is n o t the s a m e as o r i g i n a l l y tested because of the new circuit a r r a n g e m e n t (Figure 2). ** At Jg "2.5 cm/s in original,

Jg ~1.0 cm/s in current

R e v i e w of scale-up The o r i q i n a l test work The i m p o r t a n t q u e s t i o n s w h e t h e r to baffle.

were

the size,

number and a r r a n g e m e n t

of columns

and

U s i n g the simulator it was clear a single stage would not suffice unless it was very large. As a c o m p r o m i s e a column d i a m e t e r of 2.5 m was e s t a b l i s h e d which necessitated t h r e e c o l u m n s to m e e t the c a p a c i t y r e q u i r e m e n t s . The columns were a r r a n g e d in scavenger series (tailings of one feeding the next). T h i s c o l u m n s i z e and a r r a n g e m e n t w a s b a s e d p a r t l y on the e x p e r i e n c e of G i b r a l t a r Mines where three 2.1 m columns were in o p e r a t i o n [4]. The circuit of three columns (Figure 2b) met the o b j e c t i v e (Figure 4).

45

I

I

I

55

I

Column1

40

so

baffled(6 notions) [] unbaffied

35

~

n o.. @

1*2.3

4s ~

o

! so

40

25

35

20

0

I

I

I

I

20

40

60

80

100

I1 "~

30

Recovery of Zn (%) Fig.4

Simulated effect on m e t a l l u r g y of number of columns and b a f f l i n g of each column; all columns are 2.5 x 13 m.

Flotation column scale-up

373

The initial scale-up simulations a s s u m e d the u n i t s w e r e b a f f l e d i n t o 6 sections (giving an equivalent diameter of e a c h s e c t i o n of a b o u t I m) T h e significance of baffling was checked (Figure 4); it was decided not to baffle on the b a s i s of t h i s e v i d e n c e and p r a c t i c a l considerations s u c h as the potential d i f f i c u l t y of a c h i e v i n g even feed d i s t r i b u t i o n to each section. Column height was initially an issue because of b u i l d i n g r e s t r i c t i o n s . The d e c i s i o n was made to go outside and column height was set at 13 m (collection zone height of about 11 m). Column c r o s s - s e c t i o n was selected as circular, which is typical of home made devices, and is cheaper for structural r e a s o n s t h a n b u i l d i n g s q u a r e . (For installations requiring a large number of columns, square may be preferable as more can be packed into the same floor space for equivalent installed volume). T h e c o l u m n a r r a n g e m e n t adopted was the scavenger circuit (Figure 2b). This reflects the need to achieve recovery. Flexibility to r e c y c l e t h i r d c o l u m n concentrate to either first or second stage column was included but the startup o p e r a t i o n was to be open. S o m e of t h e r e s u l t s of the s i m u l a t i o n are s u m m a r i z e d in F i g u r e 4. In particular the choices of 3 columns, the scavenger circuit and no baffling are shown to meet the objective. The c i r c u i t w a s c o m m i s s i o n e d in late 1987. Typical m e t a l l u r g y F i g u r e 5 w h i c h c o n f i r m s t h a t the o b j e c t i v e is m e t . T y p i c a l conditions are given in Table 2. 45

,

,

40

coM.. +

35

,

,

55

50 Column 1÷2+3

~'~_~z~

+

N q,. o

45

|

,0 -

"6

25

35 Feedlfades

20

~

0 Fig.5

is shown in operating

20

I

I

I

40

60

80

r0030

R e c o v e r y of Zn (%) of column flotation on low grade middlings

Observed

metallurgy

TABLE 2

Typical O p e r a t i n g Variables

in the LGM Columns

COLUMN

JT

Jw

Jb (cm/s) *

Jg

TL

I 2 3

0.35/0.65 0.44/0.75 0.57/1.04

0.24 0.20 0.14

0.0/0.05 0.0/0.1 0.0/0.1

0.6/1.0 0.6/1.0 0.7/1.1

30/52 26/45 20/35

Hf cm

Cr g/min/cm 2

100 100 80

2.4 - 4.1 1.4 - 2.0 1.0 - 1.4

(*) F l o w r a t e s are given relative to column cross-sectional area, superficial rates with units cm/s JT superficial tailings rate Jw superficial wash water rate Jb superficial bias rate Jg superficial gas rate volume of collector zone (L) T L nominal residence time = Hf froth depth tailing flowrate (L/min) C r actual carrying rate (concentrate solids flowrate)

or

374

R. ESPINOSA-GOMEZet al.

Follow up testwork As indicated in Figure 2 the current circuit has no recycle to the regrind and rougher, which differs from the original circuit. Because there is no recycle, the r o u g h e r s are " p u l l e d h a r d e r " to reduce the rougher tailing. The prime consequences are, in comparison with the original circuit: a lower r o u g h e r c o n c e n t r a t e (cleaner feed) grade; coarser particles; and, increased solids flowrate. A c o m p a r i s o n of the o r i g i n a l and c u r r e n t feeds to the c l e a n e r circuit is included in Table 1. These differences precluded a strict comparison of predicted (from the pilot column and scale-up simulator) and realized metallurgy. Consequently, p i l o t column runs were repeated by operating in parallel with the circuit columns. The test conditions were carefully selected to be the same, particularly gas rate. The o r i g i n a l w o r k in 1986 had e m p l o y e d gas rates of 2-3 cm/s but experience with the large columns showed improved p e r f o r m a n c e by o p e r a t i n g b e l o w I c m / s ( T a b l e 2). O p e r a t i n g t h e p i l o t c o l u m n at 2-3 cm/s gave significantly poorer metallurgy than the plant columns at about I cm/s. With s i m i l a r gas rates the results were closer but still the plant consistently outperformed the pilot unit (Figure 6).

50

'

45

I

'

I

I

P l a n ~ .

.D I1. 4" e-

N

Pilotcolumn

40

o

"~ 3 5

Feedgrade- 26.5%( Zn+Pb)

30

L

20

I

40

=

I

60

,

I

80

,

100

Recovery of Zn + Pb (%) Fig.6 Comparison of plant and pilot scale results when pilot unit is run at a gas rate close to the operator selected gas rate (Jq ~ I cm/s). Recovery of Zn + Pb (%) is referred to the units of Pb + Zn @ecovered in the LGM concentrate with respect to the total Pb + Zn units fed to the columns. There are a number of possible reasons for the difference in results between the full scale and pilot scale units. "Wall effects" in either the collection or froth zone could be a factor. There could be differences in pulp potential and oxygen content both of which can affect sulphide mineral flotation. There could be differences in the degree of recycle between the froth and collection zones; if the recycle is larger in the full size units metallurgy will improve [5]. The physical arrangement of three columns in series does allow a degree of independent optimization of each in the plant, which is not possible in the pilot unit. Also it is likely the full size units being subject to continual tuning will outperform the pilot unit for which only limited time is available to optimize performance. The important effect of reducing gas rate to improve metallurgy derived from the plant scale experience. This example is one of the first comparing metallurgy of full size and pilot scale columns. In one other published comparison [6] the full size units again outperformed the pilot unit. This is clearly a useful finding; how general it is, and its cause, need closer examination. The differences notwithstanding the pilot unit did reveal operational details w h i c h w e r e c o n f i r m e d in plant. For example: a t e n d e n c y to reject coarse particles, especially with deep froths [I]; and the susceptibility of the lead minerals to oxidation, especially with the long residence time (see Table 2).

Flotation column scale-up

375

The inability of the pilot unit to match the plant column results means the scale-up simulator, using parameters from the pilot unit, will not accurately p r e d i c t plant metallurgy. In fact, the simulator will further downgrade the pilot results because of allowance for mixing. Experience with the simulator shows, n e v e r t h e l e s s , that it reliably estimates the required capacity. The expected metallurgy is best obtained from the pilot results directly with the expectation t h e p l a n t w i l l at least m a t c h (and p r o b a b l y exceed) this performance. CONCLUSIONS Amenability tests showed column flotation offered improved metallurgy over the c o n v e n t i o n a l mechanical cells in cleaning Pb/Zn bulk concentrate (low grade middlings) at Mount Isa Mines. The scale-up parameters and scale-up simulator proved adequate for the design of a 3 stage open scavenger circuit of 2.5 m x 13 m unbaffled columns. This circuit was commissioned in late 1987 and met e x p e c t a t i o n s . It was s h o w n that the plant columns generally gave equal or superior metallurgy compared with the pilot column. The reasons for this are discussed; no s i n g l e c a u s e is i d e n t i f i e d . The p i l o t unit did r e v e a l operational details which were observed in plant such as the tendency of Pb minerals to oxidise. ACKNOWLEDGEMENT The permission of the management of Mount Isa Mines Limited for publication of this paper is acknowledged gratefully. REFERENCES I.

Espinosa-Gomez fine particles,

R., Finch J.A & Johnson N.W., Column flotation Minerals Engineering, I (I), 3-18, (1988).

of very

2.

E s p i n o s a - G o m e z R., Y i a n a t o s J., F i n c h J.A. & J o h n s o n N.W., C a r r y i n g capacity limitations in flotation columns, Int. Symp. on Column Flotation, (Ed. K. Sastry) AIME, 143-148, (1988).

3.

Y i a n a t o s J.B., del V i l l a r R., F i n c h J.A. & Laplante A.R., Preliminary flotation column design using pilot scale data, in Copper '87, (1987).

4.

Redfearn M., Private Communication,

5.

Finch J.A. & Dobby G.S., Column Flotation,

(1986). Pergamon Press, Chap. 6 (1989).

6. Hall S.T. & Averiss S.B., Column flotation for fine tin recovery, Proc. Fine Particles, (Ed. A. Plumpton), Can. Inst. Min. Metall. (1988).

in Prod. 181-182,