Zn sulphide ore

MineralsEngineering,Vol. 6, No. I I, pp. 1183-1190, 1993 Printed in GreatBritain

0892---6875193 $6.00+0.00 © 1993PergamonPress Ltd

TECHNICAL NOTE LABORATORY STUDY OF EFFECT OF R E C Y C L E WATER ON FLOTATION OF A Cu/Zn SULPHIDE ORE

L. LIU, S.R. RAO and J.A. FINCH Dept. of Mining & Metallurgical Eng., McGill University, Montreal, Quebec, Canada, H3A 2A7 (Received I0 February 1993; accepted 7 June 1993)

ABSTRACT

Batch rougherflotation tests on Cu/Zn ore j~'om Kidd Creek using recycle water, tap and distilled water were compared. The results indicated that recycle water was not detrimental and in Cu flotation enhanced depression of pyrite due to the presence of thiosalt atut calcium ions. Keywords Flotation; recycle water; thiosalts

INTRODUCTION In order to minimize discharge to the environment water is increasingly being recycled in flotation plants. The possible impact of recycle water quality on flotation is a recurring concern [1-5]. This paper describes a laboratory study of the effect of recycle water on Cu flotation of ore from Kidd Creek (KC) 1. In particular the effect of thiosalts and Ca2+ identified in the recycle water was examined. Rougher flotation was compared using recycle water, tap water and distilled water. The effect of individual contaminants was explored by doping and by using treatment techniques to remove contaminants selectively. The possible role of thiosalts and Ca2+ produced by the ore itself during processing was also considered. The study follows preliminary work which produced conflicting results: in one case recycle waters were judged detrimental to Cu flotation [6], but in a second [7] no such effect was found. The rigorous testing conducted here shows that for KC ore recycle water was not detrimental and may be beneficial for pyrite depression. SAMPLES

Ore The head assay of the sample (rod mill feed, -8 mesh) was 0.84 ~ Cu, 5.39% Zn,0.12% Pb and 14.8% Fe. Recycle water Samples, obtained from Kidd Creek in Dec. 1990 and April 1991, were stored at about 4 deg. C. They were analyzed for cations by AA and for thiosalts and sulphite by the mercuric chloride-acidimetric 1183

1184

Technical Note

titration method [8]. This method reports thiosalts as the $2032- equivalent. Ultra-violet spectroscopy (UV) was used to explore for organic (e.g. collectors and frother) and inorganic species (e.g. thiosalts [9]). Some characteristics of the two samples are shown in Table 1. The April '91 sample showed higher Zn levels because it was taken ahead of the lime addition point. T A B L E 1 Characteristics of recycle water samples

lmnllllllnlmm

Im//l/lm//li//l

* Abs: UV absorbance ~,: wavelength of absorbance peak The presence of surface active contaminants (presumably organic) was detected from measurements of bubble size which showed the recycle waters produced smaller bubbles than either tap water or the fresh (river) water at Kidd Creek (Table 2). Their composition, however, is unknown. T A B L E 2 Number of bubbles (relative to that with Montreal tap water) in a given volume, and average bubble diameter under equivalent conditions [10]. Montreal tap water

Kidd Creek river water

Recycle Dec '90

Recycle April '91

ActivatedC treated recycle April 91

No. bubbles (%)

100

120

320

440

200

Ave. bubble dia. (mm)

2.9

2.4

1.9

1.9

2.4

PROCEDURE Flotation The standard (Kidd Creek) laboratory procedure was employed. To investigate the effect of thiosalts, activated carbon was used to remove them from recycle water [11] and thiosulphate was added to tap water. To test the effect of Ca 2+ , precipitation from recycle water with oxalic acid or Na2CO 3 was used and Ca 2+ (as CaCI2) was added to distilled water. Thiosalt/Ca 2+ generation At various stages in the tests with distilled water, the thiosalt and Ca 2+ content of the slurry liquor was determined. RESULTS Ultraviolet Spectroscopy A typical UV spectrum of a recycle water sample is shown in Figure 1 (curve a). The peak at 213 nm was due to thiosalts [9] as confirmed by the similar spectrum of a Na2S20 3 solution (curve b). This figure also shows that activated carbon can remove thiosalts (curve c). No other peaks were found.

Technical Note

l 185

3.0

2.5

A b

2.0

b

1.5

S O r a

n

b)--m.e20). ,.~0|

C e

e) ~ m m d C (S g~) ~ m d n ~

1.0

mo ~0. dnumdS Unto

0.5

200

220

240

260

280

300

320

340

380

380

400

Nanometm

Fig. 1 UV Spectra of various water samples.

Thiosalt/Ca 2+ generation The concentrations derived from the ore are shown in Table 3. The higher Ca2+ content in the Zn-stage is partly the result of pH adjustment using lime.

TABLE 3 Thiosalts and Ca 2+ derived from the ore during laboratory flotation with distilled water. Stage

(ppm)

$2032-

SO~2" (ppm)

Ca2+ (ppm)

Grinding

8

6

120

Cu-stage

34

29

130

Zn-stage

70

32

174

Flotation Figure 2 indicates that both samples of recycle water gave better selectivity than distilled water. This improvement is partly due to decreased recovery of pyrite (Figure 3). Figures 4 and 5 show the effect of activated carbon treatment of recycle water and the addition of 82032to distilled water, respectively. These results reveal a role of thiosalts in the improved selectivity; depression of pyrite by $2032- is apparent in Figure 6. Figures 7 and 8 show the effect of Ca2+: Partial removal of Ca2+ from the recycle water shifted selectivity towards that in distilled water (Figure 7); however, adding Ca2+ to distilled water had no effect (Figure 8).

1186

Technical Note

100

J

I

I

!

I

I

95 9O

85 8o a)

75

r~

65

60 12

I

t

16

14

t

I

I

I

18

20

22

24

26

Cu Grade (%) Fig.2 Recovery-grade relationship in Ca rougher stage: distilled water vs. recycle water.

100

I

I

°,°°| °°o°°

|

t

>,oO'*'°81 =z

95

Ill~e

90

,. °°°,°°°°°°'*°°°°°°"

n..

~"

75

81=,60%j 70

65 60

I,,:

I

I

I

I

I

0

5

10

15

20

25

30

Py Recovery (%) Fig.3 Chalcopyrite (Cp) recovery vs. pyrite (Py) recovery for conditions in Figure 2. (For reference, lines of equal selectivity index, SI (Cp recovery minus Py recovery) are included.)

Technical Note

100

I

a

1187

a

m

i

90

60

50

40

I 12

t~

14

16

t

I

18

20

22

24

Cu Grade (%) Fig.4 Recovery-grade relationship in Cu rougher stage: effect of activated carbon treatment of recycle water 100

90

80

60

50

40

5

I

I

I

I

10

15

20

25

Cu Grade (%) Fig.5 Recovery-grade relationship in Cu rougher stage: effect of thiosulphate addition to tap water

30

1188

Technical Note

100

i

I

I

/1

I

k~o,,p,,, ~,o; I

~' = ~ - "

I

9O

i • • _ J ~ ~ ~

..---""1

~o •

.,.*"

GP

6o

50

40

0

10

20

30

40

50

Py Recovery (%) Fig.6 Chalcopyrite (Cp) recovery vs. pyrite (Py) recovery for conditions in Figure 5.

100

i

i

i

i

u

i

I 22

24

\ A

"-"

2.5 g/I Na2CO~ I rewcle-- A I

80

8 O

distilled ,©O

n-

= o

70

60-

50

12

I 14

I 16

I 18

I 20

I

26

Cu Grade (%) Fig.7 Recovery-grade relationship in Cu rougher stage: effect of Na2CO3 treatment of recycle water (note: Ca2+ cone. reduced to 42 ppm, Zn 1 ppm, NaOH as pH regulator

Technical Note 100

9O

I

I

I

I 189 I

I

I

D

>=

60

50 12

I 14

I 16

• Recycle water (Dec '90) / ~ ~ 300 ppm Ca to distilled.water © [ ] OisUnedwater I I I I 18 20 22 24 26 Cu Grade (%)

Fig.8 Recovery-grade relationship in Cu rougher stage: effect of Ca 2+ addition to distilled water.

DISCUSSION The immediate, practical observation is that recycle water was not detrimental to Cu roughing and, indeed, was potentially beneficial. An identified benefit was depression of pyrite by thiosalts and Ca2+. Both these ions are known to have this effect [12,13] thus their presence in recycle water can be considered a bonus (at least up to the concentrations tested here). Whether recycle water will display this benefit, however, depends on the rate at which these ions are released into solution from the ore itself. In the present case more thiosalts were contributed by the recycle water than by the ore, but this was not so with Ca 2 (Table 3). This probably accounts for why doping with Ca 2 had no effect (Figure 8), the ore contributing sufficient to mask any effect of further additions. The role of thiosalts is worthy of closer study. An important task is speciation of the thiosalts, e.g. using ion chromatography. For a quick, relatively simple analysis calibration against the UV peak at 213 nm could be of use. As a cautionary note, laboratory test'work to evaluate recycle waters, while being the obvious means of doing controlled experiments, has limitations. For example, it is difficult to test for effects in cleaning (as opposed to roughing). Nevertheless, the results here add to the growing body of evidence that, in sulphide mills at least, recycling water may not be a cause for concern. A consistent quality of water rather than the quality itself may be more important.

CONCLUSION In the case of Kidd Creek ore recycle water containing up to 500 ppm thiosalts and 300 ppm calcium was not detrimental to flotation and appeared to enhance depression of pyrite in Cu rougher flotation. ME 6/I I - - F

1190

Technical Note

ACKNOWLEDGEMENTS This work forms part of the Mining Industry Research Council of Canada (MITEC) Project 90P04, sponsored by Into, Cominco, Hudson Bay Mining and Smelting, Placer Dome, and Falconbridge.

REFERENCES I°

2. .

.

5. 6. 7. 8.

.

10. 11.

12. 13.

Taggart, A.F., Handbook of Mineral Dressing, Wiley Handbook Series, 12-85 (1945). Pickett, D.E. & Joe, E.G., Water Recycling Experience in Canadian Mills, Society of Mining Engineers, Trat~v. AIME, 256, 230-235 (Sept. 1974). Forssberg, K.S.E., Jonsson, H.R. & Palsson, B.I., Full Scale Test of Process Water Reuse in a Complex Sulphide Ore Circuit, in Flotation of Sulphide Minerals (ed. K. S. E. Forssberg), Elsevier, 197-217 (1985). Marcotte, E.J., Recycled Process Water at Shebandowan Mill, presented at the CIM 94th Annual general meeting, Montreal, Canada, (April 26-30, 1992). Shackleton, T.A., The Effects of Recycle Water on Flotation, presented at the CIM 94th Annual general meeting, Montreal, Canada, (April 26-30, 1992). Rao, S.R., Gehr, R., Finch, J.A. & Biss, R., Water Treatment and Flotation Studies on Recycle Water from Mineral Processing Plants, Proc. 12th. Syrup. on Wastewater Treatment, 99-119. Gervais, V., L'eau Recyelee en Flotation, Internal Report Min. Met. Eng., McGill Univ., 15 (Juin 1989). Wasserlauf, M. & Dutrizac, J.E., The Chemistry, Generation and Treatment of Thiosalts in Mining Effluents - A Non-Critical Summaly of CANMET Investigatiol~ 1976-1982, CANMET Report 82-4E, CANMET, Energy, Mines amt Resources, Canada, (March 1982). Nickless, G. (Ed.), Inorganic Sulphur Chemistry, Elsevier Amsterdam, 224 (1968). Sutherland, K., M. Eng. Thesis, McGill Univ., (1992). Wasserlauf, M. & Dutrizac, J.E. CANMET's Project on the Chemistry, Generation and Treatment of Thiosalts in Milling Effluents, Canadian Metallurgical Quarterly, 23, No. 3,259269 (1984). Fuerstenau, M.C., Kuhn, M.C. & Elgillani, D.A., The Role of Dixanthogen in Xanthate Flotation of Pyrite, Society of Mining Engineers, Trans. AIME, 241, 148-156 (June 1968). Chander, S., Inorganic Depressants for Sulphide Minerals, in Reagents in Mineral Technology (Ed. P. Somasundaran and B. M. Moudgii), Smfactant Science Series, 27, Marcel Dekker, New York, 429-469 (1988).