Pyrite-Gold Recovery in Copper Rougher Flotation Tailings

Pyrite-Gold Recovery in Copper Rougher Flotation 

Tailings 

Eic Aminartey Agorhom 1 , William Skinner and Massimiliano Zanin 

1 Ian Wark Research Institute 

Ian Wark Research Institute, The ARC Special Research Centre for Particle and Interfaces, University of South 

Australia, Mawson Lakes Campus, Adelaide, SA 5095, Australia 

Email: Aminartey.Agorhom@mymail.unisa.edu.au 

Abstract— The present study investigates the effect of 

regrinding and aeration on the separation of pyrite from 

gold in copper rougher flotation tailings (0.07% Cu, 

0.61g/t Au, tail grades). An aeration stage was applied both 

at the head of copper flotation (copper rougher feed) and 

after regrinding of the copper rougher tailings, before 

gold/pyrite selective flotation. Also, different collector 

regimes, involving sodium iso-butyl xanthate (SIBX) and 

N-butoxycarbonyl-nbutyl thionocarbamate (XD5002), 

have been tested. It was found that aeration of the copper 

rougher feed produced lower gold (71%) and copper 

(95%) recoveries than the non-aeration of the copper 

rougher feed (73% Au and 98% Cu recoveries). Fine 

regrinding of the copper rougher tails increased both gold 

and copper recoveries in the subsequent flotation stage, 

due to improved liberation. The highest gold recovery 

from the rougher tailings (45%) was achieved without 

aeration of the reground product. However, in these 

conditions poor rejection of pyrite was achieved, and the 

concentrate gold grade was low (1.3 g/t, versus 2.3 g/t 

obtained after aerating the pulp). With respect to the 

collector scheme, increased gold and copper recoveries 

were achieved blending the two collectors (SIBX and 

XD5002) compared to XD5002 alone. However, higher 

gold (3.0 g/t) and copper (1.0%) grades were observed with 

XD5002 alone, due to better pyrite rejection. This is 

believed to be due to the high affinity of xanthates (e.g., 

SIBX) for the copper activated pyrite. 

Keywords: Depression; Aeration; Regrinding, Pyrite, 

Gold; Flotation 

I. INTRODUCTION 

Froth flotation is a widely used separating technique for the 

recovery of Cu and Au in porphyry copper-gold ores. In these 

ores, chalcopyrite and gold are the main valuable mineral/metal 

phases, with pyrite being the key sulphide gangue mineral. 

However, in these ores gold is mostly associated with pyrite 

rather than the copper minerals. Gold-pyrite and chalcopyritepyrite 

associations are problematic in porphyry copper-gold 

flotation due to the requirement to minimise sulphur content 

(improve concentrate grade) in the final Cu concentrate. For 

example, in most Cu-Au flotation plants (i.e. Telfer gold mine, 

OK Tedi, Freeport Indonesia, etc.), in order to increase Cu and 

Au grades, regrinding and depression strategies are used to 

maximise pyrite rejection in the cleaner stage. Although these 

depression strategies improve recovery and grade of copper, 

gold recovery is very often affected due to its fine-inclusions 

(~1-3 µm) in pyrite and non-sulphide gangue minerals [1]. 

Also, selectivity between chalcopyrite and pyrite in Cu-Au 

ores is a challenge due to unintentional activation of pyrite as a 

result of the dissolution of Cu 2+ or Pb 2+ ion from complex 

sulphides (i.e. Cp and galena, respectively) and its association 

with pyrite as fine complex intergrowths. It has been proposed 

that activation of pyrite occurs as an ion exchange process, 

where Fe(II) is replaced by Cu(II) on the pyrite surface [2-4]. 

The presence of Cu on pyrite promotes its interaction with 

generic sulphide collectors such as xanthate. It was observed 

that in the presence of xanthate, dixanthogen is the main 

xanthate species responsible for the flotation of Cu-activated in 

alkaline medium. Dixanthogen form as a result of anodic 

oxidation of xanthate at the surface of pyrite coupled with 

cathodic reduction of oxygen [5-6]. Consequently, the 

unintentional pyrite flotation is undesirable in a Cu-Au ore 

flotation circuit due to the detrimental effect on Cu final grade. 

Therefore, in order to improve final concentrate grade, pyrite 

depression strategies (e.g. aeration, sulphite, cyanide addition, 

etc.) have been used over the years to minimise pyrite 

recovery. 

In our previous study [7], the influence of Au mineralogy 

on its flotation was studied in a typical copper ore. A two-stage 

(Cu and pyrite) rougher flotation indicated that maximum Au 

recovery (95%) can only be achieved with pyrite flotation 

(recovery, 93%). A decrease in grind size of the flotation feed 

from 70 µm to 38 µm and without pyrite flotation stage 

resulted in a decreased Au recovery (73%) due to depression of 

pyrite/gold composites (pH 11.5). Therefore, it is crucial to 

study how regrinding of Cu tails at finer grind (p80 = 15 µm) 

and aeration can be used to maximise Au recovery and grade 

while still rejecting significant pyrite. Regrinding in the stirred 

mill (IsaMill) does not only reduce particle size, but also 

liberate Au and Cu from the pyrite mineral, and expose new 

surfaces for enhanced collector adsorption. 

In this study, the effect of aeration (both at the head of Cu 

flotation and after regrinding of copper rougher tailings) on the 

flotation behaviour of Au and Cu in a porphyry copper-gold is 

examined in detail. Copper rougher and scavenger flotation 

1

tests were performed by collector (SIBX/XD5002) addition in 

stages. Consequently, the flotation behaviour of Cu, Au and 

pyrite was examined on the basis of recovery and grade as well 

as the mechanisms responsible for pyrite depression/rejection 

using EDTA extraction techniques. 

A. Materials 

II. 

EXPERIMENTALS 

A.I. Ore 

Mineralogical characterisation of the ore revealed that 

chalcopyrite and covellite were the major copper-bearing 

minerals. Pyrite and silicates were identified as the main gold 

host minerals in the ore. Gold occurred as either liberated or 

locked in pyrite, sphalerite or biotite. Chemical analysis 

showed that the ore contained 1.7 g/t Au, 1.0% Cu, 12.6% S 

and 18.4% Fe. 

A.II. Reagents 

The collectors used were sodium iso-butyl xanthate 

(C4H9OCSSNa, abbreviated SIBX) and N-butoxycarbonyl-n 

butyl thionocarbamate (R’HN-(C=S)-OR”, abbreviated XD- 

5002), supplied by Cytec Chemicals. The frother used was 

methyl-iso-butyl carbinol (MIBC), also supplied by Cytec 

Chemicals. All the reagents were freshly prepared for each 

experiment as 1% w/w solutions. Lime was used as pH 

modifier and compressed air as flotation gas (2 L/min). 

B. Methods 

B.I. Grinding, aeration and flotation 

The schematic representation of the experimental 

procedure is shown in Fig. 1. The ore (2 kg crushed to -2 mm) 

was ground for 60 min in a closed stainless steel Galigher 

mill, in 1000 ml of demineralised water, adding 2.5 g/t 

XD5002 and 1.0 g of dry lime. This resulted in a flotation feed 

with 80 wt.% of the particles passing through 38 µm screen 

(p80=38 µm) and a mill discharge at pH 9.0. After grinding, 

the pulp was transferred to a 4.5 L Denver flotation cell. Two 

conditions, aeration and non-aeration were applied to the pulp 

before reagent conditioning. 

In the first set, the pulp was aerated for 25 min before 

SIBX and XD5002 were added in six stages. The total 

flotation time was 15 min and the pulp pH was kept constant 

at 11.5. After Cu rougher flotation, the tails were reground 

with batch stirred mill (IsaMill) to produce a flotation feed of 

p80=15 µm. Copper scavenger tests were conducted with 15 

g/t SIBX, 10 g/t XD5002 and 7.5 g/t MIBC. Two minutes time 

(2 min) was allowed for each conditioning. Four concentrates 

were collected at 1, 2, 4 and 8 min cumulatively. The detailed 

test conditions for the Cu rougher and scavenger stages are 

shown in Table 1. 

TABLE I. FLOTATION TEST CONDITIONS OF THE 

Cu ROUGHER AND SCAVENGER STAGES 

Cu rougher stage 

Cu scavenger stage 

Pulp density (30 wt.% solids) Regrinding (for 35 min in IsaMill) 

Pulp volume (4.5L) 

Pulp density (20 wt.% solids) 

Agitator speed (1200 rpm) 

Pulp volume (2.0L) 

pH (11.5) 

Agitator speed (1000 rpm) 

Total flotation time, 15 min ( 2.5 min Total flotation time (8 min) 

for each stage) 

All tests were carried out in duplicates. At the end of each 

test, concentrate and tail samples were filtered, dried at 60 0 C 

and assayed for Cu, Au, S and Fe. The flotation strategies 

employed to optimise gold recovery whiles rejecting 

significant pyrite in the copper tail are shown in Table 2. 

Feed 

60 min 

Air (5 L/min) 


d 80=38 µm 

No 

aeration 

Rougher 

block 

d 80 = 15 µm 

Scavenger blocks 

Regrind 

Circuit 

Cu rougher 

concentrate 

Air (5 L/min) 


Final Tails 

Figure 1. Simplified Flowsheet showing flotation with and without aeration of 

Cu rougher feed. 

2

TABLE II. TEST CONDITIONS FOR Au REOVERY OPTIMISATION IN 

THE COPPER ROUGHER TAILS 

Cu feed aerated (IsaMill 

regrinding, p80=15 µm) 

Test1: Aerated for 25 min and 

floated for 8 min using 

SIBX/XD5002 

Test1-1: Aerated for 50 min and 

floated using SIBX/XD5002 

A.III. EDTA extraction technique 

Cu feed non-aerated (IsaMill 

regrinding, p80=15 µm) 

Test 2: Non-aerated and floated for 

8 min using SIBX/XD5002 

Test 3: Aerated for 25 min and 

floated for 8 min using 

SIBX/XD5002 

Test 3-1: Aerated for 50 min and 

floated using SIBX/XD5002 

Test 3-2: Aerated for 25 min and 

floated for 8 min using XD5002 

Ethylene diaminetetraacetic acid (EDTA) was used to 

extract metal oxidation products (e.g. oxide/hydroxide, 

sulphate, carbonate, etc.) from the mineral surfaces [8-10]. A 

pulp volume of 0.1dm 3 was mixed with a 3% AR grade of 

EDTA solution and conditioned for 5 min while purging with 

nitrogen to prevent further oxidation of the mineral surface. 

The EDTA solution was purged with nitrogen for 10 min 

before extraction to remove residual oxygen. The amount of 

surface oxidation products extracted by EDTA was measured 

in solution by inductively coupled plasma mass spectroscopy 

(ICP-MS). 

A. Results 

III. 

RESULTS AND DISCUSSION 

A.I. Effect of aeration and liberation 

The effect of aeration on gold flotation in the copper 

rougher stage is shown in Fig.2. It can be seen that the highest 

recovery (82%) was achieved at the expense of grade (5.7 g/t) 

when the copper rougher feed was not pre-aerated before 

flotation. This is because such condition promotes pyrite 

flotation which invariably leads to higher gold recovery since 

the majority of the unliberated gold particles were associated 

with pyrite as fine inclusions (~1-3µm) [1, 7]. Although higher 

gold grade (7.6 g/t) was achieved when the copper rougher 

feed was pre-aerated before flotation, the gold flotation 

recovery (71%) and kinetics were low. 

Gold recovery (%) 

100 

80 

60 

40 

20 

(a) 

0 

0 2 4 6 8 10 12 14 

Flotation time (min) 

Aerated Cu rougher feed 

Non-aerated Cu rougher feed 

Cum. Gold Recovery (%) 

85 

80 

75 

70 

65 

60 

55 

50 

5 6 7 8 9 10 11 12 13 

Cum. Gold Grade (%) 

Cu rougher feed aerated 

Cu feed non-aerated 

Figure 2. Effect of aeration condition on (a) gold flotation rates and (b) 

gold flotation behaviour in different test conditions (Cu rougher feed aerated 

and non-aerated) using SIBX/XD5002 as collector, p80=38 µm. 

However, when the copper rougher tails (Test 1, Test 2 and 

Test 3) were reground, only 25% of the total gold lost was 

recovered in Test 1. Test 2 showed the highest gold recovery 

(45%), due to higher pyrite recovery (45%) (Table 3). When 

the reground product of Test 3 was pre-aerated before flotation, 

about 33% of gold was recovered at an improved grade (2.3 

g/t). Also, the highest gold (86%) and copper (98%) recoveries 

in the combined copper rougher and scavenger stage was 

achieved when aeration was not applied both at the head of 

copper flotation and after regrinding of the copper rougher 

tailings. 

TABLE III. FLOTATION DATA FOR Au, Cu AND Py AFTER 

REGRIND TO p80=15µm UNDER DIFFERENT TEST CONDITIONS (Au, 

Rec ±2%, Cu, Rec ±1% and Py, Rec ±4%) 

Test # 

Recovery 

(%) 

(b) 

Gold Copper Pyrite 

Grade 

(g/t) 

Error bar 


(%) 

Grade 

Total Recoveries, 

% (Cu Ro+Sc 

stage) 

In case of copper flotation, there was no significant change 

in copper recovery for the two different test conditions (Fig.3). 

The best copper grade (7.3%) was achieved when the copper 

rougher feed was pre-aerated before flotation. It has been 

demonstrated by a number of researchers that flotation of 

copper minerals such as chalcopyrite improved at higher pulp 

potential, ~300 mV [11-12]. This is evident in the flotation of 

the reground product of Test 3, where maximum copper grade 

(0.8%) was achieved as a result of significant reduction in 

pyrite recovery (16%) as compared to Test 2 (Table 3). 

Although copper recoveries were not significantly affected 

compared to the baseline flotation studies [7], copper flotation 

rate was slower when copper rougher feed was pre-aerated 

before flotation (Fig.3). This condition promotes the formation 

of metal hydroxide species on the surface of chalcopyrite 

which makes the formation of metal xanthate on the 

chalcopyrite surface difficult resulting in slower flotation rates 

(%) 


(%) 

Grade 

Test 1 25 2.2 43 0.6 10 24.5 73 96 36 

Test 2 45 1.7 54 0.3 45 54.3 86 98 62 

Test 3 33 2.3 56 0.8 16 32.4 82 97 49 

(%) 

Au 

% 

Cu 

% 

Py 

% 

3

in flotation [13]. Higher pyrite rejection (about 64%) was 

observed when both copper rougher feed and reground product 

were aerated before flotation, but this caused a significant 

reduction in gold recovery. The significant pyrite 

rejection/depression correlate with higher oxygen consumption 

rate (kla = 0.131 min -1 ) of the reground product determined 

from oxygen demand test (not shown here). The pulp potential 

(Eh) increase steadily from 269 to 342 mV SHE after aeration, 

which may be responsible for the effective pyrite depression 

under this test condition (Table 4). 

TABLE IV. PULP CHEMISTRY PARAMETERS (DO & Eh) AND 

OXYGEN CONSUMPTION RATE, kla AFTER AERATION OF 

REGROUND PRODUCT (TEST 1), p80 = 15 µm. 

Pulp parameters Initial Final 

DO (ppm) 2.72 7.76 

Eh (mV SHE) 269 342 

Cum. Copper Recovery (%) 

Gold recovery (%) 

100 

98 

96 

94 

92 

90 

88 

86 

84 

82 

100 

80 

60 

40 

20 



0 

0 2 4 6 8 10 12 14 


Cu rougher feed aerated 

Cu rougher feed non-aerated 

80 

4 6 8 10 12 14 

100 

(a) 

(b) 

Error bar 

Cum. Copper Grade (%) 

Kla (min -1 ) 0.131 0.029 

A.II. Effect of aeration time and collector suite 

Increase in aeration time from 25 min to 50 min for the 

reground products of Test 1 and Test 3 resulted in decreased 

gold, copper and pyrite recoveries. When the aeration time for 

Test 1 was increased, total gold recovery decreased from 73% 

to 70% with an improved overall gold concentrate grade (8.5 

g/t) (Table 5). A similar reduction in copper and pyrite 

recoveries were observed in Test 1-1. However, copper grade 

(7.2%) improved significantly as a result of drastic reduction in 

mass recovery. Also, increase in aeration time for the reground 

product for Test 3 showed a decreased gold recovery (81%) but 

did not impact on gold grade (5.4 g/t) (Test 3-1). There was no 

significant change in copper recovery but copper grade 

increased by 0.2%. Pyrite and mass recoveries reduced 

significantly. 

A change in collector suite, from a combination of SIBX 

and XD5002 to only XD5002 (a more Cu-sulphide selective 

collector) for Test 3 reground product (Test 3-2) resulted in a 

reduction in gold recovery from 83% to 76% at an improved 

grade (7.4%). Copper recovery also dropped marginally, by 

1%. However, copper grade increased significantly (6.8%). 

The change in collector suite has more significant impact on 

pyrite rejection than increasing the aeration time of the 

reground product (Test 3-1) (Table 5). 

Pyrite recovery (%) 

80 

60 

40 

20 

(c) 



TABLE V. FLOTATION RECOVERY AND GRADE DATA FOR Au, 

Cu AND Py IN THE COMBINED ROUGHER AND SCAVENGER STAGES 

(Au, Rec ±2%, Grade ±0.08g/t; Cu, Rec ±1%, Grade ±0.05% and Py, Rec 

±4%, Grade ±3%) 

Test # 


(%) 

Gold Copper Pyrite Mass 

Grade 

(g/t) 


(%) 

Grade 

(%) 


(%) 

Grade 

(%) 

Yield 

Test 3 82 5.4 97 5.7 49 41.9 31±2 

(%) 

0 

0 2 4 6 8 10 12 14 


Figure 3. Effect of aeration on (a) copper flotation rates; (b) copper 

flotation behaviour and (c) pyrite flotation rates in different test conditions 

using SIBX/XD5002 as collector, p80=38 µm. 

Test 3-1 81 5.4 97 5.9 28 38.4 29±2 

Test 3-2 76 7.6 96 6.8 29 37.7 18±2 

Test 1 73 

5.7 

96 5.2 36 36.9 24±2 

Test 1-1 70 8.5 94 7.2 24 37.7 15±2 

4

A.III. Effect of surface species 

To account for the differences in pyrite recovery for the 

aerated and no-aerated Cu rougher feed, EDTA extraction was 

performed on the feed, primary ground product and after 

aeration. Table 6 shows the amount of Cu, S and Fe oxidation 

species extracted. The results indicate that the concentration of 

surface Cu and Fe oxidation species in the feed was relatively 

low compared to the primary ground product. The EDTA 

extractable Cu and Fe increased approximately from 19 and 

2% (feed) to 23 and 4%, respectively, after primary grinding. 

The observed increase in Cu and Fe concentration after 

primary grinding at high pH suggests the formation of more 

Cu(OH) 2 and Fe(OH) 3 on the Cp surface, which will hinder its 

surface affinity for collector adsorption. On the other hand, the 

presence of Cu(OH) 2 in solution can cause copper activation 

of pyrite which will increase its surface affinity for collector 

adsorption. The latter may account for the high pyrite recovery 

observed after primary grinding with without aeration (Fig.3c). 

Aeration of the pulp prior to flotation subsequently 

increased the surface Cu and Fe oxidation. The EDTA 

extractable Cu and Fe increased by approximately 5 and 2%, 

respectively, after aeration. These could be related to the 

creation of a more oxidising environment where high Eh values 

are reached. It is generally accepted that pyrite is more reactive 

than chalcopyrite therefore, at this stage it can be assumed that 

the pyrite surface is strongly oxidised and covered with 

hydrophilic iron oxide/hydroxide species preventing or 

minimising their surface interaction with the collector. This 

may explain why lower pyrite recovery was observed for the 

aerated Cu rougher feed than the non-aerated Cu rougher feed. 

TABLE VI. SURFACE Cu, S AND Fe OXIDATION SPECIES 

PRESENT ON THE PYRITE SURFACE AS DETECTED BY EDTA 

EXTRACTION FOR THE FEED, PRIMARY GRIND PRODUCT AND 

AERATED PRODUCT. 

Survey/sample 

Con. 

EDTA 

Ext., 

mg/l 

Cu S Fe 

Total 

weight, 

% 

Total 

metal, 

% 

Con. 

EDTA 

Ext., 

mg/l 

B. Discussion 

The results in Fig. 3 indicate that aeration of the Cu rougher 

feed decreased gold recovery due to decreased pyrite recovery. 

The mineralogical analysis of the ore [1] showed that the 

majority of the unliberated gold particles were associated with 

pyrite. However, regrinding of the copper rougher tails (both 

Total 

weight, 

% 

Total 

metal, 

% 

Con. 

EDTA 

Ext., 

mg/l 

Total 

weight, 

Feed 29 0.25 19 1071.0 8.99 68.15 46.20 0.39 1.77 

After grinding 38 0.29 22.87 1575.0 12.39 93.85 100.8 0.79 3.62 

% 

Total 

metal, 

Aeration 48 0.36 27.87 1722.0 12.92 97.84 134.4 1.01 4.60 

% 

aerated and non-aerated feed) improved gold recovery. 

Aeration of the reground products of the aerated/non-aerated 

copper feed further decreased pyrite recovery and consequently 

decreased gold recovery. Under the aerative condition, higher 

oxidizing medium (higher Eh value, ~342 mV SHE) is created, 

which easily oxidized S 2- 2 to various surface oxidation species 

such as S, SO 2- 2- 

4 , SO 3 and S 2 O 2- 3 . Some of these surface 

oxidation species (e.g. S, polysulphides, etc.) are hydrophobic, 

but the majority is hydrophilic (SO 2- 4 , SO 2- 3 , S 2 O 2- 3 , Fe(OH) 3 ) 

and reduce pyrite floatability. These surface contaminants 

passivate pyrite surface, prevent Cu and collector adsorption 

and hence decreased pyrite flotation. This is in agreement with 

other studies in the literature, which show that passivation of 

pyrite surface by iron oxidation products reduce its flotation 

[14-15]. Also, when the tails of the non-aerated Cu rougher 

feed were reground and floated with XD5002 alone after 

aeration (Test 3-2) lower gold recovery was produced 

compared to when floated with a combination of SIBX and 

XD5002 (Test 3). This can be attributed to better performance 

of collector mixture, synergism and improved adsorption 

characteristics of collector blend than the single collector [16- 

18]. Also, the lower recovery of gold in the presence of 

XD5002 alone may be attributed to its selectivity against iron 

sulphide minerals (e.g. pyrite). 

In the case of copper, aeration and regrind do not 

significantly affect copper recoveries. However, the grade of 

copper was higher when XD5002 alone was used due to its 

lower affinity for pyrite. Better selectivity of thionocarbamate 

collectors for copper sulphides against iron sulphide is 

achieved due to their specific interaction with cupric ions and 

not with ferric, ferrous or lead ions [19-21]. The flotation 

recovery of copper was improved marginally under the aerative 

conditions than the non-aerative conditions. It has been shown 

that flotation performance of chalcopyrite improved in high 

pulp potentials [11-12]. Aeration of the pulp increases the pulp 

potential to more oxidising environment which enhances 

oxidation of collectors on chalcopyrite surface, hence improved 

copper flotation. 

CONCLUSIONS 

Regrinding and aeration improved Au recovery and grade 

due to improve liberation and significant rejection of pyrite in 

Cu rougher tails. The flotation strategies indicate that the best 

approach to maximise Au recovery and grade was nonaeration 

of Cu rougher feed and aeration of the reground 

product. The different flotation strategies do not have a 

significant effect on Cu recovery. However, the use of 

XD5002 alone together with aeration of the reground product 

of the non-aerated Cu rougher feed gave the highest Au and 

Cu grades with maximum pyrite rejection. The results 

discussed here when combined with our previous studies [1, 7] 

could provide a holistic approach of maximising Au flotation 

in a typical porphyry copper-gold ore without detrimental 

effect on Cu flotation. 

5

FUTURE WORK 

Surface analysis using X-ray spectroscopy (XPS) will be 

conducted in the future to determine the surface species 

responsible for the pyrite rejection. 

ACKNOWLEDGEMENTS 

The financial support from AMIRA International and the 

industry sponsors of the P260F project is strongly 

acknowledged. 

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6

Pyrite-Gold Recovery in Copper Rougher Flotation Tailings

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