Improvement effect of organic ligands on chalcopyrite leaching in the aqueous medium of sulfuric acid‑hydrogen peroxide-ethylene glycol

Journal Pre-proof Improvement effect of organic ligands on chalcopyrite leaching in the aqueous medium of sulfuric acid-hydrogen peroxide-ethylene glycol

A. Ruiz-Sánchez, I. Lázaro, G.T. Lapidus PII:

S0304-386X(19)31006-0

DOI:

https://doi.org/10.1016/j.hydromet.2020.105293

Reference:

HYDROM 105293

To appear in:

Hydrometallurgy

Received date:

8 November 2019

Revised date:

29 January 2020

Accepted date:

14 February 2020

Please cite this article as: A. Ruiz-Sánchez, I. Lázaro and G.T. Lapidus, Improvement effect of organic ligands on chalcopyrite leaching in the aqueous medium of sulfuric acid-hydrogen peroxide-ethylene glycol, Hydrometallurgy(2020), https://doi.org/10.1016/ j.hydromet.2020.105293

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© 2020 Published by Elsevier.

Journal Pre-proof

Improvement effect of organic ligands on chalcopyrite leaching in the aqueous medium of sulfuric acid-hydrogen peroxide-ethylene glycol A. Ruiz-Sánchez*

a,b

, I. Lázaroa, G.T. Lapidusb.

a

ro

ABSTRACT

of

Instituto de Metalurgia, Universidad Autónoma de San Luis Potosí. Av. Sierra Leona 550, Lomas 2ª sección. San Luis Potosí. México C.P. 78350. b Universidad Autónoma Metropolitana Unidad Iztapalapa. Departamento de Ingeniería de Procesos e Hidráulica, Universidad Autónoma Metropolitana Iztapalapa. San Rafael Atlixco No. 186, Col. Vicentina. México, Ciudad de México. C.P. 09340. [email protected]*

The addition of ethylenediaminetetraacetic acid (EDTA) to a 1 M H2 O2 leaching solution with low

-p

concentrations of sulfuric acid (0.007 M) and ethylene glycol (EG)(0.1 M) promotes significant increases of copper and iron leached from chalcopyrite. However, copper purification by solvent

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extraction is not possible due to the elevated stability of copper-EDTA and iron-EDTA complexes

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in the resulting leach liquor. Therefore, a two-stage process is presented that enables copper and iron dissolution at ambient temperature and pressure (26°C and 101.325 kPa, respectively), without the necessity of solvent extraction. The proposed process uses the H2 SO4 -H2 O2 -ethylene glycol

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leaching solution in combination with organic ligands (oxalic acid (OxA) or EDTA). The first stage, using the leaching solution with oxalic acid, dissolved 29.5% of iron and transformed 49% of the

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copper to an oxalate salt; while in the second stage, the H2 SO4 -H2 O2 -ethylene glycol-EDTA leaching solution favored both the rapid dissolution of the copper oxalate salt and the chalcopyrite

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that did not react in the first stage. In this manner, the pregnant leach solution (PLS) from the second stage contained 90% and 35% of the total copper and iron, respectively, which may be electrowon directly. These results showed that the use of organic ligands promotes the formation of copper and iron complexes which help to delay, but not to avoid the decomposition of hydrogen peroxide due to a Fenton reaction and therefore, this results in an increase of the percentages of copper and iron leached, which permits processing at higher pulp density (50 g/L). Keywords: Two-stage leaching process, copper concentrate, ethylenediaminetetraacetic acid, oxalic acid, chalcopyrite, covellite.

1

Journal Pre-proof 1. Introduction

The addition of organic polar solvents in the aqueous solution of hydrogen peroxide and sulfuric acid increases the percentages of copper and iron leaching from chalcopyrite (Solís and Lapidus, 2013), the most abundant copper sulfide in nature. Among the different polar organic solvents that have been studied, methanol and ethylene glycol give the best results. However, the low boiling point of methanol compared to ethylene glycol represents a practical disadvantage. For that reason, the ethylene glycol is considered the most suitable polar organic solvent for a leaching process that operates at moderate temperatures (20-50

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°C) and pressure (101.325 kPa). However, application at the industrial level for the

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leaching system formed by sulfuric acid-hydrogen peroxide-ethylene glycol has not been possible due to the following disadvantages: the use of high concentrations of ethylene

-p

glycol (3.5 M) and sulfuric acid (0.7 M) (Ruiz-Sánchez and Lapidus, 2017), as well as the

re

low efficiency (less than 2%) in the purification process (by solvent extraction) of copper as a result of highly acidic levels (0.7 M H2 SO 4 ) of the resulting leaching solution.

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To optimize the copper leaching process and increase the efficiency in the solvent extraction process, leaching studies with low concentrations of sulfuric acid (0.007 M) and

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ethylene glycol (0.1 M) with 1 M H2 O2 have been carried out. The results have shown that the use of 0.007 M H2 SO4 promotes, on the one hand, the decomposition of hydrogen

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peroxide as a result of Fenton reaction, which takes place between hydrogen peroxide and ferric or ferrous iron, catalyzed by the cupric ion (Barb et al., 1951; Pestovsky and Bakac,

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2006; Ruiz-Sánchez and Lapidus, 2017); and on the other hand, the mineralization of ethylene glycol due to the OH* radicals formed

in the Fenton reaction. However, it has

been found that the presence of EDTA in the leaching solution 0.007 M H2 SO 4 -1 M H2 O2 0.1 M EG helps to decrease the decomposition of hydrogen peroxide due to the formation of highly stable copper-EDTA and iron-EDTA complexes; thus, favoring a greater dissolution of chalcopyrite (Ruiz-Sánchez and Lapidus, 2018). Despite the significant increases in the percentages of copper and iron reported by RuizSánchez and Lapidus (2018), until today it has not been possible to purify copper by solvent extraction due to the elevated stability of the complexes of copper-EDTA and ironEDTA in the leach liquor. Furthermore, in this leaching system, the studies by Ruiz2

Journal Pre-proof Sánchez and Lapidus (2018) and by Mahajan et al. (2007) used samples of pure chalcopyrite at low pulp densities (maximum 3.75 g/L). Consequently, the experimental conditions adequate for processing of high pulp densities (greater than 10 g/L) have not been established nor has this system been used on copper flotation concentrates. Therefore, there is a need to conduct a systematic study on the H2 SO4 -H2 O2 -EG-EDTA leaching solution, either to purify the copper from the resulting leach liquor or to design a new approach to the leaching process that suppresses the dissolution of iron and allows the processing of high pulp densities, in such a manner that a copper-rich leaching liquor is

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obtained that can be sent directly to the electrowinning process.

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To achieve the aforementioned goal, a copper leaching process from a chalcopyrite concentrate is presented which obtains a copper-rich PLS and with a low iron content. The

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proposed process consists of two consecutive stages, the first of which uses a H2 SO4 -H2 O2 leaching solution for the selective dissolution of iron and the formation of

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EG-oxalic acid

solid copper oxalate; the second stage employs a H2 SO 4 -H2 O2 -EG-EDTA leach solution to

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dissolve the copper oxalate and react with the remaining chalcopyrite from the first stage.

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2. Material and methods

2.1 Copper concentrate characterization

The sample of copper concentrate used in this work originated from the state of Sonora,

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Mexico. A kilogram of copper concentrate was sieved to determine its particle size

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distribution. The different fractions obtained, as well as the original copper concentrate were digested with aqua regia and analyzed by atomic absortion spectrometry (AAS, Varian SpectrAA220fs), according to the methodology described by Ruiz-Sánchez and Lapidus (2017). 2.1.1

X-ray Diffraction analysis (XRD)

The copper concentrate was ground in an agate mortar to obtain a particle size less than 38 µm (-400 mesh). The sample was firmly compacted onto a sample holder to avoid preferential orientations. The analysis was carried out on a D8 Advance diffractometer in the range of 4°-90° for angle 2θ, at a speed 8°/min. The identification of mineralogical phases was carried out with the Diffrac EVA 5.1 software.

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Journal Pre-proof 2.1.2

Analysis by Scanning Electron Microscopy (SEM)

A one-gram sample of copper concentrate was supported on a cylindrical specimen of lowdensity epoxy resin. The specimen was polished with silicon carbide sandpaper with different grain sizes (200, 800 and 1200), until a mirror-finish surface was obtained, which was then coated with graphite to increase its conductive properties. The original copper concentrate or leach residue was analyzed on a XL30 Phillips electron microscope coupled to a micro-analysis system equipped with energy dispersive spectroscopy (EDS), using the backscattered electron technique. The analysis conditions were 20 kV, SS50 and WD 10

Mineralogical analysis

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2.1.3

of

mm.

The mineralogy involved identification of mineralogical phases by a modal analysis

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according to the methodology described by Fandrich et al. (2007). In this methodology, the

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X-ray Diffraction and SEM techniques, together with chemical analysis, permitted the reconstruction of the mineral species contained in the concentrate.

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2.2 Leaching system

The leaching tests were performed in a 2 L cylindrical stainless-steel reactor with vertical

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baffles. The reactor was temperature-controlled system using a recirculating bath (Haake DC10) with cooling water, a stainless-steel coil and a mechanical stirring system coupled to

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a stirrer with two Rushton turbine impellers rotating at a speed 400 rev/min (rpm). Each of

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the leaching tests were carried out at 26°C using 1.5 L of leaching solution. During the leach, liquor samples were drawn to quantify the concentration of copper and iron dissolved and for the determination of the hydrogen peroxide concentration, as established by RuizSánchez and Lapidus (2017). In addition, pH and Oxide-Reduction Potential (ORP) measurements were made using the HI 1618D and HI 3131B electrodes, respectively. The following reagents were used for the development of leaching experiments: hydrogen peroxide (34 %/v, J.T Baker), ethylene glycol (17.88 M, J.T Baker), sulfuric acid (98 %/w, J.T Baker), acid ethylenediaminetetraacetic disodium salt dihydrate (99.9%, JT Baker), oxalic acid dihydrate (99.5 %/w, JT Baker) and deionized water prepared in a Millipore Milli-Q system (with a resistivity of 18 MΩ.cm at 25°C).

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Journal Pre-proof

2.2.1

Leaching tests in H2 SO 4 -H2 O2 -EG-EDTA

These leaching tests employed the 0.007 M H2 SO4 -1 M H2 O2 -0.1 M EG- EDTA leaching solution at different pulp densities (gram of copper concentrate/L of leaching solution). The EDTA ligand was added in a molar ratio Rm = 1 (Ruiz-Sánchez and Lapidus, 2018). This molar ratio corresponds to the ratio of number of moles of ligand and total moles of copper and iron contained in the mass of copper concentrate for a given pulp density (Equation 1).

Two-stage leaching

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2.2.2

(1)

)

of

(

The leaching tests were carried out using the leaching system described in 2.2.1, replacing

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the EDTA ligand with oxalic acid at a molar ratio Rm=1. After 24 hours, the leach liquor was filtered, and the solid residue was oven-dried at 50 °C for 12 hours. In another leaching

re

test under the same experimental conditions, the wet solid residue obtained in the filtration

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was contacted with the leaching solution 0.007 M H2 SO 4 - 2 M H2 O2 -0.1 M EG- EDTA, with added EDTA in a ratio Rm=1 (calculated with respect to the pulp density of step 1).

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Finally, the leach liquor resulting from this second stage was filtered and the solid residue was dried at 50 °C in an oven for 12 hours.

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The solid residues corresponding to each of the stages were characterized by X-Ray Diffraction, and, additionally, the solid residue of the second stage was analyzed by SEM.

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The percentages of copper and leached iron were calculated at each stage as 100 times the ratio of copper or iron dissolved at fixed time of leaching with respect the total copper or iron present in the initial pulp density.

3. Results and discussion

3.1 Copper concentrate characterization Table 1 shows the elemental composition obtained by AAS for the copper concentrate according to the particle size distribution corresponding to the fractions +106 µm, + 53µm and +38 µm. As can be seen, the contents of Pb, Zn, Cu and Fe increase as the particle size

5

Journal Pre-proof decreases, due to the liberation of mineralogical phases (shown below Table 1) during the milling process, which precedes the flotation process.

Elemental composition, Wt% Pb 0.065

Zn 0.826

Cu 16.16

Fe 27.4

-106 + 53

0.104

0.789

18.36

29.35

-53 + 38

0.101

0.876

20.04

30.32

<38

0.14

1.46

26.04

30.16

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Particle size (µm) >106

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re

-p

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Table 1. Elemental composition of the copper concentrate at different particle sizes.

Due to the variation of the elementary composition with the particle size (Table 1), an

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average metallic composition (Table 2) in the copper concentrate was estimated that was then used for calculation of the percentage of copper and iron leached. The average metallic

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composition ( ̅̅̅̅̅̅̅) was determined from Equation 2, where n corresponds to each of the is the weight percent for the fixed particle size n (Figure 1) present in

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particle sizes,

the mineral concentrate and

represents the metal composition for the fixed particle

size n (Table 1). In addition, from Figure 1 it was found that the P 80 of the sample corresponds to 63 µm. ̅̅̅̅̅̅̅

∑

( )

Table 2. Average the copper

metal composition for concentrate. Average metallic composition, Wt% Pb 0.12

Zn 1.16

Cu 22.4

6

Fe 28.2

52.58

55 50 45 40 35 30

27.32

25 20 15

11.14

8.96

10 5 0

>106

-106 +53

-53 +38

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Particle size (m)

<38

of

Percent mass of mineral concentrate (%)

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Figure 1. Percent mass of copper concentrate based on particle size .

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From the average metal composition (Table 2), the metal distribution corresponding to each

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particle size was estimated (Table 3). The results show that the fraction with particle size < 38 µm corresponding to 52.58% of copper concentrate (Figure 1), contains 61.9, 66.5, 61.2

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and 50.8% of the Pb, Zn, Cu y Fe, respectively; while the fraction with particle size > 106 µm, corresponding to only 8.96% of copper concentrate (Figure 1), comprising 4.8%, 6.4%,

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6.5% y 8.7% of the aforementioned metals. From these results, a slow dissolution of

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approximately 7% copper is expected due to the larger particle size.

Wt%

Particle size (µm) >106

Pb 4.8

Zn 6.4

Cu 6.5

Fe 8.7

-106 + 53

23.9

18.7

22.4

28.5

-53 + 38

9.4

8.5

10.0

12.0

<38

61.9

66.5

61.2

50.8

Table 3. Total metal distribution at different particle sizes.

7

Journal Pre-proof On the other hand, the mineralogical analysis (Table 4) shows that Zn, Pb, Cu and Fe are mostly in the form of sulfides: sphalerite (Sp), galena (Gal), chalcopyrite (Cp), covelite (Cv) and pyrite (Py) This analysis also reveals the presence of binary mineralogical associations between the sulfides and the gangue (Gn), and ternarians where sphalerite (Sp) is included. This analysis also reveals the presence of binary mineralogical associations between the sulfides and gangue (Gn), and ternarians where sphalerite (Sp) is included.

3.4 6.4 12.3 2.3

Gn 51.2 5.8 26.8 2.9 5.1

12.1 9.1

7.7

-p

1.6 12.4 7.4

Cv 36.1 0 37.0 5.7

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Py 63.0 0.2 14.8

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Free Gal Cp Py Cv Gn Ternary

Cp 74.0 0.1

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Table 4. Association of minerals phases present in the copper concentrate.

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Table 4 also shows that 3.4% y 6.4% of chalcopyrite are in binary association with pyrite and covellite; similarly, 37% and 5.7% of covellite is associated with chalcopyrite and Mineralogical associations in the copper concentrate, as well as 63%

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pyrite, respectively.

of free pyrite, suggest the possibility that the copper leaching process could benefit through

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galvanic interactions, such as those seen in the GalvanoxT M process (Dixon, 2008).

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Based on the results of Tables 1-4, the copper concentrate contains 60.1% chalcopyrite, 21.5% pyrite, 2.4% covellite, 0.1% galena, 1.7% sphalerite and 14% gangue (quartz and muscovite). This mineralogical composition leads to a contribution of 93% of copper and 65% of iron from chalcopyrite, while the remaining 7% of copper and 35% of iron come from covellite and pyrite, respectively. 3.2 Leaching tests with H2 SO4 -H2 O 2 -EG-EDTA Figures 2a and 2b show the effect of pulp density on copper and iron leaching. In general, the percentages of copper and iron leached decrease as the pulp density increases. Also, regardless of the pulp density (Figure 2a), in the first hour of leaching the PLS contains 11% of the copper and only 1.5% of the iron, respectively. The 1.5% of leached iron in this

8

Journal Pre-proof period of time indicates a low dissolution of chalcopyrite or pyrite, thus confirming that 11% of the dissolved copper corresponds to the covellite phase. 100

a)

3.75 g/L 11.25 g/L 22.5 g/L

80

60

40

20

70 60 50 40 30 20 10 0

0 2

4

6

0

2

4

6

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0

of

80

b)

90

3.75 g/L 11.25 g/L 22.5 g/L

Leached Iron (Wt%)

Leached copper (Wt%)

100

8 10 12 14 16 18 20 22 24 26

Time (h)

-p

Time (h)

8 10 12 14 16 18 20 22 24 26

Figure 2. Effect of the pulp density on the leaching of (a) copper and (b) Iron. Experimental

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conditions: [EG] =0.1 M, [H2 SO4 ] =0.007 M, [H2 O2 ] =1 M and [EDTA]=0.032, 0.096 and 0.192 M.

Figures 2a and 2b show that for 3.75 g/L, 94% copper and 62% iron were obtained after 24

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hours. The leached iron corresponds approximately to the percentage of total iron in the form of chalcopyrite (65%); this suggests minimal pyrite dissolution in the leaching medium. Furthermore,

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there exists a possibility that a galvanic interaction between chalcopyrite and pyrite could be established. For the same pulp density (3.75 g/L), after 18 hours, the percentage of copper

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leaching shows slower kinetics, even though sufficient hydrogen peroxide remains in the

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solution (~ 0.83 M H2 O2 according to Figure 3b). The slow rise in the copper and iron profiles mentioned above can be attributed to the leach of the largest particles (Table 3), without ruling out a slow leaching of copper from the Cp-Gn association (Table 4); the latter possibility of leaching will be discussed in more detail in section 3.3.1 (Figure 14). The ORP profiles (Figure 3a) in the leach solution for the different pulp densities show similar behaviors in the first two hours of leaching, because the hydrogen peroxide concentration is almost constant in this time interval (Figure 3b). However, from hour two the ORP profile shows a decrease depending on the pulp density, such behavior can be related to the decrease in the concentration of hydrogen peroxide. For example, for 22.5 g/L in the range of 2-6 hours the ORP decreases due to a 30% drop in the initial H2 O2 concentration (Figure 3b). 9

0.70 0.69 0.68 0.67 0.66 0.65 0.64 0.63 0.62 0.61 0.60 0.59 0.58 0.57 0.56

1.2

a) 3.75 g/L 11.25 g/L 22.5 g/L

b)

1.0 0.8 [H2O2], M

0.6 0.4

3.75 g/L 11.25 g/L 22.5 g/L

0.2

0

2

4

6

0.0

8 10 12 14 16 18 20 22 24 26

0

c)

3.8

3.4

8 10 12 14 16 18 20 22 24 26

Time (h)

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3.0 2.8

lP

pH

3.2

2.6

3.75 g/L 11.25 g/L 22.5 g/L

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2.4

2.0

6

-p

3.6

2.2

4

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Time (h) 4.0

2

of

ORP vs SHE (V)

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2

4

6

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0

8 10 12 14 16 18 20 22 24 26 Time (h)

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Figure 3. (a) ORP, (b) hydrogen peroxide concentration and (c) pH of leaching liquor as a function of pulp density. Experimental conditions: [EG] =0.1 M, [H2 SO4 ] =0.007 M, [H2 O2 ] =1 M and [EDTA]=0.032 M, 0.096 M and 0.192 M.

The initial pH (Figure 3c) in the leaching solution was 2.8, 3.2 and 3.8 for 3.75 g/L, 11.25 g /L and 22.5 g/L, respectively. This increase in the initial pH is due to the increase in the initial EDTA concentration (0.032 M, 0.096 M and 0.192 M, respectively). However, once the dissolution of the copper concentrate commences, the pH profiles show a decrease (Figure 3c) due to the decrease in free EDTA as a result of the formation of the complexes Cu (HEDTA)-, Cu(EDTA)2-, Fe(HEDTA) and Fe(EDTA)- as indicated in the species distribution diagram (Figure 4), elaborated with the MEDUSA© (Making Equilibrium Diagrams Using Simple Algorithms) software suite at 0.6 V vs SHE shown in Figure 3a. 10

Journal Pre-proof Likewise, the decrease in pH profiles (Figure 3c) could be related to the generation of H+ ions from the oxidation of elemental sulfur to sulfate (Equation 3) (Ruiz-Sánchez and Lapidus, 2017) or by the released H+ ions in the chemical reaction between hydrogen peroxide and the Fe complex (EDTA)- (Equation 6 of section 3.2.1 shown below). (3) 1.0

0.8

of

0.6

2CuEDTA

0.4

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CuH2EDTA

FeEDTA

FeHEDTA

-p

Fraction

H4EDTA (S)

0.0 1

2

3

lP

0

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0.2

CuHEDTA

4

5

pH

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Figure 4. Species distribution diagram for EDTA elaborated with the Medusa© software suite at 25°C, considering the concentration of copper and iron that would be expected if the chalcopyrite

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(22.5 g/L) were completely leached. [EDTA] = 0.192 M, [Fe3+] = 0.113 M and [Cu2+] = 0.080 M.

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The results shown in Figures 2a and 2b were not sufficient to determine whether pyrite in free form or associated with chalcopyrite (Py-Cp) contributes significantly to the copper leaching process, therefore, an additional leaching study was performed to evaluate its possible contribution (Appendix A). The results of Appendix A showed that the presence of free and associated pyrite (in mass proportion of Py:Cp = 0.35) did not benefit copper leaching under the conditions used in this investigation, unlike results reported by Dixon et al. (2008) in an aqueous medium with ferric ion (mass ratio Py:Cp = 0.80 and a minimum temperature of 80°C). Therefore, based on these results, it is possible to affirm that in the copper leaching process from the copper concentrate with the sulfuric acid-hydrogen peroxide-EG-EDTA

leaching

solution

occurs

11

without

the

contribution

of galvanic

Journal Pre-proof interaction.

Accordingly,

leached

copper can be described by the dissolution of

chalcopyrite (Equation 4) and covellite (Equation 5), respectively. (

)

( (

3.2.1

)

(4)

)

(5)

Relationship between hydrogen peroxide concentration and ORP

It is important to mention that, in the absence of EDTA, hydrogen peroxide decomposition occurs as a result of the Fenton reaction between leached iron and hydrogen peroxide,

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catalyzed by dissolved copper (Ruiz-Sánchez and Lapidus , 2018).

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However, the decrease in the H2 O 2 concentration profile (Figure 3b) is clear evidence that

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EDTA delays, but does not prevent the decomposition of this oxidant, thus suggesting that EDTA inhibits the catalytic role of cupric ion through the formation of the Cu complex

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(EDTA)2-; this behavior is unlike that of iron, according to Koppenol and Butler (1985), where the Fe(II, III)-EDTA complexes formed in the leach liquor can react with the

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hydrogen peroxide (Equations 6 and 7), analogous to the ligand-free Fenton reaction (Equations 8 and 9). Therefore, equations 6, 7 and 10 result in the decomposition of

(

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hydrogen peroxide (Equation 11). )

)

)

(6) (

)

(7) (8)

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ur

(

(

(9) (10) (11)

In Figure 2a, it was also shown that copper leached after 24 hours from 3.75 g/L, 11.25 g/L and 22.5 g/L, was 94%, 73% and 60%, respectively. Based on these percentages of copper and considering that 89% and 11% of the copper present in the concentrate is leached according to equations 4 and 5, an estimation of the concentration of hydrogen peroxide in the leaching solution was performed for this time interval. The calculations indicate that the concentration of hydrogen peroxide after 24 hours should be 0.98 M, 0.94 M and 0.91 M, for 3.75 g/L, 11.25 g/L and 22.5 g/L, respectively. In 12

Journal Pre-proof addition, under the assumption that all elemental sulfur is oxidized to sulfate through Equation 3; the concentrations for this oxidant would correspond to approximately 0.91 M, 0.80 M and 0.68 M. However, the concentrations of hydrogen peroxide in this period correspond to 0.84 M, 0.62 M and 0.26 M (Figure 3b), thus demonstrating that hydrogen peroxide is consumed during the leaching process by reactions other than those of chalcopyrite and elemental sulfur oxidation, confirming in this manner an additional consumption due to the Fenton reaction (Equations 6 and 7). On the other hand, it is interesting that the ORP (Figure 3a) is less than the redox potential

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of the Fe3+/Fe2+ pair (E ° = 0.77V, Koppenol and Butler, 1985); therefore, this behavior can

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be attributed to the decrease in ferric and ferrous ion activity due to the formation of the Fe (EDTA)- and Fe(EDTA)2- complexes, respectively. However, it is also clear that this

-p

potential cannot be established by the redox pair Fe (EDTA)-/(EDTA)2- whose potential E

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° is equal to 0.12V (Koppenol and Butler, 1985). Therefore, according to Bockris and Oldfield (1955), the ORP in acidic hydrogen peroxide solutions can be described from the

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behavior of this oxidant on the platinum electrode, where a minimum concentration of 1 µM H2 O2 is enough to form a layer of radicals

(Equations 12 and 13) that saturate

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the electrode surface, which implies that the measured potential is dependent on the pH (Equation 14) and not on the activity of hydrogen peroxide (

) as suggested by the

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Nernst Equation (Equation 15). Therefore, a theoretical calculation from Equation 14 considering a pH of 3.4, 3.2 and 2.8 for 22.5 g/L, 11.25 g/L and 3.75 g/L, respectively,

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results in 0.635 V, 0.645 V and 0.67 V, potential values that agree well with those observed in Figure 3a. In addition, it is very important to mention that Equation 14 is valid in the pH range 0-13.5 and was determined in the absence of dissolved ions of copper and iron, and organic ligands. (12) (13) ( ) (

( )

3.2.2

(14) )

Substitutes for EDTA to decrease the decomposition of H2 O2 13

(15)

Journal Pre-proof The results of sections 3.2 and 3.2.1 demonstrate that EDTA complexes can favor the Fenton reaction that leads to the decomposition of H2 O2 ; however, the free energy of 76 kJ / mol and -33 kJ / mol, reported by Koppenol and Butler (1985) for equations 6 and 7, respectively, suggest that the reaction between the Fe(EDTA)- complex and hydrogen peroxide does not occur spontaneously and therefore the consumption of hydrogen peroxide by this complex may not be as rapid. For this reason, the replacement of EDTA with another ligand capable of forming stable complexes with the ferric ion (Table 5) may decrease hydrogen peroxide decomposition. Consequently, the following ligands were

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proposed: the oxalate ion in the form of oxalic acid and the citrate ion in the form of citric

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acid.

Table 5. Thermodynamic stability constants for copper and iron complexes with citric acid, oxalic

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Stability constants, log K 6.3 4.4 9.4 6.1 3.2 11.9 18.8 14.3 25.7

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Complex Cu (II)-Citrate Fe (II)-Citrate Fe (III)-Citrate Cu (II)-Oxalate Fe (II)-Oxalate Fe (III)-Oxalate Cu (II)-EDTA Fe (II)-EDTA Fe (III)-EDTA

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acid and EDTA (Martell et al., 2004).

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Citrate ion leaching tests resulted in a complete decomposition of hydrogen peroxide after 15 hours, and only 20% and 10% copper and leached iron, respectively. On the other hand, with the oxalate ion, it was not only possible to decrease the decomposition of hydrogen peroxide, but also a selective dissolution for iron was achieved and the transformation of the chalcopyritic copper to solid copper oxalate. Therefore, oxalic acid was chosen as a pretreatment (which in this work is denominated as the first stage) to selectively leach iron. 3.3 Leaching in two stage: First stage Figure 5a shows the copper and iron dissolution profiles in the sulfuric acid-hydrogen peroxide-ethylene glycol-oxalic acid leaching solution. As may be seen, in this leach solution 28.5% of leached iron is obtained in the first six hours; however, for the 7-24 h 14

Journal Pre-proof interval the percentage of leached iron increased only 1%, despite the fact that 0.7 M H2 O2 still remains in the leach liquor (Figure 5b); this behavior suggests a possible passivation of the chalcopyrite surface, although a study of the phenomenon is beyond the scope of this work. The low percentage of dissolved copper (<2%, Figure 5a) in the PLS is due to its transformation to solid copper oxalate, as shown in the species distribution diagram (Figure 6) elaborated at 0.75 V vs SHE (based on the ORP of Figure 5b). The formation of copper oxalate was also confirmed from an X-ray diffractogram (Figure 7) of the solid residue

of

from this stage, where the following mineral phases were also identified: pyrite, elemental

ro

sulfur, muscovite, quartz and unreacted chalcopyrite. It is important to note that the presence of galena and sphalerite was not detected because their percentages were well

35

-p

below the 5% detection limit

0.80

re

a)

lP

25

15

Copper Iron

ur

10

na

20

0 0

2

4

6

b)

0.8

0.76

0.6

0.74

0.4

0.72

0.2

0.70

Jo

5

ORP vs SHE (V)

0.78

[H2O2],M

Leached metal (Wt%)

30

1.0

8 10 12 14 16 18 20 22 24 26

0.0

0

2

4

6

8 10 12 14 16 18 20 22 24 26

Time (h)

Time (h)

Figure 5. (a) Copper and leached iron profiles in stage 1, and (b) hydrogen peroxide concentration and ORP, in the liquor as copper leaching progress.

Experimental Conditions: [EG] =0.1 M,

[H2 SO4 ] =0.007 M, [H2 O2 ] =1 M, [OxA]=0.4 M and [Pulp density] = 50 g/L.

15

Journal Pre-proof 1.0 0.9 0.8

Fraction

0.7 0.6 FeOx+

0.5 0.4

CuOx(S)

0.3 0.2

0.0 0.0

0.5

of

Fe(Ox)2-

0.1

1.0

1.5

ro

pH

2.0

-p

Figure 6. Species distribution diagram for oxalic acid elaborated using Medusa© software suite at 25°C, considering the copper and iron concentrations expected if the concentrate were completely

1

4: Muscovite 5: Pyrite 6: Quartz

1: Copper oxalate 2: Chalcopyrite 3: Elemental sulfur

lP

3500 3000

na

2500

ur

2000 1500

Jo

Counts

re

leached. [OxA]=0.40 M, [Fe3+]=0.23 M and [Cu2+]=0.17 M.

2

1000 500

4 4

0 0

10

6

20

4 1 3 3 35 15 12 1 2 2 6 30

40

50

60

70

80

90

2 Theta Figure 7. X-ray diffractogram corresponding to the solid residue of leaching in stage 1 after 24 hours. Experimental conditions: [EG] =0.1 M, [H2 SO4 ]=0.007 M, [H2 O2 ]=1 M, [OxA]=0.4 M and [Pulp density] = 50 g/L.

16

Journal Pre-proof In order to identify the species of soluble iron oxalate that is formed in the first stage, the Uv/vis spectra were obtained (Figure 8a and 8b) corresponding to model solutions in the form of ferrous sulfate (Line 1), ferrous ion-oxalic acid (Line 2), ferric ion (Line 3) and ferric ion-oxalic acid (Line 4) and compared to a 1:10 dilution for the leach liquor corresponding to the conditions in Figure 5 (Line 5) ; Each of these solutions contains approximately 1000 mg/L of total iron. Line 1 shows two well-defined absorption peaks (A and B) at λmax =300 nm and λmax =240 nm corresponding to the Uv/vis radiation absorption bands for the ferrous ion, respectively

of

(Szilágyi et al., 2009 ). In line 2, peak A disappears due to the formation of a FeOx

ro

complex between the ferrous ion and oxalic acid. Peak A also disappears in the spectra corresponding to lines 3,4 and 5, thus manifesting the formation of a complex between the

-p

ferric ion and oxalic acid. Unfortunately, the ferric ion does not absorb Uv/vis radiation,

re

which limits performing a more complete analysis for the Uv spectra corresponding to lines 3,4 and 5. However, there exists a similarity between the absorption spectra corresponding

lP

to the lines 3, 4 and 5, as well as the pale yellow color of solutions 4 and 5 compared to the absence of color in solution 1 (Figure 8c), which corresponds to the ferrous ion and oxalic

na

acid. For this reason, it is very possible that the soluble oxalate species corresponds to a complex formed by the ferric ion and oxalic acid, which is in accordance with the species

ur

distribution diagram in Figure 6. Therefore, the copper leaching process corresponding to the first stage can be described from the dissolution of covellite and chalcopyrite, according

Jo

to Equations 16 and 17, respectively. ( )

( )

17

(

)

(

)

(16) (17)

Journal Pre-proof 4

1.0

a)

5

b)

0.8

2

0.4

B

0.2

B

2

1

4

0.6

A

0.0 200 225 250 275 300 325 350 375 400 425 450

Absorbance

Absorbance

Absorbance

3

4

2

5

1

Wavelength (nm)

1 250

300

350

400

450

500

550

0 200

600

of

0 200

3

3

300

400

Wavelength (nm)

Jo

ur

na

lP

re

-p

ro

Wavelength (nm)

Figure 8. Uv/vis spectra for the identification of the soluble iron oxalate complex formed in step 1. (a) Line 1: Ferrous sulfate in an aqueous solution of 0.007 M H2 SO4 and 0.1 M EG. Line 2: Ferrous sulfate and oxalic acid in aqueous solution of 0.007 M H2 SO4 and 0.1 M EG. (b) Line 3: Ferric sulfate in aqueous solution of 0.007 M H2 SO4 and 0.1 M EG. Line 4. Ferric sulfate and oxalic acid in aqueous solution of 0.007 M H2 SO4 and 0.1 M EG, and Line 5: Leaching liquor from the first stage (Figure 5). (c) Solutions corresponding to line 2, line 4 and line 5, respectively.

The solubility of the CuOx(s) obtained in stage 1 was studied using a sample of 100 mg of solid residue from stage 1 in 250 mL of each of the following solutions: water (W), Water0.1 M EG (WE), 0.007 M H2 SO 4 (H), 0.007 M H2 SO 4 -0.1 M EG (HE) and 0.007 M 18

500

Journal Pre-proof H2 SO 4 -0.1 M EG-1M H2 O2 (HEP); this study was amplified by adding the ligand “L” EDTA in stoichiometric quantity to each of the former solutions, to form a copper-EDTA complex (from the copper present in the 100 mg of solid residue, whose analysis by AAS was 26.8% copper as copper oxalate and 14.7% as chalcopyrite), identified as WL, WEL, HL, HEL and HEPL. The results of this study (Figure 9), on the one hand, confirm the low solubility of copper oxalate (approximately 10.5 mg/L) in water, whose value is similar to that (10.6 mg /L) reported by Kralj et al. (1996) and, on the other hand, demonstrate that the presence of ethylene glycol in the WE solution increases the copper solubility (from

of

10.5 to 33.5 mg/L).

ro

This figure also shows that 0.007 M H2 SO4 negatively affects the solubility of copper oxalate due to the decrease in pH; for example, in the HE solution, the copper solubility

-p

decreases from 33.5 to 16.5 mg/L. However, the presence of 1M of hydrogen peroxide in

re

the HEP solution increases the solubility of copper by 10 mg/L. In contrast, the presence of EDTA increases the solubility of copper oxalate, obtaining in each solution more than 98

lP

mg/L of dissolved copper. Furthermore, hydrogen peroxide in HEPL only increases the copper solubility by 5 mg/L. Therefore, hydrogen peroxide is not necessary to dissolve the

na

copper oxalate and the WEL solution is sufficient to completely dissolve the copper oxalate present in the solid residue from stage 1.

ur

120

108 98

104

99

99

HL

HEL HEPL

Jo

Copper dissolved (mg/L)

100

80 60 40

33.5 26.5

20

18 16.5

10.5

0 W

WE

H

HE

HEP

WL

WEL

Test solution

19

Journal Pre-proof Figure 9. Copper dissolved from copper oxalate present in the solid residue of stage 1. Each test was carried out in a 250 mL aqueous solution using 100 mg of solid residue from stage 1, whose composition corresponds to 26.8% copper as copper oxalate.

Based on the results shown in Figure 9, the HEPL medium was selected as the leaching solution for the subsequent stage (stage 2); the addition of hydrogen peroxide in the second stage is justified by the need to oxidize the unreacted chalcopyrite still present in the solid residue of step 1, but did not make a theoretical estimate of H2 O2 necessary to oxidize the unreacted chalcopyrite based on a stoichiometry equation, therefore further leaching tests

of

were carried out to determinate the most adequate H2 O 2 concentration, finding that a

3.3.1

ro

concentration of 2 M is the most adequate. Leaching in the second stage

-p

Figure 10a shows the copper and iron dissolution behavior from the solid residue of stage

re

1. In the first few minutes, the leach liquor contains 49% of the copper and 0% of iron, while in the first hour this percentage increases to 56.5% copper and 5% iron, respectively.

lP

These results are significant because they imply that in the first stage 49% of the copper present in the concentrate was transformed to copper oxalate, of which 11% corresponds to

na

the transformation of covellite (equation 16). Therefore, the almost instantaneous copper dissolution of the second stage can be described by the dissolution of the copper oxalate

ur

(Equation 18) formed in the first stage.

(

)

(18)

Jo

( )

On the other hand, the iron leached in both stages (stage 1 ~ 29.5% and stage 2 ~ 34.5%) adds up to 64%, approximately equal to the total iron contained in the chalcopyrite (the remaining 35% of the iron is present as pyrite). Therefore, from this result it is possible to assert that the pyrite solution does not occur in the sulfuric acid-hydrogen peroxide-EGEDTA leach solution. Due to the greater stability of the Cu(II)-EDTA complex compared to the Cu(II)-Oxalate complex (Table 5), in the presence of both ligands, the cupric ion will preferably form complexes with the EDTA, as shown in the distribution diagram (Figure 11), prepared at 0.65 V vs SHE and pH 0-5 (Figure 10b). Similarly, copper and iron leached from the unreacted chalcopyrite present in the solid residue of the first stage, will also form more 20

Journal Pre-proof stable complexes with EDTA compared to with oxalate. Therefore, the unreacted chalcopyrite leaching process in the second stage can also be described with the Equation 4.

Copper Iron

90

3.5

80 70 60 50 40 30

3.0

0.66

2.5 pH 2.0

0.64

1.5 1.0

0.62

20 10

0.60

0 2

4

6

0

2

4

6

ro

0

4.0

b)

0.68 ORP vs SHE (V)

Leached metal (Wt%)

0.70

a)

100

of

110

8 10 12 14 16 18 20 22 24 26

0.0

8 10 12 14 16 18 20 22 24 26

Time (h)

-p

Time (h)

0.5

Figure 10. (a) Copper and iron dissolution in the second stage, and (b) pH and ORP in the liquor in

lP

[EDTA]=0.4 M and [Pulp density] = 50 g/L. CuOx(S)

2CuEDTA

na

1.0 0.8

ur

0.6 0.4

Jo

Fraction

re

copper leaching progress. Experimental Conditions: [EG] =0.1 M, [H2 SO4 ]=0.007 M, [H2 O2 ]=2 M,

CuHEDTA

0.2 0.0

0

1

2

pH

3

4

5

Figure 11. Species distribution diagram for oxalic acid and EDTA elaborated using Medusa© software suite at 25 ° C, considering the copper and iron concentrations expected if the concentrate were completely leached. [EDTA]=0.40 M, [OxA] =0.40 M, [Fe3+] =0.23 M and [Cu2+] =0.17 M.

The slow growth in the copper and iron extractions, initiating after 18 hours, observed in Figure 2a of section 3.2 was first attributed to the slow dissolution of the largest particles of

21

Journal Pre-proof chalcopyrite present. To test this hypothesis, a leaching test was performed on the coarse fraction of the concentrate (80 mesh corresponding to a particle size greater than 180 µm). The results for the entire concentrate and the largest size fraction are compared in Figure 12, demonstrating that the slower copper extraction after six hours, for a pulp density equal to 50g/L, is due to the presence of the coarse chalcopyrite particles. 110 100

Copper Iron

of

80

60 50

Particle size >180m

-p

40

ro

70

30 20 10 0 2

4

6

8

10 12 14 16 18 20 22 24 26

lP

0

re

Leached metal (Wt%)

90

Time (h)

na

Figure 12. (a) Effect of particle size on copper and iron dissolution profiles corresponding to the second stage. Experimental Conditions: [EG] =0.1 M, [H2 SO4 ]=0.007 M, [H2 O2 ]=2 M,

ur

[EDTA]=0.4 M and [Pulp density] = 50 g/L.

Jo

The diffractogram of Figure 13, corresponding to the solid residue of the second stage (Figure 10), shows the presence of the gangue (quartz and muscovite), pyrite, elemental sulfur, sphalerite and EDTA. These results confirm that the gangue and pyrite are not leached in the proposed leaching process. In addition, the presence of EDTA in the solid residue suggests that this ligand has been added in excess because the iron, present in the pyrite, was considered in the calculation. Therefore, the Rm ratio should be recalculated, considering only the moles of copper and chalcopyritic iron.

22

Journal Pre-proof 2000

b

a: EDTA b: Pyrite c: Elemental sulfur

d: Muscovite e: Quartz

1000

500

b

d,e d

0 10

c a a c 20

30

b

b b d c

b b

b

40 50 2 Theta

60

70

80

b 90

-p

0

a,e

of

a

ro

Counts

1500

re

Figure 13. X-ray diffractogram corresponding to the solid residue of leaching in the second stage after 24 hours. Experimental conditions: [EG] =0.1 M, [H2 SO4 ]=0.007 M, [H2 O2 ]=2 M,

lP

[EDTA]=0.4 M and [Pulp density] = 50 g/L.

The major presence of the gangue and the pyrite was also confirmed from the SEM

na

micrographs corresponding to the solid residue of the second stage (Figure 14a). It can also be observed that the chalcopyrite present in the solid residue is not associated with the

ur

gangue. Therefore, it is possible to rule out that the slow growth for the leached copper (Figure 10a) after six hours is due to the association of Cp-Gn (Table 4), supporting the

Jo

results of the Figure 12. The SEM micrographs also show the formation of elemental sulfur on the surface of the chalcopyrite (Figures 14b, c and d), confirming that, under these conditions that elemental sulfur is the major product in the chemical reactions proposed. Furthermore, the elemental sulfur observed in the SEM micrographs is similar to the porous sulfur formed in solutions with ferric chloride; according to Ammou-Chokroum et al. (1977) and Hackl et al. (1995), this elemental sulfur only contributes to slow kinetics, but is not responsible for the chalcopyrite passivation.

23

Journal Pre-proof

b)

a)

S0

Cp

Py

Gn

d)

c)

of

S0

ro

Cp

re

-p

S0

Cp

Figure 14. SEM micrographs corresponding to the solid residue of the second stage. Experimental

lP

conditions: [EG] =0.1 M, [H2 SO4 ]=0.007 M, [H2 O2 ]=2 M, [EDTA]=0.4 M and [Pulp density] = 50

na

g/L.

Finally, in Figure 15, three aqueous solutions X, Y and Z are shown, corresponding to a

ur

solution of cupric sulfate-ferrous sulfate-EDTA; a solution of copper sulfate-ferric sulfateEDTA (Y) and a dilution (1:10) of the leaching liquor obtained in the second stage. The X

Jo

and Y model solutions were prepared in the 0.007 M H2 SO 4 -0.1 M EG solution, adding ferric, ferrous and cupric sulfate salts to obtain approximately 1000 mg/L of copper and 1000 mg/L of iron, in addition to EDTA in a molar ratio 1: 1. The similarity in the colors of the Z and Y solutions suggests that the soluble species in the leach liquor from stage 2 correspond to Cu (II)-EDTA and Fe(III)-EDTA complexes. These results are in accordance with the species distribution diagram for EDTA shown in Figure 4; therefore, the CuEDTA and Fe-EDTA complexes proposed in Equation 4 are justified from the results of Figure 15.

24

-p

ro

of

Journal Pre-proof

Figure 15. Aqueous solutions of: (X) copper sulfate, ferrous sulfate and EDTA, (Y) copper sulfate,

re

ferric sulfate and EDTA (Y), and (Z) 1:10 dilution of the leach liquor obtained in stage 2. Model solutions X and Y were prepared in an aqueous solution of 0.007M H 2 SO4 and 0.1M EG, at a

lP

concentration of approximately 1000 mg /L of copper and 1000 mg/L of iron, EDTA added in a molar ratio 1: 1 for total moles of copper and iron.

na

The results discussed in sections 3.3 and 3.3.1 confirm that in the proposed process at 26 ° C and atmospheric pressure favors a second stage leach liquor with 90% of the copper and

ur

only 35% of the iron. However, despite the significant improvement achieved in this

Jo

investigation, there are still challenges to be solved: (i) increase the conversion of chalcopyrite to copper oxalate in the first stage to facilitate the selective dissolution of copper in the second stage and (ii) propose a methodology to separate iron from the leaching liquor obtained in stage 1, so that it is possible to reuse the oxalate ion and take advantage of the hydrogen peroxide remaining in this solution. The aforementioned challenges have been studied in detail and the results will be presented in a future article.

25

Journal Pre-proof 4. Conclusions

1) An increase in pulp density (from 3.75 to 22.5 g/L) for the sulfuric acid-hydrogen peroxide-EG-EDTA

leaching

solution

confirmed

a

rapid

and

quantitative

decomposition of hydrogen peroxide as a consequence of the Fenton reaction between Fe(II, III)-EDTA complexes and H2 O2 . 2) The use of oxalic acid decreases the decomposition of hydrogen peroxide and favors the selective leaching of iron and the transformation of copper to solid copper oxalate; However, in the presence of this ligand, it was not possible to leach more

of

than 30% iron due to chalcopyrite passivation. 3) Copper dissolution behavior in stage 2 showed at least two well-defined zones: the

ro

first, in the range 0-6 h, represents the rapid leaching of copper from the copper

-p

oxalate precipitate formed in stage 1 and from the small particle size unreacted chalcopyrite; while the second zone, in the 6-24 h interval, displayed a slow growth

re

in the percentage of leached copper due to the presence of larger particles. 4) In stage 2, the EDTA dosage (Rm ratio) should be recalculated considering only the

lP

total moles of copper and chalcopyritic iron.

5) The two-stage process proposed is potentially an alternative to decrease the iron

na

content in the PLS, preventing hydrogen peroxide decomposition and permitting the processing at higher pulp densities (50 g/L). Thus, obtaining in stage 2 a PLS with

ur

90% of the copper with only 35% of the iron.

Jo

6) Pyrite is not susceptible to oxidation in the proposed leaching systems. 7) The mineralogical associations and free pyrite in the copper concentrate did not modify the copper leaching process through galvanic interactions. 5. Acknowledgments

Ángel Ruiz Sánchez is grateful for the financial support of the UASLP Metallurgy Institute through the postdoctoral fellowship (UASLP-4528 project), as well as the National Council of Science and Technology (CONACyT) for the postgraduate scholarship # 284302.

26

Journal Pre-proof

6. Appendix Appendix A. Effect of galvanic interaction in the copper leaching process

To evaluate the effect of free pyrite and mineralogical associations (present in the copper concentrate) in the copper leaching process, leaching tests were carried out at the same experimental conditions used in this work by replacing the copper concentrate with pure chalcopyrite. In addition, due to the wide distribution of particle size (Table 1) present in

of

the copper concentrate, the particle size was limited to the -100 + 200 mesh fraction (75150 µm); the same particle size fraction was employed for the pure chalcopyrite. The

ro

leaching tests were performed in the leaching system described by Ruiz-Sánchez and

-p

Lapidus (2017), using 320 mL of a leaching solution of 0.7 M H2 SO4 - 1 M H2 O2 -3.5 M

re

EG at 30 ° C for 8 hours.

For this study two different experiments were proposed, the first with a constant pulp

lP

density equal to 3.75 g/L (of copper concentrate or pure chalcopyrite), and the second experiment was carried out with 3.9 g/L of copper concentrate or 2.5 g/L of pure

na

chalcopyrite, such that the initial copper content in the mineral sample was approximately 0.84 g/L.

ur

Appendix A. Results and discussion

Jo

Table A1 shows the composition of copper concentrate and pure chalcopyrite with particle size 75-150 µm. These results confirm again that the content of Pb, Zn, Cu and Fe in the copper concentrate depends on the particle size, as discussed in section 3.1 (Table 1).

Sample Copper concentrate Pure chalcopyrite

Pb, Wt% 0.14

Zn, Wt% 1.2

Cu, Wt% 21.8

Fe, Wt% 30.8

-

-

34.4

30.1

Table A1. Copper and iron content in the fraction with particle size -150 +75 µm.

Figures Aa and Ab show the copper and iron dissolution behavior for a constant pulp density of 3.75 g/L and an initial concentration of 0.84 g/L of copper. As can be seen, 27

Journal Pre-proof regardless of the pulp density, the percentage of copper leached from the copper concentrate was higher compared to copper leached from pure chalcopyrite, which is due to the presence of covellite in the concentrate. The difference between the copper profiles obtained from the copper concentrate and the chalcopyrite represented 11% of the copper, which can be assigned to the copper present in the form of covellite. On the other hand, the similarity in the iron concentration profiles (Figures Ab and Ad), regardless of the pulp density, demonstrates that the dissolution of chalcopyrite from the copper concentrate does not change due to the presence of mineralogical associations and

of

that of free pyrite. Therefore, under these experimental conditions, a galvanic interaction in the

ro

copper leaching process is not appreciable . These results are also valid in the 0.007 M H2 SO 4 -1

M H2 O2 - 0.1 M EG-EDTA leaching solution (Figure 2), where the dissolution of 11%

500

50

na

40 30

ur

20

0 0

Jo

10

2

4

b) Pure chalcopyrite Copper concentrate

400

6

Leached iron (mg/L)

60

lP

Copper concentrate Pure chalcopyrite Copper from covellite

re

a)

70

Leached copper (Wt %)

-p

copper was also found in the first hour of leaching.

300

200

100

0

8

0

Time (h)

2

4

Time (h)

28

6

8

Journal Pre-proof c)

70 60

d) Pure chalcopyrite Copper concentrate

400

50

Leached iron (mg/L)

40 30 20

300

200

100

10 0

0 0

2

4

6

0

8

ro

Time (h)

2

of

Leached copper (Wt %)

500

Chalcopyrite concentrate Pure chalcopyrite Non-chalcopyritic copper

4

6

8

Time (h)

Figure A. (a,b) Copper and iron leached at a constant pulp density of 3.75 g/L and (c, d) an initial

-p

copper concentration equal to 0.84 g/L. Experimental conditions: [EG] =3.5 M, [H2 SO4 ]=0.7 M and

Jo

ur

na

lP

re

[H2 O2 ]=1 M.

29

Journal Pre-proof

7. References Ammou-Chokroum, M., Cambazoglu, M., Steinmetz, D., 1977. Oxidation menagee de la chalcopyrite

en solution acide: Analyse cinetique des reactions: I. Modeles chimiques. Bulletin

de la Societe fran~ ise de Mineralogie et de Cristallographie.100, 149-161.

Barb, W. G., Baxendale, J. H., George, P., Hargrave, K. R., 1951. Reactions of ferrous and ferric ions

with hydrogen peroxide. Part I.—The ferrous ion reaction. Transactions of the Faraday

of

Society. 47, 462-500.

ro

Bockris, J. M., Oldfield, L. F.,1955. The oxidation-reduction reactions of hydrogen peroxide at inert metal electrodes and mercury cathodes. Transactions of the Faraday Society. 51, 249-259.

-p

Dixon, D. G., Mayne, D. D., Baxter, K. G., 2008. Galvanox™–a novel galvanically-assisted

re

atmospheric leaching technology for copper concentrates. Canadian Metallurgical Quarterly. 47(3),

lP

327-336.

Fandrich, R., Gu, Y., Burrows, D., Moeller, K., 2007. Modern SEM-based mineral liberation

na

analysis. International Journal of Mineral Processing. 84(1-4), 310-320.

ur

Hackl, R. P., Dreisinger, D. B., Peters, L., King, J. A., 1995. Passivation of chalcopyrite during

Jo

oxidative leaching in sulfate media. Hydrometallurgy. 39(1-3), 25-48. Koppenol, W. H.,

Butler, J., 1985. Energetics of interconversion reactions of oxyradicals.

Advances in Free Radical Biology and Medicine. 1(1), 91-131. Kralj, D., Breembroek, G. R., Witkamp, G. J., Rosmalen, G. M. V., Brečević, L.,1996. Selective dissolution of copper oxalate using supported liquid membranes. Solvent extraction and ion exchange. 14(4), 705-720. Mahajan, V., Misra, M., Zhong, K., Fuerstenau, M. C., 2007. Enhanced leaching of copper from chalcopyrite in hydrogen peroxide–glycol system. Minerals Engineering. 20(7), 670-674.

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Journal Pre-proof Martell, A. E., Smith, R. M., Motekaitis, R. J., 2004. NIST standard reference database 46: NIST critically selected stability constants of metal complexes database (version 8.0 for windows). Texas A and M University, College Station, TX.

Pestovsky, O., Bakac, A., 2006. Aqueous ferryl (IV) ion: Kinetics of oxygen atom transfer to substrates and oxo exchange with solvent water. Inorganic chemistry. 45(2), 814-820.

Ruiz-Sánchez, Á., Lapidus, G. T., 2017. Study of chalcopyrite leaching from a copper concentrate

of

with hydrogen peroxide in aqueous ethylene glycol media. Hydrometallurgy. 169, 192-200.

ro

Ruiz-Sánchez, Á., Lapidus, G. T., 2018. Improved Process for Leaching Refractory Copper Sulfides with Hydrogen Peroxide in Aqueous Ethylene Glycol Solutions. In Extraction 2018, The Minerals,

-p

Metals and Materials Series. 1289-1298. Springer, Cham.

re

Solís-Marcial, O. J., Lapidus, G. T., 2013. Improvement of chalcopyrite dissolution in acid media

lP

using polar organic solvents. Hydrometallurgy.131, 120-126.

Szilágyi, I., Königsberger, E., May, P. M., 2009. Spectroscopic characterisation of weak

Jo

ur

na

interactions in acidic titanyl sulfate–iron (ii) sulfate solutions. Dalton Transactions. 37, 7717-7724.

31

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Figure 8

Figure 9

Figure 10

Figure 11

Figure 12

Figure 13

Figure 14

Figure 15