Dissolution of copper from a primary chalcopyrite ore calcined with and without Fe<sub>2</sub>O<sub>3</sub> in sulphuric acid solution

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Dissolution of copper from a primary chalcopyrite ore calcined with and without Fe

2

O

3

in sulphuric acid solution

Mustafa Gülfen* & Ali Osman Aydın

Department of Chemistry, Faculty of Arts & Sciences, Sakarya University TR-54187, Esentepe Campus, Sakarya – Turkey

Email: mgulfen@sakarya.edu.tr Received 27 May 2009; revised 30 October 2009

Dissolution of copper from a primary chalcopyrite ore supplied from Damar mine area in Murgul-Artvin, Turkey, has been investigated in sulphuric acid solution after the calcination with and without Fe2O3. The chalcopyrite with and without Fe2O3 were performed by thermogravimetric (TG) analysis, and the calcined chalcopyrite samples were characterized by X-ray diffraction (XRD). In the leaching experiments, the effects of calcination temperature, sulphuric acid concentration, solid/liquid ratio, agitation rate, particle size and dissolution temperature and time on copper dissolution were examined. It was found that Fe2O3 addition contributed to sulphation during the calcination and then copper dissolution.

Keywords: Chalcopyrite, Iron(III) oxide, Sulphation, Dissolution, Sulphuric acid

Chalcopyrite (CuFeS2), a sulphidic copper mineral, is the primary sources of copper. The direct production of copper sulphate from sulphidic copper ores is an important route to recover copper. The conditions, however, are dependent on temperature and sulphatising environment and then dissolution.

Amongst the alternative processes to treat chalcopyrite, the hydrometallurgical routes without pretreatment and with pretreatment, such as oxidative roasting are considered quite attractive^1-7. Investigation of direct leaching processes involving different lixiviants such as sulphuric acid, chloride, nitric acid, ammonical solution and biological systems have been studied highlighting the major development in the recent past³. The problem associated with the iron dissolution in these processes calls for adequate purification and control methodology before recovery of the metal by electrowinning. Sulphation roasting is one of the important pretreatment techniques that may be adopted to recover copper from the sulphides. The iron control problem can be obviated to a great extent by choosing conditions for the sulphation roasting to produce water soluble copper sulphate and converting iron to its insoluble oxides. Moreover iron (III) oxide usage during the roasting contributes the sulphation of sulphidic copper ore^1,3,8-11.

Some researchers have examined the sulphation roasting of sulphidic copper ores with some additives so that water-soluble copper sulphate can be

obtained^11-18. Prasad et al.^11,17 studied the sulphation of chalcopyrite in presence of some additives such as Fe2O3, Na2SO4, FeSO4 etc. They showed that these additives contributed to the sulphation in the roasting of chalcopyrite concentrate at around 773 K temperature. They found more sulphation with Fe2O3, Na2SO4 and FeSO4 than without any addition^8,9,11,17. Neou-Syngiuna and Scordilis¹⁸ studied the sulphation of a Greek complex sulphide concentrate. They concluded that sulphation roasting can be selective and SO2 emission can be controlled in the determined conditions. In addition, they found that water-soluble sulphate could be obtained from the sulphidic ore¹⁸. The sulphation process of chalcopyrite ore during roasting is important for a subsequent dissolution.

Since water-soluble sulphate and acid-soluble oxide compounds of copper can form after the roasting, copper in the calcined ore can be dissolved easily from chalcopyrite in dilute acid solutions¹. Hydrometallurgical processes can let the usage of primary chalcopyrite as raw material. In the present study, the roasting and sulphation conditions of primary chalcopyrite with and without Fe₂O₃, the optimum conditions for the dissolution of copper from chalcopyrite in sulphuric acid solution are reported.

Experimental Procedure

The primary chalcopyrite ore supplied from Damar mine area in Murgul-Artvin, Turkey was used in this

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study. It was ground and sieved to below 310 µm particle size. The chalcopyrite ore sample including chalcopyrite (CuFeS2) and quartz (SiO2) minerals as major phases was analyzed chemically and the results are given in Table 1. The chalcopyrite samples prepared mixed with 10% Fe2O3 and without additive were calcined for 1 h at the temperatures of 373, 473, 573, 1273 K. The extent of sulphation in the calcined chalcopyrite sample was examined. The sulphation ratio (%) was calculated from the conversion of sulphides to sulphate. The quantity of sulphate formed during the calcination was determined gravimetrically with BaCl2 after the dissolution of the calcines in HCl solution. The converted sulphate in the calcine can be dissolved in HCl solution, whereas unconverted sulphides require an oxidizing reagent (HNO₃, H₂O₂ etc.).

The dissolution experiments were carried out in a beaker or a flask with reflux system on a magnetic stirrer. The conditions of experimental parameters chosen were 373, 473, 573, …, 1273 K for calcination temperature, 0.0001, 0.005, 0.01, 0.05, 0.1, 0.5, 1, 2, 3, 4, 5 M H₂SO₄ for leaching, 0.01, 0.05, 0.1 0.2, 0.4, 0.6, 0.8, …, 2.0 g/mL for solid/liquid ratio, 0, 100, 200, 700 rpm for agitation rate and 2, 4, 6, 8, 10 and 15 min at 298-373 K for dissolution temperature.

Copper and iron concentrations in the leach solutions were analyzed by atomic absorption spectrometer (Shimadzu 6701F AA). The thermal analysis experiments were carried out in static air atmosphere using Seteram TG-DTA-92 thermal analyzer. The heating rate of 10 K per min was employed in a platinum crucible. The TG curves of the chalcopyrite with and without Fe2O3 up to temperature of 1273 K are given in Fig. 1. Moreover the X-ray diffractrograms (XRD) of calcined samples were taken from Shimadzu XRD-6000 diffractometer with Cu source. The identifications of the phases in the samples were based on ASTM X-ray powder data file.

Results and Discussion

Chemical analysis

The chemical analysis of the primary chalcopyrite ore is given in Table 1. The ore contains 69.85% SiO2

as major content and 3.35% Cu, 11.15% Fe and 11.67% S as other important contents. Quartz (SiO2), chalcopyrite (CuFeS2) and dolomite [(CaMgCO3)2] were determined in the ore sample. In the present study, the primary chalcopyrite ore, not concentrated, was used. The pyrometallurgical route of chalcopyrite

ore requires its concentration by flotation. However the hydrometallurgical routes do not require any concentration and this is an advantage of cost. In addition, it may be thought that more effective sulphate formation occurs from dilute sulphide minerals in silica matrix. In other words, more iron(III) oxide per sulfur content can be added into the ore. So, primary chalcopyrite ore was used in this study.

Thermal analysis

The thermogravimetric curves of the original chalcopyrite ore (TG1) and the chalcopyrite sample mixed with 10% Fe2O3 (TG2) up to the temperature of 1273 K in air atmosphere are given in Fig. 1. The thermal analysis results showed that the chalcopyrite began to decompose above 668 K when it was heated in air. Weight gain in the chalcopyrite was noted in the temperature range 668-739 K (TG1 in Fig. 1). On the other hand, the chalcopyrite mixed with 10%

Fe2O3 showed a different TG curve in the temperature range 635-973 K (TG2 in Fig. 1). The weight gain was found as 0.332% for the chalcopyrite at 738 K

Fig. 1—Thermogravimetric curves of the chalcopyrite (TG1) and the chalcopyrite sample with 10% Fe2O3 (TG2) in air. Sample weight, 30 mg; Heating rate, 10 K per min.

Table 1—Chemical analysis of the chalcopyrite ore

Constituents wt. %

SiO2

Cu Fe S Al2O3

CaO Moisture

69.85 3.35 11.15 11.67 2.10 0.60 0.20

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and 1.657% for the chalcopyrite with Fe2O3 at 870 K.

While a weight loss began at 773 K in the chalcopyrite, a clear weight gain in the sample with Fe2O3 was noted from 773 to 873 K. Weight loss (TG1) at 773 K may be due to decomposition of chalcopyrite mineral. However weight gain of the chalcopyrite mixed Fe2O3 at 773 K may be due to reaction between Fe2O3 and SO2 and then copper sulfate formation. At the temperatures above 973 K, both the samples showed similar TG curves with respect to weight change.

Depending on the temperature, chalcopyrite during roasting in air forms sulfur, sulfur dioxide, copper sulphate, copper and iron oxides and copper ferrite (CuFe₂O₄). These calcined products are important for subsequent leaching processes and can be dissolved in different solutions such as sulphates in water, oxides in acids and sulphides in oxidative solutions (HNO₃, H₂O₂ etc.). When a chalcopyrite ore is roasted the more weight gain accounts for more sulphate formation. When it has weight loss, sulfur dioxide emission from a chalcopyrite occurs. Fe₂O₃ addition resulted in more sulphate formation because Fe₂O₃ contributed to the change of SO₂ to SO₃ as a catalyst 2, 8,10,13,19-22.

Calcination and sulphation

The chalcopyrite samples with and without Fe2O3

were calcined for 1 h in the temperature range 573-1073 K and sulphate quantities in these calcines were analyzed by dissolving in hydrochloric acid solution. However sulphides can not be dissolved in HCl solution. So the sulphation in the calcined sample can be found by dissolving with hydrochloric acid solution. The percentage of the sulphation was calculated using Eq. (1).

3

Converted sulfur to sulphate in the calcined sample

(by dissolving with HC1)

Sulphation (%) = 100

Total sulfur content in the calcined sample

(by dissolving with HC1+HNO )

×

…(1) Calcination temperatures to examine the sulphation of the chalcopyrite samples with and without Fe2O3

were chosen as 573-1073 K by applying knowledge of the thermodynamics of the Cu-Fe-S-O system:

chalcopyrite^3,9. The sulphation results are shown in Fig. 2. It may be seen that more sulphate in the

calcined chalcopyrite with and without Fe2O3 formed at the temperatures of 773, 873 and 973 K than that at lower and higher temperatures. It was noted that Fe2O3 addition contributed to increase in the sulphation of the chalcopyrite, which was also indicated by thermogravimetric and sulphate analyses of the calcined chalcopyrite sample. The sulphation in chalcopyrite will decrease the acid consumption during the dissolution.

The original chalcopyrite ore and the chalcopyrite samples calcined at 773, 873 and 973 K were characterized by X-ray diffraction analysis. XRD phases in the chalcopyrite samples is given in Table 2.

It may be seen from Table 2 that the all samples

Fig. 2—Sulphation of chalcopyrite samples with and without additive.

Table 2—XRD phase identification Calcination

temperature (K)

Chalcopyrite Chalcopyrite with Fe2O3

Original

Major Phases:

Quartz (SiO2), Chalcopyrite (CuFeS2) Minor Phase:

Dolomite [CaMg(CO3)2]

_

773

Major Phases:

Quartz (SiO2), Hematite (Fe2O3), Copper sulphate (CuSO4)

Major Phases:

873

Major Phases:

973

Major Phases:

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include quartz mineral as major phase. While quartz, chalcopyrite and dolomite were determined in the original chalcopyrite sample, hematite and copper sulphate were noted in the calcined samples. Copper sulphate formed when the chalcopyrite was calcined at the temperatures of 773 and 873 K. The calcined chalcopyrite at 973 K had less copper sulphate than those at 773 and 873 K. That the dissolution of copper from the samples was the maximum at 873 K was confirmed with copper sulphate formation8-11, 18, 19, 21-23.

Dissolution of chalcopyrite

The original chalcopyrite and the chalcopyrite mixed with Fe₂O₃ were roasted for 1 h at varying temperature (373, 1273 K) and then calcines were dissolved in 1 M H₂SO₄ solution. The results for copper and iron leaching are given in Fig. 3. It may be seen from Fig. 3 that iron dissolution was high when the ore was roasted at 673 and 773 K whereas high copper dissolutions were observed for the roasting at 773, 873 and 973 K. Because sulphate salts and oxides such as CuSO₄, FeSO₄, CuO, FeO and Fe₂O₃ form between 673-973 K temperatures, high dissolutions for copper and iron were found at these temperatures.

The chalcopyrite ore calcined for 1 h at 873 K temperature was chosen as the optimum calcination conditions, because of high copper recovery and low iron dissolution, and these samples were used in the later studies. At these conditions, copper can be dissolved selectively. If a direct leaching process was used, the copper solution would include more iron content.

Effect of acid concentration (0-5 M H2SO4) was examined for the dissolution of copper from the

calcine obtained by roasting for 1 h at 873 K. Copper recovery was around 60% in distilled water and 67-72% in the acid solutions. Iron dissolution increased at high acid concentrations. The acid concentration of 0.1 M was found to be optimum with high copper and low iron dissolution. Acid consumption may be because of hematite (low iron dissolution), copper oxy-sulphate (CuO.CuSO4) and dolomite or calcium oxide.

The leaching tests in 0.1 M H₂SO₄were conducted at different solid/liquid ratios (0.01-2.0 g/mL), using the sample calcined under the optimum conditions.

The optimum solid/liquid ratio was found to be 1.2 g/mL with 25 g/L copper and 4 g/L iron ions in the final leach liquor. In other words, copper/iron ratio changed from 0.3 in the ore to 6.25 in the leach solution.

Agitation rate (0-700 rpm) on copper dissolution was also studied and the results given in Fig. 4 showed that it was very effective up to 400 rpm. The dissolution increased slightly above 400 rpm. The agitation improved the dissolution, because of better dispersion of solids in the lixiviant^24,25.

The effect of particle size on the dissolution was examined. While the dissolution of copper with the samples of the particle size 150 µm or smaller were between 60-80%, the dissolutions decreased to a low of 20-30% for the particles above 150 µm size. This may be attributed to increase in surface area for the finer size material.

The effect of temperature and time on the dissolution experiments was studied and the results are given in Fig. 5 and in Fig. 6 for the calcine without additive and with Fe₂O₃ addition, respectively. The results showed that the copper dissolutions in the both samples were nearly 50%

within 2 min and the dissolution time was effective.

On the other hand, temperature of leaching was not

Fig. 3—The dissolutions of copper and iron from the calcined chalcopyrite (1) and the chalcopyrite calcined with 10%Fe2O3 (2).

Calcined sample, 1 g; H2SO4 (1 M), 100 mL; Contact time, 60 min; Agitation rate, 400 rpm; Temperature, 298 K.

Fig. 4—Effect of agitation rate on copper dissolution from sample calcined for 1 h at 873 K. Solid/liquid ratio, 1.2 g/mL; H2SO4, 0.1 M; Temperature, 298 K; Contact time, 60 min.

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that effective. The copper dissolution was 77% at 373 K in 15 min for the calcined chalcopyrite whereas it was 82% for the calcine mixed with Fe2O3.

Conclusions

Dissolution of copper from a primary chalcopyrite ore has been examined in sulphuric acid solution after the calcination with and without Fe₂O₃. Based on the foregoing experimental results, the following conclusions may be drawn.

The calcination of chalcopyrite resulted in weight gain between 668-739 K without additive and 635-973 K with Fe₂O₃addition because of copper sulphate formation. Fe₂O₃ addition contributed to sulphate formation.

To dissolve the copper from the chalcopyrite with or without Fe₂O₃ under the optimum conditions, primary chalcopyrite ore must be ground to smaller particle sizes than 150 µm and calcined for 1 h at 873 K temperature. Sulphuric acid concentration of 0.1 M is sufficient, and solid/liquid ratio of up to 1.2 g/mL can be maintained.

The agitation rate was found to be effective during the dissolution, while temperature was less effective.

In this process it may be expressed that copper dissolution is controlled by limit film diffusion.

It was found that Fe2O3 addition before the calcination also contributed to the copper dissolution.

Thus, Fe2O3 can be added into chalcopyrite ores before calcination for more copper sulphate formation and then copper dissolution in dilute H2SO4 solution.

Acknowledgement

The authors are thankful to The Black Sea Copper Mining Co. in Turkey.

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Fig. 5—Effect of temperature on copper dissolution on samples calcined for 1 h at 873 K. Solid/liquid ratio, 1.2 g/mL; H2SO4, 0.1 M.

Fig. 6—Effect of temperature on copper dissolution from the chalcopyrite sample calcined with 10% Fe2O3 for 1 h at 873 K.

Solid/liquid ratio, 1.2 g/mL; H2SO4, 0.1 M.