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State Key Laboratory of Complex Nonferrous Metal Resources Clean Utilization, Faculty of Land Resource Engineering, Kunming University of Science and ...
International Journal of Minerals, Metallurgy and Materials Volume 22, Number 3, March 2015, Page 241 DOI: 10.1007/s12613-015-1067-1

Extracting copper from copper oxide ore by a zwitterionic reagent and dissolution kinetics Jiu-shuai Deng, Shu-ming Wen, Jian-ying Deng, and Dan-dan Wu State Key Laboratory of Complex Nonferrous Metal Resources Clean Utilization, Faculty of Land Resource Engineering, Kunming University of Science and Technology, Kunming 650093, China (Received: 27 April 2014; revised: 3 August 2014; accepted: 3 September 2014)

Abstract: Sulfamic acid (SA), which possesses a zwitterionic structure, was applied as a leaching reagent for the first time for extracting copper from copper oxide ore. The effects of reaction time, temperature, particle size, reagent concentration, and stirring speed on this leaching were studied. The dissolution kinetics of malachite was illustrated with a three-dimensional diffusion model. A novel leaching effect of SA on malachite was eventually demonstrated. The leaching rate increased with decreasing particle size and increasing concentration, reaction temperature and stirring speed. The activation energy for SA leaching malachite was 33.23 kJ/mol. Furthermore, the effectiveness of SA as a new reagent for extracting copper from copper oxide ore was confirmed by experiment. This approach may provide a solution suitable for subsequent electrowinning. In addition, results reported herein may provide basic data that enable the leaching of other carbonate minerals of copper, zinc, cobalt and so on in an SA system. Keywords: malachite; copper; extraction; sulfamic acid; dissolution; kinetics

1. Introduction Copper, one of the most popular and valuable metals used by humans, generally exists in nature as sulfides and oxides, such as chalcopyrite, bornite, chalcocite, malachite, and chrysocolla [1−3]. Copper sulfide mineral has better floatability than copper oxide mineral, i.e., it is more easily separated from the gangue and recovered by flotation. However, the natural resources of high-grade copper sulfide are being depleted; thus, research on the separation and extraction of copper from copper oxide ores containing carbonates and silicates is gaining considerable attention [4−7]. Among these copper oxide ores, malachite is a significant copper-bearing mineral that exists in the oxidized zone of copper deposits. Malachite is extensively used in industrial production for copper extraction [8]. Hydrometallurgy is generally used to extract copper from copper oxide ores. A copper-ion solution is initially obtained, and the copper is regained by solvent extraction and elec-

trowinning [9]. Currently, the principal leaching technologies include acid leaching and ammonia leaching [10−11]. The former commonly involves the use of strong acids, such as sulfuric acid, hydrochloric acid, or nitric acid [7,9,12−13]; the latter involves the use of ammonium carbonate [14−15], ammonium hydroxide [1,16], ammonium chloride [17], ammonium sulfate [18], or ammonium nitrate [19]. Researchers have also explored a new method of leaching copper oxide ore with an organic reagent [2,20−21], although the literature contains few pertinent studies related to this approach. Acid leaching and ammonia leaching have their own advantages and disadvantages from the viewpoints of efficiency and reagent consumption. Consequently, numerous researchers are actively exploring new leaching reagents or technologies to improve leaching efficiency and minimize reagent consumption. Sulfamic acid (SA) is a colorless and relatively stable solid acid that exhibits the characteristics of both organic and inorganic acids [22−25]. X-ray and neutron diffraction studies have demonstrated that SA crystals exist in the zwit-

Corresponding author: Jiu-shuai Deng, E-mail: [email protected]; Dan-dan Wu, E-mail: [email protected] © University of Science and Technology Beijing and Springer-Verlag Berlin Heidelberg 2015

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terionic form [26−27], as shown in Fig. 1. SA is nonvolatile, odorless, minimally toxic to humans, and easy to handle. Aqueous solutions of SA exhibit the same strong acidity as solutions of hydrochloric and sulfuric acids, but are far less corrosive. SA can also react with most industrial precipitates to form soluble substances at room temperature [22]. In recent years, SA has been extensively used in acid-catalyzed reactions as an efficient and environmentally friendly heterogeneous reagent [24].

used in the experiments was analytically pure and was obtained from JHYT Chemical Reagents Co., Ltd., Tianjin, China.

Fig. 1. Zwitterion structure of sulfamic acid (SA).

Thus far, no research on the metallurgical extraction of copper from copper oxide ore with a zwitterionic reagent has been reported. The question of whether a zwitterionic reagent with hydroxy and amino groups has a favorable leaching effect on copper oxide ore is worthy of study. Meanwhile, because of its structure and properties, SA has the potential to be used for ore leaching. In this paper, the leaching process, influencing factors, and leaching kinetics of SA as a novel reagent were studied for the first time. The results provide a reference for the application of SA in leaching other carbonate ores of copper, zinc, and cobalt.

2. Experimental 2.1. Materials The experimental raw materials were taken from the copper deposit in northeast Yunnan, China. High-grade copper ore was obtained by crushing and screening the raw materials. X-ray powder diffraction (XRD) and chemical analysis were conducted to test the purity of the experimental materials. XRD was performed on a Japan Science TTR-ΙΙΙ diffractometer using a Cu Kα radiation source (λ = 0.15406 nm) operated at a voltage and current of 40 kV and 40 mA, respectively; samples were scanned over the 2θ range of 5° to 80°. Fig. 2 shows that the main mineral composition of the raw materials was malachite, quartz, calcite, and dolomite. Chemical analysis of the experimental sample (Table 1) indicated that CuO and SiO2 accounted for 45.21wt% and 18.74wt% of the sample, respectively, with other gangues containing calcium, magnesium, and aluminum, consistent with the XRD analysis results. De-ionized water prepared by a Milli−Q5O water purifier was used as the leaching solvent in the experiments. The SA

Fig. 2. X-ray diffraction pattern of the experimental sample. Table 1. Components of the experimental sample wt% CuO

SiO2

Al2O3

MgO

CaO

45.21

18.74

1.19

2.38

3.11

2.2. Procedure The leaching setup, referred to as the compound device for leaching (CDL), was custom designed; the CDL setup is shown in Fig. 3. Eight reactor units were placed in a thermostatic water bath, with each unit connected by a three-necked flask. For each flask, a Graham condenser and a mechanical stirrer were inserted into two of the necks, and the third neck, which was blocked with a ground stopper, was used for sample filling and pipetting. In the CDL, the eight Graham condensers were connected end-to-end with rubber tubes and were connected to a water inlet and outlet to condensate the steam generated during the experiment. A number of continuous magnetic stirrers were placed at the bottom of the water bath to maintain the liquid in a homogeneous state. The water bath temperature was automatically controlled, and the rotational speeds of the mechanical stirrers were adjustable. Consequently, eight sets of experiments could be simultaneously conducted in the CDL. This device was customized by Jiangsu ZBR Instrument Co., Ltd. (China). After the temperature and stirring speed were properly adjusted, 10 g of materials and 1000 mL of de-ionized water were added into each three-necked flask to conduct the leaching kinetics experiments. The effects of temperature, reagent concentration, stirring speed, and particle size were investigated. For each run, 5 mL of solution was pipetted into an enclosed chemical bottle. Inductively coupled

J.S. Deng et al., Extracting copper from copper oxide ore by a zwitterionic reagent and dissolution kinetics

plasma atomic emission spectroscopy (ICP−1000 ΙΙ, SHIMADZU, Japan) was conducted to test the copper concen-

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tration in the solution at specific times, which enabled the leaching rate x to be calculated.

Fig. 3. Compound device for leaching (CDL): (a) overall; (b) each unit.

3. Results and discussion 3.1. Reaction equations In the solution, SA ionizes as per Eq. (1): H3NSO3(s) → H+(aq) + NH 2SO −3 (aq)

(1)

Hydrogen ions and sulfamate ions with amino groups are then generated in the solution. More than one constituent unit in the malachite can react with hydrogen ions, and the following reactions occur sequentially [2]: CuCO3⋅Cu(OH)2(s) + 2H+(aq) → Cu2+(aq) + CO2(g) + H2O(aq) + Cu(OH)2(s) (2) + Cu(OH)2(s) + 2H (aq) → Cu2+(aq) + 2H2O(aq) (3) Eqs. (2) and (3) can also be expressed by the following comprehensive equation: Cu(OH)2·CuCO3(s)+ 4H+(aq) → 2Cu2+(aq) + 3H2O(aq) + CO2(g) (4) Thus, the total chemical reaction equation of SA and malachite in an aqueous solution is represented as Cu(OH)2·CuCO3(s)+4H3NSO3(s) → 2Cu2+(aq) + 4NH 2SO −3 (aq) +3H2O(aq) + CO2(g)

(5)

Furthermore, if ammonia exists in the aqueous solution, the copper ions can react with it to generate a copper–ammonia complex compound, as shown in Eqs. (6) and (7) [1]: Cu2+(aq) + 2NH3(aq)  Cu(NH 3 ) 22 + (aq)

(6)

Cu(NH 3 ) 22 + (aq)

(7)

+ 2NH3(aq) 

Cu(NH 3 ) 24 + (aq)

Let the total concentration of copper be CCu(T) and the total ammonia concentration be C NH 3 (T) . Then, on the basis of the balanced reaction, the concentration of species in the solution can be obtained. The mass fraction of any species

Xj(aq) can be determined according to the following equation [28]: vj [Xj(aq)] ≥ vi≠j[Xi≠j(aq)] (i = 1, 2,…, i ≠ j) (8) where vj is the atomic number of copper in Xj(s) and vi≠j means the atomic number of copper in Xi≠j(aq) except Xj(aq). In the Cu–NH3–H2O system, vj = vi≠j = 1, and [Xj(aq)] and [Xi≠j(aq)] are the concentrations of Xj(aq) and Xi≠j(aq), respectively. The overall species fraction–pH graph of the Cu–NH3–H2O system can be calculated on the basis of Eq. (8), as shown in Fig. 4.

Fig. 4. Species fraction–pH graph of the Cu–NH3–H2O system (E: potential).

Given that the pH value of the SA solution is less than 6, the main copper ammonia complex is Cu(NH 3 ) 22 + according to Fig. 4. Thus, Eqs. (6) and (7) are the comprehensive equations of the Cu–NH3–H2O system. 3.2. Effect of reaction temperature Fig. 5 shows the variation curves of the leaching rate (xCu) with time in an SA solution at 20–60°C with other experimental conditions held constant. The SA concentration was

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0.25 mol/L, the stirring speed was 800 r/min, and the particle size was d85 = 106 μm (d85 is the grain diameter accounted for 85wt% of all-measured particles). Fig. 5 shows that the leaching rate increased with increasing temperature. The leaching rate reached 90% after 15 min at temperatures above 40°C. At temperatures of 50 and 60°C, the corresponding leaching rate approached 100%. The thermal energy associated with the increase in temperature sped up molecular movement in the solution; thus, the chance of collision between the reagent and the mineral increased, thereby facilitating the reaction between copper and hydronium ions. Overall, SA exhibited a greater leaching speed for malachite.

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malachite reached 92.9% within 5 min and almost 100% within 15 min. When the particle size was d85 = 250 μm, the leaching rate was 79.1% within 15 min. Fig. 7 shows that the particle size strongly influenced the dissolution rate because the specific surface area of the mineral particles increased with decreasing particle size. The collision chance of the reagent with the mineral particles can thus be improved to facilitate the generation of a copper complex, thereby facilitating the dissolution of malachite.

Fig. 6. Variation curves of leaching rate with time at different sulfamic acid concentrations.

Fig. 5. Variation curves of leaching rate with time at different temperatures.

3.3. Effect of SA concentration Fig. 6 shows the variation curves of the leaching rate with SA concentration when the particle size of the sample was d85 = 106 μm, the temperature was 50°C, the stirring speed was 800 r/min, and the leaching time was 15 min. The leaching rate was observed to increase with increasing SA concentration and tended to increase more within the SA concentration range of 0.1–0.2 mol/L. Thereafter, the leaching rate increased gently with increasing reagent concentration. When the leaching time was 15 min, the leaching rate was not high at an SA concentration of 0.1 mol/L, whereas the leaching rate reached 94.1% at an SA concentration of 0.2 mol/L and almost 100% at concentrations of 0.25 and 0.3 mol/L. Therefore, the SA concentration significantly influenced the leaching of malachite. 3.4. Effect of particle size The relationship between the leaching rate in SA solution and the particle size is shown in Fig. 7. The leaching rate was observed to increase with decreasing particle size. When the particle size was d85 = 53 μm, the leaching rate of

Fig. 7. Variation curves of leaching rate with time at different particle sizes.

3.5. Effect of stirring speed The effect of stirring speed on the SA leaching of malachite is shown in Fig. 8. The copper leaching rate was observed to continuously increase as the stirring speed was increased from 200 to 1000 r/min. After 15 min of leaching, the leaching rates at stirring speeds of 200 and 1000 r/min were 91.4% and 99.9%, respectively. An increase in stirring speed enabled the solid in the solution to exhibit a more homogeneous suspension state. 3.6. Kinetic analysis The leaching process is heterogeneous; thus, a heteroge-

J.S. Deng et al., Extracting copper from copper oxide ore by a zwitterionic reagent and dissolution kinetics

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is controlled by the product-layer diffusion, the leaching kinetic equation of the shrinking core model can be expressed as follows [7,30]:

neous reaction model is generally involved [29]. Therefore, in this study, the kinetic analysis of the SA leaching of malachite was investigated on the basis of the shrinking core model.

1 – 3(1 – x)2/3 + 2(1 – x) = kdt

(9)

If the leaching rate is controlled by liquid film diffusion, the rate equation is stated as follows [7,30]: x = kl t (10) If the rate is controlled by a surface chemical reaction, then the leaching kinetics can be expressed as follows [7,30]: 1 – (1 – x)1/3 = kr t (11) where x is the leaching rate; kd and kl are the speed constants controlled by product-layer diffusion and liquid-film diffusion, respectively; kr is the speed constant of the chemical reaction; and t is the leaching time. Assuming that the malachite particles are substantially spherical geometries, we used the three aforementioned shrinking core models to assess the experimental data. On the basis of the correlation coefficient (R2) of the kinetic model data, the probability of each model was determined, as shown in Table 2.

Fig. 8. Variation curves of leaching rate with time at different stirring speeds.

In accordance with the shrinking core model, a reaction between solid and liquid reactants was assumed to occur on the outer surface of the solid. If the mineral particles possess substantially spherical geometries and the leaching process

Table 2. Apparent rate constants and correlation coefficients of different kinetic models

Parameter

T / °C

Value

d85 / μm

S / (r⋅min−1)

Surface chemical reaction 1 – (1 – x)1/3

Diffusion through the product layer 1 – 3(1 – x)2/3 + 2(1 – x)

Three dimensional diffusion model [1 – (1 – x)1/3]2

kl / min−1

R2

kr / min−1

R2

kd / min−1

R2

km / min−1

R2

20

0.038

0.263

0.021

0.709

0.020

0.949

0.010

0.983

30 40 50

0.042 0.044 0.046 0.087

0.158 0.001 0.004 0.142

0.026 0.032 0.039 0.073

0.796 0.750 0.712 0.877

0.028 0.035 0.041 0.076

0.971 0.904 0.753 0.892

0.016 0.023 0.033 0.064

0.992 0.995 0.994 0.991

60

C / (mol⋅L−1)

Diffusion through the liquid film x

0.10

0.025

0.485

0.010

0.642

0.006

0.911

0.002

0.926

0.15 0.20 0.25 0.30

0.038 0.044 0.046 0.067

0.416 0.005 0.004 0.001

0.020 0.034 0.039 0.058

0.765 0.831 0.712 0.755

0.019 0.037 0.041 0.061

0.958 0.923 0.753 0.765

0.009 0.026 0.033 0.050

0.986 0.994 0.994 0.992

250

0.045

0.515

0.024

0.854

0.023

0.988

0.011

0.988

150 106 75 53

0.050 0.046 0.052 0.128

0.331 0.004 0.569 0.368

0.033 0.039 0.053 0.108

0.875 0.712 0.899 0.896

0.035 0.041 0.061 0.112

0.987 0.753 0.939 0.886

0.020 0.033 0.051 0.062

0.992 0.994 0.991 0.998

200

0.075

0.430

0.042

0.786

0.040

0.974

0.020

0.995

400 600 800

0.079 0.082 0.046 0.088

0.457 0.286 0.004 0.095

0.048 0.052 0.039 0.073

0.839 0.766 0.712 0.829

0.050 0.055 0.041 0.077

0.973 0.939 0.753 0.845

0.027 0.031 0.033 0.062

0.996 0.997 0.994 0.993

1000

Note: T, C, and S represent the temperature, reagent concentration and stirring speed, respectively.

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In addition to the aforementioned models, the Jander equation of the three-dimensional diffusion kinetic model was proposed according to the statistical data, as shown below [29]: 2hdh/dt = k or dh/dt = DVmC0/h (12) where h is the thickness of the product layer, D is the diffusion coefficient, Vm is the volume of product, and C0 is the concentration of the penetrating species on the surface. The final rate (x) equation was obtained [2,29]: [1 – (1 – x)1/3]2 = kmt (13) where km is the apparent rate constant of the three-dimensional diffusion kinetic model [31]. The apparent reaction rate constant km was obtained from the slope of the straight line of [1 – (1 – x)1/3]2 with respect to time t; the results are shown in Table 2. The maximum

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correlation coefficient was obtained, indicating a good linear relationship between [1 – (1 – x)1/3]2 and time t. In the case that only the reagent concentration was varied and the other factors were fixed, Eq. (13) can be expressed as follows: [1 – (1 – x)1/3]2 = k0 Cαt (14) d{[1 – (1 – x)1/3]2}/dt = k0 Cα (15) where k0 is the pre-exponential factor, C the concentration of SA, and α is the index number of variable C. The relation curves between [1 – (1 – x)1/3]2 and time t at different reagent concentrations, in accordance with Eq. (15), are plotted in Fig. 9(b). Similarly, the relation curves between [1 – (1 – x)1/3]2 and time t at different particle sizes and stirring speeds are shown in Figs. 9(c) and 9(d), respectively.

Fig. 9. Relation curves of [1 – (1 – x)1/3]2 and time t at different influencing factors: (a) temperature; (b) sulfamic acid concentration; (c) particle size; and (d) stirring speed.

In the case that only temperature was varied and the other factors were fixed, Eq. (13) can be written as follows: [1 – (1 – x)1/3]2 = kt (16) The slopes of each straight line in Fig. 9(a) represent the reaction rate constants at different temperatures, as per the Arrhenius equation. Then, K = k0exp(–E/RT) (17) where K is the reaction rate constant, k0 is the pre-exponential factor, E is the apparent activation energy, R is the molar gas constant, and T is the thermodynamic tempera-

ture. The Arrhenius curve was plotted in Fig. 10, with 1/T and ln k as the horizontal and vertical ordinates, respectively; the apparent activation energy E was calculated as 33.23 kJ/mol.

4. Conclusions In this work, the dissolution kinetics of malachite in SA solutions was investigated in a batch reactor. The results led to the following conclusions:

J.S. Deng et al., Extracting copper from copper oxide ore by a zwitterionic reagent and dissolution kinetics [4]

[5]

[6]

[7]

Fig. 10. Arrhenius curve for the sulfamic acid leaching of malachite.

(1) The dissolution kinetics follows a shrinking core model with three-dimensional diffusion as the rate-controlling step. The activation energy for leaching was determined to be 33.23 kJ/mol, and the dissolution rate was very sensitive to the temperature in the range of 20–60°C. (2) Increases in the SA concentration and stirring speed increased malachite dissolution in the ranges of 0.1–0.3 mol/L and 200–1000 r/min, respectively. (3) A increase in the particle size of malachite resulted in a lower dissolution rate.

[8]

[9]

[10]

[11]

Acknowledgements This work was financially supported by the National Natural Science Foundation of China (Nos. 51168020, 51404119, and 51464029), the Natural Science Foundation of Yunnan Province, China (No. 2014Y0845), the Excellent Doctoral Dissertation and Talent Cultivation Foundation of Kunming University of Science and Technology (Nos. 41118011 and 201421066).

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