Boyd R. Davis, Michael S. Moats, Shijie Wang, Dean Gregurek, Joël Kapusta, Thomas P. Battle, Mark E. Schlesinger, Gerardo Raul Alvear Flores, Evgueni Jak, Graeme Goodall, Michael L. Free, Edouard Asselin, Alexandre Chagnes, David Dreisinger, Matthew Jeffrey, Jaeheon Lee, Graeme Miller, Jochen Petersen, Virginia S. T. Ciminelli, Qian Xu, Ronald Molnar, Jeff Adams, Wenying Liu, Niels Verbaan, John Goode, Ian M. London, Gisele Azimi, Alex Forstner, Ronel Kappes and Tarun Bhambhani (eds.)Extraction 2018The Minerals, Metals & Materials Serieshttps://doi.org/10.1007/978-3-319-95022-8_102
Alternative Lixiviant for Copper Leaching from Chalcopyrite Concentrate
This study investigated leaching kinetics by alternative lixiviants for copper leaching from chalcopyrite (CuFeS2), the most abundant copper resource in the world. As a refractory sulfide mineral, chalcopyrite shows low copper extraction due to passivation on chalcopyrite surface. Also, decrease of copper grade with high portion chalcopyrite requires the alternative leaching procedure to increase copper recovery. Therefore, alternative lixiviants such as sulfurous acid and methanesulfonic acid (MSA) were tested for both concentrate and low grade ore to enhance copper extraction. Also, an oxidant, hydrogen peroxide, was compared to ferric to find out the improvement of leaching kinetic. In concentrate leaching tests, 30 g/L MSA showed the highest copper extraction (47%), compared to other lixiviants at 75 °C. Periodical H2O2 addition enhanced copper extraction, and above 90% of copper extraction was observed within 96 h by periodical addition of 0.6% H2O2 at 75 °C. The activation energy of chalcopyrite leaching by MSA and H2O2 achieved 40 kJ/mol, which is chemical reaction control. The results of low grade ore leaching tests indicates that no significant difference among lixiviants (H2SO4, H2SO3 and MSA) with ferric was observed, all of which achieved around 37% within 24 h at room temperature. However, significant increase of copper extraction (>80%) was observed at both 20 g/L MSA and 10 g/L H2SO4 conditions by the addition of 10% H2O2.
Chalcopyrite (CuFeS2) is a refractory sulfide mineral, consisting of around 70% of copper resources in the world [1]. Problematic fact of leaching chalcopyrite by conventional solution matrix, sulfuric acid and ferric, is passivation of surface by leaching products such as elemental sulfur or jarosite [2]. The continuously decreasing copper grades (<0.5% these days) is another big challenge in copper industry. For low grade copper ores, heap, dump or in situ leaching of whole ores are preferred technologies for the processing of low grade ores [3, 4]. Because of lower copper recovery from these processes compared to other processes such as vat leaching, agitation leaching or pressure oxidized leaching, chalcopyrite leaching by alternative lixiviants should be studied to increase copper extraction from these leaching procedures with lower cost [4]. Therefore, several alternative lixiviants such as sulfurous acid and methanesulfonic acid (MSA, CH3SO3H) were studied for both chalcopyrite concentrate and low grade ore to investigate the leaching kinetics of these lixiviants.
Sulfurous acid, which has low chemical potential below 500 mV versus Ag/AgCl, can be one of alternative lixiviants. It is well known that lower than 500 mV Ag/AgCl can avoid passivation on chalcopyrite leaching, so sulfurous acid can be a candidate for alternative lixiviants [5]. Sulfurous acid was studied for gold leaching from sulfide ore with the application of H2S for sample pretreatment, which achieved 80% of gold extraction in the presence of EDTA, showing the possibility to be a lixiviant [6]. Even though leaching studies of chalcopyrite by sulfurous acid were poorly studied, sulfurous leaching studies were conducted for copper oxide [7] and chalcocite [8]. Methanesulfonic acid is a less toxic organic acid with high affinity to metal ions compared to sulfuric acid [9]. Because of its high dissolution of metal ions, MSA has been studied for electrowinning of metals such as zinc [10], nickel [11] and lead [12]. The characteristic of high metal solubility can be applied to chalcopyrite leaching tests, and several leaching studies other than chalcopyrite were carried out for leaching tests of minerals such as galena [9] and cerussite [12].
Therefore, the objective of this study is (1) to find out leaching kinetics of alternative lixiviants, (2) to optimize the leaching condition of the best performing lixiviant in chalcopyrite concentrate leaching tests, and (3) to compare and investigate copper extraction of the lixiviants in low grade ore leaching tests.
Materials and Methods
Sample Preparation
Chalcopyrite concentrate sample (P80 200 mesh) was collected from one of active mines in southern Arizona (Arizona, USA). The concentrate sample consists of 28.8% Cu, 26.8% Fe, 31.5% S and other 13% of elements based on elemental composition analysis. XRD result represented that the concentrate sample contains 95% chalcopyrite, 3% pyrite, and 2% cuprite. Low grade whole ore sample (P80 100 mesh) was also obtained from an operating copper mine of southern Arizona, USA. The result of elemental analysis reported that the grade of copper is 0.6%, Also, chalcopyrite was detected about 1.0% in the sample and other minerals such as quartz (37%), K-Felspar (35.0%), plagioclase (11%), muscovite (9.0%), biotite (1.0%), kaolinite (6.0%) and pyrite (1.0%) were also found from XRD analysis.
Leaching Tests
Chalcopyrite Concentrate Leaching Tests
Chalcopyrite leaching tests were conducted by beaker test in 1% (w/w) pulp density (1 g sample in 100 g solution) for 96 h at 75 °C. Two alternative lixiviants such as sulfurous acid and MSA (methanesulfonic acid) were tested for leaching tests. Sulfuric acid was tested as baseline tests to compare copper extraction with two lixiviants. The concentration of MSA was doubled compared to sulfuric or sulfurous acid as it generates one mole of proton from one mole of MSA, while other acids generate two moles of proton from one mole of the acids. The various concentration of lixiviants were tested in the presence of ferric. Also, hydrogen peroxide (H2O2) was used as an alternative lixiviant for concentrate leaching tests. Finally, various temperature ranges from 25 to 75 °C were tested to analyze reaction mechanism. Overall tests were summarized into Table 1.
Table 1
Experimental conditions for concentrate leaching tests
Test
Lixiviant
Lixiviant concentration
Oxidant
Oxidant concentration
Periodic addition
Time
Temperature
96 h Leaching test
H2SO4
5 and 15 g/L
Fe3+
5 g/L
–
96 h
75 °C
H2SO3
5 and 15 g/L
5 g/L
–
96 h
75 °C
MSA
10 and 30 g/L
5 g/L
–
96 h
75 °C
H2O2 Periodic addition tests
MSA
30 g/L
H2O2
1.5%
None
vs
every 24 h
96 h
75 °C
MSA & H2O2 leaching test
MSA
30 g/L
H2O2
0.3–4.5%
At every 24 h
96 h
75 °C
Temperature effect test
MSA
30 g/L
H2O2
0.9%
At every 24 h
96 h
25–75 °C
H2SO4
5 g/L
Low Grade Ore Leaching Tests
Low grade copper ore was leached by bottle roll test at room temperature and at atmospheric pressure for 24 h. 20 g sample were used in all test and make the pulp density 6% with 300 g solution in a 2.5 L Winchester bottle. Slurry agitation was provided by placing the bottle onto a bottle roller. Bottles are kept open to ensure oxygen transfer. The summary of experimental conditions we listed at Table 2.
Table 2
Experimental conditions for whole ore leaching tests
Test
Lixiviant
Lixiviant concentration
Oxidant
Oxidant concentration
Time
Temperature
Acid & ferric leaching tests
H2SO4
10 g/L
Fe3+
5 g/L
24 h
Room temperature
H2SO3
20 g/L
MSA
20 g/L
Acid & H2O2 leaching tests
H2SO4
10 g/L
H2O2
1, 3, 10%
24 h
Room temperature
MSA
20 g/L
Analytical Methods
Copper concentration from collected samples were analyzed by a single-lamp Perkin-Elmer Atomic Absorption (AA) spectrophotometer.
Results and Discussion
Chalcopyrite Leaching by Various Lixiviants with Fe3+ as an Oxidant
The kinetic results of chalcopyrite concentrate leaching by various lixiviants were shown in Fig. 1. Overall, copper extraction increased gradually for all conditions, and MSA showed slightly better copper extraction than H2SO4 and H2SO3 in most of all conditions. Also, the highest copper extraction of 47% was observed by 30 g/L MSA and 5 g/L Fe3+. To increase copper extraction, optimization of ferric concentration was conducted. Despite higher addition of ferric above 5 g/L, lower copper extraction (34%) was observed at 10 g/L ferric showing limitation of copper extraction in MSA and Fe3+ solution matrix. Therefore, H2O2 was tested as an alternative oxidant to enhance chalcopyrite leaching.
Fig. 1
Copper extraction (%) by 5 and 15 g/L of H2SO4 and H2SO3, and 10 and 30 g/L of MSA with 5 g/L ferric at 75 °C
Hydrogen Peroxide as an Oxidant for Chalcopyrite Leaching
Figure 2 illustrates the result of chalcopyrite leaching by MSA and H2O2. Compared to MSA-ferric leaching, MSA-H2O2 yielded 60% copper extraction at 96 h. By the titration of H2O2, however, the decomposition of the oxidant was observed within several hours (data not shown). Therefore, leaching test periodic addition of H2O2 at every 24 h was conducted. The periodical addition enhanced leaching kinetic within 48 h, and 80% of copper was extracted. As significant improvement for chalcopyrite leaching was observed by periodic addition of H2O2, the effect of H2O2 concentration was tested with periodic addition of H2O2.
Fig. 2
Copper extraction (%) by no further addition and periodic addition of 1.5% H2O2 at every 24 h in the presence of 30 g/L MSA and 1.5% H2O2 at 75 °C
The results set of chalcopyrite leaching tests by various H2O2 concentration are represented in Fig. 3. Concentration of H2O2 influenced positively on copper extraction, and copper extraction reached above 90%. However, higher than 0.6% H2O2 condition showed lower copper extraction, yielding 75% at 96 h. No further increase of copper extraction after 48 h and this, perhaps, could be explainable by the passivation of chalcopyrite induced from high amount of hydrogen peroxide.
Fig. 3
Effects of H2O2 concentration with the same amount of periodic addition at every 24 h from 0.3% to 4.5% on copper extraction (%) in the presence of 30 g/L MSA at 75 °C
Thermal effects of chalcopyrite leaching were tested to figure out reaction mechanism by acid and H2O2. Figure 4 shows the Arrhenius plot of (a) 30 g/L MSA (b) 5 g/L sulfuric acid in the presence of H2O2. The activation energy for chalcopyrite leaching by MSA and H2SO4 with H2O2 were calculated as 39.9 kJ/mol and 19.1 kJ/mol respectively, and MSA—H2O2 reaction was determined as chemical reaction controlled mechanism. H2SO4–H2O2 reaction was calculated in the range of diffusion controlled mechanism, but further verification is required as leaching chalcopyrite generally requires high activation energy in the range of 47—131 kJ/mol [5].
Fig. 4
Arrhenius plot of chalcopyrite concentrate leaching by a 5 g/L H2SO4 and b 30 g/L MSA with initial and periodic addition of 0.9% H2O2 at every 24 h at 25–75 °C
Chalcopyrite Low Grade Whole Ore Leaching Tests
Figure 5 illustrates the copper extraction of low grade copper ore leached by different lixiviants using ferric ion as an oxidant. The copper extraction reached the maximum within 6 h. The copper extraction of 10 g/L sulfuric acid was the highest, 37%, while only 30% copper was extracted by MSA and ferric. The copper dissolution kinetics with sulfuric and MSA using H2O2 as oxidant were shown in Fig. 6. Copper extraction increased with H2O2 concentration, and the highest copper extractions of both leaching agents were higher than 80% after 24 h. H2O2 showed stronger oxidant ability in leaching of the low grade copper ore with acid.
Fig. 5
Copper extraction (%) by 10 g/L H2SO4, 20 g/L MSA and 20 g/L H2SO3 with 5 g/L ferric in 6% pulp density at room temperature
Fig. 6
Copper extraction (%) by a 10 g/L H2SO4 and b 20 g/L MSA with various concentration of H2O2 in 6% pulp density at room temperature
Conclusion
Alternative lixiviants such as MSA (methanesulfonic acid) and sulfurous acid were compared to sulfuric acid for both chalcopyrite concentrate and whole ore leaching. MSA achieved slightly higher copper extraction compared to both sulfuric acid and sulfurous acid, and copper extraction of 47% was observed with 30 g/L MSA and 5 g/L ferric. By replacing oxidant to H2O2, copper extraction enhanced, and above 90% was achieved in the presence of MSA by periodic addition of H2O2. Activation energy of MSA and H2O2 reaction was about 40 kJ/mol, which is chemical reaction controlled mechanism. For whole ore leaching tests, H2O2 showed better copper extraction compared to ferric as an oxidant, and above 80% of copper was extracted from chalcopyrite at room temperature.
