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Selective removal of antimony from refractory gold ores by ultrasound
Hydrometallurgy 190 (2019) 105161
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Hydrometallurgy journal homepage: www.elsevier.com/locate/hydromet
Selective removal of antimony from refractory gold ores by ultrasound Ping Guo
a,b,c,d
, Shixing Wang
a,b,c,d,⁎
, Libo Zhang
a,b,c,d,⁎
T
a
State Key Laboratory of Complex Nonferrous Metal Resources Clean Utilization, Kunming University of Science and Technology, Kunming 650093, Yunnan, China National Local Joint Laboratory of Engineering Application of Microwave Energy and Equipment Technology, Kunming 650093, Yunnan, China Key Laboratory of Unconventional Metallurgical Ministry of Education, Kunming 650093, China d Faculty of Metallurgical and Energy Engineering, Kunming University of Science and Technology, Kunming 650093, Yunnan, China b c
A R T I C LE I N FO
A B S T R A C T
Keywords: Removal Antimony Refractory ore Ultrasound
Ultrasound is used to enhance the removal of antimony from the refractory gold ores in alkaline sodium sulfide leaching process. The effects of ultrasonic time, temperature, reagent concentration and ultrasonic power on antimony removal are discussed. The removal rate of antimony reached 94.50% when ultrasonic time was 60 min, sodium hydroxide concentration was 1 mol/L, sodium sulfide concentration was 2 mol/L, ultrasonic power was 1500 W and temperature was 55 °C. Under the conditions, the removal rate of antimony without ultrasound is only 58.37%. The results show that ultrasound can significantly improve the removal efficiency of antimony and reduce the leaching temperature and time of antimony. The leaching rate of gold increased from 13.35% to 40.56% after antimony removal. Moreover, the leaching rate of gold after antimony removal reached 68.90% under ultrasound. Therefore, ultrasound not only enhances the removal efficiency of antimony, but also improves the leaching rate of gold. The improvement of the leaching rate of antimony and gold is attributed to that the mineral particles are broken up and pyrite is decomposed by ultrasound.
1. Introduction Gold is widely used in jewelry, currency reserve and many industry fields. With large-scale gold mining, free milling resources increasingly depleted and the refractory ore will become the main resources in the future (Li et al., 2016). Refractory gold ore generally refers to ore with less than 80% cyanide leaching rate. There are many reasons for refractory behavior: gold is locked within pyrite/arsenopyrite (Zhang et al., 2016b), carbon-containing substances exist and gold combines with arsenic, antimony and other characteristic elements (Xing et al., 2019). In order to obtain higher gold recovery from refractory ores, it is necessary to adopt the pretreatment process before leaching. Various pretreatment methods have been used, such as roasting, pressure oxidation and biooxidation (Ming and Chen, 2014). However, these pretreatment processes have the followed disadvantages, for example, the discharge of SO2 and As2O3 in the roasting process, high investment cost for high pressure operation, and bacterial growth was inhibited by arsenic during bioleaching (Li et al., 2009; Rusanen et al., 2013; Sun et al., 2019; Ubaldini et al., 2000a). The alkaline pretreatment is an efficient method to remove arsenic, antimony and other harmful elements from ores. Espitia found that the removal amount of arsenic increased with the increase of time and hydroxyl ion
concentration in the pretreatment (Mesa Espitia and Lapidus, 2015). Awe et al. showed also that the removal rate of arsenic and antimony depended obviously on the hydroxide concentrations, temperature and the reaction time (Awe and Sandström, 2010). Although alkali pretreatment is an effective method, there are still some obvious shortcomings, such as high temperature and long time. Therefore, it is necessary to develop new alkali treatment method to overcome these disadvantages and improve the removal rate of antimony. Ultrasound has widely attracted attention in metallurgical field, especially for the leaching of refractory ores. The leaching rate of neodymium (Nd) from waste magnet reached 99.99% under ultrasound (Behera et al., 2019). Elik found that ultrasound significantly improved the leaching rate and shortened the leaching time of copper, lead, nickel, zinc and manganese in the sediments (Elik, 2007). Ultrasound increased also the leaching rate of refractory gold ores during electrochlorination because it reduced the diffusion resistance of HClO and promoted the diffusion of HClO into solid product layer and unreacted layer (Zhu et al., 2012). We also found that proper amount of sodium hydroxide could improve the leaching rate of gold and the excessive sodium hydroxide had a negative effect during the alkali pretreatment of refractory gold ores by ultrasound (Zhang et al., 2016a). These show that ultrasound can improve the leaching rate of metal. Therefore,
⁎ Corresponding authors at: State Key Laboratory of Complex Nonferrous Metal Resources Clean Utilization, Kunming University of Science and Technology, Kunming 650093, Yunnan, China. E-mail addresses: [email protected] (P. Guo), [email protected] (S. Wang), [email protected] (L. Zhang).
https://doi.org/10.1016/j.hydromet.2019.105161 Received 20 May 2019; Received in revised form 23 August 2019; Accepted 29 September 2019 Available online 19 October 2019 0304-386X/ © 2019 Elsevier B.V. All rights reserved.
Hydrometallurgy 190 (2019) 105161
P. Guo, et al.
Fig. 1. The form and distribution of gold in minerals.
microscope (VEGA3, TESCAN). Particle size of the leaching residue was analyzed by laser particle size distribution tester (JL-1177).
ultrasound is an effective tool in the metal extraction industry. In this study, ultrasound was used to intensify the removing process of antimony from the refractory gold ores. The effects of sodium sulfide concentration, sodium hydroxide concentration, temperature, time and ultrasonic power on the removal rate of antimony were studied in detail. The leaching of gold from the treated ore was also carried out.
2.3. Leaching tests The effects of concentrations of sodium sulfide (0.1–2 mol/L Na2S) and sodium hydroxide (0.5–2.5 mol/L NaOH), temperature (25–80 °C), time (20–100 min) and ultrasonic power on the removal rate of antimony were studied. The experiments were carried out in the circular beaker of 300 mL. The beaker was placed into a thermostatic waterbath equipped with a magnetic stirrer. The leaching temperature was controlled within ± 2 °C. The sodium sulfide and sodium hydroxide were firstly dissolved in water. 200 mL of the mixed solution (Na2S + NaOH) and 70 g of gold ore were added to the beaker. After the mixture was heated for 60 min with stirring, the solid residues were separated by filtration and were used to analyze the antimony content. The leaching of gold was carried out in 500 mL glass beaker. The reaction conditions are as followed: NaClO concentration is 1.5 mol/L, NaOH concentration is 1.5 mol/L, solid-liquid ratio is 3, ultrasonic power is 250 W, ultrasonic time is 2 h and the temperature is 35 °C. The gold content in the raw materials and the leach residues was determined by the fire assay method. The soluble gold was analyzed by inductively coupled plasma optical emission spectrometry. The leaching rate is calculated according to the formula.
2. Experimental 2.1. Materials The gold ore samples were obtained from Yunnan province in china. The samples were firstly dried and then grinded by ball mill. The average particle size of the mineral is 31.138 um (D50). According to mineralogical analysis, the sulfides in gold concentrate are pyrite, arsenopyrite, stibnite, sphalerite, galena, chalcopyrite and tetrahedrite. Carbonate minerals are mainly dolomite, and a small amount of calcite and siderite. Silicate minerals are mainly quartz, sericite, potassium feldspar, tetrahedrite, etc. Gold mainly exists in pyrite, arsenopyrite and other sulfides in the form of invisible gold (Fig. 1). Table 1 shows the chemical composition of gold ores determined by mineralogical analysis and X-ray fluorescence. The ore mainly contained 39.72% SiO2, 23.34% FeS2, 1.96% Sb and 24 g/t Au. The sodium sulfide and sodium hydroxide used in this experiment are all analytically pure.
C − C⎤ Leaching rate = ⎡1 − 0 × 100% ⎢ C0 ⎥ ⎦ ⎣
2.2. Characterization
where C0 represents the initial content of metal in the ore, C represents the metal content in the leaching residue.
In order to determine the content of antimony before and after leaching, the raw ore and the leaching residue were analyzed by inductively coupled plasma optical emission spectrometry. The solid sample was determined by X-Ray diffractometer (XRD, BRUKER-AXS, Germany) and mineral liberation analyzer (MLA250). The microstructure of the samples was characterized using scanning electron
3. Results and discussion 3.1. Effect of Na2S concentration The alkaline sulphide leaching was widely applied to pretreat antimony-bearing ores/concentrates. Ubaldini removed about 80% Sb from refractory ores using alkaline pretreatment method at 80 °C. (Ubaldini et al., 2000b). The Na2S concentration has remarkable influence on the removal rate of antimony. Therefore, the effect of Na2S concentration (0.1–2 mol/L) under ultrasound was firstly studied when temperature was 25 °C, time was 60 min, the NaOH concentration was 1 mol/L and ultrasonic power was 1500 W (Fig. 2). The antimony removal rate increased firstly from 47.65% to 75.2% and remained basically unchanged with the further increase of the Na2S concentration from 1.5 to 2 mol/L. The Na2S concentration has an obvious influence on the antimony leaching rate. This was mainly attributed to the decomposition of antimony sulphides, such as andorite, stibnite, and zinkenite. The decomposition of antimony sulphides can be given by the followed reactions (Celep et al., 2011a):
Table 1 Chemical composition of the gold ore samples. Compound
Content (%)
Compound
Content (%)
SiO2 FeS2 Al2O3 CaO MgO K2O As2O3 TiO2 Sb2O3 PbO Na2O
39.719 23.342 14.329 4.252 3.813 3.386 1.155 1.144 1.802 0.037 0.175
P2O5 ZnO F MnO Cr2O NiO CoO CuO ZrO SrO
0.206 0.110 0.113 0.059 0.051 0.090 0.035 0.061 0.044 0.022
(1)
2
Hydrometallurgy 190 (2019) 105161
P. Guo, et al.
Fig. 2. Effect of the Na2S concentration on the antimony removal rate (Ultrasonic power: 1500 W; Time: 60 min; NaOH: 1 mol/L; temperature: 25 °C).
Sb2 S3 + 2S2 − → Sb2 S5 4 −
(2)
SbS2− + S2 − → SbS33 −
(3)
Fig. 4. Effect of the time on the antimony removal rate (Ultrasonic power: 1500 W, Na2S:2 mol/L, NaOH: 1 mol/L, temperature: 40 °C).
not conducive to the leaching of antimony (Mavrogenes and O'Neill, 1999). The reaction will slow down due to insufficient oxygen supply. Therefore, 40 °C was used in the following experiment.
Therefore, 2 mol/L of Na2S was used in the following experiment. 3.2. Effect of temperature
3.3. Effect of time
The effect of temperature on the antimony removal rate was also investigated (Fig. 3). The leaching rate of antimony was about 75.20% at 25 °C. Celep also confirmed that a large amount of antimony was dissolved in the alkaline sulphide solution even at 20 °C (Celep et al., 2011b). Moreover, the antimony removal rate is improved with the increase of temperature. When the temperature reaches 40 °C, the antimony removal rate is 90%. This shows that the increase of the reaction temperature is beneficial to the leaching process. Celep et al. found also that the leaching rate of antimony reached 71% and 84% at 50 and 70 °C, respectively (Celep et al., 2011a). Therefore, the leaching temperature was significantly reduced by ultrasound. However, the leaching rate of antimony decreased slightly with the further increasing of temperature. Higher temperature will increase the escape of oxygen in water and short the residence time of oxygen in the solution, which is
The effect of the time on the antimony leaching rate was studied when temperature was 40 °C, the Na2S concentration was 2 mol/L, the NaOH concentration was 1 mol/L and ultrasonic power was 1500 W (Fig. 4). When the reaction time is 60 min, the antimony leaching rate reaches 90.87% and the antimony content in the leaching residue decreases to 0.26%. With the prolongation of time, the antimony leaching rate slowly decreases. This may be that antimony is oxidized by oxygen in the air and some antimony precipitates into the slag in the form of sodium pyroantimonate. The chemical reaction occurs as followed (Ubaldini et al., 2000b):
2Na3SbS3 + 7O2 + 2NaOH + 5H2 O = 2NaSb (OH)6 + 3Na2S2 O3
(4)
Therefore, 60 min was used in the following experiment. 3.4. Effect of NaOH concentration The effect of the NaOH concentration was studied when temperature was 40 °C, the Na2S concentration was 2 mol/L, time was 60 min and ultrasonic power was 1500 W (Fig. 5). It can be seen from Fig. 4 that the leaching rate of antimony increases slightly with the increase of the sodium hydroxide concentration from 0.5 to 1.0 mol/L and is unchanged from 1.0 to 2.5 mol/L. Normally, S2− reacts with water as followed:
S2 − + H2 O = HS− + OH−
(5)
It is necessary to maintain basic conditions in order to minimize hydrolysis S2− and improve the leaching efficiency (Celep et al., 2011a). Moreover, sodium hydroxide can also extract antimony ore. The increase of the NaOH concentration is beneficial to the leaching of antimony. However, excessive alkali will causes the reaction between SiO2 and NaOH to form dense Na2SiO3. Na2SiO3 will bind to the surface or pore of mineral crystals and prevent the leaching of antimony. So the antimony leaching rate does not increase with the increase of alkali concentration. Therefore, 1 mol/L of NaOH was used in the followed experiment.
Fig. 3. Effect of the temperature on the antimony removal rate (Ultrasonic power: 1500 W; Na2S:2 mol/L; NaOH: 1 mol/L; Time: 60 min). 3
Hydrometallurgy 190 (2019) 105161
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Table 2 Orthogonal test factor level. Level
Factor
1 2 3
A
B
C
D
20 60 100
25 55 75
0.1 1 2
0 600 1500
Table 3 Orthogonal experimental results and range analysis.
Fig. 5. Effect of the NaOH concentration on the antimony removal rate (Ultrasonic power: 1500 W, Na2S:2 mol/L, Time:60 min, temperature: 40 °C).
3.5. Influence of ultrasonic power The effect of the ultrasonic power on the antimony removal rate was studied when temperature was 40 °C, the Na2S concentration was 2 mol/L, the NaOH concentration was 1 mol/L and the reaction time was 60 min (Fig. 6). The leaching rate of antimony increases with the increase of the ultrasonic power from 150 W to 600 W. The maximum leaching rate is about 92.60%. The increase of ultrasonic power is beneficial to the leaching of antimony. The pulse and cavitation generated by ultrasonic waves can greatly increase the turbulence intensity and the contact area, thus enhancing the mass transfer. Zhang proved that ultrasound improved the dissolution fraction (Zhang et al., 2016c).
Number
A
B
C
D
Leaching rate of antimony
1 2 3 4 5 6 7 8 9 K1 K2 K3 Rank
1 1 1 2 2 2 3 3 3 58.15 59.19 55.69 3.49
1 2 3 1 2 3 1 2 3 45.20 67.04 60.77 21.84
1 2 3 2 3 1 3 1 2 50.66 57.38 64.98 14.31
1 2 3 3 1 2 2 3 1 49.32 59.58 64.12 14.80
30.31% 69.13% 75.00% 52.87% 67.51% 57.18% 52.43% 64.50% 50.14%
concentration (C, mol/L) and ultrasonic power (D, W) were selected as the four influencing factors in the orthogonal experiment when the NaOH concentration was fixed at 1 mol/L. Three levels were selected for the orthogonal experiment. Experimental parameters and their levels are given in Table 2, and the orthogonal array (OA) experimental used a L9 (34) (Table 3). Minitab-17 statistical software was used to analyze the experimental data of Sb extraction from L9 (34) orthogonal array. The optimal conditions are obtained based on range analysis. The results showed that temperature had the greatest influence on leaching rate of Sb followed by ultrasonic power, the sodium sulfide concentration and ultrasonic time. The orthogonal experiment results show that the optimal level is A2B2C3D3. Therefore, the optimum leaching conditions of Sb are followed: time is 60 min, temperature is 55 °C, the sodium sulfide concentration is 2 mol/L and ultrasonic power is 1500 W. Under the conditions, the average leaching rate of antimony was 94.50% after three repeated experiments with ultrasound. However, under the same reaction conditions, the leaching rate of antimony without ultrasound was only 58.37%. The leaching rate of antimony without ultrasound only increased to 70% when temperature was higher than 80 °C. Samuel found that the leaching rate of antimony was approximately 13% and 57% at 1 h and 6 h, respectively (Awe and Sandstrom, 2010). Ultrasound obviously reduces the leaching temperature and time of antimony.
3.6. Orthogonal experiment Orthogonal experiment was used to obtain the optimum leaching parameters. It can be seen from the single factor experiment that the main function of sodium hydroxide is to provide the basic conditions for the reaction and has little effect on the leaching rate of antimony. Therefore, the time (A, min), temperature (B, °C), the sodium sulfide
3.7. Gold leaching In order to study the leaching rate of gold after antimony removal, we compared the leaching rates of the raw ore and the treated ore under conventional and ultrasonic conditions, respectively (Fig. 7a). After leaching for 2 h, the leaching rate of raw ore is only 13.35% without ultrasound, the leaching rate of the treated gold ore reaches 40.56% without ultrasound and 68.90% under ultrasound. Ultrasound can also enhance leaching reaction of gold. The leaching process was basically completed after ultrasound for 2 h. The leaching rate of gold reached equilibrium. However, the leaching rate of gold increases with the increase of time in conventional leaching process. It takes 180 min to react completely. As shown in Fig. 7b, the slope of the regression linear equation represents the reaction rate. It can be seen that the frequency
Fig. 6. Effect of the ultrasonic power on the antimony removal rate (NaOH: 1 mol/L; Na2S: 2 mol/L; Time: 60 min; temperature: 40 °C). 4
Hydrometallurgy 190 (2019) 105161
P. Guo, et al.
Fig. 7. Relationship between gold leaching rate and time under different conditions (a), the Relation between 1- (1-x)1/3 and Time in the Leaching Process (b).
residue and the ultrasound-assisted leaching residue. As shown in Fig. 9, there are still large particles after conventional leaching for 6 h. After ultrasonic assisted leaching for 2 h, the particles are obviously small and uniform. The average particle size of the conventional leaching residue was about 26.84 μm (D50). However, the average particle size of the ultrasonic leaching residue was about 19.45 μm (D50). After ultrasonic extraction, the mineral surface becomes honeycomb porous. It proved that ultrasound enhanced the leaching rate and shorted time compared with the conventional leaching. The reason is that ultrasound strips the surface of material particles, reduces the mass transfer boundary layer and effectively improves the mass transfer process (Hasab et al., 2013). More importantly, the pyrite was broken by ultrasonic cavitation, which exposed the gold particles. The leaching liquid contacted with the gold phase through the pores and fissures in ore particles. In Fig. 1, the particulate gold is partly embedded around pyrite and partly completely encapsulated by pyrite. Some pyrites were decomposed after ultrasonic pretreatment. Gold particles can be fully contacted with solvents. Therefore, the leaching rate of the treated ore is higher than that of the raw ore. However, a small amount of the gold particles are still wrapped in pyrite. This part of gold has no interaction with reagents. This leads to the low leaching rate of gold. In addition, part of the leached gold is adsorbed by ferric hydroxide and reentered into the slag under alkaline conditions. The two reasons lead to that about 30% of the gold can not be leached.
factor increases under ultrasound. The frequency factor reflects the collision frequency of the reactant molecule. Therefore, the increase of the frequency factor plays a key role in promoting chemical reaction. The increase of frequency factor and the renewal of reaction interface are two coupling effects leading to the increase of chemical reaction rate. Meanwhile, ultrasound can destroy passive film and create the cavitation effect, which provide a new physical environment for the reaction (Zhang et al., 2016c). 3.8. Mineralogical analysis Fig. 8 is X-ray pattern of the raw ore and the treated ore. Although there was no significant change in the phase composition, the peak intensity of SiO2 and FeS2 phase decreased for the treated gold ore. These indicated that some substances in the raw ore (particularly FeS2) had been extracted. In refractory ores, gold is usually embedded in the lattice of pyrite (FeS2) and is in the form of highly dispersed micro-gold and sub-micro-gold (Fig. 1). The sulfide ore belongs to the refractory mineral. Even if ultrafine grinding is carried out, the gold particles cannot be completely exposed. So, gold cannot contact with leaching agent during leaching. At the same time, the sulfide ore interacts with the leaching agent and consumes a lot of reagents (Oncel et al., 2005). The decomposition of FeS2 exposes more micro and sub-micro gold. The leaching agent can make full contact with gold and the gold leaching rate is effectively improved. Fig. 9 is the SEM images of the raw ore, the convention leaching
Fig. 8. X-ray pattern of the raw gold ore (a) and the treated gold ore (b). 5
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Fig. 9. SEM of the raw gold ore (A), the conventional leaching residue (6 h) (B) and the ultrasound-assisted leaching residue (2 h) (C).
4. Conclusion
assisted leaching of neodymium from waste magnet using organic solvent. Hydrometallurgy 185, 61–70. Celep, O., Alp, I., Deveci, H., 2011a. Improved gold and silver extraction from a refractory antimony ore by pretreatment with alkaline sulphide leach. Hydrometallurgy 105 (3–4), 234–239. Celep, O., Alp, İ., Paktunç, D., Thibault, Y., 2011b. Implementation of sodium hydroxide pretreatment for refractory antimonial gold and silver ores. Hydrometallurgy 108 (1–2), 109–114. Elik, A., 2007. Ultrasonic-assisted leaching of trace metals from sediments as a function of pH. Talanta 71 (2), 790–794. Hasab, M.G., Rashchi, F., Raygan, S., 2013. Simultaneous sulfide oxidation and gold leaching of a refractory gold concentrate by chloride–hypochlorite solution. Miner. Eng. 50–51, 140–142. Li, Q., Li, D., Qian, F., 2009. Pre-oxidation of high-sulfur and high-arsenic refractory gold concentrate by ozone and ferric ions in acidic media. Hydrometallurgy 97 (1–2), 61–66. Li, Z.Y., Wang, W.W., Yue, K., Chen, M.X., 2016. High-temperature chlorination of gold with transformation of iron phase. Rare Metals 35 (11), 881–886. Mavrogenes, J.A., O’Neill, H.S.C., 1999. The relative effects of pressure, temperature and oxygen fugacity on the solubility of sulfide in mafic magmas. Geochim. Cosmochim. Acta 63 (7–8), 1173–1180. Mesa Espitia, S.L., Lapidus, G.T., 2015. Pretreatment of a refractory arsenopyritic gold ore using hydroxyl ion. Hydrometallurgy 153, 106–113. Ming, C., Chen, Z., 2014. Research Progress of Arsenic-bearing Refractory Gold Ore. Science & Technology Information. Oncel, M.S., Ince, M., Bayramoglu, M., 2005. Leaching of silver from solid waste using ultrasound assisted thiourea method. Ultrason. Sonochem. 12 (3), 237–242. Rusanen, L., Aromaa, J., Forsen, O., 2013. Pressure oxidation of pyrite-arsenopyrite refractory gold concentrate. Physicochem. Prob. Miner. 49 (1), 101–109. Sun, J.W., et al., 2019. Pilot plant test on the recovery of valuable metals from pyrite cinder by a combined process based on chlorinating roasting. T Indian I Metals 72 (4), 1053–1061. Ubaldini, S., Veglio, F., Beolchini, F., Toro, L., Abbruzzese, C., 2000a. Gold recovery from a refractory pyrrhotite ore by biooxidation. Int. J. Miner. Process. 60 (3–4), 247–262. Ubaldini, S., Veglio, F., Fornari, P., Abbruzzese, C., 2000b. Process flow-sheet for gold and
The antimony in refractory gold ores was selectively removed by ultrasound with alkaline sodium sulfide. The removal rate of antimony reaches 94.50% under the optimum conditions: the ultrasonic power is 1500 W, the Na2S concentration is 2 mol/L, temperature is 55 °C and time is 60 min and the NaOH concentration is 1 mol/L. Ultrasound enhances the removal efficiency of antimony from 58.37% to 94.50%. The influence degree of the factors is temperature > ultrasonic power > sodium sulfide concentration > reaction time. The leaching rate of gold after antimony removal increased from 13.35% to 40.56% under conventional leaching. Moreover, the leaching rate of gold after antimony removal was improved to 68.90% by ultrasound. Ultrasound breaks up mineral particles and decomposes pyrite to expose antimony and gold to leachate. Ultrasound has wide application prospects in the pretreatment and leaching field of gold ore. Acknowledgements This work was supported by the National Natural Science Foundation of China (U1702252). References Awe, S.A., Sandstrom, A., 2010. Selective leaching of arsenic and antimony from a tetrahedrite rich complex sulphide concentrate using alkaline sulphide solution. Miner. Eng. 23 (15), 1227–1236. Behera, S.S., Panda, S.K., Mandal, D., Parhi, P.K., 2019. Ultrasound and microwave
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Metals Soc. China 26 (9), 2479–2484. Zhang, Y.F., et al., 2016c. Ultrasound-assisted leaching of potassium from phosphoruspotassium associated ore. Hydrometallurgy 166, 237–242. Zhu, P., Zhang, X.J., Li, K.F., Qian, G.R., Zhou, M., 2012. Kinetics of leaching refractory gold ores by ultrasonic-assisted electro-chlorination. Int. J. Miner. Metall. Mater. 19 (6), 473–477.
antimony recovery from stibnite. Hydrometallurgy 57 (3), 187–199. Xing, Y.L., Brugger, J., Tomkins, A., Shvarov, Y., 2019. Arsenic evolution as a tool for understanding formation of pyritic gold ores. Geology 47 (4), 335–338. Zhang, G.W., Wang, S.X., Zhang, L.B., Peng, J.H., 2016a. Ultrasound-intensified leaching of gold from a refractory ore. ISIJ Int. 56 (4), 714–718. Zhang, X., Feng, Y.L., Li, H.R., 2016b. Enhancement of bio-oxidation of refractory arsenopyritic gold ore by adding pyrolusite in bioleaching system. Trans. Nonferrous
7
Contents lists available at ScienceDirect
Hydrometallurgy journal homepage: www.elsevier.com/locate/hydromet
Selective removal of antimony from refractory gold ores by ultrasound Ping Guo
a,b,c,d
, Shixing Wang
a,b,c,d,⁎
, Libo Zhang
a,b,c,d,⁎
T
a
State Key Laboratory of Complex Nonferrous Metal Resources Clean Utilization, Kunming University of Science and Technology, Kunming 650093, Yunnan, China National Local Joint Laboratory of Engineering Application of Microwave Energy and Equipment Technology, Kunming 650093, Yunnan, China Key Laboratory of Unconventional Metallurgical Ministry of Education, Kunming 650093, China d Faculty of Metallurgical and Energy Engineering, Kunming University of Science and Technology, Kunming 650093, Yunnan, China b c
A R T I C LE I N FO
A B S T R A C T
Keywords: Removal Antimony Refractory ore Ultrasound
Ultrasound is used to enhance the removal of antimony from the refractory gold ores in alkaline sodium sulfide leaching process. The effects of ultrasonic time, temperature, reagent concentration and ultrasonic power on antimony removal are discussed. The removal rate of antimony reached 94.50% when ultrasonic time was 60 min, sodium hydroxide concentration was 1 mol/L, sodium sulfide concentration was 2 mol/L, ultrasonic power was 1500 W and temperature was 55 °C. Under the conditions, the removal rate of antimony without ultrasound is only 58.37%. The results show that ultrasound can significantly improve the removal efficiency of antimony and reduce the leaching temperature and time of antimony. The leaching rate of gold increased from 13.35% to 40.56% after antimony removal. Moreover, the leaching rate of gold after antimony removal reached 68.90% under ultrasound. Therefore, ultrasound not only enhances the removal efficiency of antimony, but also improves the leaching rate of gold. The improvement of the leaching rate of antimony and gold is attributed to that the mineral particles are broken up and pyrite is decomposed by ultrasound.
1. Introduction Gold is widely used in jewelry, currency reserve and many industry fields. With large-scale gold mining, free milling resources increasingly depleted and the refractory ore will become the main resources in the future (Li et al., 2016). Refractory gold ore generally refers to ore with less than 80% cyanide leaching rate. There are many reasons for refractory behavior: gold is locked within pyrite/arsenopyrite (Zhang et al., 2016b), carbon-containing substances exist and gold combines with arsenic, antimony and other characteristic elements (Xing et al., 2019). In order to obtain higher gold recovery from refractory ores, it is necessary to adopt the pretreatment process before leaching. Various pretreatment methods have been used, such as roasting, pressure oxidation and biooxidation (Ming and Chen, 2014). However, these pretreatment processes have the followed disadvantages, for example, the discharge of SO2 and As2O3 in the roasting process, high investment cost for high pressure operation, and bacterial growth was inhibited by arsenic during bioleaching (Li et al., 2009; Rusanen et al., 2013; Sun et al., 2019; Ubaldini et al., 2000a). The alkaline pretreatment is an efficient method to remove arsenic, antimony and other harmful elements from ores. Espitia found that the removal amount of arsenic increased with the increase of time and hydroxyl ion
concentration in the pretreatment (Mesa Espitia and Lapidus, 2015). Awe et al. showed also that the removal rate of arsenic and antimony depended obviously on the hydroxide concentrations, temperature and the reaction time (Awe and Sandström, 2010). Although alkali pretreatment is an effective method, there are still some obvious shortcomings, such as high temperature and long time. Therefore, it is necessary to develop new alkali treatment method to overcome these disadvantages and improve the removal rate of antimony. Ultrasound has widely attracted attention in metallurgical field, especially for the leaching of refractory ores. The leaching rate of neodymium (Nd) from waste magnet reached 99.99% under ultrasound (Behera et al., 2019). Elik found that ultrasound significantly improved the leaching rate and shortened the leaching time of copper, lead, nickel, zinc and manganese in the sediments (Elik, 2007). Ultrasound increased also the leaching rate of refractory gold ores during electrochlorination because it reduced the diffusion resistance of HClO and promoted the diffusion of HClO into solid product layer and unreacted layer (Zhu et al., 2012). We also found that proper amount of sodium hydroxide could improve the leaching rate of gold and the excessive sodium hydroxide had a negative effect during the alkali pretreatment of refractory gold ores by ultrasound (Zhang et al., 2016a). These show that ultrasound can improve the leaching rate of metal. Therefore,
⁎ Corresponding authors at: State Key Laboratory of Complex Nonferrous Metal Resources Clean Utilization, Kunming University of Science and Technology, Kunming 650093, Yunnan, China. E-mail addresses: [email protected] (P. Guo), [email protected] (S. Wang), [email protected] (L. Zhang).
https://doi.org/10.1016/j.hydromet.2019.105161 Received 20 May 2019; Received in revised form 23 August 2019; Accepted 29 September 2019 Available online 19 October 2019 0304-386X/ © 2019 Elsevier B.V. All rights reserved.
Hydrometallurgy 190 (2019) 105161
P. Guo, et al.
Fig. 1. The form and distribution of gold in minerals.
microscope (VEGA3, TESCAN). Particle size of the leaching residue was analyzed by laser particle size distribution tester (JL-1177).
ultrasound is an effective tool in the metal extraction industry. In this study, ultrasound was used to intensify the removing process of antimony from the refractory gold ores. The effects of sodium sulfide concentration, sodium hydroxide concentration, temperature, time and ultrasonic power on the removal rate of antimony were studied in detail. The leaching of gold from the treated ore was also carried out.
2.3. Leaching tests The effects of concentrations of sodium sulfide (0.1–2 mol/L Na2S) and sodium hydroxide (0.5–2.5 mol/L NaOH), temperature (25–80 °C), time (20–100 min) and ultrasonic power on the removal rate of antimony were studied. The experiments were carried out in the circular beaker of 300 mL. The beaker was placed into a thermostatic waterbath equipped with a magnetic stirrer. The leaching temperature was controlled within ± 2 °C. The sodium sulfide and sodium hydroxide were firstly dissolved in water. 200 mL of the mixed solution (Na2S + NaOH) and 70 g of gold ore were added to the beaker. After the mixture was heated for 60 min with stirring, the solid residues were separated by filtration and were used to analyze the antimony content. The leaching of gold was carried out in 500 mL glass beaker. The reaction conditions are as followed: NaClO concentration is 1.5 mol/L, NaOH concentration is 1.5 mol/L, solid-liquid ratio is 3, ultrasonic power is 250 W, ultrasonic time is 2 h and the temperature is 35 °C. The gold content in the raw materials and the leach residues was determined by the fire assay method. The soluble gold was analyzed by inductively coupled plasma optical emission spectrometry. The leaching rate is calculated according to the formula.
2. Experimental 2.1. Materials The gold ore samples were obtained from Yunnan province in china. The samples were firstly dried and then grinded by ball mill. The average particle size of the mineral is 31.138 um (D50). According to mineralogical analysis, the sulfides in gold concentrate are pyrite, arsenopyrite, stibnite, sphalerite, galena, chalcopyrite and tetrahedrite. Carbonate minerals are mainly dolomite, and a small amount of calcite and siderite. Silicate minerals are mainly quartz, sericite, potassium feldspar, tetrahedrite, etc. Gold mainly exists in pyrite, arsenopyrite and other sulfides in the form of invisible gold (Fig. 1). Table 1 shows the chemical composition of gold ores determined by mineralogical analysis and X-ray fluorescence. The ore mainly contained 39.72% SiO2, 23.34% FeS2, 1.96% Sb and 24 g/t Au. The sodium sulfide and sodium hydroxide used in this experiment are all analytically pure.
C − C⎤ Leaching rate = ⎡1 − 0 × 100% ⎢ C0 ⎥ ⎦ ⎣
2.2. Characterization
where C0 represents the initial content of metal in the ore, C represents the metal content in the leaching residue.
In order to determine the content of antimony before and after leaching, the raw ore and the leaching residue were analyzed by inductively coupled plasma optical emission spectrometry. The solid sample was determined by X-Ray diffractometer (XRD, BRUKER-AXS, Germany) and mineral liberation analyzer (MLA250). The microstructure of the samples was characterized using scanning electron
3. Results and discussion 3.1. Effect of Na2S concentration The alkaline sulphide leaching was widely applied to pretreat antimony-bearing ores/concentrates. Ubaldini removed about 80% Sb from refractory ores using alkaline pretreatment method at 80 °C. (Ubaldini et al., 2000b). The Na2S concentration has remarkable influence on the removal rate of antimony. Therefore, the effect of Na2S concentration (0.1–2 mol/L) under ultrasound was firstly studied when temperature was 25 °C, time was 60 min, the NaOH concentration was 1 mol/L and ultrasonic power was 1500 W (Fig. 2). The antimony removal rate increased firstly from 47.65% to 75.2% and remained basically unchanged with the further increase of the Na2S concentration from 1.5 to 2 mol/L. The Na2S concentration has an obvious influence on the antimony leaching rate. This was mainly attributed to the decomposition of antimony sulphides, such as andorite, stibnite, and zinkenite. The decomposition of antimony sulphides can be given by the followed reactions (Celep et al., 2011a):
Table 1 Chemical composition of the gold ore samples. Compound
Content (%)
Compound
Content (%)
SiO2 FeS2 Al2O3 CaO MgO K2O As2O3 TiO2 Sb2O3 PbO Na2O
39.719 23.342 14.329 4.252 3.813 3.386 1.155 1.144 1.802 0.037 0.175
P2O5 ZnO F MnO Cr2O NiO CoO CuO ZrO SrO
0.206 0.110 0.113 0.059 0.051 0.090 0.035 0.061 0.044 0.022
(1)
2
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Fig. 2. Effect of the Na2S concentration on the antimony removal rate (Ultrasonic power: 1500 W; Time: 60 min; NaOH: 1 mol/L; temperature: 25 °C).
Sb2 S3 + 2S2 − → Sb2 S5 4 −
(2)
SbS2− + S2 − → SbS33 −
(3)
Fig. 4. Effect of the time on the antimony removal rate (Ultrasonic power: 1500 W, Na2S:2 mol/L, NaOH: 1 mol/L, temperature: 40 °C).
not conducive to the leaching of antimony (Mavrogenes and O'Neill, 1999). The reaction will slow down due to insufficient oxygen supply. Therefore, 40 °C was used in the following experiment.
Therefore, 2 mol/L of Na2S was used in the following experiment. 3.2. Effect of temperature
3.3. Effect of time
The effect of temperature on the antimony removal rate was also investigated (Fig. 3). The leaching rate of antimony was about 75.20% at 25 °C. Celep also confirmed that a large amount of antimony was dissolved in the alkaline sulphide solution even at 20 °C (Celep et al., 2011b). Moreover, the antimony removal rate is improved with the increase of temperature. When the temperature reaches 40 °C, the antimony removal rate is 90%. This shows that the increase of the reaction temperature is beneficial to the leaching process. Celep et al. found also that the leaching rate of antimony reached 71% and 84% at 50 and 70 °C, respectively (Celep et al., 2011a). Therefore, the leaching temperature was significantly reduced by ultrasound. However, the leaching rate of antimony decreased slightly with the further increasing of temperature. Higher temperature will increase the escape of oxygen in water and short the residence time of oxygen in the solution, which is
The effect of the time on the antimony leaching rate was studied when temperature was 40 °C, the Na2S concentration was 2 mol/L, the NaOH concentration was 1 mol/L and ultrasonic power was 1500 W (Fig. 4). When the reaction time is 60 min, the antimony leaching rate reaches 90.87% and the antimony content in the leaching residue decreases to 0.26%. With the prolongation of time, the antimony leaching rate slowly decreases. This may be that antimony is oxidized by oxygen in the air and some antimony precipitates into the slag in the form of sodium pyroantimonate. The chemical reaction occurs as followed (Ubaldini et al., 2000b):
2Na3SbS3 + 7O2 + 2NaOH + 5H2 O = 2NaSb (OH)6 + 3Na2S2 O3
(4)
Therefore, 60 min was used in the following experiment. 3.4. Effect of NaOH concentration The effect of the NaOH concentration was studied when temperature was 40 °C, the Na2S concentration was 2 mol/L, time was 60 min and ultrasonic power was 1500 W (Fig. 5). It can be seen from Fig. 4 that the leaching rate of antimony increases slightly with the increase of the sodium hydroxide concentration from 0.5 to 1.0 mol/L and is unchanged from 1.0 to 2.5 mol/L. Normally, S2− reacts with water as followed:
S2 − + H2 O = HS− + OH−
(5)
It is necessary to maintain basic conditions in order to minimize hydrolysis S2− and improve the leaching efficiency (Celep et al., 2011a). Moreover, sodium hydroxide can also extract antimony ore. The increase of the NaOH concentration is beneficial to the leaching of antimony. However, excessive alkali will causes the reaction between SiO2 and NaOH to form dense Na2SiO3. Na2SiO3 will bind to the surface or pore of mineral crystals and prevent the leaching of antimony. So the antimony leaching rate does not increase with the increase of alkali concentration. Therefore, 1 mol/L of NaOH was used in the followed experiment.
Fig. 3. Effect of the temperature on the antimony removal rate (Ultrasonic power: 1500 W; Na2S:2 mol/L; NaOH: 1 mol/L; Time: 60 min). 3
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Table 2 Orthogonal test factor level. Level
Factor
1 2 3
A
B
C
D
20 60 100
25 55 75
0.1 1 2
0 600 1500
Table 3 Orthogonal experimental results and range analysis.
Fig. 5. Effect of the NaOH concentration on the antimony removal rate (Ultrasonic power: 1500 W, Na2S:2 mol/L, Time:60 min, temperature: 40 °C).
3.5. Influence of ultrasonic power The effect of the ultrasonic power on the antimony removal rate was studied when temperature was 40 °C, the Na2S concentration was 2 mol/L, the NaOH concentration was 1 mol/L and the reaction time was 60 min (Fig. 6). The leaching rate of antimony increases with the increase of the ultrasonic power from 150 W to 600 W. The maximum leaching rate is about 92.60%. The increase of ultrasonic power is beneficial to the leaching of antimony. The pulse and cavitation generated by ultrasonic waves can greatly increase the turbulence intensity and the contact area, thus enhancing the mass transfer. Zhang proved that ultrasound improved the dissolution fraction (Zhang et al., 2016c).
Number
A
B
C
D
Leaching rate of antimony
1 2 3 4 5 6 7 8 9 K1 K2 K3 Rank
1 1 1 2 2 2 3 3 3 58.15 59.19 55.69 3.49
1 2 3 1 2 3 1 2 3 45.20 67.04 60.77 21.84
1 2 3 2 3 1 3 1 2 50.66 57.38 64.98 14.31
1 2 3 3 1 2 2 3 1 49.32 59.58 64.12 14.80
30.31% 69.13% 75.00% 52.87% 67.51% 57.18% 52.43% 64.50% 50.14%
concentration (C, mol/L) and ultrasonic power (D, W) were selected as the four influencing factors in the orthogonal experiment when the NaOH concentration was fixed at 1 mol/L. Three levels were selected for the orthogonal experiment. Experimental parameters and their levels are given in Table 2, and the orthogonal array (OA) experimental used a L9 (34) (Table 3). Minitab-17 statistical software was used to analyze the experimental data of Sb extraction from L9 (34) orthogonal array. The optimal conditions are obtained based on range analysis. The results showed that temperature had the greatest influence on leaching rate of Sb followed by ultrasonic power, the sodium sulfide concentration and ultrasonic time. The orthogonal experiment results show that the optimal level is A2B2C3D3. Therefore, the optimum leaching conditions of Sb are followed: time is 60 min, temperature is 55 °C, the sodium sulfide concentration is 2 mol/L and ultrasonic power is 1500 W. Under the conditions, the average leaching rate of antimony was 94.50% after three repeated experiments with ultrasound. However, under the same reaction conditions, the leaching rate of antimony without ultrasound was only 58.37%. The leaching rate of antimony without ultrasound only increased to 70% when temperature was higher than 80 °C. Samuel found that the leaching rate of antimony was approximately 13% and 57% at 1 h and 6 h, respectively (Awe and Sandstrom, 2010). Ultrasound obviously reduces the leaching temperature and time of antimony.
3.6. Orthogonal experiment Orthogonal experiment was used to obtain the optimum leaching parameters. It can be seen from the single factor experiment that the main function of sodium hydroxide is to provide the basic conditions for the reaction and has little effect on the leaching rate of antimony. Therefore, the time (A, min), temperature (B, °C), the sodium sulfide
3.7. Gold leaching In order to study the leaching rate of gold after antimony removal, we compared the leaching rates of the raw ore and the treated ore under conventional and ultrasonic conditions, respectively (Fig. 7a). After leaching for 2 h, the leaching rate of raw ore is only 13.35% without ultrasound, the leaching rate of the treated gold ore reaches 40.56% without ultrasound and 68.90% under ultrasound. Ultrasound can also enhance leaching reaction of gold. The leaching process was basically completed after ultrasound for 2 h. The leaching rate of gold reached equilibrium. However, the leaching rate of gold increases with the increase of time in conventional leaching process. It takes 180 min to react completely. As shown in Fig. 7b, the slope of the regression linear equation represents the reaction rate. It can be seen that the frequency
Fig. 6. Effect of the ultrasonic power on the antimony removal rate (NaOH: 1 mol/L; Na2S: 2 mol/L; Time: 60 min; temperature: 40 °C). 4
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Fig. 7. Relationship between gold leaching rate and time under different conditions (a), the Relation between 1- (1-x)1/3 and Time in the Leaching Process (b).
residue and the ultrasound-assisted leaching residue. As shown in Fig. 9, there are still large particles after conventional leaching for 6 h. After ultrasonic assisted leaching for 2 h, the particles are obviously small and uniform. The average particle size of the conventional leaching residue was about 26.84 μm (D50). However, the average particle size of the ultrasonic leaching residue was about 19.45 μm (D50). After ultrasonic extraction, the mineral surface becomes honeycomb porous. It proved that ultrasound enhanced the leaching rate and shorted time compared with the conventional leaching. The reason is that ultrasound strips the surface of material particles, reduces the mass transfer boundary layer and effectively improves the mass transfer process (Hasab et al., 2013). More importantly, the pyrite was broken by ultrasonic cavitation, which exposed the gold particles. The leaching liquid contacted with the gold phase through the pores and fissures in ore particles. In Fig. 1, the particulate gold is partly embedded around pyrite and partly completely encapsulated by pyrite. Some pyrites were decomposed after ultrasonic pretreatment. Gold particles can be fully contacted with solvents. Therefore, the leaching rate of the treated ore is higher than that of the raw ore. However, a small amount of the gold particles are still wrapped in pyrite. This part of gold has no interaction with reagents. This leads to the low leaching rate of gold. In addition, part of the leached gold is adsorbed by ferric hydroxide and reentered into the slag under alkaline conditions. The two reasons lead to that about 30% of the gold can not be leached.
factor increases under ultrasound. The frequency factor reflects the collision frequency of the reactant molecule. Therefore, the increase of the frequency factor plays a key role in promoting chemical reaction. The increase of frequency factor and the renewal of reaction interface are two coupling effects leading to the increase of chemical reaction rate. Meanwhile, ultrasound can destroy passive film and create the cavitation effect, which provide a new physical environment for the reaction (Zhang et al., 2016c). 3.8. Mineralogical analysis Fig. 8 is X-ray pattern of the raw ore and the treated ore. Although there was no significant change in the phase composition, the peak intensity of SiO2 and FeS2 phase decreased for the treated gold ore. These indicated that some substances in the raw ore (particularly FeS2) had been extracted. In refractory ores, gold is usually embedded in the lattice of pyrite (FeS2) and is in the form of highly dispersed micro-gold and sub-micro-gold (Fig. 1). The sulfide ore belongs to the refractory mineral. Even if ultrafine grinding is carried out, the gold particles cannot be completely exposed. So, gold cannot contact with leaching agent during leaching. At the same time, the sulfide ore interacts with the leaching agent and consumes a lot of reagents (Oncel et al., 2005). The decomposition of FeS2 exposes more micro and sub-micro gold. The leaching agent can make full contact with gold and the gold leaching rate is effectively improved. Fig. 9 is the SEM images of the raw ore, the convention leaching
Fig. 8. X-ray pattern of the raw gold ore (a) and the treated gold ore (b). 5
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Fig. 9. SEM of the raw gold ore (A), the conventional leaching residue (6 h) (B) and the ultrasound-assisted leaching residue (2 h) (C).
4. Conclusion
assisted leaching of neodymium from waste magnet using organic solvent. Hydrometallurgy 185, 61–70. Celep, O., Alp, I., Deveci, H., 2011a. Improved gold and silver extraction from a refractory antimony ore by pretreatment with alkaline sulphide leach. Hydrometallurgy 105 (3–4), 234–239. Celep, O., Alp, İ., Paktunç, D., Thibault, Y., 2011b. Implementation of sodium hydroxide pretreatment for refractory antimonial gold and silver ores. Hydrometallurgy 108 (1–2), 109–114. Elik, A., 2007. Ultrasonic-assisted leaching of trace metals from sediments as a function of pH. Talanta 71 (2), 790–794. Hasab, M.G., Rashchi, F., Raygan, S., 2013. Simultaneous sulfide oxidation and gold leaching of a refractory gold concentrate by chloride–hypochlorite solution. Miner. Eng. 50–51, 140–142. Li, Q., Li, D., Qian, F., 2009. Pre-oxidation of high-sulfur and high-arsenic refractory gold concentrate by ozone and ferric ions in acidic media. Hydrometallurgy 97 (1–2), 61–66. Li, Z.Y., Wang, W.W., Yue, K., Chen, M.X., 2016. High-temperature chlorination of gold with transformation of iron phase. Rare Metals 35 (11), 881–886. Mavrogenes, J.A., O’Neill, H.S.C., 1999. The relative effects of pressure, temperature and oxygen fugacity on the solubility of sulfide in mafic magmas. Geochim. Cosmochim. Acta 63 (7–8), 1173–1180. Mesa Espitia, S.L., Lapidus, G.T., 2015. Pretreatment of a refractory arsenopyritic gold ore using hydroxyl ion. Hydrometallurgy 153, 106–113. Ming, C., Chen, Z., 2014. Research Progress of Arsenic-bearing Refractory Gold Ore. Science & Technology Information. Oncel, M.S., Ince, M., Bayramoglu, M., 2005. Leaching of silver from solid waste using ultrasound assisted thiourea method. Ultrason. Sonochem. 12 (3), 237–242. Rusanen, L., Aromaa, J., Forsen, O., 2013. Pressure oxidation of pyrite-arsenopyrite refractory gold concentrate. Physicochem. Prob. Miner. 49 (1), 101–109. Sun, J.W., et al., 2019. Pilot plant test on the recovery of valuable metals from pyrite cinder by a combined process based on chlorinating roasting. T Indian I Metals 72 (4), 1053–1061. Ubaldini, S., Veglio, F., Beolchini, F., Toro, L., Abbruzzese, C., 2000a. Gold recovery from a refractory pyrrhotite ore by biooxidation. Int. J. Miner. Process. 60 (3–4), 247–262. Ubaldini, S., Veglio, F., Fornari, P., Abbruzzese, C., 2000b. Process flow-sheet for gold and
The antimony in refractory gold ores was selectively removed by ultrasound with alkaline sodium sulfide. The removal rate of antimony reaches 94.50% under the optimum conditions: the ultrasonic power is 1500 W, the Na2S concentration is 2 mol/L, temperature is 55 °C and time is 60 min and the NaOH concentration is 1 mol/L. Ultrasound enhances the removal efficiency of antimony from 58.37% to 94.50%. The influence degree of the factors is temperature > ultrasonic power > sodium sulfide concentration > reaction time. The leaching rate of gold after antimony removal increased from 13.35% to 40.56% under conventional leaching. Moreover, the leaching rate of gold after antimony removal was improved to 68.90% by ultrasound. Ultrasound breaks up mineral particles and decomposes pyrite to expose antimony and gold to leachate. Ultrasound has wide application prospects in the pretreatment and leaching field of gold ore. Acknowledgements This work was supported by the National Natural Science Foundation of China (U1702252). References Awe, S.A., Sandstrom, A., 2010. Selective leaching of arsenic and antimony from a tetrahedrite rich complex sulphide concentrate using alkaline sulphide solution. Miner. Eng. 23 (15), 1227–1236. Behera, S.S., Panda, S.K., Mandal, D., Parhi, P.K., 2019. Ultrasound and microwave
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