Abstract
On the basis of an experiment on ultrasonic enhanced ammonia leaching of low grade zinc oxide ores, the effects of the total ammonia concentration, the ratio between the NH3 concentration (CNH3) and that of ammonium sulfate (NH4)2SO4 (C(NH4)2SO4), and the ultrasound power on zinc leaching rate were studied. The results showed that the leaching efficiency of zinc observably increased with the increase of the total ammonia concentration, and that the ratios between CNH3 and C(NH4)2SO4 can remarkably affect the zinc extraction from the low grade zinc oxide ores. When the ratio between CNH3 and C(NH4)2SO4 is 2 to 1, the leaching rates of zinc are observably improved. The ultrasound can improve the leaching efficiency of zinc, and its effect was especially pronounced when the NH3 concentrations were low. The higher ultrasound power cannot sensibly improve the leaching rate of zinc, but it can improve the leaching speed and shorten the leaching time. Under the optimized conditions - total ammonia concentration of 8 mol/l, ratio between CNH3 and C(NH4)2SO4 of 2 to 1, and ultrasound power of 600 W – 83.33% of zinc is recovered.
1 Introduction
Being an important base metal, zinc (Zn) has been used in the galvanizing and the battery manufacturing industries [1, 2]. Over the past decades, the consumption of Zn sharply increased, while the stores of the high grade Zn ore decreased. With the shortage of Zn ore resource, the low grade Zn oxide ores in Lanping County in the Yunnan Province of China have attracted more and more attention [1, 3–5]. The mineralogical characteristics of the low grade Zn oxide ores from Yunnan Province are as follow: (1) the content of Zn is low [5–7]; (2) it contains large amounts of alkali gangue [8–10]; (3) to treat it with traditional hydrometallurgical technology is difficult [5, 9–11].
The increasing demand for Zn has required intensive studies on new hydrometallurgical processes for extracting Zn from low grade oxide ores [6]. An ammonia system metallurgical process was developed, and it was used for leaching Zn from low grade oxide ores [8, 11]. The ammonia system metallurgical process is not as mature as the sulfuric acid leaching system, so it has not been widely used in the modern industry. How to optimize the ammonia process is still a big problem in the field of hydrometallurgy which needs to be solved. In recent years, ultrasonic technology emerged as a preferred alternative for enhancing the leaching efficiency of the metal ores, and the effects of ultrasonic technology on the leaching of copper from the tailings [12], chromium from the multiple metal-bearing sludge [13], cobalt from the spent lithium-ion batteries [14], and silver from the solid waste [15] have been investigated. Ultrasonic technology showed particular advantages in improving metal extractions from the ores. However, the literature about the effect of ultrasound on the leaching efficiency of the low grade oxide ore is limited.
In this work, the effects of ultrasound, the total ammonia concentration, and the ratio between the concentration of NH3 (CNH3) and that of ammonium sulfate ((NH4)2SO4) C(NH4)2SO4 on the leaching recovery of Zn from the low grade Zn oxide ores were studied. The aim of this work was to develop a new hydrometallurgical technology, which intends to provide a green and economic method to extract Zn from the low grade Zn oxide ores.
2 Materials and methods
2.1 Materials and experimental setup
The low grade Zn oxide ores from Lanping County in the Yunnan Province of China were used to carry out the leaching experiments. The ores were crushed and ground to a powder of <0.075 mm with a jaw crusher and a wet ball mill. The chemical composition of the ores is given in Table 1, which shows that the Zn content in the ores is only 6.01%. The mineralogical analysis results are shown in Table 2, which shows the main Zn-containing phase is Zn oxide (ZnO, ZnCO3 and Zn4Si2O7(OH)2·H2O can be classified as oxide). The X-ray diffraction of the ores is displayed in Figure 1, which shows the ores are mainly composed of SiO2, CaCO3, PbCO3 and Zn4Si2O7(OH)2·H2O. Based on above analysis, we deduced that the main Zn-containing phase in the ores was hemimorphite (Zn4Si2O7(OH)2·H2O). The analytically pure NH3 and (NH4)2SO4 used in this experiment were obtained from Sinopharm Chemical Reagent Co., Ltd., Shanghai, China.
The chemical composition of low grade zinc oxide ore (mass fraction, %)
| ZnT | Fe | Pb | S | SiO2 | Al2O3 | MgO | CaO |
|---|---|---|---|---|---|---|---|
| 6.01 | 8.11 | 6.41 | 0.45 | 31.75 | 5.98 | 0.14 | 12.05 |
Mineralogical analysis of zinc-containing phases (mass fraction, %)
| Zinc phase | Zinc sulfate | Oxide | Sulfide | Franklinite et al | ZnT |
|---|---|---|---|---|---|
| Zinc content/% | 0.026 | 5.789 | 0.092 | 0.103 | 6.01 |
| Distribution/% | 0.43 | 96.32 | 1.53 | 1.71 | 100 |
X-ray diffraction pattern of low grade zinc oxide ore.
The ultrasonically assisted leaching experiments were performed in a 2000 ml glass reactor equipped with a magnetic stirrer, and an ultrasonic transducer was positioned at 3 cm below the pulp surface. All transducers are connected to an ultrasonic generator which generates ultrasonic waves with a frequency of 20 kHz under the powers of 200, 400 and 600 W. The ultrasonically assisted leaching apparatus is shown in Figure 2 (YTS-2000-20, Nanjing Hanzhou Science and Technology Ltd, China).
The ultrasonically assisted leaching apparatus.
2.2 The ultrasonically assisted leaching tests
In this study, the effects of (1) the total ammonia concentration (the total concentration of NH3 and (NH4)2SO4), (2) the ultrasound power and (3) the ratio between CNH3 and C(NH4)2SO4 on Zn leaching rate were studied. In all tests, the constant process parameters are as follows: temperature of 30°C, the solid to liquid ratio of 1:5 (leaching solution 1000 ml, ore 200 g), stirring speed of 300 rpm.
2.2.1 Effects of NH3 concentration and ultrasound on Zn leaching rate:
Experiment operating procedure: 200 g ore was transferred into a 2000 ml glass reactor and mixed with 1000 ml leaching liquid, which contained different total ammonia concentration (2 mol/l, 4 mol/l, 6 mol/l and 8 mol/l; the ratio between CNH3 and C(NH4)2SO4 was 1 to 1). The leaching experiments, operated with and without ultrasound, were carried out, and the ultrasound power was 200 W. After 10, 20, 30, 40, 50, 60, 90, 120 and 150 min, the concentration of Zn in the leaching solutions was measured, and the leaching rate of Zn was calculated.
2.2.2 Effects of the ratio between CNH3 and C(NH4)2SO4 on Zn leaching rate:
The ratio between CNH3 and C(NH4)2SO4 is an important parameter that can observably influence the leaching rate of Zn. The optimized ammonia concentration (8 mol/l) was obtained in Section 2.2.1, and the effects of the ratios between CNH3 and C(NH4)2SO4 on Zn leaching rate was studied under the constant process parameters.
Experiment operating procedure: 200 g ore was transferred into a 2000 ml glass reactor and mixed with 1000 ml leaching liquid, and the total ammonia concentration in the liquid was 8 mol/l. The ratios between CNH3 and C(NH4)2SO4 were 1 to 3, 1 to 2, 1 to 1, 2 to 1 and 3 to 1. The leaching experiments, operated with and without ultrasound, were carried out, and the ultrasound power was 200 W. After 10, 20, 30, 40, 50, 60, 90, 120 and 150 min, the concentration of Zn in the leaching solutions was measured, and the leaching rate of Zn was calculated.
2.2.3 Effects of ultrasound power on Zn leaching rate:
The ultrasound power is another important parameter that can observably influence the leaching rate of Zn. The optimized ratio between CNH3 and C(NH4)2SO4 on Zn leaching rate was obtained in Section 2.2.2, and the effects of the ultrasound powers on Zn leaching rate was studied under the constant process parameters.
Experiment operating procedure: 200 g ore was transferred into a 2000 ml glass reactor and mixed with 1000 ml leaching liquid, and the total ammonia concentration in the liquid was 8 mol/l. The ratio between CNH3 and C(NH4)2SO4 was 2 to 1. The ultrasound powers were 200, 400, and 600 W, respectively. After 10, 20, 30, 40, 50, 60, 90, 120 and 150 min, the concentration of Zn in the leaching solutions was measured, and the leaching rate of zinc was calculated.
2.3 Analytical methods
After the leaching experiments, the pulps were filtrated, and the leaching residues were washed with water. The leaching rate of Zn (ηZn, %) was calculated according to the following equation:
Where, CZn, V, m and WZn represented the Zn concentration of filtrate (g/l), the volume of filtrate (l), the mass of the Zn oxide ore (g) and the Zn content of the zinc oxide ore (%), respectively.
3 Results and discussion
3.1 Effects of NH3 concentration and ultrasound on Zn leaching rate
The effects of the total ammonia concentration (2 mol/l, 4 mol/l, 6 mol/l and 8 mol/l; the ratio between CNH3 and C(NH4)2SO4 was set 1 to 1) on Zn leaching rate with and without ultrasound were studied, and the leaching efficiency of Zn is summarized in Figure 3. The following comments can be made from it:
The leaching efficiency of Zn observably increases with the increase of the total ammonia concentration [16];
The ultrasound can improve the leaching efficiency of Zn, and its effect is especially pronounced when the CNH3 were low;
The Zn leaching rates in different leaching solutions with different total ammonia concentration whether carried out assisted with ultrasound are low. When the total ammonia concentration was 8 mol/l, the Zn leaching rate under the leaching experiment assisted with ultrasound was <60%.
The effects of ammonia concentrations on zinc leaching rate.
The ratio between CNH3 and C(NH4)2SO4 was 1 to 1.
In the alkaline leaching system, the dissolution process of hemimorphite can be described as follow [3].
From Equation (1), we can found out that NH4+ ions and NH3 molecules are the necessary reactants that can leach Zn from hemimorphite. The concentration of NH4+ ions and NH3 molecules in the leaching solution increased with increasing total CNH3, and as a result the leaching rates are improved. Obviously, as necessary reactants, the ratio between CNH3 and C(NH4)SO4 is another factor that can signally affect the leaching rate of Zn, and it was studied next using a total ammonia concentration of 8 mol/l.
3.2 Effects of ratio between CNH3 and C(NH4)2SO4 on Zn leaching rate
Figure 4 shows the effects of the ratios between CNH3 and C(NH4)2SO4 on the leaching rates of Zn when the total ammonia concentration was kept at 8 mol/l. According to the results shown in Figure 4, the ratios between CNH3 and C(NH4)2SO4 can remarkably affect the leaching rate of Zn from the low grade oxide ores, and two important phenomena deserve particular attention:
The effects of the ratio between CNH3 and C(NH4)2SO4 on zinc leaching rate.
When the ratios between the CNH3 and C(NH4)2SO4 were 1 to 3, 1 to 2 and 1 to 1, the leaching rates of Zn were very low, and the optimal leaching rate of Zn was <60%. The leaching rates of Zn basically remained constant after 60 min, which indicated that the leaching reaction showed in Equation (1) stopped. A reasonable explanation for this phenomenon is that the ratios were not appropriate, and the free NH4+ in the leaching solution became severely depleted. As a result, the leaching reaction stopped.
When the ratio between CNH3 and C(NH4)2SO4 was 2 to 1, which means the concentration of NH3 and that of NH4+ was 1 to 1, the leaching rates of Zn were observably improved. The leaching reaction showed in Equation (1) carried on slowly even after 60 min. A reasonable explanation for this phenomenon is that the ratio was appropriate, even after 60 min, the free NH4+ and NH3 in the leaching solution still existed. As a result, the leaching rate of Zn was seen to increase. Therefore the ratio of 2 to 1 can be chosen as the optimal ratio between CNH3 and C(NH4)2SO4, and the effects of ultrasound power on Zn leaching rates were studied under this condition.
3.3 Effects of ultrasound power on Zn leaching rate
The effects of the ultrasound powers on Zn extraction from the low grade Zn oxide ores were studied by varying the ultrasound powers at the frequency of 20 kHz and keeping the other parameters constant, and the result of Zn extraction for different durations are shown in Figure 5. From the data showed in Figure 5, the following conclusions can be made: (1) The ultrasound power cannot sensibly improve the leaching rate of Zn from the low grade Zn oxide ores, but the higher ultrasound power can improve the leaching speed and shorten the leaching time [17]. (2) The slope of the leaching rate curve gained from the leaching system with an ultrasound power of 600 W during the initial phase of the leaching experiment was the highest, and the leaching process in the leaching system with an ultrasound power of 600 W finished within 60 min, but that in the leaching system with an ultrasound power of 200 W finished within 120 min.
The effects of ultrasound power on zinc leaching rate.
In short, under optimized conditions: temperature of 30°C, solid to liquid ratio of 1:5, stirring speed of 300 rpm, reaction time of 60 min, NH3 concentration of 8 mol/l, ratio between CNH3 and C(NH4)2SO4 of 2 to 1, and an ultrasound power of 600 W, 83.33% of Zn is recovered.
4 Conclusions
The leaching efficiency of Zn was seen to increase with increasing total CNH3. The ultrasound can improve the leaching efficiency of Zn, and its effect was especially pronounced when the NH3 concentrations were low.
When the ratio between CNH3 and C(NH4)2SO4 was 2 to 1, meaning the concentration of NH3 and that of NH4+ was 1 to 1, the leaching rates of Zn were seen to improve.
The leaching process in the leaching system with an ultrasound power of 600 W finished under 60 min, but that in the leaching system with an ultrasound power of 200 W finished within 120 min.
Under optimized conditions, 83.33% of Zn can be recovered from the low grade Zn oxide ores.
About the authors
Shiwei Li obtained his doctorate from Northeastern University in 2013. Currently, he is working at the Kunming University of Science and Technology, China. His primary research interests include microwave metallurgy, hydrometallurgy, and comprehensive recovery of the wastes in metallurgy fields.
Weiheng Chen has started his MSc at the Kunming University of Science and Technology, China, where he currently carries out research on metallurgy and chemical engineering under the supervision of Professor Libo Zhang. His primary research interests include hydrometallurgy, and the comprehensive recovery of the wastes in metallurgy fields.
Shaohua Yin obtained her doctorate from Northeastern University in 2013. Currently, she is working at the Kunming University of Science and Technology, China. Her primary research interests include microwave metallurgy, the solvent extraction of rare earths and the efficient use of rare earth resources.
Aiyuan Ma is currently pursuing his doctorate at the Kunming University of Science and Technology, China. He is researching hydrometallurgy and unconventional metallurgy under the supervision of Professor Jinhui Peng. His main research subject is the extraction of zinc from the blast furnace with an ammonia system.
Kun Yang is currently pursuing her doctorate at the Kunming University of Science and Technology, China, where she is researching microwave energy application, metallurgy and chemical engineering under the supervision of Professor Jinhui Peng. Her main research subject is coupling various outfields to strengthen the leaching of nontraditional zinc resources.
Feng Xie has started his MSc at the Kunming University of Science and Technology, China, where he currently carries out research on microwave energy application, metallurgy and chemical engineering under the supervision of Professor Libo Zhang. His main research subject is the extraction and separation of rare earths by microfluidics technique.
Libo Zhang is a PhD supervisor at the Kunming University of Science and Technology, China, and mainly engages in the microwave heating applied in metallurgy, chemical engineering, materials, etc.
Jinhui Peng is a PhD supervisor at the Kunming University of Science and Technology, China, and mainly engages in microwave heating applied in metallurgy, chemical engineering, and materials science. He has received many awards, among which are the State Technological Invention Award, and the Natural Science Award of Kunming Province.
Acknowledgments
This work was supported by the National Program on Key Basic Research Project of China (973 Program, 2014CB643404), the Kunming University of Science and Technology Personnel Training Fund (KKSY201452089), and the National Natural Science Foundation of China (51404118).
References
[1] Liu ZY, Liu ZH, Li QH, Yang TZ, Zhang X. Hydrometallurgy 2012, 125–126, 137–143.10.1016/j.hydromet.2012.06.004Search in Google Scholar
[2] Li SW, Gao B, Tu GF. Hu L, Sun SC, Zhu GL, Yin SH. Constr. Build. Mater. 2014, 71, 121–131.Search in Google Scholar
[3] Li QX, Chen QY, Hu HP. J. Cent. South Univ. 2014, 21, 884–890.Search in Google Scholar
[4] He SM, Wang JK, Yan JF. Hydrometallurgy 2010, 104, 235–240.10.1016/j.hydromet.2010.06.011Search in Google Scholar
[5] Li CX, Xu HS, Deng ZG, Li XB, Li MT, Wei C. Trans. Nonferrous Met. Soc. China 2010, 20, 918–923.10.1016/S1003-6326(09)60236-3Search in Google Scholar
[6] Wang RX, Tang MT, Yang SH, Zhang WH, Tang CB, He J, Yang JG. J. Cent. South Univ. Technol. 2008, 15, 679–683.Search in Google Scholar
[7] Zhao Z, Long S, Chen Al, Huo GS, Li HG, Jia XJ, Chen XY. Hydrometallurgy 2009, 99, 255–258.10.1016/j.hydromet.2009.08.001Search in Google Scholar
[8] Liu ZY, Liu ZH, Li QH, Cao ZY, Yang TZ. Hydrometallurgy 2012, 125–126, 50–54.10.1016/j.hydromet.2012.05.006Search in Google Scholar
[9] He SM, Wang JK, Yan JF. Hydrometallurgy 2011, 108, 171–176.10.1016/j.hydromet.2011.04.004Search in Google Scholar
[10] Xu HS, Wei C, Li CX, Fan G, Deng ZG, Li MT, Li XB. Hydrometallurgy 2010, 105, 186–190.10.1016/j.hydromet.2010.07.014Search in Google Scholar
[11] Chen AL, Zhao ZW, Jia XJ, Long S, Huo GS, Chen XY. Hydrometallurgy 2009, 97, 228–232.10.1016/j.hydromet.2009.01.005Search in Google Scholar
[12] Zhang J, Wu AX, Wang YM, Chen XS. J. China Univ. Mining Technol. 2008, 18, 98–102.Search in Google Scholar
[13] Zhang P, Ma Y, Xie FC. J. Mater. Cycles Waste Manage. 2013, 15, 530–538.Search in Google Scholar
[14] Li L, Zhai LY, Zhang XX, Lu J, Chen RJ, Wu F, Amine K. J. Power Sources 2014, 262, 380–385.10.1016/j.jpowsour.2014.04.013Search in Google Scholar
[15] Oncel MS, Ince M, Bayramoglu M. Ultrason. Sonochem. 2003, 12, 237–242.Search in Google Scholar
[16] Ding ZY, Yin ZL, Hu HP, Chen QY. Hydrometallurgy 2010, 104, 201–206.10.1016/j.hydromet.2010.06.004Search in Google Scholar
[17] Xie FC, Li HY, Ma Y, Li CC, CAi TT, Huang ZY, YuanGQ. J. Hazard. Mater. 2009, 170, 430–435.Search in Google Scholar
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