Behavior of zinc from spent zinc-carbon batteries by selective leaching with sodium hydroxide

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1 Accepted Manuscript Behavior of zinc from spent zinc-carbon batteries by selective leaching with sodium hydroxide Shun Myung Shin, Gamini Senanayake, Jeong-soo Sohn, Jin-gu Kang, Dong-hyo Yang, Tae-hyun Kim PII: S X(08) DOI: doi: /j.hydromet Reference: HYDROM 2941 To appear in: Hydrometallurgy Received date: 25 July 2008 Revised date: 18 December 2008 Accepted date: 20 December 2008 Please cite this article as: Shin, Shun Myung, Senanayake, Gamini, Sohn, Jeong-soo, Kang, Jin-gu, Yang, Dong-hyo, Kim, Tae-hyun, Behavior of zinc from spent zinc-carbon batteries by selective leaching with sodium hydroxide, Hydrometallurgy (2009), doi: /j.hydromet This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.

2 Behavior of zinc from spent zinc-carbon batteries by selective leaching with sodium hydroxide Shun Myung Shin 1, Gamini Senanayake 3, Jeong-soo Sohn 1, Jin-gu Kang 1,2, Dong-hyo Yang 1, Tae-hyun Kim 1* 1 Minerals & Materials Processing Division, Korea Institute of Geoscience & Mineral Resources (KIGAM), Abstract 92 Kwahak-no, Yuseong-gu, Daejeon, Korea 2 Deparment of Resource Recycling, Korea University of Science & Technology (UST), 52,Eoeun-dong, Yuseong-gu, Daejeon, Korea 3 Faculty of Minerals and Energy, Murdoch University, Perth, WA 6150, Australia Physical methods such as crushing and sieving followed by magnetic separation steps were applied to separate non-magnetic material (88.4 wt%) from zinc-carbon spent batteries. The oversize material was processed by eddy current separation to recover zinc sheet, carbon rods, and plastics. The undersize fraction (-2.36 mm) with a metal composition of 15.5% Zn, 17.5% Mn, and 1.4% Fe was used for the leaching experiments under different conditions such as concentration of sodium hydroxide, temperature, agitation speed, and pulp density. Selective leaching using 4 mol dm -3 NaOH at 100 g dm -3 solid/liquid ratio, 80 o C and 200 rpm gave a zinc extraction of 82% and a manganese extraction of less than 0.1%. An overall zinc recovery was about 88.5% by the processes described in this study. Keywords: spent zinc-carbon batteries, selective alkaline leaching, sodium hydroxide * Corresponding author. Tel.: ; address: thkim@recycle.re.kr 1

3 1. Introduction The spent zinc-carbon batteries are composed of approximately 20% Mn, 20% Zn, magnetic materials and small amounts of carbon, plastics, and electrolyte. The spent zinccarbon batteries contain Zn, MnO 2, as well as ZnO and Mn 2 O 3 produced from discharging reaction (Bernardes et al., 2004; Park et al., 2006). About 15,000 tons of spent batteries have been annually generated as waste in Korea (Park et al., 2006). Among them, zinccarbon batteries and alkaline manganese batteries, which account for almost 90% of waste batteries, are composed of zinc, manganese and iron. Currently these spent zinc-carbon batteries are treated as general wastes and dumped in the landfills or incinerated. However, the metals contained in spent batteries disposed in landfills seep into the groundwater while incineration leaves behind exhaust gases, both methods polluting the environment. Thus, it is necessary to develop technologies to prevent the environmental pollution and recycle valuable metals. Hydrometallurgical processes are considered environmentally suitable and economical for treating even materials of low metal grade at small scale. They can process secondary resources containing different impurities (Rao et al., 1993; Jha et al., 2000) Reductive acid leaching of non-magnetic fraction of spent zinc-carbon batteries dissolves zinc, manganese, and iron and requires further unit operations for the separation and recovery of metal values. In the present study, alkaline leaching is used for the selective leaching of zinc from spent zinc-carbon batteries leaving iron and manganese in the residue. Experiments were conducted to examine the effect of various conditions such as reaction time, temperature, agitation speed, pulp density, and concentration of sodium hydroxide on the dissolution behavior of zinc. 2

4 2. Experimental 2.1. Sample preparation Figure 1. shows a schematic diagram of a typical zinc-carbon battery packaged in a zinc can that serves as both a container and an anode whilst the cathode is a mixture of manganese dioxide and carbon powder. Spent zinc-carbon batteries were collected from one of the regional collection centers in Seoul. A series of mechanical processing steps was conducted in the following sequence to yield enriched Zn and Mn particles: crushing, magnetic separation, sieving, and classification. After the spent zinc-carbon batteries were crushed and separated by magnetic separation, the non-magnetic material was subjected to screening with a 2.46 mm (8 mesh) sieve following the scheme shown in Figure 2. Thus, the physical treatment applied herein yielded 3 kinds of fractions, namely, magnetic material, non-magnetic 2.46 mm oversize and undersize. The undersize fraction was used as a feedstock for the leaching experiments. The preferred crystal pattern of zinc in the feedstock was determined using a XRD (RTC-300, Rigaku, Japan) with Cu K-α radiation, and the hand-picked zinc can from the spent zinccarbon battery also was analyzed by XRD in order to identify the form of zinc in the sample. The composition of the undersize was determined to be 15.5% Zn, 17.5% Mn, and 1.4% Fe by acid digestion and atomic absorption spectrophotometry (AAS, SpectrAA-400, Varian) Leaching procedure Sodium hydroxide solutions (500 ml) in the concentration range mol dm -3 were used in an experimental set up described in a previous publication (Shin et al., 2007). 3

5 After stabilization of the solution at the required temperature, the spent battery powder was added and the solution was agitated with a PTFE paddle at a constant rotation speed. Samples (5 ml) were filtered and analyzed for Mn, Zn, and Fe by AAS during leaching. 3. Results and Discussion 3.1. Composition of valuable metals in spent zinc-carbon batteries The magnetic and non-magnetic material content in different types of zinc-carbon batteries is shown in Table 1. The spent zinc-carbon batteries were separated into 10% magnetic material and 89% non-magnetic material consisting of 31% of 2.46 mm oversize and 58 % of 2.46 mm undersize. The elemental analysis of spent zinc-carbon batteries is shown in Table 2. The magnetic material contains 10.2% Fe, whereas the nonmagnetic materials for the oversize and undersize fractions contain only 0.1% Fe and 1.4% Fe, respectively. Therefore, most of iron in the spent batteries can be readily recovered by magnetic separation. It is interesting to note that the nonmagnetic 2.46 mm undersize contains most of Mn (91.8%) and a large portion of Zn (63.6%) available in the feed. The crushed zinc carbon battery sample contained both powder and plate type zinc. 37% of zinc still remained in the 2.46 mm oversize. This zinc sheets in the nonmagnetic 2.46 mm oversize could also be recovered by eddy current separation from plastics and vinyl (Park, et al., 2006) Characterization of feedstock samples 4

6 Zinc-carbon batteries contain primarily zinc and manganese dioxide in an electrolyte of ammonium chloride. At the battery anode, zinc is oxidized to produce energy producing the zinc oxide and zinc hydroxide. The reactions are as follows (Rao, 2006): Zn + MnO 2 + 2NH 4 Cl Zn(NH 3 ) 2 Cl 2 + Mn 2 O 3 H 2 O (1) 4Zn + 8MnO 2 + 8H 2 O + ZnCl 2 4Mn 2 O 3 H 2 O + ZnCl 2 Zn(OH) 2 (2) Zn + 4OH - ZnO H 2 O (3) Usually, spent zinc carbon batteries are not discharged completely, therefore, some metallic zinc may still remain in the batteries. The amorphous nature of the 2.46 mm undersize fraction used for leaching made the XRD analysis difficult. In order to confirm the presence of zinc metal, zinc can was hand-picked from spent batteries and analyzed by XRD. The XRD pattern (Figure 3) shows characteristic peaks of zinc metal as well as zinc oxide so remnant zinc metal is expected within the feedstock for leaching Potential-pH diagrams and zinc dissolution In the caustic soda leach process (Merrill and Lang, 1965; Cusanelli et al., 1973; Valdez and Dean, 1975; Eacott et al., 1984), zinc is selectively dissolved in sodium hydroxide solutions, leaving behind iron and manganese in the leach residue. The published potential-ph diagrams (Hayes, 1993) for zinc-water system show that both zinc metal and zinc oxide can be dissolved in strong alkali according to Equations 4 and 5. The free energy and equilibrium constant for the dissolution of zinc metal is much larger than that for zinc oxide and both decrease with increasing temperature. 5

7 Zn + 2NaOH = Na 2 ZnO 2 + H 2 (4) ZnO + 2NaOH = Na 2 ZnO 2 + H 2 O (5) Figure 4 shows the potential-ph diagrams for zinc-water system to highlight the effect of temperature. At 25 o C the ZnO/ZnO 2-2 line shifts to the right indicating the need for a higher ph or concentrated alkali to dissolve a high concentration of zinc(ii) in the form of ZnO 2-2 ions. However, the increase in temperature from 25 o C to 80 o 2- C shifts the ZnO/ZnO 2 line to the left indicating the need for relatively low alkaline ph values to dissolve 0.1 mol dm -3 ZnO 2-2 at higher temperatures. Nevertheless, the calculated equilibrium concentration of zinc(ii) (g dm -3 ) in the form of ZnO 2-2 decreases with increasing temperature but increases with increasing alkali concentration (Figure 5). These preliminary calculations based on the assumption of (i) unit activity coefficients and (ii) the absence of ion-association, are useful in the rationalisation of zinc concentration in leach liquors, as described in section Selective leaching of zinc According to Figure 5, the predicted solubility of zinc(ii) in 4 mol dm -3 NaOH at 80 o C is about 12 g dm -3, which is similar to the measured value of approximately 17 g dm -3 in Table 3. However, there are significant analytical errors involved in AAS analysis due to large dilution factors. The zinc dissolution in 4 mol.dm -3 NaOH at 80 o C after 30 min increased from 7 g dm -3 to 17.6 g dm -3 with an increase in solid/liquid ratio from 50 to 200 g.dm -3 but there was a corresponding decrease in zinc extraction from 95% to 40% due to the saturated solubility of zinc(ii) being controlled by the sodium hydroxide concentration. However, zinc extraction after 30 min was about 80% at 100 g dm -3 pulp density and was 6

8 unaffected by changing the agitation speed from 50 rpm to 400 rpm. Thus, further testing was conducted at 200 rpm using 4 mol dm -3 NaOH and 100 g dm -3 pulp density. From the starting undersize fraction of initial mass ratio of Zn:Mn:Fe = 11:12:1, zinc was selectively leached to produce a leach liquor of 17 g dm -3 Zn, compared to low concentrations of manganese (9 mg dm -3 ) and iron (< 0.1 mg dm -3 ) (Table 3). The standard potential-ph diagram for the Mn-H 2 O system indicates manganese(ii) predominates as the complex anion MnO 2-2 in alkaline media at ph>12 used in this study. Figure 7 shows zinc extraction after 30 min as a function of initial sodium hydroxide concentration. The zinc extraction increased from 25% to 80% with increasing NaOH concentration from 2 mol dm -3 to 4 mol dm -3. This increase is also consistent with Figure 5 that shows an increase in dissolved zinc (II) concentration at 80 o C with an increase in NaOH concentration. According to Figure 5, the increase in temperature from 25 o C to 80 o C is expected to cause a decrease in concentration of dissolved zinc(ii) from 48.6 g dm -3 to 11.7 g dm -3. However, based on the feed analysis and pulp density, the highest possible zinc(ii) concentration is 15.5 g dm -3, so zinc extraction was practically insensitive to the leaching temperature range under the conditions used. But at a higher concentration of 6 mol dm -3 NaOH, the zinc extraction increased from 81% after 30 min to 87% after 120 min. Further analysis of zinc(ii) speciation on the basis of complexes such as Zn(OH) 2-4, Zn(OH) - 3, and Zn(OH) 2 0 is beyond the scope of this preliminary study. 4. Summary and conclusions 7

9 In this preliminary study, leaching of zinc from spent zinc-carbon battery powder in alkaline media was investigated for the selective extraction of zinc value in the batteries. The results show that: (1) 82% Zn can be selectively leached with <0.1% Mn from the spent batteries by stirring for 30 min with 4 mol dm -3 NaOH, 80 at 100 g dm -3 pulp density. (2) The concentration of zinc is dependent on the NaOH concentration and higher pulp densities decreased % zinc extraction; (3) An overall recovery of about 89% Zn from spent zinc carbon batteries was achieved by physical separation, screening and leaching. Acknowledgement This study was supported by a grant from the Resource Recycling R&D Center (RRDC), a 21C Frontier R&D Program of the Ministry of Education, Science and Technology (MEST) of Korea. The authors would like to thank the MEST for the financial support. References Bernardes, A.M., Espinosa, D.C.R., Tenorio, J.A.S., Recycling of batteries: a review of current processes and technologies, J. Power Sources, 130, Cusanelli, D.C., Coffin, L.D., Rajcevic, H.P., U.S. Patent: Eacott, J.G., Robinson, M.C., Busse, E., Burgener, J.E., Burgener, P.E., Techno-economic feasibility of zinc and lead recovery from electric arc furnace baghouse dust, Canadian Min. Metal. Bull. 77(869),

10 Rao, S.R., 2006, Resource Recovery and Recycling from Metallurgical Wastes, Elsevier, Amsterdam, pp. 543 Hayes, P.C., Process Principles in Minerals and Materials Production, Hayes Publishing Company, QLD 4075, Brisbane, pp. 540 Jha, M.K., Kumar,V., Singh, R.J., Review of hydrometallurgical recovery of zinc from industrial wastes, Conservation & Recycling 33, Merrill, C.C., Lang R.S., USBM Report RI: Park, J.T. Kang, J.G.., Sohn, J.S., Yang, D.H., Shin, S.M., Physical Treatment for Recycling Commercialization of Spent Household Batteries, J. Korean Inst. of Resources Recycling 15(6), Rao, K.S., Sahoo, P.K., Jena, P.K., Extractions of zinc from ammoniacal solutions by Hostarex DK-16, Hydrometallurgy 31, Shin, S.M., Kang, J.G.., Yang, D.Y., Sohn, J.S., Development of Metal Recovery Process from Alkaline Manganese Batteries in Sulfuric Acid Solutions, Materials Transactions 48(2), Valdez, E.G., Dean K.C., USBM Report: Youcai, Z., Stanforth, R., Integrated hydrometallurgical process for production of zinc from electric arc furnace dust in alkaline medium, J. Hazardous Materials B 80,

11 Table captions Table 1. The weight-percentage of magnetic and nonmagnetic materials in various types of spent zinc-carbon batteries. Table 2. Average composition of valuable metals in spent zinc-carbon batteries. Table 3. Metal ion composition of leach liquor 10

12 Figure captions Fig. 1. Schematic diagram of a typical zinc-carbon battery cross section Fig. 2. Process diagram for physical separation of battery components Fig. 3. XRD patterns of zinc sheets from as is spent zinc-carbon batteries. Fig. 4 Potential-pH diagram for zinc-water system in the temperature range o C and 0.1 mol dm -3 Zn(II) (based on HSC 6.1). Fig. 5. Effect of temperature and sodium hydroxide concentration on zinc(ii) in Eq. 2 (based on equilibrium constant in Fig.4) Fig. 6. Effect of initial NaOH concentration on the zinc extraction after 30 min (80, 100 g dm -3 pulp density, 250 rpm, -8 mesh) Fig. 7. Variation of zinc extraction with reaction time. (6.0 mol dm -3 NaOH, 80, 100 g dm -3 pulp density, 200 rpm, -8 mesh) 11

13 Figure1 Fig. 1. Schematic diagram of a typical zinc-carbon battery cross section

14 Figure2 10.3% Spent zinc-carbon batteries Shape separation Crushing (under 10 or 20 mm) 1.3% Magnetic separation Magnetic material Non-magnetic material 88.4% Iron scrap 30.8% 8 mesh oversize 8 mesh undersize Eddy current separation Zinc-sheet Carbon rod, plastics Chemical treatment Fig. 2. Process diagram for phyical separation of battery components 57.6%

15 Figure3 : ZnO : Zn Fig. 3. XRD patterns of zinc sheets from as is spent zinc-carbon batteries.

16 Figure4 Eh (Volts) Zn - H2O - System at 25.00, 40.00, and C Zn(+2a) ZnO ZnO2(-2a) Zn H 2O limits C:\HSC6\EpH\Zn40-80.iep ph ELEMENTS Molality Pressure Zn 1.000E E+00 Fig. 4 Potential-pH diagram for zinc-water system in the temperature range o C and 0.1 mol dm -3 Zn(II) (based on HSC 6.1).

17 Figure5 [Zn(II)] g dm [NaOH] mol dm -3 T o C 25 Fig. 5. Effect of temperature and sodium hydroxide concentration on zinc(ii) in Eq. 2 (based on equilibrium constant in Fig.4)

18 Figure6 Zn Extraction(%) NaOH Concentration (M) Fig. 6. Effect of initial NaOH concentration on the zinc extraction after 30 min (80, 100 g dm -3 pulp density, 250 rpm, -8 mesh)

19 Figure7 Zn Extraction(%) Time (min) Fig. 7. Variation of zinc extraction with reaction time. (6.0 mol dm -3 NaOH, 80 o C, 100 g dm -3 pulp density, 200 rpm, -8 mesh)

20 Table 1. The weight-percentage of magnetic and nonmagnetic materials in various types of spent zinc-carbon batteries. Battery type sieve size Magnetic Nonmagnetic material (wt.%) (mm) Material (wt.%) Total mm mm (wt.%) AA C D R25A Ave Loss 1

21 Table 2. Average composition of valuable metals in spent zinc-carbon batteries. (%) Fe, % Mn, % Zn, % magnetic material nonmagnetic +8 mesh mesh material Total

22 Table 3. Metal ion composition of leach liquor Metal Fe Zn Cu Mn Concentration of metal ion mg dm -3 (ppm) < g dm -3 < mol dm -3 NaOH leaching solution at 80 o C, and 200 rpm after 30 min leaching time. 1