Session 8: Thermal Treatment & Recyclingpublished_or_final_versio

Shih, K

Tang, Y

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Title Copper Stabilization in Beneficial Use of Waterworks Sludge andCopper-laden Electroplating Sludge for Ceramic MaterialsAuthor(s) Shih, K; Tang, YCitationThe 1st Symposium of International Waste Working Group -Asian Region Branch (IWWG-ARB), Sapporo, Japan, 18-21 March2013. In the Proceedings of the 1st Symposium of InternationalWaste Working Group - Asian Region Branch, 2013, p. article no.8-5Issued Date 2013URL http://hdl.handle.net/10722/190270Rights Creative Commons: Attribution 3.0 Hong Kong LicenseThe 1st IWWG-ARB Symposium, 18-21 March 2013, Hokkaido University, Japan   1 Copper Stabilization in Beneficial Use of Waterworks Sludge and Copper-laden Electroplating Sludge  for Ceramic Materials  Kaimin Shih*, Yuanyuan Tang  Department of Civil Engineering, The University of Hong Kong, Pokfulam Road, Hong Kong SAR, China 1. INTRODUCTION Industrial processes such as electroplating always produce solid sludge containing significant amounts of toxic metal-laden compounds (Peng & Tian, 2010). In China, electroplating sludge discarded every year contains more than 100,000 tons of hazardous metals (Wang, 2006). A widely accepted treatment process is the stabilization/solidification (S/S) method, which can convert hazardous wastes into chemically stable solids (Sophia & Swaminathan, 2005; Chen et al., 2011). The S/S method achieves pollutant encapsulation through an interlocking framework of hydrated minerals (Sophia & Swaminathan, 2005; Zhou et al., 2006). In general, the S/S products are ultimately disposed of in secure landfills (Chen et al., 2011). Even after solidification and encapsulation, the metal-laden sludge still exhibits considerable long term metal leachability (Yousuf et al., 1995). The limited number of landfills capable of accepting S/S substances, together with their adverse environmental impacts (Malviya & Chaudhary, 2006), has made the development of effective and financially viable treatment technologies essential.  In our previous studies (Tang et al., 2010; 2011), the simulated copper-sludge were found to be able to react with the aluminum-rich precursors and form CuAl2O4 spinel phases after a 3-h sintering process. The metal leachability after thermal treatment was also significantly reduced due to the formation of spinel phases (Tang et al., 2010; 2011). As a waste-to-resource technology, the use of waste sludge resulting from water and wastewater treatment processes has attracted much attention (Babatunde & Zhao, 2007). In water treatment, for example, all processing systems generate a substantial amount of sludge with the residues of treatment chemicals used as coagulants (commonly aluminum-based), and the use of aluminum-rich sludge as raw material for ceramic products has shown promise (Vicenzi et al., 2005).  Since water treatment works in Hong Kong use aluminum-based coagulants (aluminum sulphate, aluminum chloride, poly aluminum sulphate, etc.) to facilitate particulate sedimentation. In this study, we attempted to evaluate the potential use of such waterworks sludge for immobilizing metal-laden electroplating sludge within a 3-h sintering scheme. The 1st IWWG-ARB Symposium, 18-21 March 2013, Hokkaido University, Japan   2 2. MATERIALS AND METHODS 2.1. Sample preparation The Cu-containing electroplating sludge was collected from an industrial sludge treatment facility in Guangdong Province in China, and the collected sludge was dried at 105 oC for further sintering experiments in this study. The sludge elemental compositions detected via X-ray fluorescence spectroscopy (XRF; JEOL JSX-3201Z) was normalized by their oxide forms (Table 1) and showing copper as the predominant constituent. A waterworks sludge sample collected in Hong Kong was heated for using as an aluminum-rich ceramic precursor. The sludge was dried and fired at 900 oC for 30 min to remove the organic content and then ground into powder for elemental composition analysis by XRF. Normalization into metal oxides (Table 2) shows aluminum to be the predominant constituent. Samples for sintering experiments were prepared by mixing 900 oC calcined waterworks sludge with the dried electroplating sludge for a total dry weight of 60 g at a Cu:Al molar ratio around 1:2.5 (with excess alumina available for copper incorporation). The mixing process was carried out by ball milling the powder in water slurry for 18 h. The slurry samples were dried and homogenized by mortar grinding, pressed into 20-mm pellets at 480 MPa to ensure consistent compaction of the powder samples for the sintering process. Table 1-Major compositions of the dehydrated copper-bearing electroplating sludge Components CuO SO3 Al2O3 SiO2 CaO Fe2O3 Others Weight Percentage (wt%) 64.74 19.91 4.94 3.19 3.07 2.57 0.77 Table 2-Major compositions of incinerated waterworks sludge. Components Al2O3 SiO2 P2O5 Fe2O3 SO3 K2O CaO TiO2 MnO As2O3 Weight Percentage (wt%) 56.53 30.16 3.81 6.17 0.55 1.28 0.48 0.31 0.66 0.05 2.2. Metal incorporation To identify the potential phases responsible for the metal incorporation mechanisms in a 3-h short sintering scheme, the pelletized powder mixture samples were fired in a high-temperature furnace (LHT 02/16 LB, LBR, Nabertherm Inc.) for a fixed 3-h dwelling time at targeted sintering temperatures ranging from 750 to 1250 oC. After sintering, the samples were air-quenched and ground into powders for XRD analysis and the leaching test. Phase transformation during sintering was monitored using the powder XRD technique. The step-scanned XRD pattern of each powder sample was recorded by a Bruker D8 Advance X-ray powder diffractometer equipped with Cu Kα1,2 X-ray radiation source (40 kV, 40 mA) and a LynxEye detector. The 2θ scanning range was 10 to 90º, and the step size was 0.02º with a scan speed of 0.8 s/step. Qualitative phase identification was executed by matching powder XRD patterns with The 1st IWWG-ARB Symposium, 18-21 March 2013, Hokkaido University, Japan   3 those retrieved from the standard powder diffraction database of the International Centre for Diffraction Data (ICDD PDF-2, Release 2008).  2.3. Leaching procedure A prolonged leaching test was employed in this study to further the discussion of the long-term leachability and leaching behavior of waste materials. As the goal of this test was to distinguish the leaching characteristics of different copper-bearing phases, single-phase samples were considered preferable in the leaching experiment. Therefore, after identifying the potential copper-containing phase(s) in the sintered products, single-phase copper samples were further fabricated by extending the sintering time. In the modified leaching procedure, 10 mL of pH 2.9 acetic acid solution was used as the leaching fluid for 0.5 g of sample powder in each leaching vial. The leaching vials were rotated end-over-end at 60 rpm for agitation periods of 0.75 to 22 days. At the end of each agitation period, the leachates were filtered with 0.2 µm syringe filters. Their pH values were measured with a pH meter (Thermo Scientific), and their metal concentrations with an ICP-AES (Perkin-Elmer Optima 3300 DV). 3. RESULTS AND DISCUSSION 3.1. Characterization of raw materials The XRD pattern of the 105 oC dried electroplating sludge in Figure 1 shows that the predominant crystalline Cu-containing phase was detected to be posnjakite (Cu4(SO4)(OH)6(H2O), PDF#83-1410). Other Cu-containing crystalline phases were identified as malachite (Cu2(OH)2CO3, PDF#76-0660) and copper oxide (CuO, PDF#80-1268). The XRD pattern in Figure 2 further indicates that the aluminum component may exist as mullite and poor-crystalline phase(s) in the calcined sludge. A strong quartz signal was also found, which may reflect the second-largest component (silicon) detected by XRF.  The 1st IWWG-ARB Symposium, 18-21 March 2013, Hokkaido University, Japan   4  Figure 1. XRD pattern of the dehydrated copper-bearing electroplating sludge. The crystalline phases are identified as:  posnjakite (Cu4(SO4)(OH)6(H2O), PDF#83-1410);  gypsum (Ca(SO4)(H2O)2, PDF#70-0982);  malachite (Cu2(OH)2CO3, PDF#76-0660);  silicon oxide (SiO2, PDF#82-1569);  copper oxide (CuO, PDF#80-1268);  magnetite (Fe3O4, PDF#0866).   Figure 2. XRD pattern of waterworks sludge calcined at 900 oC for 30 min. The standard patterns retrieved from the ICDD database include quartz (SiO2, The 1st IWWG-ARB Symposium, 18-21 March 2013, Hokkaido University, Japan   5 PDF#79-1910) and mullite (3Al2O3⋅2SiO2, PDF#79-1455). 3.2. Incorporation of copper during sintering process XRD patterns in Figure 3 demonstrate the phase transformation at temperatures ranging from 650 to 1150 oC in a 3-h sintering scheme. The peaks of CuAl2O4 phase were first observed in the 650 oC sintered sample. The increased peak intensity was found in the sample sintered at 850 oC for 3 h. However, the substantial development of the CuAl2O4 spinel phase occurred when the sample was sintered at 1000 oC. The signal of CuAl2O4 spinel phase continued until the temperature reached 1150 oC. Further heating will cause the generation of the other copper-containing phases, i.e. CuAlO2, Cu2O and CuO. The decomposition of CuAl2O4 spinel at higher temperatures can be organized in the following way (Tang et al., 2010):  2CuAl2O4 → 2CuAlO2 + Al2O3 + 0.5O2                       (1) 2CuO → Cu2O + 0.5O2                          (2) Cu2O + Al2O3 → 2CuAlO2                                 (3)  When the transformation of aluminum and silicon was considered, at temperatures lower than the decomposition temperature of the CuAl2O4 spinel, the excess aluminum and silicon existed as mullite, together with the calcium silicate phase. But at higher temperatures, due to the decomposition of the CuAl2O4 spinel structure the excess aluminum existed as α-Al2O3, which was different from the regeneration of mullite phase when sintering CuO with kaolinite and mullite precursors (Tang et al., 2011).  According to the CuAl2O4 XRD pattern database (PDF#78-1605), its major peaks are located at 2θ = 36.868, corresponding to the diffraction planes of (3 1 1). Therefore, the 2θ range of 36.5-37.2o was selected to further observe the variation of CuAl2O4 spinel with the elevated temperatures (Figure 4). The substantial increase of CuAl2O4 peak intensity occurred at 950 oC, and similar peak intensities within the temperature range of 950-1050 oC were observed. The decomposition of CuAl2O4 spinel was observed with the decrease of CuAl2O4 peak intensity due to the reaction shown in Eqs. (1-3).  The 1st IWWG-ARB Symposium, 18-21 March 2013, Hokkaido University, Japan   6   Figure 3. XRD patterns of the Cu-electroplating sludge + waterworks sludge system sintered at 650 to 1150 oC for 3 h. The crystalline phases are identified as: CuO (PDF#80-1268), CuAl2O4 (PDF#78-1605), CaCu2O3 (PDF#34-0284), Cu2O (PDF#77-0199), CuAlO2 (PDF#75-2356), α-Al2O3 (PDF#10-0173), anhydrite (CaSO4, PDF#37-1496), CaSO4⋅2H2O (PDF#70-0982) mullite (PDF#79-1455), cristobalite (PDF#76-0938), quartz (PDF#79-1910), and calcium silicate (CaSiO4, PDF#33-0303).  The 1st IWWG-ARB Symposium, 18-21 March 2013, Hokkaido University, Japan   7   Figure 4. Comparison of the growth of CuAl2O4 spinel phase by XRD patterns in 2θ between 36.6o and 37.2o for the Cu-electroplating sludge + waterworks sludge samples sintered at 650-1250 oC for 3 h.  3.3. Leachability of copper in product phase(s)  From section 3.2, the CuAl2O4 spinel was the predominant copper-containing product phase when sintering copper-sludge with waterworks sludge. Therefore, single-phase CuAl2O4 was prepared for the prolonged leaching experiments. To ensure the complete transformation into the CuAl2O4 without residual reactants, the Cu/Al molar ratio = 1:2 mixture pellets were sintered at 990 °C for 20 d and ball milled into powder form. The leachability of CuO, as the mainly existed form in copper-laden sludge heating without any addictives, was compared with that of CuAl2O4 product phase. When leaching CuO and CuAl2O4 samples in an acidic environment, the reaction processes can be described as:  CuO + 2H+ → Cu2+ + H2O                   (4) CuAl2O4 + 8H+ → Cu2+ + 2Al3+ + 4H2O                (5)  The copper concentrations in both the CuO and CuAl2O4 leachates are presented in Figure 5. The leached copper in CuO leachate reached around 2000 mg/L. However, throughout the entire leaching process, the concentration of the leached copper from the CuAl2O4 was significantly lower than that of the CuO leachate at the end of The 1st IWWG-ARB Symposium, 18-21 March 2013, Hokkaido University, Japan   8 leaching experiment. Figure 5 and its inset show that the leached copper from the CuO sample is two orders of magnitude greater than that from the CuAl2O4 sample. The result of prolonged leaching test favorably confirmed the good stabilization achieved through incorporating copper into a CuAl2O4 structure.   Figure 5. Variation of copper concentrations in the leachates from CuO and CuAl2O4 powder samples. The leaching solutions were acetic acid solution at pH 2.9. Each leaching vial was filled with 10 mL of extraction fluid and 0.5 g of powder, and then tumbled end-over-end from 0.75 to 22 d. 4. CONCLUSIONS When sintering the mixtures of copper-electroplating sludge and waterworks sludge precursors, the peaks of the CuAl2O4 phase were clearly identified, together with the disappearance of the initial copper-hosting phases (posnjakite, malachite) in the starting material. Sintering the sample mixture at 850 oC shows a distinguishable CuAl2O4 peak, and a substantial peak development was found at 950 oC. The maximum generation of the CuAl2O4 spinel was observed at around 1000 oC, and the CuAlO2 phase was observed at temperatures higher than 1100 oC. The leaching results show explicitly that the CuAl2O4 product phase is superior to the copper oxide phase for immobilizing hazardous copper over longer leaching periods.  As the waterworks sludge is able to initiate the crystallization of the CuAl2O4 at an attainable sintering temperature (~1000 oC), the incorporation of copper-sludge into the fabrication process of some common ceramic products, such as those used for The 1st IWWG-ARB Symposium, 18-21 March 2013, Hokkaido University, Japan   9 construction purposes, may be an effective and economical strategy to reduce the environmental hazard of copper-laden sludge. REFERENCES Babatunde A.O. & Zhao Y.Q. (2007) Constructive approaches toward water treatment works sludge management: An international review of beneficial reuses. Crit. Rev. Env. Sci. Tec., 37, 129-164. Chen Y.L., Ko M.S., Lai Y.C., Chang J.E. (2011) Hydration and leaching characteristics of cement pastes made from electroplating sludge. Waste Manage, 31, 1357-1363. Malviya R., & Chaudhary R. (2006) Factors affecting hazardous waste solidification/stabilization: A review. J. Hazard. Mater., 137, 267-276. Peng G. & Tian G. (2010) Using electrode electrolytes to enhance electrokinetic removal of heavy metals from electroplating sludge. Chem. Eng. J., 165, 388-394. Sophia A.C. & Swaminathan K. (2005) Assessment of the mechanical stability and chemical leachability of immobilized electroplating waste. Chemosphere, 58, 75-82. Tang Y., Shih K., Chan K. (2010) Copper aluminate spinel in the stabilization and detoxification of simulated copper-laden sludge. Chemosphere, 80, 375-380. Tang Y., Chui S.S.Y., Shih K., Zhang L. (2011) Copper stabilization via spinel formation during the sintering of simulated copper-laden sludge with aluminum-rich ceramic precursors. Environ. Sci. Technol., 45, 7609-7610. Vicenzi J., Moura Bernardes A., Perez Bergmann C. (2005) Evaluation of alum sludge as raw material for ceramic products. J. Ind. Ceram., 25, 171-180 Wang Q. (2006) Industrial solid waste disposal and recycling, China Environmental Science Press, Beijing. Yousuf M., Mollah A., Vempati R.K., Lin T.C., Cocke D.L. (1995) The Interfacial Chemistry of Solidification Stabilization of Metals in Cement and Pozzolanic Material Systems. Waste Manage, 15, 137-148. Zhou Q., Milestone N.B., Hayes M. (2006) An alternative to Portland Cement for waste encapsulation-The calcium sulfoaluminate cement system. J. Hazard. Mater., 136, 120-129.  

Copper Stabilization in Beneficial Use of Waterworks Sludge and Copper-laden Electroplating Sludge for Ceramic Materials

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Copper Stabilization in Beneficial Use of Waterworks Sludge and Copper-laden Electroplating Sludge for Ceramic Materials

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