Immobilization of Lead in Cathode Ray Tube Funnel Glass with

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Immobilization of Lead in Cathode Ray Tube Funnel Glass with Beneficial Use of Red Mud for Potential Application in Ceramic Industry Chang-Zhong Liao, Minhua Su, Shengshou Ma, Kaimin Shih, Yong Feng, Chengshuai Liu, and YingKeung Ho ACS Sustainable Chem. Eng., Just Accepted Manuscript • DOI: 10.1021/ acssuschemeng.8b02852 • Publication Date (Web): 27 Sep 2018 Downloaded from http://pubs.acs.org on October 6, 2018

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ACS Sustainable Chemistry & Engineering

Immobilization of Lead in Cathode Ray Tube Funnel Glass with Beneficial Use of Red Mud for Potential Application in Ceramic Industry

Chang-Zhong Liao a,b,#, Minhua Su c,d,#, Shengshou Ma a, Kaimin Shih b,*, Yong Feng b, Chengshuai Liu a,* and YingKeung Ho b

a

Guangdong Key Laboratory of Integrated Agro-environmental Pollution Control and

Management, Guangdong Institute of Eco-environmental Science & Technology, Guangzhou, China b c

Department of Civil Engineering, The University of Hong Kong, Hong Kong SAR

School of Environmental Science and Engineering, Guangzhou University, Guangzhou, China

d

Guangdong Provincial Key Laboratory of radioactive contamination control and resources, Guangzhou University, Guangzhou, China

*Corresponding author: Dr. Kaimin Shih, E-mail: [email protected]; Tel: +852 2859-1973; Fax: +852 2559-5337. Dr. Chengshuai Liu, E-mail: [email protected]; Tel: +86 20 87024373; fax: +86 20 87024123. # Authors contributed equally to this manuscript.

1 ACS Paragon Plus Environment

ACS Sustainable Chemistry & Engineering 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

ABSTRACT: The soon-to-become obsolete cathode ray tube (CRT) funnel glass can cause potential hazard to environment because of its high level of lead content. Red mud is a hazardous material due to its high alkalinity. Reusing them for ceramic industry by immobilizing into a chemically resistant matrix is an alternative strategy. In this study, the potential use of red mud to immobilize lead content in the CRT funnel glass was investigated. Results show that the lead in the CRT funnel glass was successfully incorporated into a chemically durable crystalline magnetoplumbite (PbFe12O19). The X-ray diffraction (XRD) results indicated that magnetoplumbite was the major lead-bearing crystalline phase in the products. The loading capacity of CRT funnel glass reached up to 25 wt.% in the mixture. Rietveld quantitative XRD analysis showed that Pb could be effectively incorporated into magnetoplumbite at a moderate temperature (900 ℃). Results from prolonged toxicity characteristic leaching procedure demonstrated that the leached lead concentration from the product was three orders of magnitude lower than that from the CRT funnel glass. Both the effective Pb incorporation and the substantial reduction of leached Pb after sintering with red mud suggested a promising method for the sustainable management of CRTs and red mud.

Keywords: CRT Funnel Glass; Magnetoplumbite; Lead Immobilization; Red Mud; Rietveld Quantitative Analysis.


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Introduction The rapid development of technology has revolutionized the electronics industry and considerably shortened the life span of electronic devices, causing a significant increase in the generation of electrical and electronic waste.1 Thus far, cathode ray tubes (CRTs) for televisions and computers have been generally abandoned, and the demand for new CRTs has continuously declined.2 Almost no CRT manufacturers have attempted to recover the glass from end-of-life CRTs into brand new monitors.1 The considerable number of obsolete CRTs makes their disposal a global environmental issue.3 In the European Union, 50,000–150,000 tons of CRTs are discarded every year.4 In the United States, despite the recovery of 6.9 million tons of CRTs, 330,000 tons are currently stockpiled by processors.5 In China, 43.11 million tons of CRT glass waste were generated in 2013.1 In Hong Kong, more than 490,000 television sets and CRT monitors are discarded annually from households.6 A CRT contains a considerable amount of lead, particularly in its rear part.7,8 As the rear part of the CRT, the funnel glass concentrates most of the lead content of the CRT; the total lead content commonly ranges between 22 and 28 wt.%.3,9 Hence, the CRT funnel glass is categorized as hazardous waste mostly because of the toxicity of lead. Lead is a non-biodegradable toxic metal. It may be released from the residues of many industrial processes, waste products, or the waste incineration ashes and then bio-accumulated via food chains to hazardous levels, damaging the kidneys and the nervous and reproductive systems.1,10 Children’s mental development is threatened by exposure to even low levels of lead.11 Inadequate management (e.g., disposal in landfills and open dumping) of CRT funnel glass leads to considerable environmental pollution because of the potential leaching of lead from the broken glass.3,6,7 Therefore, the global prevention of lead contamination through an appropriate disposal of lead-bearing CRT waste is urgently needed.



The recycling of lead from obsolete CRTs is uneconomic because lead is not as valuable as gold, silver, and other rare metals.1 Further, a considerable amount of highly toxic residue is generated during the recycling process.2 Besides recycling, vitrification is an alternative technology for the treatment of CRTs.12 However, this technology has the inconvenient drawback of its high cost. Treatment by vitrification is more expensive than disposal in landfills or stabilization into cementitious matrices because of the high energy consumption during vitrification.13 An effective and reliable treatment of waste CRTs requires a sound management strategy that is environmentally friendly and economically feasible.3

Recently, the incorporation of hazardous metals (e.g., Ni, Cu, Zn, and Cd) into a specific crystalline phase via thermal treatment has been well investigated and demonstrated to be a promising approach for hazardous waste treatment because of its cost-effectiveness and superior acid resistance.14-18 Further, a recent study demonstrated that magnetoplumbite (PbFe12O19) can be prepared by sintering the pure forms of lead hydroxide (Pb(OH2) and hematite (Fe2O3) (PbO + 6Fe2O3 → PbFe12O19) via a solid state reaction, simulating the stabilization process for the potential lead-bearing species in the sludge.10 The magnetoplumbite phase shows an extraordinarily higher chemistry durability in the case of acid corrosion than PbO.10 It has been pointed out that using CaCO3 as additive in the reactive system can enhance the incorporation of Pb into magnetoplumbite by Fe-rich precursor.19 Though these works offer the possibility of immobilizing Pb from the CRT funnel glass into magnetoplumbite, many efforts just focus on the reaction among the pure chemicals. The incorporation of Pb into magnetoplumbite by industrial wastes (such as red mud) when using CRT funnel glass as the target pollutant has not been investigated so far. Red mud is a type of waste residue from the Bayer process in the alumina extraction industry. The production of red mud is huge, more than 120 million tons per year globally.20 Because


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of its high aluminum (Al), iron (Fe), and calcium (Ca) content, red mud has been suggested as a low-cost raw material for the production of bricks and other ceramic products, depending on the final purposes of the utilization of stabilized products.21 Moreover, our previous study has proven that red mud is enriched with Fe2O3, showing a great potential for the treatment of CRT funnel glass to form magnetoplumbite.22

Therefore, in this study, red mud is beneficially used to treat CRT funnel glass. A number of processing parameters, including the mixing ratios of CRT funnel glass and red mud, the sintering temperature, and the dwell time, will be addressed. The quantitative X-ray diffraction (XRD) with the Rietveld refinement method is used to optimize the treatment process. Prolonged TCLP is conducted to evaluate the immobilization effect of lead in the obtained product, as compared to the CRT funnel glass.

Experimental Section Materials and sample preparation CRT funnel glass and red mud were used as the raw materials. The CRT funnel glass was collected from a CRT recycling center in Hong Kong. The red mud was collected from the Guangxi Pingguo alumina refinery (in China). Both the CRT funnel glass and the red mud were ball-milled into powder form and then dried at 120 °C for 12 h for the subsequent experiment. The mineralogical composition of the CRT funnel glass powder and red mud was verified by XRD. No obvious evidence of the crystalline phase was observed in the XRD pattern of the CRT funnel glass (Figure S1, Supplementary Material). Further, the major crystalline phases of red mud are hematite, perovskite, andradite, cancrinite, kaolinite, diaspore, gibbsite, and calcite, as reported by our previous study.22 The chemical composition analysis of the CRT funnel glass was performed on an X-ray fluorescence (XRF)



spectroscope (JEOL, JSX-3201Z), and the XRF result is shown in Figure S2 (Supplementary Material). PbO accounted for 21.5 wt.% of the CRT funnel glass powder. The Chemical compositions of red mud (metallurgical view) can be seen in Table S1 (Supplementary Material), which show that the Fe2O3 component makes up 39.45 wt.%.

In practice, the levels of metals to be incorporated into the construction ceramics will be low to ensure that the product properties are not compromised. However, to study the incorporation efficiency and mechanism of lead-containing phases and to immobilize Pb, the CRT funnel glass powder and the red mud were homogeneously mixed with different mixing weight proportions (CRT/red mud: 5/95, 10/90, 15/85, 20/80, 25/75 and 30/70), as listed in Table 1. The well-blended mixtures were pressed into pellets under an axial pressure of 250 MPa. Finally, the pellets were subjected to a well-controlled thermal treatment scheme. The sintering was conducted in a top-hat furnace (Nabertherm GmbH, Germany). The sintering temperatures were in the range of 700–1200 °C. The ramp up/down rate was 10 °C/min. The dwell times for the sintering were fixed at 1, 2, 3, 5, 7, and 10 h, respectively. After sintering, the fired samples were cooled to room temperature. To study the microstructure of the product, the sample was polished using decreasing grain sizes of a diamond paste for the scanning electron microscope (SEM) characterization performed using Hitachi S-3400N VPSEM at 20 kV.

XRD characterization The X-ray powder diffraction data were collected from a Bruker D8 Advance X-ray powder diffractometer equipped with a LynxEye detector and a Cu-Kα radiation source (λ = 1.541 Å) at 40 kV and 40 mA, respectively. The XRD measurements were performed in the 2θ ranged from 10° to 110° with a 0.02° step and a 2-s counting time at each step. Crystalline phases


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were identified via the Bruker software Diffrac-plus EVA supported by the Powder Diffraction File (PDF) database of the International Centre for Diffraction Data (ICDD, 2008). To quantify the contents of both the crystalline and the amorphous phases, the powder samples were mixed with 20% (in mass) CaF2 (Merck, Germany) as the internal standard. The Rietveld quantitative phase analysis was performed using the TOPAS 4.2 software (Bruker AXS, Germany).

Metal stabilization evaluation The leachability of the sintered sample was tested by a leaching procedure modified from the U.S. EPA Toxicity Characteristic Leaching Procedure (TCLP), using an acetic acid solution with a pH value of 4.88 ± 0.05 (extraction fluid #1) as the leaching fluid. To prepare the leaching sample, pellets with 25 wt.% of the CRT funnel glass and 75 wt.% of the red mud were initially sintered at 900 °C for 5 h. Then, the fired pellets were ground into a powder and subsequently pressed into pellets for another sintering at 900 °C for 10 h. The two-step sintering procedure was used to further ensure the complete formation of magnetoplumbite and its homogeneous distribution in the sample. The sintered pellets were crushed into coarse particles. These coarse particles were ball-milled for 12 h to ensure the homogeneity of the powder for TCLP. For the sake of comparison, the CRT funnel glass powder was produced in a prolonged TCLP experiment. The Brunauer-Emmett-Teller (BET) surface area of the leaching samples was measured using the nitrogen adsorption-desorption isotherms at liquid nitrogen temperature (77 K) on a Beckman Coulter SA3100 surface area and pore size analyzer. During the leaching test, each leaching vial was filled with 10 mL of the TCLP extraction fluid and 0.5 g of powder (solid-to-liquid ratio = 1:20). The vials were rotated endover-end at 60 rpm for agitation periods between 18 h and 21 days. At the end of each specified leaching period, the leachates were centrifuged and then filtered with 0.45-µm



nylon syringe filters. The concentrations of the leached ions were measured by an inductively coupled plasma atomic emission spectrometer (ICP-OES Optima 8000, Perkin Elmer).

Results and Discussion Optimization of mixing weight proportions of CRT funnel class and red mud To investigate the optimal weight proportions of the CRT funnel glass powder and the red mud for lead immobilization, the pellets of the CRT funnel glass and the red mud with various mixing weight proportions were sintered at 800 C and 1000 °C for 5 h, respectively. The XRD results are shown in Figures 1 and 2, and the phase compositions are summarized in Table 2. After heated at 800 °C for 5h, the XRD patterns of both C5R95 (5 wt.% CRT + 95 wt.% red mud) and C10R90 (10 wt.% CRT + 90 wt.% red mud) sintered samples were very similar, implying that the crystalline phases of C5R95 and C10R90 were alike. Five crystalline phases, including hematite (PDF no. 73-2234), gehlenite (PDF no. 79-2421), andradite (PDF no. 78-0319), perovskite (PDF no. 72-1192), and nepheline (PDF no. 090338), were identified in the sintered C5R95 and C10R90 samples. No Pb-Si-O crystalline phases (e.g., PbSiO3, Pb2SiO4, and Pb4SiO6) were observed; this is may because these lead silicates melt at temperatures in the range of 700-760 °C.23 In the C5R95 and C10R90 samples sintered at 800 °C for 5 h, magnetoplumbite (PDF no. 41-1373) was not detected (Figure 3a). However, when these two samples were sintered at 1000 °C for 5 h, magnetoplumbite was remarkably formed (Figure 3b). When the contents of the CRT funnel glass were increased to 15-25 wt.%, magnetoplumbite was found after treatment at 800 °C for 5 h (Figure 1b). Note that magnetoplumbite was not observed in the C30R70 sample sintered at 800 °C for 5 h (with as high as 30 wt.% of the CRT funnel glass) (Figure 1c). The reasons of not observing magnetoplumbite in 800 °C-sintered C5R95, C10R90 and C30R70 samples are likely due to: (i) the chemical compositions of C5R95, C10R90, and C30R70 are not


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within the area of producing magnetoplumbite in the Fe2O3-Al2O3-CaO-SiO2-TiO2-Na2OPbO-K2O-MgO phase diagram (mixture of CRT funnel glass and red mud); and (ii) the thermal driving force for the interaction between PbO in the CRT funnel glass and Fe2O3 in the red mud is not sufficient at 800 °C. For all 1000 °C-sintered samples, the diffraction signals of magnetoplumbite could always be detected by XRD. In Figure 3, note that the CRT percentage in the mixture considerably affected the formation of the magnetoplumbite phase. The intensities of the characteristic peak (114) in the XRD pattern of the magnetoplumbite phase increased remarkably with an increase in the loading of the CRT funnel glass. However, they decreased when the loading of the CRT funnel glass was more than 25 wt.%. These results indicated that the maximum loading amount of the CRT funnel glass for the incorporation of Pb into magnetoplumbite was approximately 25 wt.%. Therefore, for the subsequent studies on the effects of the sintering temperature and the dwell time on the magnetoplumbite formation, the content of the CRT funnel glass was chosen to be 25 wt.% in the mixture.

Effect of sintering temperature on the formation of magnetoplumbite Different sintering temperatures can provide different driving forces to overcome the energy barriers present in solid-state reactions. A thermodynamic condition is one of the most important factors that promotes the solid-state reactions.18 The C25R75 mixture containing 25 wt.% of the CRT funnel glass and 75 wt.% of the red mud was prepared to determine the effect of the sintering temperature on the formation of magnetoplumbite. The XRD patterns of the sintered C25R75 samples are shown in Figure 4. When sintering at 700 °C for 5 h, we observed no magnetoplumbite formation. The major crystalline phases in the 700 °C sintered sample were still hematite, andradite, perovskite, and nepheline (Table 3). The formation of magnetoplumbite was observed at 800 °C and up to 1100 °C. When the temperature was



elevated to 1200 °C, the diffraction signals of magnetoplumbite disappeared (Figure 4b). Magnetoplumbite might become amorphous as the molten product at 1200 °C. The phase equilibrium diagram of the PbO–Fe2O3 system shows that magnetoplumbite melts at a high temperature.24 Our experimental results also showed that the 1200 °C sintered sample was molten (as shown in Figure S3, Supplementary Material). This may explain why the diffraction signals of magnetoplumbite in the 1200 °C sintered sample were not detected by XRD.

In Figure 4b, we noted that the intensities of the characteristic peak of magnetoplumbite varied significantly when the sintering temperature changed from 700 °C to 1200 °C. To quantitatively evaluate the incorporation level of Pb into magnetoplumbite by red mud, we had to measure the amount of magnetoplumbite in the sintered samples. A quantitative XRD analysis of the sintered samples was performed using the Rietveld refinement method. The results of the Rietveld quantitative XRD analysis are summarized in Table 3. The weight fraction of the magnetoplumbite phase in the sintered samples increased at temperatures up to 900 °C but decreased when the temperature was more than 900 °C. The amount of the magnetoplumbite phase was approximately 13.9 wt.% after sintering at 900 °C for 5 h. The weight fractions of the residual glass (amorphous phase) in the samples decreased remarkably with an increase in the temperature.

Effect of dwell time on the formation of magnetoplumbite From an economic point of view, a relatively short heat treatment is very attractive for the ceramic industry. To further minimize the dwell time to achieve sufficient efficiency of the incorporation of Pb into magnetoplumbite, the effect of the sintering time on the formation of magnetoplumbite during the sintering of a mixture of the CRT funnel glass and the red mud


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was investigated. The XRD patterns of the sintered C25R75 sample at 900 °C for various dwell times are shown in Figure S4 (Supplementary Material). These XRD patterns were very similar to each other, indicating the same phase compositions. Six crystalline phases, i.e., hematite, gehlenite, andradite, perovskite, nepheline, and magnetoplumbite, could be identified for all the sintered samples (Table 4). The phase quantification results showed that the weight fraction of magnetoplumbite increased with an increase in the dwell time. The weight fraction of hematite decreased obviously with an increase in the dwell time, while no considerable change was observed for the other crystalline phases (i.e., gehlenite, andradite, perovskite, and nepheline). This indicated that the Pb incorporation reaction mainly occurred between PbO and Fe2O3 to form magnetoplumbite (PbO + 6Fe2O3 → PbFe12O19). As the dwell time increased from 1 h to 7 h, the weight fractions of PbFe12O19 increased from 9.65 wt.% to 14.92 wt.%. Upon sintering for 10 h, the amount of magnetoplumbite increased slightly, compared with that in the sample sintered for 7 h, indicating that further sintering at 900 °C to increase a significant amount of magnetoplumbite is unlikely. On the basis of the XRF results of the CRT funnel glass and the phase quantification result of the C25R75 sample sintered at 900 °C for 10 h, we concluded that approximately half of the Pb in the CRT funnel glass was successfully incorporated into magnetoplumbite (detailed calculations can be found in Text S1, Supplementary Material). The residual Pb contents might exist in the amorphous region or in the form of a solid solution in the other crystalline phases. In the CRT funnel glass, the Pb atom is firmly fixed by encapsulation in the cavity of the glass network, which mainly consists of the –O–Si–O– network and/or partly consists of the structural component of the glass network such as –O–Si–O–Pb–O–.25 This particular structure makes it very difficult to extract and incorporate a large portion of lead from the glass by using conventional methods.26 However, our strategy showed that the use of red mud could easily and effectively incorporate Pb from the CRT funnel glass into a chemically 11 ACS Paragon Plus Environment


durable magnetoplumbite phase. As shown in Figure 5, the elemental mappings of the C25R75 sample sintered at 900 °C for 5 h revealed that the Pb contents were concentrated in the magnetoplumbite grains present in the white area in the backscattered SEM image. They also showed that the magnetoplumbite grains were surrounded by Si- and Ca-rich phases, which might play an important role in hindering the release of Pb in the case of chemical corrosion. In the SEM image shown in Figure 5, six different contrasts are found, indicating the six phases in the sample. The lack of one phase in the SEM image may correspond to perovskite, because its quantity was only 1.23 wt.% (Table 4).

Leaching performance of the product The surface areas of the CRT funnel glass powder and the as-obtained C25R75 product were 1.61 and 1.65 m2/g, respectively. The similarities in the surface areas for these two samples indicated that the surface area need not be taken into account in a comparison of their leachability.

Figure 6 summarizes the leached Pb concentrations in the leachates of the CRT funnel glass and the sintered C25R75 sample. After 18 h of leaching, the concentration of the leached Pb from the CRT funnel glass was approximately 290 mg/L, while that from the sintered C25R75 was only 9.6 mg/L. This indicated that the initial concentration of leachable Pb from sintered C25R75 was 30 times less than that obtained from the CRT funnel glass. In the case of the CRT funnel glass, the amount of leachable Pb gradually increased with an increase in the leaching time. The leached Pb concentration from the CRT funnel glass reached 424 mg/L after 16 days of leaching. However, the concentration of the leached Pb from the sintered C25R75 sample exhibited a dramatic decrease with an increase in the leaching time. This was probably because (i) the Pb2+ ions reacted with the Fe3+ ions or the other ions to


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form colloids and then, precipitated on the surface of the particles; or (ii) the already-formed amorphous ferric hydroxide (Fe(OH)3 or Fe(OOH) absorbed the Pb2+ ions and then precipitated with the undissolved particles. These precipitation processes could lead to a significant decrease in the concentration of the Pb2+ ions in the leachates. Further, the decreasing Fe concentrations (Figure S5, Supplementary Material) in the leachates might serve as evidence to support the above explanation. At the end of the leaching experiments (21 days), the Pb concentration in the leachate of sintered C25R75 was around 0.05 mg/L, which was three orders of magnitude lower than that from the CRT funnel glass. Such a low leachable Pb concentration in the leachate from the sintered product might be attributed to the following reasons: (i) Pb was incorporated into a more resistant phase (i.e., magnetoplumbite PbFe12O19). (ii) The re-precipitation of ferric hydroxide (Fe(OH)3 or Fe(OOH) on the undissolved particles acted as a critical barrier to prevent the lead from leaching out. The concentrations of the other predominant ions (i.e., Si, Mg, Ca, and Na) in the leachates from the CRT funnel glass and sintered C25R75 are listed in Table S2 (Supplementary Material). No substantial change in concentration was observed for these ions during the leaching experiments.

Conclusions In this study, we demonstrated successful CRT funnel glass stabilization via sintering with red mud. In the sintered products, the major Pb-bearing crystalline product phase was magnetoplumbite (PbFe12O19), which was chemically durable. The XRD results indicated that the maximum loading of the CRT funnel glass was 25 wt.% in the mixture. When the loading of the CRT funnel glass in the mixture was 30 wt.%, the formation of magnetoplumbite was not observed in the sintered products. The results from the Rietveld quantitative analysis showed that the effective formation of magnetoplumbite in the mixture with 25 wt.% of the



CRT funnel glass and 75 wt.% of the red mud could be obtained via sintering at a relative low temperature (i.e., 900 °C). After sintering at 900 °C for 10 h, we observed that the formation of magnetoplumbite increased to 15 wt.%, corresponding to the incorporation of approximately half of the Pb contents into magnetoplumbite. The prolonged TCLP results indicated that the leachable lead concentration from the sintered product was more than three orders of magnitude lower than that from the CRT funnel glass. This result suggested that the product obtained from the CRT funnel glass and the red mud exhibited excellent acid resistance. The stabilized products may be more safely disposed in landfill or made into bricks/tiles for construction purposes. The results generated from this work may also provide new insights in controlling the release of lead from a wide variety of glassy-matrices in waste glass, waste incineration ashes, sludge and treatment residues.

ACKNOWLEDGMENTS This study was funded by the National Natural Science Foundations of China (41701560, 41673135), Research Grants Council of Hong Kong (Projects 17212015, C7044-14G, and T21-771/16R), GDAS’ Special Project of Science and Technology Development (2017GDASCX-0834), the Science and Technology Foundation of Guangzhou, China (201704020200) and the Scientific Platform and Innovation Capability Construction Program of GDAS (2016GDASPT-0212, 2017GDASCX-0406).

Appendix A. Supplementary material Supplementary data associated with this manuscript can be found in the online version.


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(26) Miyoshi, H.; Chen, D.; Akai, T. A Novel Process Utilizing Subcritical Water to Remove Lead

from

Wasted

Lead

Silicate

Glass,

Chem.

doi.org/10.1246/cl.2004.956.


Lett.

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(2004)

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Captions of Tables and Figures Table 1. Samples of CRT funnel glass powder and red mud mixtures for lead immobilization.

Table 2. Summary of major crystalline phases observed in the samples of CRT funnel glass and red mud mixtures sintered at 800 °C and 1000 °C for 5 h.

Table 3. Phase quantification results for the C25R75 sample sintered at 700-1200 °C for 5 h.

Table 4. Phase quantification results for the C25R75 sample sintered at 900 °C for 1, 3, 5, 7, and 10 h.

Figure 1. Phase identification results of the samples (C5R95, C10R90, C15R85, C20R80, C25R75, and C30R70) sintered at 800 °C for 5 h.


Figure 3. Intensities of the characteristic peak of magnetoplumbite in the XRD patterns of different mixture samples sintered at (a) 800 °C and (b) 1000 °C for 5 h.

Figure 4. (a) XRD patterns of the sintered samples with 25 wt.% CRT + 75 wt.% red mud at temperatures ranging from 700 °C to 1200 °C for 5 h; (b) intensities of the characteristic peak of the magnetoplumbite phase.



Figure 5. Backscattered SEM image of the C25R75 sample sintered at 900 °C and 5 h. EDX elemental mappings (Pb, Fe, Si, Ca, and Al) show the different phases in the product and the Pb-rich magnetoplumbite (white area, marked with 2).

Figure 6. Lead concentrations in the leachates of the CRT funnel glass and the sintered C25R75 product. The leaching fluid is extraction fluid #1 of TCLP, an acetic acid solution with a pH value of 4.88 ± 0.05.


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Table 1. Samples of CRT funnel glass powder and red mud mixtures for lead immobilization.

Sample

CRT funnel glass, wt.%

Red mud, wt.%

C5R95

5

95

C10R90

10

90

C15R85

15

85

C20R80

20

80

C25R75

25

75

C30R70

30

70

Table 2. Summary of major crystalline phases observed in the samples of CRT funnel glass and red mud mixtures sintered at 800 °C and 1000 °C for 5 h. 800 °C

1000 °C

Crystalline PDF no.

C5

C10 C15 C20 C25 C30

phases

All samples R95 R90 R85 R80 R75 R70

hematite

73-2234

√

√

√

√

√

√

√

magnetoplumbite 41-1373

×

×

√

√

√

×

√

Gehlenite

79-2421

√

√

√

√

√

√

√

Andradite

78-0319

√

√

√

√

√

√

√

perovskite

72-1192

√

√

√

√

√

√

√

Nepheline

09-0338

√

√

√

√

√

√

√

“√” represents detectable while “×” represents not detectable.



Page 22 of 33

Table 3. Phase quantification results for the C25R75 sample sintered at 700-1200 °C for 5 h. Phase (wt.%)

700 °C 800 °C 900 °C 1000 °C 1100 °C 1200 °C

Hematite

√

9.07

3.34

3.6

9.35

√

Magnetoplumbite

~0

7.18

13.90

13.11

8.21

~0

Gehlenite

-

0.30

0.52

2.02

2.38

√

Andradite

√

31.74

31.34

31.72

35.95

√

Perovskite

√

1.80

2.64

1.95

5.42

√

Nepheline

√

24.16

30.65

29.37

30.41

√

Amorphous

-

25.76

18.12

18.23

8.28

-

“√” represents detectable while “-” represents not available.

Table 4. Phase quantification results for the C25R75 sample sintered at 900 °C for 1, 3, 5, 7, and 10 h.

Phase (wt.%)

1h

3h

5h

7h

10 h

Hematite

6.90

4.07

3.22

2.10

2.49

Gehlenite

1.47

2.08

4.18

3.85

2.79

Andradite

32.32

32.3

32.42

32.57

33.78

Perovskite

1.12

1.24

1.23

1.39

1.07

Nepheline

24.79

28.76

29.25

28.70

28.00

Magnetoplumbite

9.65

13.46

13.90

14.92

15.16

Amorphous

23.77

18.09

15.8

16.48

16.72


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Figure 3. Intensities of the characteristic peak of magnetoplumbite in the XRD patterns of different mixture samples sintered at (a) 800 °C and (b) 1000 °C for 5 h.


Page 24 of 33

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Figure 4. (a) XRD patterns of the sintered samples with 25 wt.% CRT + 75 wt.% red mud at temperatures ranging from 700 °C to 1200 °C for 5 h; (b) intensities of the characteristic peak of the magnetoplumbite phase.

Figure 5. Backscattered SEM image of the C25R75 sample sintered at 900 °C and 5 h. EDX elemental mappings (Pb, Fe, Si, Ca, and Al) show the different phases in the product and the Pb-rich magnetoplumbite (white area, marked with 2).



Figure 6. Lead concentrations in the leachates of the CRT funnel glass and the sintered C25R75 product. The leaching fluid is extraction fluid #1 of TCLP, an acetic acid solution with a pH value of 4.88 ± 0.05.


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TABLE OF CONTENTS (TOC) GRAPHIC

Schematic illustration of immobilization of two hazardous solid wastes (cathode ray tube (CRT) funnel glass and red mud) into a chemically durable matrix.



Phase identification results of the samples (C5R95, C10R90, C15R85, C20R80, C25R75, and C30R70) sintered at 800 °C for 5 h. 93x95mm (300 x 300 DPI)

ACS Paragon Plus Environment

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Figure 2. Phase identification results of the samples (C5R95, C10R90, C15R85, C20R80, C25R75, and C30R70) sintered at 1000 °C for 5 h. 288x201mm (300 x 300 DPI)



Intensities of the characteristic peak of magnetoplumbite in the XRD patterns of different mixture samples sintered at (a) 800 °C and (b) 1000 °C for 5 h. 178x72mm (300 x 300 DPI)


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(a) XRD patterns of the sintered samples with 25 wt.% CRT + 75 wt.% red mud at temperatures ranging from 700 °C to 1200 °C for 5 h; (b) intensities of the characteristic peak of the magnetoplumbite phase. 132x78mm (300 x 300 DPI)



Backscattered SEM image of the C25R75 sample sintered at 900 °C and 5 h. EDX elemental mappings (Pb, Fe, Si, Ca, and Al) show the different phases in the product and the Pb-rich magnetoplumbite (white area, marked with 2). 156x78mm (300 x 300 DPI)


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Lead concentrations in the leachates of the CRT funnel glass and the sintered C25R75 product. The leaching fluid is extraction fluid #1 of TCLP, an acetic acid solution with a pH value of 4.88 ± 0.05. 288x201mm (300 x 300 DPI)


Immobilization of Lead in Cathode Ray Tube Funnel Glass with

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