lcd screens - indium leaching
LCD SCREENS - INDIUM LEACHING A.P. GABRIEL*, B.B. GIORDANI*, A.KASPER*. AND H.M. VEIT* * PPGE3M – Materials Engineering Department, Federal University of Rio Grande do Sul – UFRGS. Av. Bento Gonçalves, 9500, Setor IV, Prédio 43426, CEP: 91501-970, Porto Alegre, Brazil.
SUMMARY: 1. INTRODUCTION. 2. MATERIAL AND METHODS. 3. RESULTS AND DISCUSSIONS. 4. CONCLUSIONS. AKNOWLEDGEMENTS. REFERENCES
1. INTRODUCTION Liquid crystal displays (LCDs) are present in many electronic devices, such as televisions, computers, cell phones, GPS (among others) (Figure 1). This range of applications combined with an increasing amount of new launches, with new technologies and an increasingly frequent disposal of old equipment, evidences the necessity of a correct discard or the incentive to recycle this waste.
Figure 1: Examples of equipments with LCD technology. Incorrect disposal can cause damage to the environment but also makes it impossible to send materials for recycling. Thus, a large number of defective or obsolete LCDs equipment gradually becomes part of electronic waste. LCD monitors are composed of an LCD screen, polymeric parts and printed circuit boards (PCB). The screen is one of the main components of LCDs, which may contain some kinds of rare and precious metals, among them, indium. According Juchneski, the basic structure of the LCD screen can be seen in Figure 2, where the items 1 to 6 are shown the various components that compose the screen. Item 1 is the vertically polarizing film; item 2 is the layer of glass with ITO (Indium Tin Oxide); item 3 the liquid crystal; item 4 the other glass layer with ITO; item 5 is the horizontal polarizing film and item 6 is the diffuser sheet.
Proceedings Sardinia 2017 / Sixteenth International Waste Management and Landfill Symposium/ 2 - 6 October 2017 S. Margherita di Pula, Cagliari, Italy / © 2017 by CISA Publisher, Italy
Sardinia 2017 / Sixteenth International Waste Management and Landfill Symposium / 2 - 6 October 2017
Figure 2: Structure of the an LCD screen. In the vitreous layers, the Indium chemical element is found in the form of an indium / tin oxide. ITO contains a large portion of indium oxide (90%) and a small portion of tin oxide (10%). ITO is a transparent and conductive material. Thus, the aim of this work was to test leaching solutions to extract indium present in LCD screen
2. MATERIAL AND METHODS Initially, two LCD monitors of different brands and year of manufacture were collected. These monitors were weighed and disassembled manually. The monitors were separated into three main parts: polymeric frame, polymeric components and screen (containing glass layers, polarizing films and liquid crystal). Figure 3 shows the components that were separated from the LCD monitors.
(a)
(b)
(c)
Figure 3: LCD monitor disassembled: (a) screen (b) polymeric components (c) polymeric frame. Afterwards, only the screens were comminuted in a Servitech model CT-242 ball mill to obtain a powder. The milling time was monitored and every hour a sample was collected for analysis, ending with 6 hours of milling. The particle size analysis of the samples was performed using a Laser Diffraction (CILAS 1180). The next step was the leaching test. HCl (hydrochloric acid) and HNO3 (nitric acid) were used in a concentration of 0.5 and 6M. These leaching tests were performed only with the milled powder for 6 hours. For the leaching, a mechanical stirrer was used for 4hrs at room
Sardinia 2017 / Sixteenth International Waste Management and Landfill Symposium / 2 - 6 October 2017
temperature (28°C) and with heating at 60°C. The solid/liquid ratio was 1/100. The concentration of indium obtained in the leaching tests was determined using ICP-OES. Table 1: Parameter used in the Leaching test. Reagent
Concentration
HCl
0.5 M and 6 M
HNO3
0.5 M and 6 M
Temperature 28°C and 60°C 28°C and 60°C
Leaching time
Amount of Material
Amount of reagent
4 horas
0,5g
50ml
4 horas
0,5g
50ml
3. RESULTS AND DISCUSSION It is possible to observe in table 2, that monitors and screens have slight variations in weight, although some monitors may contain a heavier polymeric substrate when compared to other monitors. Table 2: Mass of collected samples. Brand Year of Manufacture A 2005 B 2006
Mass Total 4,3kg 4,0kg
Mass Screen 0,46kg 0,37kg
Figure 4 shows the different particle sizes obtained compared to the milling time. It is possible to note that, after 4 hours of milling, the particle size is stabilized around 5 microns.
Figure 4: Result of particle size analysis.
Figure 5 show the material obtained after 6 hours of milling.
Sardinia 2017 / Sixteenth International Waste Management and Landfill Symposium / 2 - 6 October 2017
Figure 5: Material obtained in milling.
Table 3 presents the results of the leaching tests. The results with hydrochloric acid did not show a great variation as a function of concentration or temperature. While for nitric acid, it is noticed that, for low concentrations, the leaching of the indium was not efficient. While the temperature did not have great influence. The best result was found for 6M nitric acid at 60°C with 20.44 mg/l of indium. However, considering the cost involved in using a concentrated acid at high temperature, the most feasible result would be the use of 0.5M hydrochloric acid at room temperature. These results are compatible with the literature, since Yang et al. found approximately 26 mg/l of indium to 1M HCl. Table 3: Leaching results. Reagent HCl HNO3
Concentration 0.5 M 6M 0.5 M 6M
28°C (mg/l) 16.71 20.34 6.35 19.91
60°C (mg/l) 18.40 19.29 9.57 20.44
4. CONCLUSIONS It was possible to observe that the LCD monitors are extremely heterogeneous. Through the manual disassembly, it was possible to obtain three main parts: polymeric structures, polymeric components and screens. The screens are produced in a "sandwich" format containing layers of glass, polymeric films and liquid crystals. The inner glass surface contains deposits of ITO (indium tin oxide) containing significant levels of indium. After milling the screen in a ball mill and analyzing the particle size distribution, it was observed that after 4 hours of milling the material reaches very similar particle sizes, around 5µm. The leaching tests, to extract ITO from the LCD screens, presented good results. The results were consistent with the literature, and it was possible to extract 20.44 mg/l of indium. The leaching at high temperature is not required since the indium content extracted at room temperature and 60ºC were similar. In this context, the most interesting result was obtained with 0.5M hydrochloric acid at room temperature, with 16.71mg/l of indium.
Sardinia 2017 / Sixteenth International Waste Management and Landfill Symposium / 2 - 6 October 2017
AKNOWLEDGEMENTS The authors thanks CAPES and CNPq for financial supports.
REFERENCES Chou, W.L. and Huang, Y.H. (2009) Electrochemical removal of indium ions from aqueous solution using iron electrodes. Journal of Hazardous Materials 172 46–53. Gabriel A.P., Grochau I.H., Santana R.M.C.,Veit H.M. Reciclagem de Carcaças de Monitores: Propriedades Mecânicas e Morfológicas. Polímeros, vol. 23, n. 6, p. 823-831, 2013. Juchneski, N. C. F. (2013). Monitores de LCD: Caracterização dos materiais e processamento mecânicos das placas de circuito impresso. Porto Alegre, 103 p. Dissertação (Mestrado) – Universidade Federal do Rio Grande do Sul. Lu R., Ma E. and Xu Z. (2012) Application of pyrolysis process to remove and recover liquid crystal and films from waste liquid crystal display glass. Jornal Hazardous Materials. v243:311318. Murugan, R., V.; Bharat, S., Deshpande, A., P.; Varughese, S. and Haridoss, P. (2008). Milling and separation of the multi-component printed circuit board materials and the analysis of elutriation based on a single particle model. In: Powder Technology. 183; 169-176. Yang J., Retegan T. and Ekberg C. (2013) Indium recovery from discarded LCD panel glass by solvent extraction. Hydrometallurgy 137; 68–77.
SUMMARY: 1. INTRODUCTION. 2. MATERIAL AND METHODS. 3. RESULTS AND DISCUSSIONS. 4. CONCLUSIONS. AKNOWLEDGEMENTS. REFERENCES
1. INTRODUCTION Liquid crystal displays (LCDs) are present in many electronic devices, such as televisions, computers, cell phones, GPS (among others) (Figure 1). This range of applications combined with an increasing amount of new launches, with new technologies and an increasingly frequent disposal of old equipment, evidences the necessity of a correct discard or the incentive to recycle this waste.
Figure 1: Examples of equipments with LCD technology. Incorrect disposal can cause damage to the environment but also makes it impossible to send materials for recycling. Thus, a large number of defective or obsolete LCDs equipment gradually becomes part of electronic waste. LCD monitors are composed of an LCD screen, polymeric parts and printed circuit boards (PCB). The screen is one of the main components of LCDs, which may contain some kinds of rare and precious metals, among them, indium. According Juchneski, the basic structure of the LCD screen can be seen in Figure 2, where the items 1 to 6 are shown the various components that compose the screen. Item 1 is the vertically polarizing film; item 2 is the layer of glass with ITO (Indium Tin Oxide); item 3 the liquid crystal; item 4 the other glass layer with ITO; item 5 is the horizontal polarizing film and item 6 is the diffuser sheet.
Proceedings Sardinia 2017 / Sixteenth International Waste Management and Landfill Symposium/ 2 - 6 October 2017 S. Margherita di Pula, Cagliari, Italy / © 2017 by CISA Publisher, Italy
Sardinia 2017 / Sixteenth International Waste Management and Landfill Symposium / 2 - 6 October 2017
Figure 2: Structure of the an LCD screen. In the vitreous layers, the Indium chemical element is found in the form of an indium / tin oxide. ITO contains a large portion of indium oxide (90%) and a small portion of tin oxide (10%). ITO is a transparent and conductive material. Thus, the aim of this work was to test leaching solutions to extract indium present in LCD screen
2. MATERIAL AND METHODS Initially, two LCD monitors of different brands and year of manufacture were collected. These monitors were weighed and disassembled manually. The monitors were separated into three main parts: polymeric frame, polymeric components and screen (containing glass layers, polarizing films and liquid crystal). Figure 3 shows the components that were separated from the LCD monitors.
(a)
(b)
(c)
Figure 3: LCD monitor disassembled: (a) screen (b) polymeric components (c) polymeric frame. Afterwards, only the screens were comminuted in a Servitech model CT-242 ball mill to obtain a powder. The milling time was monitored and every hour a sample was collected for analysis, ending with 6 hours of milling. The particle size analysis of the samples was performed using a Laser Diffraction (CILAS 1180). The next step was the leaching test. HCl (hydrochloric acid) and HNO3 (nitric acid) were used in a concentration of 0.5 and 6M. These leaching tests were performed only with the milled powder for 6 hours. For the leaching, a mechanical stirrer was used for 4hrs at room
Sardinia 2017 / Sixteenth International Waste Management and Landfill Symposium / 2 - 6 October 2017
temperature (28°C) and with heating at 60°C. The solid/liquid ratio was 1/100. The concentration of indium obtained in the leaching tests was determined using ICP-OES. Table 1: Parameter used in the Leaching test. Reagent
Concentration
HCl
0.5 M and 6 M
HNO3
0.5 M and 6 M
Temperature 28°C and 60°C 28°C and 60°C
Leaching time
Amount of Material
Amount of reagent
4 horas
0,5g
50ml
4 horas
0,5g
50ml
3. RESULTS AND DISCUSSION It is possible to observe in table 2, that monitors and screens have slight variations in weight, although some monitors may contain a heavier polymeric substrate when compared to other monitors. Table 2: Mass of collected samples. Brand Year of Manufacture A 2005 B 2006
Mass Total 4,3kg 4,0kg
Mass Screen 0,46kg 0,37kg
Figure 4 shows the different particle sizes obtained compared to the milling time. It is possible to note that, after 4 hours of milling, the particle size is stabilized around 5 microns.
Figure 4: Result of particle size analysis.
Figure 5 show the material obtained after 6 hours of milling.
Sardinia 2017 / Sixteenth International Waste Management and Landfill Symposium / 2 - 6 October 2017
Figure 5: Material obtained in milling.
Table 3 presents the results of the leaching tests. The results with hydrochloric acid did not show a great variation as a function of concentration or temperature. While for nitric acid, it is noticed that, for low concentrations, the leaching of the indium was not efficient. While the temperature did not have great influence. The best result was found for 6M nitric acid at 60°C with 20.44 mg/l of indium. However, considering the cost involved in using a concentrated acid at high temperature, the most feasible result would be the use of 0.5M hydrochloric acid at room temperature. These results are compatible with the literature, since Yang et al. found approximately 26 mg/l of indium to 1M HCl. Table 3: Leaching results. Reagent HCl HNO3
Concentration 0.5 M 6M 0.5 M 6M
28°C (mg/l) 16.71 20.34 6.35 19.91
60°C (mg/l) 18.40 19.29 9.57 20.44
4. CONCLUSIONS It was possible to observe that the LCD monitors are extremely heterogeneous. Through the manual disassembly, it was possible to obtain three main parts: polymeric structures, polymeric components and screens. The screens are produced in a "sandwich" format containing layers of glass, polymeric films and liquid crystals. The inner glass surface contains deposits of ITO (indium tin oxide) containing significant levels of indium. After milling the screen in a ball mill and analyzing the particle size distribution, it was observed that after 4 hours of milling the material reaches very similar particle sizes, around 5µm. The leaching tests, to extract ITO from the LCD screens, presented good results. The results were consistent with the literature, and it was possible to extract 20.44 mg/l of indium. The leaching at high temperature is not required since the indium content extracted at room temperature and 60ºC were similar. In this context, the most interesting result was obtained with 0.5M hydrochloric acid at room temperature, with 16.71mg/l of indium.
Sardinia 2017 / Sixteenth International Waste Management and Landfill Symposium / 2 - 6 October 2017
AKNOWLEDGEMENTS The authors thanks CAPES and CNPq for financial supports.
REFERENCES Chou, W.L. and Huang, Y.H. (2009) Electrochemical removal of indium ions from aqueous solution using iron electrodes. Journal of Hazardous Materials 172 46–53. Gabriel A.P., Grochau I.H., Santana R.M.C.,Veit H.M. Reciclagem de Carcaças de Monitores: Propriedades Mecânicas e Morfológicas. Polímeros, vol. 23, n. 6, p. 823-831, 2013. Juchneski, N. C. F. (2013). Monitores de LCD: Caracterização dos materiais e processamento mecânicos das placas de circuito impresso. Porto Alegre, 103 p. Dissertação (Mestrado) – Universidade Federal do Rio Grande do Sul. Lu R., Ma E. and Xu Z. (2012) Application of pyrolysis process to remove and recover liquid crystal and films from waste liquid crystal display glass. Jornal Hazardous Materials. v243:311318. Murugan, R., V.; Bharat, S., Deshpande, A., P.; Varughese, S. and Haridoss, P. (2008). Milling and separation of the multi-component printed circuit board materials and the analysis of elutriation based on a single particle model. In: Powder Technology. 183; 169-176. Yang J., Retegan T. and Ekberg C. (2013) Indium recovery from discarded LCD panel glass by solvent extraction. Hydrometallurgy 137; 68–77.
