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Potassium dichromate and sulfuric acid leaching of metal indium from the LCD display
ZHANG xinle
(Shanghai second industrial university institute of urban construction and environme

ntal engineering, Shanghai 201209)

Abstract:The cooperative effects of sulfuric acid and potassium dichromate as oxidant were observed to leach the oxide of indium from the wasted liquid crystal displays (including the In2O3,InO and In2O). With the LCD powder as raw experimental material, effects of the consumption of sulfuric acid and potassium dichromate,reaction time and reaction temperature on leaching rate of the oxide of indium from the wasted liquid crystal displays were obereved. The experiment using nitric acid, hydrochloric acid and sulfuric acid as contrast leaching agent were carried out. With the temperature as 50 ° C and the consumption dosage of sulfuric acid as 7.6675×10-3(mol/gLCD) ,56.75% of the maximum of the leaching rate was obtained. Join the 0.075g potassium dichromate in the maximum leaching rate, can make

the mixed liquid Indium Leaching rate to get the maximum value of 100%.The experimental results of using precipitation method to extract indium from the leaching solution of wasted LCD show that 78.85% of the recovery rate of indium of precipitation from the leaching solution was obtained.

Key words:The waste liquid crystal displays;Indium; Potassium dichromate; Sulfuric acid

0 Introduction

Liquid crystal display (LCD) rapid development since the 1990 s, and gradually mature, since it has high resolution and good image color, environmental protection, save electricity, light and easy to carry, etc, has been widely used in household appliances, computer and communication products
[1]

. In 2009, according to industry statistics,

Chinese LCD TV market overall sales to 21.668 million units, up 80.5% from 2008, sales of 86.75 billion yuan, up 50.6% from a year earlier. A total of 400 million units throughout the CRT (Cathode Ray Tube) TV is used, the next five years the upgrading of the CRT TV, will make the LCD TV into the development of the fast lane. According to IDC China PC display market quarterly tracking reports, in 2009 China PC monitor overall market size of 40.03 million, compared with 18.9% growth in 2008. CRT overall shipments has dropped to 1.3% in 2009, in the third quarter and the fourth quarter, CRT shipments has been reduced to below 1%, has been largely withdraw from the market; LCD shipments of 98.7%, annual growth rate of 27.2%. According to the 2013-2017 Chinese LCD market present situation analysis and investment prospects the research report, according to the data in the 2013 national display total

cumulative output has reached 132.57 million units, year-on-year growth of 8.52% in 2012. The production of liquid crystal display is in rapid growth stage. [2]

Ghost LCD has certain environmental risks, but also contains significant resource use value of material, such as gold, silver, indium, tin, copper, zinc and other metals and plastics, glass and other materials. One of the rare metals and heavy metal, glass and so on all are precious resources, especially rare metal indium is extremely scarce. Indium quality in the LCD screen performance, become an irreplaceable element in liquid crystal display production. Due to the natural resources of indium is not rich, is now fully aware of the recovery of indium. At present, about 70% indium product used in production of liquid crystal display components, a LCD glass substrate indium content higher than 0.03%, in general, indium content in the raw material is more than 0.002% has the collection value, thus it can be seen in the liquid crystal display indium recovery value extremely. Reported global reserves account for only 1/6 of the gold reserves of indium, and 70% of indium products used for liquid crystal displays of indium tin oxide production, due to high quality indium in the LCD screen performance, become irreplaceable in liquid crystal display production element, a LCD glass substrate is higher than 0.03%, content of indium in recovery value

extremely.

Waste LCD glass, light weight, low density, general density in 2.6 g, 3 cm - following; There is no alkali metal ions; Good chemical stability; Thermal stability is strong, thermal expansion coefficient (30-40) x 10-7 ℃; Has a very strong mechanical strength, can be used to mix cement clay brick, waste glass, etc. Can also through chemical methods of recycling waste LCD metal indium of indium tin oxide (ITO).

This topic based on a lot of in the waste LCD panel recyclable metal elements, especially one of the rare metal indium, indium tin oxide (ITO), as an essential part of the LCD display of a material, it has the very high collection value and significance.

At present our country for resource recovery of electronic waste recycling is the focus of the recovery of gold, silver, palladium and other rare metals and base metals such as copper, the main recovery methods include mechanical processing method[3], pyrometallurgy and

hydrometallurgy, etc. As a kind of rare metal indium, exists only in a minority of natural mineral, its exploitation is difficult and the high demand, mainly in the form of indium tin oxide exists in liquid crystal display panels, deposited on the filter by sputtering technology. Currently 84% of the world's dosage of indium is on the manufacturing

of liquid crystal display (LCD)

[4]

, so the indium recovery become the

important content of waste recycling LCD. Has a patent retrieval abroad and our country Taiwan area indium recycling
[5]

, found that the vast

majority of the acid leaching process, through electrochemical or metal replacement method processing recycling metal indium leaching solution, the domestic related research started late, the indium recovery technology method and its process of pollution control, in-depth research, lack of system is far from the degree project demonstration.

Germany, Japan and our country Taiwan area

[6]

. Comprehensive

domestic and foreign resource recycling of rare metal indium in the liquid crystal display technology, current research is mainly about the separation of indium recovery process by altering the chemical method for separation of the form, consists of two steps: the first step for acid leaching, use effective components from the raw material into the acid solvent solution; The second step for the separation and enrichment, to isolate the indium leaching liquid and further refined form indium products.

Developing a strong oxidizing and strongly acidic without volatile (easy operation in practice) of leaching agent for efficient the metal indium leaching waste liquid crystal displays. From the perspective in the literature, indium oxide from the LCD glass substrate into ions dissolved

in the liquid phase states need to adopt the acid mainly has the oxidation and acid such as nitric acid and aqua regia were strong acid. Given the strong hydrochloric acid and nitric acid strong oxidizing and strong volatility in practical industrial application might as well as the operation of the workers' health effects on the environment, relatively strong sulfuric acid has no volatile, but its oxidizing than nitric acid and aqua regia, therefore, this research intends to adopt the coordination effect of sulfuric acid and oxidant leaching of the waste liquid crystal display metal indium oxide (including In2O3, InO and In2O), the oxidant is heavy chromium acid potassium. Test research contents include ratio of sulfuric acid and potassium dichromate and dosage, reaction time and reaction temperature on the metal indium leaching effect from the LCD, its research content has not been reported in the Chinese and foreign literature, the objective of the research results of extracting indium from the LCD practice has important guiding significance.

1. Experimental

1.1 comparing different dosage of three kinds of acid test

Under the condition of atmospheric pressure condition, takes 25 ml different concentration solutions leaching 10 g waste LCD fragments, placed on the magnetic stirrer reaction time four hours

Table 1.1 hydrochloric acid by a scale Solution concentration
(mol/L) 0.119 0.148 0.197 0.293 0.571 2.000 6.000 2.975×10-4 3.7×10-4 4.925×10-4 7.325×10-4 1.4275×10-3 5×10-3 1.5×10-2

num Volume ratio(37.5% acid ber /water)
1 2 3 4 5 6 7 1/100.0 1/80.0 1/60.0 1/40.0 1/20.0 1/5.0 1/1.0

HCl dosage (mol/LCDg)

Table 1.2 sulfuric acid by a scale num Volume ratio(98% acid ber /water)
1 2 3 4 5 6 7 1/100.0 1/80.0 1/60.0 1/40.0 1/20.0 1/5.0 1/1.0

Solution concentration
(mol/L) 0.182 0.227 0.302 0.449 0.876 3.067 9.200

H2SO4 dosage (mol/LCDg)

4.55×10-4 5.675×10-4 7.55×10-4 1.1225×10-3 2.19×10-3 7.6675×10-3 2.3×10-2

Table 1.3 the amount of nitric acid num Volume ratio(69% acid ber /water)
1 2 3 4 1/100.0 1/80.0 1/60.0 1/40.0

Solution concentration
(mol/L) 0.158 0.198 0.262 0.390

HNO3 dosage (mol/LCDg)

3.95×10-4 4.95×10-4 6.55×10-4 9.75×10-4

5 6 7

1/20.0 1/5.0 1/1.0

0.762 2.667 8.000

1.905×10-3 6.6675×10-3 2×10-2

1.2 under the condition of different time compared with three kinds of acid test

In different time, the state of the atmospheric pressure condition, take 25 ml volume for the configuration of the optimal solution leaching 10 g waste LCD fragments are placed on the magnetic stirrer.

1.3 under the condition of different temperature contrast experiment was carried out in three acid

Under the condition of different temperature, atmospheric pressure condition, take 25 ml volume for the configuration of the optimal solution leaching 10 g waste LCD pieces placed on the magnetic stirrer reaction time four hours.

1.4 add different number in sulfuric acid potassium dichromate contrast experiment was carried out the optimal parameters are obtained

Under atmospheric pressure condition through the above three steps to get the optimal parameters of conditions, to join different dose

of potassium dichromate leaching 10 g old pieces of LCD.

1.5 with precipitation from containing indium LCD extract indium leaching liquid

In adding NaOH solution with optimal parameters make the indium precipitation, filtration and drying, sediment, weigh and sediment in sulfuric acid, make its dissolution, using ICP instrument analyze the output of the sediment.

2.1 concentration effect

Normal temperature state, change the use of three kinds of acid concentration, take 25 ml volume ratio (acid/water) were 0.01, 0.0125, 0.167, 0.025, 0.05, 0.2, 1 solutions of different concentration leaching 10 g old LCD fragmentation reaction for four hours. (see table 3.1) to leaching efficiency as the ordinate, the abscissa denotes the different volume ratio of acid concentration do figure.

Table 2.1 three acid dosage, the leaching rate of indium in the LCD
1 Volume ratio (37.5%acid/ water) The concentration of the indium (ug/mL) acid/LCD (mol/g) The leaching rate of indium(%) Volume ratio (98%acid/w ater) The concentration of the indium (ug/mL) acid/LCD (mol/g) The leaching rate of indium(%) Volume ratio (69%acid/w ater) The concentration of the indium (ug/mL) acid/LCD (mol/g) The leaching rate of indium(%) 2.975× 10-4 7.79 3.7 ×10-4 7.98 4.925 ×10-4 8.53 7.325 ×10-4 11.37 1.4275 ×10-3 19.34 5 ×10-3 47.95 1.5 ×10-2 47.67 0.01 0.0125 0.167 0.025 0.05 0.2 1 2 3 4 5 6 7

0.85

0.87

0.93

1.24

2.11

5.23

5.2

HCl H2SO4 HNO3

0.01

0.0125

0.167

0.025

0.05

0.2

1

0.33

0.61

0.93

1.82

3.31

5.72

5.85

4.55 ×10-4 3.03

5.675 ×10-4 5.59

7.55 ×10-4 8.53

1.1225 ×10-3 16.68

2.19 ×10-3 30.34

7.6675 ×10-3 52.44

2.3 ×10-2 53.63

0.01

0.0125

0.167

0.025

0.05

0.2

1

0.75

1.32

1.89

3.74

5.85

5.87

5.8

3.95 ×10-4 6.88

4.95 ×10-4 12.10

6.55 ×10-4 17.33

9.75 ×10-4 34.29

1.905 ×10-3 53.63

6.6675 ×10-3 53.81

2 ×10-2 53.17

The leaching rate of indium basic is proportional to the three kinds

of acid concentration, ratio of 1:5 in nitric acid and water, a maximum indium leaching rate was 53.81%.

2.2 time

State under normal temperature, acid/LCD fragments as 7.6675 x 10-3 (mol/g) under the condition of different contrast test of time. (see table 3.2)

Table 2.2 three acid leaching time, the leaching rate of indium in the LCD
time(hrs) The concentration of the indium 3.11 4.81 5.3 5.35 2 3 4 5

HCl H2SO4 HNO3

(ug/mL) The leaching rate of indium (%) The concentration of the indium (ug/mL) The leaching rate of indium (%) The concentration of the indium 3.18 4.99 5.95 5.98 46.85 53.35 53.63 53.72 5.11 5.82 5.85 5.86 28.51 44.09 48.59 49.05

(ug/mL) The leaching rate of indium (%) 29.15 45.74 54.55 54.82

The leaching rate of indium basic is proportional to the three kinds of acid leaching time, when the room temperature, the amount of nitrate was 7.6675 x 10-3 (mol/gLCD), the leaching rate of indium is a maximum of 54.82%. 2.3 temperature effect In acid/LCD pieces of 7.6675 x 10-3 (mol/g) under the condition of experiment in different temperature. (see table 3.3) Table 2.3 three acid temperature on the effect of indium leaching rate in the LCD
temperature(°C) The concentration of the indium 5.1 5.28 5.58 5.61 20 30 40 50

HCl H2SO4 HNO3

(ug/mL) The leaching rate of indium (%) The concentration of the indium (ug/mL) The leaching rate of indium (%) The concentration of the indium (ug/mL) The leaching rate of 42.44 45.01 47.03 50.24 4.63 4.91 5.13 5.48 45.10 45.93 52.99 56.75 4.92 5.01 5.78 6.19 46.75 48.40 51.15 51.43

indium (%)

The leaching rate of indium basic is proportional to the three kinds of acid, reaction temperature, when 50 ° C, the amount of sulfuric acid is 7.6675 x 10-3 (mol/gLCD), the leaching rate of indium is a maximum of 56.75%. 2.4 the influence of adding potassium dichromate sulfuric acid At 50 ° C to sulfuric acid/LCD pieces of 7.6675 x 10-3 (mol/g) under the condition of adding different doses of potassium dichromate contrast experiment was carried out. (see table 3.4) Table 2.4 the influence of adding potassium dichromate sulfuric acid
numb er 1 2 3 4 5 K2Cr2O7/LCD (mol/g) 0 4.2517×10-5 8.5034×10-5 1.70068×10-4 2.55102×10-4 Intensity The concentration of the values 261.7 299.5 301.6 304 304.6 indium(ug/mL) 6.19 7.08215 8.657628 10.45817 10.90831 The leaching rate of indium 56.75% 64.92% 79.37% 95.87% 100%

K2Cr2O7(g)

0 0.125 0.25 0.5 0.75

The leaching rate of indium basic is proportional to the mass to join the potassium dichromate, when the dosage of potassium dichromate is 0.075 g/gLCD reaction after 4 hours, a maximum indium leaching rate was 100%. 2.5 with precipitation from leaching liquid containing indium LCD test study on extracting indium Indium precipitation, analysis of sediment: take 20 ml with optimal

parameters (i.e., the sulfuric acid/LCD pieces of 7.6675 x 10-3 mol/g) adding 30 ml solution with concentration of 34.6% (100 g water dissolve 53 gnaoh) NaOH indium precipitation, filtration and drying, sediment 3.66 g, weigh and 0.05 g sediment to join 25 ml3. 067 mol/L of sulfuric acid, make its dissolution, using ICP instrument analyze the output of the sediment, draw the conclusion: the concentration of the indium is 0.094 ug/ml, calculated indium recovery was 78.85%. 3 Conclusions and prospect 3.1 test conclusion (1) with LCD as sample, using hydrochloric acid, sulfuric acid, nitric acid test, through the comparisons of dosage, time and temperature tests is: 50 ° C in the amount of sulfuric acid is 7.6675 x 10-3 (mol/gLCD), the leaching rate of indium is a maximum of 56.75%. (2) the influence of adding potassium dichromate sulfuric acid: 50 ° C in the amount of sulfuric acid is 7.6675 x 10-3 (mol/gLCD), the amount of potassium dichromate test showed that when the dosage of potassium dichromate is 0.075 g/gLCD response 4 hours later, a maximum indium leaching rate was 100%. (3) using precipitation from extracting indium leaching liquid containing indium LCD: take 20 ml with optimal parameters (i.e., the sulfuric acid/LCD pieces of 7.6675 x 10-3 mol/g, the concentration of indium is 10.90831 ug/ml) adding 30 ml solution with concentration of

34.6% (100 g water dissolve 53 gnaoh) NaOH indium precipitation, filtration and drying, sediment 3.66 g, weigh and 0.05 g sediment to join 25 ml3. 067 mol/L of sulfuric acid and dissolved, then using ICP instrument analyze the output of the sediment, the concentration of indium is 0.094 ug/ml. Indium recovery rate of 78.85% is calculated.

References [1] China electronics news. LCD industry showed a trend of the big three. Electronic industrial equipment, 2007150 (7) : 10-12 [2] TAKAHASHI K, SASAKI A, DODBIBA G, et al. Recovering indium from the liquid crystal display of discarded cellular phones by means of chloride-induced vaporization at relatively low temperature[J].Metallurgical and Materials Transactions A, 2009, 40A:891-900. [3] LIN K L, HUANG Wujang, SHIE J L, et al.The utilization of thin film transistor liquid crystal display waste glass as a pozzolanic material[J]. J Hazard Mater, 2009, 163(2/3):916-921. [4] KIM H J, KEMBAUM S, SELIGER G.Emulation-base control of a disassembly system for LCD monitors[J].International Journal of advanced manufacturing technology, 2009, 40(3/4):383-392. [5] K. -S. Park, W. Sato, G. Grause, et al. Recovery of indium from In2O3 and liquid crystal display powder via a chloride volatilization process

using polyvinyl chloride, Thermochimica Acta(2008), doi:10.1016/j.tca.2009.03.003. [6] PARK K S, SATO W, GRAUSE G, et al.Recovery of indium form In2O3 and liquid crystal display powder via a chloride volatilization process using polyvinyl chloride[J].Thermochimica Acta, 2009, 493(1/2):105- 108.


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