Notes Bull. Korean Chem. Soc. 2009, Vol. 30, No. 12 3141 DOI 10.5012/bkcs.2009.30.12.3141
The Removal of Tin from ITO-scrap via Ozonization
Jung-ChulPark
Department ofEngineering inEnergy & Applied Chemistry, GreenFusionTechnology Center,Silla University, Busan 617-736, Korea.E-mail: parqc@silla.ac.kr
Received September 28, 2009, Accepted November4, 2009
KeyWords: Removal, Tin, Indium, ITO, Ozonization
Indium is estimated to havean abundancein the earth’s crust of0.05 ppm, which is similar tothat ofsilver. As with other comparatively rare metals,indium becomes moreconcentrated in by-productsarisingduring theextraction ofmajor metals suchas zinc.1
Consumption of indiumis expectedtoincrease throughout thenextdecade,especially by dint ofgrowthfor liquid crystal displays,high-definitiontelevision,semiconductormaterials, batteries,low-temperaturesolders, and electronicapplication.
Indium isused in variousforms such as indium oxide/indium- tin oxide, indium metal and alloy,and indium compounds.2,3 Flat panel display applications for indiuminthe formof IndiumTinOxide(ITO) are themostimportant enduses, more than one-half of the world’s indiumconsumption. The glass plate coated with ITO which is formed by doping indium oxide with approximately 10%of tin oxide, exhibitselectrical con
ductivity withoutsignificantly affecting transparency, and has beenusedas transparent electrodes forflat panel displays.
ITOfilms are generally fabricatedbyDC magnetronsputter ing usingITO ceramic target. Magnetron sputtering is favoured because itis easilyappliedtolargearea with good uniformity.
However,ITO targets should be replacedbefore a large portion of ITO material (60 ~ 70%) has been usedbecause of race track formation.4-6So, it mightbe said that the recycling of unused ITOtarget is indispensable as indium is a trace element and veryexpensive.
As shownin In1.82Sn0.18O3 obtained bydopingindium oxide with approximately 10% oftin oxide, tinis the major impurity in recoveryprocess of indium metal from ITO target-scrap.
Indium and tin arechemically verysimilar and separationone fromthe other in solution isa knottyproblem.Rapid separation of indium from tin by sublimationhasbeenreported.7 The proceduredeveloped was based upon the volatility of indium acetylacetonateat moderatetemperature.Another method con
cernsneutralization of solutions containingtin topH 1 followed bycementation with indium8,9 or by treatingwith NaOHto a pHvalue of 2.8.10,11 Electrolyticrecovery of indiumfrom con
centratedsulfatesolutions has beensuggested.12 A two-stage electrolytic procedure was proposed involving recovery of indium in apparatus withflat cathodes andcompleteextraction onthe flow-through porouscathodes. Numerous investigators havestudied to recover indium from solutionby solvent ex- traction.13,14The newlydevelopedmethodto remove tin and purifyindiummetal from ITOtargetscrap has been reported using molten NaOH.15
It is well known that ozone exhibitsthe strongoxidizing
power. Therefore, Sn(II)O・xH2。are easily oxidizedtothe high er oxidationstateSn(IV)O2・xH2。in solution byozonization.
Moreover, in an alkaline solution [HSn(II)O2「species are transformed into[Sn(IV)O3]2-byozonization. In therecovery process of indiummetal, Snspeciesarereadily removed in a washing step,which givesrise to highly purifiedindiummetal.
Inthispaper, we demonstrate a newmethodto removetin and purify indiummetal fromITOtarget scrap via ozonization.
ExperimentalSection
ITO target-scrap wasobtained from Samsung Corning Co., Ltd. The samplewas crushed and pulverized. The resulting powder wasleached in 3M H2SO4 solutionat80 oCfor 1.5 h, and then filteredto remove undissolved materials. The obtained solutionwastreated with NaOH, which resulted in suspension composed of metalhydroxideprecipitates. The ozonization wasperformed using an ozonizer(Ozontech,LAB model) in thissuspension. The ozonizationwas conducted for 2 h as a function of ozoneconcentration.The ozone concentrationwas verifiedwith the variation of O2 flow rate(0.5, 1, and 2 Liter per Minute (LPM)). Forthe recovery of purifiedindiummetal, the indium sponge was obtainedby cementation in sulfuric acid solution using aluminum plate (pH- 3, 50 oC). X-ray diffraction patternof the recoveredindiummetalwas achieved bySchmadzu 6000 model with Cu-Ka radiation. Theelemental analysis wasperformed by inductively coupledplasma-emiss ion spectroscopy (ICP) with Labtam8400 model.
Results and Discussion
Table 1 shows the ICP elemental analysis result of ITO target-scrap as received.It reveals that ITO target composes a doping range of approximately 10%oftin oxidecomparedto indiumoxide.
The powder of ITO target scrap was leached using 3 M H2SO4 at80 oC for1.5 h and filtered to removeundissolved materials. The obtained solution was treated with NaOH, which resulted in a suspendedsolution withmetal hydroxide
Table 1. ICP elemental analysis of ITO target scrap as received
purity (%) purity (ppm)
In Sn Cr Pb Ni Al Zn Cu Cd Fe Mo
74.84 7.50 < 1 1 < 1 < 1 < 1 18 < 1 22 < 1
3142 Bull.KoreanChem. Soc. 2009, Vol. 30, No. 12 Notes
Table 2. ICP elemental analysis of metal hydroxide precipitates after ozone (or. oxygen) treatment
In (%) Sn (%) Sn removal (%)
metal hydroxide precipitates after O2 treatment 60.95 1.320 82.40
metal hydroxide precipitates after O3 treatment 60.87 0.016 99.79
aThe concentration ofozone: 11 g/h (O2 flowrate: 2 LPM).
Table 3. ICP elemental analysis of the finally recovered indium metal
purity (%) purity (ppm)
In Sn Cr Pb Al Ti Cd Ni Zn Cu Fe Mo Mg Mn Co
99.96 231 < 1 5 7 < 1 < 1 36 13 16 50 < 1 < 1 < 1 < 1
(%
) 드
-
。
ro->
OE 은 으
」」_
Figure 1. The Sn removal (%) of the metal hydroxide precipitates as a function of O3 concentration.
precipitates. The concentration of ozone wascontrolled and infusedinto the suspended solution for 2h.Figure 1 shows the Snremoval (%) of the metal hydroxide precipitatesas a func
tion ofO3 concentration.Itreveals that thehigherthe concent
ration of ozone,the Snremoval (%)of the metalhydroxide precipitates higher.
Based on the result of Snremovalviaozonization, it is re
commended that themoreeffectiveSn removalneedsHNO3
dissolution of ITOscrap because Sn2+ species are easily trans formed into amorphous stannic acid, SnO^xH?。which is readily removed underfilteringprocess.16 Asshown in Table2, theozone treatment is moreeffective in Sn removal compared to oxygen. Moreespecially, a considerable Sn removal (99.79%) has been obtained in the ozonetreated sample. TheSnremoval byozone treatment can beexpressedby followingchemical equations:
Sn2+ + 3OH- M [HSnO2「+ H2O (1) [HSnO2「+ OH- + 1/2O2 M [SnOs]2- + H2O (2) [HSnOz]- + OH- + 1/3O3 M [SnOa]2- + H2O (3)
As ozoneexhibitsthehigher oxidizing powerthan oxygen, Sn(II)species are moreeffectivelyoxidized into Sn(IV) in an
alkalinesolution.Therefore, the finallystable [SnOM2- can be easilyremoved. As Na2SnO3 is soluble inwaterand removed in a washing step, high purity of In(OH)3 canbe easily reco vered,which is well coincident with PourbaixE-pH diagram indicating that Sn(OH)2 and Sn(OH)4 transform into HSnO2- or SnO32- in an alkaline solution.17
The resulting In(OH)3 powder was dissolved using 6 M H2SO4 solution.Indium was recovered as sponge metalthrough cementation withaluminum plateonthe basis of standard re
duction potentials (Eo for In3+/In = -0.338 V, Eo for Al3+/Al = -1.68 V)in H2SO4 solution with pHvalue of 1.5 at 60 oC.
Indium sponge metal is smeltedat 400oC by excess NaOH which is used for preventingindium from oxidation and ab sorbingmetalimpurities.ICPanalysis reveals that thepurity of indium metal is found to beapproximately99.96%without anyfurther purification step.
Acknowledgments. I amgratefulto GMS21 Co., Ltd. for supplyingITOtargetscrap.
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