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J. Environ. Eng. Manage., 17(6), 435-439 (2007)

CHARACTERIZATION OF HALOPHOSPHATE PHOSPHOR POWDERS

RECOVERED FROM THE SPENT FLUORESCENT LAMPS

Tien-Chin Chang,1,* Sea-Fue Wang,2 Sheng-Jie You3 and Akela Cheng41Institute of Environmental Planning and Management

National Taipei University of Technology

Taipei 106, Taiwan2Department of Materials and Mineral Resources Engineering

National Taipei University of Technology

Taipei 106, Taiwan3Department of Bioenvironmental Engineering

Chung Yuan Christian University

Taoyuan 320, Taiwan4Chung Tai Resource Technology Corp.

Taipei 100, Taiwan

Key Words: Halophosphate, recycling, fluorescent lamps, phosphor powder, thermal desorption

ABSTRACT

This paper investigated the characteristics of phosphor powders recovered from the spentfluorescent lamps. The results from inductively coupled plasma and X-ray diffraction analysisindicate that the halophosphate phosphor contains contaminations from rare-earth phosphor as wellas the glass tube. After the thermal desorption/distillation process, the mercury was effectivelyremoved from the phosphor powder. Though they have similar particle size distribution andmorphology, the recovered phosphor (6.5 m) has a smaller particle size than that of fresh phosphor(7.7 m), as a result of erosion during the recycling process. Since the luminescence properties ofthe recovered samples deviated from those of the fresh sample, it would alter the luminance andchromaticity of the lamps. The recovered phosphor can be mixed with the fresh phosphor and usedin the fluorescent lamps again.

*Corresponding author

Email: [email protected]

INTRODUCTION

Fluorescent lamps contain hazardous substanceswhich can harm the environment if the item is simplyput out with the trash. This item contributes mercurywhich make its way into landfills or incinerators, andrequire substantial cost and effort to assure that thesehazardous substances are not released into air or water.Most countries including United States, Germany, Ja-pan, and Taiwan have classified fluorescent lamps ashazardous waste. Due to persistent mismanagement oflamps, the Environmental Protection Agency (EPA) ofthe United States has published the new hazardouswaste lamp rule that adds waste lamps to the federallist of universal wastes [1], which are regulated underthe Resource Conservation and Recovery Act. Fur-thermore, land disposal restriction (LDR) treatmentrequirements for characteristic wastes went in to effect

on May 8, 1992 [2]. Recycling of fluorescent lamps isthus needed to be put in place to prevent pollutionfrom mercury and mercury containing phosphors. Theissue has also drawn the attention from EPA of Tai-wan and the same policy has thus been executed since2002. Quantities of the recycling for fluorescent lampsin Taiwan corresponding to years of 2002, 2003, 2004and first half of 2005 are 523,500, 7,891,700,4,363,700, and 2,369,500 kg, respectively, whichleads the percentage of the recycling for the fluores-cent lamps among the Asia countries.

Most lamp recyclers employ the dry recyclingprocess in order to meet the LDR standards [3]. Up tonow, several systems, including those developed byAdvanced Environmental Recycling Corporation(USA), Mercury Recovery Services (USA), SafetySupport Service (Japan), SepaDyne (Japan), MRTsystem (Sweden), were developed to recover the mer-


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436 J. Environ. Eng. Manage., 17(6), 435-439 (2007)

cury from mercury-containing phosphors. In thosesystems, not only the hazardous mercury was col-lected and purified into a level of 99.999% Hg, butalso the phosphors usually containing transition met-als and rare earth metals were recycled.

Several studies have reported the characteriza-tion and recovery process of mercury from the spentfluorescent lamps [4-6]. However, the effect of the dryrecycling processing on the physical characteristicsand functional performances of the recovered phos-phor powder has not been reported to date. Accord-ingly, this paper investigated the processing and char-acteristics of phosphor powders recovered from thespent fluorescent lamps. The chemistry, crystal struc-ture, powder characteristics and the luminescenceproperties of the recovered phosphor were character-ized and compared to those of the fresh phosphor. Thefeasibility of the recycling the phosphor powder from

the spent fluorescent lamps was also discussed.

EXPERIMENTAL PROCEDURE

1. Recycling Process

The spent fluorescent lamps were obtained fromthe Chung-Tai Resource Technology Corp., sponsoredby several companies in Taiwan. The phosphor pow-der was collected from the spent fluorescent lamps us-ing MRT End Cut Machine (ECM 5000, Karlskrona,Sweden). In this system, the spent fluorescent lampswere fed into the machine automatically and then sub-jected to several processing steps including identifica-tion of the tube, hole-making by row burners, end-cutting, and discharge of the mercury-containingphosphor from the glass tube by air blowing. Powdersof different qualities were collected in drums beneaththe cyclone. Mercury emissions to the air are so lowas to be negligible. The mercury contaminated phos-phor powders were then subjected to a purificationtreatment including a distillation and sieving process.The thermal desorption/distillation was carried out atthe temperatures above the boiling point of mercury(375 C) in order to remove the mercury and the or-

ganic residues. The purpose of the subsequent sievingis to get rid of granule contaminations from the glasstube and the electrode.

2. Analytic Methods

The particle analysis of the phosphor powderswere performed using light scattering (Horiba Instru-ments, Irvine, CA) measurements. Analyses of com-position were carried out on the recovered and freshphosphors. Powders were ground with a mortar andpestle into fine particles. Approximately 0.1 g of eachsample was dissolved in concentrated H2SO4 andheated at 80-90 C for 48 h. These solutions were thendiluted to 50 mL with H2O and HCl. Analyses were

performed using an Inductively Coupled Plasma MassSpectrometry (ICP-MS) (Spectrametrics Inc.). As acheck, microwave digestion was also used to dissolvepowders in the solution. The morphologies of phos-phor powders were observed by scanning electron mi-croscopy (SEM). X-ray diffraction (XRD) was used toidentify the structures of the products using a RigakuD/Max B with Cu K1 radiation at 40 kV. Emissionspectra were measured by a spectrofluorophotometer(Shimadzu RF-5301), which is equipped with thestandard lamp. The excitation spectra can be obtainedby scanning wavelength from 220 to 450 nm, emissiveat 650 nm. The emission wavelength was scannedfrom 500 to 750 nm, excited at 405 nm. The halo-phosphate phosphor powders recovered from the spentfluorescent lamps were characterized and comparedwith the fresh phosphor provided by the manufacturer.

RESULTS AND DISCUSSION

The phosphor powders recovered from the spentfluorescent lamps were subjected to the thermal de-sorption/distillation at the temperatures between 300and 800 C. The compositions of the phosphor pow-ders before and after the thermal treatment, obtainedfrom ICP analyses, are listed in Table 1. The phosphor

Table 1. Compositions of the recovered and fresh

phosphors

Content (wt%)ConstituentFresh phosphor Recovered phosphor

CaO 50.9 49.5

P2O5 35.7 34.9

Y2O3 3.28 3.09

F 2.48 2.43

Al2O3 1.21 1.16

SrO 1.14 1.13

Sb2O3 1.04 0.91

MnO 0.80 0.82

La2O3 0.79 0.97

C 0.63 0.70

BaO 0.54 0.83

Cl 0.50 0.44

Gd2O3 0.20

Tb4O7 0.20 0.16

Eu2O3 0.18 0.19

SiO2 0.14 1.88

ZnO 0.10 0.02

Fe2O3 0.05 0.12

Na2O 0.05 0.33

SO3 0.04 0.06

HgO 0.03

GeO2 0.02 0.02

PbO 0.23

MgO

0.09K2O 0.06


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Chang et al.: Recovery of Halophosphate Phosphor Powders 437

Fig. 1. Particle size distributions of the (a) recovered

and (b) fresh phosphor powders.

composition is mainly consist of Ca5(PO4)3 (F,Cl):(Sb,Mn) (halophosphate) [7-8]. Apart from the halo-phosphate, small amount of rare-earth elements in-cluding La, Gd, Tb, and Eu were detected in the re-covered phosphor. It is expected that small amount ofother phosphors merged and contaminated the halo-

phosphate powders during the process, though a XRDsystem was installed in the recycling system to iden-tify the type of the phosphors, before they were dis-charged from the glass tube by air blowing and col-lected in drums.

Based on the results in Table 1, 0.03 wt% ofHgO was detected in the phosphor powders before thethermal treatment. The mercury content is negligibleafter high temperature treatment. It clarifies that thethermal desorption/distillation effectively removed themercury residue in the phosphor powders. In additionto the environment issue, the results in our study indi-

cate that the mercury residue also alters the chroma-ticity of the phosphor powders.The thermal treated phosphor powders were then

through a sieving process to remove contaminationsfrom the glass tube and the electrode. The particle sizedistributions and SEM micrographs of the recoveredphosphor powders after purification, comparing tothose of the fresh phosphor powders are shown in Figs.1 and 2. Though they have a similar bimodal particlesize distribution, the recovered phosphor (6.5 m) hasa smaller mean particle size than that of fresh phos-phor (7.7 m). The slight reduction in the particle sizemight be due to the fact that the surface layer or

coated layer of the phosphor particle was stripped off,as a result of erosion during the recycling process. The

Fig. 2. SEM micrographs of the (a) recovered and (b)

fresh phosphor powders.

SEM micrographs shown in Fig. 2 revealed a round-shape morphology for both the recovered and freshpowders. These results manifest that the recyclingprocess does not alter the particle size distribution andthe morphology of the phosphor.

Though the physical characteristics of the recov-ered and the fresh phosphors do not have a significantdifference, the XRD results shown in Fig. 3 appar-ently indicate an unidentified second phase exists inthe recovered phosphors, in addition to theCa5(PO4)3(F,Cl):(Sb,Mn) phosphor. The second phasemay be due to the contaminations from the glass tubes,

which is consistent with the appearance of the SiO2,Na2O, MgO, K2O, and PbO constituents in recoveredphosphors, as shown in Table 1. These residues aretypical components in the glass tubes of fluorescentlamps.

In the halophosphate compound, the UV radia-tion, generated by the mercury discharge, is absorbedby Sb

3+and partly transferred to Mn

2+[9-10]. The 254

nm radiation of the mercury discharge is hardly ab-sorbed by the Mn

2+. The combination of a blue (Sb

3+)

and a yellow (Mn2+

) emission bands results in a whitelight. The spectral energy distributions of the freshand recovered halophosphor are shown in Fig. 4. Both

powders show a strong absorption in near UV region.It is clear from the figures that excitation curve is a

(a)

(b)

(a)

(b)

Particle size (m)


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438 J. Environ. Eng. Manage., 17(6), 435-439 (2007)

(b)

2 (degree)

JCPDS 860740

(a)

20 25 30 35 40 45 50 55 60

Intensity

(A.

U.

)

Fig. 3. XRD patterns for the (a) recovered and (b) fresh

phosphor powders.

Intensity

(a) (b)

0

100

200

300

400

500

600

700

800

300 400 500 600 700

0

100

200

300

400

500

600

700

800

(b)

Intensity

(a)

300 400 500 600 700

Wavelength (nm)

Fig. 4. Spectra energy distribution of the fresh and

recovered halophosphor: (a) and (b) are the

excitation and emission spectras of fresh

phosphor powders, respectively; (c) and (d) are

the excitation and emission spectras of recovered

phosphor powders, respectively.

distinct peak for the fresh phosphor and a broad bandfor the recovered phosphor. The excitation peakmaximum for the recovered sample shifts toward

shorter wavelength (from 406 to 352 nm).The emission spectra indicate a broad band for

both cases. For the fresh sample, the broad emissionband peaking at around 576 nm presents a warm-white emission. However, the emission spectrum ofrecovered samples is centering at 452 nm which is de-parting from the white light. The differentiation of theemission spectra may be due to the effect of the impu-rity ions. Since the photoluminescence properties ofthe recovered halophosphate deviated from those ofthe fresh phosphor, it would alter the luminance andchromaticity of the lamps. The recovered phosphorcan be blended with fresh phosphors and employedagain in the fluorescent lamps.

CONCLUSIONS

In this study, the physical characteristics, crystalstructure and the luminescence properties of the re-covered phosphor were characterized and compared to

those of the fresh phosphor. The experimental resultsshowed that the halophosphate contains small amountof rare-earth elements including La, Gd, Tb, and Eu,due to the contamination from other phosphors duringthe recycling process. In addition, the impurity fromthe glass tube, including the SiO2, Na2O, MgO, K2O,and PbO constituents were detected in the phosphorpowders. It was also observed that the content of mer-cury was negligible after the thermal desorp-tion/distillation treatment, which effectively removethe mercury residue in the phosphor powders. The re-covered phosphor (6.5 m) has a particle size smallerthan that of fresh phosphor (7.7 m) due to the erosionduring the recycling process, though they have a simi-lar particle size distribution and morphology. Finally,both the excitation and emission spectra of the recov-ered and fresh phosphors are different due to the effectof the impurity ions. It would alter the luminance andchromaticity of the lamps.

ACKNOWLEDGEMENTS

The authors would like to thanks the Environ-mental Protection Administration of the Republic ofChina for financial support under the project of EPA-

92-HA15-03-A056 and appreciate Chung-Tai Re-source Technology Company for assistance during theperiod of study.

REFERENCES

1. USEPA, Hazardous Waste Management System;Modification of the Hazardous Waste Program;Hazardous Waste Lamps; Final Rule. FederalRegister, 64(128) 36466-36490 (1999).

2. Morris, M.I., I.W. Osborne-Lee and G.A. Hulet,Demonstration of New Technologies Required forthe Treatment of Mixed Waste Contaminated with

260 ppm Mercury. ORNL/TM-2001/147, Officeof Science and Technology, Department of Energy,

2 (degree)2 (degree)

Intensity(A

.U.)

Wavelength (nm)

Inten

sity

(c) (d)


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Chang et al.: Recovery of Halophosphate Phosphor Powders 439

Oak Ridge, TN, pp. 31-39 (2002).3. Morturd, J., Fluorescent lamp collection and

separation method and apparatus. J. Clean. Prod.,5(3), 231-231 (1997).

4. Tanel, B., B. Reyes-Osorno and I.N. Tansel,

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14 (2005).

7. Stevels, A.L.N., Recent developments in the

application of phosphors. J. Lumin., 12(1), 97-107(1976).

8. Dobrowolski, R. and J. Mierzwa, Investigation of

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fluorescent lamps. Mater. Chem. Phys., 34(3-4),

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9. Fonda, G.R., Energy transfers in the calcium

halophosphate phosphors. Brit. J. Appl. Phys.,6(Suppl. 4), S69-S72 (1955).

10. Davis, T.S., E.R. Kreidler, J.A. Parodi and T.E.

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Discussions of this paper may appear in the discus-sion section of a future issue. All discussions shouldbe submitted to the Editor-in-Chief within six monthsof publication.

Manuscript Received: May 30, 2007

Revision Received: June 22, 2007and Accepted: July 3, 2007

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