Recovery of Gallium and Arsenic from Gallium Arsenide Waste in the Electronics Industry

Wei-Ting Chen1

Lung-Chang Tsai2

Fang-Chang Tsai3

Chi-Min Shu2

1Doctoral Program, Graduate School

of Engineering Science and

Technology, National Yunlin University

of Science and Technology (NYUST),

Douliou, Yunlin, Taiwan, ROC2Department of Safety, Health, and

Environmental Engineering, NYUST,

Douliou, Yunlin, Taiwan, ROC3Key Laboratory for the Green

Preparation and Application of

Functional Materials, Ministry of

Education, Faculty of Materials

Science and Engineering, Hubei

University, Wuhan, P. R. China

Research Article

Recovery of Gallium and Arsenic from GalliumArsenide Waste in the Electronics Industry

Gallium arsenide (GaAs) has both high saturated electron velocity and high electron

mobility, making it useful as a semiconductor material in a variety of applications,

including light-emitting diodes (LEDs), integrated circuits (ICs), and microwave appli-

ances. A side effect of the use of gallium (Ga) is the production of a relatively large

amount of hazardous waste. This study aimed at the recovery of Ga and arsenic (As)

from GaAs waste using hydrometallurgical methods involving leaching and coagu-

lation and a dry annealing process that involves annealing, vacuum separation, and

sublimation by heating. Our research has shown that GaAs can be leached using nitric

acid (HNO3) to obtain 100% Ga and As with a leaching solution at pH 0.1, with

subsequent adjustment of the leaching solution to pH 3 with sodium hydroxide

(NaOH). Another method used a leaching solution at pH 2, then adjusting to pH 11

using NaOH. Ferric hydroxide (FeO(OH)) was added at 908C after NaOH was added to the

leaching solution. At pH 2 and 11, 55.5 and 21.9% of the As could be removed from the

hazardous waste, respectively. The Ga could also be precipitated. When GaAs powder

was heated to 10008C over 3 h, 100% As removal was achieved, and 92.6% of the Ga was

removed by formation of 99.9% gallium trioxide (Ga2O3). Arsenic was vaporized when

the temperature was elevated to 10008C, allowing arsenic trioxide (As2O3) to condense

with 99.2% purity. The Ga2O3 powder produced was then dissolved and electrolyzed,

allowing for 95.9% recovery of Ga with a purity of 99.9%.

Keywords: Annealing process; Ferric hydroxide; Gallium trioxide; Hydrometallurgy; Lean source

Received: April 25, 2011; revised: September 24, 2011; accepted: October 14, 2011

DOI: 10.1002/clen.201100216

1 Introduction

In the electronics industry, silicon is currently the substrate of

choice for manufacturing [1]. Although silicon is widely used in

manufacturing semiconductor products because of its stability,

low cost, and consistency, it has many disadvantages. Because of

these disadvantages, other semiconductor materials are sometimes

substituted for silicon to meet the requirements of advanced tech-

nologies. Gallium (Ga) is a metallic element in Group 3 of the

Periodic Table. In the 1970s, researchers discovered that Ga could

be combined with elements of Group 15 to generate new materials

with semiconducting properties [2]. In recent years, Ga and indium

(In) have emerged as important strategic metals because of their

importance in the electronics industry [3]. Ga and In are used in a

variety of semiconductor materials, including gallium arsenide

(GaAs) and indium phosphide (InP). Because these compounds pos-

sess high saturated electron velocity, high electron transmission,

and semi-insulating properties. GaAs and InP are suitable for man-

ufacturing optical devices, such as advanced semiconductors, DVDs,

laser diodes, and other electronic devices [1, 4]. Due to the antici-

pated increase in the use of Ga and In and given their similar

chemical properties, concerted efforts have been made to recover

Ga and In from alternative sources such as ores and wastes [5].

One possible strategy for the recovery of these metals is liquid–

liquid extraction. Liquid–liquid extraction has been applied to the

separation and recovery of Ga and In [6]. One of the most common

general methods for the extraction of metal ions from aqueous

solution is the reaction of the metal ion with a specific agent to

form a metal chelate, followed by solvent extraction [7–10]. Mixtures

of ions can be separated selectively because of the availability of a

wide variety of extractants and diluents [7]. A variety of extractants

have been used to extract Ga, including 8-hydroxyquinoline, which

has been one of the most studied extractants [11–14]. Some efforts

have also been made to recover Ga from Bayer liquor [15–18], a

product of the Bayer process for refining bauxite to produce

alumina. Additionally, various amines with high molecular weights

have been used in the separation of Ga from waste GaAs [19–23]. The

use of chelating agents and amines of high molecular weight as

extractants has limitations, including long equilibration time, the

required use of chemical modifiers, the loss of extractant due to

aqueous miscibility, and the need for rigid control of phase variables

Correspondence: Professor C.-M. Shu, Department of Safety, Health, andEnvironmental Engineering, NYUST, 123, University Rd., Sec. 3, Douliou,Yunlin, Taiwan 64002, ROCE-mail: [email protected]

Abbreviations: As, arsenic; As2O3, arsenic trioxide; FeO(OH), ferrichydroxide; Ga, gallium; GaAs, gallium arsenide; Ga2O3, galliumtrioxide; H2SO4, sulfuric acid; HNO3, nitric acid; In, indium; NaOH,sodium hydroxide; Na2S, sodium sulfide

Clean – Soil, Air, Water 2012, 40 (5), 531–537 531

� 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim www.clean-journal.com

[7]. Ongoing discussion highlights the emerging interest in Ga recov-

ery from different types of so-called ‘‘lean sources’’, and we have

pursued alternative methods to recover Ga and As from GaAs waste

by applying hydrometallurgical methods, including leaching and

coagulation, as well as dry type processes, including annealing,

vacuum separation, and sublimation by heating. We then compared

our results to identify the advantages and disadvantages of each of

these methods.

2 Experimental process

2.1 Sample source and pre-treatment

The experimental sample was purchased from a silicon wafer fab-

ricator in Tainan City’s science-based industrial park. The rejected

wafers that contained Ga metal were ground before dissolving in the

leaching solution. To ensure the stability and consistency of the

samples, these waste wafers were first dried in an oven at 1058C for

48 h and then ground until the powder could pass through a 20-mesh

sieve.

2.2 Analysis of component elements

An atomic absorption spectrometer (AA) (Perkin Elmer, 5100) and an

inductively coupled plasma atomic emission spectrometer (ICP-AES;

Optima, 5100DV) were employed to determine the metal ion con-

centration in the aqueous phase and to analyze the ores. For the

partition studies, equal volumes (10 mL) of the aqueous and organic

phases were shaken at room temperature (25� 38C) for 5 min to

ensure complete equilibration. The two phases were separated, and a

suitable aliquot of the aqueous phase was assayed for the metal ion

concentration. Based on three tests, the value of 95% extraction for

Ga (III) was associated with a variation coefficient of �3% [24].

2.3 Dissolution of samples

Sulfuric acid (H2SO4) and nitric acid (HNO3) were used as leaching

agents. Different experimental conditions, such as concentration,

solid/liquid (S/L) ratio, and leaching time, were varied. To ensure that

we had optimized the leaching conditions, the solution was sub-

jected to purification following the analysis of metal ion

concentration.

2.4 Adjustment of solution pH

Sodium hydroxide (NaOH) was used to precipitate metal ions in the

various leaching solutions. The addition of various concentrations of

NaOH made it possible to precipitate metal ions over a pH range of 1–

13. To identify the pH at which each metal precipitates, subsequent

analysis was applied to the filtrate.

2.5 Removal of arsenic

Sodium sulfide (Na2S) and ferric hydroxide (FeO(OH)) were added to

the leaching solution to precipitate arsenic (As), and the quantity of

As recovered was assessed by AA or ICP analysis.

2.6 Annealing process

Samples were heated in an oven, and As was the first substance to

sublime during the heating process due to its low bp. After the

annealing process, gallium trioxide (Ga2O3) was obtained.

2.7 Acquiring gallium metal by electrolysis

The compound Ga2O3 was acquired during the annealing process.

To obtain pure Ga metal, the Ga2O3 was ground into powder. The

powder was then dissolved into a leaching solution, and the solution

was electrolyzed to extract the Ga metal.

3 Results and discussion

3.1 Determination of trace concentrations

To obtain spectroscopic signatures and to quantify the amounts of

various elements in the samples, we employed methods suggested in

Acid Digestion of Sediments, Sludges, and Soils (NIEA R353.00C), and Soil

Quality – Extraction of Trace Metals Soluble in Aqua Regia (NIEA S321.63B)

(www.niea.gov.tw/analysis/method/ListMethod.asp?methodtype¼SOIL).

The major and trace elements, determined by ICP-AES, included

silver (Ag), aluminum (Al), boron (B), barium (Ba), bismuth (Bi),

calcium (Ca), cadmium (Cd), cobalt (Co), chromium (Cr), copper

(Cu), iron (Fe), Ga, In, magnesium (Mg), manganese (Mn), sodium

(Na), nickel (Ni), lead (Pb), strontium (Sr), thallium (Tl), zinc (Zn), and

As. These results are presented in Tab. 1, which shows that the

concentrations of As and Ga were 46 and 42%, respectively. The

residual 12% consisted of insoluble materials.

3.2 Determination of the optimum extraction

method

3.2.1 Effects of using various acids as extractants for Ga

and As

As reported by Lee and Nam [25], HNO3 is more effective for the

extraction of Ga from GaAs waste than hydrochloric acid (HCl)

or H2SO4. Figures 1 and 2 shows the extraction efficiencies of Ga

and As with H2SO4 and HNO3 using an S/L of 3 g/100 mL with a

constant stirring speed at room temperature for 1 h. The percentages

of recovered Ga were 14, 22, 25, 26, and 29%, and the percentages of

recovered As were 11, 13, 14, 15, and 18% using 1, 2, 3, 4, or 5 N H2SO4,

respectively. Comparing the extraction efficiencies for different

acids, HNO3 was found to recover Ga and As better than H2SO4.

Ga and As were almost completely extracted using 4 N HNO3.

From these results, we concluded that increasing the concentration

of HNO3 also increased the extraction efficiencies of Ga and As.

3.2.2 The effect of GaAs concentration in a HNO3

solution

The extraction efficiencies for Ga and As using 4 N HNO3 as an

extractant with a constant stirring speed at room temperature for

1 h are shown in Fig. 3. The extraction efficiencies for Ga were 98,

99.9, 99.9, 84, and 69%, and for As, we obtained 98, 98, 99, 86,

and 65%. The optimal recoveries of Ga and As occur when S/L of

3 g/100 mL.

532 W.-T. Chen et al. Clean – Soil, Air, Water 2012, 40 (5), 531–537


3.2.3 The effect of leaching time

The effect of time on leaching waste containing GaAs with 4 N HNO3

at room temperature with an S/L of 3 g/100 mL is shown in Fig. 4.

Figure 4 shows that the leaching efficiency tended to decrease as

the contact time increased. A short contact time was found to be

suitable for the optimal extraction of Ga and As from GaAs waste,

and results in the removal of most of the Ga from the surface of

the GaAs particles [26]. Half an hour of contact time was found to be

optimal.

3.3 Removal of impurities

3.3.1 Removal of impurities by coagulation using Na2S

The leaching solution contained two elements, Ga and As, which

must be separated before purification. Table 2 shows the concen-

trations of the precipitated Ga and As following the pH adjustment

with NaOH. When the pH was adjusted to 3, the precipitation

efficiencies of Ga and As were 37.9 and 33.7%, respectively. The

results of As removal by coagulation with Na2S are given in

Tab. 3. The As removal efficiencies were 29.6, 90.5, and 3.7%, with

2.9, 6.3, and 9.9 g of Na2S, respectively. During the coagulation

experiment, arsenic trisulfide (As2S3) precipitated with 6.3 g

Na2S, and the As removal efficiency reached 90.5%; moreover, Ga

precipitated at the same time. Therefore, adding Na2S not only

removed As but also resulted in removal of Ga due to co-

precipitation.

Figure 1. Effect of H2SO4 concentration on the extraction of Ga and As(conditions: S/L¼3 g/100mL, constant stirring speed, and room tempera-ture, 1 h).

Table 1. Chemical analysis of gallium arsenide waste samples

Acid digestion of sediments, sludges, and soils (NIEA R353.00C)

Sample number Ga (g/L) As (g/L)

1 12.597 13.9062 12.946 13.9493 13.021 13.5954 12.567 13.8415 12.309 13.990Average 12.604 13.822Percentage (%) 42 46

Soil quality – extraction of trace metals soluble in aqua regia(NIEA S321.63B)

Sample number Ga (g/L) As (g/L)

1 12.846 13.9982 12.290 13.8733 12.208 13.8904 12.679 13.7015 13.008 13.806Average 12.606 13.854Percentage (%) 42 46

Figure 2. Effect of HNO3 concentration on the extraction of Ga and As(conditions: S/L¼3 g/100mL, constant stirring speed, and room tempera-ture, 1 h).

Figure 3. Extraction of Ga and As from starting materials with variableGaAs contents (conditions: 4N HNO3, constant stirring speed, roomtemperature).

Figure 4. Variation in extraction efficiency over the duration of extraction(conditions: S/L¼ 3 g/100mL, 4NHNO3, constant stirring speed, and roomtemperature).

Clean – Soil, Air, Water 2012, 40 (5), 531–537 Recovery of Ga and As from GaAs Waste in the Electronics Industry 533


3.3.2 Removal of impurities by coagulation with

FeO(OH)

The leaching solution was adjusted to pH 2 and 11 with NaOH and

FeO(OH) (As/Fe, 1:10) was then added to remove arsenic. Table 4

shows that As and Ga precipitated at pH 2 and that the precipitation

efficiencies for As and Ga were 40.2 and 37.2%, respectively. The

results of As removal with FeO(OH) are displayed in Tab. 5, which

shows that the As removal efficiency was 55.5%. As presented in

Tab. 6, As and Ga dissolved in the leaching solution at pH 11,

resulting in a drop in the precipitation efficiencies for As and Ga

to 21.9 and 16.5%, respectively. By adding FeO(OH) to the leaching

solution after pH adjustment, 36.1% of the As was removed, and

44.7% of the Ga was co-precipitated, as shown in Tab. 7.

The results of the attempt to remove impurities by coagulation

with FeO(OH) were similar to the results obtained for gallium

Table 2. Concentrations of Ga and As after pH adjustment with NaOH

Metal Ga As

Conditions pH 0.1 pH 3 pH 0.1 pH 3

Concentration of leaching solution (g/L) 13.401 8.317 12.860 8.530Precipitation efficiency (%) (13.401� 8.317)/13.401¼ 37.9 (12.860� 8.530)/12.860¼ 33.7

Table 3. Precipitation efficiencies for coagulation with Na2S at pH 3

Metal Ga As

Addition of Na2S (g) 2.9 6.3 9.9 2.9 6.3 9.9Concentration of leaching solution (g/L) 4.231 0.054 8.215 6.003 0.807 8.215Precipitation efficiency (%) 49.1 99.4 1.2 29.6 90.5 3.7

(8.317� 4.231)/8.317¼ 49.1 (8.530� 6.003)/8.530¼ 29.6(8.317� 0.054)/8.317¼ 99.4 (8.530� 0.807)/8.530¼ 90.5(8.317� 8.215)/8.317¼ 1.2 (8.530� 8.215)/8.530¼ 3.7

Table 4. Concentrations of Ga and As at pH 2

Metal Ga As

Conditions pH 0.1 pH 2 pH 0.1 pH 2Concentration of leaching solution (g/L) 12.684 7.963 13.980 8.367Precipitation efficiency (%) (12.684� 7.963)/12.684¼ 37.2 (13.980� 8.367)/13.980¼ 40.2

Table 5. Precipitation efficiencies for coagulation with FeO(OH) at pH 2

Metal Ga As

Addition of FeO(OH) (g) 9.9 9.9Concentration of leaching solution (g/L) 2.435 3.722Precipitation efficiency (%) (7.963� 2.435)/7.963¼ 69.4 (8.367� 3.722)/8.367¼ 55.5

Table 6. Concentrations of Ga and As at pH 11

Metal Ga As

Conditions pH 0.1 pH 11 pH 0.1 pH 11Concentration of leaching solution (g/L) 12.468 10.417 13.670 0.673Precipitation efficiency (%) (12.468� 10.417)/12.468¼ 16.5 (13.670� 10.673)/13.670¼ 21.9

Table 7. Precipitation efficiencies for coagulation with FeO(OH) at pH 11

Metal Ga As

Addition of FeO(OH) (g) 9.9 9.9Concentration of leaching solution (g/L) 5.756 6.818Precipitation efficiency (%) (10.417� 5.756)/10.417¼ 44.7 (10.673� 6.818)/10.673¼ 36.1



hydroxide (Ga(OH)3). The recovery efficiency of Ga was decreased by

adding FeO(OH) to coagulate the impurities.

3.3.3 Removal of impurities by annealing process

Because the bps of Ga and As differ, the two metals can be separated

through an annealing process. The GaAs sample was heated at

different temperatures in an oven. Figure 5 demonstrates the As

removal and Ga loss efficiencies at various temperatures over 3 h.

The As removal efficiency was 91.6% when the temperature was

9008C but rose to 100% when the temperature reached 10008C.

Figure 6 shows that the As removal efficiencies were 66.8, 75.8,

72.2, and 74.4%. The removal efficiency was not reduced when the

heating time was increased. These data are illustrated in Fig. 7:

Arsenic could be removed completely when the temperature

reached 10008C, and material remaining following As sublimation

was assumed to be Ga2O3. Arsenic trioxide (As2O3) was passed

through a cooling system, and As vapor was condensed at the cooler

temperature. Using this method, we were able to achieve purities for

Ga2O3 and As2O3 of 99.9 and 99.2%, respectively. As shown in Figs. 8

and 9 and Tab. 8, the component and weight percentage of product

were the same as those found by the standard material analysis

using energy dispersive spectrometry (EDS). This confirms that pure

Ga2O3 was obtained. The Ga2O3 was dissolved and subsequently

electrolyzed at 4 A of current for 3 h to yield Ga metal at a purity

of 99.9% and with 95.9% recovery.

Figure 5. Removal efficiency based on the Ga and As content over a 3 hremoval period at various temperatures.

Figure 6. Concentration variation of Ga and As versus time at 5008C.

Figure 7. Concentration variation of Ga and As versus time at 9008C.

Figure 8. Constituent elements in Ga2O3 products (1000�).

Figure 9. Constituent elements in Ga2O3 standard (1000�).

Table 8. Weight percentages of elements in the Ga2O3 product and

standard

Element Ga O

Weight percentage of product (%) 98.70 1.30Weight percentage of standard (%) 98.72 1.28



4 Conclusions

More than 99% of the Ga and As in our sample was extracted using

4 N HNO3 at room temperature for half an hour. To obtain high

purity and high recovery efficiency, the impurities were removed by

chemical coagulation. Arsenic was experimentally removed by

coagulation with Na2S and FeO(OH), and we found that coagulation

was not beneficial for As removal. It was found that a different

method was needed to recover Ga and remove As. As shown in

Fig. 10, Ga in waste wafers can be recovered efficiently using an

annealing process, due to the temperature differences in the bps of

the two metals. Ga and As can be completely separated at a tempera-

ture of 10008C. One of the resulting products was identified as Ga2O3

by EDS analysis. Because the bp of As is lower than that of Ga, As can

be vaporized during annealing. The As vapors were condensed by a

cooling system, and the resulting product, As2O3, was obtained as

white crystals. This dry method not only resulted in both high purity

and a high efficiency of recovery for Ga but also reduced the use of

acids and other chemicals used in the hydrometallurgical methods.

The dry method does not result in the formation of toxic gases or

harmful waste products such as As vapors, chlorine vapor, or acidic/

alkaline solutions, which are quite commonly observed when other

methods are used. We, therefore, recommend this annealing process

as an environmentally friendly recovery method.

Acknowledgments

This study was guided by the late professor Hung-Yuan Fang and

carried out by his team of environmental and microbiological

researchers. Without his meticulous instruction and positive feed-

back, this study could not have been completed.

The authors have declared no conflict of interest.

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Recovery of Gallium and Arsenic from Gallium Arsenide Waste in the Electronics Industry

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