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Recycling arsenic from gallium arsenide scraps through sulfurizing thermal treatment Jianguo Li, Lu Zhan, Bing Xie, and Zhenming Xu ACS Sustainable Chem. Eng., Just Accepted Manuscript • DOI: 10.1021/ acssuschemeng.6b02962 • Publication Date (Web): 18 Feb 2017 Downloaded from http://pubs.acs.org on February 20, 2017
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Recycling arsenic from gallium arsenide scraps through sulfurizing
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thermal treatment ∗
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Lu Zhana , Jianguo Lia, Bing Xiea, Zhenming Xub
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a Shanghai Key Lab for Urban Ecological Processes and Eco-Restoration, School of Ecological
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and Environmental Science, East China Normal University, 500 Dong chuan Road, Shanghai, China
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b School of Environmental Science and Engineering, Shanghai Jiao Tong University
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800 Dong chuan Road, Shanghai, China
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Abstract
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Due to the superior electronic properties, gallium arsenide (GaAs) is widely used in integrated
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circuits which are the core elements of most electric and electronic equipment. With the
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obsolescence of these equipment, a large number of GaAs scraps are generated, which may
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possess potential threats to human beings and the environment if treated improperly. In this paper,
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an integrated process combining sulfurization and evaporation is proposed to recycle arsenic from
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gallium arsenide (GaAs) scraps. The sulfides of arsenic can be easily evaporated and recycled.
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More importantly, it satisfies the environmentally friendly requirements because of the low
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toxicity of the arsenic sulfides. Using solid sulfur as the sulfurizing agent, 88.2% of arsenic can be
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extracted from GaAs scraps under the optimized condition of 5 K/min heating rate, 453 K
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mid-section temperature, 40 min mid-section holding time, 1073 K final temperature and 60 min
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the corresponding holding time. The behavior of arsenic during the sulfurizing thermal process is
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discussed in details. After the instrument examinations of XRD, EDS and XPS, the sulfurizing
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mechanism
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2GaAs+ ( 2x+3) S → 2 AsSx + Ga2 S3 . This research can provide the theoretical foundation for
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recycling arsenic from GaAs scraps or other e-waste containing arsenic.
is
explored
and
the
reaction
equation
is
deduced
as
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Corresponding author phone:
[email protected] +86
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54341064;
fax:+86
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e-mail:
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Key Words
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arsenic; sulfurization; recycle; gallium arsenide; scraps
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1. Introduction
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At present, electronic information industry has been advancing at a high speed, which results
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in the shorter service life of electronic products. Then a large number of waste electrical and
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electronic equipment(WEEE) come into being, which are serious potential threats to the
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ecological environmental security1, 2. According to statistics, about 41.8 million tons of WEEE
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were generated around the world in 2014, and it is predicted that it will increase to 49.8 million
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tons in 2018 with the growth rate of 4%~5% per annum3, 4. Arsenic plays an indispensable role in
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these electronic products. High-purity arsenic is usually applied to produce semiconductor
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materials such as gallium arsenide (GaAs), indium arsenide (InAs) and indium gallium arsenide
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(InGaAs). The electron mobility of these materials is five times that of silicon, which is the
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traditional semiconductor material. According to the information from United States Geological
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Survey (USGS), in 2014 around 34 tons of arsenic were employed to produce GaAs chips in US5.
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In recent years, due to the excellent properties, semiconductor materials containing arsenic are
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widely used in the manufacturing of smartphones, computers, optoelectronic products, LEDs and
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other electronic products6.
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The rapid upgrade of electronic applications will lead to sharply increasing demand of arsenic,
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which may be a potential hazard to the environment. From several previous investigations7-11,
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severe arsenic pollutions threatening the human health and environment occurred in the proximity
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of some places where e-wastes are disassembled. On the other hand, it is found that the proportion
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of metals in the e-wastes is around 40%, including gold, silver, palladium, copper, iron and some
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others12. These precious metals mostly exist in the integrated circuit (IC) chips and light-emitting
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diode (LEDs), where arsenic also exists13. People usually recycle precious metals by
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hydrometallurgy or pyro-metallurgy14,
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because of its low economic interest. Arsenic often gets into the effluent or dusts during the
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precious metal extracting.
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, however, arsenic doesn’t obtain enough attention
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So far, numerous studies have been done to remove arsenic from solid wastes. Some
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researchers used strong acid/alkali/oxidant to make arsenic leach into aqueous solutions, and then
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recycled arsenic in the form of precipitate via adding a variety of reagents16-19. There are also
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some researchers developing technologies to remove arsenic in the form of elementary substance
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or oxide by high temperature calcination20-22. However, some defects in these processes could
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never be ignored. The generation of waste liquid, waste gas, waste residue and leachate have a
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detrimental influence on environment and human health. And the hydrometallurgical technology
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needs a large number of reagents, which would increase the cost greatly. The traditional
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incineration process always needs a complex matched tail gas treatment device. Vacuum
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metallurgy separation (VMS) is considered to be a green and efficient method which is widely
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applied to the metal purification and alloy separation, including the treatment of arsenic23-25. But
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the complicated operations, high energy demands and the consumption require great expense.
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Additionally, Tunez et al.26 recycled gallium and arsenic in the form of chlorides. Although
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chlorides are easier to evaporate, the operating temperature is too low to apply to the treatment of
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WEEE containing plastic and resin.
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Among various compounds of arsenic, the toxicity of sulfide is the least. The applications of
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sulfurization for arsenic removal have been mentioned in published literatures. B.A Luganov et
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al.27 investigated the removal of arsenic in high-arsenic-bearing ores with the method of
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sulfurization and roasting. An invention patent applied by Li et al.28 introduced an approach to
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remove arsenic from arsenic flue dusts by combining sulfurization and evaporation.
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Industrial-grade sulfur was utilized as the sulfurizing agent in the patent. However, to our
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knowledge, sulfurization is never involved in the disposal of e-wastes, let alone applied to the
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arsenic removal. In fact, removing arsenic by sulfurization is actually a promising method. For
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one thing, sulfurizing agent which refers to solid sulfur in this study is very cheap and easily
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available. For another, the sulfides of arsenic have the advantages of low toxicity and low boiling
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points, which can assure its better environmental property and easier feasibility. This technology
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has greatly reduced the potential arsenic pollution and achieved the reclamation of arsenic and
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gallium.
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Taking GaAs scraps as the research object, this paper applied sulfurization and evaporation to
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extract arsenic by using solid sulfur as the sulfurizing agent. The theoretical feasibility of 3
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recycling arsenic through sulfurization was analyzed. The influencing factors were discussed and
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optimized. Further, the sulfurization mechanisms were explored and the reaction equation was
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deduced.
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2. Materials and Methods
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2.1 materials and apparatus
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GaAs scraps (Fig. 1) are adopted as the research objects in this paper. Inductively Coupled
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Plasma Optical Emission Spectroscopy analysis indicated the components of the scraps contained:
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As 47.8%, Ga 47.2% and others 5%.
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Figure 1. GaAs scraps
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Fig. 2 presents the main apparatus for the sulfurization and condensation. The quartz tube is
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1000 mm long with the external diameter of 50 mm and the thickness of 5 mm. The heating zone
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is about 150 mm long and the temperature can reach 1773 K. The two sides of the quartz tube
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outside the furnace are used as the condensing zones. Two conical flasks surrounded by cold water
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are connected with the tube, which can facilitate the condensation and collection of superfluous
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sulfur.
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Figure 2. Single temperature horizontal tubular furnace system 4
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2.2 methods
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At first, the GaAs scraps were pulverized and thoroughly mixed with excessive sulfur. The
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nitrogen gas flowed through the system for about 10 minutes before heating. Since then, the whole
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experiments were under the nitrogen atmosphere. Then the furnace was heated to the preset
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temperature (named mid-section temperature) to complete sulfurization at the heating rate of 5
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K/min, which was determined by some pre-experiments. Secondly, the temperature was further
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raised to another preset temperature (named final temperature) with the purpose of evaporating the
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generated arsenic sulfides. Next, the condensed products were heated to remove the superfluous
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sulfur. Finally, the condensate was scraped off the tube wall and collected for further instrument
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examinations.
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2.3 analysis
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The concentrations of arsenic and gallium in initial samples and residues are examined by
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Inductively Coupled Plasma Optical Emission Spectroscopy (ICP, ICAP6300, THERMO
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ELECTRO, U.S.A). The elemental distribution of the condensate peeled from the quartz tube was
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examined using Scanning Electron Microscope with X-ray Energy Dispersive analysis (SEM,
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Hitachi S-4800, Japan). The phase of the condensate was characterized by X-Ray Diffraction
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(XRD-6100, SHIMADZU, Japan) with Cu Kα radiation, operated at 40 kV and 25 mA over an
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angle of 20°
