Article pubs.acs.org/est
Volatile Organic Compounds and Metal Leaching from Composite Products Made from Fiberglass-Resin Portion of Printed Circuit Board Waste Jie Guo, Ying Jiang, Xiaofang Hu, and Zhenming Xu* School of Environmental Science and Engineering, Shanghai Jiao Tong University, 800 Dongchuan Road, Shanghai 200240, People’s Republic of China S Supporting Information *
ABSTRACT: This study focused on the volatile organic compounds (VOCs) and metal leaching from three kinds of composite products made from fiberglass-resin portion (FRP) of crushed printed circuit board (PCB) waste, including phenolic molding compound (PMC), wood plastic composite (WPC), and nonmetallic plate (NMP). Released VOCs from the composite products were quantified by air sampling on adsorbent followed by thermal desorption and GC-MS analysis. The results showed that VOCs emitted from composite products originated from the added organic components during manufacturing process. Phenol in PMC panels came primarily from phenolic resin, and the airborne concentration of phenol emitted from PMC product was 59.4 ± 6.1 μg/m3, which was lower than odor threshold of 100% response for phenol (180 μg/m3). VOCs from WPC product mainly originated from wood flour, e.g., benzaldehyde, octanal, and D-limonene were emitted in relatively low concentrations. For VOCs emitted from NMP product, the airborne concentration of styrene was the highest (633 ± 67 μg/m3). Leaching characteristics of metal ions from composite products were tested using acetic acid buffer solution and sulphuric acid and nitric acid solution. Then the metal concentrations in the leachates were tested by ICP-AES. The results showed that only the concentration of Cu (average = 893 mg/L; limit = 100 mg/L) in the leachate solution of the FRP using acetic acid buffer solution exceeded the standard limit. However, concentrations of other metal ions (Pb, Cd, Cr, Ba, and Ni) were within the standard limit. All the results indicated that the FRP in composite products was not a major concern in terms of environmental assessment based upon VOCs tests and leaching characteristics.
■
INTRODUCTION Since the mid-1990s, electronic waste has been recognized as the fastest-growing component of the solid-waste stream, and waste printed circuit board (PCB), an essential part of electronic waste, contains 28% metals, including Cu, Al, Sn, etc.1,2 Chemical methods including pyrometallurgy and hydrometallurgy are widely used for recovery of precious metals from waste PCB.3 Mechanical−physical processes consisting of comminution and separation (by differences of density, weight, size, magnetic properties, etc.) are also used to recycle waste PCB.4 After separation, the recycled metals can be sold or sent to recovery operations. However, large amounts of fiberglassresin portion (FRP) with low value are generated during the recycling process. Usually, the FRP consisting of glass fibers and resin powder is discarded or disposed in landfill, causing environmental pollution and resource-wasting. In view of ever-increasing environmental concerns and disposal costs, reuse and recycling are considered as the best practices for the treatment of voluminous FRP waste. Based on the concept of waste reutilization, some researchers studied filling methods to reuse the FRP as filler for some products, © 2011 American Chemical Society
such as bricks and composite boards made from FRP, and modified polypropylene filled with FRP.5,6 In our previous studies,7−9 three other kinds of composite products have been successfully prepared by combining the FRP and other additives, including phenolic molding compound (PMC), wood plastic composite (WPC), and nonmetallic plate (NMP). Previous studies proved the technical feasibilities of the filling of the FRP in different products. There were many advantages of these filling methods: (1) the FRP was used directly without modification; (2) the treated amount was large as the filling content could be up to 40%; (3) the properties of composite products met relevant standards, and glass fibers in the FRP could reinforce the mechanical properties of composite products to some extent. The FRP is a byproduct of the waste PCB when it is being recycled. The components of the FRP are very complex, and Received: Revised: Accepted: Published: 1028
August 23, 2011 October 31, 2011 December 5, 2011 December 5, 2011 dx.doi.org/10.1021/es2029558 | Environ. Sci. Technol. 2012, 46, 1028−1034
Environmental Science & Technology
Article
Figure 1. Recycling process of waste PCB and schematic production of composite products made from FRP.
VOCs Detection Method. A headspace solid-phase microextraction method followed by gas chromatography−mass spectrometry (HS-SPME-GC-MS) analysis method was used for quantitative analysis of VOCs released from wood flour, composite granules, WPC, and NMP samples. Three grams of those samples were weighed into a vial sealed with hole-caps and silicone septa, respectively, then the vial was immersed in a water bath at 40 °C. After 20 min of sample conditioning, an activated carbon fiber was exposed to the sample headspace for 30 min and immediately desorbed for 4 min at 200 °C in the gas chromatograph. The concentrations of VOCs emitted from WPC product and NMP product were detected according to NIOSH (National Institute for Occupational Safety and Health) 2549. The sampling was conducted using Tenax TA tubes. Two glass bottles with volume of 15 L were designed. Then 2 kg of WPC product and NMP product were cut into short pieces, and placed in the bottles. After the samples equilibrated for 24 h, pumps were used to collect air samples at 0.05 L/min for a sample volume of 3 L as shown in Figure S1. The following authentic standards were used for verification and quantification of identified compound. Styrene (99.5%), heptanal (99.5%), 6-methyl-5-hepten-2-one (98%), phenol (99.5%), tetradecane (98%), 6,10-dimethyl-5,9-undecadien-2one (97%), 2,5-cyclohexadiene-1,4-dione (97%), pentadecane (98%), hexadecane (98%) and isopropyl myristate (98%) were obtained from Aladdin-reagent Inc. (Shanghai, China). Benzaldehyde (99.5%), octanal (99.5%), decanal (97%), nonanal (96%), longifolene (99%), D-limonene (96%), ethylbenzene, (99.8%), o-xylene (99.5%), and methanol (99.9%) were all obtained from Shanghai Anpel Scientific Instrument Co., Ltd. (Shanghai, China). The Tenax TA tubes were analyzed using a Markes thermal desorber (TD) coupled to an Agilent GC6890N-MS5973N.
the FRP contains some hazardous materials, such as residual metals after corona electrostatic separation. In addition, organic additives such as phenolic resin, unsaturated resin, and styrene are used during the production of composite products. So it is likely that composite products may emit volatile organic compounds (VOCs) during use of the products. Leaching tests have been used to evaluate the environmental behavior of hazardous substances. Leaching characteristics of electronic waste, such as computer CPUs,10 cellular phones,11 and computer PCB12 have been studied. They demonstrated that Pb was the metal that most frequently exceeded regulatory thresholds. When PCB waste was treated by cement solidification13 or reused for cement mortar,14 leaching tests showed that the leaching level of Pb was far below the regulatory level. In this study, two aspects of environmental behavior of composite products were studied to evaluate the potential impact of composite products: (1) airborne concentrations of VOCs emitted from composite products were detected by GCMS (gas chromatography−mass spectrometry) analysis; (2) leaching tests were used to detect the leachability of metals in the composite products.
■
EXPERIMENTAL SECTION Materials. The waste PCB without electronic components was collected from a local PCB factory that recycles electronic waste. The PCB consisted of woven fiberglass mat impregnated with epoxy resin, and only copper was coated on the base plates. After the waste PCB was treated by mechanical−physical process,15 FRP was obtained for producing composite products as shown in Figure 1. Three representative composite products, including PMC product containing 20% FRP,7 WPC product containing 15% FRP,8 and NMP containing 20% FRP9 were chosen as testing samples. Samples for leaching tests were crushed into small particles with particle sizes less than 9.5 mm. 1029
dx.doi.org/10.1021/es2029558 | Environ. Sci. Technol. 2012, 46, 1028−1034
Environmental Science & Technology
Article
Desorption was carried out at 300 °C for 10 min. The column used for GC-MS was 30 m × 0.25 mm with 1.4-μm film thickness (DB-VRX). The oven program was as follows: initial temperature at 35 °C held for 4 min, ramped to 150 at 8 °C/ min, then ramped to 300 at 15 °C/min, hold 5 min. Helium was used as carrier gas at a flow of 1.2 mL/min. The MS was scanned in the range m/z 33−650. Compounds observed by GC-MS were identified by search in the NIST 08 mass spectral library and comparison with authentic standards if available. Criteria for positive identification of compounds were satisfactory match (similarity >80%) in NIST 08 and a retention time of ±0.02 min to that of an authentic standard. Quantification was carried out using six-point calibration curves made from three individually weighted solutions of authentic standards in methanol. The concentrations listed in Tables 1 and 2 were the average of 3 parallel testing results. The quantification limit was 10 μg/m3.
and deionized water (pH 4.93). The leachability tests were performed in polyethylene bottles (2 L). Fifty grams of FRP, PMC, WPC, and NMP samples and 1 L of extraction fluid were added to achieve the desired solid/liquid ratio of 1:20. The HJ/ T299 method, which is similar to SPLP (synthetic precipitation leaching procedure), is used to evaluate the leaching characteristics when composite products are exposed to acid rain waters. However, the pH and weight of extraction fluid used in the HJ/ T299 were different from those of the SPLP. For HJ/T299 tests, the acid solution containing sulphuric and nitric acids in a 2/1 ratio by weight (2 drops per L) was used to prepare the extraction solution (pH 3.2). Then, 100 g of solid samples and 1 L of extraction fluid were added in polyethylene bottles (2 L) to achieve the desired solid/liquid ratio of 1:10. The bottles for both methods were then placed on a rotary agitator at 30 rpm. After a prescribed extraction period of 18 h, the bottles were removed from the agitator and their contents were filtered through a 0.7-μm glass-fiber filter paper under vacuum to collect the leachates. Then the leachate samples were analyzed for metals by inductively coupled plasma atomic emission spectrometer (ICP-AES, IRIS Advantage 1000). Results of HJ/T300 and HJ/T299 methods are reported in mg/L. For quality control purposes, sample blanks were performed for each metal. Microshapes and Elemental Composition Analysis. The microshapes of FRP were analyzed by an optical microscope (Olympus BX-51). Scanning electron microscopes (Sirion 200, FEI, Netherlands) and energy-dispersive X-ray spectroscopy (INCA X-Act, Oxford, UK) (SEM-EDX) were used for the elemental analysis of FRP. Prior to the analysis, the FRP was sputter-coated with a thin layer of gold.
Table 1. Main Volatile Components Emitted from WPC Product no.
tR/min
similaritya
1 2 3 4 5 6 7 8 9 10 11 12
4.849 4.935 5.711 6.268 6.394 6.542 7.183 8.149 9.69 12.676 12.757 13.048
95 91 96 96 97 92 83 96 92 97 91 93
13 14 15 16
13.277 13.942 15.138 17.471
91 98 96 95
a
compound styrene heptanal benzaldehyde 6-methyl-5-hepten-2-one phenol octanal D-limonene nonanal decanal tetradecane longifolene 6,10-dimethyl-5,9-undecadien2-one 2,5-cyclohexadiene-1,4-dione pentadecane hexadecane isopropyl myristate
μg/m3 18.4 ± 3.0 12.6 ± 2.1
