消费类电子设备的全面元素分析外文文献

Comprehensive elemental analysis of consumer electronic devices Rare earth precious and critical elements Dylan T Buechler b Nadezhda N Zyaykinaa b Cole A Spencerb Emily Lawsonb 1 Natasha M Plossb 1 Inez Hua a b aPurdue University Lyles School of Civil Engineering 550 Stadium Mall Drive West Lafayette IN 47906 United States bPurdue University Division of Environmental and Ecological Engineering 500 Central Drive West Lafayette IN 47906 United States a r t i c l ei n f o Article history Received 14 June 2019 Revised 18 October 2019 Accepted 8 December 2019 Keywords Electronic waste Consumer electronics Precious metals Rare earth elements Electronics recycling Value recovery a b s t r a c t Over the past few decades electronic devices of all kinds and especially consumer electronics have evolved in function and composition in parallel to increasing manufacture and use There is great poten tial for recovering economic value and reducing environmental impact by recycling devices and extract ing various elements However there are few studies that comprehensively identify the elemental content of electronic devices or electronic waste In the present study consumer electronics and components hard drives ethernet hubs portable media players printers answering machines mobile phones Digital Versatile Disc DVD players computer wiring and printed circuit boards and electronic waste low grade scrap from one commercial recycling facility were analyzed for rare earth precious and critical metals The overall procedure included size reduction microwaveassisteddigestion andInductivelyCoupledPlasma OpticalEmission Spectroscopy ICP OES analysis Fifty six elements were quantifi ed or detected in these devices 14 rare earth elements six platinum group metals 20 critical metals and 16 other elements including some precious metals A single device could include a wide range of elements 48 metals were quantifi ed in the computer hard drives The esti mated economic value of the metals in each device ranged from 12 94 USD computer wiring to 454 USD hard drives The variety of metals in electronic devices suggests that end of life management strategies should focus on recycling and recovery which also decreases the overall environmental impacts of the devices especially associated with mining and refi ning metals 2019 Elsevier Ltd All rights reserved 1 Introduction Mobile phones personal computers PCs printers answering machines ethernet hubs and similar devices are generally catego rized as small information technology IT and telecommunications equipment The current trends in their product lifecycles are far from the ideal closed loop scenario The global quantity of small IT electronic waste e waste generated in 2016 amounts to 3 9 million metric tons with projection of increase by approximately 45 in 2020 Bald et al 2017 Although the average lifespan of many IT devices is an estimated 4 to 6 years Kumar et al 2017 consumers in the United States U S China and major European Union EU economies tend to purchase certain devices more fre quently for example smartphones have an estimated lifespan of 2 years Bald et al 2017 Every stable element in the periodic table has an application in modern technology Reck and Graedel 2012 Specialty metals and metalloids are added to electronic devices in trace quantities to ensure functionality To name a few arsenic As is used in radio frequency amplifi ers indium In forms part of touch screens con ductive coatings germanium Ge is integrated in displays and light emitting diodes LEDs tungsten W acts as a heat sink while silver based inks Ag on composite boards create electrical path ways through a device USGS 2016 Computer hard disk drives magnets require neodymium Nd dysprosium Dy and praseody mium Pr in signifi cant quantities Habib et al 2015 Because of its resistance to acid corrosion Tantalum Ta is included in capac itors on printed circuit boards PCBs Ueberschaar et al 2017 Therefore further growth in the manufacture of electronic devices will drive demand for certain elements including the https doi org 10 1016 j wasman 2019 12 014 0956 053X 2019 Elsevier Ltd All rights reserved Corresponding author at Purdue University Division of Environmental and Ecological Engineering 500 Central Drive West Lafayette IN 47906 United States E mail address hua purdue edu I Hua 1 Present address McCutcheon High School U S Highway 231 South Lafayette IN 47909 United States Waste Management 103 2020 67 75 Contents lists available at ScienceDirect Waste Management journal homepage Critical Raw Materials CRM which are elements at risk of limited supply It was suggested that e waste could serve as a secondary source of the CRM Ueberschaar et al 2017 Lister et al 2014 Marra et al 2018 However the recycling statistics estimate that the global recycling rates for many specialty elements As In Ge Nd Dy Ta etc are as low as less than 1 Reck and Graedel 2012 UNEP 2011 The low rates are due to challenges related to collection thermodynamic separation and techno economic feasibility In fact a recent publication reports rare earth metals critical metals and platinum group metals in landfi lls in the United Kingdom Guti rrez Guti rrez et al 2015 An encouraging initiative which is expected to have a powerful public resonance boosting the collection rates is a proposal to use exclusively recycled metal from e waste for creating all the medals for the upcoming 2020 Olympic Games in Tokyo Japan Leader et al 2017 Stimulated by a number of factors such as legislation the scarcity of the primary resources and environmental and pub lic health considerations global efforts are being made to develop pyro hydro and bio metallurgical technologies to combat the low recycling rates and recover economic value from discarded electronic devices Quantifi cationoftheelementalcompositionofversatile e waste streams to build the related knowledge database is the starting point for developing any approaches for value recovery Elemental analysis of e waste composition is conducted on a particulate surface by X Ray Diffraction XRD X Ray Fluorescence XRF and similar scanning methods Habib et al 2015 Kohl and Gomes 2018 Theplasmaassociatedanalyticaltechniques AtomicAbsorptionSpectroscopy AAS InductivelyCoupled Plasma Optical Emission Spectroscopy ICP OES and Inductively Coupled Plasma Mass Spectrometry ICP MS are often preferred due to much lower detection limits Ueberschaar et al 2017 Lister et al 2014 Marra et al 2018 Kolias et al 2014 Das and Ting 2017 Ramanathan and Ting 2015 Mello et al 2015 Given the highly heterogeneous nature of the electronic waste streams standardized analytical methodologies are still in development Traditionally studies on e waste focus on about 10 elements that are present either in relatively abundant amounts Al Fe Cu Ni Zn or regulated by Restriction of Hazardous Substances RoHS or other legislation due to their toxicity As Cd Pb Hg Kohl and Gomes 2018 Kolias et al 2014 Mello et al 2015 The trend is to broaden the analytical perspective and evaluate larger amounts of elements in waste electronics Semi quantitative classifi cation of 47 elements into 3 abundance categories was performed for con stituents of desktop computer towers Kohl and Gomes 2018 Another study group characterized 54 metals in Printed Circuit Boards from 24 types of waste electrical and electronic equipment WEEE fi nding greatly varying distribution patterns at different sampling points of the WEEE processing plant Oguchi et al 2013 A recent study Bookhagen et al 2018 reports an analytical protocol to assess 57 elements in smartphones in a single process ing approach The authors report that the same method is applica ble for assessment of total amounts of elements in other IT equipment The present study aims to contribute to building the knowledge database of the total elemental composition 56 elements of small IT and telecommunication equipment Separate waste streams namely mobile phones portable music players a printer an Ethernet hub an answering machine components from manual disassembly of desktop PC towers hard disk drives wiring and printed circuit boards as well as a DVD player were investigated for their elemental composition in order to assess the potential for economic value recovery Additionally a sample from an e waste recycling facility in the United States located in the state of Indiana representing mixed multi device scrap prepared for smelting has been evaluated 2 Materials and methods 2 1 Materials and samples Ultrapure water resistivity 18 2 MO cm at 25 C Thermo Scientifi c Barnstead Nanopure USA was used to prepare all reagents and standards The aqua regia solution used for micro wave assisted digestion of e waste powders consisted of trace metal grade hydrochloric 35 and nitric 70 acids Fisher Chemical USA A 68 element standard and Yttrium internal stan dard both in 2 nitric acid Exaxol USA and argon 99 997 and ultra high purity liquid nitrogen both supplied by Indiana Oxygen were used for ICP OES The samples analyzed in this study were obtained from similar devices that were disassembled into individual parts multiple devices with the same functionality that were combined as a whole or a single device as its own sample These are denoted as dissembled combined and stand alone respectively see Table 1 Two Dell desktop towers were disassembled into different components including printed circuit boards PCBs and wiring integrated drive electronics IDE cables included A combined fraction from the towers comprised of the plastic and metallic casings hard drives and other miscellaneous parts were not considered in this study From the PCBs the electrolytic capacitors were removed From the printer the plastic casing was stripped away leaving the rest as a single sample Similar device types were combined before further processing and analysis Three iPods were combined to produce one sample The same was done with eight mobile phones exclusive of batter ies only These samples were processed in their entirety including the plastic metal covers The following single devices were processed in their entirety and each considered its own sample an answering machine an ethernet hub a DVD player and a hard disk drive The full list of devices mentioned above with descriptions and weights can be found in Table 1 All samples used in this study with their respective weights and the mass fraction of the sample relative to the whole device it came from is shown in Table 2 For example the PCBs were 14 04 percent of the total weight of the two desktop towers 2452 2 17460 and only 12 14 percent from the printer was left after removal of the plastic casing The low grade scrap came from an e waste recycling facility Indianapolis IN USA and comprised of mixed multi device fi nely shredded scrapfromwhichtheplasticfractionwaspredominantly separated Samples were sized reduced below 1 18 mm using various methods All samples were initially processed in an industrial mobile shredder Shred It USA Further steps included manual cutting and grinding with an industrial blender IKA A11 Basic Analytical Mill USA equipped with a A11 3 beater and a cryogenic mill Spex Sample Prep 6770 Freezer Mill USA Ultra high purity liquid nitrogen Indiana Oxygen USA was used in both the IKA blender and cryogenic mill The size reduced sample was then passed through a 1 18 mm sieve The fi ne fraction was collected for further experiments while the coarse fraction was returned into cryogenic grinding All devices underwent multiple size reduc tion cycles In cases when mass of a device exceeded the amount needed for testing the printer the answering machine and the DVD player a custom built sample divider functioning as a riffl e splitter Gerlach et al 2002 was used for sub sampling 2 2 Analytical set up The moisture and volatiles fraction was determined gravimetri cally using an oven Thermo Scientifi c General Protocol Ovens 68D T Buechler et al Waste Management 103 2020 67 75 Germany at 110 C for 2 h The ignitable content was found by ashing the samples in a muffl e furnace Dentsply Ney Vulcan D 130 USA at 800 C for two hours and measuring the weight loss Through testing these procedures were suffi cient to remove all moisture volatile and combustible material from the samples A microwave digestion system Mars 6 CEM USA equipped with a MARSXpress vessel was used to dissolve the powders of electronic devices Samples were prepared in triplicate with 0 5 g of powder and 12 mL of aqua regia per analysis A 30 minute pre digestion at room temperature was followed by digestion at 200 C for 50 min These are similar conditions to an earlier study that used US EPA SW 846 Method 3051a to digest ground elec tronic scrap material and also compared other methods of wet digestion Das and Ting 2017 The pre digestion was performed to eliminate the hazard for a potentially vigorous reaction due to volatile or easily oxidized organic species Method 3051a 2007 The non digested solids were quantitatively separated by vacuum fi ltration through glass microfi ber fi lters Whatman 934 AH England dried at 110 C and gravimetrically quantifi ed To evaluate the elemental composition on the particles surface X ray Photoelectron Spectroscopy XPS Kratos AXIS Ultra DLD Imaging XPS UK was applied to the following solids a PCB sample prior MWAD and non digested solids fraction after MWAD from the PCBs printer mobile phones and low grade scrap Although this method only characterizes the chemical composition on the surface the data provides insight to what the digestion effi ciency might be The detection limit for the XPS analysis is 0 1 atomic percent or the percentage of a particular atom relative to the total number of atoms on the surface If the ratio of number of atoms of the given element to the total number of atoms is less than 1 1000 the element is not detected For element determination fi ltrates from MWAD were diluted by 30 20 000 fold with 2 nitric acid and tested with an ICP OES iCAP 7400 Thermo Scientifi c China Yttrium Y served as an internal standard The instrument settings can be found on line in Table S1 an E Component Method parameters including the list of elements acquisition wavelengths limits of detection LOD and quantitation LOQ can be found on line in Table S2 an E Component Elements are reported as detected but not quantifi able and denoted as D in the tables if the signal was greater than LOD but less than the LOQ Elements are reported as not detected or ND if the response was below the LOD If mea surement of a check standard was less than 90 accurate the element concentration reading in samples was rejected To calculate the potential economic value based on metal recov ery the following equation was used Value of ElementUSD kg mg of element kg of sample Price USD mg of element This calculation was carried out using the estimated average market prices for 2018 according to the USGS Mineral Commodity Summaries 2019 report USGS 2019 and assumes total quantity of element is recovered from the device 3 Results and discussion 3 1 Moisture volatiles and ignitable content The moisture and volatiles fraction for the PCBs wiring printer answering machine ethernet hub and DVD player is below 1 confi rming that these devices are mostly composed of dry matter These results agree with earlier analyses of similar components Bizzo et al 2014 Fig 1 shows the average ignitable content of the same set of samples This portion mostly corresponds to poly meric material but the elements such as lead and cadmium that volatilize at temperatures of 800 C Chen and Yang 1998 may contribute to these weight losses The answering machine and DVD player are comprised of the greatest amount of combustible material both around 78 The wiring and PCBs were in the lower range 23 and 32 combustible material respectively Similar results for the organic fraction in PCBs from computers were previ ously reported Yamane et al 2011 3 2 Evaluation of undigested solid fraction Although the decomposition of solid samples is remarkably accelerated by microwave radiation Balcerzak 2002 Das and Ting 2017 incomplete digestion of the electronic powders still occurred Different solvent composition is required to digest silica containing compounds that do not dissolve in aqua regia but use of hydrofl uoric acid was impossible in this study The frac tion of non digested solid relative to the initial sample is as fol lows PCBs 24 2 2 45 wiring 35 5 3 18 printer 16 9 6 27 iPods 49 03 0 79 mobile phones 49 03 6 70 answering machine 92 55 2 65 ethernet hub 74 1 1 87 hard drive 50 11 2 33 low grade scrap 31 85 2 27 The weight of the Table 1 Electronic devices included in this study Device categoryDevice informationStatusTotal mass g Desktop TowerDell Optiplex 790Disassembled7560 Desktop TowerDell Optiplex gx 270Disassembled9900 PrinterHP LaserJet 4100TNDisassembled12 960 iPodiPod Nano 1 GBCombined 1 a36 2 iPodiPod Touch 32 GBCombined 1 85 iPodiPod Classic 20 GBCombined 1 139 9 Mobile PhonePantech Model C5519 Combined 2 b79 3 Mobile PhoneSamsung N ACombined 2 99 4 Mobile PhoneSamsung N ACombined 2 73 9 Mobile PhoneMotorola RazorCombined 2 88 1 Mobile PhoneAlcatel N ACombined 2 64 8 Mobile PhoneSamsung Galaxy S6Combined 2 100 43 Mobile PhoneSamsung Galaxy S3Combined 2 96 4 Mobile PhoneSamsung MovistarCombined 2 50 6 Bluetooth EarpieceMotorola H499Stand Alone14 1 Answering MachineCasio PHONEMATE NA Stand Alone375 7 VGA to Mini DisplayPort Adapter AppleStand Alone32 8 Ethernet HubLinksys 5 Port Workgroup Switch Stand Alone156 6 Mobile DVD Player Viewer RCA N AStand Alone904 9 Hard DriveN AStand Alone221 8 a All 1 items were combined together to form a composite sample iPods b All 2 items were combined together to form a composite sample mobile phones Table 2 Samples derived from electronic devices Sample typeMass g Mass fraction of device Answering machine372 599 15 Ethernet hub162 3103 64 Hard drive185 583 63