ReviewPrecious metals recovery from waste printed circuit boards: A review for current status and perspective
Introduction
The information and communication technology (ICT), which is considered as a “general-purpose technology” (Williams, 2011) because it could interacts with and enhances other technologies (Wang and Xu, 2015), restructures societies and economies all over the world in these decades (Umair et al., 2015). As a consequence, large amounts of e-waste, which have influenced greatly on human interactions with the environment, are discarded constantly (Wang and Xu, 2015).
According to the Solving the E-Waste Problem (StEP) Initiative, about 49 million tons of e-waste are generated in 2012 around the world, and it will be 65.4 million tons in 2017 (Yoshida et al., 2016). In Europe, e-waste is generated with a resultant increase by 16–28% every five years, which is three times as fast as the average rate for municipal waste (Rahmani et al., 2014). China, one the largest generators of e-waste in the world, generates more than 5 million TV sets, 4 million refrigerators, 5 million computers, and 10 million mobile phones annually now (He et al., 2006, Liu et al., 2014). Due to the leverage of huge unit sales globally, the manufacturing of electrical and electronic equipment (EEE) is a major demand sector for precious metals (gold, silver, and platinum-group) and special metals (selenium, tellnium, bismuth, antimuth, and indium) with a strong further growth potential (Chancerel et al., 2009). Actually, after the use phase, the waste EEE (WEEE) could be utilized as an important source to recover these “trace elements” (Chancerel, 2010).
Over the past decades, the investigations on integrated recycling processes (Razi, 2016, Baxter and Hanssen, 2016, Yoshida et al., 2016) for waste desktop computers, waste mobile phone, waste cathode ray tube TVs, and so on, have achieved great progresses. Nevertheless, some technical obstacles are also existed that limit the industrial application of WPCBs recycling (Wang and Xu, 2015). Hence, up to now, the e-waste recycling should be developed toward more depth and refinement to promote industrial production of e-waste resource recovery (Wang and Xu, 2015). In this article, the recycling processes and techniques of precious metals from waste PCBs (WPCBs) is mainly focused on.
PCBs, which provide interconnection between software and hardware, are found in all EEE. Over recent years, the average rate of world PCBs manufacture increases by 8.7% annually—much higher in Southeast Asia (10.8%) and mainland China (14.4%) (Huang et al., 2009). The percentage of WPCBs is huge (about 3%) (Sohaili et al., 2012) among the e-waste amount and even more in some EEEs, like TV set (7.04%), computer (18.76%), and mobile phone (21.3%) (Duan et al., 2011).
WPCBs, which are resource-rich, are generally referred to as “urban mines”. At a rough estimate, one-third of the weight of WPCBs consists of metals, mainly Cu (∼16%), Sn (∼4%), Fe (∼3%), Ni (∼2%), and Zn (∼1%) (Chen et al., 2013). In addition, precious metals like Au (0.039%), Ag (0.156%), and Pd (0.009%) (Chehade et al., 2012), which are used as contact materials or plating layers because of their electric conductivity and chemical stability (Chen et al., 2013), are 10 times (Eygen et al., 2016) more abundant in WPCBs than in natural ores. Thereby, it is obvious that recycling precious metals from WPCBs is greatly significant. For example, recycling of gold and other precious metals from WPCBs in China in 2007 totaled U.S. $2.6 billion, with other metals contributing a further U.S. $0.4 billion (Hagelüken and Corti, 2010). However, these recycling activities are dominantly occurred in unregulated cottage industries with artisanal processes without pollution controls. Anyway, from the sustainable viewpoint, the recycling of WPCBs becomes more and more attractive because of the low ore concentration, difficult mining conditions and other factors (Hagelüken and Corti, 2010).
As a matter of fact, the e-waste recycling and management is not simple and straightforward at present (Mella et al., 2014). The “mineralogy” of WPCBs is much different comparing to of the natural ores for metals refining (Hagelüken and Corti, 2010): first, up to 60 different elements are closely interlinked with complex assemblies and sub-assemblies (Hagelüken and Corti, 2010), such as copper, iron, aluminium, lead and tin etc., as well as precious metals, whose physical and chemical properties are much different, as presented in Fig. 1; second, the metals contained in WPCBs usually cross-link to organics which are usually toxic and potential to bioaccumulate, such as brominated flame retardants, polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/Fs), polybrominated diphenyl ethers (PBDEs), chlorinated dioxin, and polycyclic aromatic (Johnson et al., 2007). During unregulated disposal activities, these hazardous substances are usually released, resulting in an extreme damage to the environment and human health (Wang and Xu, 2015, Davis and Grab, 2015). According to a report, about 76,000 metric tons of PBDEs, which have been shown to disrupt endocrine hormones and generally contained in WPCBs, are released into the environment each year at e-waste sites in China (Wang and Xu, 2015, Stone, 2009). Hence, the composition of WPCBs is much more complex than natural mines that make processes for recycling valuable metals more complex, resulting in efficient and environmentally sound processing of the WPCBs requires special attention (Hagelüken and Corti, 2010).
In order to explore and complete an appropriate and thorough system to recover precious metals from WPCBs from industrial application viewpoint, this paper reviews and analyzes the current related metals recycling technologies. Then, an integrated technological route, including metals enrichment and precious metals recovery, is proposed. Finally, in order to promote the development of metals (precious metals) recovery from WPCBs, some improvements and recommendations in techniques and the future trend are also put forward.
Section snippets
Current state of recycling metals from WPCBs
Generally, the concentrations of precious metals, which are much lower than those of base metals, in WPCBs, are very high than those of any richest conventional natural ores (Gurung et al., 2012). Precious metals are recovered from ores by the traditional matte-smelting-refining technique (Mpinga et al., 2015), including two stages: (1) grounded by conventional multistage crushing and ball milling, or by semi-autogenously grinding, and then smelted; (2) the matte is hydro-metallurgically
Integrated metals enrichment process for WPCBs
According to the previous analysis, the metallic elements are often covered with or encapsulated by various plastic or ceramic materials on WPCBs (Guo et al., 2015a, Guo et al., 2015b); therefore, a pre-treatment course is indispensable to expose metals to be active (Guo et al., 2015a, Guo et al., 2015b). Due to the good environmental property, high efficiency and easy operability, mechanical-physical separation, which is based on the differences of materials in physical characteristics
Precious metals recovery from WPCBs
Recovery of precious metals is essential due to their high value contents. Hence, recycling precious metals from WPCBs should be given enough attention to. Hydro-metallurgical treatment process could be preferred over pyro-metallurgy for the recovery of precious metals (Akcil et al., 2015), because of (1) low waste gas emission comparing to pyro-process which releases harmful and toxic gas (dioxins/furans, Cl2, Br2 and CO2) and volatile metals (Pb, Hg, Cr6+, Cd), dust, together with others like
Future recommendations
At present, “mechanical crushing + hydrometallurgy” technology, which is considered as an advanced technology and adopted dominantly currently to deal with WPCBs, is developed by Daimler-Benz Uim Research Center, Germany (Yang, 2013). This technology involves five-stage treatments for precious metals recovery, including primary crushing, liquid nitrogen refrigeration, classification, electrostatic separation, as well as hydrometallurgical dissolving and recovery for precious metals. Although
Acknowledgements
This work was supported by the National Natural Science Foundation of China (51534005). The authors are grateful to the reviewers who help them improve the paper by many pertinent comments and suggestions.
References (77)
- et al.
Thiosulfate leaching of gold—a review
Miner. Eng.
(2001) - et al.
Environmental message framing: enhancing consumer recycling of mobile phones
Resour. Conserv. Recycl.
(2016) - et al.
Process development for recovery of copper and precious metals from waste printed circuit board with emphasize on palladium and gold leaching and precipitation
Waste Manag.
(2013) - et al.
Study on the influence of various factors in the hydrometallurgical processing of waste printed circuit boards for copper and gold recovery
Waste Manag.
(2013) - et al.
An advanced study on the hydrometallurgical processing of waste computer printd boards to extract their valuable content of metals
Waste Manag.
(2014) - et al.
Metallurgical recovery of metals from electronic waste: a review
J. Hazard. Mater.
(2008) - et al.
A model for partnering with the informal e-waste industry: rationale, principles and a case study
Resour. Conserv. Recycl.
(2015) - et al.
Examining the technology acceptance for dismantling of waste printed circuit boards in light of recycling and environment concerns
J. Environ. Manag.
(2011) - et al.
Adsorption of platinum(IV), palladium(II) and gold(III) from aqueous solutions onto l-lysine modified crosslinked chitosan resin
J. Hazard. Mater.
(2007) - et al.
Recovery of metal values from waste printed circuit boards using alkali fusion-leaching-separation process
Hydrometallurgy
(2015)
Recovery of gold and silver from spent mobile phones by means of acidothiourea leaching followed by adsorption using biosorbent prepared from persimmon tanin
Hydrometallurgy
Optimizing the thiosulfate leaching of gold from printed circuit boards of discarded mobile phone
Hydrometallurgy
WEEE recovery strategies and the WEEE treatment status in China
J. Hazard. Mater.
Recycling of waste printed circuit boards: a review of current technologies and treatment status in China
J. Hazard. Mater.
Dynamics of spherical metallic particles in cylinder electrostatic separators/purifiers
J. Hazard. Mater.
Extraction of gold(III) from hydrochloric acid solutions by CTAB/n-heptane/iso-amyl alcohol/Na2SO3 microemulsion
J. Hazard. Mater.
Solvent extraction of gold from polysulfide solution
Hydrometallurgy
Direct leach appraches to Platinum Group Metal (PGM) ores and concentrates: a review
Miner. Eng.
A review of human exposure to polybrominated diphenyl ethers(PBDEs) in China
Int. J. Hyg. Environ. Health
Gold extraction by chlorination using a pyrometallurgical process
Miner. Eng.
Estimation of waste from computers and mobile phones in Iran
Resour. Conserv. Recycl.
Recovery of gold from secndary sources—a review
Hydrometallurgy
Aqueous metal recovery techniques from e-scrap: hydrometallurgy in recycling
Miner. Eng.
Social impact assessment of informal recycling of electronic ICT waste in Pakistan using UNEP SETAC guidelines
Resour. Conserv. Recycl.
Gold electrowining from aqueous-alcoholic thiourea solutions
Hydrometallurgy
Ion exchange recovery of silver from concentrated base metal-chloride solutions
Hydrometallurgy
Recovery of silver(I) using a thiourea-modified chitosan resin
J. Hazard. Mater.
Degradation of brominated epoxy resin and metal recovery from waste printed circuit boards through batch sub/supercritical water treatments
Chem. Eng. J.
Size-controlled preparation of Cu2O nanoparticles from waste printed circuit boards by supercritical water combined with electrokinetic process
J. Hazard. Mater.
Leaching of Au, Ag, and Pd from waste printed circuit boards of mobile phone by iodide lixiviant after supercritical water pre-treatment
Waste Manag.
Ferric sulphate leaching of metals from waste printed circuit boards
Int. J. Miner. Process.
E-Waste recycling process in Indonesia, the Philippines, and Vietnam: a case study of cathode ray tube TVs and monitors
Resour. Conserv. Recycl.
Precious metal recovery from waste printed circuit boards using cyanide and non-cyanide lixiviants—a review
Waste Manag.
Recycling of Electronic Waste in China and India: Workplace and Environmental Contamination
Substance Flow Analysis of the Recycling of Small Waste Electrical and Electronic Equipment—An Assessment of the Recovery of Gold and Palladium
Assessment of precious metal flows during preprocessing of waste electrical and electronic equipment
J. Ind. Ecol.
Recovery of gold, silver, palladium, and copper from waste printed circuit boards
Electronic waste disassembly with industrial waste heat
Environ. Sci. Technol.
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