Frontiers of Environmental Science & Engineering

ISSN 2095-2201

ISSN 2095-221X(Online)

CN 10-1013/X

2015 Impact Factor: 1.799

Cover Story   2017, Volume 11 Issue 5
See Mengmeng Wang, Quanyin Tan, Joseph F. Chiang & Jinhui Li, 2017, 11(5): 1 for more information
   Online First

Administered by

Current Issue

, Volume 11 Issue 5 Previous Issue    Next Issue
For Selected: View Abstracts Toggle Thumbnails
Recovery of rare and precious metals from urban mines—A review
Mengmeng Wang, Quanyin Tan, Joseph F. Chiang, Jinhui Li
Front. Environ. Sci. Eng.. 2017, 11 (5): 1-.

Abstract   HTML   PDF (1463KB)

Distribution characteristics of various RPMs in urban mines are summarized.

Conventional and emerging RPM recycling technologies are reviewed systematically.

Advantages and shortcomings of various technologies are discussed and highlighted.

Urban mining is essential for continued natural resource extraction. The recovery of rare and precious metals (RPMs) from urban mines has attracted increasing attention from both academic and industrial sectors, because of the broad application and high price of RPMs, and their low content in natural ores. This study summarizes the distribution characteristics of various RPMs in urban mines, and the advantages and shortcomings of various technologies for RPM recovery from urban mines, including both conventional (pyrometallurgical, hydrometallurgical, and biometallurgical processing), and emerging (electrochemical, supercritical fluid, mechanochemical, and ionic liquids processing) technologies. Mechanical/physical technologies are commonly employed to separate RPMs from nonmetallic components in a pre-treatment process. A pyrometallurgical process is often used for RPM recovery, although the expensive equipment required has limited its use in small and medium-sized enterprises. Hydrometallurgical processing is effective and easy to operate, with high selectivity of target metals and high recovery efficiency of RPMs, compared to pyrometallurgy. Biometallurgy, though, has shown the most promise for leaching RPMs from urban mines, because of its low cost and environmental friendliness. Newly developed technologies—electrochemical, supercritical fluid, ionic liquid, and mechanochemical—have offered new choices and achieved some success in laboratory experiments, especially as efficient and environmentally friendly methods of recycling RPMs. With continuing advances in science and technology, more technologies will no doubt be developed in this field, and be able to contribute to the sustainability of RPM mining.

Figures and Tables | References | Supplementary Material | Related Articles | Metrics
Silicon carbide waste as a source of mixture materials for cement mortar
Zhengwu Jiang, Qiang Ren, Haoxin Li, Qing Chen
Front. Environ. Sci. Eng.. 2017, 11 (5): 2-.

Abstract   HTML   PDF (489KB)

SiC waste decreases the fluidity of fresh mortar.

Mortar with SiC waste exhibits lower strength at early ages but higher strength at later ages.

SiC waste decrease the shrinkage rate of cement mortar.

SiC waste has some impacts on the hydration of the cement-SiC waste system.

SiC waste densifies the microstructure of hardened cement paste.

This paper presents an investigation of the feasibility of recycling silicon carbide waste (SCW) as a source of mixture materials in the production of cement mortar. Mortars with SCW were prepared by replacing different amounts of cement with SCW, and the properties of the resulting mortars, such as the fluidity, strength and shrinkage, were studied in this work. Thermogravimetry-differential scanning calorimetry and scanning electron microscopy were employed to understand the reasons for the property changes of the mortars. The results indicate that SCW decreases the initial and 1-h fluidity of fresh mortar but improves the loss of fluidity. The mortar with SCW exhibits a lower strength at 3 d and 7 d but a higher strength at 28 d and 56 d compared to the control. The shrinkage rate of cement mortar with SCW shows an obvious decrease as the replacement ratio increases. In addition, the content of calcium hydroxide in hardened paste also shows that SCW has some impact on the hydration of the cement-SCW system. The microstructures of the hardened paste also show evidence for a later strength change of mortar containing SCW. This work provides a strategic reference for possibly applying SCW as a mixture material in the production of cement mortar.

Figures and Tables | References | Related Articles | Metrics
An updated review and conceptual model for optimizing WEEE management in China from a life cycle perspective
Xiaolong Song, Jingwei Wang, Jianxin Yang, Bin Lu
Front. Environ. Sci. Eng.. 2017, 11 (5): 3-.

Abstract   HTML   PDF (553KB)

China is now implementing a series of latest regulations on WEEE management.

Website-based collection pattern for WEEE has gradually appeared in China.

Current WEEE management system is focused on centralized disassembly rather than the whole life cycle of WEEE.

A conceptual framework for life cycle management of WEEE is proposed.

Waste electrical and electronic equipment (WEEE) is a rapidly growing category of solid waste. China is now facing WEEE problems from both growing domestic generation and illegal imports. Currently, the amount of WEEE formally treated has increased steadily in China. The layout of the formal sector has been basically completed. Meanwhile, by controlling illegal disassembly activities, the informal sector has been gradually transformed to formal one. Beginning with the overview of the WEEE recycling industry in China, this paper first lists the latest progress in WEEE management from such aspects as the new edition of China RoHS Directive (Restriction of Hazardous Substances Directive), the updated WEEE Treatment List, the updated WEEE fund standard, the revised National Hazardous Waste List, and a brand-new plan on extended producer responsibility. In so doing, we elucidate the current challenges on WEEE management in detail: the imbalance between fund levies and subsidies, the gap in the supervision scope, the homogenization of recycling industry and the lack of life cycle approaches. Finally, a conceptual framework for integrated management of WEEE is proposed from a life cycle perspective. Overall, the life cycle management of WEEE includes three aspects: developing life cycle information for decision-making, implementing life cycle engineering with life cycle tools, and improving WEEE legislation based on life cycle thinking. By providing specific operating strategies, this life cycle framework should help to optimize WEEE management in developing countries where legislation is imperfect and the recycling system is relatively immature.

Figures and Tables | References | Related Articles | Metrics
Recycling polymeric waste from electronic and automotive sectors into value added products
Abhishek Kumar, Veena Choudhary, Rita Khanna, Romina Cayumil, Muhammad Ikram-ul-Haq, Veena Sahajwalla, Shiva Kumar I. Angadi, Ganapathy E. Paruthy, Partha S. Mukherjee, Miles Park
Front. Environ. Sci. Eng.. 2017, 11 (5): 4-.

Abstract   HTML   PDF (350KB)

• Polymer fraction was separated from waste PCBs by froth floatation.

• Addition of waste PCBs to polypropylene reduced the overall impact strength.

• Up to 9 wt.% rubber was added to PP/25 wt.% PCB composites as impact modifier.

• Mechanical, structural, rheological properties of composites were investigated.

• Electronic and automotive waste were successfully utilized in PP composites.

The environmentally sustainable disposal and recycling of ever increasing volumes of electronic waste has become global waste management issue. The addition of up to 25% polymeric waste PCBs (printed circuit boards) as fillers in polypropylene (PP) composites was partially successful: while the tensile modulus, flexural strength and flexural modulus of composites were enhanced, the tensile and impact strengths were found to decrease. As a lowering of impact strength can significantly limit the application of PP based composites, it is necessary to incorporate impact modifying polymers such as rubbery particles in the mix. We report on a novel investigation on the simultaneous utilization of electronic and automotive rubber waste as fillers in PP composites. These composites were prepared by using 25 wt.% polymeric PCB powder, up to 9% of ethylene propylene rubber (EPR), and PP: balance. The influence of EPR on the structural, thermal, mechanical and rheological properties of PP/PCB/EPR composites was investigated. While the addition of EPR caused the nucleation of the β crystalline phase of PP, the onset temperature for thermal degradation was found to decrease by 8%. The tensile modulus and strength decreased by 16% and 19%, respectively; and the elongation at break increased by ~71%. The impact strength showed a maximum increase of ~18% at 7 wt.%–9 wt.% EPR content. Various rheological properties were found to be well within the range of processing limits. This novel eco-friendly approach could help utilize significant amounts of polymeric electronic and automotive waste for fabricating valuable polymer composites.

Figures and Tables | References | Supplementary Material | Related Articles | Metrics
Performance evaluation of waste electrical and electronic equipment disassembly layout configurations using simulation
Ozan Capraz, Olcay Polat, Askiner Gungor
Front. Environ. Sci. Eng.. 2017, 11 (5): 5-.

Abstract   HTML   PDF (287KB)

Alternative layout configurations for WEEE disassembly systems (WDS) are evaluated.

An efficient modeling approach for simulation of manual WDS is proposed.

Effect of various transfer systems on the performance criteria is investigated.

Learning curve effect in WDS layout simulation models is investigated.

Managerial implications are provided to increase the practical impact of the study.

Recycling of waste electrical and electronic equipment (WEEE) is crucially important since it handles hazardous waste according to ever tightening laws and regulations and it adds benefits to economy and sustainable environment. Disassembly is one of the most important processes performed during the recovery of WEEE. The overall goal of disassembly is to maximize the retrieval of various metals and plastics contained in WEEE in order to reduce their negative effects on human health and environmental sustainability and to increase economic gains. This study aims to evaluate alternative layout configurations for WEEE disassembly systems (WDS). In this context, various configurations were compared in terms of pre-defined performance criteria, such as the total number of disassembled WEEE and the total revenue from sales, using simulation models. The results of this study show that the performance of a WDS was significantly affected by output transfer systems along with the specialization of operators on certain types of WEEE.

Figures and Tables | References | Related Articles | Metrics
Preparing graphene from anode graphite of spent lithium-ion batteries
Wenxuan Zhang, Zhanpeng Liu, Jing Xia, Feng Li, Wenzhi He, Guangming Li, Juwen Huang
Front. Environ. Sci. Eng.. 2017, 11 (5): 6-.

Abstract   HTML   PDF (281KB)

Anode graphite was found to keep the original characteristics and configuration.

Some oxygen-containing groups were embedded into the structure of anode graphite.

Anode graphite were recycled by preparing graphene with oxidation-reduction method.

Preparing graphene with anode graphite consumed less concentrated H2SO4 and KMnO4.

With extensive use of lithium ion batteries (LIBs), amounts of LIBs were discarded, giving rise to growth of resources demand and environmental risk. In view of wide usage of natural graphite and the high content (12%–21%) of anode graphite in spent LIBs, recycling anode graphite from spent LIBs cannot only alleviate the shortage of natural graphite, but also promote the sustainable development of related industries. After calcined at 600°Cfor 1 h to remove organic substances, anode graphite was used to prepare graphene by oxidation-reduction method. Effect of pH and N2H4·H2O amount on reduction of graphite oxide were probed. Structure of graphite, graphite oxide and graphene were characterized by XRD, Raman and FTIR. Graphite oxide could be completely reduced to graphene at pH 11 and 0.25 mL N2H4·H2O. Due to the presence of some oxygen-containing groups and structure defects in anode graphite, concentrated H2SO4 and KMnO4 consumptions were 40% and around 28.6% less than graphene preparation from natural graphite, respectively.

Figures and Tables | References | Related Articles | Metrics
Comparison on End-of-Life strategies of WEEE in China based on LCA
Bin Lu, Xiaolong Song, Jianxin Yang, Dong Yang
Front. Environ. Sci. Eng.. 2017, 11 (5): 7-.

Abstract   HTML   PDF (490KB)

Unit and Components Reuse are compared with materials recovery based LCA.

The obsolete refrigerator and Power Supply of computer are taken as the examples.

End-of-Life hierarchy is reasonable for the obsolete power supply of computer.

Reuse is not necessarily suitable for obsolete refrigerators.

The secondary lifespan of reused products/components is the key factor.

As the Electrical and Electronic Equipment (EEE) are upgraded more frequently in China, a large quantity of Waste Electrical and Electronic Equipment (WEEE) was and will be generated. It becomes an urgent issue to develop and adopt an effective End-of-Life (EoL) strategy for EEE in order to balance the resource recovery and environmental impacts. In an EoL strategy hierarchy for EEE, reuse strategy is usually deemed to be prior to materials recovery and other strategies. But in practice, the advantages and disadvantages of different strategies are always context-dependent. Therefore, main EoL strategies for EEE in China need to be evaluated in environment and resources aspects from the life cycle perspective. In this study, the obsolete refrigerator and Power Supply Unit (PSU) of desktop PC are both taken as the target products. Life Cycle Assessment (LCA) is applied to assess the environmental impacts of different EoL scenarios in China: Unit Reuse Scenario (URS), Component Reuse Scenario (CRS) and Materials Recovery Scenario (MRS). The LCA results show that the EoL strategies hierarchy is reasonable for the part of computer, but not necessarily suitable for obsolete refrigerators. When the policy makers promote or demote one EoL strategy especially reuse, it is necessary to take subsequent impacts into consideration.

Figures and Tables | References | Supplementary Material | Related Articles | Metrics
A critical review on the recycling of copper and precious metals from waste printed circuit boards using hydrometallurgy
Zebing Wu, Wenyi Yuan, Jinhui Li, Xiaoyan Wang, Lili Liu, Jingwei Wang
Front. Environ. Sci. Eng.. 2017, 11 (5): 8-.

Abstract   HTML   PDF (288KB)

Waste PCBs have a high content of valuable metals.

Hydrometallurgical technology has been widely used to extract valuable metal.

The recycling of waste PCBs using hydrometallurgy was critically reviewed.

Currently, increasing amounts of end-of-life (EoL) electronic products are being generated due to their reduced life spans and the unavailability of suitable recycling technologies. In particular, waste printed circuit boards (PCBs) have become of global concern with regard to environmental issues because of their high metal and toxic material contents, which are pollutants. There are many environmental threats owed to the disposal of electronic waste; off-gasses, such as dioxins, furans, polybrominated organic pollutants, and polycyclic aromatic hydrocarbons, can be generated during thermal treatments, which can cause serious health problems if effective off-gas cleaning systems are not developed and improved. Moreover, heavy metals will dissolve, and release into the ground water from the landfill sites. Such waste PCBs contain precious metals which are of monetary value. Therefore, it is beneficial to recover the metal content and protect the environment from pollution. Hydrometallurgy is a successful technique used worldwide for the recovery of precious metals (especially gold and silver) from ores, concentrates, and waste materials. It is generally preferred over other methods because it can offer high recovery rates at a relatively low cost. This article reviews the recent trends and developments with regard to the recycling of precious metals from waste PCBs through hydrometallurgical techniques, such as leaching and recovery.

Figures and Tables | References | Related Articles | Metrics
Thermal degradation characteristics and products obtained after pyrolysis of specific polymers found in Waste Electrical and Electronic Equipment
Evangelia C. Vouvoudi, Aristea T. Rousi, Dimitris S. Achilias
Front. Environ. Sci. Eng.. 2017, 11 (5): 9-.

Abstract   HTML   PDF (267KB)

Pyrolysis of plastics from WEEE is a promising technique for the production of fuel.

Pyrolysis of different types of polymers results in very different products.

Existence of different polymers in a blend act synergistically.

Thermal degradation characteristics of a blend are different compared to neat polymers.

Modern societies strongly support the recycling practices over simple waste accumulation due to environmental harm caused. In the framework of sustainable recycling of plastics from WEEE, pyrolysis is proposed here as a means of obtaining secondary value-added products. The aim of this study was to investigate the thermal degradation and the products obtained after pyrolysis of specific polymers found in the plastic part of WEEE, using thermogravimetric analysis and a pyrolizer equipped with a GC/MS. Polymers studied include ABS, HIPS, PC and a blend having a composition similar to that appearing in WEEE. It was found that, PC shows greater heat endurance compared to the other polymers, whereas ABS depolymerizes in three-steps. The existence of several polymers in the blend results in synergistic effects which decrease the onset and final temperature of degradation. Moreover, the fragmentation occurred in the pyrolyzer, at certain temperatures, resulted in a great variety of compounds, depending on the polymer type, such as monomers, aromatic products, phenolic compounds and hydrocarbons. The main conclusion from this investigation is that pyrolysis could be an effective method for the sustainable recycling of the plastic part of WEEE resulting in a mixture of chemicals with varying composition but being excellent to be used as fuel retrieved from secondary recycling sources.

Figures and Tables | References | Related Articles | Metrics
Copper recovery from waste printed circuit boards concentrated metal scraps by electrolysis
Xiaonan Liu, Qiuxia Tan, Yungui Li, Zhonghui Xu, Mengjun Chen
Front. Environ. Sci. Eng.. 2017, 11 (5): 10-.

Abstract   HTML   PDF (182KB)

WPCBs concentrated metal scraps were directly and successfully recycled by electrolysis.

Factors that affect the electrolysis were discussed in detail.

Copper recovery rate and copper purity are up to 97.32% and 99.86% respectively.

Copper recovery is the core of waste printed circuit boards (WPCBs) treatment. In this study, we proposed a feasible and efficient way to recover copper from WPCBs concentrated metal scraps by direct electrolysis and factors that affect copper recovery rate and purity, mainly CuSO4·5H2O concentration, NaCl concentration, H2SO4 concentration and current density, were discussed in detail. The results indicated that copper recovery rate increased first with the increase of CuSO4·5H2O NaCl, H2SO4 and current density and then decreased with further increasing these conditions. NaCl, H2SO4 and current density also showed a similar impact on copper purity, which also increased first and then decreased. Copper purity increased with the increase of CuSO4·5H2O. When the concentration of CuSO4·5H2O, NaCl and H2SO4 was respectively 90, 40 and 118 g/L and current density was 80 mA/cm2, copper recovery rate and purity was up to 97.32% and 99.86%, respectively. Thus, electrolysis proposes a feasible and prospective approach for waste printed circuit boards recycle, even for e-waste, though more researches are needed for industrial application.

Figures and Tables | References | Related Articles | Metrics
Pyrolysis of WEEE plastics using catalysts produced from fly ash of coal gasification
Marika Benedetti, Lorenzo Cafiero, Doina De Angelis, Alessandro Dell’Era, Mauro Pasquali, Stefano Stendardo, Riccardo Tuffi, Stefano Vecchio Ciprioti
Front. Environ. Sci. Eng.. 2017, 11 (5): 11-.

Abstract   HTML   PDF (305KB)

The effect of fly ash derived catalysts on pyrolysis of WEEE plastics was investigated.

A waste stream is recovered as a valuable resource for a new process.

Refused derived catalysts reduce the environmental impact and production costs.

Higher yields of light oil are obtained using fly ash derived catalysts.

Fly ash derived catalysts boost cracking effect and increase monoaromatics content in the oil.

Catalytic pyrolysis of thermoplastics extracted from waste electrical and electronic equipment (WEEE) was investigated using various fly ash-derived catalysts. The catalysts were prepared from fly ash by a simple method that basically includes a mechanical treatment followed by an acid or a basic activation. The synthesized catalysts were characterized using various analytical techniques. The results showed that not treated fly ash (FA) is characterized by good crystallinity, which in turn is lowered by mechanical and chemical treatment (fly ash after mechanical and acid activation, FAMA) and suppressed almost entirely down to let fly ash become completely amorphous (fly ash after mechanical and basic activation FAMB). Simultaneously, the surface area resulted increased. Subsequently, FA, FAMB and FAMA were used in the pyrolysis of a WEEE plastic sample at 400°C and their performance were compared with thermal pyrolysis at the same temperature. The catalysts principally improve the light oil yield: from 59wt.% with thermal pyrolysis to 83 wt.% using FAMB. The formation of styrene in the oil is also increased: from 243 mg/g with thermal pyrolysis to 453 mg/g using FAMB. As a result, FAMB proved to be the best catalyst, thus producing also the lowest and the highest amount of char and gas, respectively.

Figures and Tables | References | Supplementary Material | Related Articles | Metrics
Managing economic and social profit of cooperative models in three-echelon reverse supply chain for waste electrical and electronic equipment
Jian Li, Zhen Wang, Bao Jiang
Front. Environ. Sci. Eng.. 2017, 11 (5): 12-.

Abstract   HTML   PDF (271KB)

The four model of a three-echelon reverse supply chain (RSC) for WEEE are studied.

Optimal coordination strategies in four models are compared.

The model C make the RSC of WEEE achieve maximum economic and social benefit.

Duopolistic retailers make the RSC achieve maximum economic and social benefit.

In addition to maximizing economic benefits, reverse supply chains should further seek to maximize social benefits by increasing the quantity of waste electrical and electronic equipment (WEEE). The paper investigates cooperative models with different parties in a three-echelon reverse supply chain for WEEE consisting of a single collector, a single remanufacturer, and two retailers based on complete information. In addition, the optimal decisions of four cooperative models and the effect of the market demand of remanufactured WEEE products and the market share of two retailers on the optimal decisions are discussed. The results indicate that optimal total channel profit and recycle quantity in a reverse supply chain are maximized in a centralized model. The optimal total channel profit and recycle quantity increase with an increase in the market demand of remanufactured WEEE products. The three-echelon reverse supply chain consisting of duopolistic retailers maximizes total channel profit and recycle quantity in a reverse supply chain for WEEE.

Figures and Tables | References | Related Articles | Metrics
Improvement potential of today’s WEEE recycling performance: The case of LCD TVs in Belgium
Paul Vanegas, Jef R. Peeters, Dirk Cattrysse, Wim Dewulf, Joost R. Duflou
Front. Environ. Sci. Eng.. 2017, 11 (5): 13-.

Abstract   HTML   PDF (2645KB)

A methodology to assess WEEE recycling performance is presented.

MFA and Economic and Environmental evaluations are performed for LCD TVs in Belgium.

Ferrous metals and aluminium have high recycling rates.

Recycling of precious metals and plastics can improve substantially.

Waste of electrical and electronic equipment (WEEE) constitutes one of the most relevant waste streams because of the quantity and presence of valuable materials. However, there is limited knowledge on the resource potential of urban mining WEEE, as data on material composition, and the efficiency of current recycling treatments are still scarce. In this article, an evaluation of the recycling performance at a national level for one of the fastest growing e-waste streams: LCD TVs is carried out through the following four steps. Firstly, material characterisation is performed by means of sampling of the waste stream. Secondly, a material flow analysis is conducted by evaluating the separation performance of a recycling plant in Belgium. Thirdly, the recovered economic value and avoided environmental impact (EI) of the analysed recycling system is assessed. Finally, the potential of urban mining for Belgium is forecasted. The analysis shows that while recycling performance for ferrous metals and aluminium are relatively high; there is substantial room to better close the material loops for precious metals (PM) and plastics. PMs and plastics account for 66 % of the economic value in LCD TVs and 57% of the EI. With the current, commonly applied recycling technology only one-third of the PM and housing plastics are recycled; meaning that for these materials, at a national level for Belgium, there is a potential for improvement that represents 3.3 million euros in 2016 and 6.8 million euros in 2025.

Figures and Tables | References | Supplementary Material | Related Articles | Metrics
14 articles