Waste electrical and electronic equipment (WEEE) has received extensive attention as a secondary source of metals. Because WEEE also contains toxic substances such as heavy metals, appropriate ...management of these substances is important in the recycling and treatment of WEEE. As a basis for discussion toward better management of WEEE, this study characterizes various types of WEEE in terms of toxic metal contents. The fate of various metals contained in WEEE, including toxic metals, was also investigated in actual waste treatment processes. Cathode-ray tube televisions showed the highest concentration and the largest total amount of toxic metals such as Ba, Pb, and Sb, so appropriate recycling and disposal of these televisions would greatly contribute to better management of toxic metals in WEEE. A future challenge is the management of toxic metals in mid-sized items such as audio/visual and ICT equipment because even though the concentrations were not high in these items, the total amount of toxic metals contained in them is not negligible. In the case of Japan, such mid-sized WEEE items as well as small electronic items are subject to municipal solid waste treatment. A case study showed that a landfill was the main destination of toxic metals contained in those items in the current treatment systems. The case study also showed that changes in the flows of toxic metals will occur when treatment processes are modified to emphasize resource recovery. Because the flow changes might lead to an increase in the amount of toxic metals released to the environment, the flows of toxic metals and the materials targeted for resource recovery should be considered simultaneously.
► Appropriate management of toxic metals contained in WEEE is important during recycling and treatment of WEEE. ► CRT TVs contain large amount of toxic metals with high concentration and thus appropriate management is highly important. ► Mid-sized equipment is a future target for managing toxic metals in WEEE because the total amount is not negligible. ► Changes in the flows of toxic metals will occur when treatment processes are modified to emphasize resource recovery. ► The flows of toxic metals and valuable materials should be managed simultaneously in recycling and treatment of WEEE.
► End-of-life electrical and electronic equipment (EEE) as secondary metal resources. ► The content and the total amount of metals in specific equipment are both important. ► We categorized 21 EEE ...types from contents and total amounts of various metals. ► Important equipment types as secondary resources were listed for each metal kind. ► Collectability and possible collection systems of various EEE types were discussed.
End-of-life electrical and electronic equipment (EEE) has recently received attention as a secondary source of metals. This study examined characteristics of end-of-life EEE as secondary metal resources to consider efficient collection and metal recovery systems according to the specific metals and types of EEE. We constructed an analogy between natural resource development and metal recovery from end-of-life EEE and found that metal content and total annual amount of metal contained in each type of end-of-life EEE should be considered in secondary resource development, as well as the collectability of the end-of-life products. We then categorized 21 EEE types into five groups and discussed their potential as secondary metal resources. Refrigerators, washing machines, air conditioners, and CRT TVs were evaluated as the most important sources of common metals, and personal computers, mobile phones, and video games were evaluated as the most important sources of precious metals. Several types of small digital equipment were also identified as important sources of precious metals; however, mid-size information and communication technology (ICT) equipment (e.g., printers and fax machines) and audio/video equipment were shown to be more important as a source of a variety of less common metals. The physical collectability of each type of EEE was roughly characterized by unit size and number of end-of-life products generated annually. Current collection systems in Japan were examined and potentially appropriate collection methods were suggested for equipment types that currently have no specific collection systems in Japan, particularly for video games, notebook computers, and mid-size ICT and audio/video equipment.
Soil batch leaching tests are conducted worldwide to quantify the leaching of hazardous substances from contaminated soil. In the extracts of soil batch leaching tests, some inorganic substances such ...as arsenic and lead are released both in colloidal and dissolved form. Recent studies have found that soil colloidal particles with small diameters persist in the filtrate even after the extracts are filtered through a membrane filter (MF) with a pore size of 0.45 μm, and they might affect the concentration of arsenic or lead. This study evaluated the effects of 0.45- or 0.4-μm MF materials on filtrate turbidity and leaching concentrations of inorganic hazardous elements during batch leaching tests. Turbidity and arsenic and lead concentrations in the filtrates of the tested soil samples varied greatly depending on the MF material. These findings indicate that the MF material affects the removal rate of colloidal arsenic or lead and therefore affects the results of leaching tests.
•The turbidities of soil batch tests differ among membrane filter (MF) materials.•Pb concentrations also differ according to MF material for three soil types.•High correlation is observed between Pb concentration and turbidity.•MF material affects the As of soil batch tests for some soil types.•Uniformity of MF materials or reducing turbidity is important for reproducibility.
Geogenic contaminants, such as arsenic, are often found in soil recovered from coastal areas. These contaminants may leach out when the soil is used as embankment material. Moreover, the leaching of ...such contaminants might be influenced by environmental changes, such as dry-wet cycles, and higher environmental risks due to a larger amount of leaching are anticipated in some cases. In this study, therefore, soil recovered from tsunami deposits was subjected to dry-wet cycles under three different drying conditions to investigate how environmental changes affect the leaching behavior. To evaluate the physical and chemical changes in the soil surface, microscopic/spectroscopic studies were conducted. Batch leaching tests revealed that dry-wet cycles slightly alter the leaching behavior of most elements, such as Fe, Si, Na, Ca, etc. Arsenic leaching was seen to increase in certain dry-wet cycles before decreasing, and microscopic/spectroscopic confirmed that this increase was likely due to pyrite oxidation. These dry-wet cycles can disintegrate pyrite morphology and cause pyrite oxidation, leading to a more acidic leaching condition that accelerates arsenic leaching. After a certain oxidation procedure, the resulting ferric hydroxide may prevent the pyrite surfaces from further oxidation. The Fe oxides and hydroxides can also act as arsenic adsorbents, preventing the increase in arsenic concentration.
•An air table was applied to sort bottom ash from municipal solid waste incinerator.•The effect of variables (air injection, vibration, end slope) was evaluated.•Metal-abundant high-density particles ...were separated by stepwise sorting.•The amount of metals in sorted fraction was determined by a milling process.•For particles 0.5–2 mm, 68% of non-ferrous metals present in high-density fraction.
Valuable non-ferrous (NFe) metals are contained in municipal solid waste incineration (MSWI) bottom ash (BA). The applicability of an air table for separating NFe metal-abundant particles in MSWI BA (<8 mm) was studied. A stepwise separation procedure was developed based on the performance tests of the air table conducted by changing three variables (air injection, vibration, and end slope). As a result of the stepwise separation, six bulk density ranges (<0.7 to >1.1 g/cm3 at intervals of 0.1 g/cm3) were prepared from non-magnetic fractions with four size ranges (4–8, 2–4, 1–2, and 0.5–1 mm). The effectiveness of air table sorting was evaluated based on dry particle density and proportion of metals. NFe metals were obtained by sieving (>0.5 mm) after a ball mill process, confirming that NFe metals accounted for 3.2% of the < 8 mm MSWI BA. The highest particle density of each size fraction and the proportion of NFe metals in the fractions were 3.19 g/cm3 and 59.9% (4–8 mm), 2.97 g/cm3 and 28.8% (2–4 mm), 2.78 g/cm3 and 10.4% (1–2 mm), and 2.87 g/cm3 and 4.4% (0.5–1 mm). In the 0.5–2 mm particles, the highest density fraction contained 68.7% of the NFe metals, which were expected to be recovered by applying an air table separator to MSWI BA 0.5–2 mm.
A large amount of excavated soils with low-level As contamination caused by civil construction projects is of great concern in Japan. This study investigated the chemical speciation and ...extractability of As in 24 soil samples from the sites affected and unaffected (naturally contaminated) by anthropogenic pollution. The results of As K-edge XANES demonstrated that naturally contaminated soils were grouped into two types: (i) soils containing FeAsS-like and As2S3-like species (ave. 53%, hereafter As-S species) and (ii) soils with no or minor As-S species (ave. 3%). Clear differences were found in As, Fe, and S fractionations by sequential extraction. From naturally contaminated soils enriched with As-S species, more than 50% of As was extracted in the oxidizable fraction. Arsenic was mainly recovered in the reducible fraction for naturally contaminated soils with no or minor As-S species and anthropogenically contaminated soils. The μ-XRF and μ-XAFS revealed that the naturally contaminated soils containing As-S species were abundant in pyrite framboids (∼20 μm in diameter) in which As occurred as multiple oxidation states. The results suggest that framboidal pyrite becomes a source of As in naturally contaminated soils after being excavated and exposed to the surface environment.
The number of underground construction projects is increasing worldwide, resulting in the production of a huge amount of waste excavated material. Excavated soils from alluvial plains are rich in ...pyrite. When these soils are exposed to air, the pyrite oxidizes, resulting in the generation of H2SO4, which acidifies the soil and releases potentially harmful trace metals and metalloids such as arsenic into the environment. Polarized light microscopy and field‐emission scanning electron microscopy (FE‐SEM) revealed the presence of framboidal pyrite within the shells of microorganisms in alluvial soil samples collected in Japan. Analysis with FE‐SEM/energy‐dispersive X‐ray spectrometry and electron probe microanalysis (EPMA) revealed that this framboidal pyrite contained As. When soaked in distilled water for 6 h or in 1 M HCl for 2 h, the framboidal pyrite remained unchanged; however, when it was soaked in 10% H2O2 for 6 h, it was oxidized and swelling was observed on the surface of pyrite microcrystals. A 1 M HCl extraction test indicated that arsenic release from framboidal pyrite would be difficult under acidic conditions. Framboidal pyrite in alluvial sediment is stable at low pH; however, it is unstable under oxidative conditions, suggesting that waste alluvial soil should be kept under reducing conditions. The chemical stability of geogenic arsenic in pyrite in soils and sediments provides a useful way to determine a correct handling of the soils for reclamation or as a covering material.
Core Ideas
Chemical stability of framboidal pyrite in acidic or oxidative conditions was examined.
Geogenic As was accumulated mostly in framboidal pyrite.
Framboidal pyrite was stable in acidic conditions but was unstable in oxidative conditions.
► The fate of 55 metals during shredding and separation of WEEE was investigated. ► Most metals were mainly distributed to the small-grain fraction. ► Much of metals in WEEE being treated as ...municipal waste in Japan end up in landfills. ► Pre-sorting of small digital products reduces metals to be landfilled at some level. ► Consideration of metal recovery from other middle-sized WEEE is still important.
In Japan, waste electrical and electronic equipment (WEEE) that is not covered by the recycling laws are treated as municipal solid waste. A part of common metals are recovered during the treatment; however, other metals are rarely recovered and their destinations are not clear. This study investigated the distribution ratios and substance flows of 55 metals contained in WEEE during municipal waste treatment using shredding and separation techniques at a Japanese municipal waste treatment plant. The results revealed that more than half of Cu and most of Al contained in WEEE end up in landfills or dissipate under the current municipal waste treatment system. Among the other metals contained in WEEE, at least 70% of the mass was distributed to the small-grain fraction through the shredding and separation and is to be landfilled. Most kinds of metals were concentrated several fold in the small-grain fraction through the process and therefore the small-grain fraction may be a next target for recovery of metals in terms of both metal content and amount. Separate collection and pre-sorting of small digital products can work as effective way for reducing precious metals and less common metals to be landfilled to some extent; however, much of the total masses of those metals would still end up in landfills and it is also important to consider how to recover and utilize metals contained in other WEEE such as audio/video equipment.
Municipal solid waste (MSW) is converted to various materials through treatment processes, which in turn distributes potentially toxic elements (PTEs) to recyclable materials. This study is focused ...on establishing an inventory of combustible wastes with the objective of identifying specific sources of PTEs (B, Cr, Cu, Zn, As, Sb, Ba, and Pb). The combustible wastes were classified into 26 components by the criterion, which can be conveniently identified by the public. Each component of the combustible wastes was ignited at 450 °C, to reduce organic matters and increase the proportional content of the target PTE, before undergoing inductively coupled plasma analysis. The inventory of PTE contents in the waste components was developed from the ash and the ignition loss of each component. The contribution of waste components to the total amount of PTEs was estimated based on the element content and the proportion in waste. Through this series of processes, specific sources of waste components containing PTEs were presented. This work can contribute to the reduction of toxicity of MSW and incineration residues that are to be recycled.
In assessing the environmental risk of contaminated soil and waste, it is crucial to understand the contaminants’ leaching characteristics. There are various leaching test methods such as single ...batch leaching test, serial batch leaching test, column water flow test, and tank leaching test. This paper outlines the test method and the results of the accuracy evaluation test of the up-flow percolation test.
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