Characterization of alkali-activated thermally treated incinerator bottom ash

The fine fraction (<14mm) of incinerator bottom ash (IBA) obtained from a UK energy from waste plant has been milled and thermally treated at 600, 700, 800 and 880 degrees C. Treated materials have been activated with Ca(OH)(2) (10wt%) and the setting times and compressive strengths at different curing times measured. In addition to decomposition of CaCO(3) to CaO, thermal treatment increases the content of gehlenite (Ca(2)Al(2)SiO(7)), wollastonite (CaSiO(3)) and mayenite (Ca(12)Al(14)O(33)). Thermally treated samples were significantly more reactive than milled IBA and heating to 700 degrees C produced a material which rapidly set. Silica, gehlenite and wollastonite were the main crystalline phases present in hydrated samples and a mixed sulphate-carbonate AFm-type phase (Ca(4)Al(2)O(6)(CO(3))(0.67)(SO(3))(0.33).11H(2)O) formed. Significant volumes of gas were generated during curing and this produced a macro-porous microstructure that limited strength to 2.8MPa. The new materials may have potential for use as controlled low-strength materials.     

The disposal of radioactive ferric floc

An iron hydroxide floc is used as treatment for adsorbing low amounts of actinides during nuclear fuel re-processing. This waste is cemented only after pre-treatment with Ca(OH)(2). Characterisation of all simulant material has been undertaken using XRD, TGA and SEM/EDS. The floc is a moderately alkaline colloidal slurry containing approximately 15wt% solids, with the main particulate being an amorphous hydrated iron oxide. The main phase formed during pre-treatment appears to be an X-ray amorphous hydrated calcium-ferrate phase. Embedded within this are small amounts of crystalline Ca(OH)(2), calcite, Fe(6)(OH)(12)(CO(3)), Ca(6)Fe(2)(SO(4))(3)(OH)(12).26H(2)O and Ca(3)B(2)O(6), and can form depending on concentrations of Ca(OH)(2) and time. Apart from Ca(OH)(2) and calcite, none of the crystalline phases detected during pre-treatment are detected when the floc is encapsulated in an OPC/PFA composite cement hydrated for 90 days. The main crystalline phase detected in the hardened wasteform is a solid solution hydrogarnet, Ca(3)AlFe(SiO(4))(OH)(8), known as C(3)(A,F)SH(4) in cement chemistry nomenclature.     

Influences of chemical activators on incinerator bottom ash

This research has applied different chemical activators to mechanically and thermally treated fine fraction (<14 mm) of incinerator bottom ash (IBA), in order to investigate the influences of chemical activators on this new pozzolanic material. IBA has been milled and thermally treated at 800 degrees C (TIBA). The TIBA produced was blended with Ca(OH)(2) and evaluated for setting time, reactivity and compressive strength after the addition of 0.0565 mole of Na(2)SO(4), K(2)SO(4), Na(2)CO(3), K(2)CO(3), NaOH, KOH and CaCl(2) into 100g of binder (TIBA+Ca(OH)(2)). The microstructures of activated IBA and hydrated samples have been characterized by X-ray diffraction (XRD) and thermogravimetry (TG) analysis. Thermal treatment is found to produce gehlenite (Ca(2)Al(2)SiO(7)), wollastonite (CaSiO(3)) and mayenite (Ca(12)Al(14)O(33)) phases. The thermally treated IBA samples are significantly more reactive than the milled IBA. The addition of Na(2)CO(3) can increase the compressive strength and calcium hydroxide consumption at 28-day curing ages. However, the addition of Na(2)SO(4), K(2)SO(4), K(2)CO(3), NaOH and KOH reduces the strength and hydration reaction. Moreover, these chemicals produce more porous samples due to increased generation of hydrogen gas. The addition of CaCl(2) has a negative effect on the hydration of TIBA samples. Calcium aluminium oxide carbonate sulphide hydrate (Ca(4)Al(2)O(6)(CO(3))(0.67)(SO(3))(0.33)(H(2)O)(11)) is the main hydration product in the samples with activated IBA, except for the sample containing CaCl(2).     

Multi-regime transport model for leaching behavior of heterogeneous porous materials

Utilization of secondary materials in civil engineering applications (e.g. as substitutes for natural aggregates or binder constituents) requires assessment of the physical and environment properties of the product. Environmental assessment often necessitates evaluation of the potential for constituent release through leaching. Currently most leaching models used to estimate long-term field performance assume that the species of concern is uniformly dispersed in a homogeneous porous material. However, waste materials are often comprised of distinct components such as coarse or fine aggregates in a cement concrete or waste encapsulated in a stabilized matrix. The specific objectives of the research presented here were to (1) develop a one-dimensional, multi-regime transport model (i.e. MRT model) to describe the release of species from heterogeneous porous materials and, (2) evaluate simple limit cases using the model for species when release is not dependent on pH. Two different idealized model systems were considered: (1) a porous material contaminated with the species of interest and containing inert aggregates and, (2) a porous material containing the contaminant of interest only in the aggregates. The effect of three factors on constituent release were examined: (1) volume fraction of material occupied by the aggregates compared to a homogeneous porous material, (2) aggregate size and, (3) differences in mass transfer rates between the binder and the aggregates. Simulation results confirmed that assuming homogeneous materials to evaluate the release of contaminants from porous waste materials may result in erroneous long-term field performance assessment.     

Separability studies of construction and demolition waste recycled sand

The quality of recycled aggregates from construction and demolition waste (CDW) is strictly related to the content of porous and low strength phases, and specifically to the patches of cement that remain attached to the surface of natural aggregates. This phase increases water absorption and compromises the consistency and strength of concrete made from recycled aggregates. Mineral processing has been applied to CDW recycling to remove the patches of adhered cement paste on coarse recycled aggregates. The recycled fine fraction is usually disregarded due to its high content of porous phases despite representing around 50% of the total waste.This paper focus on laboratory mineral separability studies for removing particles with a high content of cement paste from natural fine aggregate particles (quartz/feldspars). The procedure achieved processing of CDW by tertiary impact crushing to produce sand, followed by sieving and density and magnetic separability studies. The attained results confirmed that both methods were effective in reducing cement paste content and producing significant mass recovery (80% for density concentration and 60% for magnetic separation). The production of recycled sand contributes to the sustainability of the construction environment by reducing both the consumption of raw materials and disposal of CDW, particularly in large Brazilian centers with a low quantity of sand and increasing costs of this material due to long transportation distances.     

Treatment of waste printed circuit board by green solvent using ionic liquid

Recycling of waste printed circuit boards (WPCBs) is an important subject not only for the protection of environment but also for the recovery of valuable materials. A feasibility study was conducted to dissolve bromine epoxy resins of WPCBs using ionic liquid (IL) of 1-ethyl-3-methylimizadolium tetrafluoroborate [EMIM(+)][BF(4)(-)] (nonaqueous green solvent) for recovering copper foils and glass fibers. Experimental results indicated that the initial delamination had seen from the cross-section of the WPCBs by mean of metallographic microscope and digital camera when WPCBs were heated in [EMIM(+)][BF(4)(-)] at 240°C for a duration of 30min. When temperature was increased to 260°C for a duration of 10min, the bromine epoxy resins of WPCBs were throughout dissolved into [EMIM(+)][BF(4)(-)] and the separations of copper foils and glass fibers from WPCBs were completed. This clean and non-polluting technology offers a new way to recycle valuable materials from WPCBs and prevent the environmental pollution of WPCBs effectively.     

Constitutive model for municipal solid waste incorporating mechanical creep and biodegradation-induced compression

A constitutive model is proposed to describe the stress–strain behavior of municipal solid waste (MSW) under loading using the critical state soil mechanics framework. The modified cam clay model is extended to incorporate the effects of mechanical creep and time dependent biodegradation to calculate total compression under loading. Model parameters are evaluated based on one-dimensional compression and triaxial consolidated undrained test series conducted on three types of MSW: (a) fresh MSW obtained from working phase of a landfill, (b) landfilled waste retrieved from a landfill after 1.5 years of degradation, and (c) synthetic MSW with controlled composition. The model captures the stress–strain and pore water pressure response of these three types of MSW adequately. The model is useful for assessing the deformation and stability of landfills and any post-closure development structures located on landfills.     

Porous materials produced from incineration ash using thermal plasma technology

This study presents a novel thermal plasma melting technique for neutralizing and recycling municipal solid waste incinerator (MSWI) ash residues. MSWI ash residues were converted into water-quenched vitrified slag using plasma vitrification, which is environmentally benign. Slag is adopted as a raw material in producing porous materials for architectural and decorative applications, eliminating the problem of its disposal. Porous materials are produced using water-quenched vitrified slag with Portland cement and foaming agent. The true density, bulk density, porosity and water absorption ratio of the foamed specimens are studied here by varying the size of the slag particles, the water-to-solid ratio, and the ratio of the weights of the core materials, including the water-quenched vitrified slag and cement. The thermal conductivity and flexural strength of porous panels are also determined. The experimental results show the bulk density and the porosity of the porous materials are 0.9–1.2 g cm^?3 and 50–60%, respectively, and the pore structure has a closed form. The thermal conductivity of the porous material is 0.1946 W m^?1 K^?1. Therefore, the slag composite materials are lightweight and thermal insulators having considerable potential for building applications.     

Characterization of MSWI bottom ashes towards utilization as glass raw material

The characterization of the bottom ashes produced by two Portuguese municipal solid waste incinerators (MSWI) was performed with the aim of assessing the feasibility of using this waste as raw material in the production of glass that can be further processed as glass-ceramics for application in construction. Density and particle size distribution measurements were carried out for physical characterization. Chemical characterization revealed that SiO(2), a network glass former oxide, was present in a relatively high content (52-58wt%), indicating the suitability for this waste to be employed in the development of vitreous materials. CaO, Na(2)O and K(2)O, which act as fluxing agents, were present in various amounts (2-17wt%) together with several other oxides normally present in ceramic and glass raw materials. Mineralogical characterization revealed that the main crystalline phases were quartz (SiO(2)) and calcite (CaCO(3)) and that minor amounts of different alkaline and alkaline-earth aluminosilicate phases were also present. Thermal characterization showed that the decomposition of the different compounds occurred up to 1100 degrees C and that total weight loss was <10wt%. Heating both bottom ashes at 1400 degrees C for 2h resulted in a melt with suitable viscosity to be poured into a mould, and homogeneous black-coloured glasses with a smooth shiny surface were obtained after cooling. The vitrified bottom ashes were totally amorphous as confirmed by X-ray diffraction. The results from the present experimental work indicate that the examined bottom ashes can be a potential material to melt and to obtain a glass that can be further processed as glass-ceramics to be applied in construction.     

Carbonization of waste PVC to develop porous carbon material without further activation

Efficient removal of chlorine from PVC achieved by two-stage heat-treatment (280 and 410 degrees C) provided chlorine-free isotropic pitch containing additive. The pitch was stabilized and carbonized into porous carbons with surface areas of approximately 300 m2/g. Resultant porous carbons showed three pore structures of supermicropore, micropore and mesopore. The generation of CO2 from the decomposition of the CaCO3 additive in waste PVC is responsible for the development of porous structures. The surface area of the carbonized product increased after the removal of CaO.     

Examining the concept of convenient collection: An application to extended producer responsibility and product stewardship frameworks

Increasingly, Extended Producer Responsibility (EPR) and Product Stewardship (PS) frameworks are being adopted as a preferred policy approach to promote cost-effective diversion and recovery of post-consumer solid waste. Because the application of EPR/PS generally requires the creation of a separate and often parallel collection and/or management system, key to increasing the amount of waste recovered is to maximize the convenience of the collection system to maximize consumer participation. Convenient collection is often mandated in EPR/PS laws, however it is not defined. Convenience is a subjective construct rendering it extremely difficult to define. However, based on a dissection of post-consumer collection efforts under a generic EPR/PS system, this paper identifies and examines five categories of convenience – knowledge requirements, proximity to a collection site, opportunity to drop-off materials, the draw of the collection site, and the ease of the process—and the various factors of convenience within each of these categories. By using a simplified multiple criteria decision analysis, this paper proposes a performance matrix of criteria of convenience. Stakeholders can use this matrix to assist in the design, assessment, and/or implementation of a convenient post-consumer collection system under an EPR/PS framework.     

Effect of technology development on potential environmental impacts from heavy metals in waste smartphones

Technology development has brought beneficial changes in the functions of smartphones but has the potential to impact the environment due to the high generation of waste smartphones. Thus, this study evaluates and compares environmental impact potentials from metals in waste smartphones to figure out the effect of smartphone model replacements on hazardous waste, resource depletion, and toxicity potentials. The total threshold limit concentration (TTLC) analysis is used to determine whether the waste smartphones would be classified as hazardous waste, and the life-cycle impact assessment methods are used to evaluate resource depletion, cancer, non-cancer, and ecotoxicity potentials. The TTLC results showed that the smartphone technology development did not reduce hazardous waste potentials. The life-cycle impact assessment results showed that the technology development overall reduced resource depletion potential but increased toxicity potential. In addition, priority metals contributing to the potentials were identified to effectively manage their environmental impacts. This study can provide fundamental information for smartphone manufacturers, waste smartphone recyclers and disposers, and e-waste policymakers to circulate resources and to prevent environmental pollutions from hazardous and toxic materials.     

Validation of Microtox as a first screening tool for waste classification

The Waste Framework Directive (WFD; 2008/98/EG) describes how waste materials are to be classified as hazardous or not. For complex waste materials chemical analyses are often not conclusive and the WFD provides the possibility to assess the hazardous properties by testing on the waste materials directly. As a methodology WFD refers to the protocols described in the CLP regulation (regulation on Classification, Labeling and Packaging of chemicals) but the toxicity tests on mammals are not acceptable for waste materials. The DISCRISET project was initiated to investigate the suitability of alternative toxicity tests that are already in use in pharmaceutical applications, for the toxicological hazard assessment of complex waste materials. Results indicated that Microtox was a good candidate as a first screening test in a tiered approached hazard assessment. This is now further validated in the present study. The toxic responses measured in Microtox were compared to biological responses in other bioassays for both organic and inorganic fractions of the wastes. Both fractions contribute to the toxic load of waste samples. Results show that the Microtox test is indeed a good and practical screening tool for the organic fraction. A screening threshold (ST) of 5 geq/l as the EC₅₀ value in Microtox is proposed as this ST allows to recognize highly toxic samples in the screening test. The data presented here show that the Microtox toxicity response at this ST is not only predictive for acute toxicity in other organisms but also for sub lethal toxic effects of the organic fraction. This limit value has to be further validated. For the inorganic fraction no specific biotest can be recommended as a screening test, but the use of direct toxicity assessment is also preferable for this fraction as metal speciation is an important issue to define the toxic load of elutriate fractions. A battery of 3 tests (Microtox, Daphnia and Algae) for direct toxicity assessment of this fraction is recommended in literature, but including tests for mechanistic toxicity might be useful.     

Networking possibilities for waste recycling in Miyagi prefecture, Japan

Successful case studies for waste recycling in Japan have not been evaluated. The evaluation of economic efficiency and environmental effects were lacking at the time the actual network was established. A waste/resource input/output (I/O) coincidence retrieval system called ZENESYS was developed to examine the usefulness of a waste-exchange network in a nonmanufacturing district. We analyzed data from the Miyagi prefecture, a region without heavy industry. The data were collected from 77 companies using a questionnaire and interviews. A total of 33 possible waste exchange links arose after analysis using ZENESYS. However, these were frail networks that relied heavily on the construction industry. Two waste recycling technologies were selected from the ZENESYS database: reclaiming fuel from waste plastic and making construction materials from bottom ash. Evaluation of the environmental effects and economics of these two technologies showed they were both suitable for the environment, but no profit was made from reclaiming fuel from waste plastics. We concluded that in an area with no heavy industry, it may be difficult to adopt recycling technologies that have high environmental and economic performance. Materials are difficult to circulate among manufacturing industries even if a waste-exchange network exists, and resources are consumed during transportation and recycling.     

Leaching and mechanical behaviour of concrete manufactured with recycled aggregates

The reuse of debris from building demolition is of increasing public interest because it decreases the volume of material to be disposed to landfill. This research is focused on the evaluation of the possibility of reusing recycled aggregate from construction or demolition waste (C&D) as a substitute for natural aggregate in concrete production. In most applications, cement based materials are used for building construction due to their cost effectiveness and performance; however their impact on the surrounding environment should be monitored. The interstitial pore fluid in contact with hydrated cementitious materials is characterized by persistent alkaline pH values buffered by the presence of hydrate calcium silicate, portlandite and alkaline ions. An experimental plan was carried out to investigate concrete structural properties in relation to alkali release in aqueous solution. Results indicate that the presence of recycled aggregate increases the leachability of unreactive ions (Na, K, Cl), while for calcium the substitution resulted in a lower net leaching. In spite of the lower mechanical resistance (40% less), such a waste concrete may be suggested as more environmentally sustainable.     

Leaching behaviour of synthetic aggregates

In the framework of EU project "Utilising innovative kiln technology to recycle waste into synthetic aggregate" (BRST-CT98-5234), the leaching behaviour of synthetic aggregates has been studied to assess its environmental compatibility in the various stages of its use. Since the conditions are very different for the different uses, the assessment calls for a variety of different leaching conditions. The pH dependence test is used to cover important differences in pH environment to which the materials are exposed to as well as for an assessment of the buffering capacity of the material. Synthetic aggregate features a low buffer capacity, which makes it sensitive to externally imposed pH conditions. Utilisation and storage exposed to acidic conditions needs to be avoided. The results of the pH dependence test and column leaching test are mutually consistent. The CEN TC 154 method appears to provide systematically low values due to the arbitrary selection of test conditions. Synthetic aggregate studied to date will not adversely affect the concrete in its service life. The main issue for aggregate use is the recycling and the "end of life" condition, when the material becomes construction debris. Not metals, but oxyanions, such as Cr VI and Mo are most relevant under these conditions. A concise test has been applied to assess crucial aspects of leaching for different production mixes.     

Treatment of copper industry waste and production of sintered glass-ceramic.

Copper waste is iron-rich hazardous waste containing heavy metals such as Cu, Zn, Co, Pb. The results of leaching tests show that the concentration of these elements exceeds the Turkish and EPA regulatory limits. Consequently, this waste cannot be disposed of in its present form and therefore requires treatment to stabilize it or make it inert prior to disposal. Vitrification was selected as the technology for the treatment of the toxic waste under investigation. During the vitrification process significant amounts of the toxic organic and inorganic chemical compounds could be destroyed, and at the same time, the metal species are immobilized as they become an integral part of the glass matrix. The copper flotation waste samples used in this research were obtained from the Black Sea Copper Works of Samsun, Turkey. The samples were vitrified after being mixed with other inorganic waste and materials. The copper flotation waste and their glass-ceramic products were characterized by X-ray analysis (XRD), scanning electron microscopy and by the toxicity characteristic leaching procedure test. The products showed very good chemical durability. The glass-ceramics fabricated at 850 degrees C/2 h have a large application potential especially as construction and building materials.     

Waste electrical and electronic equipment (WEEE) management in Korea: generation, collection, and recycling systems

In Korea, generation of waste electrical and electronic equipment (WEEE), or electronic waste (e-waste), has rapidly increased in recent years. The management of WEEE has become a major issue of concern for solid waste communities due to the volumes of waste being generated and the potential environmental impacts associated with the toxic chemicals found in most electronic devices. Special attention must be paid when dealing with WEEE because of toxic materials that it contains (e.g., heavy metals, polybrominated diphenyl ethers, phthalates, and polyvinyl chloride). If managed improperly, the disposal of WEEE can adversely affect the environment and human health. Environmental regulatory agencies; electronic equipment manufacturers, retailers, and recyclers; environmental nongovernmental organizations; and many others are much interested in updated statistics with regard to how much WEEE is generated, stored, recycled, and disposed of. In Korea, an extended producer responsibility policy was introduced in 2003 not only to reduce the amount of electronic products requiring disposal, but also to promote resource recovery from WEEE; the policy currently applies to a total of ten electrical and electronic product categories. This article presents an overview of the current recycling practices and management of electrical and electronic waste in Korea. Specifically, the generation rates, recycling systems and processes, and recent regulations of WEEE are discussed. We estimated that 1 263 000 refrigerators, 701 000 washing machines, 1 181 000 televisions, and 109 000 airconditioning units were retired and handled by the WEEE management system in 2006. More than 40% of the products were collected and recycled by producers. Four major producers’ recycling centers and other WEEE recycling facilities are currently in operation, and these process a large faction of WEEE for the recovery of valuable materials. Much attention should still be paid to pollution prevention and resource conservation with respect to WEEE. Several suggestions are made in order to deal with electronic waste management problems effectively and to prevent potential impacts.     

Waste polyvinylchloride derived pitch as a precursor to develop carbon fibers and activated carbon fibers

Polyvinylchloride (PVC) was successfully recycled through the solvent extraction from waste pipe with an extraction yield of ca. 86%. The extracted PVC was pyrolyzed by a two-stage process (260 and 410 degrees C) to obtain free-chlorine PVC based pitch through an effective removal of chlorine from PVC during the heat-treatment. As-prepared pitch (softening point: 220 degrees C) was spun, stabilized, carbonized into carbon fibers (CFs), and further activated into activated carbon fibers (ACFs) in a flow of CO2. As-prepared CFs show comparable mechanical properties to commercial CFs, whose maximum tensile strength and modulus are 862 MPa and 62 GPa, respectively. The resultant ACFs exhibit a high surface area of 1200 m2/g, narrow pore size distribution and a low oxygen content of 3%. The study provides an effective insight to recycle PVC from waste PVC and develop a carbon precursor for high performance carbon materials such as CFs and ACFs.     

Use of recycled plastic in concrete: a review

Numerous waste materials are generated from manufacturing processes, service industries and municipal solid wastes. The increasing awareness about the environment has tremendously contributed to the concerns related with disposal of the generated wastes. Solid waste management is one of the major environmental concerns in the world. With the scarcity of space for landfilling and due to its ever increasing cost, waste utilization has become an attractive alternative to disposal. Research is being carried out on the utilization of waste products in concrete. Such waste products include discarded tires, plastic, glass, steel, burnt foundry sand, and coal combustion by-products (CCBs). Each of these waste products has provided a specific effect on the properties of fresh and hardened concrete. The use of waste products in concrete not only makes it economical, but also helps in reducing disposal problems. Reuse of bulky wastes is considered the best environmental alternative for solving the problem of disposal. One such waste is plastic, which could be used in various applications. However, efforts have also been made to explore its use in concrete/asphalt concrete. The development of new construction materials using recycled plastics is important to both the construction and the plastic recycling industries. This paper presents a detailed review about waste and recycled plastics, waste management options, and research published on the effect of recycled plastic on the fresh and hardened properties of concrete. The effect of recycled and waste plastic on bulk density, air content, workability, compressive strength, splitting tensile strength, modulus of elasticity, impact resistance, permeability, and abrasion resistance is discussed in this paper.