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Distributions of trace elements within MSWI bottom and combined ash components: Implications for reuse practices
Abstract
Concentrations of 25 inorganic elements were measured in both bulk ash and individual ash components from residuals at three municipal solid waste incineration (MSWI) facilities in the US (two combined ash (CA) and one bottom ash (BA)). Concentrations were assessed based on particle size and component to understand the contribution from each fraction. The results found that among facilities, the finer size fractions contained elevated concentrations of trace elements of concern (As, Pb, Sb) when compared to the coarse fraction, but concentrations varied among facilities depending on the type of ash and differences in advanced metals recovery processes. This study focused on several constituents of potential concern, As, Ba, Cu, Pb, and Sb, and found that the main components of MSWI ash (glass, ceramic, concrete, and slag) are sources of these elements in the ash streams. For many elements, concentrations were significantly higher in CA bulk and component fractions opposed to BA streams. An acid treatment procedure and scanning electron microscopy/energy-dispersive x-ray spectroscopy analysis revealed that some elements, such as As in concrete, are result of the inherent properties of the component, but other elements, such as Sb, form on the surface during or after incineration and can be removed. Some Pb and Cu concentrations were attributed to inclusions in the glass or slag introduced into the material during the incineration process. Understanding the contributions of each ash component provides critical information for developing strategies to reduce trace element concentrations in ash streams to promote reuse opportunities.
... Furnace bottom ash is not suitable for use as a building material admixture such as cement and concrete because of its low activity, coarse particles, and uneven distribution, and thus it has not been effectively utilized at present [21]. Bottom ash and coal gangue are largely landfilled or stockpiled, occupying resources, releasing harmful gases for a long time, and damaging the ecological environment [22]. Chinese scholars have also conducted many studies examining the application of furnace bottom ash and coal gangue in the field of mine-filling materials. ...
To realize the large-scale utilization of municipal solid waste incineration (MSWI) fly ash in the field of building materials and to reduce the cost of coal mine backfill mining, the effects of the mixing ratio of cementitious materials, the particle size distribution of aggregates, and the amount and mass concentration of cementitious materials on the properties of backfill materials were experimentally investigated, and the microstructure of the hydration products was analyzed. The results showed that as the mass ratio of MSWI fly ash to bottom ash increased, the rate of expansion of the cementitious system continued to increase, and the compressive strength of the cementitious system continued to decrease. The Al (aluminum) and AlN (aluminum nitride) in the fly ash reacted with water to generate gas, causing the expansion of the cementitious materials; NaOH increased the alkalinity of the solution, which promoted the formation of more bubbles, thereby improving the expansion performance of the cementitious material. When the content of NaOH was 0.9%, the sample rate of expansion could reach 15.9%. The addition of CaCl2 promoted the early hydration reaction of the cementitious material, forming a dense microstructure, thus improving the early strength and rate of expansion of the cementitious material. The compressive strength of the backfill body increased as the fractal dimension of the aggregate particles increased, and the particle grading scheme of group S1 was optimal. The 1-day, 3-day, and 28-day strengths of the backfill body of group S1 reached 0.72 MPa, 1.43 MPa, and 3.26 MPa, respectively. It is recommended to choose a backfill paste concentration ranging between 78.5% and 80% and a reasonable amount of cementitious material between 20% and 25%. After the MSWI fly ash was prepared as a backfill material, the leaching of potentially harmful elements in the fly ash was greatly reduced, and the concentration of dioxin was reduced to 13 ng TEQ/kg. This was attributed to the dilution of the cement, the physical encapsulation of gel products, and the isomorphous replacement of Ca2+ in calcium aluminate chloride hydrate.
... Potential sources of heavy metals and phosphorus in MSWI fly ash (Jupp et al., 2020;Loginova et al., 2019;Mertoglu-Elmas, 2017;Xinghua et al., 2016;Spreadbury et al., 2023). must be reduced before the reuse or disposal of the ash to fulfill the requirements set by legislation (Loginova et al., 2019;Xinghua et al., 2016;Weibel et al., 2021). ...
In line with the objectives of the circular economy, the conversion of waste streams to useful and valuable side streams is a central goal. Ash represents one of the main industrial side-products, and using ashes in other than the present landfilling applications is, therefore, a high priority. This paper reviews the properties and utilization of ashes of different biomass power plants and waste incinerations, with a focus on the past decade.
Possibilities for ash utilization are of uttermost importance in terms of circular economy and disposal of landfills. However, considering its applicability, ash originating from the heat treatment of chemically complex fuels, such as biomass and waste poses several challenges such as high heavy metal content and the presence of toxic and/or corrosive species. Furthermore, the physical properties of the ash might limit its usability. Nevertheless, numerous studies addressing the utilization possibilities of challenging ash in various applications have been carried out over the past decade. This review, with over 300 references, surveys the field of research, focusing on the utilization of biomass and municipal solid waste (MSW) ashes. Also, metal and phosphorus recovery from different ashes is addressed.
It can be concluded that the key beneficial properties of the ash types addressed in this review are based on their i) alkaline nature suitable for neutralization reactions, ii) high adsorption capabilities to be used in CO2 capture and waste treatment, and iii) large surface area and appropriate chemical composition for the catalyst industry. Especially, ashes rich in Al2O3 and SiO2 have proven to be promising alternative catalysts in various industrial processes and as precursors for synthetic zeolites.
The washing pretreatment can facilitate the beneficial uses of Waste-to-Energy (WTE) ash as construction materials. In this study, bottom ash, fly ash, and combined ash were washed in the lab-scale processes with water and solutions of nitric acid (0.1, 0.5, 1 M) and sodium hydroxide (0.1, 0.5, 1 M) to understand the physicochemical transformation of ash and determine the ash streams processing by the changes in mass, chemical composition, mineral composition, and leachability of the three separated fractions: (i) washed ash, as the product; (ii) filter cake, as by-product, containing washed-out dust and reprecipitates; and (iii) dissolved ash compounds in wastewater. The results showed that 50% of the fly ash remained in the washed product, while other fly ash compounds were dissolved (e.g., Ca, chloride salts) or collected as filter cake, indicating severe materials loss via washing. Washing of the bottom and combined ash reduced the amorphous phases to 20–75% and transformed them into more stable crystalline phases (e.g., quartz in washed products and calcite in filter cake). After NaOH washing of combined ash, hydrocalumite-group minerals precipitated in the filter cake by-product. Water washing decreases the Cl concentration in the bottom/combined ash, thus avoiding chloride corrosion when the ash is utilized in construction. Applying water washing for combined ash processing is an effective option when the single pretreatment stream is executed; otherwise, only washing bottom ash fractions for aggregate uses is associated with stabilizing fly ash before disposal or other applications when separate ashes management streams are required.
Recycling plastic is an important step towards a circular economy. Attaining high-quality recycled plastics requires the separation of plastic waste by type, color, and size prior to reprocessing. Automated technology is key for sorting plastic objects in medium- to high-volume plants. The current state of the art of commercial equipment for sorting plastic as well as challenges faced by Material Recovery Facilities (MRFs) to sort post-consumer plastics are analyzed here. Equipment for sorting plastic recyclables were identified using publicly available information obtained from manufacturers’ websites, press releases, and journal articles. Currently available automated sorting equipment and artificial intelligence (AI)-based sorters are evaluated regarding their functionality, efficiency, types of plastics they can sort, throughput, and accuracy. The information compiled captures the progress made during the ten years since similar reports were published. A survey of MRFs, reclaimers, and brokers in the United States identified methods of sorting used for plastic, sorting efficiency, and current practices and challenges encountered at MRFs in sorting plastic recyclables. The commercial sorting equipment can address some of the challenges that MRFs face. However, sorting of film, multilayered, blended, or mixed-material plastics is problematic, as the equipment is typically designed to sort single-component materials. Accordingly, improvements and/or new solutions are considered necessary.
Mining processes in the iron ore mine of Boukhadra, Tebessa (NE Algeria) generated thousands of tons of mining wastes every year, which represents a real threat to the environment, leading to hazardous effects for the resident population of the region. The aim of this study is the selective sorting of the Boukhadra mining wastes for valorization. This will facilitate the recycling of the mineral substances (lime-stone, iron, marls) on the one hand and it makes it possible to minimize the volume of stocks and their environmental impacts on the other hand. To do this, and taking into account the chemical properties of wastes, we recommend an optical separation management using a color camera and a microprocessor linked to the ejection system (valve or pump), the color measurement tests performed on Boukhadra waste rocks samples using Matlab codes converted from Algorithms showed that each rock has a specific color (Red Green Blue value) or RGB. For this purpose, the use of three optical separators that sort according to algorithmic commands (RGB interval) will contribute to the separation of the Boukhadra mining wastes and consequently simplify their reuse.
Bottom and combined ash samples from municipal solid waste incinerator (MSWI) facilities in Florida were compared with industry aggregate standards to determine suitability for use as a road base. Although MSWI ashes tested in this work generally conformed to these standards for bearing strength (i.e., limerock bearing ratios above 100%), blending with commercially available aggregates is proposed as a strategy for improving overall material homogeneity and quantity. This work presents that MSWI ash can exhibit acceptable parameters defined in existing specifications for road-base materials on their own or by blending with commercially available aggregates, bolstering existing supplies of base materials while contributing to landfill diversion. The overall trend for bearing strength decreases with increasing MSWI bottom ash replacement (except for recycled asphalt pavement), but there appears to be a positive correlation between blend coefficients of uniformity (C u) and bearing strength (R 2 ¼ 0.5290). This suggests that gradation and material types may be parameters for identifying potential blends for advanced testing and developing quality control and assurance standards for material production and construction.
Generally, Fly ashes (FAs) in Municipal Solid Waste Incinerator (MSWI) are classified as hazardous waste and commonly managed in a mixed way even though distinct FA in incineration flows have different characteristics. Thus, it can cause improper management of fly ashes and an increase in cost as well as the volume of residual ashes sent to the hazardous landfill. In this study, Bottom ash (BA), Secondary furnace ash (SFA), Superheater ash (SHA), Boiler chamber ash (BCA), Economizer ash (EA), and Baghouse Filter Ash (BHFA) have been sampled separately from different locations at an MSWI plant. An integrated approach involving physical, chemical, mineralogy, and leaching behavior was used to characterize the residual ashes. Results point out that the average diameter of ash particles varies from 4.87 μm for BHFA to 6825 μm for BA, with three distinct zones. The Blaine fineness value increases when the median size of ash particles decreases. All values of Loss on Ignition (LOI) at 550 °C are less than 3%, indicating a suitable burning. The main mineralogical crystalline phases in ashes were KCl, NaCl, Mg.6Al1.2Si1.8O6, CaCO3, CaSO4, CaSO3, and SiO2. Among the considered heavy metals, leaching tests identified high levels of hazardous waste for Pb, Cd, Cu, and Zn in BHFA as well as for Pb and Zn in SHA. BA, SFA, BCA, and EA are categorized as non-hazardous according to the TCLP (USEPA-1311). In terms of EN 12457-2 test, BA and SFA are inert waste; but SHA, BCA, and EA are classified as hazardous waste due to a significant level of Cl. The results show that the characteristics of ash in the separate location of the MSWI process is essential to have an economical and proper solution for ash management.
Bottom ash from waste incineration is heterogeneous and contains different materials. Previous studies on the material composition of bottom ash provide only limited information as to composition, because large pieces present in bottom ash were not investigated nor were all materials separated and analysed. The objective of the present study is to provide the complete and detailed composition of bottom ash encompassing an extensive range of different materials. Altogether, nine bottom ash samples with a mass of 3000 kg each were sieved to eight size fractions, whereby small particles adhering to larger pieces were separated by water and added to the respective size fractions. In the sorting analysis of all size fractions, the materials enclosed in molten mineral material and materials present as composites (e.g. transformers and batteries) were considered. The material characterisation revealed that the size fraction > 50 mm contains most of the iron (up to 50% of the total iron) and copper (about 20% of the total copper), while batteries, coins, silver and gold are almost exclusively present between 16 and 50 mm. The fractions between 8 and 16 mm show the highest share of aluminium (up to 50% of the total aluminium) and glass (up to 60% of the total glass). While the metal content is underestimated, if large pieces of material are disregarded, the multi-step approach applied in this study enables a complete determination of materials in bottom ash, which is essential for optimising material recovery in bottom ash treatment.
Municipal solid waste incineration (MSWI) bottom ash is an environmentally harmful solid waste that cannot be recycled without pre-treatment. The chloride content in bottom ash (BA) is a major obstacle that restricts its application as secondary building materials. Here, the chemical speciation of the chlorides in BA is systematically studied with multiple analytical techniques, i.e., quantitative XRD, microanalysis and XPS. In addition to halite (NaCl), several chloride-rich minerals are present in BA. These phases are hydrous metal oxides, ettringite, decomposed hydration products (C4A3) and incineration slag with a chloride content of 3.2%, 1.4%, 2.1% and 1.3%, respectively. For the first time, the real-time leaching profiles of chloride (up to 80 h) from BA were obtained with a chloride-ion specific electrode to explain the leaching mechanism. In the initial stage of leaching, highly soluble alkali salts (NaCl) and physisorbed chlorides (especially those adsorbed on hydrous metal oxides) are released, which is controlled by diffusion. Later, the leaching is controlled by the solubility/reactivity of the chloride-containing phases, such as ettringite and incineration slag. The results show that the release of chloride is not only a diffusion-controlled process, as reported in the literature, but also a reaction-controlled phenomenon, during which the chloride-rich phases decompose and release chlorides that are associated with them via sorption/incorporation.
Florida geologic units and soils contain a wide range in concentrations of naturally-occurring arsenic. The average range of bulk rock concentrations is 1 to 13.1 mg/kg with concentrations in accessary minerals being over 1000 mg/kg. Florida soils contain natural arsenic concentrations which can exceed 10 mg/kg in some circumstances, with organic-rich soils often having the highest concentrations. Anthropogenic sources of arsenic have added about 610,000 metric tons of arsenic into the Florida environment since 1970, thereby increasing background concentrations in soils. The anthropogenic sources of arsenic in soils include: pesticides (used in Florida beginning in the 1890’s), fertilizers, chromated copper arsenate (CCA)-treated wood, soil amendments, cattle-dipping vats, chicken litter, sludges from water treatment plants, and others. The default Soil Cleanup Target Level (SCTL) in Florida for arsenic in residential soils is 2.1 mg/kg which is below some naturally-occurring background concentrations in soils and anthropogenic concentrations in agricultural soils. A review of risk considerations shows that adverse health impacts associated with exposure to arsenic is dependent on many factors and that the Florida cleanup levels are very conservative. Exposure to arsenic in soils at concentrations that exceed the Florida default cleanup level set specifically for residential environments does not necessarily pose a meaningful a priori public health risk, given important considerations such as the form of arsenic present, the route(s) of exposure, and the actual circumstances of exposure (e.g., frequency, duration, and magnitude).
Ceramic foodwares are among the products used by people on daily basis without being cautious of exposures to heavy metals through possible leaching from the glaze ceramics. This study investigated the levels of heavy metals found in some commonly used ceramic foodwares in Nigeria with the aim of determining levels of human exposures through the use of the ceramics. To achieve this, acid digestion was carried out for the total metal concentrations and leaching tests were done using 4% acetic acid as a leaching agent. Metal concentrations were quantified using flame atomic absorption spectrometry (FAAS) and particle-induced X-ray emission spectrometry (PIXES) analysis. All the ceramic foodwares studied were found to contain varied amounts of heavy metals in their glazes, with concentrations in the range of 26.45–2071.46, 5.20–547.00, 1.24–2681.02, 2590.00–8848.40, 6.42–654.66, 112.69–649.95, 63.38–2518.51, and 3786.51–8249.44 μg g−1 for Pb, Cd, Zn, As, Cu, Cr, Mn, and Fe, respectively. Concentrations of the metals leached from the ceramics were in the range of 0.11–0.97, 0.01–0.28, 0.00–4.19, 1.93–15.00, 0.01–0.41, 0.09–0.60, 0.01–2.14, and 0.01–11.53 mgL−1 for Pb, Cd, Zn, As, Cu, Cr, Mn, and Fe, respectively. Comparing the ratio of the metals leached from the ceramic wares with those of the metal oxides in the ceramics, it was noticeable that not all the metals detected in the ceramic samples were domiciled in the glaze but in the clay materials used for the ceramics.
The aim of this article is to present the research carried out over a 10 year period to develop an environmentally safe method for recycling air pollution control (APC) residues. The initial studies aimed to formulate a mixture of weathered bottom ash (WBA), APC residues and Portland cement (PC) to be used as a sub-base in road constructions. Mechanical performance was subsequently enhanced by preparing a mortar prior to mixing it with WBA in order to obtain a granular material. After testing different formulations, the optimum mortar consisted of 50 % APC residues and 50 % PC. The evaluation was carried out based on the concentration release of the heavy metals and metalloids included in the Catalan legislation for revalorization of residues. After the applicability of the granular material was successfully demonstrated at laboratory scale from an environmental and mechanical point of view, a pilot scale plant was designed in order to assess its performance in a real scenario during 4 month. Thus, three roads were built: two containing 100 % granular material and a third containing 100 % WBA. The results showed that the immobilisation of all toxic species from APC residues is accomplished by the pozzolanic effect of the cement. The WBA, APC, and PC proportions show to be the most appropriate for compliance with regard to environmental and mechanics requirements.
The use of alternatives, especially recycled materials, as substitute to naturally mined aggregates in concrete is an issue that is garnering more consideration with respect to the construction industry. This research contribution presents work in which bottom ash from a waste to energy facility was used as a partial aggregate replacement in Portland cement concrete (PCC). Compressive strength testing of specimens demonstrated a decrease in strength with increasing ash replacement percentages. This effect was significantly larger for the samples containing <9.5 mm ash fraction, this was attributed to the reactivity of the aluminum in the ash. The effect of aging the ash on concrete properties was assessed through an accelerated carbonation experiment. Carbonation was found to have little effect on the strength and durability properties of ash-amended PCC. Ash-amended concrete containing the larger ash size fraction was able to meet set design strengths at low replacement percentages (25 %).
The reutilisation of MSWI natural weathered bottom ash (WBA) in many applications such as road and underground constructions, embankments or as an aggregate replacement is a common practice in many developed countries. Its potential environmental risk has regularly been evaluated from the point of view of the leaching of heavy metals and metalloids. Nevertheless, the influence over steel rebar when reinforced concrete is exposed to the contact with WBA has been poorly assessed before. In this study, it has been possible to evaluate in terms of days the probability of corrosion in a common case of WBA reutilisation, which is in contact with reinforced concrete formulated with conventional Portland cement. The corrosion monitoring indicates that the probability of corrosion of steel rebar is higher than 90 % with a corrosion rate (CI) estimated to be 11.6 µm year−1. The aggressive conditions imposed by WBA suppose an important withdrawal if the application of reutilisation involves contact with steel rebar.
Recycled crushed glass is the main by-product of the glass recycling industry. Insufficient knowledge of the geotechnical characteristics of recycled glass and its environmental risks are the primary barriers in its application in road works. An extensive suite of geotechnical and environmental tests were undertaken on two common types of recycled crushed glass (fine recycled glass and medium recycled glass) to study the potential of using them in road works as alternatives to natural aggregates. Recycled glass was found to exhibit either equivalent or superior workability, hydraulic conductivity and shear strength to natural aggregates within the same soil classification and demonstrated the potential to substitute natural sand and gravel mixtures in a range of road applications. To address the environmental concerns of using recycled glass in road work applications, a comprehensive series of chemical and environmental tests including total and leachate concentration for a range of contaminant constituents including heavy metals and aromatic hydrocarbons were carried out. Test results were compared with environmental protection authorities’ requirements and indicated that no leaching hazard will be experienced during the service life of recycled glass in road work applications. Other possible environmental risks along with health and safety precautions and management suggestions have also been discussed.
Recycled concrete aggregate (RCA) has excellent mechanical properties and is often used as base course in pavement construction. However, highly alkaline leachate from RCA has been observed in laboratory studies. The associated high-pH leaching patterns can be of concern, especially when compared to the neutral pH environment observed in actual road sections using RCA as base course. In this study, the pH-dependent leaching concentrations of trace elements copper (Cu) and zinc (Zn) and the oxyanion chromium (Cr) were investigated on unfractionated RCA samples and fractionated RCA samples (i.e., fine particles <0.075 mm, sand-sized particles <4.75 mm and >0.075 mm, and gravel-sized particles <75 mm and >4.75 mm). A pH-buffering plateau was observed between pH 4.9 and 7.0 in the acid neutralization capacity curve. Cu and Zn showed the highest levels of leaching at pH≅2, and the lowest leaching at pH>7.5. Cr showed the lowest level of leaching between pH 5.0 and 6.5, and higher leaching concentrations towards the acid and alkali directions. The fine particles tended to leach more Cu and Zn than sand- and gravel-sized particles at 2<pH<13, while leaching of Cr from the fine fraction was not elevated except at pH<2.
Dispose and utilization of municipal solid waste incinerator bottom ash (MWSIBA) is one of the imperative issues in environmental protection. The applicability of substitution for natural aggregate with MWSIBA in asphalt mixture was investigated by the performance and micro structure of asphalt mixtures with diverse porosity levels of MWSIBA (varying the replacement percentage). The effects of porosity of MWSIBA on asphalt mixture performance were captured by determination of Marshall stability, tensile strength, dynamic stability and the maximum flexural-tensile strain. The horizontal vibration extraction procedure test was implemented for the heavy metal leaching concentration to evaluate the environmental safety of MWSIBA asphalt mixture. Chemical and micro-morphologic characterization for MSWIBA were conducted to explore the mechanism of moisture damage resistance of asphalt mixture. Results indicated that porosity and replacement rate of MWSIBA exerted impacts on properties of asphalt mixture. The rutting resistance of asphalt mixture decreased due to the addition of MWSIBA, resulting in a reduction in high temperature performance. MWSIBA with porosity no less than 19% was beneficial to the improvement of moisture susceptibility and low temperature performance of asphalt mixture, while high mixing amount of MWSIBA was unfavorable to the properties of asphalt mixture. The water immersion stimulated the hydration reaction in MWSIBA, leading to the formation of C-(A)-S-H gel with strong cementation property, which enhanced the adhesion between MWSIBA and asphalt binder. MWSIBA asphalt mixture presented lower heavy metal concentration and better environmental safety than MSWIBA.
Municipal solid waste incineration (MSWI) ash is often managed through co-disposal with unburned wastes in landfills, a practice previously reported to result in enhanced leaching of pollutants (e.g., heavy metals) in landfill leachate. The objective of this study was to evaluate the effect of co-disposed unburned wastes on per- and polyfluoroalkyl substances (PFAS) in MSWI ash landfill leachate. Leachate was collected from four landfills containing MSWI ash, either as a sole waste stream or co-disposed of with sewage sludge and MSW screenings. Samples of ash and unburned materials were collected and assessed separately for leachable PFAS in the laboratory. All samples were analyzed for 26 PFAS. Results showed that greater ash content was associated with lower leachate PFAS concentrations. The pure ash monofill exhibited the lowest PFAS in landfill leachate (290 ng L⁻¹) while the landfill contained a large amount of unburned waste had the highest PFAS (11,000 ng L⁻¹). For laboratory leaching tests, average ∑26PFAS concentration in lab ash leachate (310 ng L⁻¹) was 10 and 24 times lower than observed in lab sewage sludge leachate (3,200 ng L⁻¹) and lab MSW screenings leachate (7,500 ng L⁻¹), respectively. Leachate from the ash-only landfill had ∑26PFAS concentration similar to what was measured in the ash itself. On the contrary, ∑26PFAS concentration in co-disposal landfill leachates were similar to those in PFAS-rich unburned waste itself, regardless of the percentages of landfilled unburned wastes. We hypothesize that leachate generated in co-disposal scenarios preferentially flows through PFAS-rich unburned materials and that biotransformation of precursors enhanced by unburned waste degradation further contributes to higher concentrations of terminal PFAS in ash co-disposal sites. Landfill operators should expect PFAS in leachates to be higher when PFAS-rich unburned wastes are disposed of alongside MSWI ash, even if the unburned fraction is small.
Fly ash from municipal solid waste incineration (MSWI-FA) contains leachable heavy metals. In the present study the correlations between heavy metal content, particle size, speciation distribution with respect to water leaching are investigated, using a combination of solid-state bulk analytical techniques, leaching treatments, sequential extractions and thermodynamic geochemical modelling. Among the analyzed heavy metals, Zn and Pb are the most abundant in any grain size class, followed by Cu, Cr, Cd and Ni, with concentration that tends to increase with a decrease of the grain size. The phase composition is constituted of salt (halite, sylvite, anhydrite and syngenite), which provide the main minerals regardless of the particle size class; calcite, quartz and gehlenite occur in comparatively lower amounts, while 50% wt is composed of amorphous fraction. Heavy metal leaching is strongly correlated to speciation distribution, and in particular to the fraction (F1) associated with salt, carbonate and weak surface sorption. Leaching from speciation due to surface complexation on Al/Fe (hydr)oxide becomes relevant at acidic regime. Particle size and heavy metal content, in turn, moderately correlate with leaching. The F1-speciation as a function of particle size does not exhibit a definite trend shared by all heavy metals under investigation. This suggests that i) differences in speciation distribution, rather than bare heavy metal content or particle size, govern leaching from MSWI-FA; ii) F1 can be regarded as a marker of the potential heavy metal leaching; iii) a comparatively modest efficiency in managing MSWI-FA is expected from grain size separation strategies.
About half the copper reaching the marketplace has been scrap at least once, so scrap recycle is of the utmost importance. This chapter describes scrap recycling in general, major sources and types of scrap, and physical beneficiation techniques for isolating copper from its coatings and other contaminants.
Size and magnetic separation of incineration bottom ash (IBA) are common for ferrous metals recovery, however, their influences on the mineral phase and the element redistribution, and subsequently the induced variation of metal leaching potential herein remain limited understanding. The lack of research in this field may misunderstand IBA performances, cause confused results for comparison among various studies, and potentially lead to biased conclusions. We herein quantitatively investigate the effects of size and magnetic separation on the IBA based on element distribution, leaching behavior, morphology, and mineralogy with statistical analysis. For preparation, sieving was performed with the original IBA (to obtain 7 size-fractions termed as OR1-7, respectively), followed by magnetic separation of each, to further yield magnetic fractions (MF1-7) to discriminate nonmagnetic fractions (NF1-7). In this study, we show that size and magnetic separation may pose significant yet different impacts on different fractions, which would affect their leaching potential concerning their respective downstream applications.
In recent years, complex new bottom ash treatment processes for enhanced metal recovery have been implemented in Switzerland, producing residual bottom ash fractions with various qualities. This study focusses on three different treatment processes by characterizing all arising fractions in detail. Thereby the factors influencing the composition of these fractions are identified and their recycling potential in Switzerland is investigated. However, high legislative requirements on total contents of heavy metals represent a high barrier for bottom ash recycling in Switzerland. Therefore, the recycling potential is further evaluated based on the waste legislation applied in the Netherlands, where recycling of bottom ash has a long tradition. There, threshold values for bottom ash recycling are based on leachate concentrations and not on total contents as in Switzerland. However, Swiss Waste Legislation also knows threshold values based on leachate concentrations for certain waste materials. The leaching tests applied in these two countries, however, are different. The comparison of both leaching tests reveals that the setup and conditions, especially the considered pH range, significantly influence the leaching of heavy metals. With emphasis on problematic pollutants, the possibilities for new applications of these fractions are evaluated based on Swiss and Dutch legal threshold values. The comparison within the legal frameworks of these two countries allows recognizing opportunities and risks related to bottom ash recycling.
This study systematically investigated the acid washing of incineration bottom ash (IBA) of municipal solid waste, focusing on the removal and leaching of heavy metals (Pb, Zn, Cr, Cd, Cu, and Ni), as well as their pH-dependent behavior. A series of small-scale laboratory acid washing tests with different nitric acid concentrations and washing periods were conducted. The concentrations of metals in the washing water were measured to evaluate the metal removal efficiency. Then, one stage batch leaching test was conducted for washed IBA to evaluate the leaching reduction efficiency of washing. The results showed that the maximum metal removal efficiencies for Zn, Cu, and Ni (62–76%) were higher than those for Pb, Cr, and Cd (17–25%), which were reached at the highest acid addition for most of the metals. Increasing the washing period did not always increase the metal removal efficiency. The maximum leaching reduction efficiencies were higher for Zn, Cr, and Cu (93–98%) than those for Pb, Ni, and Cd (73–79%). Both washing and leaching processes showed a similar metal concentration-pH profile for each metal. For Pb, Zn, Cr, and Cd, the metal concentration-pH profile generally followed the metal hydroxide solubility versus pH curves. For Cu and Ni, the concentration of metal decreased with the increasing pH first and then kept at a stable concentration higher than the solubility of the hydroxide, indicating that Cu and Ni in the IBA washing water and leachates did not exist dominantly as their hydroxides.
Laboratory studies indicate that municipal solid waste incineration (MSWI) bottom ash (BA) can serve as a suitable road base material. However, very little is known about how field-scale design variables, such as layer thickness and compaction effort, and changes in moisture content over time affect the long-term performance of MSWI BA base courses. Understanding how these parameters affect the physical performance of BA base courses is necessary for developing construction specifications and guidelines specific to this material-a critical step in promoting widespread reuse practices. In this study, processed MSWI BA aggregate was tested in a field-scale test facility that replicated real-world scenarios to examine their effects on two important material properties: resilient modulus and permanent deformation. These results suggest that layer thickness, compaction effort, and moisture content can affect the base layer's resilient modulus and the permanent deformation, with moisture content having the most significant impact. Moisture content above the material's optimum decreased base modulus and increased permanent deformation, but the degree of deformation proportionally decreased with increasing layer thickness. Based on these results, guidelines on designing and reusing MSWI BA as a base course are discussed, suggesting optimal performance from highly compacted, thicker layers while stressing a need for tight control of moisture during and post-construction.
From the simple water wall incinerators of the late 19th century, the concept of waste-to-energy incineration has evolved dramatically. Initially, waste treatment had no energy recovery objective at all. To date, state of the art facilities exist and are coupled with not only mechanisms to recover heat and energy in combined heat and power plants, but sophisticated mechanisms to clean flue gas, utilize wastewater, and assimilate diverse streams of waste with high efficiency. This paper reviews the evolution of waste-to-energy incineration with the prime objective of evaluating progress made in solving problems, past and present concerns and future prospects in the industry. The review shows that waste-to-energy incineration has played a significant role in reducing the global waste problem and by maximizing its potential today, much more can be achieved. Nevertheless, the root problem notably the growing waste volume in today's society has not been fully addressed. An understanding of this evolution capacitates players in the waste-to-energy industry to better understand problems and formulate practical solutions which will steer waste to energy incineration towards more growth in the interim and devise lasting solutions for the distant future.
Trace metals concentrations of 25 elements were determined for 22 subcomponents of biodegradable and non-biodegradable waste samples representing the United States municipal solid waste (MSW) stream collected during three separate waste sorts. The subcomponent trace metal concentrations and estimated composition results were used to predict trace metal concentrations present in the overall MSW stream along with MSW compost and waste to energy (WTE) ash, which were compared to health-based standards (i.e., US EPA regional screening levels) and to values previously reported in the literature. These estimates for potentially problematic elements like As and Sb could be attributed to abundant base materials in MSW, while other elements, such as Pb, were calculated at much lower concentrations than other published studies. This suggests that trace metals measured in actual MSW compost and WTE ash could originate not only from MSW base components but also from other sources, such as highly concentrated low-mass wastes (e.g., e-waste). While the removal of small quantity components with high metal concentrations may reduce concentrations of some potentially problematic metals (e.g., Pb), others (e.g., As and Sb) are likely to persist in quantities that impede reuse and recycling since they are present in the more abundant base MSW components (e.g., papers, plastics, organics). Promoting meaningful reductions in potentially problematic trace metals in MSW-derived materials may require reevaluating their presence in higher-volume, lower-concentrated MSW components such as paper, plastics, and organics.
Concentrations of antimony have been determined for paints and enamels that are available to the consumer or accessible to the public by x-ray fluorescence spectrometry. The metalloid was only present in consumer paints of a speciality (e.g. artistic) nature, but was common in old household paints as an anti-chalking agent and in brightly-coloured contemporary exterior paints (on roads, street furniture and playground equipment, for example) as a colour fastener with concentrations ranging from a few hundred to about 25,000 μg g-1. Antimony was also found in contemporary container glass and ceramic products as an additive or opacifier and as a colour fastener in enamels at concentrations up to a few thousand μg g-1. Overall, the yellow pigment, lead antimonate, was only evident in two ceramic products analysed, with Sb concentrations exceeding 62,800 μg g-1. Available data in the literature suggests that, while Sb concentrations up to 30 μg g-1 are bioaccessible in exterior paints and that concentrations of up to 20 mg L-1 are migratable in some ceramicware, no relevant regulations are currently in place. Given our lack of understanding of the health impacts of Sb, more studies on its toxicity and mobility from commonly encountered products are called for.
The total and leachable metal content from mixtures of weathered municipal solid waste incinerator bottom ash (MSWI BA) and conventional natural or recycled aggregates was investigated with a focus on utilization of MSWI BA as a partial component in a road base. Two weathered bottom ashes were combined with various aggregates in multiple replacement percentages of up to 85% traditional aggregate, with the goal of mitigating leaching and direct human exposure risk. Al leaching was found to decrease proportionally to the mass of bottom ash included in the blended products, with over 90% reduction in blends with 85% recycled concrete aggregate (RCA). Release of Sb from the bottom ashes was predominantly controlled by solubility. Sb concentrations were reduced from 0.043 and 0.037 mg/L to 0.006 and 0.007 mg/L for facility A and B respectively blended with the highest tested proportion of RCA, near compliance drinking water standards of 0.006 mg/L. The high pH and presence of calcium-bearing minerals in recycled concrete appeared to facilitate significant immobilization of Sb in comparison to other aggregates. Similar results were observed for several other elements and material blends. Results indicate that blending MSWI BA with conventional aggregates is a feasible recycling application. Blending effectively mitigates environmental risk associated with the un-encapsulated use of MSWI BA in road construction.
The glass and enamelled decorations of bottles of alcoholic beverages sourced from retailers in the UK were analysed by x-ray fluorescence spectrometry for various heavy metals. In the glass substrate, lead, cadmium and chromium were present at concentrations up to about 1100 g g-1, 1100 g g-1 and 3000 g g-1, respectively, but their environmental and health risks are deemed to be low significance. Of more concern from an environmental and, potentially, occupational exposure perspective are the concentrations and mobilities of Pb and Cd in the enamels of many bottles. Thus, Pb concentrations up to about 100,000 g g-1 were found on the décor of various wine bottles and a beer bottle, and Cd concentrations of up to 20,000 g g-1 were measured in the decorated regions on a range of spirits, beer and wine bottles. Moreover, maximum concentrations that leached from enamelled glass fragments according to a standard test that simulates water and other liquids percolating through a landfill were about 1200 and 3200 g L-1 for Pb and Cd, respectively, with several fragments exceeding the US Model Toxins in Packaging Legislation and, therefore, defined as “hazardous”. Given that safer decorative alternatives are available and that a precautionary principle should be adopted for toxic heavy metals, the pervasive use of Pb and Cd in the enamels of consumer bottles is brought into question.
To assess the feasibility of incorporating municipal solid waste incineration (MSWI) bottom ash (BA) as a replacement for traditional raw materials in cement kiln feed, an industrial-scale kiln trial was performed. Leach testing and chemical and physical characterization data from a cement product made at a replacement percentage of 2.8% by mass of kiln feed were comparable to results from ordinary portland cement. The concentrations of constituents of concern in leach tests were generally below risk-based screening levels or of similar or lower magnitude than leachate from control products. Ash-amended cement exhibited greater early age reactivity, and this was reflected in initial mortar compressive strength results; ultimate compressive strength results were higher in the control mortar. The ash-amended and control cements were similar in characteristic, but quantitative x-ray diffraction results reveal differences in alite and aluminate formation during the clinker formation process.
Municipal solid waste incineration bottom ash fractions ≤4 mm are the most contaminated ones in terms of potentially toxic elements (PTEs). In order to estimate potential environmental impacts, it is important to understand the association of the PTEs with the mineral phases. Large area phase mapping (SEM/EDX) using “PhAse Recognition and Characterization - PARC” software in combination with quantitative X-ray powder diffraction has been used to characterize amorphous and crystalline BA phases for the first time. The results show that one of the main incineration products was melilite and an amorphous phase with a melilitic composition. The ratio of crystalline to amorphous melilite was 1:2. They formed an inhomogeneous layer around BA particles and contained a high percentage of the PTEs, i.e., Cu, Zn, Ni and Cr. Other major sources of PTEs (especially Ni and Cu) were iron oxides produced during incineration and the weathering products, such as calcite and ettringite (Cu and Zn). After extensive characterization of BA, a sequential extraction procedure (SEP) was performed, which exposed bottom ash to different chemical environments designed to dissolve specific phases and release their PTEs into solution. The extracted solutions and solid residues generated from the extraction procedure were analyzed to identify the association between PTEs and dissolved phases of BA. By combining SEP results with information obtained via large area phase mapping it is shown that SEP can be used for studying the association of PTEs with the phase that cannot be investigated with XRD/EDX, such as organic matter and Fe-Mn-hydrous oxides. Furthermore, according to SEP results a high percentage (40–80 wt%) of each investigated PTE can be considered immobile and not susceptible to leaching in the environment.
Ceramic fragments and fractionated (<2 mm) sediment have been sampled from two beaches in southwest England, along with sediment from a control beach where ceramic waste was lacking. Analysis of the glazed ceramic surfaces by X-ray fluorescence (XRF) spectrometry returned concentrations of Pb up to 729,000 mg kg⁻¹, while XRF analysis of sediment samples revealed high but heterogeneous concentrations of Pb at the two sites impacted by ceramic waste (median = 292 and 737 mg kg⁻¹) compared with the control beach (median ~ 20 mg kg⁻¹). These observations are attributed to the disposal of contemporary and historical ceramic products, and the subsequent attrition of material and contamination of local sediment. Extraction of a milled ceramic composite (Pb = 2780 mg kg⁻¹) by 1 M HCl, revealed a high (34%) environmental mobility and availability of Pb; extraction in a solution of protein, however, suggested a low (0.1%) bioaccessibility to sediment-ingesting invertebrates.
Development of temperature, CO2 level, and moisture was followed during several months of outdoor ageing of municipal solid waste incineration bottom ash (IBA) in seventeen 5000-ton piles, in order to obtain input data for possible optimization of the ageing process in terms of faster/better drying prior to the metal recovery operation. In addition, measured thermal conductivity and specific heat capacity of IBA were combined with calculated thermal output and used as input to a model originally developed for accessing temperature development in hardening concrete structures. The results show that the temperature in pile's core increased to 90-94 °C in two-three weeks and remained stable for at least another month. The temperatures in the outer 80 cm of the pile were shown to be affected by outside temperatures while effects of precipitation on temperature development were shown in the upper 50 cm. The used thermal model described the observed temperatures in large part of the pile well; however, it failed to describe the temperature level observed towards the top of the pile. This may be caused by an unaccounted transport process. The CO2 measured inside the pile was constantly at ''zero-level" thus indicating an incomplete carbonation. The moisture content was found to decrease during the ageing; however, significantly better data needs to be gathered especially for the period after the quenching, where the largest variation seemed to take place. The leaching of chloride, sulfate, Na, As, Ba, Cd, Cr, Cu, Hg, Ni, Pb, Se, Zn and dissolved organic carbon (DOC) from all IBA samples was shown to comply with the leaching limit values for Category 3; i.e. the IBA was found suitable for utilization in e.g. an unbound subbase of a road or a parking space. For the next phase of this project an optimized treatment was proposed which is based on using a telescopic radial stacker allowing construction of a less-compacted, higher/steeper pile with a smaller footprint which may further improve air transport through the pile, prevent excessive infiltration of precipitation, and save facility space. In addition, all ferrous material will be purposely left inside the aging piles in order to facilitate the temperature increase and to shorten the total drying time prior to the advanced metal recovery.
Coal combustion residuals (CCR) from energy generation may pose a risk to human health and the environment if not managed properly. Because of new regulations for the management of CCR, generators must dispose of these materials in lined landfill units similar to municipal solid waste (MSW) landfills. Generators could opt to construct dedicated units for CCR (monofilling) or by placing them in MSW landfills (co-disposal). The distinct chemical environments of these two disposal scenarios may cause a noticeable difference in pollutant mobilization from CCR. Batch leaching tests were employed to simulate CCR monofilling and MSW co-disposal. Landfill leachate promoted higher release of As and V from fly ash compared to ash leached with synthetic rainwater. Changes in pH do not account for the added release and other characteristics intrinsic to MSW leachate play a dominant role. When fly ash disposal is modeled, As release is forecasted to be almost 690 tons under a co-disposal scenario, compared to 18 tons when ash is monofilled. These observations highlight the need for better long-term planning when deciding the disposal routes for municipal, commercial, and industrial byproducts.
Municipal Solid Waste Incineration Bottom Ash (MSWI BA) is of increasing interest as a secondary construction material worldwide. In most cases, MSWI BA is used in isolated conditions. However, according to the Dutch Green Deal B-076 in 2012, by 2020 all MSWI BA should be used in a non-sealed environment in the Netherlands. However, freshly produced. MSWI BA normally does not match environmental legislation due to high leaching of chlorides, sulfates, and potentially toxic elements. Because different particle size fractions of MSWI BA are of interest for designing optimized concrete recipes, it is beneficial to analyze the whole range of MSWI BA fractions in detail. In this study, 14 size fractions of MSWI BA were analyzed to determine the total elemental composition and leaching capacity, mineralogical composition, and shape variety of fine particles. From the point of view of mineralogical composition, 6 particle size fractions (<180 μm, 180–500 μm, 0.5–1 mm, 1–4 mm, 4–22 mm, > 22 mm) can be distinguished. All together the analyses showed that almost all fractions of the investigated MSWI BA can be used as secondary building materials. However, because the leaching of fine fractions is 5–10 times higher than of coarse fractions, all these fractions must undergo various treatments to allow them to match the environmental legislation. Thus, to decontaminate MSWI BA from potentially toxic elements, a division into three size groups is suggested: fine (<125 μm), medium (125 μm - 1 mm), and coarse fractions (over 1 mm).
Municipal Solid Waste Incinerator (MSWI) Bottom Ash has been used as a substitute for traditional aggregates in road construction; however, this material is little understood. The work presented in this paper pursues the study on the mechanical performance of bottom ash, proven by Le et al. (2017). Using a coupling technique for the first time, the physicochemical aspects and hydromechanical resistance of bottom ash were evaluated and analyzed. Physicochemical tests were first carried out, followed by oedometer tests under a wetting path. This coupled evaluation underlined the role of principal mineralogical components of the studied bottom ash as well as the link with its hydromechanical properties. Tests results showed that the principal constituent of bottom ash is SiO2, which thus affects the characteristics of bottom ash. Given the physical stability of SiO2 which generated a compacted material being less sensitive to water and chemical reactions, and bottom ash’s other characteristics, this demonstrates why bottom ash could be a viable material in roadworks.
Fly ash from municipal solid waste incineration contains a large potential for recyclable metals such as Zn, Pb, Cu and Cd. The Swiss Waste Ordinance prescribes the treatment of fly ash and recovery of metals to be implemented by 2021. More than 60% of the fly ash in Switzerland is acid leached according to the FLUWA process, which provides the basis for metal recovery. The investigation and optimization of the FLUWA process is of increasing interest and an industrial solution for direct metal recovery within Switzerland is in development. With this work, a detailed laboratory study on different filter cakes from fly ash leaching using HCl 5% (represents the FLUWA process) and concentrated sodium chloride solution (300 g/L) is described. This two-step leaching of fly ash is an efficient combination for the mobilization of a high percentage of heavy metals from fly ash (Pb, Cd ! 90% and Cu, Zn 70-80%). The depletion of these metals is mainly due to a combination of redox reaction and metal-chloride-complex formation. The results indicate a way forward for an improved metal depletion and recovery from fly ash that has potential for application at industrial scale.
Bottom ash (BA) from waste-to-energy (WtE) plants contains valuable components, particularly ferrous (Fe) and non-ferrous (NFe) metals, which can be recovered. To assess the resource recovery potential of BA in the Czech Republic, it was necessary to obtain its detailed material composition. This paper presents the material composition of BA samples from all three Czech WtE plants. It was found that the BA contained 9.2-22.7% glass, 1.8-5.1% ceramics and porcelain, 0.2-1.0% unburnt organic matter, 10.2-16.3% magnetic fraction, 6.1-11.0% Fe scrap, and 1.3-2.8% NFe metals (in dry matter). The contents of individual components were also studied with respect to the BA granulometry and character of the WtE waste collection area.
Differences during the last 15 years in materials' composition in Municipal Solid Waste Incineration (MSWI) regarding bottom ash (BA) were assessed as a function of particle size (> 16, 8–16, 4–8, 2–4, 1–2 and 0–1 mm). After sieving, fractions > 2 mm were carefully washed in order to separate fine particles adhering to bigger particles. The characterization took into account five types of materials: glass (primary and secondary), ceramics (natural and synthetic), non-ferrous metals, ferrous metals and unburned organic matter. The evaluation was performed through a visual (> 2 mm) and chemical (0–2 mm) classification. Results showed that total weight of glass in the particles over 16 mm has decreased with respect to 1999. Moreover, the content of glass (primary and secondary) in BA was estimated to be 60.8 wt%, with 26.4 wt% corresponding to primary glass in > 2 mm size fractions. Unlike 1999, in which glass was the predominant material, ceramics are currently the major phase in bottom ash (BA) coarse fractions. As for the metals, respect to 1999, results showed a slight increase in all size fractions. The greatest content (> 22 wt%) of ferromagnetic was observed for the 2–4 mm size fraction while the non-ferrous type was almost non-existent in particles over 16 mm, remaining below 10 wt% for the rest fractions. In the finest fractions (< 2 mm), about 60 to 95% of non-ferrous metals corresponded to metallic aluminium. The results from the chemical characterization also indicated that the finest fractions contributed significantly to the total heavy metals content, especially for Pb, Zn, Cu, Mn and Ti.
This study aims to identify the chemical species and leaching behavior of Cd, Zn, Pb, Cu and Cr in a fly ash with high content of calcium collected from the incineration of municipal solid waste (MWS), based on the sequential leaching procedure. A thermodynamic pseudo-equilibrium model was also developed to evaluate the possible chemical compounds of these heavy metals in the fly ash. The results indicate that, approximate 30% of Cu was distributed in the organic bound fraction and very likely combined with some organic ligands. Pb exhibited the highest fraction among these five metals in water soluble fraction, accounting for about 7.5%. It thus potentially causes a menace to the surroundings. In terms of model calculation, the metallic chlorides in the fly ash were responsible for the leaching of Pb, Zn, Cd and Cu even under a rigorous environmental condition (pH = 2) where the oxides and/or metallic ferrites were rarely mobile. The leaching of Cr and Cd in the fly ash was controlled by a dissolution mechanism whereas the fate of Pb, Zn and Cu was controlled by the precipitation/sorption. Cu and Zn in fly ash have been proven to associate with Ca-bearing compounds through precipitation/sorption during leaching test while Pb mainly exists as sulfate and phosphate.
The leaching of Sb from waste-to-energy (WtE) bottom ash (BA) often exceeds the Dutch limit value of 0.32 mg kg−1 for recycling of BA in open construction applications. From the immobilization mechanisms described in the literature, it could be concluded that both Ca and Fe play an important role in the immobilization of Sb in WtE BA. Therefore, Ca and Fe containing compounds were added to the samples of the sand fraction of WtE BA, which in contrast to the granulate fraction is not recyclable to date, and the effect on the Sb leaching was studied by means of batch leaching tests. Results showed that addition of 0.5 and 2.5% CaO, 5% CaCl2, 2.5% Fe2(SO4)3 and 1% FeCl3 decreased the Sb leaching from 0.62 ± 0.02 mg kgDM−1 to 0.20 ± 0.02, 0.083 ± 0.044, 0.25 ± 0.01, 0.27 ± 0.002 and 0.29 ± 0.02 mg kgDM−1, respectively. Due to the increase in pH from 11.41 to 12.53 when 2.5% CaO was added, Pb and Zn leaching increased and exceeded the respective leaching limits. Addition of 5% CaCO3 had almost no effect on the Sb leaching, as evidenced by the resulting 0.53 mg kgDM−1 leaching concentration. This paper shows a complementary enhancement of the effect of Ca and Fe, by comparing the aforementioned Sb leaching results with those of WtE BA with combined addition of 2.5% CaO or 5% CaCl2 with 2.5% Fe2(SO4)3 or 1% FeCl3. These lab scale results suggest that formation of romeites with a high Ca content and formation of iron antimonate (tripuhyite) with a very low solubility are the main immobilization mechanisms of Sb in WtE BA. Besides the pure compounds and their mixtures, also addition of 10% of two Ca and Fe containing residues of the steel industry, hereafter referred to as R1 and R2, was effective in decreasing the Sb leaching from WtE BA below the Dutch limit value for reuse in open construction applications. To evaluate the long term effect of the additives, pilot plots of WtE BA with 10% of R1 and 5% and 10% of R2 were built and samples were submitted to leaching tests at regular intervals over time. The Sb leaching from untreated WtE BA was just below or above the Dutch limit value. The Sb leaching from the pilot plots of BA with additives first remained stable around 0.13 mg kg−1 but had a tendency to slightly increase after 6 months, indicating the need for further research on the effect of weathering, and more specifically of carbonation, on Sb leaching from WtE BA.
This chapter describes production of secondary copper—recovery of copper from scrap. It emphasizes the scrap recycling in general, major sources and types of scrap, and physical beneficiation techniques for isolating copper from its coatings and other contaminants. The purest copper scrap is simply re-melted and recast in preparation for manufacture and use. Less pure copper scrap is re-smelted and re-refined. Alloy scrap is usually recycled directly to make new alloy. Considerable scrap must be physically treated to isolate its copper from its other components. An important example of this is recovery of copper from wire and cable. It is done by: chopping the wire and cable into small pieces to liberate its copper; physically isolating its copper by means of a specific gravity separation (air table). Copper recovery from used automobiles and electronic devices follows a similar pattern, i.e.: Liberation by size reduction (shredding); isolation of copper by magnetic, specific gravity, and eddy-current separation. The copper from these processes is then re-smelted and re-refined. Old (obsolete) scrap is often discarded in landfills. There is, however, an increasing tendency to recycle this material due mainly to the increased cost and decreased availability of landfill sites.
Bottom ash is the most significant by-product from municipal solid waste incineration (MSWI). The mineral fraction of bottom ash can be reused as secondary building and road material, and the non-ferrous metals can be recovered. Basically, there are two types of bottom ash treatment technologies for metal recovery: dry and wet separation. Conventional dry separation is commonly applied in many European countries. In 2004, Rem innovated a wet bottom ash process in Amsterdam, the Netherlands. In 2008, an innovative dry bottom ash treating technology was implemented by a company called INASHCO. All three technologies are able to recover coarse non-ferrous metals from bottom ash. However, they show different abilities on recovering the fine heavy non-ferrous (HNF) metals (< 2 mm). The paper will introduce these three bottom ash separation technologies, and compare fine HNF recovery. Conventional bottom ash treatment is a dry separation process, which is designed to recover the steel and the coarse aluminum and copper-alloy particles larger than 10-15 mm from the ash. The innovative wet process (AEB wet separation) screens the ash wet into several fractions (0-2 mm, 2-6 mm, 6-20 mm and 20-40 mm) and classifies the 0-2 mm in a cyclone to take out the sludge (0-45 micron). Each size fraction is treated separately to recover non-ferrous metals. The treated size is down to 100 μm. Collaborating with Delft university of Technology (TU Delft), INASHCO developed a new bottom ash dry treatment plant in 2008. The INASHCO technology sifts < 2 mm mineral particles from the bottom ash input. To measure the HNF metal contents, the < 2 mm fractions from three plants were processed in the laboratory or at the plant. The < 2 mm HNF metal recovery of the conventional dry separation was not measured. However, the low recovery rate of HNF in 2-6 mm and aluminum in the 0-2 mm treated by the conventional bottom ash treatment indicates that the dry separation has a poor recovery on the < 2 mm HNF. More than 3 kg fine HNF metals are lost in each ton of bottom ash which is treated by conventional dry separation. The AEB wet process shows a better separation in the fine fraction, but there is around 2.5 kg/ton unrecovered HNF in < 2 mm. An additional wet process is necessary for the fine HNF recovery, like jigging or a Humphrey spiral. The INASHCO dry separation shows a lower loss of fine metals and no additional treatment is needed. Moreover, the fine NF metals are produced at a grade so that they can be treated together with the other coarse HNF metals. This helps to decrease the investment and treating cost. In fact, the INASHCO sifter works better on tiny HNF metals recovery compared with the traditional sieving process. Both the AEB wet separation and INASHCO dry separation display a better HNF and precious metals recovery compared with conventional dry separation. However, higher investment is required for the wet separation. By the INASHCO separation, < 2 mm HNF and precious metals are recovered with coarse metals and hardly lost in the process rejects; moreover, the cost is relatively lower than the wet separation. As a result, INASHCO dry separation is an economical, effective and wieldy bottom ash treatment.
The recovery of packaging steel from municipal solid waste (MSW) plays an important role in scrap recycling. Post-consumer packaging steel quality depends strongly on the procedure and the technology employed for its collection and recovery. Household refuse management systems include classification, compost and incineration plants. In Spain, MSW incineration is carried out by nine incinerators that generate a total of around 40 000 t of ferrous scrap every year. Two types of furnace are used for the incineration process, namely mobile grate furnaces (MGF) and fluidised bed furnaces (FBF). Slag from the process is comprised by the incombustible materials of MSW (vitreous materials, ceramic materials, ferrous and nonferrous metals). Slag accounts for 85–95% of the total solid waste mass. About 95% of the metallic fraction corresponds to ferrous scrap. The objective of this paper was to determine the current quality of scrap from incinerators and to study the causes of alteration of steel, i.e. of the corrosion of its surface, attempting to relate these parameters with the technology used in the combustion of MSW and the cooling treatment applied to the slag. A process for enhancing the quality of ferrous scrap from MSW is described, which includes fragmentation and magnetic separation stages.
This document summarizes information from worldwide sources on the beneficial use of residues from the combustion of municipal. The information presented, including results of numerous research projects, field demonstrations, and actual full-scale projects, demonstrates that the ash can be safely used. It includes data on ash characteristics, environmental considerations, guidance on selected ash use applications, and information on federal and state regulations and policies affecting ash use.
Municipal solid waste incinerator (MSWI) bottom ash was size fractionated into six fractions, with the respective particle size of <0.45mm, 0.45-1mm, 1-2mm, 2-4mm, 4-8mm and >8mm. The contents and fractionation of Cu, Zn, Cd in the size fractionated MSWI bottom ash were investigated. The results showed the contents and fractionation of Cu, Zn and Cd varied among the different particle sizes, which were related to their thermodynamic characteristics. High content of Cu was found in the bottom ash with the particle size of <0.45mm and >4mm, due to its lithophilic property and the function of entrainment. The content of Zn showed a relatively even distribution among the various particles. The content of Cd showed a decreasing trend with the increase of the particle size, due to its high volatility. Besides, the carbonate bound fraction of Cd showed a decreasing trend with the increase of the particle size, while the carbonate bound fraction of Cu showed an increasing trend. The organic matter bound fraction of Cu increased when the particle size increased. The results also showed the fine ash contained a higher level of unstable Cd than the large ash, while the large ash had a higher level of unstable Cu comparatively.
Glass Historical ApplicationBatching IssuesFurnace/Forehearth VolatilizationFurnace Stack EmissionsProduct use in ServiceApplied Ceramic Labels (ACL)Facility Disposal/LandfillConclusions
The objective of this study is to the use of municipal solid waste incinerator (MSWI) fly ash as a partial replacement of fine aggregate or mineral filler in stone matrix asphalt (SMA) mixture. For saving natural rock and reusing solid waste, basic oxygen furnace slag (BOF slag) was used as part of coarse aggregate. And this makes SMA mixtures contain more than 90% solid waste materials by mass. A comparative study of the performance of two mixes designed using superior performance asphalt pavements (SUPERPAVE) and Marshall mix design procedures was carried out in this research. Samples from both mixes were prepared at the design asphalt contents and aggregate gradations and were subjected to a comprehensive mechanical evaluation testing. These tests included Marshall stability, water sensibility, resilient modulus, fatigue life and rutting. In all the performed tests SUPERPAVE mixtures proved their superiority over Marshall mixtures. TCLP test for environmental impact indicated that asphalt is an effective stabilization and solidification agent for heavy metal in MSWI ash. The heavy metal leachates in TCLP tests have great positive correlation with their initial concentration in waste. But Ni is an exception that lower initial concentration leaded to higher cumulative leaching rate.
The average antimony concentration in municipal solid waste is estimated to be about 10–60 ppm. Thermodynamical models predict a volatile behavior for antimony compounds, yet literature mass balances show that about 50% of the antimony input remains in the grate ashes. This fact can be explained by the formation of thermally stable antimonates in the fuel bed due to interactions with alkali or earth-alkali metals. Thermogravimetric experiments revealed an increased thermal stability for antimony oxide in presence of oxygen and calcium oxide. Spiking experiments on the test incinerator TAMARA showed that chlorination processes have a strong effect on antimony volatilization whereas high fuel-bed temperatures and addition of antimony oxide only have a moderate effect. In the grate ashes, antimony shows a pH-depending leaching property, which is typical for anionic species. This fact supports the thesis that antimony is present in the grate ashes in an anionic speciation.
The particles with diameter >1 mm present in the bottom ash of Municipal solid waste incinerator (MSWI) were characterized by identifying the main constituent materials. This characterization may be used to evaluate the potential applications of bottom ash and its environmental hazards, and to evaluate the possibilities of recycling its main components. The effectiveness of the voluntary recycling programs of bottom ash can also be assessed. The main components of the bottom ash are glass, magnetic metals, minerals, synthetic ceramics, paramagnetic metals and unburned organic matter. The 4–25 mm size fraction accounts for approximately 50% of the bottom ash weight and comprises mainly glass (>50% of this fraction), synthetic ceramics (>26%) and minerals (>8%), and thus appears to be suitable for reuse as secondary building materials or for glass recycling. Magnetic metals accumulate in the 1–6 mm particle size fraction (6% of this fraction). Heavy metals accumulate in the fraction under 1 mm, unlikely the acid-soluble fraction, which diminishes as particle size diminishes.
In Flanders, recycling of bottom ash is mainly inhibited by the high leaching of Cu. Although it has been proved that dissolved organic C plays a major role in the Cu leaching, the possible role of inorganic Cu mineral speciation has never been experimentally examined. In this study the speciation of Cu is investigated using a combination of optical microscopy and electron microprobe –WDX/EDX. Several Cu species were determined. Metallic Cu (with or without an oxide shell), CuO and Cu2O were the most abundant. These particles were most likely present in wire-like structures. Copper also occurred as alloy (brass, bronze, zamak), and was found frequently together with typical elements such as Ca, Cl and S. Finally, small metallic Cu particles seemed to be trapped in or precipitated on oxides and silicates. Based on this Cu speciation study, pure Cu minerals were selected and leached as a function of time. The solubility after equilibrium of all studied Cu minerals never exceeded 20 μg/L (which equals 10% of the total Cu leaching).The effect of heating (2 h at 400 °C) on the speciation of Cu was investigated using the same combination of techniques. Results show that metallic Cu seemed to be converted to Cu oxide (mostly CuO) and that the particles were more porous after heating. These conclusions were verified by XRD analysis of the heated pure Cu minerals. After heating, the Cu minerals were also leached as a function of time, to study the impact on Cu leaching. Results indicate that their leaching had slightly increased in comparison with the non-heated Cu minerals. However, the major decrease in Cu leaching in heated bottom ash, more than neutralizes this effect and thus can be attributed to the destruction of organic matter and not to the (small) change in Cu speciation.