Municipal Solid Waste Incineration Bottom Ash Research Articles

Characterization of Fine Fractions from the Processing of Municipal Solid Waste Incinerator Bottom Ashes for the Potential Recovery of Valuable Metals

Municipal waste incinerator bottom ashes contain copper contents comparable to those of low-grade ores in addition to other valuable metals. While the processing of coarse fractions (>2 mm) is state of the art, the fines with their residual metal content are landfilled. This paper presents the results from a mineralogical characterization of fine fractions from the processing of municipal solid waste incinerator bottom ashes. From the results, possible approaches for a recovery of copper from the fine fraction are derived. Spatially resolved phase analysis reveals that the material contains a very heterogenic mixture of naturally occurring compounds as well as particles of alloys, metals, artificial oxides, and sulfides. The most interesting element to recover is copper. Copper can be found in the form of alloys, simple sulfides (XS), and oxides (XO). During the incineration process, new phases are generated that differ from natural ones and therefore can be called artificial minerals. Additionally, several components are partially altered due to oxidation, especially after the prolonged outside storage of the bottom ash. Crystalline silicate and glass particles are only sporadically enriched in Cu. Based on these results, different processing techniques are discussed. Due to the small particle size distribution and the physical and physico-chemical properties of the particles, flotation seems to be the most promising technique for the enrichment of copper from municipal solid waste incineration bottom ash (MSWI-BA) fine fractions.

Material and chemical composition of municipal solid waste incineration bottom ash fractions with different densities

Bottom ash is the main solid residue from municipal solid waste incineration (MSWI). The material can be utilised in the construction industry but high requirements for this option are often not met by material generated during ordinary bottom ash treatment. Hence, the objective of the present study is to investigate the suitability of density separation for bottom ash to generate mineral material fractions with different properties. MSWI bottom ash samples were sieved to a size of 2–4 mm and 4–8 mm, respectively, washed and dried before being fed to a density separation processes. Thereby, the density fractions 3000 kg/m3 were generated and, subsequently, sorted into mineral material, glass, metals and unburnt organic matter. Mineral material with a density above 2400 kg/m3 and even more above 3000 kg/m3 shows a very high content of Fe, Cu and Zn of up to 448,000 mg/kg, 61,000 mg/kg and 44,000 mg/kg, respectively. Hence, the high density fraction of mineral material could be used as a raw material for metal production. Glass with a density above 2400 kg/m3 has a Pb content of up to 87,000 mg/kg, while the Pb content of lower density glass is decreased.

Grain-Size Specific Characterisation and Resource Potentials of Municipal Solid Waste Incineration (MSWI) Bottom Ash: A German Case Study

Municipal solid waste incineration (MSWI) is a major element of modern waste management and produces annually around 5.7 million tonnes of bottom ash (BA) in Germany. In order to save natural resources and protect the environment, utilisable materials need to be recovered from BA. It was the aim of the present study to determine metal and mineral resource potentials of MSWI BA based on a characterisation study of raw and aged BA of the MSWI plant in Kassel (Germany). The BA investigated consisted of 82.2% mineral materials, 16.3% metals, and 1.5% unburnt organic matter. Overall, 12.1% and 3.6% of the MSWI BA were theoretically recoverable as native ferrous (Fe) and non-ferrous (NFe) metals, respectively. Assuming state-of-the-art recovery technology, 10.7% and 2.0% of the BA were actually extractable as Fe and NFe metals. The processed BA, as a mixture, did not comply with current German limit values for use as a construction material mainly due to excessive soluble salt contents. Coarser grain size fractions were less contaminated, resulting in a utilisable potential of less than 30% of the BA as a construction material. Hence, grain-size specific processing routes need to be developed for MSWI BA to fully exploit its mineral resource potential.

Determination of metal-abundant high-density particles in municipal solid waste incineration bottom ash by a series of processes: Sieving, magnetic separation, air table sorting, and milling

Valuable non-ferrous (NFe) metals are contained in municipal solid waste incineration (MSWI) bottom ash (BA). The applicability of an air table for separating NFe metal-abundant particles in MSWI BA (<8 mm) was studied. A stepwise separation procedure was developed based on the performance tests of the air table conducted by changing three variables (air injection, vibration, and end slope). As a result of the stepwise separation, six bulk density ranges (<0.7 to >1.1 g/cm3 at intervals of 0.1 g/cm3) were prepared from non-magnetic fractions with four size ranges (4–8, 2–4, 1–2, and 0.5–1 mm). The effectiveness of air table sorting was evaluated based on dry particle density and proportion of metals. NFe metals were obtained by sieving (>0.5 mm) after a ball mill process, confirming that NFe metals accounted for 3.2% of the < 8 mm MSWI BA. The highest particle density of each size fraction and the proportion of NFe metals in the fractions were 3.19 g/cm3 and 59.9% (4–8 mm), 2.97 g/cm3 and 28.8% (2–4 mm), 2.78 g/cm3 and 10.4% (1–2 mm), and 2.87 g/cm3 and 4.4% (0.5–1 mm). In the 0.5–2 mm particles, the highest density fraction contained 68.7% of the NFe metals, which were expected to be recovered by applying an air table separator to MSWI BA 0.5–2 mm.

The use of calcium sulfo-aluminate cement as an alternative to Portland Cement for the recycling of municipal solid waste incineration bottom ash in mortar.

Municipal solid waste incineration generates large quantities of bottom ash that should be recycled. Current use of municipal solid waste incineration bottom ash (MSWI-BA) in cementitious materials is mostly in Ordinary Portland Cement (OPC). This paper considers using MSWI-BA as sand substitution in Calcium Sulfoaluminate Cement (CSA) as an alternative to OPC. A comparison between OPC and CSA mortars containing 0-2 mm MSWI-BA is conducted. The MSWI-BA used was treated to remove the ferrous and non-ferrous metals in order to obtain a better mineral fraction. Different percentages (0%, 25%, 50%, 75%, and 100%) of standard sand were substituted by MSWI-BA based on equivalent volume. Experimental results showed that the compressive strength and porosity of the CSA mortars were superior to OPC after substitution at 1, 7, 28, and 90 days. The compressive strength of OPC mortars with 25% substitution decreased by 40% compared to 11% for CSA mortars at 90 days. This is due to the difference in pH between the two cement pastes as OPC in contact with the MSWI-BA leads to a reaction with the aluminum content which releases hydrogen gas, increases the porosity, and decreases the compressive strength.

Potential Use of Incineration Bottom Ash in Construction: Evaluation of the Environmental Impact

Knowledge of the long-term leaching behavior of potentially harmful substances is crucial for the assessment of the environmental compatibility of reusing municipal solid-waste incineration bottom ash (MSWI BA) in construction, i.e., as a road base layer. BA fractions obtained from wet-processing aiming at the improvement of environmental quality were used to investigate the mobility of relevant substances. Eluates from laboratory-scaled leaching procedures (column percolation and lysimeters) were analyzed to learn about the long-term release of substances. Unsaturated conditions and artificial rainwater (AR) were used in the lysimeter tests to simulate field conditions. In addition, batch test eluates were generated at usual liquid-to-solid ratios (L/S) for compliance testing purposes. A variety of cations and anions was measured in the eluates. The wet treatment reduces the leaching of chloride and particularly sulfate by more than 60%. The release of typical contaminants for the treated MSWI BA such as the heavy metals Cu and Cr was well below 1% in the conducted leaching tests. An increase in the Sb concentration observed in the lysimeter experiments starting at L/S 0.75 L/kg and in the column experiment at L/S 4 L/kg is assumed to be related to decreasing concentrations of Ca and thus to the dissolution of sparingly soluble calcium antimonate. The same leaching mechanism applies with V, but the concentration levels observed are less critical regarding relevant limit values. However, on the long term the behavior of Sb could be problematic for the application of MSWI BA in construction.Graphic

Preparation of additive-free glass-ceramics from MSW incineration bottom ash and coal fly ash

An additive-free glass-ceramics was prepared entirely from municipal solid waste incineration bottom ash (BA) and coal fly ash (CFA), which provided new sight for the synthesis of waste-derived glass-ceramics and reduced its production cost. By varying temperature and proportion of BA and CFA, the thermal behaviour, crystalline species, microstructure, physical-mechanical-chemical properties, and metals leaching of glass-ceramics were studied. The results showed that the variation of temperatures did not change the crystal types of glass-ceramics, but affect the crystal volume and morphology. With the basicity increasing from 0.15 (G1, BA/CFA = 30/70) to 0.41 (G5, BA/CFA = 70/30) at 950 °C, the main crystalline phases evolved from single anorthite to coexisting anorthite and diopside, and the compressive strength showed a volcano trend. Among different glass-ceramics, G3 with 50% BA and 50% CFA sintered at 1000 °C demonstrated the most promising properties with density of 2.55 ± 0.02 g/cm3, water absorption of 0.1 ± 0.01%, and compressive strength of 299.09 ± 21.19 MPa, as well as good corrosion resistance to strong acid/alkali solutions. Besides, the metals leaching and ecological risk assessment results of the additive-free glass-ceramics demonstrated a low risk for the metal contamination in the final products and heavy metals were well fixed into the coexistence system of amorphous and crystalline phases. The achieved additive-free glass-ceramics showed competitive properties and environmentally friendly features. Therefore, the preparation of additive-free glass-ceramics from BA and CFA can be considered as a feasible and promising method to realize their efficient utilization and simultaneously reduce the cost of waste-derived glass-ceramics.

Effect of partially replacing ordinary Portland cement with municipal solid waste incinerator ashes and rice husk ashes on pervious concrete quality.

Pervious concrete (PC) provides multiple benefits, including reducing stormwater runoff, purifying water, recharging groundwater, and reducing the heat island effect. This study aims to determine an effective way to reuse municipal solid waste incinerator (MSWI) fly ash (FA), MSWI bottom ash (BA), and rice husk ash (RHA) as single or binary partial replacements for ordinary Portland cement (OPC) in PC. The ashes and PC specimens were characterized via X-ray fluorescence spectroscopy, X-ray powder diffraction, field emission-scanning electron microscopy, and Fourier transform infrared spectroscopy. The compressive strength, water permeability, and toxicity characteristic leaching procedure (TCLP)-released metals were investigated to evaluate the PC quality. The main components of the ashes were similar to those of OPC, suggesting that the ashes could be reused as cement materials; however, the cementitious activity of the ashes, especially MSWI FA, was relatively low. All ashes except 1100°C MSWI FA met the standard requirements and can be applied as pozzolanic materials. The three PC specimens with binary replacements containing RHA (550, 700, and 900°C) and MSWI BA (1100°C) showed a synergistic effect and exhibited a higher 90-day compressive strength than the other specimens with single and binary ash replacements containing RHA (550 and 900°C). The water permeability ranged between 0.106 and 0.391cm/s, and the TCLP-released metal concentrations from all specimens met the regulatory standards of Taiwan. The results indicated that replacement with MSWI BA and RHA in cement materials provides an acceptable compressive strength and water permeability.

Use of pretreatment to prevent expansion and foaming in high-performance MSWI bottom ash alkali-activated mortars

This study has investigated the impact of foaming and expansion of municipal solid waste incinerator (MSWI) bottom ash (BA) during alkali reaction. Furthermore, the activity enhancement of the BA has been investigated. Based on the microanalytic appearance and compressive strength of the samples, the results show that the reaction between the metallic aluminium in the BA and alkali in the activator, which produced large quantities of hydrogen, is the primary cause for both foaming and expansion. The residual organic matter and unburnt substances in the BA are the main factors that affect the activity. However, the alkali defoaming and calcination-melting pretreatments completely prevented the expansion and calcining further improved the BA activity. The alkali activated materials prepared with the BA calcined at 700 °C, granulated blast furnace slag, and slaked lime followed by alkali defoaming pretreatment produced the best mechanical properties.

Investigated stress-strain relationships of municipal solid waste incineration bottom ash

To investigate the stress-strain relationship of municipal solid waste incineration bottom ash (MSWIBA), taking MSWIBA samples with a dry density of ρd = 1.5 g/cm3 as examples, a series of consolidated drained triaxial tests were carried out on MSWIBA. The test results showed that the stress-strain relationship of MSWIBA showed an obvious strain softening phenomenon when their curing ages and confining pressure were relatively small, and the stress-strain relationship showed an obvious strain hardening phenomenon when the curing ages and confining pressure were large. The improved Duncan-Chang model can reflect the strain softening and strain hardening phenomenon of MSWIBA. There is a transformation phenomenon of the stress-strain relationship in MSWIBA, and the curing age and confining pressure are the main influencing factors of its transformation phenomenon. The ‘postfailure modulus’ was proposed to distinguish the transformation phenomenon of MSWIBA, and its transformation mechanism was analyzed in detail. A practical stress-strain relation model is proposed for MSWIBA, which can take into account the transformation phenomenon. Moreover, the patterns of the stress-strain relationship were identified based on the critical confining pressure.

Experimental study on the strength behaviors of municipal solid waste incineration bottom ash using ultrasonic wave velocity tests

To investigate the physico-mechanical properties of municipal solid waste incineration bottom ash (MSWIBA), the factors influencing the strength characteristics of MSWIBA were studied using an ultrasonic wave velocity test, to investigate its physico-mechanical properties. The test results show that the curing age, dry density, temperature, particle size, moisture content, and soaking time in water affect the strength of MSWIBA. The analyses of the wave velocity suggest that the strength of MSWIBA increases with its curing age and dry density. The strength increases rapidly over a curing age of 3–7 days but increases slowly after 14 days. In addition, the strength increases under an increase in temperature within the range of 20–50 °C, and it tends to stabilize above 50 °C. Moreover, the moisture content and particle size have a significant effect on the strength. MSWIBA, with a particle size of 0–2 mm, exhibits the greatest strength, and its strength is maximal at the optimum moisture content (15%). The soaking time in water has an adverse impact on the strength of MSWIBA during the first 80 h, decreasing its strength by approximately 5%. Moreover, the Poisson’s ratio of MSWIBA is determined using wave velocity ratios from elastic theory.

Physical and Chemical Properties, Pretreatment, and Recycling of Municipal Solid Waste Incineration Fly Ash and Bottom Ash for Highway Engineering: A Literature Review

Municipal solid waste incineration (MSWI) has been widely used due to its benefits in reducing waste and recovering energy. However, MSWI fly ash and bottom ash are increasing rapidly, causing harm to human health and the environment. This paper discussed the production process, physical and chemical properties, leaching properties, pretreatment methods, and applications of fly ash and bottom ash. By summarizing the previous literature, it is found that MSWI fly ash and bottom ash have mechanical properties similar to natural aggregate. Many beneficial attempts have been made in cement concrete aggregates, ceramic raw materials, and highway engineering materials. Due to concerns about the leaching of heavy metals in fly ash, its application in highway engineering is limited. The application of bottom ash in asphalt pavement is rare because of the side effect on the performance of asphalt mixture. Considering the solidification effect of cement on heavy metals and the low cost of fly ash and bottom ash, the application in cement‐stabilized macadam base has broad application prospects. This is beneficial to reduce the construction cost and promote the process of waste incineration, especially in developing countries.

Mechanical Properties of Municipal Solid Waste Incinerator (MSWI) Bottom Ash as Alternatives of Subgrade Materials

The rapid development of industrialization, urbanization, and population of the society augments the rising amount of municipal solid waste (MSW). With the advantage of considerably reducing mass and volume of solid wastes and generating energy, the incineration is a widely used treatment method for MSW. During the incineration process, the organic substances contained in the wastes are combusted, and the massive residues are remained. Of the incineration residues, bottom ash takes up to 80–90%, and the remainders are fly ash along with air pollution control residues. Dealing with the municipal solid waste incineration (MSWI) bottom ash in a sustainable manner is the primary principle. Significantly, MSWI bottom ash has been successfully utilized in diverse beneficial applications in recent decades, especially in civil engineering applications. This paper investigates the mechanical properties and validity of MSWI bottom ash as applicable substitutes of conventional subgrade materials. For this reason, a series of direct shear and CBR tests are performed on specimens with different water contents and dry densities.

MSWI Bottom Ash Application to Resist Sulfate Attack on Concrete

This research provides a strategy for partially replacing cement with municipal solid waste incineration (MSWI) bottom ash (BA) to improve the performance of concrete against sulphate attack. Mortar strength tests were performed firstly to evaluate the hydration activity of the ground BA. Concrete specimens were cured in standard conditions and immersed in a solution that contained 10% sodium sulfate. Then, the compressive strength of these specimens was measured to investigate the mechanical properties and durability of the concrete. Next, the capillary porosity of the concrete was determined from the volume fractions of water lost in specimens. Finally, the transport of the sulphate solution in concrete was analyzed using capillary rise, crystallization rate, and solution absorption tests. The results indicated that BA had a certain hydration activity. The equivalent replacement of cement by BA decreased the compressive strength of the specimens but increased the durability of the concrete. There was an excellent correlation between capillary rise height, sulfate solution absorption amount, crystallization rate, and coarse capillary porosity. The addition of BA can decrease the coarse capillary porosity and further slow the capillary transport and crystallization of sulfate solution in concrete. Overall, the replacement of cement with BA can improve the durability of concrete and actualize the utilization of MSWI residues as a resource.

Factors affecting properties of MSWI bottom ash employing cement and fiber for geotechnical applications

The present study is based on municipal solid waste incineration (MSWI) bottom ash stabilization when amended with cement and fiber. To simulate the effect of inclusion of cement and fibers on the behavior of MSWI bottom ash, numerous experiments were performed. The CBR test was considered as a basic parameter during the study. For CBR, a comparison was made among different test specimens under soaked and unsoaked conditions, with and without cement and fibers. The maximum dry unit weight of the bottom ash reduces, and moisture content rises due to the inclusion of cement and fiber. The results revealed that the relatively better combination was found to be highest gain of CBR value in case of 8% cement and 1% fiber. The study results also demonstrated that addition of fiber used to stabilize MSWI bottom ash reduces the stiffness as well as changes the behavior from brittle to ductile. Due to the free availability, such material can be used in compacted fills, embankments and road construction in very liberal manner. A multiple linear regression analysis of test results was carried out in order to develop a mathematical relationship to understand the intensity of different factors, i.e., MSWI bottom ash, cement content, fiber content, fiber length and curing period. The simulated model agreed reasonably with the experimental results.

Mechanical characteristics of municipal solid waste incineration bottom ash treated with cement and fiber

The present study deals with the effect of addition of cement and fiber on the compaction and strength behavior of municipal solid waste incineration (MSWI) bottom ash. Heavy compaction tests were conducted to evaluate the compaction behavior, while unconfined compression tests (UCS) and split tensile strength (STS) tests were conducted to evaluate the strength properties of MSWI ash. For UCS testing, the specimens were cured for 7, 14, 28, and 90 days, whereas for STS testing, after 7, 14, and 28 days, respectively. The test results showed maximum dry unit weight of the bottom ash reduces and optimum moisture content rises due to the inclusion of cement and fiber. The study results also demonstrated that the addition of fiber used to stabilize MSWI bottom ash reduces the stiffness as well as changes the behavior from brittle to ductile. The fiber with cement can be successfully used as reinforcement material for the modification of MSWI ash. A multiple linear regression analysis of test results was carried out in order to develop a mathematical relationship to understand the intensity of different factors, i.e., MSWI bottom ash, cement content, fiber content, fiber length, and curing period. The simulated model agreed reasonably with the experimental results.

Metals Leaching in Permeable Asphalt Pavement with Municipal Solid Waste Ash Aggregate

The leaching behaviors of four heavy metals (Zn, Pb, Cu and Cr) from unbounded municipal solid waste incineration-bottom ash aggregate (MSWI-BAA) and permeable asphalt (PA) mixture containing MSWI-BAA were investigated in the laboratory. The horizontal vibration extraction procedure (HVEP) test and a simulated leaching experiment were conducted on MSWI-BAA with three particle sizes, but only the simulated leaching experiment was carried out on a type of PA specimen (PAC-13) with and without these MSWI-BAAs. Leaching data were analyzed to investigate the leaching characteristics, identify the factors affecting leaching and assess the impact on the surrounding environment. Results indicated that the leaching process was comprehensively influenced by contact time, leaching metal species and MSWI-BAA particle size, regardless of MSWI-BAA alone or used in PAC-13 mixture. The leaching concentrations of Cr, Zn and Pb from MSWI-BAA in HVEP testing was strongly related to MSWI-BAA particle size. The use of MSWI-BAA in PAC-13 mixture did not change the basic tendency of heavy metal leaching, but it led to an increase of Cr and Zn in leachate overall. The leachate from the MSWI-BAA and PAC-13 mixture with MSWI-BAA was shown to be safe for irrigation and would have very little negative impact on surrounding surface and underground water quality.

Zero-waste approach in municipal solid waste incineration: Reuse of bottom ash to stabilize fly ash

Abstract In this paper a simple method for all waste recovery through municipal solid waste incineration (MSWI) is presented. For the first time, MSWI fly ash (FA) is treated using MSWI bottom ash (BA), which is considered as a new urban mining source due to its pozzolanic characteristics. The proposed technology involves mixing these ashes with two other components: flue gas desulphurization residue and coal fly ash. Thermal annealing at a low temperature (120 °C for 4 h) can also be performed, to accelerate some reactions, but it is not necessary for stabilization. The efficacy of the process is demonstrated by the comparison of elemental concentrations in leaching solutions that are detected in the untreated ashes and the obtained stabilized materials, which show the reduced solubility of leachable Zn and Pb (with respect to the starting MSWI FA). The chemical, morphological, and structural characterization of the obtained materials makes it possible to propose and discuss a stabilization mechanism, which was attributed to carbonation and formation of calcium silicate hydrate (C–S–H). In particular, for the stabilized sample, X-ray Diffraction analysis confirmed the formation of calcite, whereas the sample morphology shows some fibrils that may be due to amorphous C–S–H with a Ca/Si ratio that is slightly smaller than 1.5. Because the proposed method employs wastes produced at the same location, it is reasonable to conclude that the method may be directly applied to incinerator plants due to the simplification of the MSWI FA waste management strategy, which generally involves its transport and stabilization treatment before landfilling. Finally the saved carbon dioxide emissions and the economic benefits that are a result of the new urban mining proposed approach have been evaluated for Europe. In particular the avoid of MSWI FA landfilling was evaluated to save approximately 1.6 M€/day, and the saved carbon dioxide emissions introduced into the atmosphere is approximately 960 kt/year.

In-situ measurements of high-temperature dielectric properties of municipal solid waste incinerator bottom ash

Abstract Microwave heating is a potential green technology demonstrating many advantages over conventional heating methods. Prior to designing an industrial microwave process, however, a fundamental knowledge of the dielectric properties of the material to be thermally treated is imperative, as these properties determine the response of the material to an applied electromagnetic field. In this study, the fundamental interactions between microwave energy and municipal solid waste incinerator (MSWI) bottom ash (BA) are investigated through in-situ complex permittivity measurements. Using an enhanced version of the cavity perturbation method, the dielectric properties were determined from room temperature up to 1100 °C at a frequency close to the industrial 2.45 GHz. The results demonstrated that BA is a low-loss microwave absorber up to 320 °C, above which microwave flash pyrolysis of the organic matter abruptly enhances the dielectric loss of BA, resulting in a thermal runaway. The addition of water and graphite to BA induces a higher dielectric constant and loss factor. The evolution of the dielectric properties as a function of temperature is correlated to changes in the material as determined by Simultaneous Differential Scanning Calorimetry, Thermogravimetric Analysis and High Temperature X-ray Diffraction. The reported results form a baseline for the assessment of the MSWI BA response under microwave irradiation.

Critical examination of recycled municipal solid waste incineration ash as a mineral source for portland cement manufacture – A case study

Municipal solid waste incineration (MSWI) ash has the potential to be used as mineral feed for portland cement manufacture but is not currently used in this manner in much of the world. A scoping study was performed using samples and data from Florida, US, to assess the potential magnitude of material that may be recycled to create a viable clinker. Results indicate that MSWI ash possesses the elemental ingredients to serve as a partial kiln feed replacement. Large amounts of MSWI can be used based on mineralogy alone, but chloride and alkali content limitations decrease allowable replacement amounts, especially for fly ash. Average allowable replacement percentages that did not exceed standard chloride and alkali limits were 6.4%, 0.33%, and 1.17% for bottom ash, fly ash and combined ash, respectively. MSWI bottom ash may be the preferred material stream in the absence of pre-processing techniques such as washing. The scoping study found that available MSWI ash could supply a large amount of the current kiln feed demand, and a feasibility and cost assessment supports that both MSWI facility and cement kiln operators have justification to pursue this technology with more detailed evaluations.