Leaching characteristics of slag from the melting treatment of municipal solid waste incinerator ash

CFD-DEM simulations of municipal solid waste gasification in a pilot-scale direct-melting furnace

A multiphase CFD-DEM model was built to simulate the waste-to-energy gasifying and direct melting furnace in a pilot demonstration facility. The characterizations of feedstocks, waste pyrolysis kinetics, and charcoal combustion kinetics were first obtained in the laboratory and used as model inputs. The density and heat capacity of waste and charcoal particles were then modelled dynamically under different status, composition, and temperature. A simplified ash melting model was developed to track the final fate of waste particles. The simulation results were in good agreement with the site observations in both temperature and slag/fly-ash generations, verifying the CFD-DEM model settings and gas-particle dynamics. More importantly, the 3-D simulations quantified and visualized the individual functioning zones in the direct-melting gasifier as well as the dynamic changes throughout the whole lifetime of waste particles, which is otherwise technically unachievable for direct plant observations. Hence, the study demonstrates that the established CFD-DEM model together with the developed simulation procedures can be used as a tool for the optimisation of operating conditions and scaled-up design for future prototype waste-to-energy gasifying and direct melting furnace.

Study on the reduction of chlorine and heavy metals in municipal solid waste incineration fly ash by organic acid and microwave treatment and the variation of environmental risk of heavy metals

Municipal solid waste incineration (MSWI) fly ash usually needs to undergo dechlorination or heavy metal stabilization pretreatment for further treatment, recycling or disposal. In this paper, the removal effect of chlorine in fly ash by water washing, lactic acid, citric acid and microwave treatment was studied, and XANES was used to analyze chlorine chemical form in fly ash. In addition, the heavy metals in fly ash were also checked. The results indicated that double washing and triple washing could remove 88.0 % and 95.5 % of chlorine from fly ash respectively. The "double water washing + microwave/organic acid" could remove about 96.6 % of chlorine, and 42.9 % and 47.2 % of insoluble chloride respectively. The microwave treatment could maximize the stabilization of heavy metals with a BI value of 39.1 %, 0.11 %, 1.65 %, 15.4 % and 3.98 % for Cd, Cr, Cu, Pb and Zn. The elution of heavy metals by citric acid was obvious. "Double water washing + citric acid" removed 87.0 % of Cd, 17.2 % of Cr, 11.9 % of Cu, 39.6 % of Pb and 43.6 % of Zn, but the environmental risk of Cu and Cr increased about 2-3 % after the treatment. The results of this study provide guidance for the pretreatment of fly ash before resource utilization.

Investigation of Mechanochemically Treated Municipal Solid Waste Incineration Fly Ash as Replacement for Cement

Municipal solid waste incineration (MSWI) fly ash has been classified as hazardous waste in China because of the leachable toxic heavy metals and high concentrations of chlorides and polychlorinated dibenzo-p-dioxins and polychlorinated dibenzofurans (PCDD/Fs). Currently, the main treatment method is still landfilling after chemical treatment or cement solidification, and an effective approach to realize fly ash utilization is still lacking. In the present work, the fly ash was firstly water-washed to remove the soluble chlorine salts, which can improve the performance of the produced cement mortar in later work. Mechanochemical pre-treatment was adopted to destroy the PCDD/Fs and improve the heavy metals’ stabilization. The results show that 75% of PCDD/Fs can be degraded and that most of the heavy metals are stabilized. After the mechanochemical pre-treatment, the average particle size of the fly ash decreases to 2–5 μm, which is beneficial for promoting the activation energy and accelerating the hydration process in cement mortar production. The compressive and flexural strengths of the fly ash cement mortar improve to 6.2 MPa and 32.4 MPa, respectively, when 35% of the OPC is replaced by treated fly ash. The similarity in the 3-day and 28-day strength with or without the addition of the treated ash shows the light influence of the fly ash addition. Thus, the mechanochemical process can stabilize the heavy metals and activate the fly ash, allowing it to partly substitute ordinary Portland cement in building materials, such as cement raw materials and concrete.

Comparison of trace element mobility from MSWI ash before and after plasma vitrification

A common perception of plasma arc treatment systems for municipal solid waste incineration ash is that the resulting vitrified slag is inert from an environmental perspective. Research was conducted to examine this hypothesis and to assess whether reduced pollutant release results from pollutant depletion during the process of the ash with plasma, or encapsulation in the glassy vitrified matrix. The concentrations of four discrete municipal solid waste incineration ash samples before and after plasma arc vitrification in a bench-scale unit were compared. Slag and untreated ash samples were leached using several standardized approaches and mobility among the four metals of interest (e.g. As, Cd, Pb and Sb) varied across samples, but was generally high (as high as 100% for Cd). Comparison across methods did not indicate substantial encapsulation in the vitrified slag, which suggests that reduced pollutant release from plasma arc vitrified slag is due to pollutant depletion by volatilization, not encapsulation. This has significant implications for the management of air pollution control residues from waste-to-energy facilities using plasma arc vitrification.

Contaminants of concern (CoCs) pivotal in assessing the fate of MSW incineration bottom ash (MIBA): First results from India and analogy between several countries

Present study characterizes municipal solid waste incineration bottom ash (MIBA) from three incineration plants in Delhi with an intent to serve the dual objectives: a) assessing the disposal/reuse options for Delhi MIBA, b) evaluating variability in results across the countries (including India) and assessing if is significant enough to influence the fate of MIBA of varied origin. A review on leaching studies of MIBA (50 research papers) was conducted which aided in achieving both the objectives. Delhi MIBA samples were analysed for chemical composition. The two commonly adopted leaching tests i.e., TCLP and EN 12457-2, were conducted and the results were checked against regulatory threshold levels (RTLs) to achieve the first objective. Leaching concentration of the contaminants was compared with the compiled literature and RTLs to accomplish the second objective. The compendium of literature most importantly revealed the physicochemical parameters which are pivotal in determining the fate of MIBA but have been missing from many studies. Ten such parameters were identified: Cr, Cu, Mo, Sb, Cl^-,SO₄^2-, Cd, Pb, Ni and Zn and are referred as contaminants of concern (CoCs). Delhi MIBA was found suitable for disposal to non-hazardous waste landfills and unsuitable for unrestricted reuse. CoCs identified in Delhi MIBA were identical to those observed in literature (except Cd, Pb and Zn). The variability in leaching concentration of CoCs, observed from comparative assessment of results, spanned nearly 2 to 3 log₁₀ magnitudes for Cu, Cr, Pb, Sb and Zn while 1 to 2 log₁₀ magnitudes for Mo, Cl^-andSO₄^2-.

Phase changes during various treatment processes for incineration bottom ash from municipal solid wastes: A review in the application-environment nexus

Incineration technology has been widely employed, as an effective method to decrease the volume of waste disposal. In this review, relationships between municipal solid waste (MSW) inputs and residues after combustion-specifically, the incineration bottom ashes (IBA) of MSW, were discussed, with an emphasis on the geoenvironmental impacts of IBA associated with the complex crystal and amorphous phase reactions and changes during combustion and from their downstream treatments, whereas, their influences on IBA leaching behaviors are considered as another focus. This review summarizes the IBA leaching behaviors based on literature, showing the leaching variabilities induced by natural weathering and artificial intervention conditions, such as accelerated carbonation, washing treatment, stabilization/solidification, and thermal treatments, all of which can be attributed to changes of mineral phases and microstructure. It helps to understand IBA characteristics and transitions in application-environment nexus, and better reuse it for multiple applications.

Using water-based drilling cuttings from shale gas development to manufacture sintered bricks: a case study in the southern Sichuan Basin, China

Large amounts of water-based drilling cuttings (WDC) would be generated during the drilling of shale gas wells, which would occupy land resources and pose significant threat to soil and groundwater environment. The aim of this study was to assess the feasibility of using WDC as a replacement of natural clay to prepare sintered bricks. To determine the optimum preparation condition, the weight loss on ignition, bulk density, water absorption, and compressive strength of the samples were tested. Meanwhile, the environmental performance of the final products was evaluated and micro-analysis was conducted via X-ray diffraction and scanning electron microscopy. The results showed that using WDC to manufacture sintered bricks was technically feasible, but the physical mechanical performance would significantly decrease with the increase of the replacement ratio because of the presence of less silica and excessive calcium. The addition of waste glass and fly ash could promote the generation of molten glassy phase and form the crystal particle bonding structure, which would contribute to the physical-mechanical performance of WDC sintered bricks. Some mineral components in raw materials decomposed and formed minerals with better thermal stability during the sintering process. Under the optimum preparation conditions (mass ratio of WDC: waste glass: fly ash at 40:20:40, sintering temperature at 900 °C, and insulation time at 2 h), the physical-mechanical and environmental performance of WDC sintered bricks could meet the requirements of corresponding Chinese standards and ASTM standards. Thus, in this study, an effective solution to recycle WDC from shale gas development is provided.

Addressing environmental sustainability of plasma vitrification technology for stabilization of municipal solid waste incineration fly ash

Fly ash from municipal solid waste incineration is considered as a hazardous waste, which would raise great threats on environmental safety due to the inherent toxic heavy metals and organic pollutants. In this study, we applied the life cycle assessment to evaluate the thermal plasma vitrification process for stabilization of fly ash from municipal solid waste incineration. We established four scenarios: (i) plasma vitrification, including centralized and off-site plasma treatment, (ii) fuel-based vitrification, (iii) water-washing treatment followed by a rotary kiln, and (iv) conventional solidification and landfill. We found that the environmental impacts, especially toxicity to ecosystem quality and human health, could be significantly reduced by deploying plasma vitrification technology. We also found that centralized plasma vitrification facilities possessing larger treatment capabilities with clean electricity could further reduce the environmental impacts. In contrast, the water-washing treatment exhibited the highest environmental impacts due to the emissions of vaporized heavy metals. Based on the LCA and sensitivity analysis, we confirmed that the thermal plasma vitrification should be considered as an environmentally-friendly solution to sustainable treatment of fly ash from municipal solid waste incineration. Lastly, we provided several perspectives and prospects of plasma vitrification for realizing the sustainable materials management.

Hazardous waste characterization implications of updating the toxicity characteristic list

In the US, the toxicity characteristic leaching procedure (TCLP) determines if a waste is toxicity characteristic (TC) hazardous based on leached concentrations of specific chemicals. The TC limits were originally derived from drinking water standards (DWS) adjusted by a dilution attenuation factor of 100. The TC limits have not been updated along with DWS revisions. This research examines potential implications of updating the TC limits to account for new DWS thresholds and elements, as well as tap-water risk thresholds; this allows a further expanded evaluation of elements that might be regulated as drinking water standards in the future. Fossil fuel combustion residues, batteries, electronic wastes, municipal solid waste incineration (MSWI) ashes, and treated wood were examined with TCLP and the leached metal concentrations were compared to revised TC thresholds. The two wastes most affected by updated TC limits would be batteries and MSWI ashes. Thallium and antimony, which were not included on the original TC list, exceeded the TC thresholds for batteries and MSWI ash, respectively. Copper, a chemical used in current preserved wood formulations, did not cause currently marketed treated wood to be hazardous waste, but arsenic did for older wood products.

The Hazardous Status of High Density Sludge from Acid Mine Drainage Neutralization

Classification of waste is an essential part of waste management to limit potential environmental pollution; however, global systems vary. The objective was to understand the waste classification of high density sludge (HDS) from acid mine drainage (AMD) treatment, according to selected global systems. Three sludges from two limestone treatment plants, and three others from a limestone and lime treatment plant from the Mpumalanga coalfields of the Republic of South Africa (RSA) were evaluated. Systems for the RSA, Australia, Canada, China, and the United States Environmental Protection Agency (USEPA) were considered. The USEPA system rated all six sludges non-hazardous, Canadian and Chinese systems allocated a hazardous status to one sludge from the limestone treatment plants based on Ni solubility. The RSA system considered two of the sludges from limestone treatment plants to be higher risk materials than did the other countries. This was due mainly to the RSA system’s inclusion of Mn and use of appreciably lower minimum soluble levels for As, Cd, Pb, Hg, and Se. None’s use of lime resulted in higher soluble Mn. Minimum leachable concentration thresholds for Cd, Hg, Pb, As, and Se in the RSA system were below method detection limits for Toxicity Characteristic Leaching Procedure (TCLP) extracts, making the guidelines impractical, and revision is advised. Considering all the systems, the probability that the HDS from the coalfields of Mpumalanga, South Africa will be classified as hazardous waste increases if the material is only subjected to limestone treatment because of Ni solubility.

Leaching of metals from asphalt pavement incorporating municipal solid waste incineration fly ash

Rising municipal solid waste incineration (MSWI) makes it imperative to recycle the fly ash (FA). FA can be solidified by asphalt and then applied in the asphalt road. However, little information on the metal leaching and associated with risks from asphalt solidified forms for FA is available. In the present study, metal leaching characteristics and long-term leaching potential from the asphalt-based FA matrices was determined based on the national standard method and simulating the actual using of the solidified forms in highways, respectively. The immobilization effect of asphalt on MSWI FA is well. Leaching velocity was in the order of magnitude of 10^~10^-6 cm h^-1 during the entire leaching period. At the early age, leaching velocity of metals is high, especially Zn, Cd, and Ba. Cumulative leaching concentration of metals and leaching time has positive correlation. Only considering the leaching of simulating acid, leaching of metals in asphalt-based matrices is very slow, and the leaching toxicity of metals is lower than the Chinese National Standard.

Effect of water-washing on the co-removal of chlorine and heavy metals in air pollution control residue from MSW incineration

The present study systemically investigated the effect of a water-washing process on the removal of harmful chlorides, sulfates, and heavy metals in the air pollution control (APC) residue from municipal solid wastes incineration (MSWI), for sake of a better reuse and disposal of this kind of waste. In addition, the kinetic study was conducted to reveal the releasing mechanism of relevant element in the residue. The results show that, over 70wt.% of chlorides and nearly 25wt.% of sulfates in the residue could be removed by water washing. Based on an economical consideration, the optimal operation conditions for water washing of APC residue was at liquid/solid (L/S) ratio of 3mL:1g and extracting time of 5min. As expected, the concentrations of Co, Cr, Fe, Ni, V and Cu in the washing effluent increased with time during the washing process. However, the extracting regime differs among different heavy metals. The concentrations of Ba and Mn increased firstly but declined afterwards, and concentrations of Pb and Zn gradually declined while Cd and As kept constant with the increase of extracting time. It is worth mentioning that the bubbling of CO₂ into the washing effluent is promisingly effective for a further removal of Pb, Cu and Zn. Furthermore, kinetic study of the water washing process reveals that the extracting of heavy metals during water washing follows a second-order model.

Construction material properties of slag from the high temperature arc gasification of municipal solid waste

Slag from the high temperature arc gasification (HTAG) of municipal solid waste (MSW) was tested to evaluate its material properties with respect to use as a construction aggregate. These data were compared to previously compiled values for waste to energy bottom ash, the most commonly produced and beneficially used thermal treatment residue. The slag was tested using gradations representative of a base course and a course aggregate. Los Angeles (LA) abrasion testing demonstrated that the HTAG slag had a high resistance to fracture with a measured LA loss of 24%. Soundness testing indicated a low potential for reactivity and good weathering resistance with a mean soundness loss of 3.14%. The modified Proctor compaction testing found the slag to possess a maximum dry density (24.04kN/m(3)) greater than conventionally used aggregates and WTE BA. The LBR tests demonstrated a substantial bearing capacity (>200). Mineralogical analysis of the HTAG suggested the potential for self cementing character which supports the elevated LBR results. Preliminary material characterization of the HTAG slag establishes potential for beneficial use; larger and longer term studies focusing on the material's possibility for swelling and performance at the field scale level are needed.

Processing Clinker from Wastes: A New Raw Material Source for a Global Change

The final destination of the wastes generated in the manufacture of pulp paper is one of the growing concerns in this sector, since the European regulations are becoming stricter in regard to their landfill. So it is urgent to seek ways for their valorization through incorporation in other product as, although not usually dangerous, they are generated in substantial quantities.In this work the following residues were used: (i) calcareous sludge generated in the chemical recovery circuit of the production process; (ii) biological sludge generated in the secondary wastewater treatment step and (iii) fly ash from the combustion of biomass in cogeneration operation. The first stage of work was the waste characterization. Then different blends were prepared and submitted to distinct firing cycles to obtain Portland clinker, the main component of the ordinary cement. Using only wastes in adjusted proportions and under tuned firing cycle, it was possible to obtain ecological Portland clinker. Moreover, it was possible to reduce, by about 50 °C, the clinkering temperature in relation to the value used in cement industry, which results in economical and procedural benefits.

Preparation of clinker from paper pulp industry wastes

The production of paper pulp by the Kraft method generates considerable amounts of wastes. Namely, lime mud generated in the recovery circuit of chemical reagents, biological sludge from the wastewater treatment of wood digestion process and fly ash collected in the fluidized bed combustor used to generate electricity from biomass burning. The final destination of such wastes is an important concern, since environmental regulations are becoming stricter regarding their landfill. Driven by this fact, industries are looking for more sustainable solutions, such as the recycling in distinct products. This work tested these wastes as secondary raw materials to produce clinker/cement that was then experienced in mortar formulations. The first step involved the residues detailed characterization and a generated amounts survey. Then, specific but simple steps were suggested, aiming to facilitate transport and manipulation. Distinct blends were prepared and fired in order to get belitic and Portland clinkers. The Portland clinkers were processed at lower temperatures than the normally used in the industry due to the presence of mineralizing impurities in some wastes. Belite-based cements were used to produce mortars that developed satisfactory mechanical strength and did not reveal signs of deterioration or durability weaknesses.

Variation and correlation of content and leachability of hazardous metals in MSW molten slag

To increase the amount of accessible municipal solid waste molten slag (MSWS) for its use in aggregates such as sand, MSWS must be deemed environmentally safe. Municipal solid waste (MSW) is a heterogeneous waste source used in MSWS and varies in chemical composition. Due to its nature, there is great concern about hazardous metal contamination among users of MSWS. In this study, MSWS samples were obtained weekly for 1 year from a typical incineration ash melting facility for municipal solid waste in Japan. Variation in heavy metal contents and the leachability of MSWS were investigated using two content analysis methods and two leaching tests, respectively. There is a weak correlation between metal content and concentration, and the leachability of metals in slag could not be reduced by decreasing its metal content. No measured values of hazardous metal concentration and metal content exceed the regulation levels stipulated in Japanese Industrial Standards A5031 and A5032, respectively, thereby demonstrating that the slag can be safely utilized as road and concrete aggregates. However, metal concentrations varied widely and differed by greater than 1 order of magnitude and Pb concentrations of several MSWS samples approach the regulation level. Therefore, frequent monitoring of lead leachability of MSWS and storing MSWS for several weeks to obtain a high quality that is more homogeneous in chemical composition are demanded. This study provides fundamental information for controlling the quality of MSWS and the contributing factors for achieving a safe slag recycling system.

Environmental impact assessment of a WtE plant after structural upgrade measures

The study focuses on analysing the evolution of environmental impacts caused by a medium-large Italian WtE plant before and after revamping and maintenance operations, with the aim of providing an evaluation of how much these structural upgrade measures may affect the total environmental performance. LCA methodology was applied for the modelling and comparison of six WtE scenarios, each describing the main structural upgrades carried out in the plant over the years 1996-2011. The comparison was conducted by adopting 1ton of MSW as the functional unit, and the net contribution from energy recovery to power generation was distinguished by defining consistent national grid electricity mixes for every year considered. The Ecoindicator99 2.09 impact assessment method was used to evaluate the contribution to midpoint and endpoint categories (e.g. carcinogens, respiratory inorganics and organics, climate change, damage to human health). Lastly, the "Pedigree quality matrix" was applied to verify the reliability and robustness of the model created. As expected, the results showed better environmental scores after both the implementation of new procedures and the integration of operations. However, while a net reduction of air emissions seems to be achievable through dedicated flue gas treatment technologies, outcomes underscored potentials for improving the management of bottom ash through the adoption of alternative options aimed to use that solid residue mainly as filler, and to decrease risks from its current disposal in landfill. If the same effort that is put into flue gas treatment were devoted to energy recovery, the targets for the WtE plant could be easily met, achieving a higher sustainability. This aspect is even more complex: national policies for implementing greener and renewable energy sources would result in a lower impact of the national energy mix and, hence, in a lower net avoided burden from energy recovery. The study confirmed the expected improvements, indicating quantitatively the lower environmental impact resulting from structural upgrade operations in a WtE plant. Furthermore, the work highlights the importance of considering the evolution of the national energy mix in LCA studies, especially during the present years of transition from fossil fuels to renewable sources.

Inertization of heavy metals present in galvanic sludge by DC thermal plasma

Galvanic sludge results from the treatment of effluents generated by the industrial metal surface treatment of industrial material, which consists in the deposition of a metal on a surface or a metal surface attack, for example, electrodeposition of conductors (metals) and non conductive, phosphate, anodizing, oxidation and/or printed circuit. The treatment proposed here is exposure of the galvanic sludge to the high temperatures provided by thermal plasma, a process which aims to vitrify the galvanic sludge and render metals (iron, zinc, and chromium) inert. Two different plasma reactors were assembled: with a DC transferred arc plasma torch and with a DC nontransferred arc plasma torch. In this way it was possible to verify which reactor was more efficient in the inertization of the metals and also to investigate whether the addition of quartzite sand to the sludge influences the vitrification of the material. Quantification of water content and density of the galvanic raw sludge were performed, as well as analyzes of total organic carbon (TOC) and identify the elements that make up the raw sludge through spectroscopy X-ray fluorescence (XRF). The chemical composition and the form of the pyrolyzed and vitrified sludge were analyzed by scanning electron microscopy with energy-dispersive X-ray spectrometer (SEM-EDS) analysis, which it is a analysis that shows the chemical of the sample surface. The inertization of the sludge was verified in leaching tests, where the leachate was analyzed by flame atomic absorption spectroscopy (FAAS). The results of water content and density were 64.35% and 2.994 g.cm(-3), respectively. The TOC analysis determined 1.73% of C in the sample of galvanic raw sludge, and XRF analysis determined the most stable elements in the sample, and showed the highest peaks (higher stability) were Fe, Zn, and Cr. The efficiency of the sludge inertization was 100% for chromium, 99% for zinc, and 100% for iron. The results also showed that the most efficient reactor was that with the DC transferred arc plasma torch and quartzite sand positively influenced by the vitrification during the pyrolysis of the galvanic sludge.

Mercury leaching characteristics of waste treatment residues generated from various sources in Korea

In this study, mercury (Hg) leaching characteristics of the waste treatment residues (fly ash, bottom ash, sludge, and phosphor powder) generated from various sources (municipal, industrial, medical waste incinerators, sewage sludge incinerator, oil refinery, coal-fired power plant, steel manufacturing plant, fluorescent lamp recycler, and cement kiln) in Korea were investigated. First, both Hg content analysis and toxicity characteristic leaching procedure (TCLP) testing was conducted for 31 collected residue samples. The Hg content analysis showed that fly ash from waste incinerators contained more Hg than the other residue samples. However, the TCLP values of fly ash samples with similar Hg content varied widely based on the residue type. Fly ash samples with low and high Hg leaching ratios (RL) were further analyzed to identify the major factors that influence the Hg leaching potential. Buffering capacity of the low-RL fly ash was higher than that of the high-RL fly ash. The Hg speciation results suggest that the low-RL fly ashes consisted primarily of low-solubility Hg compounds (Hg2Cl2, Hg(0) or HgS), whereas the high-RL fly ashes contain more than 20% high-solubility Hg compounds (HgCl2 or HgSO4).

Enrichment and solubility of trace metals associated with magnetic extracts in industrially derived contaminated soils

Magnetic fractions (MFs) in industrially derived contaminated soils were extracted with a magnetic separation procedure. Total, soluble, and bioaccessible Cr, Cu, Pb and Zn in the MFs and non-magnetic fractions (NMFs) were analyzed using aqua regia and extraction tests, such as deionized water, toxicity characteristic leaching procedure (TCLP), and gastric juice simulation (GJST) test. Compared with the non-magnetic fractions, soil MFs were enriched with Fe, Mn, Pb, Cd, Cr, Cu, and Ni. Extraction tests indicated that soil MFs contained higher water, TCLP, and GJST-extractable Cr, Cu, Pb, and Zn concentrations than the soil NMFs. The TCLP-extractable Pb concentration in the MFs exceeded the USEPA hazardous waste criteria, suggesting that soil MFs have a potentially environmental pollution risk. Solubility of trace metals was variable in the different extraction tests, which has the order of GJST > TCLP > water. TCLP test showed Cu and Zn were more mobile than Cr and Pb while bioaccessibility of trace metal defined by GJST test showed the order of Cu ≈ Cr ≈ Zn > Pb. These findings suggested that the MFs in the industrially derived contaminated soils had higher possibility of polluting water bodies, and careful environmental impact assessment was necessary.

Utilization of municipal sewage sludge as additives for the production of eco-cement

The effects of using dried sewage sludge as additive on cement property in the process of clinker burning were investigated in this paper. The eco-cement samples were prepared by adding 0.50-15.0% of dried sewage sludge to unit raw meal, and then the mixtures were burned at 1450 °C for 2 h. The results indicated that the major components in the eco-cement clinkers were similar to those in ordinary Portland cement. Although the C(2)S phase formation increased with the increase of sewage sludge content, it was also found that the microstructure of the mixture containing 15.0% sewage sludge in raw meal was significantly different and that a larger amount of pores were distributed in the clinker. Moreover, all the eco-cement pastes had a longer initial setting time and final setting time than those of plain cement paste, which increased as the sewage sludge content in the raw meal increased. All the eco-cement pastes had lower early flexural strengths, which increased as the sewage sludge content increased, while the compressive strengths decreased slightly. However, this had no significant effect on all the strengths at later stages. Furthermore, the leaching concentrations of all the types of eco-cement clinkers met the standard of Chinese current regulatory thresholds.

Size-dependent enrichment of waste slag aggregate fragments abraded from asphalt concrete

Authors consider the environmental prospects of using melted waste slag as the aggregate for asphalt pavement. In particular, the enrichment of slag-derived fragments in fine abrasion dust particles originated from slag asphalt concrete and its size dependency were concerned. A series of surface abrasion tests for asphalt concrete specimens, containing only natural aggregates as reference or 30 wt% of substituted slag aggregates, were performed. Although two of three slag-asphalt concretes generated 1.5-3.0 times larger amount of abrasion dust than the reference asphalt concrete did, it could not be explained only by abrasion resistance of slag. The enrichment of slag-derived fragments in abrasion dust, estimated on the basis of the peak intensity of quartz and heavy metal concentrations, had size dependency for all slag-asphalt concretes. Slag-derived fragments were enriched in abrasion dust particles with diameters of 150-1000 μm. Enrichment factors were 1.4-2.1. In contrast, there was no enrichment in abrasion dust particles with diameter less than 75 μm. This suggests that prior airborne-size fragmentation of substituted slag aggregates does not need to be considered for tested slag aggregates when environmental risks of abrasion dust of slag-asphalt pavement are assessed.

Leaching behaviour of bottom ash from RDF high-temperature gasification plants

This study investigated the physical properties, the chemical composition and the leaching behaviour of two bottom ash (BA) samples from two different refuse derived fuel high-temperature gasification plants, as a function of particle size. The X-ray diffraction patterns showed that the materials contained large amounts of glass. This aspect was also confirmed by the results of availability and ANC leaching tests. Chemical composition indicated that Fe, Mn, Cu and Cr were the most abundant metals, with a slight enrichment in the finest fractions. Suitability of samples for inert waste landfilling and reuse was evaluated through the leaching test EN 12457-2. In one sample the concentration of all metals was below the limit set by law, while limits were exceeded for Cu, Cr and Ni in the other sample, where the finest fraction showed to give the main contribution to leaching of Cu and Ni. Preliminary results of physical and geotechnical characterisation indicated the suitability of vitrified BA for reuse in the field of civil engineering. The possible application of a size separation pre-treatment in order to improve the chemical characteristics of the materials was also discussed.

Effect of annealing treatment on the crystallisation and leaching of dumped base metal smelter slags

Leaching tests of base metals contained in two smelter slags were undertaken in ammonia and nitric acid solutions aiming to recover Co, Cu and Zn. Leaching tests were conducted at 25 and 60°C at pH=0 and 3 in HNO(3) and pH=12 in NH(4)OH media. XRD analysis revealed that the dumped slags were amorphous. Annealing these slags at 1180°C produced crystalline phases comprising diopside, magnetite and fayalite. SEM and EDS analysis revealed that Cu and Pb compounds have concentrated in the magnetite phase, whereas another phase rich in Zn and Cu was located in the diopside matrix. ICP-OES analysis of the pregnant leaching solutions (PLS) showed that 30-60% of Co, Cu and Zn were released from the amorphous slags treated in HNO(3) at pH=0, and lesser in ammonia. However, the contamination by Fe and Pb was higher at pH=0. The contamination of the PLS obtained by leaching of the crystallised slags remained low. The low Fe and Pb contamination was attributed in this case to the chemical stability of the crystalline phases formed upon annealing treatment. The higher solubilisation of metals contained in amorphous slags was attributed to the collapse of silicate structures during nitric acid leaching at pH∼0.

Water washing effects on metals emission reduction during municipal solid waste incinerator (MSWI) fly ash melting process

This study investigated that water washing effects on the metals emission reduction in melting of municipal solid waste incinerator (MSWI) fly ash. Experimental conditions were conducted at liquid-to-solid (L/S) ratio 10, 20, and 100 for water-washing process and its subsequent melting treatment at 1450 degrees C for 2h. The simple water-washing process as a pre-treatment for MSWI fly ash can remove most of the chlorides, leachable salts, and amphoteric heavy metals from the MSWI fly ash, resulting in the washed ash having lowered chlorine content. MSWI fly ashes washed by L/S ratio 10 and above that were melted at 1450 degrees C produced slag containing relatively high vitrificaton ratio of Cu and Pb. Besides, the vitrification ratios of Na, K, Ca, and Mg in washed MSWI fly ash were also higher than that of MSWI fly ash. The results indicated that washed MSWI fly ash can reduce the emission of metallic chlorides during its subsequent melting treatment.

Distribution of heavy metals from iron bath-melting separation process applied to municipal solid waste incineration fly ash

Fly ash generated from municipal solid waste (MSW) incineration is frequently classified as hazardous material and requires special disposal. The management of the large amount of fly ash has caused increasing problems in China. This work describes a novel approach for melting MSW incineration fly ash, and the distribution of heavy metals was characterized during the iron bath-melting separation process. Four hundred grams of pelletized fly ash was fed into the furnace in molten iron bath atmosphere. After the melting separation process, the distribution of heavy metals in samples and the leaching characteristics of the slag were investigated. The results indicated that iron bath-melting promoted the transfer of Cr, Mn and Cu from the slag phase to the iron phase, which also improved Zn and Pb volatilization. The leaching concentrations, determined by the Chinese Standard Method (rollover leaching procedure) of the target metals of the slag from leaching tests were lower than the Chinese regulatory thresholds. Therefore, this method was proposed as an environmentally friendly technology to achieve a satisfactory solution for MSW incineration fly ash management.

Recycling municipal incinerator fly- and scrubber-ash into fused slag for the substantial replacement of cement in cement-mortars

Fly- and scrubber-ash (weight ratio of approximately 1:3) from municipal solid waste incinerators (MSWI) are a major land-fill disposal problem due to their leaching of heavy metals. We uniformly mixed both types of ash with optimal amounts of waste glass frit, which was then melted into a glassy slag. The glassy slag was then pulverized to a particle size smaller than 38microm for use as a cement substitute (20-40% of total cement) and blended with sand and cement to produce slag-blended cement-mortar (SCM) specimens. The toxicity characteristics of the leaching procedure tests on the pulverized slag samples revealed that the amount of leached heavy metals was far below regulatory thresholds. The compressive strength of the 28-day cured SCM specimens was comparable to that of ordinary Portland cement mortars, while the compressive strength of specimens cured for 60 or 90 days were 3-11% greater. The observed enhanced strength is achieved by Pozzolanic reaction. Preliminary evaluation shows that the combination of MSWI fly- and scrubber-ash with waste glass yields a cost effective and environmentally friendly cement replacement in cement-mortars.

Feasibility study on solidification of municipal solid waste incinerator fly ash with circulating fluidized bed combustion coal fly ash

The objective of this study was to assess the feasibility of solidification of municipal solid waste incinerator (MSWI) fly ash with circulation fluidized bed combustion (CFBC) fly ash, which is unsuitable as a cement replacement due to its high amounts of carbon, lime and anhydrite. The solidification process was conducted on samples prepared from MSWI fly ash, binders (cement clinkers and CFBC fly ash were mixed at two replacement ratios) and water (water/solid weight ratio = 0.4), among which the MSWI fly ash replaced each binder at the ratio of 0, 20, 40, 60 and 80% by dry weight. The samples were subjected to compressive strength tests and Toxicity Characteristic Leaching Procedure and the results showed that all solidified MSWI fly ash can meet the landfill standard imposed by US EPA after 28 days of curing. Micro-analysis (X-ray diffraction, scanning electron microscopy and Fourier transform infrared spectrophotometry) revealed that the main hydrate products were C-S-H gel and ettringite, which have a positive effect on heavy metals retention. Therefore, this method provides a possibility to achieve a cheap and effective solution for MSWI fly ash management and use for CFBC fly ash.

Use of vitrified MSWI bottom ashes for concrete production

Bottom ashes from a north Italian municipal solid waste incinerator (MSWI) were vitrified at 1450 degrees C without adding any vitrifying agent, then ground and sieved to different granulometry (ranging from 50 microm to 20mm), and used as filler, sand, or aggregate for concrete. Samples were characterized via slump tests (UNI 9418), alkali-silica reactivity (UNI 8520/22 and ASTM C 298), and compression strength tests (UNI 6132, 6132/72, 6686/72), and compared to reference samples obtained without vitrified bottom ashes (VBA). Our results show that vitrified bottom ashes are unsuitable as a sand substitute; however, concrete containing up to 20 wt.% of VBA filler used as a substitute for cement and up to 75 vol.% of VBA as a substitute for natural aggregate retains the same mechanical properties as reference samples. Alkali-silica or other detrimental reactions were not observed in VBA-containing concrete samples after a period of two years. The results of this work demonstrate that vitrified bottom ashes from MSWI can be used instead of natural aggregates in mortar and concrete production.

High temperature behavior of electrostatic precipitator ash from municipal solid waste combustors

Municipal solid waste (MSW) flue gas residues require further treatment prior to disposal or reuse, and vitrification is one of the main solidification-stabilization processes. This paper investigates the high temperature behavior of MSW flue gas residues, performed in laboratory experiments up to 1400 degrees C, and coupled with thermogravimetric analyses, X-ray diffraction, chemical and electron microprobe analyses. Melting temperatures of electrostatic precipitator (ESP) ash are in the range of 1202-1272 degrees C, whereas semi-dry scrubber residues melt between 1900 and 2300 degrees C. We show that the mean liquidus temperature of flue gas residues can be simply evaluated from their CaO content, by using the CaOSiO2Al2O3 ternary diagram. For ESP ash, the liquidus phase is a Zn-rich aluminous spinel, followed by anorthite at 1225 degrees C, and melilite at 1190 degrees C. The total mass loss reaches 18 wt.% at 1300 degrees C. Moreover, 90% of evaporation takes place below 1000 degrees C, linked to evaporation of C, Cl, S, Na, K, and of the toxic metals Hg, Cd, Pb, Cu. Due to the high partial pressure of chlorine during heating, chloride is the most probable form of evaporation for Cd, Pb, and Cu. However, most of Zn, Cr, Ni, Sb and Sn remain in the vitrified product.