Porosity is possibly an important parameter with respect to leaching of constituents from cement ... more Porosity is possibly an important parameter with respect to leaching of constituents from cement monoliths. During its lifetime, the pore structure of cementitious matrices changes due to carbonation and leaching. This paper discusses the effects of both accelerated carbonation and continuous leaching on the porosity, and, conversely, how porosity affects leaching properties. Two sample types are investigated: a mortar with MSWI-bottom ash substituting the sand fraction and a cement paste with 30 wt% of the cement substituted by a flue gas cleaning residue. The samples have been intensively carbonated in a 20% CO 2 atmosphere for up to 60 days and were subsequently leached. The porosity was investigated by mercury intrusion porosimetry.
Mortars with varying water-to-cement (w/c) ratio were spiked with heavy metals. After hardening, ... more Mortars with varying water-to-cement (w/c) ratio were spiked with heavy metals. After hardening, some samples were carbonated in a CO2 chamber, others were carbonated using supercritical CO2 (SCC). Porosity and carbonation depth of treated and untreated samples were compared. Leaching was tested using the diffusion (NEN 7345) and extraction test (based on DIN 38414-S4). The results show that carbonation decreases
A cement-stabilized MSWI fly ash w as leached according to the diffusion test NEN 7345. The influ... more A cement-stabilized MSWI fly ash w as leached according to the diffusion test NEN 7345. The influence of carbonation during leaching was tested by bubbling N 2 , air or CO 2 through the leachant. The original test, where no gas is bubbled, was used as a reference. The periodically renewed leachant was analysed for its ionic concentrations. Porosity measurements, XRD and scanning electron microscopy (SEM) analysis were performed.
An overview is presented on possible mechanisms that control the leaching behaviour of the oxyani... more An overview is presented on possible mechanisms that control the leaching behaviour of the oxyanion forming elements As, Cr, Mo, Sb, Se, V and W in cementituous systems and alkaline solid wastes, such as municipal solid waste incinerator bottom ash, fly ash and air pollution control residues, coal fly ash and metallurgical slags. Although the leachability of these elements generally depends on their redox state, speciation measurements are not common. Therefore, experimental observations available in the literature are combined with a summary of the thermal behaviour of these elements to assess possible redox states in freshly produced alkaline wastes, given their origin at high temperature. Possible redox reactions occurring at room temperature, on the other hand, are reviewed because these may alter the initial redox state in alkaline wastes and their leachates. In many cases, precipitation of oxyanions as a pure metalate cannot provide a satisfactory explanation for their leaching behaviour. It is therefore highly likely that adsorption and solid solution formation with common minerals in alkaline waste and cement reduce the leachate concentration of oxyanions below pure-phase solubility.
Development of treatment methods to reduce Sb leaching from municipal solid waste incinerator (MS... more Development of treatment methods to reduce Sb leaching from municipal solid waste incinerator (MSWI) bottom ash, such as accelerated carbonation, is being complicated by insufficient understanding of Sb geochemistry. The leaching of antimonate (Sb(V)) and antimonite (Sb(III)) in MSWI bottom was studied as a function of pH and degree of carbonation. While total (Sb(V) + Sb(III)) leaching was lowest (1.2 mg kg À1 ) at the natural pH (i.e. 10.6) of uncarbonated bottom ash, HPLC-ICP-MS analysis showed that acidification and carbonation increased Sb(V) leaching, but decreased Sb(III) leaching, probably because SbðIIIÞðOHÞ À 4 became less stable. PHREEQC geochemical modelling suggested that Sb(V) concentrations approached equilibrium with the romeites, i.e. calcium antimonates, Ca 1.13 Sb 2 (OH) 0.26 Á0.74H 2 O at pH = 10.6 and Ca[Sb(OH) 6 ] 2 at pH = 8. It is hypothesised that not interaction with ettringite but dissolution of romeite controls antimonate leaching in the pH range 8-11 in MSWI bottom ash, because while Ca is preferentially leached from romeite, the mineral structures containing more Ca at higher pH are less soluble. A model was proposed where acidification and carbonation both lead to lower Ca 2+ and/or hydroxyl concentration, which removes Ca 2+ and hydroxyls from the romeite structure and leads to comparably higher Sb(V) concentration in equilibrium with romeite. Sb solubility depends on pH and Ca 2+ availability in this model, which has implications for bottom ash valorisation and risk assessment.
Three types of wastes, metallurgical slag from Pb production (SLG), the sand-sized (0.1-2 mm) fra... more Three types of wastes, metallurgical slag from Pb production (SLG), the sand-sized (0.1-2 mm) fraction of MSWI bottom ash from a grate furnace (SF), and boiler and fly ash from a fluidised bed incinerator (BFA), were characterized and used to replace the fine aggregate during preparation of cement mortar. The chemical and mineralogical behaviour of these wastes along with the reactivities of the wastes with lime and the hydration behaviour of ordinary Portland cement paste with and without these wastes added were evaluated by various chemical and instrumental techniques. The compressive strengths of the cement mortars containing waste as a partial substitution of fine aggregates were also assessed. Finally, leaching studies of the wastes and waste containing cement mortars were conducted. SLG addition does not show any adverse affect during the hydration of cement, or on the compressive strengths behaviours of mortars. Formation of expansive products like ettringite, aluminium hydroxide and H 2 gas due to the reaction of some constituents of BFA and SF with alkali creates some cracks in the paste as well as in the cement mortars, which lower the compressive strength of the cement mortars. However, utilization of all materials in cement-based application significantly improves the leaching behaviour of the majority of the toxic elements compared to the waste as such.
Leaching of heavy metals from MSWI bottom ash exceeds some of the Flemish limit values for recycl... more Leaching of heavy metals from MSWI bottom ash exceeds some of the Flemish limit values for recycling the material as granular construction application. In particular, leaching of Cu, Zn and Pb often exceeds the limit value, with Cu being the most critical. In order to recycle bottom ash, treatment is therefore required. The bottom ash studied was divided on-site into four fractions using a large-scale wet sieving installation: a sludge fraction (Ø 0-0.1 mm), a sand fraction (Ø 0.1-2 mm) and two gravel fractions (Ø 2-6 and 6-50 mm). The two gravel fractions complied with the limit values after 3 months of natural ageing. The sand and sludge fraction did not reach the limit value for Cu. Four weeks of accelerated carbonation resulted in an important decrease of Cu leaching from these two fractions, although the limit value is still exceeded. In view of applying carbonation as one of the treatment methods in an integrated industrial application, two tests were additionally performed. The use of stack gas as carbonating medium was verified by setting up an accelerated carbonation experiment at the incineration plant. Also, the depth of carbonation was measured in a 10 cm thick sample of the sand fraction after different periods of treatment. After 3 months of natural ageing only the upper 4 cm underwent a significant carbonation, while after one week of accelerated carbonation the total sample was carbonated. A model was developed to predict these experimental results.
A number of indicators are evaluated and used to measure the environmental performance of the ind... more A number of indicators are evaluated and used to measure the environmental performance of the industry and energy sectors in Flanders and their progress towards sustainability: eco-efficiency, existence of a certified Environmental Management System, environmental expenditures, production of sustainable energy, environmental damage by electricity production, cost of environmental levies and number of registered complaints. The indicators are evaluated in relation
The leaching of heavy metals, such as copper, from municipal solid waste incinerator (MSWI) botto... more The leaching of heavy metals, such as copper, from municipal solid waste incinerator (MSWI) bottom ash is of concern in many countries and may inhibit the beneficial reuse of this secondary material. Previous studies have focused on the role of dissolved organic carbon (DOC) on the leaching of copper. Recently, a study of the Energy Research Centre of The Netherlands (ECN) showed fulvic acid-type components to exist in the MSWI bottom ash leachates and to be likely responsible for the generally observed enhanced copper leaching. These findings were verified for a MSWI bottom ash (slashed circle 0.1-2 mm) fraction from an incinerator in Flanders. The filtered leachates were subjected to the IHSS fractionation procedure to identify and quantify the fractions of humic acid (HA), fulvic acid (FA) and hydrophilic organic carbon (Hi). The possible complexation of fulvic acid with other heavy metals (e.g., lead) was also investigated. The identified role of fulvic acids in the leaching of copper and other heavy metals can be used in the development of techniques to improve the environmental quality of MSWI bottom ash. Thermal treatment and extraction with a 0.2 M ammonium-citrate solution were optimized to reduce the leaching of copper and other heavy metals. The effect of these techniques on the different fractions of organic matter (HA, FA, Hi) was studied. However, due to the obvious drawbacks of the two techniques, research is focused on finding other (new) techniques to treat MSWI bottom ash. In view of this, particle size-based separation was performed to evaluate its effect on heavy metal leaching and on HA, FA and Hi in MSWI bottom ash leachates.
An integrated installation for treatment of municipal solid waste and comparable waste from indus... more An integrated installation for treatment of municipal solid waste and comparable waste from industrial origin is described. It consists of three grate furnace lines with flue gas treatment by half-wet scrubbing followed by wet scrubbing, and an installation for wet treatment of bottom ash.
The contribution of the emission of PCBs by a municipal waste incinerator in Wilrijk, a relativel... more The contribution of the emission of PCBs by a municipal waste incinerator in Wilrijk, a relatively industrialized district in the largest city of Flanders, to the total emission to air and to the total human intake was estimated. Therefore it was compared to the emission of PCBs by evaporation from PCB containing applications (transformers, capacitors, paint, ink, etc.) and to the intake of PCBs with food. As there was a lack of PCB data from the incinerator, the PCB emission concentration was estimated using three different approaches. A PCB measurement of the incinerator emission, performed later on, fell within the predicted range of 0.0004-0.005 ng TEQ/Nm 3 .
Municipal solid waste incinerator (MSWI) bottom ash often cannot be recycled as construction mate... more Municipal solid waste incinerator (MSWI) bottom ash often cannot be recycled as construction material in Flanders, because leaching of Cu exceeds the limit value of 0.5 mg/kg. Leaching of other components such as Mo and Sb is critical as well, but limit values for these elements are to date only informal. A treatment technique was investigated to lower pollutant leaching: extraction with solutions of organic complexants to remove Cu. Six different solutions were used, of which washing with citric acid and ammonium citrate decreases Cu leaching to below the limit value. Extraction was then performed with different concentrations of ammonium citrate. Subsequent washing of the extracted material with distilled water appears to be vital to remove all residual ammonium citrate. Extraction with a 0.2 M solution of ammonium citrate followed by three washing steps decreases metal leaching to below the limit values.
The 0.1-2 mm fraction of a MSWI-bottom ash cannot be used as granular construction material becau... more The 0.1-2 mm fraction of a MSWI-bottom ash cannot be used as granular construction material because leaching of Cu exceeds Flemish limit values. In addition, leaching of Ba, Mo and Sb exceeds informal limit values. Leaching characteristics thus need to be improved. Carbonation was the chosen treatment method and this was performed by placing samples in a CO 2 chamber. The CO 2 percentage and the temperature of the chamber atmosphere, as well as the initial humidity of the samples, were varied to optimize carbonation parameters. Metal leaching was tested with the EN 12457 extraction test. Carbonation decreased Cu leaching from 3.3 to 1.0 mg/kg, but not yet to below the official limit value of 0.5 mg/kg. Leaching of Mo and Sb remained fairly constant or even increased after carbonation, but their limit values are only informal. Ba leaching decreased to below the informal limit value. Carbonation also caused Cr leaching to increase, in some cases to above the official limit value. Of the tested parameters, a CO 2 percentage of 10% and a carbonation temperature of 50°C in the atmosphere, together with ash humidity between 13% and 25% appeared to give the best leaching results. The main carbonation reactions took place within the first 24 h.
Geochemical modelling of leaching of oxyanion forming elements such as arsenic (As) and selenium ... more Geochemical modelling of leaching of oxyanion forming elements such as arsenic (As) and selenium (Se) is frequently not successful. A consistent thermodynamic dataset of As and Se was therefore composed, not only including precipitation, but also adsorption and solid solution, and was applied to the pH-dependent leaching behaviour of As and Se in an alkaline residue with a pH 11.1 from the lime treatment of sulphuric acid wastewaters from the production of non-ferrous metals. The As and Se content ranged up to 6.7 wt% and 0.29 wt%, respectively and speciation analysis showed that 96.3% of As occured as arsenate whereas Se speciation comprised 79% selenate and 21.0% selenite. XRD and SEM/EDX analysis showed that arsenate occurred as rauenthalite (Ca 3 (AsO 4 ) 2 ·10H 2 O), associated with gypsum, the most important mineral. Arsenate and arsenite concentrations were only slightly below equilibrium with rauenthalite and calciumarsenite (CaHAsO 3 ), respectively and consideration of adsorption and solid solution only marginally improved model predictions. Selenate (Se VI ) and selenite (Se IV ), on the other hand, were far from equilibrium with their corresponding calcium metalate. The application of solid solutions and adsorption of Se VI and Se IV oxyanions with gypsum, calcite and ettringite significantly improved model predictions but missing thermodynamic data and especially the lack of a comprehensive model for solid solution and surface exchange with calcite and ettringite still hampered efficient modelling.
In Flanders, the northern part of Belgium, about 31% of the produced amount of MSWI bottom ash is... more In Flanders, the northern part of Belgium, about 31% of the produced amount of MSWI bottom ash is recycled as secondary raw material. In view of recycling a higher percentage of bottom ash, a particular bottom ash fraction (Ø 0.1-2 mm) was studied. As the leaching of this bottom ash fraction exceeds some of the Flemish limit values for heavy metals (with Cu being the most critical), treatment is required.
The recycling potential of municipal solid waste incinerator (MSWI) bottom ash may be limited by ... more The recycling potential of municipal solid waste incinerator (MSWI) bottom ash may be limited by the leaching of antimony (Sb). Therefore, treatment methodologies need to be developed. The pH-dependent leaching behaviour of this oxyanion-forming element in fresh and weathered bottom ash is, however, not understood. Sb leaching was investigated in a wide range of both pH and extent of carbonation. Sb came close to equilibrium with calcium antimonate (Ca[Sb(OH) 6 ] 2 ) at acid and neutral pH. Therefore, adsorption experiments with synthetic calcite (CaCO 3 ), ettringite (Ca 6 Al 2 (SO 4 ) 3 (OH) 12 ·26H 2 O), gypsum (CaSO 4 ·2H 2 O), and portlandite (Ca(OH) 2 ) and adsorption modelling to hydrous ferric oxides (HFO) and amorphous aluminium minerals (AAM) were conducted to investigate which minerals decrease Sb leaching below equilibrium with calcium antimonate. At pH > 12, calcium antimonate comes into solution due to portlandite formation, but the subsequent increase in Sb leaching is reduced due to strong interaction of Sb with portlandite and ettringite. Ettringite appears to be an important host mineral for Sb at the natural pH of mildly weathered bottom ash (11.8) because a minimum in leaching is observed. When pH is decreased below 10.5, ettringite dissolves and Sb comes into solution, approaching equilibrium with calcium antimonate near pH 9. Gypsum showed no affinity for Sb. The interaction of calcite with Sb was not clear. Adsorption modelling suggested that HFO, rather than AAM, control Sb leaching when pH < 9. During carbonation, Sb leaching first increased, most likely due to dissolution of ettringite. Then, Sb leaching decreased, since the pH became low enough to allow sorption by HFO.
Zinc ashes, muffle furnace fragments and lead slags from non-ferrous industries were applied to p... more Zinc ashes, muffle furnace fragments and lead slags from non-ferrous industries were applied to pave roads in the North of Belgium. From an inventory it appeared that there are at least 490 km of such roads. In our survey the materials on these roads were characterised. The total metal concentration, the availability and the leaching as a function of time were determined. It appeared that these materials contain high concentrations of heavy metals, some of which are readily available. The high leaching of some metals makes them as such unsuitable as secondary construction material. Methods for the application of these materials for road construction were examined where the materials replaced part of the sand and gravel fraction in lean concrete and in bituminous mixtures, or where they replaced the sand in sand-cement mixtures, all these to be used for road foundations, cycle tracks, etc. When lead slags were applied in lean concrete, a material was obtained complying with the standards for secondary construction materials and with sufficient compressive strength for road foundations. When zinc ashes or muffle fragments were used to replace sand in sand-cement mixtures, again a suitable construction material was obtained. The other combinations tried out were rather unsuccessful, because of high metal leaching and/or poor compressive strength.
Porosity is possibly an important parameter with respect to leaching of constituents from cement ... more Porosity is possibly an important parameter with respect to leaching of constituents from cement monoliths. During its lifetime, the pore structure of cementitious matrices changes due to carbonation and leaching. This paper discusses the effects of both accelerated carbonation and continuous leaching on the porosity, and, conversely, how porosity affects leaching properties. Two sample types are investigated: a mortar with MSWI-bottom ash substituting the sand fraction and a cement paste with 30 wt% of the cement substituted by a flue gas cleaning residue. The samples have been intensively carbonated in a 20% CO 2 atmosphere for up to 60 days and were subsequently leached. The porosity was investigated by mercury intrusion porosimetry.
Mortars with varying water-to-cement (w/c) ratio were spiked with heavy metals. After hardening, ... more Mortars with varying water-to-cement (w/c) ratio were spiked with heavy metals. After hardening, some samples were carbonated in a CO2 chamber, others were carbonated using supercritical CO2 (SCC). Porosity and carbonation depth of treated and untreated samples were compared. Leaching was tested using the diffusion (NEN 7345) and extraction test (based on DIN 38414-S4). The results show that carbonation decreases
A cement-stabilized MSWI fly ash w as leached according to the diffusion test NEN 7345. The influ... more A cement-stabilized MSWI fly ash w as leached according to the diffusion test NEN 7345. The influence of carbonation during leaching was tested by bubbling N 2 , air or CO 2 through the leachant. The original test, where no gas is bubbled, was used as a reference. The periodically renewed leachant was analysed for its ionic concentrations. Porosity measurements, XRD and scanning electron microscopy (SEM) analysis were performed.
An overview is presented on possible mechanisms that control the leaching behaviour of the oxyani... more An overview is presented on possible mechanisms that control the leaching behaviour of the oxyanion forming elements As, Cr, Mo, Sb, Se, V and W in cementituous systems and alkaline solid wastes, such as municipal solid waste incinerator bottom ash, fly ash and air pollution control residues, coal fly ash and metallurgical slags. Although the leachability of these elements generally depends on their redox state, speciation measurements are not common. Therefore, experimental observations available in the literature are combined with a summary of the thermal behaviour of these elements to assess possible redox states in freshly produced alkaline wastes, given their origin at high temperature. Possible redox reactions occurring at room temperature, on the other hand, are reviewed because these may alter the initial redox state in alkaline wastes and their leachates. In many cases, precipitation of oxyanions as a pure metalate cannot provide a satisfactory explanation for their leaching behaviour. It is therefore highly likely that adsorption and solid solution formation with common minerals in alkaline waste and cement reduce the leachate concentration of oxyanions below pure-phase solubility.
Development of treatment methods to reduce Sb leaching from municipal solid waste incinerator (MS... more Development of treatment methods to reduce Sb leaching from municipal solid waste incinerator (MSWI) bottom ash, such as accelerated carbonation, is being complicated by insufficient understanding of Sb geochemistry. The leaching of antimonate (Sb(V)) and antimonite (Sb(III)) in MSWI bottom was studied as a function of pH and degree of carbonation. While total (Sb(V) + Sb(III)) leaching was lowest (1.2 mg kg À1 ) at the natural pH (i.e. 10.6) of uncarbonated bottom ash, HPLC-ICP-MS analysis showed that acidification and carbonation increased Sb(V) leaching, but decreased Sb(III) leaching, probably because SbðIIIÞðOHÞ À 4 became less stable. PHREEQC geochemical modelling suggested that Sb(V) concentrations approached equilibrium with the romeites, i.e. calcium antimonates, Ca 1.13 Sb 2 (OH) 0.26 Á0.74H 2 O at pH = 10.6 and Ca[Sb(OH) 6 ] 2 at pH = 8. It is hypothesised that not interaction with ettringite but dissolution of romeite controls antimonate leaching in the pH range 8-11 in MSWI bottom ash, because while Ca is preferentially leached from romeite, the mineral structures containing more Ca at higher pH are less soluble. A model was proposed where acidification and carbonation both lead to lower Ca 2+ and/or hydroxyl concentration, which removes Ca 2+ and hydroxyls from the romeite structure and leads to comparably higher Sb(V) concentration in equilibrium with romeite. Sb solubility depends on pH and Ca 2+ availability in this model, which has implications for bottom ash valorisation and risk assessment.
Three types of wastes, metallurgical slag from Pb production (SLG), the sand-sized (0.1-2 mm) fra... more Three types of wastes, metallurgical slag from Pb production (SLG), the sand-sized (0.1-2 mm) fraction of MSWI bottom ash from a grate furnace (SF), and boiler and fly ash from a fluidised bed incinerator (BFA), were characterized and used to replace the fine aggregate during preparation of cement mortar. The chemical and mineralogical behaviour of these wastes along with the reactivities of the wastes with lime and the hydration behaviour of ordinary Portland cement paste with and without these wastes added were evaluated by various chemical and instrumental techniques. The compressive strengths of the cement mortars containing waste as a partial substitution of fine aggregates were also assessed. Finally, leaching studies of the wastes and waste containing cement mortars were conducted. SLG addition does not show any adverse affect during the hydration of cement, or on the compressive strengths behaviours of mortars. Formation of expansive products like ettringite, aluminium hydroxide and H 2 gas due to the reaction of some constituents of BFA and SF with alkali creates some cracks in the paste as well as in the cement mortars, which lower the compressive strength of the cement mortars. However, utilization of all materials in cement-based application significantly improves the leaching behaviour of the majority of the toxic elements compared to the waste as such.
Leaching of heavy metals from MSWI bottom ash exceeds some of the Flemish limit values for recycl... more Leaching of heavy metals from MSWI bottom ash exceeds some of the Flemish limit values for recycling the material as granular construction application. In particular, leaching of Cu, Zn and Pb often exceeds the limit value, with Cu being the most critical. In order to recycle bottom ash, treatment is therefore required. The bottom ash studied was divided on-site into four fractions using a large-scale wet sieving installation: a sludge fraction (Ø 0-0.1 mm), a sand fraction (Ø 0.1-2 mm) and two gravel fractions (Ø 2-6 and 6-50 mm). The two gravel fractions complied with the limit values after 3 months of natural ageing. The sand and sludge fraction did not reach the limit value for Cu. Four weeks of accelerated carbonation resulted in an important decrease of Cu leaching from these two fractions, although the limit value is still exceeded. In view of applying carbonation as one of the treatment methods in an integrated industrial application, two tests were additionally performed. The use of stack gas as carbonating medium was verified by setting up an accelerated carbonation experiment at the incineration plant. Also, the depth of carbonation was measured in a 10 cm thick sample of the sand fraction after different periods of treatment. After 3 months of natural ageing only the upper 4 cm underwent a significant carbonation, while after one week of accelerated carbonation the total sample was carbonated. A model was developed to predict these experimental results.
A number of indicators are evaluated and used to measure the environmental performance of the ind... more A number of indicators are evaluated and used to measure the environmental performance of the industry and energy sectors in Flanders and their progress towards sustainability: eco-efficiency, existence of a certified Environmental Management System, environmental expenditures, production of sustainable energy, environmental damage by electricity production, cost of environmental levies and number of registered complaints. The indicators are evaluated in relation
The leaching of heavy metals, such as copper, from municipal solid waste incinerator (MSWI) botto... more The leaching of heavy metals, such as copper, from municipal solid waste incinerator (MSWI) bottom ash is of concern in many countries and may inhibit the beneficial reuse of this secondary material. Previous studies have focused on the role of dissolved organic carbon (DOC) on the leaching of copper. Recently, a study of the Energy Research Centre of The Netherlands (ECN) showed fulvic acid-type components to exist in the MSWI bottom ash leachates and to be likely responsible for the generally observed enhanced copper leaching. These findings were verified for a MSWI bottom ash (slashed circle 0.1-2 mm) fraction from an incinerator in Flanders. The filtered leachates were subjected to the IHSS fractionation procedure to identify and quantify the fractions of humic acid (HA), fulvic acid (FA) and hydrophilic organic carbon (Hi). The possible complexation of fulvic acid with other heavy metals (e.g., lead) was also investigated. The identified role of fulvic acids in the leaching of copper and other heavy metals can be used in the development of techniques to improve the environmental quality of MSWI bottom ash. Thermal treatment and extraction with a 0.2 M ammonium-citrate solution were optimized to reduce the leaching of copper and other heavy metals. The effect of these techniques on the different fractions of organic matter (HA, FA, Hi) was studied. However, due to the obvious drawbacks of the two techniques, research is focused on finding other (new) techniques to treat MSWI bottom ash. In view of this, particle size-based separation was performed to evaluate its effect on heavy metal leaching and on HA, FA and Hi in MSWI bottom ash leachates.
An integrated installation for treatment of municipal solid waste and comparable waste from indus... more An integrated installation for treatment of municipal solid waste and comparable waste from industrial origin is described. It consists of three grate furnace lines with flue gas treatment by half-wet scrubbing followed by wet scrubbing, and an installation for wet treatment of bottom ash.
The contribution of the emission of PCBs by a municipal waste incinerator in Wilrijk, a relativel... more The contribution of the emission of PCBs by a municipal waste incinerator in Wilrijk, a relatively industrialized district in the largest city of Flanders, to the total emission to air and to the total human intake was estimated. Therefore it was compared to the emission of PCBs by evaporation from PCB containing applications (transformers, capacitors, paint, ink, etc.) and to the intake of PCBs with food. As there was a lack of PCB data from the incinerator, the PCB emission concentration was estimated using three different approaches. A PCB measurement of the incinerator emission, performed later on, fell within the predicted range of 0.0004-0.005 ng TEQ/Nm 3 .
Municipal solid waste incinerator (MSWI) bottom ash often cannot be recycled as construction mate... more Municipal solid waste incinerator (MSWI) bottom ash often cannot be recycled as construction material in Flanders, because leaching of Cu exceeds the limit value of 0.5 mg/kg. Leaching of other components such as Mo and Sb is critical as well, but limit values for these elements are to date only informal. A treatment technique was investigated to lower pollutant leaching: extraction with solutions of organic complexants to remove Cu. Six different solutions were used, of which washing with citric acid and ammonium citrate decreases Cu leaching to below the limit value. Extraction was then performed with different concentrations of ammonium citrate. Subsequent washing of the extracted material with distilled water appears to be vital to remove all residual ammonium citrate. Extraction with a 0.2 M solution of ammonium citrate followed by three washing steps decreases metal leaching to below the limit values.
The 0.1-2 mm fraction of a MSWI-bottom ash cannot be used as granular construction material becau... more The 0.1-2 mm fraction of a MSWI-bottom ash cannot be used as granular construction material because leaching of Cu exceeds Flemish limit values. In addition, leaching of Ba, Mo and Sb exceeds informal limit values. Leaching characteristics thus need to be improved. Carbonation was the chosen treatment method and this was performed by placing samples in a CO 2 chamber. The CO 2 percentage and the temperature of the chamber atmosphere, as well as the initial humidity of the samples, were varied to optimize carbonation parameters. Metal leaching was tested with the EN 12457 extraction test. Carbonation decreased Cu leaching from 3.3 to 1.0 mg/kg, but not yet to below the official limit value of 0.5 mg/kg. Leaching of Mo and Sb remained fairly constant or even increased after carbonation, but their limit values are only informal. Ba leaching decreased to below the informal limit value. Carbonation also caused Cr leaching to increase, in some cases to above the official limit value. Of the tested parameters, a CO 2 percentage of 10% and a carbonation temperature of 50°C in the atmosphere, together with ash humidity between 13% and 25% appeared to give the best leaching results. The main carbonation reactions took place within the first 24 h.
Geochemical modelling of leaching of oxyanion forming elements such as arsenic (As) and selenium ... more Geochemical modelling of leaching of oxyanion forming elements such as arsenic (As) and selenium (Se) is frequently not successful. A consistent thermodynamic dataset of As and Se was therefore composed, not only including precipitation, but also adsorption and solid solution, and was applied to the pH-dependent leaching behaviour of As and Se in an alkaline residue with a pH 11.1 from the lime treatment of sulphuric acid wastewaters from the production of non-ferrous metals. The As and Se content ranged up to 6.7 wt% and 0.29 wt%, respectively and speciation analysis showed that 96.3% of As occured as arsenate whereas Se speciation comprised 79% selenate and 21.0% selenite. XRD and SEM/EDX analysis showed that arsenate occurred as rauenthalite (Ca 3 (AsO 4 ) 2 ·10H 2 O), associated with gypsum, the most important mineral. Arsenate and arsenite concentrations were only slightly below equilibrium with rauenthalite and calciumarsenite (CaHAsO 3 ), respectively and consideration of adsorption and solid solution only marginally improved model predictions. Selenate (Se VI ) and selenite (Se IV ), on the other hand, were far from equilibrium with their corresponding calcium metalate. The application of solid solutions and adsorption of Se VI and Se IV oxyanions with gypsum, calcite and ettringite significantly improved model predictions but missing thermodynamic data and especially the lack of a comprehensive model for solid solution and surface exchange with calcite and ettringite still hampered efficient modelling.
In Flanders, the northern part of Belgium, about 31% of the produced amount of MSWI bottom ash is... more In Flanders, the northern part of Belgium, about 31% of the produced amount of MSWI bottom ash is recycled as secondary raw material. In view of recycling a higher percentage of bottom ash, a particular bottom ash fraction (Ø 0.1-2 mm) was studied. As the leaching of this bottom ash fraction exceeds some of the Flemish limit values for heavy metals (with Cu being the most critical), treatment is required.
The recycling potential of municipal solid waste incinerator (MSWI) bottom ash may be limited by ... more The recycling potential of municipal solid waste incinerator (MSWI) bottom ash may be limited by the leaching of antimony (Sb). Therefore, treatment methodologies need to be developed. The pH-dependent leaching behaviour of this oxyanion-forming element in fresh and weathered bottom ash is, however, not understood. Sb leaching was investigated in a wide range of both pH and extent of carbonation. Sb came close to equilibrium with calcium antimonate (Ca[Sb(OH) 6 ] 2 ) at acid and neutral pH. Therefore, adsorption experiments with synthetic calcite (CaCO 3 ), ettringite (Ca 6 Al 2 (SO 4 ) 3 (OH) 12 ·26H 2 O), gypsum (CaSO 4 ·2H 2 O), and portlandite (Ca(OH) 2 ) and adsorption modelling to hydrous ferric oxides (HFO) and amorphous aluminium minerals (AAM) were conducted to investigate which minerals decrease Sb leaching below equilibrium with calcium antimonate. At pH > 12, calcium antimonate comes into solution due to portlandite formation, but the subsequent increase in Sb leaching is reduced due to strong interaction of Sb with portlandite and ettringite. Ettringite appears to be an important host mineral for Sb at the natural pH of mildly weathered bottom ash (11.8) because a minimum in leaching is observed. When pH is decreased below 10.5, ettringite dissolves and Sb comes into solution, approaching equilibrium with calcium antimonate near pH 9. Gypsum showed no affinity for Sb. The interaction of calcite with Sb was not clear. Adsorption modelling suggested that HFO, rather than AAM, control Sb leaching when pH < 9. During carbonation, Sb leaching first increased, most likely due to dissolution of ettringite. Then, Sb leaching decreased, since the pH became low enough to allow sorption by HFO.
Zinc ashes, muffle furnace fragments and lead slags from non-ferrous industries were applied to p... more Zinc ashes, muffle furnace fragments and lead slags from non-ferrous industries were applied to pave roads in the North of Belgium. From an inventory it appeared that there are at least 490 km of such roads. In our survey the materials on these roads were characterised. The total metal concentration, the availability and the leaching as a function of time were determined. It appeared that these materials contain high concentrations of heavy metals, some of which are readily available. The high leaching of some metals makes them as such unsuitable as secondary construction material. Methods for the application of these materials for road construction were examined where the materials replaced part of the sand and gravel fraction in lean concrete and in bituminous mixtures, or where they replaced the sand in sand-cement mixtures, all these to be used for road foundations, cycle tracks, etc. When lead slags were applied in lean concrete, a material was obtained complying with the standards for secondary construction materials and with sufficient compressive strength for road foundations. When zinc ashes or muffle fragments were used to replace sand in sand-cement mixtures, again a suitable construction material was obtained. The other combinations tried out were rather unsuccessful, because of high metal leaching and/or poor compressive strength.
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Papers by T. Van Gerven