Fraction Of Bottom Ash Research Articles

Sequential extraction procedure of municipal solid waste incineration (MSWI) bottom ash targeting grain size and the amorphous fraction

Introduction: Bottom ash (BA) constitutes a significant by-product obtained during the incineration of municipal solid waste in waste-to-energy (WtE) plants. BA is a heterogeneous material made of different fractions, glass, minerals, metals, and unburned residual organic matter. Due to the non-hazardous nature of the unburned material, BA can be effectively recycled, becoming a valuable resource. However, BA displays a high content of potentially toxic elements (PTEs) within its finer grain size. The presence of these elements raises concerns regarding the potential toxicity associated with BA.Materials and methods: The release of PTEs in the smaller fraction (0.063–0.2 mm; 0.3–0.5 mm; 2–4 mm; bulk <4 mm) of BA collected from the Parma WtE plant was investigated using a new five-step sequential extraction procedure (SEP). Through this method, both leached solutions and solid residues were analyzed by inductively coupled plasma-mass spectroscopy (ICP-MS), X-ray powder diffraction (XRPD), and X-ray fluorescence (XRF) analysis. This integrated approach provided valuable insights into the mineralogy, chemical composition, and PTEs leachability of BA.Results and discussion: The novelty of this work is the development of a new SEP protocol specifically designed and planned for an anthropogenic material such as BA. The weight reduction recorded after each step is linked to the progressive disappearance of both crystalline and amorphous phases. Water-soluble phases, such as salts, are the first to react, followed by the carbonate fraction in the second step. At the end of the procedure, only quartz, corundum, and Ti-oxide are identified. Among the PTEs, Pb exhibits the highest release, particularly during the acid attack, followed by Zn. The significant release of Ni during the oxidizing and reducing steps can potentially be linked to hydroxides and metallic alloys, respectively. The integration of XRF and Rietveld refinement results on solid residues enabled the identification of several types of amorphous materials and their chemical evolution during the sequential extraction.

Utilization of size-fractionated pozzolanic bottom ash to immobilize heavy metals in MSW incinerator fly ash

Fly ash (FA) from Municipal solid waste incineration (MSWI) is disposed of in landfills after the immobilization of hazardous heavy metals. Pozzolans found in the fine-fraction of MSWI bottom ash (BA) have the potential to immobilize heavy metals. The aim of this study was to examine the effect of size-fractionated BA in immobilizing heavy metals in FA, in order to enhance the effective utilization of resources. BA was applied at two distinct fractions (d<0.25 and d<2.0 mm) when considerable amorphous reactive pozzolans (i.e., siliceous and aluminous) were present. In order to conduct the experiments, FA, BA, and water were mixed in a ratio of 10:1:10, dried at room temperature and in an oven at 120 °C for 4 h, and settled for 4, 8, 16, 30, and 60 days. The results showed that under the air-dried conditions, both BA fractions significantly immobilized Pb and Zn. Pb and Zn leaching stabilized at about 99.9% and 95.6%, respectively, over 16 days with a BA fraction of d< 0.25 mm in an air-dry environment. The pH reduction, the calcite, C-S-H gel, and several new secondary minerals formation demonstrated that the carbonation and pozzolanic reactions were the immobilization mechanisms. Despite the method's simplicity, the findings suggested a potential approach of utilizing residual BA fractions that can be reused directly in the incineration facility. Therefore, this technique can minimize the amount of raw materials required as a metal stabilizer, reduce the amount of waste sent to landfills, and create a new material that can be reused as fillers.

ANALISIS PENINGKATAN NILAI CBR LEMPUNG PLASTISITAS TINGGI TERSTABILISASI SEMEN DAN ABU DASAR

Improvement of soft clay with cement, lime, asphalt, and other additives has been done for few decades. Utilization of waste materials i.e gypsum, marble, rubber; rice hush ash, cane hush ash, saw-dust ash etc. The industrial wasted usage from coal burning process as pozzolanic agent has been proven improving the physical and mechanical properties of soil. This study aims to determine effect of bottom ash combined with cement to improve strength and permeability of high plasticity clay. CBR and hydraulic conductivity tests in the laboratory were carried out to study the changes. Several variations fraction of bottom ash (5%/10%/15%) and cement (3%/5%) were determined in this study. curing processes for 7 days and 28 days was carried out before testing the CBR and permeability. The test results of CBR and permeability of clay were 0.78% and 6E-09 m/sec, respectively. The addition of 3% cement and 5% bottom ash does not qualify soil as aggregate of sub-grade because the CBR value is &lt;12%. The best value was at fraction of 5% cement and 15% bottom ash, with CBR value of 38.60% and k=3.99E-08 m/s. The higher content of cement or bottom ash and curing time, soil properties are better. Composition of 5% cement and bottom ash on ranges of 10%-15% can be used as sub-grade. Keywords: bottom ash, curing, hydraulic conductivity, soaked, stabilization, CBR

From waste incineration by-products to functional materials: a “Chimie douce” route to VOCs mineral adsorbents

One of today’s major world challenges is the accumulation and the storage of tens of millions of tons per year of final materials resulting from the incineration of domestic and industrial waste. This raises the question of the recycling of these “raw materials”, while making allowance for environmental, economic, social and public health aspects. Our strategy targets the incorporation of waste incineration by-products in a totally circular economy. We propose an innovative process combining templated sol–gel growth of an inorganic or hybrid silica-based network with a solubilized fraction of bottom ash coming from the combustion of industrial and household wastes. The resulting materials engineered via aerosol processing demonstrate maximum adsorption capacity of model pollutant compounds (1-2 dichlorobenzene) competitive with activated carbons currently used in modern incineration plants. We believe that they have the potential to replace conventional activated carbon commonly used in incineration plants, enabling the first step of the long road of recycling final waste.Graphical abstract

Effects of enhanced metal recovery on the recycling potential of MSWI bottom ash fractions in various legal frameworks.

In recent years, complex new bottom ash treatment processes for enhanced metal recovery have been implemented in Switzerland, producing residual bottom ash fractions with various qualities. This study focusses on three different treatment processes by characterizing all arising fractions in detail. Thereby the factors influencing the composition of these fractions are identified and their recycling potential in Switzerland is investigated. However, high legislative requirements on total contents of heavy metals represent a high barrier for bottom ash recycling in Switzerland. Therefore, the recycling potential is further evaluated based on the waste legislation applied in the Netherlands, where recycling of bottom ash has a long tradition. There, threshold values for bottom ash recycling are based on leachate concentrations and not on total contents as in Switzerland. However, Swiss Waste Legislation also knows threshold values based on leachate concentrations for certain waste materials. The leaching tests applied in these two countries, however, are different. The comparison of both leaching tests reveals that the setup and conditions, especially the considered pH range, significantly influence the leaching of heavy metals. With emphasis on problematic pollutants, the possibilities for new applications of these fractions are evaluated based on Swiss and Dutch legal threshold values. The comparison within the legal frameworks of these two countries allows recognizing opportunities and risks related to bottom ash recycling.

Full-scale accelerated carbonation of waste incinerator bottom ash under continuous-feed conditions

Bottom ash (BA) is the dominant residue derived from the incineration of municipal solid waste or refuse-derived fuel (RDF). Costs for the disposal of the material chiefly depend on the leachability of salts and trace metals which may be cut by ageing the BA for several months to promote carbonation via uptake of carbon dioxide (CO2). Enhanced exposure to CO2 sources has been referred to as accelerated carbonation. Here we report on the successful implementation of the accelerated carbonation of BA in a continuously fed full-scale rotating drum reactor. The reactor was operated with the fine fraction (< 20 mm) of BA from an RDF incinerator and the exhaust of a combined heat and power unit was used as the reactant gas. The system was tested in 15 experiments and the process efficiency was addressed by maximizing the reactor loading and minimizing the BA residence time. Results confirmed that the reactor loading depended on the rotation-normalized mass flow rate of BA where the slope and intercept of the characteristic varied with the design of the reactor discharge and the use of mixing tools. According to leaching test results, BA residence times as low as 60 min were sufficient to render the carbonated BA a non-hazardous waste and convert it to a material suited for geotechnical applications. This outperforms previous laboratory findings and opens new perspectives for implementing the accelerated carbonation at incinerator sites.

Numerical Analysis on Solid Particle Erosion in Elbow of a Slurry Conveying Circuit

This study investigates the solid particle erosion in an elbow of a slurry conveying circuit by using a commercial computational fluid dynamics (CFD) code FLUENT. Erosion wear was predicted by using the Euler-Lagrange model applied with a turbulence scheme of standard k-ε. In the present study, the effect of various design parameters, namely radius of bend-to-pipe diameter (r/D) ratio, pipe diameter (D), bend curvature angle, and bend radius angle, was studied. The radius of the r/D ratio varied from 1.4 to 1.7. The flow velocity varied between 2 and 5 m/s and the solid concentration was kept constant, i.e., 10 vol.%. The mean size fraction of bottom ash varied from 102 to 300 μm. Numerical simulation results show that erosion rate increases with velocity, particle size, and pipe diameter. The optimum value of the r/D ratio was between 1.5 and 1.6. Lower erosion wear occurred near the entrance of the elbow and reached the maximum near 60° of the bend curvature. The particle size range of 162–230 μm was found critical for high erosion wear.

Valorization of MSWI Bottom Ash as a Function of Particle Size Distribution, Using Steam Washing

Treatments to reduce the leaching of contaminants (chloride, sulfate, heavy metals) into the environment from bottom ash (BA) are investigated, as a function of the ash’s particle size (s). The aim is to make BA suitable for reuse as secondary raw material, in accordance with the legal requirements. Such treatments must be economically feasible and, possibly, have to use by-products of the plant (in this case, steam in excess from the turbine). For the sake of completeness and comparison, carbonation is performed on those BA particle size classes that are not positively responsive to steam washing. BA is partitioned into four different particle size classes (s ≥ 4.75, 4.75 &gt; s ≥ 2, 2 &gt; s ≥ 1 and s &lt; 1 mm, corresponding to 36, 24, 13 and 27 wt%, respectively). In the case of s ≥ 2 mm (60 wt%), steam washing is effective in reducing to under the legal limits the leaching of chlorides, sulfate and heavy metals (Zn, Cu, Cd, Pb). It has been observed that steam washing causes both removal and dissolution of thin dust adherent to the BA’s surface. BA with 2 &gt; s ≥ 1 (~13 wt% of total BA) requires a combination of steam washing and carbonation to achieve a leaching below the legal limits. The finest BA fraction, s &lt; 1 mm (~27 wt% of total BA), is treated by carbonation, which reduces heavy metals leaching by 85%, but it fails to sufficiently curb chlorides and sulfates.

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.

Zinc recovery from Waste-to-Energy fly ash – A pilot test study

Zinc recovery from MSWI fly ash using acidic leaching and chemical precipitation was studied at pilot scale. The leached fly ash was re-incinerated in order to destroy toxic dioxins. 75–150 kg/h of fly ash from a Swedish Waste-to-Energy plant was mixed with scrubber liquids from the same flue gas treatment system in a continuously stirred vessel. The resulting slurry was dewatered in a vacuum belt filter. Hydroxide precipitation of the produced leachate, at a pH of around 9, followed by filtration of the formed crystals in a membrane filter press produced a filter cake with up to 80 wt% Zn(OH)2 in dry solids, calculated from Zn(tot). Up to 70% of the zinc content in the fly ash could be recovered. Two 4-hour full scale ash re-incineration tests were performed: leached fly ash was mixed with the waste at a ratio corresponding to a situation where all the fly ash was continuously re-incinerated. The tests showed only an 8% mass increase of produced fly ash, which means that most of it ended up in the bottom ash, although some elements could potentially accumulate in the system if all the fly ash was to be continuously re-incinerated. No negative effects were observed on the bottom ash quality, which suggests that a large portion of the toxic fly ash could be transformed into the bottom ash fraction.

An algorithm for the use of MSWI bottom ash as a building material in road pavement structural layers

Municipal solid waste incinerator (MSWI) bottom ash (constituting approximately 80–90%) and fly ash are by-products of the incineration of solid waste. In general, MSWI residues are primarily discarded into landfills. To address the continuous growth of landfills and to implement zero waste and circular economy policies, researchers are focusing on more efficient ways of using MSWI bottom ash. To that end, the best practices show that MSWI bottom ash is suitable for civil engineering applications, especially roads. Therefore, the subject of this research was the performance of subgrade and different unbound and bound pavement structural layers containing bottom ash. An algorithm was also introduced to facilitate the use of MSWI bottom ash as a building material. Soil and mineral aggregate mixtures with different percentages (0–100%) of bottom ash were designed and analysed, and more than 10 testing subjects containing a high amount of MSWI bottom ash were tested in the laboratory. The research revealed the suitability of the 0/2 fraction of bottom ash to improve soil and to enhance the performance of asphalt concrete mixture AC 16 PD in which the 0/4 fraction of sand is replaced with the 0/2 fraction of bottom ash. Furthermore, the suitability of mixtures composed of mineral aggregates and MSWI bottom ash or only of MSWI bottom ash (100%) to construct sub-base and base courses was confirmed.

In-depth mineralogical quantification of MSWI bottom ash phases and their association with potentially toxic elements

Municipal solid waste incineration bottom ash fractions ≤4 mm are the most contaminated ones in terms of potentially toxic elements (PTEs). In order to estimate potential environmental impacts, it is important to understand the association of the PTEs with the mineral phases. Large area phase mapping (SEM/EDX) using “PhAse Recognition and Characterization - PARC” software in combination with quantitative X-ray powder diffraction has been used to characterize amorphous and crystalline BA phases for the first time. The results show that one of the main incineration products was melilite and an amorphous phase with a melilitic composition. The ratio of crystalline to amorphous melilite was 1:2. They formed an inhomogeneous layer around BA particles and contained a high percentage of the PTEs, i.e., Cu, Zn, Ni and Cr. Other major sources of PTEs (especially Ni and Cu) were iron oxides produced during incineration and the weathering products, such as calcite and ettringite (Cu and Zn). After extensive characterization of BA, a sequential extraction procedure (SEP) was performed, which exposed bottom ash to different chemical environments designed to dissolve specific phases and release their PTEs into solution. The extracted solutions and solid residues generated from the extraction procedure were analyzed to identify the association between PTEs and dissolved phases of BA. By combining SEP results with information obtained via large area phase mapping it is shown that SEP can be used for studying the association of PTEs with the phase that cannot be investigated with XRD/EDX, such as organic matter and Fe-Mn-hydrous oxides. Furthermore, according to SEP results a high percentage (40–80 wt%) of each investigated PTE can be considered immobile and not susceptible to leaching in the environment.

RESOURCES FROM RECYCLING AND URBAN MINING: LIMITS AND PROSPECTS

Direct and indirect effects (DIERec) of the recovery of secondary resources are in the range of 500 million tons per year in Germany; energy savings are 1.4 million TJ. These savings are between 10 and 20% of the total. The effects of materials recovery exceed those of energy recovery by far except for secondary plastic material, where DIERec from energy recovery is higher by factor of 2.7. Untapped potential for the recovery of secondary resources exists in the fine fraction of bottom ash from municipal solid waste incineration, mainly Cu and precious metals, and in urban mining.

Fresh Bottom Ash Characteristics Dependence on Fractional Composition

Waste incineration process generates two main by-products streams: fly ash and bottom ash. Bottom ash is composed of a variety of oxides, heavy metals and salts. Chemical materials distributed unevenly in different fractions of bottom ash. This study investigates the heavy metals (Pb, Cd) content dependence of bottom ash and fraction composition. Studies were performed with five different fractions (0–2 mm; 2–5.6 mm; 5.6–11.2 mm; 11.2–22,4 mm; 22.4–40 mm) of fresh bottom ash. After a one-step leaching test (distilled water was used as a solvent), was determinate, that highest concentrations of the lead (Pb) (from 0.141 to 0.146 mg/l) are leached from the smallest (0–2 mm 2–5.6 mm) bottom ash fractions particles. Heavy metals concentration in these fractions eluates respectively was 2.83 and 2.91 times higher than the limit value of leaching. The highest concentration of cadmium (4.214 mg/l) was determinate in 0–2 mm fraction bottom ash eluate. concentration of cadmium was 1.40 times higher than the limit value of leaching. It can be concluded that 0–2 mm; 2–5.6 mm fraction bottom ash can’t be used in civil engineering, without pre-treatment (eg. washing or aging).

Hydrogen gas generation from metal aluminum-water interaction in municipal solid waste incineration (MSWI) bottom ash

In the present research, municipal solid waste incineration (MSWI) bottom ash (BA) residues from three incinerators (N, K, and R) in Japan were collected for hydrogen gas generation purpose. The samples were split into four particle size fractions: (1) d≤0.6, (2) 0.6≤d≤1.0, (3) 1.0≤d≤2.0, and (4) 2.0≤d≤4.75mm for the characterization of metal aluminum, the relationship between the present metal aluminum and hydrogen gas production, and the influence of external metal aluminum on the enhancement of hydrogen gas. The batch experiments were performed for each BA fraction under agitated (200rpm) and non-agitated conditions at 40°C for 20days. The highest amount of hydrogen gas (cumulative) was collected under agitation condition that was 39.4, 10.0, and 8.4 L/kg of dry ash for N2, R2, and K2 (all fraction 2), respectively. To take the benefit of the BA high alkalinity (with initial pH over 12), 0.1 and 1g of household aluminum foil were added to the fractions 2 and 3. A Significantly larger amount of hydrogen gas was collected from each test. For 0.1g of aluminum foil, the cumulative amount of gas was in the range of 62 to 78 L/kg of dry ash and for 1g of aluminum foil the cumulative amount of hydrogen was in the range of 119–126 L/kg of dry ash. This indicated that the hydrogen gas yield was significantly a function of supplementary aluminum and the intrinsic alkaline environment of the BA residues rather than ash source or particle size.

A two-stage treatment for Municipal Solid Waste Incineration (MSWI) bottom ash to remove agglomerated fine particles and leachable contaminants

In this lab study, a two-stage treatment was investigated to achieve the valorization of a municipal solid waste incineration (MSWI) bottom ash fraction below 4mm. This fraction of MSWI bottom ash (BA) is the most contaminated one, containing potentially toxic elements (Cu, Cr, Mo and Sb), chlorides and sulfates. The BA was treated for recycling by separating agglomerated fine particles (≤125µm) and soluble contaminants by using a sequence of sieving and washing. Initially, dry sieving was performed to obtain BA-S (≤125µm), BA-M (0.125–1mm) and BA-L (1–4mm) fractions from the original sample. The complete separation of fine particles cannot be achieved by conventional sieving, because they are bound in a cementitious matrix around larger BA grains. Subsequently, a washing treatment was performed to enhance the liberation of the agglomerated fine particles from the BA-M and BA-L fractions. These fine particles were found to be similar to the particles of BA-S fraction in term of chemical composition. Furthermore, the leaching behavior of Cr, Mo Sb, chlorides and sulfates was investigated using various washing parameters. The proposed treatment for the separation of agglomerated fine particles with dry sieving and washing (L/S 3, 60min) was successful in bringing the leaching of contaminants under the legal limit established by the Dutch environmental norms.

Immobilization of antimony in waste-to-energy bottom ash by addition of calcium and iron containing additives

The leaching of Sb from waste-to-energy (WtE) bottom ash (BA) often exceeds the Dutch limit value of 0.32mgkg−1 for recycling of BA in open construction applications. From the immobilization mechanisms described in the literature, it could be concluded that both Ca and Fe play an important role in the immobilization of Sb in WtE BA. Therefore, Ca and Fe containing compounds were added to the samples of the sand fraction of WtE BA, which in contrast to the granulate fraction is not recyclable to date, and the effect on the Sb leaching was studied by means of batch leaching tests. Results showed that addition of 0.5 and 2.5% CaO, 5% CaCl2, 2.5% Fe2(SO4)3 and 1% FeCl3 decreased the Sb leaching from 0.62±0.02mgkgDM−1 to 0.20±0.02, 0.083±0.044, 0.25±0.01, 0.27±0.002 and 0.29±0.02mgkgDM−1, respectively. Due to the increase in pH from 11.41 to 12.53 when 2.5% CaO was added, Pb and Zn leaching increased and exceeded the respective leaching limits. Addition of 5% CaCO3 had almost no effect on the Sb leaching, as evidenced by the resulting 0.53mgkgDM−1 leaching concentration. This paper shows a complementary enhancement of the effect of Ca and Fe, by comparing the aforementioned Sb leaching results with those of WtE BA with combined addition of 2.5% CaO or 5% CaCl2 with 2.5% Fe2(SO4)3 or 1% FeCl3. These lab scale results suggest that formation of romeites with a high Ca content and formation of iron antimonate (tripuhyite) with a very low solubility are the main immobilization mechanisms of Sb in WtE BA. Besides the pure compounds and their mixtures, also addition of 10% of two Ca and Fe containing residues of the steel industry, hereafter referred to as R1 and R2, was effective in decreasing the Sb leaching from WtE BA below the Dutch limit value for reuse in open construction applications. To evaluate the long term effect of the additives, pilot plots of WtE BA with 10% of R1 and 5% and 10% of R2 were built and samples were submitted to leaching tests at regular intervals over time. The Sb leaching from untreated WtE BA was just below or above the Dutch limit value. The Sb leaching from the pilot plots of BA with additives first remained stable around 0.13mgkg−1 but had a tendency to slightly increase after 6months, indicating the need for further research on the effect of weathering, and more specifically of carbonation, on Sb leaching from WtE BA.

Sustainable High Quality Recycling of Aggregates from Waste-to-Energy, Treated in a Wet Bottom Ash Processing Installation, for Use in Concrete Products.

Nowadays, more efforts towards sustainability are required from the concrete industry. Replacing traditional aggregates by recycled bottom ash (BA) from municipal solid waste incineration can contribute to this goal. Until now, only partial replacement has been considered to keep the concrete workability, strength and durability under control. In this research, the feasibility of a full aggregate replacement was investigated for producing prefabricated Lego bricks. It was found that the required compressive strength class for this purpose (C20/25) could be achieved. Nevertheless, a thorough understanding of the BA properties is needed to overcome other issues. As BA is highly absorptive, the concrete’s water demand is high. This workability issue can be dealt with by subjecting the fine BA fraction to a crushing operation to eliminate the porous elements and by pre-wetting the fine and coarse BA fractions in a controlled manner. In addition, a reactive NaOH washing is needed to avoid formation of longitudinal voids and the resulting expansion due to the metallic aluminum present in the BA. Regarding the long-term behavior, heavy metal leaching and freeze-thaw exposure are not problematic, though there is susceptibility to acetic and lactic acid attack and maybe increased sensitivity to alkali-silica reaction.

Aluminum and aluminum alloys in municipal solid waste incineration (MSWI) bottom ash: A potential source for the production of hydrogen gas

Bottom ash residues from three incinerators (K, N, and R) in Japan were used to characterize the metal aluminum and aluminum alloys and their potential for hydrogen gas generation. The samples were sieved into four fractions: (1) d ≤ 0.6 mm, (2) 0.6 ≤ d ≤ 1.0 mm, (3) 1.0 ≤ d ≤ 2.0 mm, and (4) 2.0 ≤ d ≤ 4.75 mm for characterization and hydrogen gas evolution experiments. Based on microscopic and microanalytical (SEM-EDX) examinations, the metal aluminum alloys with high purity (>90 wt% Al in most occurrences) and various sizes were randomly distributed in the ash particles. X-ray diffraction (XRD) analysis was carried out to identify the primary and secondary mineral phases in the ash residues before and after the hydrogen gas generation experiments. Batch experiments were performed to evaluate the hydrogen generation potential in each bottom ash fraction under agitated (200 rpm) and non-agitated conditions at 40 °C for 20 days. The highest amount of hydrogen gas (cumulative) under agitation was 39.4, 10.0, and 8.4 l/kg of dry ash for N2, R2, and K2, respectively. Under non-agitated condition, N2, R2, and K2 also yielded the highest amount of hydrogen, which was 38.3, 6.5, and 6.8 l/kg of dry ash, respectively. As a result of these experiments, the metal aluminum aggregates considerably converted to gel-like and crystalline Al-rich hydrate phases. The inherent alkalinity of the ash environment (pH ≥ 12) and the existence of metal aluminum were considered the key parameters to trigger and maintain the hydrogen generation reactions.

Effect of CaO on retention of S, Cl, Br, As, Mn, V, Cr, Ni, Cu, Zn, W and Pb in bottom ashes from fluidized-bed coal combustion power station

This work was conducted to evaluate whether Ca-bearing additives used during coal combustion can also help with the retention of some other elements. This work was focused on the evaluation of bottom ashes collected during four full-scale combustion tests at an operating thermal fluidized-bed power station. Bottom ashes were preferred to fly ashes for the study to avoid interference from condensation processes usually occurring in the post-combustion zone. This work focused on the behaviors of S, Cl, Br, As, Mn, V, Cr, Ni, Cu, Zn, W, and Pb. Strong positive correlations with CaO content in bottom ashes were observed (for all four combustion tests) for S, As, Cl and Br (R=0.917–0.999). Strong inverse proportionality was calculated between the contents of Pb, Zn, Ni, Cr and Mn and CaO, so these elements showed association to materials other than Ca-bearing compounds (e.g., to aluminosilicates, organic matter, etc.). Somewhat unclear behaviors were observed for W, Cu, and V. Their correlation coefficients were evaluated as statistically “not significant”, i.e., these elements were not thought to be significantly associated with CaO. It was also discovered that major enrichment of CaO in the finest bottom ash fractions could be advantageously used for simple separation of elements strongly associated with these fractions, mainly S and As, but also Cl or Br. Removal of 5% of the finest ash particles brings about a decrease in As concentration down to 77%–80% of its original bulk ash content, which can be conveniently used e.g., when high As content complicates further ash utilization.