Heavy metal speciation in various types of fly ash from municipal solid waste incinerator

Fly ash (FA) from municipal solid waste incinerators has been known as hazardous waste, which is mostly because of the high content of heavy metal and dioxins. Besides the content, the form of the heavy metals in fly ash is also very important, because it is tightly related with the leaching behavior of fly ash in diverse circumstances. To evaluate the environment potential risk of fly ash, the Tessier chemical extraction method was adopted. In this study, four kinds of fly ash were examined, one sample from China (CFA) and the other three from Japan (RFA, CaFA and NaFA). Five metal elements were detected and they were Ni, Cr, Cd, Pb, and Cu. The result of total heavy metals’ concentration showed CFA has the lowest content. As to the Tessier chemical extraction experiments, the results show that Cd, Pb, and Cu have higher leaching risk in the environment than other heavy metals. The result of leaching test experiment showed that the more exchangeable speciation of Cd, Cr and Pb in FA, the more it could leach out in natural environment.     

The application and evaluation research of coffee residue ash into mortar

Coffee residue is usually regarded as a kind of agriculture waste; as its quantity increases the treatment of coffee residue will become an environmental problem. This research is innovative in that it derives the possibility of recycle application using coffee residue ash for cement replacement. In this research, coffee residue is burned in an electronic oven to three kinds of coffee residue ash at 500, 600 and 700 °C, and then appropriate apparatus is used to check the chemical and physical properties of these three types of coffee residue ash. After a general comparison, this study selected 500 and 600 °C coffee residue ashes with 2, 3, 5, 10 and 15 % cement replacements to make 5 cm³ cube mortar specimen to test different curing ages’ compressive strength. Through measurement and experiment, this research found that the compressive strength decreased by adding 500 or 600 °C coffee residue ash into the mortar. By considering waste reduction and practice application, this research derives that using the 600 °C coffee residue ash with 10 % replacement is better than others application, such using result also can get valuable efficiencies of financial and CO₂ reduction.     

Synthesis of zeolite from waste fly ash for adsorption of CO2

Zeolitic sorbents for CO₂ adsorption were prepared from waste coal fly ash (FA) through hydrothermal treatment at various ratios of NaOH/FA and NaAlO₂/FA, including an initial alkali fusion step. The fusion step decomposed the fly ash into very small amorphous particulate zeolite forms. The fly ash was converted to Na-P1 type with a NaOH/FA ratio of 0.5 and Na-A type with a NaAlO₂/FA ratio of 0.53. The product properties were affected by the reaction temperature: Na-P1 and Na-A types were formed at 100°C. Temperatures above 140°C led to the formation of more sodalite because of the redissolving and recrystallization of zeolite crystals. Alkali metal and alkaline earth metal cations were impregnated in the synthesized Na-P1 and Na-A zeolite through an ion-exchange method. The completed zeolitic sorbents were applied to the adsorption of low-level CO₂. As a result of the experiments, calcium ions were found to be the best for CO₂ adsorption owing to their electrostatic behavior and acid-base interaction.     

Aqueous leaching of cattle manure incineration ash to produce a phosphate enriched fertilizer

Ash produced from the combustion of livestock manure contains large amounts of phosphorus (P), which is an important resource as a fertilizer. Some studies have extracted and recovered P from incinerated biomass ash using inorganic acid or alkaline agents, which produce wastewater that requires treatment and is expensive due to the cost of chemicals. Livestock manure ash contains not only P, but also water soluble salts, which could be a negative influence on plant growth and shall be preferably removed from the recovered fertilizer. In this study, we removed salinity from cattle manure incineration ash by simple aqueous leaching, while retaining the P content. The optimal condition was a 20 min leaching time at a liquid/solid (L/S) ratio of 10 mL g-ash^?1. Under this condition, over 90 % of Cl and 20 % of Na in the original ash was removed, while over 99 % of the P was retained in the leached residue. The leached residue met the fertilizer standard in Japan in terms of citrate soluble fertilizer components and contained few heavy metals. X-ray analyses of the ash indicated that Cl was mainly present as KCl in the original ash, while P was mainly present as Ca compounds in the ash.     

Evaluation of bioaccessible arsenic in fly ash by an in vitro method and influence of particle-size fraction on arsenic distribution

A huge amount of fly ash is produced by coal-fired power plants every year in China and leads to increasing environmental problems associated with disposal and treatment. It will be very helpful for the study of management and disposal of solid waste to understand the bioaccessibility and environmental behaviors of arsenic in fly ash. In this paper, an in vitro physiologically-based extraction test was applied to estimate the solubility and bioaccessibility of arsenic in fly ash in the human gastrointestinal tract. The fly ash samples were sieved into different fractions with different particle sizes (100–60, 60–10, 10–2.5, <2.5 μm). The influence of particle size on both total and bioaccessible arsenic was also investigated. The results demonstrated that arsenic concentrations in fly ash were significantly correlated with particle size. The proportion of bioaccessible arsenic (gastric and intestinal arsenic) accounting for the total arsenic was in the range of 36–67 %. The statistic analysis indicated that total arsenic in fly ash was linearly correlated with bioaccessible arsenic. The results illustrated that bioaccessible arsenic was dominated by total arsenic.     

Optimizing Cr(VI) adsorption on activated carbon produced from heavy oil fly ash

In order to explore the beneficial utilization of heavy oil fly ash (HOFA) generated in the power plants, the present study is intended to optimize the chromium(VI) [Cr(VI)] adsorption on activated carbon produced from HOFA. The raw HOFA obtained from a power plant was washed by nitric/hydrochloric acid and activated at 800 °C with a holding time of 60 min to produce fly ash activated carbon (FAC). Phosphoric acid was used as a chemical agent to improve the surface characteristics of the HOFA during the activation process. Batch adsorption experiments were employed to evaluate the effects of different parameters such as initial Cr(VI) concentration, pH, and FAC dose on the removal of Cr(VI) from aqueous solution. A total of 17 adsorption experimental runs were carried out employing the detailed conditions followed the response surface methodology based on the Box–Behnken design. The results indicate that developed FAC has the potential for removing Cr(VI) from wastewater. Under the test conditions, a maximum of 91.51 % Cr(VI) removal efficiency was achieved.     

The potential of SO2 for reducing corrosion in WtE plants

Due to the high-temperature boiler corrosion induced by chloride-rich fly ash deposits, steam generation in today’s Waste-to-Energy (WtE) plants is typically designed only for 40 bar/400 °C as an economic compromise between acceptable corrosion rate and maximum power generation. The high-corrosive metal chlorides in the fly ash can react with SO₂ forming low-corrosive sulfates. The sulfation efficiency is enhanced by high SO₂ levels and sufficient residence time of the flue gas at high-temperatures (700–900 °C). The fly ash sulfation was tested in full scale in a Swedish WtE plant by applying the economic sulfur recirculation method. Probes of several alloys (16Mo3, Inconel 625, Sanicro 28) were exposed for 1000 h at controlled material temperatures in the superheater position, at normal and during sulfating operation respectively. Analyses of the fly ash showed that the molar Cl/S was decreased to values well below 1 and the corresponding corrosion rates of the individual material samples were less than half when sulfur recirculation was in operation. These positive findings demonstrate that the sulfur recirculation process has high potential for low-corrosive high-temperature steam generation (T ≈ 500 °C) and improved electricity production. Further steam superheating can be realized by staged superheating using small amounts of secondary fuel.     

Stabilization/solidification of MSW incineration residues from facilities with different air pollution control systems. Durability of matrices versus carbonation

This paper discusses the stabilisation/solidification process with Portland cement applied to municipal solid waste incineration residues. Two types of residues were considered: fly ash (FA) produced in an electrostatic precipitator, and air pollution control (APC) residues from a semi-dry scrubber process. Cement pastes with different percentages of FA and APC residues were characterised according to their physical properties, the effect of the hydration products and their leaching behaviour. Portland pastes prepared with APC residues showed a rapid setting velocity in comparison with setting time for those pastes substituted with FA residues. Portland cement hydration was retarded in FA pastes. Leaching test results showed that heavy metals (such as Zn, Pb and Cd) and sulphates are immobilised within the paste, whereas chlorides are only partially retained. The carbonation process increases the leachability of S04(2-) and heavy metals such as Zn and Cr.     

Effects of fly ash addition on physical properties of porous clay-fly ash composites via polymeric replica technique

The porous composites of clay and fly ash have the potential to be used in many fields, such as catalyst support and gas adsorbents. In this study, various ratios of fly ash (1–2) with different percentage of suspension (50–70 wt%) were applied to produce porous clay-fly ash composites via polymeric replica technique. Fabrication process starts by mixing clay and fly ash in distilled water to form slurry. The process is followed by fully immersing polymer sponge in slurry. The excess slurry is then removed through squeezing. Finally, the sponge coated with slurry is sintered at 500 and 1250 °C for 1 h. It is found that the compressive strength of porous composites improves significantly (0.178–1.28 MPa) when the amount of clay-fly ash suspension mixture (50–70 wt%) increases. The compressive strength of porous composites is mainly attributed to the mullite, quartz and amorphous phase formations. These results are supported by X-ray diffraction analysis. On the other hand, increase in the amount of suspension reduces the apparent density (from 2.44 to 2.32 g/cm³) and porosity (from 97 to 85 %). The reduction in apparent density is believed to be caused by the presence of high fly ash content in porous composites. The melted fly ash cenospheres have closed the internal pores and increased density of samples. Higher suspension level not only reduces porosity, but also increases close pores of the porous composites. The results are justified through the observation from the structures of porous clay-fly ash composites.     

Color analysis of combustion ashes of seawater-soaked wood: estimation of salt concentration

The color of wood ash is normally white, but black color ash was observed when seawater-soaked wood was combusted. In order to check the conditions for generation of black ash, we examined both ashing temperatures from 500 to 800 °C and seawater salt densities for wood soaking. As seawater salt densities rose, the ash color got black at ashing temperatures of 500 and 700 °C. The colors of the ash were analyzed by a spectrophotometer, and color space L* a* b* was measured. The L* value and wood ash yield showed a negative correlation when the ashing temperature was at 600 °C. Salt concentration in wood (SC) was practicably estimated from the L* value (R ² = 0.51) by the approximation formula [SC (%) = 11.82e^?0.038L*]. By scanning electron microscope (SEM) observation, black ash of 600 °C was fully covered by translucent material. It was composed of Na, Mg and Cl by energy dispersive X-ray spectroscopy analysis, and seemed to be crystallized seawater salt. Washed black ash was also observed by SEM, translucent seawater salt was removed and the wood tissue was observed. Black ash was found to be carbonized wood tissue residue, and it was generated when seawater salt exists with a woody biomass.     

Recycling of combined coal-biomass ash from electric power plant waste as a cementitious material: characteristics and improvement

Combined coal-biomass ash has an enormous impact on environmental quality near electric power plants. This paper describes an alternative to disposal in which the ash is used to produce cementitious materials. Ash was obtained from combustion of coal and biomass containing four mass ratios of anthracite, bitumen, rice husks, and eucalyptus bark. The cement-forming properties were systematically characterized including compressive strength development, durability, and expansion in water. The ash samples were ground to increase the specific surface area, and then used to partially replace ASTM Type I Portland cement in mixtures containing 15, 30, or 45 % ash by mass. The water-binder material's (Portland cement with or without combined coal-biomass ash) ratios (w/c) were held constant at 45, 55, or 65 % by mass. Types A, B, and D ash behaved similarly, while the properties of type C ash were slightly different. Increasing the ash fraction in Portland cement mixtures increased the water requirement and resulted in lower compressive strength. Thorough mechanical grinding reduced the porosity and significantly enhanced the material properties.     

Fate and behavior of selected heavy metals with mercury mass distribution in a fluidized bed sewage sludge incinerator

In this paper, emission and distribution behavior of six heavy metals (As, Cd, Cr, Ni, Pb, and Hg), particulate matter and mass distribution of mercury within the different streams of a fluidized bed sewage sludge incinerator are presented. At the inlet of air pollution control devices (APCDs); Cd, Cr, Ni and Pb were mainly enriched in coarse particles; comparatively As content was higher in fine particles (<PM_2.5). The concentration of heavy metals in total particulate matter and PM_2.5, at the inlet of APCDs, were in the order of Cr > Ni > Pb > As > Cd. Mercury was almost always distributed in flue gas. Metals, other than mercury, were efficiently removed in APCDs and their concentrations in bottom ash, with fly ash being higher, whereas for that in wastewater, then waste sand was lesser. Overall mercury removal efficiency of APCDs was 98.6 %. More than 83.3 % of mercury was speciated into oxidized form at the inlet of APCDs, attributed by higher chlorine content in sludge. Mercury was mainly distributed in wastewater (78.4 %), wastewater from a spray dry reactor (16.8 %), fly ash in a hopper (3.4 %) and flue gas (1.4 %). This result is one of the first for data to be obtained; more experiments are required to control emission from such sources.     

New technology and application of brick making with coal fly ash

China has ranked first in the coal fly ash emission in the world. The multipurpose use of the fly ash from power plant waste is always an important topic for the Chinese environmental protection, which has drawn the concern of the government, scientific research departments, manufacturing enterprises and industry experts. This paper introduces an experimental research on how to recycle fly ash effectively, a kind of new technology of making bricks by which fly ash content could be amounted to 50–80 %. The article introduces raw materials of fly ash brick, production process and key control points. It introduces how to change the technical parameters of the existing brick-making mechanical device, optimize the parameters combination and improve the device performance. High-content fly ash bricks are manufactured, which selects wet fly ash from power plants, adding aggregate with reasonable ratio and additives with reasonable dosage, and do the experimental research on manufactured products for properties, production technology and selection about technology parameters of production equipment. All indexes of strength grade, freezing-thawing resisting, and other standards of the studied bricks reached the national standards for building materials industry.     

Chemical changes in different types of coal ash during prolonged,large scale,contact with seawater

In this study, we followed the chemical changes occurring in coal ash exposed to prolonged (300 days), large scale, contact with running seawater. Four major components (Al, Ca, Mg, Fe) and seven minor and trace elements (Cd, Cr, Cu, Mn, Zn, Pb, Hg) were measured in four coal ash types: fly and bottom ash freshly obtained from coal-fired power plant, and old ash (crushed and blocks) recovered from the sea after 3-5 years contact with seawater. Changes occurred in the chemical composition of the coal ash along the experiment: Fe increased in fresh ash, Al increased in old ash and Ca increased in all ash types except old ash blocks. Cu and Hg decreased in fresh fly ash while Cr increased, Cd decreased in all ash types except bottom ash, and Mn decreased in bottom ash. Most of the changes occurred in the fresh fly ash, and not in the old ash, indicating equilibrium after prior exposure to seawater. In addition, more changes occurred in fresh fly ash than in bottom ash, emphasizing the differences between the two ash types. While the changes in the concentrations of the major elements may be an indication of the integrity of the ash matrix, the only elements of environmental significance released to the environment were Hg and Cd. However, calculated seawater concentrations were much lower than seawater quality criteria and therefore the coal ash was considered suitable for marine applications concerning seawater quality.     

Precious Metals in Municipal Solid Waste Incineration Bottom Ash

Municipal solid waste incineration (MSWI) bottom ash contains economically significant levels of silver and gold. Bottom ashes from incinerators at Amsterdam and Ludwigshafen were sampled, processed, and analyzed to determine the composition, size, and mass distribution of the precious metals. In order to establish accurate statistics of the gold particles, a sample of heavy non-ferrous metals produced from 15 tons of wet processed Amsterdam ash was analyzed by a new technology called magnetic density separation (MDS). Amsterdam’s bottom ash contains approximately 10 ppm of silver and 0.4 ppm of gold, which was found in particulate form in all size fractions below 20 mm. The sample from Ludwigshafen was too small to give accurate values on the gold content, but the silver content was found to be identical to the value measured for the Amsterdam ash. Precious metal value in particles smaller than 2 mm seems to derive mainly from waste of electrical and electronic equipment (WEEE), whereas larger precious metal particles are from jewelry and constitute the major part of the economic value. Economical analysis shows that separation of precious metals from the ash may be viable with the presently high prices of non-ferrous metals. In order to recover the precious metals, bottom ash must first be classified into different size fractions. Then, the heavy non-ferrous (HNF) metals should be concentrated by physical separation (eddy current separation, density separation, etc.). Finally, MDS can separate gold from the other HNF metals (copper, zinc). Gold-enriched concentrates can be sold to the precious metal smelter and the copper-zinc fraction to a brass or copper smelter.     

The chemical characteristics of ashes from cattle, swine and poultry manure

Animal manure is waste that contains large amounts of fertilizer resources. Incineration technology is effective in decreasing the volume of animal manure and concentrating the nutrients. In this study, the nutrient concentration and chemical compounds of several types of animal manure ash were examined to promote their recycling for agriculture. The nutrient concentration of manure ash was dependent on the reduction rate of solid materials by incineration. The phosphorus (P) and potassium (K) of cattle and layer manure were not concentrated greatly because of high silicon (Si) and calcium (Ca) concentrations, respectively. On the other hand, the P concentration of swine manure and broiler litter was increased to 10.1–12.0 % (3.6–4.6 times compared with original materials), equivalent to that of phosphate rock used as fertilizer material. The K concentration of broiler litter ash (16.1 %) was highest of all. The phosphate compounds of cattle and swine manure ashes were determined as Ca₉Fe(PO₄)₇ or Ca₉MgK(PO₄)₇. Hydroxyapatite (Ca₅(PO₄)₃(OH)) was detected in layer manure and broiler litter ashes. By acid treatment of ash, P and K availability of the fertilizer made from layer manure ash (33 % of materials) was equivalent to that of conventional chemical fertilizer.     

Effect of carbonation on the leaching of organic carbon and of copper from MSWI bottom ash

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.Natural weathering and accelerated carbonation resulted in a significant decrease of the Cu leaching. Natural weathering during 3 months caused a decrease of Cu leaching to <50% of its original value, whereas accelerated carbonation resulted in an even larger decrease (to ca. 13% of its initial value) after 2 weeks, with the main decrease taking place within the first 48 h.Total organic carbon decreased to ca. 70% and 55% of the initial concentration in the solid phase, and to 40% and 25% in the leachate after natural weathering and after accelerated carbonation, respectively. In the solid material the decrease of the Hy fraction was the largest, the FA concentration remained essentially constant. The decrease of FA in the leachate can be attributed partly to an enhanced adsorption of FA to Fe/Al (hydr)oxides, due to the combined effect of a pH decrease and the neoformation of Al (hydr)oxides (both due to carbonation). A detailed study of adsorption of FA to Fe/Al (hydr)oxides showed that significant adsorption of FA occurs, that it increases with decreasing pH and started above pH 12 for Fe (hydr)oxides and around 10 for Al (hydr)oxides. Depending whether FA or Hy are considered the controlling factor in enhanced Cu leaching, the decreasing FA or Hy in the leachate explains the decrease in the Cu leaching during carbonation.     

Characterisation of Organic Matter and Carbon Cycling in Rehabilitated Lignite-rich Mine Soils

Open-cast lignite mining in the Lusatian mining district resulted in rehabilitated mine soils containing up to four organic matter types: (1) recent plant litter, (2) lignite deposited by mining activity, (3) carbonaceous ash particles deposited during amelioration of the lignite-containing parent substrate and (4) airborne carbonaceous particles deposited during contamination. The influence of lignite-derived carbon types on the organic matter development and their role in the soil carbon cycle was unknown. This paper presents the findings obtained during a six year project concerning the impact of lignite on soil organic matter composition and the biogeochemical functioning of the ecosystem. The organic matter development after rehabilitation was followed in a chronosequence of rehabilitated mine soils afforested in 1966, 1981 and 1987. A differentiation of the organic matter types and an evaluation of their role within the ecosystem was achieved by the use of ¹⁴C activity measurements, ¹³C CPMAS NMR spectroscopy and wet chemical analysis of plant litter compounds. The results showed that the amount and degree of decomposition of the recent organic matter derived from plant material of the 30 year old mine soil was similar to natural uncontaminated forest soil which suggests complete rehabilitation of the ecosystem. The decomposition and humification processes were not influenced by the presence of lignite. On the other hand it was shown that lignite, which was thought to be recalcitrant because of its chemical structure, was part of the carbon cycle in these soils. This demonstrates the need to elucidate further the stabilisation mechanisms of organic matter in soils.     

灰场回水减少的原因分析及对策

针对老燃煤发电厂贮灰场回水逐年减少的状况，采取了在贮灰场水面上安装可移动式漂浮筏的措施，作为灰场回水取水的漂浮泵站，增加了灰场回水流量，解决了因回水不足而使用水库水作补水的问题。     

Leachate generation and biogas energy recovery in the Jebel Chakir municipal solid waste landfill,Tunisia

A survey was conducted between 2006 and 2008 in order to identify municipal solid waste (MSW) composition and its influence on leachate generation and to assess the amount of biogas yield from the Jebel Chakir landfill in Tunis City. The organic fraction was the predominant compound in the MSW, followed by paper, fine, plastic, leather, rubber, metal, textile, glass and ceramic. The average MSW moisture content varies from 60 % in the wet season to 80 % in the dry one. The recognised MSW composition is well representative if compared to that of cities in developing countries. A large leachate quantity is produced in the landfill of Jebel Chakir, despite the negative water balance of the site. Based on the annual MSW landfilled quantities and using the LandGEM model, the expected peak landfill gas (LFG) production is estimated to occur 1 year after the landfill closure with a rate of 3.53 × 10⁷ m³/year. The analysis of the potential conversion of LFG to electric energy shows it at a total LFG-to-electricity energy of around 257 GWh with a heating value of 4,475 kcal/m³ based on an LFG collection efficiency of 33 % and energy efficiency of 33 % giving an economic feasibility for a 10 MW power plant.