Zn In Fly Ash Research Articles

Study on the accelerated carbonation of MSWI fly ash under ultrasonic excitation: CO2 capture, heavy metals solidification, mechanism and geochemical modelling

The current carbonation technology of municipal solid waste incineration fly ash (FA) has disadvantages such as low carbon sequestration efficiency, harsh conditions, and complicated equipment. An ultrasonic chemical method coupled with wet-carbonization technology is proposed. The effects of the FA ultrasonic carbonation (UC) method on CO2 capture, heavy metals (HMs) release and solidification were investigated, and geochemical model of FA was explored. The results showed that UC improved the CO2 capture capacity, and the carbonation efficiency increased from 14.1 % to 18.8 % because the ultrasonic physical and chemical excitation improved the mass transfer efficiency and strengthened the gas–liquid-solid three-phase carbonation reaction. UC inhibited the release of Pb and Zn into the liquid phase (0.002 mg/L and 0.004 mg/L) and increased the solidification efficiency of Pb and Zn in FA (99.99 % and 100 %) because free Pb and Zn converted carbonates completely. UC FA had a single component, small particle size, high degree of homogenization, and contained slender nano-CaCO3 crystals. The acid neutralization capacities of original FA, FA4, and FA9 were 10, 8, and 3 meq/g because the carbonation reaction neutralized the alkaline substance. The content of carbonate minerals was the highest in UC FA and the pH of carbonate-minerals controlled dissolution/precipitation was mainly between 6 and 10. The HMs were in a soluble state (pH < 6) and the amphoteric HMs were affected by soluble hydroxides, the leaching concentration increasing (pH > 10). Therefore, UC FA had the potential of economical, environmentally friendly, and resource-based applications when avoiding strong acid and alkali application scenarios.

Characteristics of MSWI fly ash with acid leaching treatment

The chemical and mineralogical characteristics of fly ash from a municipal solid waste incineration (MSWI) in China and the influence of processing parameters on heavy metals removal during leaching were investigated in this work. The fly ash particles had complex surface structure with limited specific surface area. The alkali chloride and metal salts in MSWI fly ash showed evidently impact on leaching efficiency. Metal leachability was related to their properties and speciation in fly ash. Water-soluble salts such as KCl, NaCl and CaCl2 in fly ash were easily washed out. In this study, removal efficiency by water washing was achieved to 93.1% for Cl, 41.4% for Na, 48.5% for K and 24.8% for Ca, respectively. Mineralogical analysis also revealed change of fly ash mineral phases and specification distribution after water washing. Under liquid to solid ratio of 40:1 L/kg and treatment time of 120 min, the leaching process achieved high dropping yields of toxicity characteristic leaching procedure (TCLP) concentrations for Cu, Zn Cd and Pb (80%–100%), moderate dropping yields for As (30%–80%) and relatively low dropping yields of Ni (< 30%). In addition, heavy metals such as Pb and Zn in fly ash with twice water washing treatment at a low liquid-solid ratio could reach lower TCLP concentrations. The result indicated that the combination process of twice water washing and one acid washing could significantly reduce the environmental risk of MSWI fly ash.

Vitrification of municipal solid waste incineration fly ash with B2O3 as a fluxing agent

In this paper, B2O3 was used as a fluxing agent to reduce the melting temperature of municipal solid waste incineration (MSWI) fly ash and promote the glassy phase formation. Ash fusion temperature (AFT) test, atomic absorption spectroscopy (AAS), X-ray diffraction(XRD), scanning electron microscope (SEM) and thermodynamic calculation were carried out. The results showed that the flow temperature decreased from 1211 °C to 986 °C with an increase in the B2O3 content from 0 to 15 wt%. The melting slag lead to a decrease in the surface area and an increase in the mass transfer resistance of heavy metals. Thus, the agglomeration of the fly ash particles became easier with the reduced viscosity of the liquid slag. The volatilization of Pb, Cd and Zn in fly ash was inhibited. The leaching behavior of heavy metals was evaluated, the results indicated that Zn and Cu were stable whereas the Pb and Cd were soluble in glassy slag.

Study on the species of heavy metals in MSW incineration fly ash and their leaching behavior

This study aims to identify the chemical species and leaching behavior of Cd, Zn, Pb, Cu and Cr in a fly ash with high content of calcium collected from the incineration of municipal solid waste (MWS), based on the sequential leaching procedure. A thermodynamic pseudo-equilibrium model was also developed to evaluate the possible chemical compounds of these heavy metals in the fly ash. The results indicate that, approximate 30% of Cu was distributed in the organic bound fraction and very likely combined with some organic ligands. Pb exhibited the highest fraction among these five metals in water soluble fraction, accounting for about 7.5%. It thus potentially causes a menace to the surroundings. In terms of model calculation, the metallic chlorides in the fly ash were responsible for the leaching of Pb, Zn, Cd and Cu even under a rigorous environmental condition (pH=2) where the oxides and/or metallic ferrites were rarely mobile. The leaching of Cr and Cd in the fly ash was controlled by a dissolution mechanism whereas the fate of Pb, Zn and Cu was controlled by the precipitation/sorption. Cu and Zn in fly ash have been proven to associate with Ca-bearing compounds through precipitation/sorption during leaching test while Pb mainly exists as sulfate and phosphate.

Distribution patterns of Cd, Cu, Mn, Pb and Zn in wood fly ash emitted from domestic boilers

Wood fuels being a renewable source of primary energy have been considered environmentally friendly. However, wood combustion in domestic boilers is a source of air pollution. The lack of a dust collection device is the reason why flue gases emit a significant load of particulate pollutants into the air, including heavy metals. The aim of this research was to assess the environmental hazard caused by both emissions of heavy metals during wood combustion in domestic boilers and their chemical forms present in fly ash.From the various wood fuels burnt in domestic boilers, the fly ash selected for this study came from the combustion of briquettes of softwood from non-polluted areas, and from burning hardwood fuel from trees exposed to pollutants from heavy traffic. The wood fuels satisfy the quality demands determined in the EN 14961 Solid Biofuels - Fuel quality assurances. However, the concentrations of Cd, Cu, Pb and Zn in the fly ash are considerably higher than the appropriate limit values determined for soil improvers. Sequential extraction shows that Cd and Zn are associated mainly with the water leaching and carbonate fractions, regarded as mobile and bioavailable, and pose the potentially greatest hazard to the environment and human health. Cu, Mn and Pb associated with less mobile fractions may not pose a direct air quality hazard but, due to their high concentrations, medium-term and long-term effects on soils and surface and subsurface waters should be considered.

Wood pellet fly ash and bottom ash as an effective liming agent and nutrient source for rye grass ( Lolium perenne L.) and oats ( Avena sativa)

Fly ash (FA) and bottom ash (BA) from a softwood pellet boiler were characterized and evaluated as soil amendments. In a greenhouse study, two plant species (rye grass, Lolium perenne L. and oats, Avena sativa) were grown in three different treatments (1% FA, 1% BA, non-amended control) of a silty loam soil. Total concentrations of plant nutrients Ca, K, Mg, P and Zn in both ashes were elevated compared to conventional wood ash. Concentrations of Cd, Cr, Pb, Se and Zn were found to be elevated in the FA relative to BA and the non-amended soil. At 28 d, oat above-ground biomass was found to be significantly greater in soil amended with FA. Potassium and Mo plant tissue concentrations were significantly increased by addition of either ash, and FA significantly increased Zn tissue concentrations. Cadmium and Hg tissue concentrations were elevated in some cases. As soil amendments, either pellet ash is an effective liming agent and nutrient source, but high concentrations of Cd and Zn in FA may preclude its use as an agricultural soil amendment in some jurisdictions. Lower ash application rates than those used in this study (i.e. <1%) may still provide sufficient nutrients and effective neutralization of soil acidity.

Metal resource potential of residues from municipal solid waste (MSW) melting plants

Fly ash and molten metal residues from municipal solid waste (MSW) melting plants are attracting considerable attention in Japan as an urban mine due to their high metal content. The study aimed at identifying the content of valuable metals in fly ash and molten metal and quantitatively evaluating the metal resource potential through comparison with ore and annual consumption. It was found that not only Zn and Pb but also rare metals such as Ag, Bi, Ga, Ge, Pd, In, Sb, Sn, Te, and Tl were highly concentrated in fly ash, and that the content was mainly influenced by the feedstock supplied to the melting plant. Cu content was extremely high in molten metals. The content of Zn, Pb, Cu, Ag, In, and Pd in fly ash was almost equal to or higher than that in crude ore. Particularly, Zn in fly ash was increased to almost the same level of Zn ore concentrate by simple water washing. Also, the estimated amount of Ga, Ge, Pd, Sb, Sn, and Zn in fly ash and molten metal occupied a high proportion of the annual consumption amount in Japan. These facts revealed that fly ash and molten metals from MSW melting plants have high metal resource potential.

Leaching characteristics of heavy metals during cement stabilization of fly ash from municipal solid waste incinerators

The leaching characteristics of heavy metals in products of cement stabilization of fly ash from a municipal solid waste incinerator were investigated in this paper. The stabilization of heavy metals such as Cd, Pb, Cu, and Zn in fly ash from such incinerators was examined through the national standard method in China based on the following factors: additive quantity of cement and Na2S, curing time, and pH of leaching liquor. The results showed that as more additives were used, less heavy metals were leached except for Pb, which is sensitive to pH of the leachate, and the worse effect was observed for Cd. The mass ratio of cement to fly ash = 10% is the most appropriate parameter according to the national standard method. When the hydration of cement was basically finished, stabilization of heavy metals did not vary after curing for 1 d. The mixtures of cement and fly ash had excellent adaptability to environmental pH. The pH of leachate was maintained at 7 when pH of leaching liquor varied from 3 to 11.

Concentrations of heavy metals in fly ash from a coal-fired power plant with respect to the new Finnish limit values

In Finland, the new limit values for heavy metals in fertilizers used in agriculture and in forestry came into force in March 2007, and for materials used as earth construction agents, in June 2006. From the utilization point of view, it was notable that the total heavy metal concentrations (Cd, Cu, Pb, Cr, Mo, Zn, As, Ni, Ba, and Hg) in fly ash from a coal-fired power plant were lower than those limit values. The concentrations of the easily soluble elements Ca, Mg, Na, P, and Zn in the fly ash were between 3.5 and 35 times higher than those found in the coarse mineral soils of Finland. Fly ash is a potential agent for soil remediation and for improving soil fertility. If inorganic materials and by-products are utilized in earthworks, the content of harmful compounds must be low and the harmful components must be tightly bound to the matrix. Therefore, a five-stage sequential extraction procedure was used to evaluate the extractability of different elements in fly ash into the following fractions: (1) the water-soluble fraction, (2) the exchangeable fraction (CH3COOH), (3) the easily reduced fraction (NH2OH-HCl), (4) the oxidizable fraction (H2O2 + CH3COONH4), and (5) the residual fraction (HF + HNO3 + HCl).