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Coal fly ash (FA) is an abundant commodity in many countries using steam coal for power production. In some countries (e.g. Israel) all the FA is utilized whereas in some countries only low percentage is used (e.g. USA). The main mode of utilization is in the civil engineering industries as cement or clinker additive or for concrete production. In Israel (2014) 1.3 Mt of highly basic type F FA has been produced, mostly from South African and Colombian coals, in the utilities. A potential application for type F FA could be as an efficient scrubber for hazardous acidic wastes (e.g. the phosphate industry). The scrubbing efficiency of FA stems from interactions of the aluminosilicate surface of the particles with trace elements or with fine precipitates of ionic solids (e.g. SrCO 3 ). The process changes the chemical and physical nature of the FA surface. These changes have been studied using SEM, TEM, XRD and particle size measurements of non-treated, compared to treated FA with acidic or neutral aqueous solutions. The results indicate that an appreciable part of the outer lime layer and part of the glassy aluminosilicate material is dissolved, revealing the mullite skeleton as well as Ti, and Fe species. Moreover, formation of mixed ettringite/thaumasite and halite particles is observed. Thus, this study can lead to a better understanding of the fixation mechanisms of the trace elements by coal FA. [ABSTRACT FROM AUTHOR]

Abstract: The speciation of Ga, Ge, Ni, V, S and Fe in fly ash from IGCC power plant were investigated for possible further extraction process by combining conventional mineral and chemical analysis, leaching tests, wet sequential extraction, Mössbauer and XAFS spectroscopies. The results shown that Ge occurs mainly as water-soluble species, GeS and/or GeS2 and hexagonal GeO2. Ga is present as an oxide, Ni occurs mainly as nickeline (NiAs), with minor proportions of Ni arsenates and vanadium as V(III) with minor amounts of V(IV) in the aluminosilicate glass matrix. Pyrrhotite and wurtzite-sphalerite are sulfide species containing Fe and Zn, but an important fraction of iron is also present in the aluminosilicate glass. These clear differences between the speciation of the above elements in this material and those reported for fly ash from conventional PC combustion. [Copyright &y& Elsevier]

Abstract: Water-soluble germanium species (GeS2, GeS and hexagonal-GeO2) are generated during coal gasification and retained in fly ash. This fact together with the high market value of this element and the relatively high contents in the fly ashes of the Puertollano Integrated Gasification in Combined Cycle (IGCC) plant directed our research towards the development of an extraction process for this element. Major objectives of this research was to find a low cost and environmentally suitable process. Several water based extraction tests were carried out using different Puertollano IGCC fly ash samples, under different temperatures, water/fly ash ratios, and extraction times. High Ge extraction yields (up to 84%) were obtained at room temperature (25°C) but also high proportions of other trace elements (impurities) were simultaneously extracted. Increasing the extraction temperature to 50, 90 and 150°C, Ge extraction yields were kept at similar levels, while reducing the content of impurities, the water/fly ash ratio and extraction time. The experimental data point out the influence of chloride, calcium and sulphide dissolutions on the Ge extraction. [Copyright &y& Elsevier]

Abstract: The abatement capacity of trace inorganic elements was studied in a large Pulverized Coal Combustion (PCC) power plant equipped with a wet limestone Flue Gas Desulphurisation (FGD) system. High proportions of most elements were retained as fly ash as consequence of the efficiency of the electrostatic precipitator (ESP, 99.6% of fly ash) and slag (11%). The most volatile elements, such as S and F are retained by the FGD gypsum, and Cl by the filtered water; whereas the moderately volatile elements, As and B, are retained mainly by fly ash, reaching very high abatement efficiencies for these elements when considering the whole plant (>92%). Selenium and Hg are still retained by the whole system with relatively high proportions (89% and 67%); however a prominently proportion is emitted; Se (11%) and Hg (29%), attaining gaseous/PM rate at the emissions reaching 0.08 and 290, respectively. The gaseous emissions are below the limits according to the European directive 2001/80/EC for large combustion plants and the PRTR threshold values with the exception of Hg emissions and particulate Se, As, Zn, Cu, Ni, and Cr. Remediation actions to prevent and/or reduce the gaseous and PM emissions as well as the determination of leachable potential of trace inorganic pollutants retained in FGD gypsum, especially F in view of its disposal, are of significant relevance. [Copyright &y& Elsevier]

Abstract: The (co)-firing of low-cost alternative fuels is expected to increase in the forthcoming years in the EU because of the economic and environmental benefits provided by this technology. This study deals with the impact of the different coal/waste fuel ratio of the feed blend on the mineralogy, the chemical composition and especially on the leaching properties of fly ash. Different blends of coal, petroleum coke, sewage sludge, wood pellets, coal tailings and other minor biomass fuels were tested in PCC (pulverised coal combustion) and FBC (fluidized bed combustion) power plants. The co-firing of the studied blends did not drastically modify the mineralogy, bulk composition or the overall leaching of the fly ash obtained. This suggests that the co-firing process using the alternative fuels studied does not entail significant limitations in the re-use or management strategies of fly ash. [Copyright &y& Elsevier]

Abstract: In this study, the application of some zeolitised fly ashes and synthetic zeolites to the decontamination of the leachate produced in a municipal solid waste (MSW) treatment plant and to the liquid waste from a pig farm was analyzed. Thus, the reduction of organic matter (BOD and COD), ammonium and total nitrogen, phosphorus and metals contents after a zeolite treatment was evaluated. Several synthetic zeolites were tested: some commercial zeolites and other synthetic zeolites and zeolitised ashes obtained after a coal fly ash alkaline hydrothermal process. Two forms of contact between the zeolitic material and the liquid waste were tested: in a stirred tank and in a column. In addition, other variables determined were the amount of zeolite and the residence time. The results showed that zeolites, especially zeolitised fly ash, clearly produced a strong reduction in the leachate nitrogen and phosphorus content. [Copyright &y& Elsevier]

• Inorganic trace pollutants are studied in a coal-fired power station in China. • The aqueous (NH 4) 2 SO 4 slurry (pH 3.2) is enriched in inorganic trace pollutants. • NH 3 -FGD performance for the retention efficiency of trace pollutants is questioned. • Acidic conditions of the aqueous (NH 4) 2 SO 4 slurry could lead to low FGD efficiencies. • Operating conditions may affect Hg fate across the PCC-SCR-ESP-NH 3 -FGD. The behaviour and speciation of inorganic trace pollutants were studied in a 270 MWh coal-fired power station equipped with denitrification (DeNOx)-based selective catalytic reduction (SCR), electrostatic precipitators (ESP) and ammonia flue gas desulphurisation (NH 3 -FGD) controls. The aqueous (NH 4) 2 SO 4 slurry (pH 3.2) showed remarkably high concentrations of SO 4 2−, Cl−, Fe, NH 4 +, PO 4 3−, and F− and was substantially enriched in multiple trace pollutants, e.g. Mn, Ni, Zn, and As, which can be ascribed to the diffusion of gaseous pollutants released during combustion and to the partial dissolution of fly ash (FA) particles entrained in the flue gas FGD. These processes were favoured by the iteration of the FGD water re-circulation cycles within the scrubber. Three major unresolved performance issues remain for the NH 3 -FGD with respect to the retention efficiency of major and trace pollutants: (i) the high concentration of soluble salts and major and minor trace elements in the aqueous (NH 4) 2 SO 4 slurry could lead to entrainment of droplets and particles with the outgoing (OUT)-FGD gas; (ii) the ionic strength, as a result of the high concentration of the elements associated with soluble salts and major and minor elements, could lead to diminishing diffusivity of gaseous pollutants into the aqueous phase, where these are supposed to dissolve; and (iii) the acidic conditions of the aqueous (NH 4) 2 SO 4 slurry, caused by Fe-hydrolysis, could lead to low FGD efficiencies. Operating conditions at this power station affect Hg partitioning and fate across the PCC-SCR-ESP-NH 3- FGD. [ABSTRACT FROM AUTHOR]