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The transition from limestone to lime-based flue gas desulphurisation system (FGD) was tested in a power station fired with high sulphur (S)-petroleum coke to better control the emissions of key pollutants. To this end, as a request of the power station owner to IDÆA-CSIC, we surveyed the power station fired with 70% S-petroleum coke and equipped with a slaked lime-based FGD, and compared the results with data from our previous works conducted at the same power station but operated with lower co-firing rates and a limestone FGD, the purpose being to improve the understanding on the impact that different FGD technologies may have on the fate, speciation and, ultimately, the emissions of key pollutants from the power station. Our observations suggest that the reaction pathways and speciation of key trace pollutants in the gypsum slurry including Cl, Mo, Hg and Se remained largely unchanged with the transition from limestone to lime-based FGD. By contrast, As, Cr, B, U and V speciation in the gypsum slurry was sensitive not only to the FGD sorbent, likely in response to differences in the pH, but also to the absence of ligands such as F−.The highly alkaline lime slurry neutralised the H+ released by the formation of metal-complexes. This favoured the stability of trace elements in their oxy-anionic forms or forming hydroxyl complexes, as opposed to the acidic conditions in limestone-FGD gypsum from previous works. Enrichment in Mo, V and Ni in the fly ash was primarily associated with the combustion of a petroleum coke. Other elements such as Pb, As, Zn, Cu and Se were also enriched in the fly ash relative to the boiler slag. • The use of slaked lime is a promising alternative for limestone flue gas desulphurisation (FGD). • The speciation of Cl, Mo, Hg and Se remained unchanged with the transition to lime-based FGD. • As, Cr, B, U and V speciation was sensitive to response to differences in pH and absence of ligands such as F−. • The alkaline conditions favoured the stability of trace elements in their oxyanionic forms or forming hydroxyl complexes. • The replacement of lime may benefit the power plant as hydroxide and other ionic complexes offer more manageable options. [ABSTRACT FROM AUTHOR]

The Israeli quarry industry produces 57 Mt of raw material and ∼4–6 Mt of associated sub-economical by-products annually. These sub-economical quarry fines are not used because production and transportation costs considerably exceed their retail value. Therefore these by-products, are stored in large piles of fine grain size particles, create environmental risks to their surrondings. This paper evaluates the possibility of mixing the sub-economical quarry by-products of two Israeli quarries with sub-economical Class F coal fly ash (<20 wt.% CaO) to form an economical aggregate sand substitute to be used as a concrete filler product. To study the feasibility of the aggregate as partial substitute to sand in concrete several analyses, including leaching experiements (EN12457-2), analytical techinques (SEM-EDX, ICP-MS, ICP-AES, and XRD), as well as an analysis of the mechanical and chemical properties of the concrete aggregate (strength, workability, and penetration) were performed. Scrubbing quarry waste with coal fly ash was found to be very effective for reducing the leaching rate of potentially harmful trace elements. In addition, adding fly ash with quarry fines as partial substitute to sand enhanced the performance of the concrete mixture and the properties of the fresh and harden concrete. [ABSTRACT FROM AUTHOR]

There is interest in recovering phosphate (P(V)) from secondary sources, such as waste water streams for potential use as fertilizers reducing the environmental impacts of P(V) discharges and providing alternative phosphorus sources. The goal of this work was to provide an understanding of P(V) removal by fly ash (FA) from coal power plants. Phosphate removal using Ca(II) rich FA was evaluated in terms of i) sorption equilibrium, ii) sorption kinetics under the expected pH values and P(V) concentrations in wastewaters effluents, and iii) P(V) availability of the FAs in agricultural applications. At the pH values (6–9) expected for wastewater effluents, P(V) removal proceeds as a combination of CaO(s) dissolution and brushite (CaHPO 4 (s)) formation on the FA particles. This process avoids the formation of relatively insoluble Ca–phosphates, such as, hydroxyapatite (Hap) with limited fertilizing properties. High P-loadings were achieved (up to 50 mgP-PO 4 /g FA (5% P(V) by weight)) at a pH of 8. The removal kinetics data were well described as a diffusion-based process of phosphate ions (H 2 PO 4 − and HPO 4 2− ) on FA particles, and the CaO(s) dissolution process was discarded as the rate controlling step. The P(V) availability from loaded samples was determined via an agronomical assay with NaHCO 3 solutions with P(V) release ratios of 10–30 mgP-PO 4 /g in FA, confirming the appropriateness of this material as a potential fertilizer, even in calcareous soils. [ABSTRACT FROM AUTHOR]

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: Coal-based power generation produces over 750Mt of coal ash per year globally, but under 50% of world production is utilised. Large amounts of fly ash are either stored temporarily in stockpiles, disposed of in ash landfills or lagooned. Coal ash is viewed as a major potential source of release of many environmentally sensitive elements to the environment. This paper encompasses over 90 publications on coal fly ash and demonstrates that a large number of elements are tightly bound to fly ash and may not be easily released to the environment, regardless of the nature of the ash. This review provides an extensive look at the extent to which major and trace elements are leached from coal fly ash. It also gives an insight into the factors underlying the leachability of elements and addresses the causes of the mobility. The mode of occurrence of a given element in the parent coal was found to play an important role in the leaching behaviour of fly ash. The amount of calcium in fly ash exerts a dominant influence on the pH of the ash–water system. The mobility of most elements contained in ash is markedly pH sensitive. The alkalinity of fly ash attenuates the release of a large number of elements of concern such as Cd, Co, Cu, Hg, Ni, Pb, Sn or Zn among others, but at the same time, it enhances the release of oxyanionic species such as As, B, Cr, Mo, Sb, Se, V and W. The precipitation of secondary phases such as ettringite may capture and bind several pollutants such ash As, B, Cr, Sb, Se and V. [Copyright &y& Elsevier]

Abstract: This study deals with the synthesis of geopolymers from co-fired fly ash and blast furnace slags. Geopolymer bodies were simultaneously synthesized in open and closed curing conditions in order to elucidate the role of this parameter on their resultant properties. Open curing conditions produce solid bodies characterized by high porosity, low compressive strength and exacerbated leaching of certain oxyanionic metalloids. By contrast, protected curing promotes the binder development, giving rise to higher strength and less porous systems. This imposes physical restrictions to leaching which decreases and/or retards releases of oxyanionic metalloids in comparison to open curing conditions. Fly ash-slag-based geopolymers may immobilize a number of trace pollutants such as Be, Bi, Cd, Co, Cr, Cu, Nb, Ni, Pb, REE, Sn, Th, U, Y and Zr, regardless of the curing conditions. Due to geopolymers displaying weak assimilation capacity for oxyanionic species, their successful regarding oxyanionic retention is strongly dependent on porosity and therefore on curing conditions applied. [Copyright &y& Elsevier]

This study deals with the use of fly ash as a starting material for geopolymeric matrices. The leachable concentrations of geopolymers were compared with those of the starting fly ash to evaluate the retention of potentially harmful elements within the geopolymer matrix. Geopolymer matrices give rise to a leaching scenario characterised by a highly alkaline environment, which inhibits the leaching of heavy metals but may enhance the mobilization of certain oxyanionic species. Thus, fly ash-based geopolymers were found to immobilise a number of trace pollutants such as Be, Bi, Cd, Co, Cr, Cu, Nb, Ni, Pb, Sn, Th, U, Y, Zr and rare earth elements. However, the leachable levels of elements occurring in their oxyanionic form such as As, B, Mo, Se, V and W were increased after geopolymerization. This suggests that an optimal dosage, synthesis and curing conditions are essential in order to obtain a long-term stable final product that ensures an efficient physical encapsulation. [Copyright &y& Elsevier]

The Puertollano Integrated Coal Gasification Combined Cycle (IGCC) Power Plant (Spain) fly ash is characterized by a relatively high content of Ga and V, which occurs mainly as Ga2O3 and as Ga3+ and V3+substituting for Al3+ in the Al–Si fly ash glass matrix. Investigations focused on evaluating the potential recovery of Ga and V from these fly ashes. Several NaOH based extraction tests were performed on the IGCC fly ash, at different temperatures, NaOH/fly ash (NaOH/FA) ratios, NaOH concentrations and extraction times. The optimal Ga extraction conditions was determined as 25°C, NaOH 0. 7–1M, NaOH/FA ratio of 5L/kg and 6h, attaining Ga extraction yields of 60–86%, equivalent to 197–275mg of Ga/kg of fly ash. Re-circulation of leachates increased initial Ga concentrations (25–38mg/L) to 188–215mg/L, while reducing both content of impurities and NaOH consumption. Carbonation of concentrated Ga leachate demonstrated that 99% of the bulk Ga content in the leachate precipitates at pH 7. 4. At pH 10. 5 significant proportions of impurities, mainly Al (91%), co-precipitate while >98% of the bulk Ga remains in solution. A second carbonation of the remaining solution (at pH 7. 5) recovers the 98. 8% of the bulk Ga. Re-dissolution (at pH 0) of the precipitate increases Ga purity from 7 to 30%, this being a suitable Ga end product for further purification by electrolysis. This method produces higher recovery efficiency than currently applied for Ga on an industrial scale. In contrast, low V extraction yields (<64%) were obtained even when using extreme alkaline extraction conditions, which given the current marked price of this element, limits considerably the feasibility of V recovery from IGCC fly ash. [Copyright &y& Elsevier]

Abstract: The use of zeolitic material synthesized from coal fly ash for the immobilization of pollutants in contaminated soils was investigated in experimental plots in the Guadiamar Valley (SW Spain). This area was affected by a pyrite slurry spill in April 1998. Although reclamation activities were completed in a few months, residual pyrite slurry mixed with soil accounted for relatively high leachable levels of trace elements such as Zn, Pb, As, Cu, Sb, Co, Tl and Cd. Phytoremediation strategies were adopted for the final recovery of the polluted soils. The immobilization of metals had previously been undertaken to avoid leaching processes and the consequent groundwater pollution. To this end, 1100kg of high NaP1 (Na6[(AlO2)6(SiO2)10]·15H2O) zeolitic material was synthesized using fly ash from the Teruel power plant (NE Spain), in a 10m3 reactor. This zeolitic material was manually applied using different doses (10000–25000kg per hectare), into the 25cm topsoil. Another plot (control) was maintained without zeolite. Sampling was carried out 1 and 2years after the zeolite addition. The results show that the zeolitic material considerably decreases the leaching of Cd, Co, Cu, Ni, and Zn. The sorption of metals in soil clay minerals (illite) proved to be the main cause contributing to the immobilization of these pollutants. This sorption could be a consequence of the rise in pH from 3.3 to 7.6 owing to the alkalinity of the zeolitic material added (caused by traces of free lime in the fly ash, or residual NaOH from synthesis). [Copyright &y& Elsevier]

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]

Elemental composition and mineralogy of a high ash feed coal (ash: 49.7 wt.%), and its bottom and fly ash from a Brazilian power plant (Presidente Médici Power Plant or UTPM-446 MW) was determined using ICP-MS, ICP-AES, X-ray diffraction (XRD) and scanning electron micrography (SEM). Most trace elements in coal fall in the usual range determined for world coals. However, concentrations of some elements were higher than the expected for coals, including Cs Rb and heavy rare earth elements (REEs). This might be due to the high content of detrital minerals of the studied coal, given that these elements are usually associated with clay minerals. Elements were classified into three groups based on the analysis of trace element concentrations in fly and bottom ashes, and enrichments or depletions of these concentrations in relation to the coal: Group I (volatile elements with subsequent condensation): As, B, Bi, Cd, Ga, Ge, Mo, Pb, S, Sb, Sn, Tl and Zn; Group II (no volatile elements enriched in bottom ash vs. fly ash): Ca, Fe, Mn, P, Ti and Zr; Group III (low volatile elements with no partitioning between fly and bottom ashes): Al, Ba, Be, Co, Cr, Cs, Hf, K, Li, Mg, Na, Ni, Rb, Sr, Th, U, W, Y and most of REE. The mass balance for trace elements obtained demonstrated that the volatile emission of the trace elements studied is very low. According to the leachable proportion obtained, the elements may be classified as follows: B (40–50%)>Mo>Cu>Ge=Li=Zn=As>, Ni, Sb, Tl, U>Ba, Cd, Sr, V (0.3–2%). For the other elements studied, the leachable fraction is in most cases <1% of the bulk content. [Copyright &y& Elsevier]

Abstract: The properties of coal fly ash are strongly dependent on the geological origin and the combustion process of the coal. It is important to characterize regional fly ash in detail to ascertain its potential uses as raw material in the production of high value products. The physicochemical properties of fly ash coming from the “Jose Lopez Portillo” coal-fired power plant, Coahuila, Mexico (MFA), are presented in this work. A detailed study of trace elements, the chemical composition of the amorphous phase, thermal stability and the leaching of contaminant elements under different conditions are included. MFA is composed of mullite, quartz, calcite, magnetite and an amorphous phase. This material contains mainly silica (59.6%), alumina (22.8%) and magnetite (5.6%). Its amorphous phase (78.3%) has a high silica (49.4%) and alumina (14.4%) content. According to its mineralogical and chemical composition, MFA is potentially useful as a raw material for making cement, silica, and alumina, as well as low silica/alumina ratio zeolites. Deleterious elements could be removed during the zeolitization process or with an additional acid treatment. Because of its morphological properties and structural and thermal stability, MFA can be used in thermal isolation and refractory materials and as a support for heterogeneous catalysts. [Copyright &y& Elsevier]

Coal fly ash (FA) is abundant in countries that use steam coal for power production. The resultant FA is Class F FA (<20% CaO, Al 2 O 3 + SiO 2  > 70%, <6% Loss on Ignition) and can be used as an excellent scrubber and fixation reagent for acidic wastes containing toxic trace elements. In Spain, less than 50% of the abundant FA is currently being used. This paper reports on the potential use of Class F FA as a neutralization and fixation reagent for the hazardous sludge waste of the phosphate industry. Several analytical techniques (ICP-MS, ICP-AES, SEM-EDX, and XRD), and leaching experiments (EN12457-2) were used for this study. The results identify the best FA/waste ratios for full neutralization and fixation. Furthermore, adding a high calcium carbonate material prevents the excessive leaching of As, Mo, and Se, and facilitates full neutralization and fixation. Furthermore, the use of a safe aggregate (produced by mixing coal phosphate waste with fly ash and/or bivalve shells) as a partial substitute for sand improves the quality of concrete for civil engineering projects and is environmentally safe. [ABSTRACT FROM AUTHOR]

Currently, in Israel, phosphate acidic wastes formed during the production of phosphoric acid (H3PO4) using hydrochloric acid (HCl) are stored in large ponds. At present, this waste is only neutralized using lime (CaO) or calcite (CaCO3). This paper investigated the potential use of Class F (<20% CaO) coal fly ash (FA) as a fixation reagent of the neutralized hazardous phosphate industry waste. Studies have shown that FA can be an efficient scrubber and fixation reagent for various kinds of acidic toxic waste. Several analytical techniques including ICP-AES, ICP-MS, SEM-EDX, and XRD, ion penetration and compression/flexure strength tests (according to ASTM C1202, IS26/4.1, and 4.2 protocols), as well as leaching experiments (EN12457-2) were used to study the fixation quality and potential utilization of the fixated product as partial substitute to sand in concrete. Scrubbing phosphate waste with the FA was found to effective in reducing the leaching rate of toxic trace elements. Moreover, the use of aggregates as a partial substitute for sand in concrete improves the mechanical and chemical properties and is environmental safe. Thus, these procedures would eliminate costly treatment and storage of these toxic wastes relatively inexpensively as well as enhance industrial concrete for civil engineering projects. [ABSTRACT FROM AUTHOR]

The present study investigates the geochemical characteristics of the flue gas desulfurization gypsum (FGD Gp) generated from a pulverized-coal combustion (PCC) power plant in Xinjiang, Northwest China, with special emphasis on manufacturing fire-resistant panels using this FGD Gp as well as the fly ash collected from the same power plant. The physical, mechanical and insulating properties of the manufactured panels are also determined. The FGD Gp is characterized by low trace element concentration and low leachable potential for environment-concerned trace elements, indicating it can be reused with low environmental implication. Fire-resistant panels were successfully made from pure FGD Gp, pure commercial gypsum (CGp) and different FGD Gp/fly ash and CGp/fly ash mixtures. With the same gypsum/fly ash proportion, the FGD Gp/fly ash panels present relatively lower density, lower water absorption and lower mechanical strength, but higher moisture contents and better insulating capacities than the CGp/fly ash panels. The pure FGD Gp panel presents the best insulating capacity (52 min), much higher than that of the pure CGp panel (42.8 min). The mechanical and insulating properties of the panels are reduced with the increasing of fly ash proportion in the mixtures, but even prepared with 80% fly ash, the manufactured panels can still be used as benign fire-resistant panels with no significantly physico-chemical, and mechanical limitations. Therefore, manufacture of fire-resistant panels from FGD-Gp and fly ash is a very promising application for these coal combustion by-products which are substantially being generated in large amounts from Xinjiang power plants. The manufactured fire-resistant panels can be used in large amount as insulating construction and building materials with low environmental implication and high economic value. [ABSTRACT FROM AUTHOR]

Abstract: Fly ash (FA) disposal in landfills has a significant economic and environmental burden. A promising approach for FA valorisation aside from building purposes is the recovery of valuable elements since FA has a huge potential role as a source of valuable metals. In most cases, reported work in this area has been of theoretical research and further development work is needed. Germanium and gallium occur in relatively high proportions and mainly as water soluble and oxide species, respectively in the Puertollano Integrated Gasification Combined Cycle (IGCC) fly ash. Both the speciation and concentrations of Ge and Ga in this IGCC FA allowed starting research for developing extraction methods. High but not regular extraction yields were achieved in previous investigations. The aim of this research work is focused on the optimisation of Ge and Ga extraction conditions from IGCC FA for its feasible industrial application regardless the operational conditions of the IGCC plant. To this aim, first the daily, monthly, and yearly variability of Ge and Ga concentrations in IGCC fly ashes were determined. Samples were taken during almost 10years. Then a number of extraction tests were carried out using different extractants to cover a wide range of extraction conditions (acid, alkaline, complexant, reducing and oxidising), on IGCC FA samples produced under different operating conditions. High and regular Ge extraction yields (up to 83% after 2h leaching period) may be achieved using a weak acid solution. Gallium yielded up to 70 and 64% extraction after a 24h leaching period using a weak acid and alkaline solution, respectively. [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 mobility of inorganic pollutants is of key concern for a range of industrial and engineering applications of fly ash produced during the combustion of lignite in power generation. This paper investigates the role that the geochemical features of lignite, the ash composition and the partitioning of elements during combustion play in determining leaching properties of lignite fired by-products. The work is based on surveys on three lignite-fired power plants in Greece. Calcium-rich ashes show a high abatement potential for SO2 and other gaseous pollutants. For most elements, the concentrations in the parent lignite and the ashes follow the same trend. Relative enrichments in Cd, Co, Cr, Cu, Mo, Ni, Pb, U, V, W, Zn fingerprint the regional and local geological settings of the lignite basins. The total and leachable concentrations of highly volatile elements are strongly influenced by the interaction with ubiquitous free lime. A broad array of elements is highly insoluble in alkaline ash, while a few oxyanionic-forming elements display substantial mobility. Their mode of occurrence in the parent lignite plays a primary role in the leaching of combustion ashes. The outcomes of this study may assist in addressing the impact of co-firing high ash or high Ca alternative fuels on the leaching properties of combustion by-products. [Copyright &y& Elsevier]

In this study the purity of the germanium end-products obtained by two different precipitation methods carried out on germanium-bearing solutions was evaluated as a last step of a hydrometallurgy process for the recovery of this valuable element from the Puertollano Integrated Gasification Combined Cycle (IGCC) fly ash. Since H2S is produced as a by-product in the gas cleaning system of the Puertollano IGCC plant, precipitation of germanium as GeS2 was tested by sulfiding the Ge-bearing solutions. The technological and hazardous issues that surround H2S handling conducted to investigate a novel precipitation procedure: precipitation as an organic complex by adding 1,2-dihydroxy benzene pyrocatechol (CAT) and cetyltrimethylammonium bromide (CTAB) to the Ge-bearing solutions. Relatively high purity Ge end-products (90 and 93% hexagonal-GeO2 purity, respectively) were obtained by precipitating Ge from enriched solutions, as GeS2 sulfiding the solutions with H2S, or as organic complex with CAT/CTAB mixtures and subsequent roasting of the precipitates. Both methods showed high efficiency (>99%) to precipitate selectively Ge using a single precipitation stage from germanium-bearing solutions. [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]

Abstract: The phase-mineral and chemical composition of six fractions recovered from two fly ashes (FAs) produced in the Soma power station (Turkey) was characterized to predict their possible environmental concerns and potential utilization directions. A combination of conventional separation procedures including sieving, hand picking, sink–float and magnetic separations, as well as leaching and evaporation, was used to isolate the following fractions: (1) char concentrates (CCs); (2) light fractions (<1 g cm−3) (LFs); (3) water-soluble residues (WRs); (4) magnetic fractions (MFs); (5) nonmagnetic coarse-grained fractions (>63 μm) (NCFs); and (6) nonmagnetic fine-grained fractions (<63 μm) (NFFs). CCs (3.3–3.4%) are composed of char (61–68%) and some inorganic phases, and are highly enriched in U>S>Mn>Mo>Fe>Sb. LFs (0.4–0.8%) contain porous cenosphere, spongy, and vesicular char types (21–54%) impregnated by calcite, anhydrite, portlandite, and clay minerals. These fractions show high concentrations of Sb>Se>As. WRs (1.7–2.6%) consist of gypsum, portlandite, Ca oxalate, and calcite (92–98%), and are highly enriched in water-soluble Sb>Mo>S>Ca. The greatest amounts (1–37%) leached from FAs reveal Sb>Mo>S>Ca>Sr>Se>(B, Na)>Li. MFs (1.4–2.3%) are concentrated in magnetite, hematite, and Fe-spinel (31–39%), and are highly enriched in Mn>Fe>Co>Cu>Ni>Zn>(Mo, Yb)>(Lu, Tm, Y)>(Er, Ho, Mg)>Sb. NCFs (49–56%) include mostly coarse-grained glass, quartz, calcite, and mullite, and these are the poorest in trace elements fractions. NFFs (39–47%) contain dominantly fine-grained glass, calcite, quartz, char, and mullite, and are slightly enriched in some chalcophile elements. Possible environmental concerns are related mainly to the trace element mobility in WRs, LFs, and CCs, while the potential utilization directions are connected mostly with the composition of MFs, WRs, CCs, LFs, and NFFs. [Copyright &y& Elsevier]

Abstract: The phase–mineral and chemical composition of feed coals (FCs) and their bottom ashes (BAs) and fly ashes (FAs) produced in the Soma thermo-electric power station (TPS), Turkey, was characterized. FCs are high-ash Soma subbituminous coals abundant in moisture and Ca, and depleted in S. The inorganic composition (in decreasing order of significance) of FCs includes calcite, quartz, kaolinite, illite+muscovite, chlorite, plagioclase, gypsum, pyrite, montmorillonite, K-feldspar, dolomite, siderite, ankerite, opal, and volcanic glass. The results for 57 elements studied show that Ca>Nb>Cs>(V, Li) have significantly higher contents in FC ashes than the respective Clarke values for coal ashes. The water-soluble residues isolated from FCs include gypsum, calcite, inorganic amorphous matter, Ca–Mg–Na–K phase, and opal. These residues are enriched in Na>Se>S>B>Mg>Mo>Sr>Ca>K. The phase–mineral composition of BAs and FAs includes mainly glass, quartz, char, mullite, plagioclase, calcite, and portlandite; and, to a lesser extent, illite+muscovite, melilite, hematite, anhydrite, lime, cristobalite, kaolinite, and magnetite. Minor amounts of K-feldspar, dolomite, ankerite, Fe-spinel, gypsum, and Ca–K–Na phase also occur in BAs and FAs. FAs are enriched in inorganic matter, glass, cristobalite, mullite, Fe oxides, lime, and anhydrite, and depleted in mineral matter, char, quartz, clay minerals, melilite, portlandite, and carbonates in comparison with BAs. Only Se is significantly enriched in BAs and FAs compared to FC ashes. Most of the trace elements (in particular As, Bi, Cd, Ge, Pb, Sn, Tl, and W) are more abundant in FAs, while BAs are more enriched in Ca, Cs, Fe, Ho, Mn, P, Sc, Se and Tb. Significant percentages (11–59%) of elements initially present in FCs, namely S>Sb>Sn>Ta>Mo>Bi>Zn>Ni>Na>(Lu, Tm)>B, were emitted by stack emissions and not captured by the cleaning equipment in the Soma TPS. Some genetic features, properties, possible environmental concerns, and potential utilization directions related to FCs, BAs, and FAs are also discussed. [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]

The sorption of phosphate by K-zeolites synthesized from fly ash (FA) by hydrothermal conversion is investigated in this study. The aim is the synthesis of Ca bearing K-zeolites to recover phosphate from urban and industrial wastewater effluents. The loaded zeolites are considered as a by-products rich in essential nutrients such K and P (KP1) with a potential use as slow release fertilizer. A number of synthesis conditions (temperature, KOH-solution/FA ratio, KOH concentration, and activation time) were applied on two FA samples (FA-TE and FA-LB) with similar glass content but different content of crystalline phases, to optimize the synthesis of a zeolitic sorbent suitable for the subsequent phosphate uptake. Merlinoite and W rich zeolitic products synthesized from FA-LB and FA-TE were found to have sorption properties for phosphate removal. A maximum phosphate sorption capacity of 250 mgP-PO 4 /g and 142 mgP-PO 4 /g for the zeolitic products selected (KP1-LB and KP1-TE, respectively) was achieved. The dominant phosphate sorption mechanism, in the pH range (6–9) of treated wastewater effluents, indicated that sorption proceeds via a diffusion-controlled process involving phosphate ions coupled with calcium supply dissolution from K-zeolitic products and subsequent formation of brushite (CaHPO 4 2H 2 O(s)). The phosphate loaded sorbent containing a relatively soluble phosphate mineral is appropriate for its use as a synthetic slow release fertilizer. The simultaneous valorisation of fly ash waste and the P recovery from treated wastewaters effluents, (a nutrient with scarce natural resources and low supply) by obtaining a product with high potential for land restoration and agriculture will contribute to develop one example of circularity. Unlabelled Image • Activated K zeolites were produced from two fly ash. • Ca bearing K-zeolites, Merlinoite and W rich zeolitic were synthetized. • Ca-bearing K-Zeolites are suitable carriers to recover P from wastewater. • Phosphate removal process by Ca-bearing K zeolites involves the formation of (CaHPO 4 (s)). • Brushite (CaHPO 4 (s)) has suitable properties as a slow-release fertilizer. [ABSTRACT FROM AUTHOR]

Processing granitoid rock for civil engineering, countertops, and paving generates sub-economical (transportation costs exceed their retail value) granite powder sludge. This paper evaluates the possibility of mixing granite waste (GW) produced at the Spanish quarries of Galicia with a second sub-economical substance, Class F coal fly ash (FA <20 wt% CaO). The GW would reduce the leachability of toxic trace elements enriched in Colombian fly ashes and form a sand-like product that could serve as a substitute product and would reduce the costs in industrial concrete and civil engineering projects. To investigate both the capability of the GW to reduce FA leaching (by physical adsorption) and the potential use of the aggregate product as a partial substitute in industrial concrete, the physical (e.g. morphology, crystallographic patterns, and surface area), mineralogical, and chemical (including leachability and chemical composition) properties of the aggregate product were tested. Moreover, properties of the concrete (compressive strength, ion penetration, workability, and electron microscope scanning results (SEM)) were also analyzed. The use of the end scrubbed product in the concrete mixture was found to enhance the performance of the concrete mixture, reducing the leaching of the hazardous elements, and improving the concrete produced. Image 1 • Evaluate the potential of using coal fly ashes and granitoid waste powder as partial substitute to natural sand in concrete. • Fixation process: aluminate/silicate anions of the fly ash–Ca2+ as mediators-silicate anions of the granitoid waste powder. • End products (aggregates and concrete) are considered to have better performances and were found as non-hazardous. • Original method could reduce environmental pollution by reducing use of natural sources, waste storing and energy demand. [ABSTRACT FROM AUTHOR]