F. Plana

Synthesis of zeolites from coal fly ash: an overview

Coal combustion by-products production in USA and EU is estimated in around 115 million tons per year. A large portion of this production is accounted for the coal fly ash (CFA). Cement and concrete manufacturing consumes most of the CFA produced. Zeolite synthesized from CFA is a minor but interesting product, with high environmental applications. Zeolites may be easily obtained from CFA by relatively cheap and fast conversion processes. This paper provides an overview on the methodologies for zeolite synthesis from CFA, and a detailed description of conventional alkaline conversion processes, with special emphasis on the experimental conditions to obtain high cation exchange capacity (CEC) zeolites. Zeolitic products having up to 3 meq g 1 may be easily obtained from high-glass CFA by direct conversion. A review of potential applications of different zeolitic products for waste water and flue gas treatment is also given. The examination of the data presented by different authors reveals that one of the main potential application of this material is the uptake of heavy metals from polluted waste waters. The zeolitic material may be also used for the uptake of ammonium from polluted waters but high concentrations of other cations may considerably reduce the ammonium absorption efficiencies due to ion competition. Some of the zeolites synthesized may be also used as molecular sieves to adsorb water molecules from gas streams or to trap SO2 and NH3 from lowwater gaseous emissions. D 2002 Elsevier Science B.V. All rights reserved.

Synthesis of zeolites from fly ash at pilot plant scale. Examples of potential applications

This study focuses on the synthesis of zeolites from Spanish fly ashes at laboratory (g and kg sample size) and pilot plant (metric ton sample size) scales, and on the potential application of the synthesized zeolitic material. To this end, eleven Spanish fly ashes were selected and characterized in detail. A matrix of experimental parameters was built to optimize the synthesis of mono-mineral zeolite products from the different fly ashes. This was achieved by using Parr digestion bombs, KOH and NaOH as activation agents, under experimental conditions ranging from T = 150 to 200°C, t = 3 to 48 h, C = 0.5 to 5 M, P = 4.7 to 15.3 atm, and solution/sample ratio from 2 to 18 ml g 1 . Subsequently, experiments to synthesize NaP1 zeolite were scaled up to kg sample and pilot plant scale. The zeolitic material obtained at these two scales was very similar. The NaP1 zeolite content was estimated as 40%. The major potential applications of the zeolites obtained were tested by determining the cation exchange capacity (CEC) with ammonium and different heavy metals. The results showed CEC values from 160 to 260 meq. 100 g 1 for NaP1, herschelite, KM, linde F and K-chabazite for the majority of the cations investigated. The zeolitic material synthesized at pilot-plant scale yielded the following CECs for these heavy metals: 68 meq. 100 g -1 for Ni 2+ , 90 meq. 100 g -1 for Cd 2+ , 95 meq. 100 g -1 for Zn 2+ , 98 meq. 100 g -1 for Pb 2+ , 110 meq. 100 g -1 for Fe 2+ , 130 meq. 100 g -1 for Ba 2+ , 210 μeq, 100 g -1 for Cu 2+ and 260 meq. 100 g -1 for Cr 3+ .

Extraction of soluble major and trace elements from fly ash in open and closed leaching systems

Abstract This study focuses on the mobility of water-soluble major and trace elements in six Spanish fly ashes using room temperature open and closed and heated (90°C) closed leaching systems in an attempt to reduce the content of undesirable species in coal combustion by-products to increase their potential applications. The leaching trends of the trace impurities are consistent with the dissolution of small solid particles or coatings on the surface of the ash solid phases rather than with the dissolution of a homogeneous glass phase. The leaching rate of the different trace impurities can be arranged in decreasing order as B≥Mo≥Se>Li>Sr≥Cr≥As=Ba=Cd=V>Sn>Rb=Zn≥Cu=Ni=Pb>U>Co>Mn. Although several elements showed increased mobility in the room temperature open leaching system with respect to the closed extraction, the differences obtained for major impurities were not significant with the exception of the extraction ratios obtained for As and V in high lime fly ashes. The extraction ratios were higher for the heated leaching than those obtained for room temperature extraction for the elements Al, Si, K, Na, Ba, Cr, Rb, Sr and V. However, the mobility of major impurities (Ca and Fe) and heavy metals did not increase considerably in the heated extraction (generally

Use of coal fly ash for ceramics : a case study for a large Spanish power station

Abstract Ceramic products with up to 50 wt% of mullite and 16 wt% of feldspars were obtained from binary mixtures of fly ash from the Teruel power station (NE Spain) and plastic clays from the Teruel coal mining district. The firing behaviour of fly ash and the ceramic mixtures was investigated by determining their changes in mineralogy and basic ceramic properties such as colour, bulk density, water absorption and firing shrinkage. To determine the changes on heating suffered by both the fly ash and the ceramic bodies, firing tests were carried out at temperatures between 900 and 1200°C in short firing cycles. The resulting ceramic bodies exhibit features that suggest possibilities for use in paving stoneware manufacture, for tiling and for conventional brickmaking.

Geological controls on the mineral matter and trace elements of coals from the Fuxin basin, Liaoning Province, northeast China

Abstract This study summarizes the results of geological, petrographical, geochemical and mineralogical studies performed to determine the geological controls on coal quality of the Fuxin deposit, Liaoning Province, in northeast China. The study is focused on the Haizhou mine, which currently mines a coal-bearing clastic Lower Cretaceous series affected by a diabase intrusion. Three major coal seams are differentiated: the Taiping, the Middle and the Shunjawan. Fuxin coal is a high quality coal with low ash and sulphur contents (4.0 to 18.0% HTA and 0.3 to 0.8%S tot ) and high calorific value (5600 to 7500 cal/g, as received basis). Coal impurities (both major and trace elements) are at very low concentrations; only a high Mn concentration (up to 8600 ppm) was detected. The rank of Fuxin coal (mainly high volatile B-bituminous coal) is clearly influenced by the diabase intrusion, which has induced the formation of natural coke from coal. Natural coke surrounds the diabase dykes and sills with a thickness ranging from a few centimetres up to 1.5 m. In addition, a wide aureole made up of high volatile A-bituminous coal formed around the coke. The diabase intrusion was not a major source of elemental mobilization, Mn being the only element clearly enriched in the coal (by 1 to 2 orders of magnitude). However, major changes in major and trace element distribution (affinities) were induced in the coal by the intrusion. The geochemical study revealed that these changes were the consequence of the mobilization of organic-, sulphide- and carbonate-associated elements.

Mineralogy and geochemistry of coal from the Liupanshui mining district, Guizhou, south China

Abstract This study focuses on the geochemistry and mineralogy of 23 coal seams from the Shuicheng and Luizhi coal fields from the Late Permian Liupanshui coal mining district, in the west of Guizhou province in southern China. Coal rank ranges widely from high volatile bituminous to low volatile bituminous and anthracite. Major mineral phases present in the Liupanshui coal are kaolinite, quartz, pyrite, and calcite. Traces of other primary minerals are marcasite, gypsum, and dolomite. The Shuicheng coal usually has higher kaolinite and quartz contents than the Luizhi coal. Marcasite occurs indiscriminately in the different coal seams without a clear distribution pattern. The presence of other minerals, such as rutile, anatase, tourmaline, zircon, and phosphates, was also noted. The total sulphur content of Liupanshui coals is higher in the marine-influenced coal seams (up to 7.5% dry), and lower in the nonmarine-influenced coals (as low as 0.3%). In the Luizhi coal field, the coal is characterised by a high sulphur and iron content, whereas in the Shuicheng coal field, contents varied from low to high, depending on the coal seams. An inverse geochemical distribution was detected for the mean contents of Ca–Mn–Ge, with lower contents in the Luizhi coal field. The Liupanshui coals are characterised by relatively high contents of Mn, V, Cu, Li, Zr, Nb, Hf, Ta, Tl, Th, and U, when comparing with the usual concentration ranges in bituminous coals. Trace elements in coals from Liupanshui showed narrow variations in their concentrations among coal seams and coal. Three major trace element affinities (aluminium-silicates, sulphides, and carbonates) accounted for the occurrence and distribution of most of the elements studied were determined.

Identification and chemical characterization of industrial particulate matter sources in Southwest Spain

Abstract A detailed physical and chemical characterization of coarse particulate matter (PM10) and fine particulate matter (PM2.5) in the city of Huelva (in Southwestern Spain) was carried out during 2001 and 2002. To identify the major emission sources with a significant influence on PM10 and PM2.5, a methodology was developed based on the combination of: (1) real-time measurements of levels of PM10, PM2.5, and very fine particulate matter (PM1); (2) chemical characterization and source apportionment analysis of PM10 and PM2.5; and (3) intensive measurements in field campaigns to characterize the emission plumes of several point sources. Annual means of 37, 19, and 16 μg/m3 were obtained for the study period for PM10, PM2.5, and PM1, respectively. High PM episodes, characterized by a very fine grain size distribution, are frequently detected in Huelva mainly in the winter as the result of the impact of the industrial emission plumes on the city. Chemical analysis showed that PM at Huelva is characterized by high PO4 3− and As levels, as expected from the industrial activities. Source apportionment analyses identified a crustal source (36% of PM10 and 31% of PM2.5); a traffic-related source (33% of PM10 and 29% of PM2.5), and a marine aerosol contribution (only in PM10, 4%). In addition, two industrial emission sources were identified in PM10and PM2.5: (1) a petrochemical source, 13% in PM10 and 8% in PM2.5; and (2) a mixed metallurgical-phosphate source, which accounts for 11–12% of PM10 and PM2.5. In PM2.5 a secondary source has been also identified, which contributed to 17% of the mass. A complete characterization of industrial emission plumes during their impact on the ground allowed for the identification of tracer species for specific point sources, such as petrochemical, metallurgic, and fertilizer and phosphate production industries.

Petrology, mineralogy and geochemistry of the Permian and Triassic coals in the Leping area, Jiangxi Province, southeast China

Abstract Permian and Triassic coals from a series of mines in Jiangxi Province, China, exhibit a number of unusual geochemical, mineralogical, and petrographic characteristics. The high volatile bituminous Permian coals have high concentrations of the suberinite-like maceral “barkinite.” The origin, and even the distinct character, of “barkinite” are in dispute and, consequently, it has not been recognized as a distinct maceral by the International Committee for Coal and Organic Petrology (ICCP). The Permian bituminous coals have relatively high concentrations of pyrite and marcasite. Otherwise, detrital minerals dominate their geochemistry. The Triassic coals, all from one mine complex, have higher rank (a Permian coal is also mined). Most samples straddle the low volatile bituminous/semi-anthracite boundary. The one semi-anthracite-rank Permian coal shows signs of incipient coking. A Triassic coal in the same fault block is coked by an igneous intrusions found in the mine. The coals have, in general, been dolomitized. Aside from the geochemical imprint of the dolomitization, trace element associations suggesting a contribution from a detrital mineral assemblage dominate the coals.

Geochemistry, mineralogy, and technological properties of the main Stephanian (Carboniferous) coal seams from the Puertollano Basin, Spain

This study is focused on the occurrence and distribution of mineral matter and major and trace elements in the high volatile bituminous coal from Puertollano (south-central Spain). The relationship between ash behaviour and inorganic composition, as well as the possible formation of fouling and slagging deposits in boilers during the conversion process, were investigated. The Puertollano coals do not exhibit plastic properties, despite their rank, probably because of their high ash and inertinite contents. The Puertollano coal has medium to low total S content (0.48% to 1.63% db, with a mean of 1.0% db) and is characterised by relatively high contents of Si, Pb, Sb, and Cs. Some elements such as As, Cd, Co, Cr, Cu, Ge, Li, Mn, Ni, W, and Zn are also present in relatively high contents. The enrichment in a number of heavy metals could be attributed to the common sulphide ores occurring near the Puertollano coal deposit. The following trace elements affinities are deduced: (a) sulphide affinity: As, Co, Cd, Cu, Ni, Sb, Tl, and Zn; (b) aluminum–silicate affinity: K, Ti, B, Co, Cr, Cs, Cu Ga, Hf, Li, Nb, Rb, Sn, Ta, Th, V, Zr, and LREE; (c) Carbonate affinity: Ca, Mg, Mn, and B; (d) organic affinity: B. The very high Si levels and the anomalous enrichment in Cs, Ge, Pb, Sb, and Zn shown by the Puertollano coals account for the high contents of these elements in the Puertollano fly ash when compared with the other Spanish coal fly ashes. The chemical composition of the high temperature ash (HTA) is consistent with the trend shown by the ash fusion temperatures (AFT) and also with the predictive indices related to slagging and fouling propensities. Thus, the ash fusion temperatures increase with high values of Al2O3 as well as with the decrease in Fe2O3, CaO, and MgO.

Determination of element affinities by density fractionation of bulk coal samples

Abstract A review has been made of the various methods of determining major and trace element affinities for different phases, both mineral and organic in coals, citing their various strengths and weaknesses. These include mathematical deconvolution of chemical analyses, direct microanalysis, sequential extraction procedures and density fractionation. A new methodology combining density fractionation with mathematical deconvolution of chemical analyses of whole coals and their density fractions has been evaluated. These coals formed part of the IEA-Coal Research project on the Modes of Occurrence of Trace Elements in Coal. Results were compared to a previously reported sequential extraction methodology and showed good agreement for most elements. For particular elements (Be, Mo, Cu, Se and REEs) in specific coals where disagreement was found, it was concluded that the occurrence of rare trace element bearing phases may account for the discrepancy, and modifications to the general procedure must be made to account for these.