Roberto Juan

Mobility of trace elements from coal and combustion wastes

The mobility of > 30 trace elements from four Spanish coals was investigated using sequential extraction procedures. The total leachable fractions were obtained by comparing the total trace element content in the bulk coal samples with the extractable content. The high-temperature ash of these coals, and the fly ash and slag produced during the combustion of one of the coals in a large power plant, were also investigated to determine the trace element mobilities in the combustion wastes. The results demonstrate that the elements associated with sulfides, sulfates and organic matter in coal show the highest extraction rates (As, B, Be, Mn, Mo, Ni, Pb, Se, Sr, U, V, Y and Zn), while elements with aluminosilicate affinities have lower mobilities. Many elements with organic affinity have a water-leachable fraction. Trace element mobilities in high-temperature ash and in fly ash are very similar. Bearing in mind the conditions used for obtaining the combustion wastes and the behaviour of the trace elements during the sequential extraction, it can be deduced that the most labile elements are associated possibly with oxides (Ge, Mn, Mo, Se, V, W, and Zn) and salts such as sulfates, borates and arsenates. The most refractory phases contain the elements with the lowest extraction rates (Cr, Ga, Rb, Sb, Sn, Th, Zr and REE). Important fractions of the Mo, Sr and V contents are water-extractable and readily exchangeable. The results demonstrate that trace element mobility in coal and combustion wastes depends on the mode of occurrence of these elements and on their behaviour during coal combustion.

Seasonal evolution of suspended particles around a large coal-fired power station: Chemical characterization

Abstract The present work focuses on the seasonal evolution of total suspended particles (TSP) around the Teruel power station in Northeastern Spain. The results show a marked seasonal trend, along the sampling period (July 1995–July 1996), which is characterized by levels of the elements studied in TSP that were higher (up to one order of magnitude) in spring-summer and decreased progressively towards winter. This trend contrasts with the seasonal evolution reported by most of the studies carried out in industrial and urban areas in Central and Northern Europe. The origin of this seasonal TSP trend may be related to: (a) higher summer oxidation which increased levels of secondary TSP; (b) higher convective circulation in summer which raised levels of soil-related particles and primary anthropogenic particles; (c) higher frequency of intrusion episodes of Sahara air masses in summer and spring; and (d) lower aerosol scavenging potential in summer. A clear grain-size fractionation was observed for the different ions determined. SO 4 2− and NH 4 + were concentrated in the finest grain-size fraction (0.3−0.6 μm); NO 3 − , Cl − , K + , Mg 2+ , Na + and minor amounts of NH 4 + were concentrated in the 1.2−5.0 μm fractions; and Ca 2+ increased with the particle diameter. S-bearing species were (NH 4 ) 2 SO 4 (mascagnite), (NH 4 ) 2 Ca(SO 4 ) 2 · H 2 O (koktaite) and CaSO 4 · 2H 2 O (gypsum). Mascagnite was the dominant species in the finest grain size fraction (0.3−0.6 μm), whereas koktaite was also present in the 0.6−1.2 μm fraction, and gypsum predominated in the other fractions.

Ion exchange uptake of ammonium in wastewater from a Sewage Treatment Plant by zeolitic materials from fly ash

The potential value of zeolitic materials (ZM) obtained from a hazardous waste, such as coal fly ash, for the retention of NH(4)(+) present in liquid effluents from a Sewage Treatment Plant (STP) is studied. A wastewater sample was taken from an STP in Zaragoza (Spain) after conventional treatment at the Plant. The water was treated with different amounts of three ZM: NaP1 zeolite, K-F zeolite and K-Chabazite/K-Phillipsite zeolites all of them in powdered and granulated state. The wastewater was treated by two kinds of processes: continuous stirring batch experiments with powdered ZM, and fixed packed bed of granulated ZM in a column. The powdered materials reduced about 80% of NH(4)(+) from wastewater, even in the presence of Ca(2+), which competes with NH(4)(+) for the cation exchange sites in zeolites. Around 70% of NH(4)(+) reduction was achieved with granulated materials. In both cases, moderate ZM/wastewater ratios had to be used to achieve those results, with K-zeolites slightly less effective in NH(4)(+) retention.

Characterisation of an Egyptian coal by Mossbauer and FT-IR spectroscopy☆ ☆

Six coal samples collected from Maghara Coal Mine, North Sinai, Egypt, at different depths (52–87 m) were characterised by Mossbauer (MS) and Fourier Transform Infrared (FT-IR) spectroscopy. The moisture and ash content and the ultimate analysis are given. The iron minerals were studied by MS. Jarosite (ferric sulphate) and pyrite have been found in the sample taken at 52 m. However, ferrous sulphate and pyrite are present in the other samples. On the other hand, several structural parameters such as Har/Hal and Har/Car were calculated from FT-IR spectra as a function of depth. These parameters give a quantitative determination of the aromaticity, which was found in the range between 0.46 and 0.59, similar to that reported in the literature for subbituminous coals.

Structural changes in humic acids during the coalification process

Abstract Humic acids from four coals, varying in rank from peat to subbituminous coal, have been characterized by elemental analysis, acidic groups, molecular weight, electrophoresis and visible, FT-i.r. and CP/MAS 13C n.m.r. spectroscopy. The humic acids increase in carbon content, molecular weight, condensation degree and aromaticity (fa) with increasing maturation of the parent coals, while the oxygen content decreases with a loss of oxygen functional groups. The presence of lignin-like polymers, poly-saccharides and peptidic materials in humic acids from peat was established using i.r. and 13C n.m.r. spectroscopy. The structural changes observed in humic acids are in agreement with the recognized coalification theory and tend to support the hypothesis of condensation of humic acids into insoluble humin of coal.

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.

Influence of temperature and regeneration cycles on Hg capture and efficiency by structured Au/C regenerable sorbents.

The objective of this work is to evaluate a novel regenerable sorbent for mercury capture based on gold nanoparticles supported on a honeycomb structured carbon monolith. A new methodology for gold nanoparticles deposition onto carbon monolith support has been developed to obtain an Au sorbent based on the direct reduction of a gold salt onto the carbon material. For comparison purposes, colloidal gold method was also used to obtain Au/C sorbents. Both types of sorbents were characterized by different techniques in order to obtain the bulk gold content, the particle size distribution and the chemical states of gold after deposition. The mercury capture capacity and mercury capture efficiency of sorbents were tested in a bench scale facility at different experimental conditions. The regenerability of the sorbents was tested along several cycles of Hg capture-regeneration. High retention efficiencies are found for both types of sorbents comparing their gold content. Moreover, the high retention efficiency is maintained along several cycles of Hg capture-regeneration. The study of the fresh sorbent, the sorbent after Hg exposition and after regeneration by XPS and XRD gives insight to explain those results.

Germanium recovery from gasification fly ash: evaluation of end-products obtained by precipitation methods.

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 H(2)S is produced as a by-product in the gas cleaning system of the Puertollano IGCC plant, precipitation of germanium as GeS(2) was tested by sulfiding the Ge-bearing solutions. The technological and hazardous issues that surround H(2)S 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-GeO(2) purity, respectively) were obtained by precipitating Ge from enriched solutions, as GeS(2) sulfiding the solutions with H(2)S, 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.

Distribution of sulfur in coals of the Teruel mining district, Spain

Abstract The total, pyritic, sulfate and organic sulfur contents of the Albian coals of the Teruel Coal Mining District were determined. The results have enabled us to describe the distributive characteristics of the sulfur in the study area in terms of coal seam, stratigraphic series and sedimentary basin. The accepted influences of the marine depositional environment and the diagenetic evolution of the coal seams on the sulfur content are reflected in this distribution. Moreover, it is demonstrated that this distribution is modified by the massive leaching of sulfates from continental sourcelands towards the sedimentary basin. Owing to this, the coal seams from proximal series without marine influence have a higher sulfur content than the coal seams from the series with a clear marine influence, which is contrary to what has normally been reported.

Characterisation of atmospheric particulates around a coal-fired power station

Abstract The present work focuses on the characterisation of total suspended particulates (TSP) around the Teruel power station in NE Spain with special emphasis on sulphate aerosols due to their acidification potential. The specific objectives are the determination of the seasonal evolution of TSP levels and chemistry, and investigation of possible neutralisation processes for acidic aerosols in the atmosphere. Concentrations of the elements studied in TSP show a marked seasonal trend in the study period (July 1995 to July 1997) characterised by higher levels in spring–summer and relative low levels in autumn and winter. In the case of sulphate aerosols, this pattern may be attributed to higher SO 2 oxidation in the summer and autumn, and to the higher frequency of impact of the emission plume on the surface in this period. A seasonal trend of SO 2 oxidation rates is also found. The soil-related elements show a similar seasonal trend which is interpreted to be a consequence of the typical Mediterranean atmospheric dynamics (Sahara air mass intrusions, convective dynamics, and low precipitation scavenging during summer.) In addition to seasonal variations, a clear grain-size fractionation is observed for the different ions determined. SO 4 2− and NH 4 + are concentrated in the finest grain-size fraction, while NO 3 − , Cl − , K + , Mg 2+ , Na + are concentrated in relatively coarser fractions, and Ca 2+ levels increase with the particle diameter. Neutralisation of sulphate acidic aerosols is carried out by NH 4 + and minor amounts of Ca 2+ . The sulphate neutralising compounds are described by different analytical methods.