Zdeněk Klika

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.

Effect of boiler output on trace element partitioning during coal combustion in two fluidised-bed power stations

Abstract The main aim of this study was a detailed comparison of trace element partitioning during combustion of bituminous coal and lignite in two circulating fluidised-bed units at 40 and 100% boiler output. The elements considered here are: S, Cl, Br, V, Cr, Co, Ni, Cu, Zn, Ge, As, Se, Sn, Sb, W, Hg, and Pb. The trace element concentrations in combustion products show enrichment of most of the elements in fly ash related to bottom ash as well as the slight element enrichment in fly ash at 40% boiler output compared with the 100% output. Using an element balance calculation the proportion of each element in bottom ash, fly ash and emissions was determined. Results showed that at both boiler outputs the highest relative percentages of elements that entered into emissions were Hg and Cl.

Fluorescence of reduced charge montmorillonite complexes with methylene blue: Experiments and molecular modeling

The intensity of fluorescence of montmorillonites fully saturated by methylene blue (MB) is very poor due to energy dissipation in MB aggregates. A series of reduced charge montmorillonites (RCM) were prepared from Na-homoionic SWy and Ca homoionic SAz with the aim to decrease the MB aggregation. Fine tuning MB adsorption degree by charge reduction and MB concentration enabled controlled production of different dye species from aggregates via dimers to monomers. It was shown that the intensity of the fluorescence of low-loaded MB-RCM complexes is enhanced by several orders of magnitude with respect to dye-saturated original montmorillonites. XRD analyses, molecular modeling, and diffuse reflectance spectroscopy revealed that low MB-loaded RCMs are very probably adsorbed mainly on the external montmorillonite surface as isolated dye molecules. Such a state cannot be achieved in the solid state without very careful tailoring of the host-guest interaction.

Molecular simulations of montmorillonite intercalated with aluminum complex cations. Part I: Intercalation with [Al13O4(OH)(24+x)(H2O)(12−x)]((7−x)+)

AbstractThe structure of montmorillonite intercalated with [Al13O4(OH)24+x(H2O)12−x](7−x)+ cations (Al13(7− x)+ for short), where x = 0,2 an 4, has been studied using the Cerius2 modeling environment. The Crystal Packer module used in the present study takes into account only the nonbonded interactions between the silicate layer and the Keggin cations. Minimization of the total sublimation energy led to the following conclusions: the structure of the interlayer (that is, the orientation of Keggin cations and the basal spacing) depends on the charge of cations (that is, on the degree of hydrolysis, x). The values of basal spacings in the range 19.38–20.27 Å have been obtained, depending on the charge and arrangement of cations in the interlayer. The dominating contribution to the total sublimation energy comes from the electrostatic interactions. Translations of Al13(7−x)+ cations along the 2:1 layers give only small fluctuations of the total sublimation energy and basal spacings. No preference for the position of Al13(7− x)+ cations in the interlayer of montmorillonite was found during translation along the 2:1 layers. This result confirmed the inhomogeneous distribution of cations in the interlayer and turbostratic stacking of layers.

The adsorption of methylene blue on montmorillonite from acid solutions

Abstract The adsorption of methylene blue (MB) on montmorillonite from acid solutions has not yet been studied in detail. In this paper the adsorption of this dye on Ca/SAz montmorillonite from 0.32, 0.80 and 1.60 M HCl solutions at ambient temperature and after 2 hours leaching was carefully studied and evaluated. Under the above conditions the MB/SAz intercalates formed are practically insoluble. In contrast to the adsorption of methylene blue on montmorillonite from aqueous solutions, the adsorption from acid solutions consists of two adsorption waves. The intercalated samples from the first and second waves were studied using X-ray powder diffraction (XRD), FTIR, Vis spectroscopy, and scanning electron microscopy (SEM) equipped with a microprobe system. The adsorption of MB in the first wave is attributed to ion exchange of the dye cationic species (MB+, MB22+, H-aggregates, MBH2+ and H+) for the original interlayer cations of montmorillonite. The percentages of MBH2+ and H+ based on total adsorbed MB were estimated for varying HCl concentrations. The second adsorption wave is linked to the precipitation of MB species on the outer MB/SAz surface.

Effect of unburned carbon content in fly ash on the retention of 12 elements out of coal-combustion flue gas

The aim of this study was to evaluate whether unburned carbon particles present in fly ash can help in the retention of S, Cl, Br, As, Se, Cu, Ni, Zn, Ga, Ge, Rb, and Pb out of flue gas during the coal combustion at fluidised-bed power station where the coal was combusted along with limestone. The competitive influence of 10%-25% CaO in fly ashes on the distribution of studied elements was studied as well to be clear which factor governs behaviour of studied elements. Except of S (with significant association with CaO) and Rb and Pb (with major affinity to Al2O3) the statistically significant and positive correlation coefficients were calculated for the relations between unburned carbon content and Br (0.959), Cl (0.957), Cu (0.916), Se (0.898), Ni (0.866), As (0.861), Zn (0.742), Ge (0.717), and Ga (0.588) content. The results suggest that the unburned carbon is promising material in terms of flue gas cleaning even if contained in highly calcareous fly ashes.

Molecular simulations of montmorillonite intercalated with aluminum complex cations; Part II, Intercalation with Al(OH) 3 -fragment polymers

The Crystal Packer module in the Cerius2 modeling environment has been used to study the structure of montmorillonite intercalated with Al(OH)3-fragment (gibbsite-like) polymers. Basal spacings in gibbsite-like polymers arranged in 2 layers in the interlayer of montmorillonite varied in the range 19.54–20.13 Å, depending on the type and arrangement of Al(OH)3 fragments. The inhomogeneous distribution of intercalating species in the interlayer and, consequently, the turbostratic stacking of layers has been found for gibbsite-like polymers as well as in the case of Keggin cations (Čapková et al. 1998). The dominating contribution to the total sublimation energy comes from electrostatic interactions for both intercalating species, gibbsite-like polymers and Keggin cations.

Enhanced fluorescence of selected cationic dyes adsorbed on reduced-charge montmorillonite

Abstract The aggregation of three cationic dyes (CD), crystal violet (CV), Nile blue (NB) and rhodamine B (RB) in aqueous solution was studied by visible absorption spectrophotometry and compared with methylene blue (MB). The distribution of the dye species (monomers, dimers, trimers, and tetramers) in aqueous solutions with different concentrations of dye was calculated using equilibrium stepwise aggregation constants Kn. These cationic dyes were intercalated into montmorillonite (SAz-1) and its reduced charge form (RC-SAz(210)) prepared by heating lithium montmorillonite (Li/SAz-1) at 210°C. The fluorescence of fully saturated CD/SAz and low-CD loaded CD/RC-SAz(210) complexes was studied. Visible absorption spectra of CD aqueous solutions and visible absorption spectra and X-ray diffraction patterns (d001) of the CD/SAz and CD/RC- SAz(210) solid complexes were obtained and evaluated. Large fluorescence intensities were found for CV/RC-SAz(210) and NB/RC-SAz(210) complexes in the same way as for the complex of methylene blue with reduced-charge montmorillonite MB/RCM(210) described previously.

Calculation of element distributions between inorganic and organic parts of coal

A procedure for calculation of the quantitative element distribution between inorganic and organic parts of coal is proposed. Individual coal fractions with different contents of inorganic matter are prepared from the original coal sample and the following input data are determined for each coal fraction: (1) weight of the fraction; (2) concentration of elements for the distribution to be calculated; (3) sum of crystalline phases and the ash content. Furthermore, during the procedure the following assumptions were used: (a) non-crystalline phases in coal are neglected; (b) concentrations of elements bonded to the organic part of coal are constant and independent of the content of crystalline phases in individual coal fractions; (c) the relation between the mass of the inorganic part of coal fractions and the concentration of elements bonded on the inorganic part can be approximated by a quadratic function. Using two samples of different coals the procedure was applied for calculation of the distribution of Pb, Ge and As between inorganic and organic parts of coal.

Vermiculite as efficient sorbent of CeIII and CeIV

Environmental context Cerium, a Technology Critical Element with many technical, agricultural, and medicinal applications, is increasingly being discharged to the environment. One of the best ways to remove cerium from wastes is its fixation into inexpensive bulk material such as vermiculite. This paper investigates the mechanism of CeIII and CeIV uptake and capture by vermiculite in neutral and acidic aqueous solutions. Abstract This study focussed on the mechanism of CeIII and CeIV uptake on vermiculite (Ver), which has been studied sporadically. Chemical equilibrium and leaching experiments in acid solutions were evaluated using batch experiments and changes of mineral composition were monitored by X-ray powder diffraction analysis. The concentrations of Ce, Na, K, Ca, Mg, Al and Si were determined by atomic emission spectroscopy coupled with inductively coupled plasma (AES-ICP). The data for CeIII uptake on Ver in neutral aqueous solution were fitted both with adsorption and ion-exchange models. The latter, with a calculated selectivity constant =14.30 (L mmol–1)k–1, showed a better fit with experimental data than adsorption models. The uptake of CeIII on Ver at pH 2 was also controlled by intensive leaching of cations from 2:1 layers and therefore these data were not fitted. A much higher uptake of CeIV on Ver (~6 mequiv. g–1, i.e. ~210mgg–1) at pH 2 and 6 in comparison with the cation-exchange capacity of original vermiculite (1.28 mequiv. g–1) was found and explained. With regard to the different rate of CeIV species fixation on Ver, their different CeIV solubility in NaCl solution, aqueous acid solution (pH 2), and 3M H2SO4, three species of CeIV bonded on vermiculite are proposed. They are ion-exchanged CeIV, CeIV–complex 1 and CeIV–complex 2. The CeIV species uptake on Ver was quantitatively determined both for pH 2 and 6. The new findings show a very effective method of cerium uptake, especially from acidic aqueous solutions.