Synthesis and characterization of novel chromium pillared clays

New chromium pillared clays of basal spacing 2.45 nm were synthesized and characterized. The chromium oligomers used for intercalation were prepared by quick addition of base and acid to Cr(III) monomeric solutions followed by reflux. The synthesized clays exhibit increased BET surface area and higher micropore volume compared to clays with lower galleries, pillared either by smaller Cr(III) oligomers or by Cr(III) monomers. Important parameters affecting the d0 0 1 basal spacing were studied, e.g. the pH of the pillaring solution, the intercalation time, the chromium concentration and the counter-anion present in the chromium solutions. Scanning electron micrographs were acquired to demonstrate changes of the clay texture before and after pillaring. The thermal behavior of the synthesized clays was also examined. © 2004 Elsevier B.V. All rights reserved

Clay-catalyzed phenomena of cationic-dye aggregation and hydroxo-chromium oligomerization

Higher dye aggregates, organized in layers, were catalytically obtained by intercalating C.I. Basic Blue 41 into montmorillonite and bentonite at very high dye:clay ratios, i.e., larger than 200% of the cation exchange capacity (CEC). Further oligomerization of the chromium oligomers, inserted into montmorillonite intercalated with hydroxo-chromium complexes, was also recognized as clay-promoted. Formation of higher agglomerates proceeding through interactions with the host aluminosilicate suggests that the clays act as aggregation catalysts equally with organic and inorganic compounds. Scanning electron microscopy (SEM) was employed to examine the microstructure of the hybrid materials constructed; both high-order assemblies of the monoazo-cationic dye and higher Cr(III) oligomers characteristically modify the surface morphology of the intercalated clays. © 2009 Elsevier Inc. All rights reserved

Sorption characterization of a cationic dye retained by clays and perlite

The adsorption of C.I. Basic Blue 41 onto raw perlite, expanded perlite, bentonite and montmorillonite was characterized. Sorption experiments demonstrated that the clays are more efficient adsorbents compared with the perlites but their dye retention is less increased with pH and temperature. Higher dye aggregates are formed in all aluminosilicates due to the existence of adsorption locations that promote the agglomeration of the dye. The presence of dye monomers in bentonite indicates a second type of adsorption sites impairing the dyestuff aggregation. Seven adsorption models were applied to the experimental data; the obeying of the Langmuir and Harkins-Jura isotherms was better for the clays while the Freundlich, Halsey, Henderson, BET and Smith models fitted more successfully to the perlites. The applicability of the adsorption equations was correlated with the uniformity, homogeneity and distribution of the adsorption sites, the incorporation of self-assembled dye aggregates and the formation of self-organized multilayers of dye into the adsorbents. Thermodynamic quantities that characterize the sorption phenomena, i.e., enthalpy, entropy and free energy change of the adsorption, were calculated leading to conclusions on the efficiency of the adsorbing substrates and the properties of the sorbent-dye systems. © 2008 Elsevier Inc. All rights reserved

Evaluation of low-rank coals as raw material for Fe and Ca organomineral fertilizer using a new EDXRF method

A rapid and reliable method for analyzing Fe and Ca in low-rank Greek coals was developed. The presence of Fe and Ca is of importance regarding the potential use of these coals as raw material for organomineral fertilizers. Samples were collected from the main Greek lignite deposits and standards were prepared using Atomic Absorption Spectroscopy (AAS), which were also employed in the Energy Dispersive X-ray Fluorescence (EDXRF) method. The new method offers the advantages of being timesaving, non-destructive and can be easily incorporated in a fertilizer production line. Analysis of low-rank Greek coals demonstrated a significant Fe and Ca content ranging from 0.15 to 1.97 wt.% for Fe and from 0.04 to 2.51 wt.% for Ca. When both EDXRF and AAS techniques were applied, the Fe and Ca concentration values differed less than 5%, demonstrating that both techniques are reliable for low-rank coals in the above concentration range. These EDXRF results may be used as a preliminary test regarding the application of Greek coals in organomineral fertilizer production, given that in these coals iron and calcium are the most abundant metals. © 2008 Elsevier B.V. All rights reserved

Interactions between C.I. Basic Blue 41 and aluminosilicate sorbents

Four aluminosilicate sorbents (montmorillonite, bentonite, raw perlite, and expanded perlite) were employed for retention of the cationic dye C.I. Basic Blue 41. Interactions between the clay and the dyestuff were investigated at several temperatures and clay:dye ratios. The mechanism behind the adsorption involves the formation of H-aggregates of the dye on both clays, followed by dye migration into the interlayer in the case of montmorillonite. Time-dependent absorbance spectra revealed the presence of various dye species in montmorillonite. Introduction of the dye molecules into the interlamellar space occurs more rapidly in bentonite than in montmorillonite. The dye molecules inserted between the clay leaves adopt different orientations and, eventually, stack in layers at increased dye loadings for both montmorillonite and bentonite. Higher dye aggregates are then present as suggested by diffuse reflectance spectroscopy. Dye sorption on both raw and expanded perlite proceeds via H-aggregate formation as well. © 2005 Elsevier Inc. All rights reserved

Chemistry of metal-humic complexes contained in Megalopolis lignite and potential application in modern organomineral fertilization

Lignite samples from two deposits located in the Megalopolis Basin, Southern Greece, were evaluated for their potential applicability as raw materials for the production of organomineral fertilizers. Fundamental chemical analyses were carried out to demonstrate high humic substances and metal contents. To determine their relative distribution in the Megalopolis lignite extract, eight elements, namely Na, K, Cd, Mn, Mg, Pb, Zn, and Cu, were studied both in H2O and in Na4P2O7/NaOH solutions. The behavior of these metals showed significant variations; Zn, Pb, Cd, and Cu associate mostly to the humic substances and proved scarce in the water extract. Contrarily, K and Mg gave a significantly low total yield in the Na4P2O7/NaOH solution, while Mn was classified among the least extracted elements. Further enrichment of Megalopolis humic substances in these metals was achieved; Pb and Mg proved the most and least retained metal, respectively. Decomplexation titration curves of humic matter saturated with these metal ions demonstrated that novel organomineral fertilizing materials may develop based on optimized metal ion and humate contents, which can retain metals in a soluble form within a wide pH range. Formation of complexes between humic substances and Zn, Cd, and Mg was clearly indicated. © 2009 Elsevier B.V. All rights reserved

Fe(III)-humate complexes from Megalopolis peaty lignite: A novel eco-friendly fertilizer

Fe(III)-humate complexes were synthesized from Greek peaty lignite of the Megalopolis Basin. The preparation was carried out under mild and low-energy conditions producing a biodegradable, eco-friendly and effective material to substitute the synthetic chelates Fe-EDDHA, Fe-EDTA and Fe-DTPA. Due to both the existing expanded configuration of the humic substances (that make binding sites accessible to the metal ions) and the ionization of functional groups, alkaline environment facilitates the association between Fe(III) ions and the lignite-derived humic substances. UV-vis and IR spectra revealed coordination of the metal ions with the carboxylic and phenolic groups of the oxygen-rich humic substances. Fe(III)-humate complexes were proved stable in a wide pH range similar to Fe-EDDHA synthetic chelates. Furthermore, the presence of K+ and humic matter increases the agronomic value of this material establishing alternative applications for Megalopolis peaty lignite. © 2009 Elsevier Ltd. All rights reserved