The removal of dyes from textile wastewater: a study of the physical characteristics and adsorption mechanisms of diatomaceous earth

The feasibility of using diatomite for the removal of the problematic reactive dyes as well as basic dyes from textile wastewater was investigated. Methylene blue, Cibacron reactive black and reactive yellow dyes were considered. Physical characteristics of diatomite such as pH(solution), pH(ZPC), surface area, Fourier transform infrared, and scanning electron microscopy were investigated. The surface area of diatomite was found to be 27.80 m(2) g(-1) and the pH(ZPC) occurred around pH of 5.4. The results indicated that the surface charge of diatomite decreased as the pH of the solution increased with the maximum methylene blue removal from aqueous solution occurring at basic pH of around (1011). Adsorption isotherms of diatomite with methylene blue, hydrolysed reactive black and yellow dyes were constructed at different pH values, initial dye concentrations and particle sizes. The experimental results were fitted to the Langmuir, Freundlich, and Henry models. The study indicated that electrostatic interactions play an important role in the adsorption of dyes onto diatomite. A model of the adsorption mechanism of methylene blue onto diatomite is proposed. (C) 2003 Elsevier Ltd. All rights reserved.

Sulfur-tolerant NOx storage traps: an infrared and thermodynamic study of the reactions of alkali and alkaline-earth metal sulfates

The sulfur tolerance of a barium-containing NOx storage/reduction trap was investigated using infrared analysis. It was confirmed that barium carbonate could be replaced by barium sulfate by reaction with low concentrations of sulfur dioxide (50 ppm) in the presence of large concentrations of carbon dioxide (10%) at temperatures up to 700 degreesC. These sulfates could at least be partially removed by switching to hydrogen-rich conditions at elevated temperatures. Thermodynamic calculations were used to evaluate the effects of gas composition and temperature on the various reactions of barium sulfate and carbonate under oxidizing and reducing conditions. These calculations clearly showed that if, under a hydrogen-rich atmosphere, carbon dioxide is included as a reactant and barium carbonate as a product then barium sulfate can be removed by reaction with carbon dioxide at a much lower temperature than is possible by decomposition to barium oxide. It was also found that if hydrogen sulfide was included as a product of decomposition of barium sulfate instead of sulfur dioxide then the temperature of reaction could be significantly lowered. Similar calculations were conducted using a selection of other alkaline-earth and alkali metals. In this case calculations were simulated in a gas mixture containing carbon monoxide, hydrogen and carbon dioxide with partial pressures similar to those encountered in real exhausts during switches to rich conditions. The results indicated that there are metals such as lithium and strontium with less stable sulfates than barium, which may also possess sufficient NOx storage capacity to give sulfur-tolerant NOx traps.

Speciation of Rare-Earth Metal Complexes in Ionic Liquids: A Multiple-Technique Approach

The dissolution process of metal complexes in ionic liquids was investigated by a multiple-technique approach to reveal the solvate species of the metal in solution. The task-specific ionic liquid betainium bis(trifluoromethylsulfonyl)imide ([Hbet][Tf2N]) is able to dissolve stoichiometric amounts of the oxides of the rare-earth elements. The crystal structures of the compounds [Eu-2(bet)(8)(H2O)(4)][Tf2N](6), [Eu-2(bet)(8)(H2O)(2)][Tf2N](6)center dot 2H(2)O, and [Y-2(bet)(6)(H2O)(4)][Tf2N](6) were found to consist of dimers. These rare-earth complexes are well soluble in the ionic liquids [Hbet][Tf2N] and [C(4)mim]- [Tf2N] (C(4)mim = 1-butyl-3-methylimidazolium). The speciation of the metal complexes after dissolution in these ionic liquids was investigated by luminescence spectroscopy, H-1, C-13, and Y-89 NMR spectroscopy, and by the synchrotron techniques EXAFS (extended X-ray absorption fine structure) and HEXS (high-energy X-ray scattering). The combination of these complementary analytical techniques reveals that the cationic dimers decompose into monomers after dissolution of the complexes in the ionic liquids. Deeper insight into the solution processes of metal compounds is desirable for applications of ionic liquids in the field of electrochemistry, catalysis, and materials chemistry.

An assessment of the earth pressure coefficient in overconsolidated clays

The determination of the earth pressure coefficient K 0 in a natural clay deposit is a problem of considerable significance in geotechnical engineering. While the methods for evaluation of K 0 are reliable for normally consolidated soils, significant difficulties still exist in evaluating K 0 in overconsolidated clays, given that it is influenced by the stress history of the material, together with the age, structure, mineralogical composition and depositional environment. Indeed, some of these factors are responsible for the soil becoming anisotropic. The existing framework for prediction of K 0 in overconsolidated soils does not account for any influences caused by anisotropy. The work reported in this paper evaluates the validity of a revised relationship between K 0oc and OCR (overconsolidation ratio) using data obtained from laboratory investigations. The tests were performed on reconstituted and undisturbed samples of Belfast Upper Boulder Clay, London Clay and Gault Clay. Tests were also performed on reconstituted samples of kaolin. The values of K 0oc were determined using various approaches, including on-sample measurements. The results have confirmed that reliable predictions of K 0oc can be made using the proposed relationship.

Stochastic analysis of free surface flow through earth dams

This research investigated the unconfined flow through dams. The hydraulic conductivity was modeled as spatially random field following lognormal distribution. Results showed that the seepage flow produced from the stochastic solution was smaller than its deterministic value. In addition, the free surface was observed to exit at a point lower than that obtained from the deterministic solution. When the hydraulic conductivity was strongly correlated in the horizontal direction than the vertical direction, the flow through the dam has markedly increased. It is suggested that it may not be necessary to construct a core in dams made from soils that exhibit high degree of variability.

Rare-earth complexes of ferrocene-containing ligands: Visible-light excitable luminescent materials

The ferrocene-derivatives bis(ferrocenyl-ethynyl)-1,10-phenanthroline (Fc(2)phen) and ferrocenoyltrifluoroacetone (Hfta) have been used to synthesize ferrocene-containing rare-earth beta-diketonate complexes. The complexes [Ln(tta)(3)(Fc(2)phen)] and [Ln(fta)(3)(phen)] (where Ln = La, Nd, Eu, Yb) show structural similarities to the tris(2-thenoyltrifluoroacetonate)(1,10-phenanthroline)lanthanide(III) complexes, [Ln(tta)(3)(phen)]. The coordination number of the lanthanide ion is 8, and the coordination sphere can be described as a distorted dodecahedron. However, the presence of the ferrocene moieties shifts the ligand absorption bands of the rare-earth complexes to longer wavelengths so that the complexes can be excited not only by ultraviolet radiation but also by visible light of wavelengths up to 420 nm. Red photoluminescence is observed for the europium(III) complexes and near-infrared photoluminescence for the neodymium(III) and ytterbium(III) complexes. The presence of the ferrocene groups makes the rare-earth complexes hydrophobic and well-soluble in apolar organic solvents.

Rare-earth nitroquinolinates: Visible-light-sensitizable near-infrared emitters in aqueous solution

Water-soluble, stable, and easily synthesizable 1:4 complexes of rare-earth ions with 8-hydroxy-5-nitroquinolinate ligands have been prepared. These complexes can be sensitized by visible light with wavelengths up to 480 nm and show near-infrared emission in aqueous solution. The incorporation of a nitro group in the quinoline moiety shifts its absorption bands to longer wavelengths and also increases its molar absorptivity by a factor of 2.5, thereby significantly enhancing its light-harvesting power. The presence of the nitro group also increases the solubility of the resulting complexes, making them water-soluble. (c) Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007.

Visible-light-sensitized near-infrared luminescence from rare-earth complexes of the 9-hydroxyphenalen-1-one ligand

The unique absorption properties of the 9-hydroxyphenalen-1-one (HPHN) ligand have been exploited to obtain visible-light-sensitizable rare-earth complexes in 1: 3 and 1: 4 metal-to-ligand ratios. In both stoichiometries (1:3,tris,Ln(PHN)3;1:4, tetrakis, A[ Ln( PHN)(4)], with Ln being a trivalent rare-earth ion and A being a monovalent cation), the complexes of Nd(III),Er( III), and Yb(III) show typical near-infrared luminescence upon excitation with visible light with wavelengths up to 475 nm. The X-ray crystal structures of the tris complexes show solvent coordination to the central rare-earth ion, whereas in the tetrakis complexes, the four PHN-ligands form a protective shield around the central ion, preventing small solvent molecules from coordinating to the rare-earth ion, at least in the solid state.