The removal and recovery of Cr(VI) by Li/Al layered double hydroxide (LDH)

Hexavalent Cr has been identified as one of the toxic metals commonly present in industrial effluents. Among the treatment techniques developed for removing Cr(VI) from waste waters, sorption is most commonly applied, due to its simplicity and efficiency. However, few adsorbents can be recycled and reused cost-effectively. In this study, the removal and recovery of Cr(VI) from water using Li/Al LDH was investigated. The removal of Cr(VI) by Li/Al LDH was evaluated in a batch mode. The results demonstrated that Cr(VI) adsorption onto Li/Al LDH occurs by replacing the Cl(-) that originally exists in the interlayer of the adsorbent. The degree of Cr(VI) adsorption observed for Li/Al LDH was relatively high and the process occurred rapidly; however, a portion of adsorbed Cr(VI) was gradually desorbed, due to the Li de-intercalation of Li/Al LDH. Lithium de-intercalation from Li/Al LDH with interlayer Cl(-) and interlayer Cr(VI) follows the first order kinetics and has the activation energies of 76.6 and 41.5 kJ mol(-1), respectively. The properties of thermal unstability and the high adsorption capacity of Li/Al LDH may lead to the development of an innovative technique for the removal of Cr(VI) from Cr(VI)-containing wastewater. That is, Li/Al LDH may be used as an effective adsorbent for the adsorption of Cr(VI) in an ambient environment. Following the adsorptive process, the adsorbed Cr(VI) may be released, using heated water to treat the Cr(VI)-containing Li/Al LDH particles. Through this hydrothermal treatment of the used adsorbent, Cr(VI) can be recovered and the solid product (gibbsite) can be recycled for further use.     

Strain energy density – a molecular appraisal

Abstract

The interaction potential between two clusters simulating the crack tip on the lattice level is derived in this work. Employing molecules as the building blocks and the Lennard‐Jones potential as the Green's function, the close‐form solution shows that the 1/r‐type of singularity is an intrinsic behavior of the energy field when mutual attraction dominates the lattice interactions. This behavior is now proven, explicitly, to be independent of the constitutive equation of the material.     

EDM electrode manufacturing using RP combining electroless plating with electroforming

This study investigates an effective method for manufacturing electrical discharge machining (EDM) electrodes using the rapid prototyping (RP) system based on electroless plating (nickel plating) and electroforming (copper). This method was shown to finish the development of die-sinking electrical discharge machining (EDM) electrodes, shorten the electrode manufacturing process, decrease the manufacturing duration as well as the cost of electrodes. The electrode prototype was drawn with Pro/E 3D CAD, and the CAD model was then transformed into the stereo lithography (STL) file format. A Zcorp 402 3DP rapid prototyping machine was adopted to make a gypsum powder electrode prototype with a complex appearance. The gypsum material is sealed by resin permeation, enhancing its water-resistance and strength. Electroless plating was then performed to introduce electric conductivity onto the gypsum electrode surface, followed by copper electroforming of the thickness about 1 mm to obtain the EDM electrode. Furthermore, die-sinking electric discharge machining was performed. Test results indicate that no crack was found on the electrode and that the electrical discharge machining effects are promising.     

Antimicrobial polyester

Two N‐halamine siloxane precursors, 5,5‐dimethyl‐3‐(3′‐triethoxysilylpropyl)hydantoin and 3‐(3′‐triethoxysilylpropyl)‐7,7,9,9‐tetramethyl‐1,3,8‐triazaspiro[4.5]decane‐2,4‐dione, have been synthesized and coated onto polyester fiber surfaces. The coated polyester was rendered biocidal after exposure to household bleach solution by converting the heterocyclic precursors to N‐halamine moieties. The thermal properties of these coated polyester samples were determined with differential scanning calorimetry. The chlorinated polyester swatches were challenged with Staphylococcus aureus (ATCC 6538) and Escherichia coli O157 : H7 (ATCC 43895) with contact times ranging from 1 to 30 min. The biocidal testing showed that the chlorinated samples inactivated S. aureus and E. coli O157 : H7 within 5 and 30 min of contact, respectively. Standard washing tests indicated that the chlorinated coated fibers were very resistant to loss of the coating through hydrolyses. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Progressive coding and transmission of digital diagnostic pictures

In radiology, as a result of the increased utilization of digital imaging modalities, such as computed tomography (CT) and magnetic resonance imaging (MRI), over a third of the images produced in a typical radiology department are currently in digital form, and this percentage is steadily increasing. Image compression provides a means for the economical storage and efficient transmission of these diagnostic pictures. The level of coding distortion that can be accepted for clinical diagnosis purposes is not yet well-defined. In this paper we introduce some constraints on the design of existing transform codes in order to achieve progressive image transmission efficiently. The design constraints allow the image quality to be asymptotically improved such that the proper clinical diagnoses are always possible. The modified transform code outperforms simple spatial-domain codes by providing higher quality of the intermediately reconstructed images. The improvement is 10 dB for a compression factor of 256:1, and it is as high as 17.5 dB for a factor of 8:1. A novel progressive quantization scheme is developed for optimal progressive transmission of transformed diagnostic images. Combined with a discrete cosine transform, the new approach delivers intermediately reconstructed images of comparable quality twice as fast as the more usual zig-zag sampled approach. The quantization procedure is suitable for hardware implementation.     

The adsorption and catalytic transformations of chromium on Mn substituted goethite

Goethite widely occurs in the environment and its role in photoreduction of toxic Cr(VI) to less toxic Cr(III) has been previously reported in the literature. However, natural goethite is rarely stoichiometric and usually contains certain substitutional cations, such as Mn(III) or Mn(IV), which, on the other hand, is an oxidant for Cr(III). In order to provide more insight into the fate of Cr(VI) in the environment, the influence of Mn-substitution in goethite on its Cr(VI) photoreduction capability needs to be clarified. The objectives of this study were to evaluate the adsorption and photo-transformations of Cr on Mn-substituted goethite with Mn/(Mn + Fe) molar ratios ranging from 0 to 0.1. The results showed that Cr adsorption and photo-catalytic transformation on goethite were strongly influenced by the Mn content of goethite. When the system was under illumination, Cr(VI) reduction was decreased with increasing Mn-substitution in goethite. The re-oxidation of photo-reduced product, i.e., Cr(III), at the Mn sites on the surface of goethite is responsible for the lower Cr(VI) photo-reduction capacity of Mn-substituted goethite. The role of goethite in the reduction of Cr(VI) may be overestimated unless its Mn-substituted counterparts are considered. The effectiveness of Mn sites in goethite to increase toxic Cr(VI) has important implications in determining the fate and threat of Cr(VI) contamination.     

Effects of cell correlations in a matched-filter PN codeacquisition for direct-sequence spread-spectrum systems

Rapid pseudonoise (PN) code acquisition with matched-filter correlators has been very popular in direct-sequence (DS) spread-spectrum systems. Conventionally, the analysis of this acquisition method is based on the assumption that the detections among cells are independent. However, there may be strong correlations among cell detections for the case that the cell size is less than a chip duration. In this paper, the mean acquisition time performance of the acquisition method is analyzed with the cell correlations being taken into account. Numerical results show that depending on the threshold value and other system parameters, the effect of cell correlations may be over 20% of the mean acquisition time for signal-to-noise ratios (SNR) of practical interest. The analytical results are substantiated by computer simulations     

Ultrafast heating and thermomechanical coupling induced by femstosecond lasers

This work focuses on the ultrafast thermomechanical waves generated by the hot electrons excited by ultrafast, ultra-intense lasers. The dominating effects during the short-time transient, including ultrafast thermalization and relaxation between electrons and phonons, result in thermomechanical coupling that cannot be described by Fourier’s law alone. The various thermomechanical properties are grouped to characterize the ultrafast heating and deformation. A finite-difference differential formulation is used as a general tool to tackle the new set of coupled equations that are formulated to describe the severe impingement of a hot-electron blast in the presence of nonequilibrium heating, rapid expansion/contraction of the metal lattices, phonon relaxation, and thermomechanical coupling.     

A stable finite difference scheme for thermal analysis in an N-carrier system

In this study, we extend the concept of the well-known parabolic two-step model for micro heat transfer to model the energy exchanges in a generalized N-carrier system with heat sources. We show that the multi-carrier system satisfies an energy estimate. Based on this result, a finite difference scheme is then developed for thermal analysis in the multi-carrier system. The developed numerical scheme is shown to satisfy a discrete analogue of the energy estimate, implying that it is unconditionally stable. The method is illustrated by several numerical examples.