Selective separation of gold from iron ore samples using ion exchange resin

Gold in iron ore samples is separated from iron (major matrix cation), antimony and vanadium using anion exchange resin in (0.2 M) HBr, potassium peroxodisulfate and acetone:water:nitric acid media. The exchangeable anion Cl⁻ of the ion exchanger Dowex 1X 4 is replaced by Br⁻ using (6 M) HBr solution. Certified reference material DGP-M1, spiked ferric magnetic oxide, gold radioactive tracer ¹⁹⁸Au and gold standard solutions are used to study the adsorption efficiency and the yield recovery of tetrabromoaurate AuBr₄⁻ from the resin. Ten eluents have been tried to elute gold from the column, and it has been found that a 10 ml potassium peroxodisulfate and 240 ml acetone:water:nitric acid [125:5:5] solution fulfills the objective. The set up of the separation procedure allows quantitative adsorption of gold by the resin, while the major matrix cation (Fe) and others (Cd, Ag, Cu, V, Sb, Ti) have been passed through the column with the feeding solution (0.2 M) HBr. The resin selectivity coefficient (K) of separating Au from Fe has been found to be K_Fe^Au≈6.4×10¹¹. The eluted Au is treated with K₂S₂O₈ and H₂O₂ for spectrophotometric determination as rhodamine-B complex at 555.6 nm. The linearity, detection limit, precision, and accuracy of the determination method have been found to be up to 2.0 μg g⁻¹, 0.018 μg g⁻¹, 0.009 μg g⁻¹ and 3%, respectively.     

Saloplastic Macroporous Polyelectrolyte Complexes: Cartilage Mimics

Complexes of sodium poly(4-styrenesulfonate) (NaPSS) and poly(diallyldimethylammonium chloride) (PDADMAC) were formed on mixing equimolar solutions in high salt concentration. Under ultracentrifugal fields, the complex precipitates were transformed into compact polyelectrolyte complexes (CoPECs), which showed extensive porosity. The mechanical properties of CoPECS make them attractive for bioimplants and tissue engineering applications. Free NaPSS chains in the closed pores of CoPECs create excess osmotic pressure, which controls the pore size and contributes to the mechanical resistance of the material. The mechanical properties of CoPECs, modulated by the ionic strength of the doping medium, were studied by uniaxial tensile testing and the stress-strain data were fit to a three-element Maxwell model which revealed at least two regimes of stress relaxation.     

In vivo imaging of intrinsic optical signals in chicken retina with functional optical coherence tomography

Visually evoked intrinsic optical signals (IOSs) were measured in vivo for the first time to our knowledge from all retina layers of the chicken retina with a combined functional optical coherence tomography and electroretinography (ERG) system. IOS traces were recorded from a small volume in the retina with 3.5 μm axial resolution and 7 ms time resolution. Comparison of the IOS and ERG traces shows a correlation between the positive and negative IOS measured from different retinal layers and the timing of the a and b waves in the ERG recording.     

Determination of the formation constant for the inclusion complex between Lanthanide ions and Dansyl chloride derivative by fluorescence spectroscopy: Theoretical and experimental investigation

In this paper, a sensitive, easy, efficient, and suitable method for the calculation of K_f values of complexation between one derivative of Dansyl chloride [5-(dimethylamino) naphthalene-1-sulfonyl 4-phenylsemicarbazide] (DMNP) and Lanthanide(III) (Ln) ions is proposed, using both spectrofluorometric and spectrophotometric methods. Determination of K_f showed that DMNP was mostly selective towards the erbium (III) ion. The validity of the method was also confirmed calculating the Stern–Volmer fluorescence quenching constants (K_sv) that resulted in the same consequence, obtained by calculating the K_f of complexation values. In addition, the UV–vis spectroscopy was applied for the determination of K_f only for the Ln ions that had interactions with DMNP. Finally, the DFT studies were done on Er³⁺ and the DMNP complex for distinguishing the active sites and estimating the pair wise interaction energy. It can be concluded that this derivative of Dansyl chloride with inherent high fluorescence intensity is a suitable reagent for the selective determination of the Er³⁺ ion which can be used in constructing selective Er³⁺ sensors.     

Algorithms for two-machine flow-shop sequencing with precedence constraints

This paper considers the problem of minimizing the maximum completion time in a two-machine flow-shop for which precedence constraints on the jobs are specified. If one job has precedence over another, then the second of these jobs cannot be processed on a machine until the first of them is completed on that machine. A powerful new lower bounding rule which uses Lagrangean relaxation is developed. Then several dominance theorems are presented which are used to eliminate some jobs from the problem. The lower bound is used in three branch and bound algorithms, two of which employ well-known branching rules while the third uses a new branching rule. The algorithms are compared and tested on problems with up to 80 jobs.     

Theoretical application of z-dependent gain coefficient to describe amplified spontaneous emission

Based on the geometrical modeling of the unified gain coefficient and the reported amplified spontaneous emission (ASE) output energy measurement ε(ASE) versus amplifying excitation length, l(AMP) in a KrF laser oscillator, we managed, as an example, to explain the ASE output energy behavior both numerically and analytically. In this approach, introducing the ASE gain-coefficient profile for the KrF laser, g(0,KrF)(ASE), was not avoidable. It was found that while the g(0,KrF)(ASE) profile follows the introduced gain-modeling formulation, it is, however, slightly lower than the KrF laser gain profile, g(0,KrF)(exp), deduced from the measurements reported by different researchers. The present approach, up to the present time, is able to explain all of the existing ambiguities on understanding the ASE behavior.     

Some aspects of physical and numerical modeling of water hammer in pipelines

In this work, a computational method was used for the prediction of water transmission failure. The proposed method allowed for any arbitrary combination of devices in the water pipeline system. The method used was by a scale model and a prototype (real) system for a city main water pipeline where transient flow was caused by the failure of a transmission system.     

Non-aqueous PVAc dispersions prepared in a reactive epoxy functionalized PDMS liquid medium

The system vinyl acetate (VAc)/poly(dimethylsiloxane) diglycidylether (PDMS-DGE) is a typical example of two monomers where both components are polymerizable in a “one-pot” procedure by two distinct reaction mechanisms. Non-aqueous dispersions (NAD) are obtained in a first step by free-radical polymerization of the dispersed VAc-PVAc phase. The study of the reaction kinetics has shown that the polymerization rate is mainly influenced by the partition coefficient of VAc between both phases in presence. The colloidal characteristics of the NAD, such as particle size, stability and viscosity were examined in function of monomer and initiator concentrations. Preliminary UV curing tests of the PDMS-DGE phase in the presence of a cationic photoinitiator have shown that PVAc/PDMS two-phase coatings can be obtained, without any solvent emission.