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Highly efficient sorbents for phosphate removal from aqueous solutions based on the calcined forms of Fe(III)-substituted Layered Double Hydroxides (LDH) materials have been developed in this study. Hydrotalcite-like materials with Mg/M(3+) approximately 3 (where M=Al(3+), Fe(3+) or combined) have been synthesized following simple co-precipitation method and were subsequently calcined in air at 450 degrees C. Both as-synthesized and calcined materials were characterized by means of X-ray Diffraction (XRD), Inductively Coupled Plasma Atomic Emission Spectroscopy (ICP-AES), elemental (C) analysis, N(2) porosimetry, Scanning Electron Microscopy (SEM). All the materials were evaluated for the sorption of phosphates by batch equilibrium sorption experiments and kinetic measurements (effect of contact time). It was shown that chlorides or nitrates, being the charge-balancing anions in the LDH structure, are more easily exchanged by phosphates compared to carbonates. In the Fe(III)-modified LDHs, an increase of the Fe loading led to the decrease of the sorption efficiency. The maximum uptake of phosphates for both the Mg-Al LDH and Mg-Fe LDH samples containing mainly carbonates as charge-balancing anions was relatively low (ca.

The stress-deformation behavior of a non-Newtonian surface subject to an oscillatory shearing flow was theoretically as well as experimentally investigated. The rheological properties of such an interface were interpreted using the complex viscosity surface fluid model. The measurements of surface shear viscoelasticity of an air-liquid surface were performed with the in-house built oscillatory torsional interfacial viscometer. The behavior of the liquid-liquid interface was described based on the exact solution obtained from the analysis of the interfacial rheometer, assuming a non-Newtonian surface and Newtonian bulk phases. The interfacial angular velocity distributions are illustrated as functions of surface viscous and elastic components described by the complex viscosity surface fluid model. An extensive experimental investigation of the surfactant concentration and temperature dependence of the surface viscoelasticity of aqueous gelatin solutions was carried out. The surface rheological behavior encompasses both shear thickening and shear thinning, below and above a characteristic frequency, respectively. The characteristic frequency is independent of temperature, except at 35°C. The surface shear elasticity attains maximum values at a characteristic frequency which is independent of surfactant concentration and temperature, except at 40°C. The temperature dependence of the surface shear viscoelasticity and the origin of the characteristic frequency are explained in terms of the two conformations of gelatin molecules, namely, the α-conformation at 40 and 45°C, and the β-conformation at 35°C. In general, it was found that the temperature and surfactant concentration dependence of the surface shear elasticity was more complex than the corresponding dependence of the surface shear viscosity. Moreover, the experimental results proved the appropriateness of the complex viscosity surface fluid model and the viability of the oscillatory torsional interfacial rheometer.

The yield stresses of aqueous laterite suspensions as functions of solids concentration and suspension pH, or ζ potential, were measured using the direct vane method. In addition, capillary rheometer shear stress—shear rate data were taken for the most concentrated test suspension, and these were used to estimate the yield stress by various extrapolations, and to compare them with the directly measured value using the vane geometry. Detailed characterizations of all test suspensions were carried out. The yield stress was found to depend strongly on suspension pH, attaining a minimum at the isoelectric point occurring at high pH. It was found to follow approximately a straight-line relationship with the square of the ζ potential, and its dependence on solids concentration is described by a two-parameter nonlinear relationship which gives the appropriate behavior in both the dilute limit and the concentrated limit near maximum packing.In situ particle size measurements by sedimentation suggest that the degree of flocculation is high under acidic conditions. The capillary rheometer data reflect strongly non-Newtonian, shear thinning behavior.

It has been claimed [R. L. Kao, D. A. Edwards, D. T. Wasan, and E. Chen, J. Colloid Interface Sci. 148, 247 (1992)] that the surface dilatational viscosity at high rates of interface expansion can be measured using the maximum bubble pressure method. However, Kao et al. arbitrarily omitted the bulk viscous term from the equation governing bubble growth (their Eq. [15]) on the grounds that it is negligible compared to the capillary term only. It is shown here that such an omission is inadmissible since the bulk viscous term is large in comparison to the surface dilatational viscosity term which also appears in Eq. [15]. In addition, Eq. [17] in Kao et al. cannot be used in interpreting σ (∇S · vS) data since it alludes to a surface tension which is intrinsically different from the thermodynamic surface tension σ appearing in the equation.