Geochemical evaluation and environmental application of Yemeni natural zeolite as sorbent for Cd<Superscript>2+</Superscript> from solution: kinetic modeling,equilibrium studies,and statistical optimization

Yemeni natural zeolite was characterized by XRD, SEM, FTIR and XRF as well as its applicability as a sorbent material for Cd²⁺ ions in aqueous solutions. The zeolitic sample is clinoptilolite-K of heulandite group with intermediate Si/Al ratio. The removal% of Cd²⁺ by natural clinoptilolite was investigated as a function of contact time, zeolite dose, pH and initial concentration of Cd²⁺ ions. Kinetic experiments indicated that sorption of Cd²⁺ follows two steps: rapid ion exchange process on the outer surface is followed by slow adsorption process on the inner surface of clinoptilolite. The equilibrium was attained after 120 min, and the results were fitted well with pseudo-second order and Elovich kinetic models. The Cd²⁺ removal% is strongly dependent on pH value and increases with the increasing pH value. Equilibrium sorption isotherm of Cd²⁺ by clinoptilolite was described well using the Langmuir, Freundlich, and Temkin isotherms models. However, the data relatively well fitted with Freundlich model (R ² = 0.97) rather than by the other models. Response surface methodology in conjunction with central composite rotatable statistical design was used to optimize the sorption process. The model F-value indicated the high significance of second-order polynomial model to represent the interaction between the operating parameters. From the Design Expert’s optimization function, the predicted optimum conditions for maximum removal% of Cd²⁺ (80.77%) are 116 min contact time, 0.27 gm dose, and pH 7 at an initial Cd²⁺ concentration of 25 mg/L.     

Vehicle effects on seismic response of a simple‐span bridge during shake tests

Presence of vehicles on a bridge has been observed many times during past earthquakes. Although in practice, the engineers may or may not include the live load contribution to seismic weight in design, current bridge design codes do not specify a certain guideline. A very limited research has been conducted to address this issue from design point of view. The focus of this research is to experimentally assess the effect of a vehicle on the seismic response of a bridge through a large‐scale model. In this scope, a 12‐meter long bridge, having a one lane deck with concrete slab on steel girders, has been shaken under five different ground motions obtained from recent earthquakes that occurred in Turkey, in its transverse direction, both with and without a vehicle on top of the deck. The measured results have indicated that top slab transverse acceleration and bearing displacements can reduce up to 18.7% in presence of a vehicle during seismic tests, which is an indication of reduction in substructure forces. The main reason for the reduction in seismic response of the bridge in the presence of live load can be ascribed to the increase in damping of the system due to mass damper‐like action induced by the vehicle. This beneficial effect cannot be observed in vertical seismic response. Copyright © 2014 John Wiley & Sons, Ltd.