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Mihajlovic M.T.,Belgrade Waterworks and Sewerage | Lazarevic S.S.,University of Belgrade | Jankovic-Castvan I.M.,University of Belgrade | Jokic B.M.,University of Belgrade | And 2 more authors.
Chemical Industry and Chemical Engineering Quarterly | Year: 2014

The main purpose of this research was to explain the differences in the adsorption mechanisms and adsorption capacities of natural and Fe(III)-modified zeolite for Pb2+, Zn2+ and Cd2+. The adsorbents were characterized with respect to their phase composition, morphology, specific surface area, cation exchange capacity and point of zero charge. Batch adsorption experiments were performed as a function of the initial ion concentration and temperature, at constant initial pH value of 5.5±0.1. The adsorption isotherms at 25, 40, 55 and 70 °C suggest that the sequence of adsorption efficiency of both zeolites is Pb2+ > Zn2+ > Cd2+. The adsorption capacities of both zeolites increased with increasing temperature. The equilibrium adsorption data were best described by the Langmuir adsorption isotherm. This study revealed that the adsorption capacity of the Fe(III)-modified zeolite is much higher than that of natural zeo-lite for all investigated ions owing to the higher: specific adsorption caused by the new functional groups formed on the zeolite surface, ion exchange due to the presence of easily exchangeable ions, and hydroxide precipitation caused by higher point of zero charge of the Fe(III)-modified zeolite compared to natural zeolite. Source


Maksimovic S.,Military Technical Institute Belgrade | Blazic M.,Military Technical Institute Belgrade | Maksimovic M.,Belgrade Waterworks and Sewerage
Journal of Applied Engineering Science | Year: 2010

An attention in this paper is focused on developing computation procedures during design of flight structures with respects fatigue and fracture mechanics Here are developed analytic expressions for the stress intensity factor (SIF) in 3-D solid type structural components for crack growth analyses. Damages of structural components are modeled with semi-elliptic surface cracks. Structural components are under cyclic loads and load spectra. Results of presented analytic model of FIN are compared with finite element results. Good agreement between presented analytic and finite element results is obtained. Strength analysis with respect static fracture mechanics is illustrated on nose landing gear problem of light training aircraft. Source


Vasovic I.,Institut Gosa | Maksimovic S.,Military Technical Institute Belgrade | Maksimovic K.,City of Belgrade Secretariat for Communal and Housing Affairs Office of Water Management | Stupar S.,University of Belgrade | And 2 more authors.
Mathematical Problems in Engineering | Year: 2014

An attention in this paper is focused on the stress analysis and the determination of fracture mechanics parameters in low pressure (LP) turbine rotor discs and on developing analytic expressions for stress intensity factors at the critical location of LP steam turbine disc. Critical locations such as keyway and dovetail area experienced stress concentration leading to crack initiation. Major concerns for the power industry are determining the critical locations with one side and fracture mechanics parameters with the other side. For determination of the critical locations in LP turbine rotor disc conventional finite elements are used here. For this initial crack length and during crack growth it is necessary to determine SIFs. In fatigue crack growth process it is necessary to have analytic formulas for the stress intensity factor. To determine analytic formula for stress intensity factor (SIF) of cracked turbine rotor disc special singular finite elements are used. Using discrete values of SIFs which correspond to various crack lengths analytic formula of SIF in polynomial forms is derived here. For determination of SIF in this paper, combined J -integral approach and singular finite elements are used. The interaction of mechanical and thermal effects was correlated in terms of the fracture toughness. © 2014 Ivana Vasovic et al. Source


Mihajlovic M.T.,Belgrade Waterworks and Sewerage | Lazarevic S.S.,University of Belgrade | Jankovic-Castvan I.M.,University of Belgrade | Kovac J.,Jozef Stefan Institute | And 3 more authors.
Clean Technologies and Environmental Policy | Year: 2015

The adsorption of Pb2+, Cd2+, and Zn2+ from equimolar multicomponent solutions onto natural and Fe(III)-modified zeolites was studied by batch experiments in order to determine the influence of the competitive effect on the efficiency ions removal at different initial concentrations and different temperatures. Kinetic and equilibrium studies showed that affinity of both zeolites was the highest for Pb2+ and much lower for Zn2+ and Cd2+. The competitive effect was negligible at lower concentrations, while Zn2+ and especially Cd2+ ions adsorption was suppressed as the concentrations were increased. Affinity of natural zeolite toward the ions was lower than that of the modified zeolite, as was shown for adsorption from single-component solutions. External film diffusion was the rate-controlling step at lower concentrations and for ions of higher affinity for the adsorbent, while intraparticle diffusion was dominant at higher concentrations and for ions of lower affinity for the adsorbent. The increasing spontaneity of the adsorption process with increasing temperature and the positive values of enthalpy of adsorption indicated the endothermic nature of the adsorption process. Structural investigations of the adsorbents loaded with Pb2+, Cd2+, and Zn2+ ions by X-ray photoelectron spectroscopy (XPS) confirmed the higher content of the ions in the surface and subsurface regions of the Fe(III)-modified than of the natural zeolite. XPS depth profiles of the loaded Fe(III)-modified zeolite showed that surface mechanisms of adsorption were dominant in the case of lead and cadmium, while zinc loading on the zeolite sample was governed mainly by an ion-exchange process. © 2014 Springer-Verlag Berlin Heidelberg. Source


Milojkovic I.,Jaroslav Cerni Institute for the Development of Water Resources | Andric S.,Belgrade Waterworks and Sewerage
Integrating Water Systems - Proceedings of the 10th International on Computing and Control for the Water Industry, CCWI 2009 | Year: 2010

The water industry has come to recognise the value of sound asset management practice indelivering cost effective services to customers. It is striving to improve performance and deliver savings to shareholders, both public and private. Asset management of wastewater operation and maintenance needs to provide top management decision. The aims for this have to be minimum costs with maximum benefits. The aims specified later in the document have been realized through multi criteria methodVIKOR, especially in not developed sewerage systems in low-income countries. The accuracy bands are based on the system adopted in England andWales. As a guide to the definition of priorities, the performance indicators (PI) included in IWA's (International Water Association) proposal are divided into three levels, according to their importance as management tools. Method VIKOR has been used for a new evaluation significance PI in Belgrade for PIs. © 2010 Taylor & Francis Group, London. Source

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