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Stoica-Guzun A.,Polytechnic University of Bucharest | Stroescu M.,Polytechnic University of Bucharest | Jinga S.I.,Polytechnic University of Bucharest | Mihalache N.,University of Bucharest | And 5 more authors.
International Journal of Biological Macromolecules | Year: 2016

In this study bacterial cellulose-magnetite composites were synthesised for the removal of chromium(VI) from aqueous solutions. Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), thermogravimetric analysis and X-ray Photoelectron Spectroscopy (XPS) were used to characterize the bacterial cellulose-magnetite composites and to reveal the uniform dispersion of nanomagnetite in the BC matrix. Magnetic properties were also measured to confirm the magnetite immobilization on bacterial cellulose membrane. The effects of initial Cr(VI) concentration, solution pH and solid/liquid ratio upon chromium removal were examined using the statistical Box-Behnken Design. Because of the possibility of magnetite dissolution during chromium(VI) adsorption, the degree of iron leaching was also analysed in the same conditions as Cr(VI) adsorption. From the factors affecting chromium(VI) adsorption the most important was solution pH. The highest Cr(VI) removal efficiency was observed at pH 4, accompanied by the lowest iron leaching in the solution. The adsorption experiments also indicated that the adsorption process of chromium(VI) is well described by Freundlich adsorption model. Our results proved that the BC-magnetite composites could be used for an efficient removal of chromium(VI) from diluted solutions with a minimum magnetite dissolution during operation. © 2016 Elsevier B.V. Source

Fechet R.,CEPROCIM S.A. | Zlagnean M.,Research and Development National Institute for Metals and Radioactive Resources
10th International Multidisciplinary Scientific Geoconference and EXPO - Modern Management of Mine Producing, Geology and Environmental Protection, SGEM 2010 | Year: 2010

Perspective conception is characterized by including of wastes assembly problems in sphere of general actions for environment protection taking into account as any nonvalorized waste or least non-used, pollute the environment. Processing of solid minerals sterile and obtaining of sub-products which are economically usable has major importance, both from economical and ecological point of view, through environment protection. Researches had followed elaboration of ecological technologies of processing the waste as mineral sterile, in order to obtain recovered products. By superior using of mineral compounds resulted from waste as mineral sterile or decantation stock-piles, products with economic value may be obtained, such as Portland cement, bricks, bolts, concrete slabs, BCA and BCU, etc. These researches put the base of a new approach mode of mining residues problem. It was followed that experimental models carried out at laboratory scale to contain equipments and installations of concentration with a low degree of pollution. Products obtained from pond sterile are according to the requirements imposed by quality norms in force. © SGEM2010 All Rights Reserved by the International Multidisciplinary Scientific GeoConference SGEM Published by STEF92 Technology Ltd. Source

Filcenco Olteanu A.,Research and Development National Institute for Metals and Radioactive Resources | Dobre T.,Polytechnic University of Bucharest | Panturu E.,Research and Development National Institute for Metals and Radioactive Resources | Radu A.D.,Research and Development National Institute for Metals and Radioactive Resources | Akcil A.,Suleyman Demirel University of Turkey
Hydrometallurgy | Year: 2014

The aim of this paper consists in defining optimal conditions of controlled and selective gold leaching contained in copper-gold slag, by wet chlorination. Studies were conducted on three types of copper-gold slag, resulting as by-products from pyrometallurgical processing of non-ferrous raw materials. Due to high levels of copper in slag, an oxidative pre-treatment is necessary to separate gold from accompanying elements and also for copper recovery. After nitric acid pre-treatment, nearly 87% of Cu was readily extracted, and lead and silver contents in all three types of solid samples have been reduced by 91.34% and 96.29%, respectively. Selective leaching of the solid phase resulting after HNO3 pre-treatment was done by wet chlorination, using nascent chlorine (Cl2) as the leaching agent, with the presence of hydrochloric acid (HCl). The chlorine was obtained "in situ" by the reaction of sodium hypochlorite (NaOCl, 5% Cl2) and HCl. In this study, the effect of nitric acid pre-treatment, redox potential (Eh) given by sodium hypochlorite (NaOCl) consumption, hydrochloric acid concentration, temperature and leaching time have been studied. The potential required for a rapid leaching rate and for avoiding the reduction of gold is 950 mV (vs AgCl/Ag(KCl sat)). The 5% NaOCl consumption required for gold leaching from pre-treated samples was lower than NaOCl consumption necessary for original sample leaching. The highest gold extraction yield (98%) was obtained after 6 h at ambient temperature, solid/liquid ratio (w/v) 1:2 and 4 M HCl. In order to explain experimental results a mathematical model of the simultaneous gold, copper, lead and silver dissolution has been developed. It considers at particle level, the competition between surface reaction and the diffusion of the active species by a gel coating that covers the dissolving particle. © 2014 Elsevier B.V. Source

Botez A.,Research and Development National Institute for Metals and Radioactive Resources | Dobre T.,Polytechnic University of Bucharest | Panturu E.,Research and Development National Institute for Metals and Radioactive Resources | Filcenco-Olteanu A.,Research and Development National Institute for Metals and Radioactive Resources
Central European Journal of Chemistry | Year: 2014

This paper characterizes uranium (VI) sorption from synthetic solutions using a fixed bed Purolite resin SGA 600 U/3472 system. The effect of the sulphate anion presence in the liquid phase on sorbtion dynamics and equilibrium is analysed. In the industrial processing of solutions obtained from leaching of uranium ore (alkaline/acid), in a continuous system, there are several compounds which strongly compete with uranium for ion exchange sites and consequently these substances depress the uranium adsorption. The influence of vanadate, molybdate, chloride, and nitrate is known, therefore, in this paper, the adsorption equilibrium isotherms for uranium (VI) are obtained for different sulphate ion concentrations in solution. The adsorption capacity variation of the Purolite resin SGA 600U/3472 with the number of adsorption/desorption cycles is also studied. The experimental results reveal the negative impact of high sulphate ion content in solution on the adsorption capacity of the resin Purolite SG 600 U / 3472 with uranium (VI) and therefore it is considered one of the compounds which strongly affect the uranium adsorption. [Figure not available: see fulltext.] © 2014 Versita Warsaw and Springer-Verlag Wien. Source

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