Metal release from contaminated estuarine sediment under pH changes in the marine environment

The contaminant release from estuarine sediment due to pH changes was investigated using a modified CEN/TS 14429 pH-dependence leaching test. The test is performed in the range of pH values of 0-14 using deionised water and seawater as leaching solutions. The experimental conditions mimic different circumstances of the marine environment due to the global acidification, carbon dioxide (CO2) leakages from carbon capture and sequestration technologies, and accidental chemical spills in seawater. Leaching test results using seawater as leaching solution show a better neutralisation capacity giving slightly lower metal leaching concentrations than when using deionised water. The contaminated sediment shows a low base-neutralisation capacity (BNCpH 12 = -0.44 eq/kg for deionised water and BNCpH 12 = -1.38 eq/kg for seawater) but a high acid-neutralisation capacity when using deionised water (ANCpH 4 = 3.58 eq/ kg) and seawater (ANCpH 4 = 3.97 eq/kg). Experimental results are modelled with the Visual MINTEQ geochemical software to predict metal release from sediment using both leaching liquids. Surface adsorption to iron- and aluminium- (hydr)oxides was applied for all studied elements. The consideration of the metal-organic matter binding through the NICA-Donnan model and Stockholm Humic Model for lead and copper, respectively, improves the former metal release prediction. Modelled curves can be useful for the environmental impact assessment of seawater acidification due to its match with the experimental values.This work was supported by the Spanish Ministry of Economy and Competitiveness, Project No. CTM 2011-28437-C02-01, ERDF included. M. C. Martı´n-Torre was funded by the Spanish Ministry of Economy and Competitiveness by means of FPI. Fellowship No. BES-2012-053816

Improvement in dielectric and ferroelectric property of dysprosium doped barium bismuth titanate ceramic

The dysprosium doped barium bismuth titanate ceramic with general formula BaBi4-xDyxTi4O15 (BBDT) were prepared by solid-state reaction process. The effect Dy3+ on Bi3+ sites on the structural, microstructure, dielectric, conductivity and ferroelectric behaviour of BaBi4Ti4O15 ceramics were investigated. X-ray diffraction and Raman analysis confirmed the above compositions to be monophasic with orthorhombic structure and belonged to the m = 4 member of the Aurivillius family of oxides. The SEM micrographs show well define grains in all ceramics. From the dielectric behavior as a function of temperature it was observed that the maximum dielectric constant decreases and transition temperature increases with an increase in Dy content. The diffuse nature of the dielectric behavior of BBDT ceramics obtained from the modified Curie-Weiss law and it was attributed to the A site cationic disorder. The frequency dependence AC conductivity obeys the power law and the DC conductivity shows a thermally activated process. Ativation energies were obtained from the Arrhenius law and it is observed that oxygen vacancy () are mainly responsible for the conduction mechanism in the systems. The ferroelectric properties were studied by P-E hysteresis loop and it observed that the remnant polarization increases with Dy doping