Sule Aytas

Biosorption of uranium(VI) from aqueous solution using calcium alginate beads.

In this paper, sorption potentials of uranium ions were studied using alginate polymer beads in diluted aqueous solutions. The ability of alginate beads to adsorb uranium(VI) from aqueous solution has been studied at different optimized conditions of pH, U(VI) concentration, contact time, biomass dosage and temperature. In order to determine the adsorption characteristics, Langmuir, Freundlich, and Dubinin-Radushkevich adsorption isotherms were applied to the adsorption data. The thermodynamic parameters such as variations of enthalpy DeltaH, entropy DeltaS and variation of Gibbs free energy DeltaG were calculated from the slope and intercept of lnK(d) vs. 1/T plots. The results suggested that alginate beads could be suitable as a sorbent material for adsorption and removal of uranium ions from dilute aqueous solutions.

Adsorption characteristic of U(VI) ion onto thermally activated bentonite.

In this study, the effect of pH, contact time, temperature, and initial metal concentration on U(VI) adsorption on thermally activated bentonite (TAB) was investigated. Graphical correlation of various adsorption isotherm models like, Freundlich, and Dubinin-Radushkevich have been carried out for TAB. Various thermodynamic parameters, such as, Gibbs free energy, entropy and enthalpy of the on-going adsorption process have been calculated. In order to reveal the adsorptive characteristic of bentonite samples, surface area, FT-IR, and DTA-TG spectra analyses were carried out. The results show that TAB samples can be an alternative low cost adsorbent for removing U(VI) ions from aqueous solutions.

Activity concentration of caesium-137 in agricultural soils.

In this study, we measured 137Cs activity concentrations in the soil samples taken from agricultural lands in the Buyuk Menderes Basin in Turkey in 1997 and 1998. The soil samples were collected from 42 sites in this Basin. The activity concentration of 137Cs was found to range between 2.81+/-0.17 Bq.kg(-1) and 20.75+/-0.29 Bq.kg(-1). The effect of organic matter, clay, silt and sand contents and pH of the soil on the relative adsorption of the 137Cs on the soil surface were also studied.

Biosorption of radiostrontium by alginate beads: application of isotherm models and thermodynamic studies

Radioactive strontium is one of the major radioactive contaminant and its contamination is a very serious concern. Therefore, there is a need for economic, effective, non-toxic, readily available and abundant adsorbent or biosorbent to remove strontium from solutions. In this study, biosorption of 85Sr as a surrogate for 90Sr onto alginate beads was investigated in a batch system. Alginate beads were prepared from Na-alginate via cross-linking with divalent calcium ions according to the egg box model. The effect of several parameters such as pH, initial strontium concentration, contact time, dosage of alginate beads and temperature were investigated. In order to optimize the design of biosorption system for the removal of strontium, it is important to establish the most appropriate correlation for equilibrium curves. The experimental isotherm data were described by 6 different biosorption isotherm models, namely Langmuir, Freundlich, Dubinin–Radushkevich, Temkin, Flory–Huggins and Brunauer, Emmer and Teller, with constants obtained from linear and non-linear regression methods. The thermodynamic parameters (∆H°, ∆S° and ∆G°) for strontium biosorption were also determined. The results indicate that these alginate beads have a good potential for the biosorption of strontium from solutions.

Investigation of uranium biosorption from aqueous solutions by Dictyopteris polypodioides brown algae

The biosorption of uranium from aqueous solutions by Dictyopteris polypodioides brown algae was investigated. The effect of pH, uranium concentration, mass of the adsorbent, temperature and contact time on the removal efficiency were studied and the results were simulated by Langmuir, Freundlich and Dubinin–Radushkevich isotherm models. Kinetics data could be satisfactorily reproduced by the pseudo-second order equation and thermodynamic parameters were determined in order to evaluate the uranium uptake behavior. SEM/EDS and FT-IR were additionally used to characterize the algae and comprehend the sorption process which can be described as a combination of several mechanisms, including physical sorption, ion exchange and complexation.

Vertical distribution of 226Ra and 210Po in agricultural soils in Buyuk Menderes Basin, Turkey

The vertical distribution of (226)Ra and (210)Po was investigated in the cultivated soils of the Buyuk Menderes Basin in Turkey. Five soil cores down to a depth of about 50 cm were taken from each site and divided into strata of 2-3 cm intervals. The samples were analyzed for their (226)Ra and (210)Po activity concentrations using radioanalytical methods. Down-core concentration profiles of (226)Ra and (210)Po in the soil cores from five sites are obtained. The activity concentrations of soil cores range from 80 to 1170 Bq kg(-1) for (226)Ra and from 10 to 870 Bq kg(-1) for (210)Po with the depth. Analysis of the vertical soil profiles indicate that the activity concentrations of (226)Ra and (210)Po for soil strata at all the sites have not extremely changed with depth.

Activity concentration of radium-226 in agricultural soils

Fourty two soil samples were collected to a depth of 20 cm from the Aegean Region of Turkey. The activity concentrations of 226Ra in the samples were determined by a radioanalytical method. The radiochemical yield for pure 226Ra was found to be 90.02±2.74%. The average concentration of 226Ra was 0.150 Bq.g-1 and its distribution fitted a normal curve. The average absorbed dose rate was found to be 61 nGy.h-1. The data were evaluated to explain of 226Ra distribution in the agricultural area and compared with other results in the literature.

Natural radioactivity of riverbank sediments of the Maritza and Tundja Rivers in Turkey

This article represents the first results of the natural radionuclides in the Maritza and Tundja river sediments, in the vicinity of Edirne city, Turkey. The aim of the article is to describe the natural radioactivity concentrations as a baseline for further studies and to obtain the distribution patterns of radioactivity in trans-boundary river sediments of the Maritza and Tundja, which are shared by Turkey, Bulgaria and Greece. Sediment samples were collected during the period of August 2007–April 2010. The riverbank sediment samples were analyzed firstly for their pH, organic matter content and soil texture. The gross alpha/beta and 238U, 232Th and 40K activity concentrations were then investigated in the collected sediment samples. The mean and standard error of mean values of gross alpha and gross beta activity concentrations were found as 91 ± 11, 410 ± 69 Bq/kg and 86 ± 11, 583 ± 109 Bq/kg for the Maritza and Tundja river sediments, respectively. Moreover, the mean and standard error of mean values of 238U, 232Th and 40K activity concentrations were determined as 219 ± 68, 128 ± 55, 298 ± 13 and as 186 ± 98, 121 ± 68, 222 ± 30 Bq/kg for the Maritza and Tundja River, respectively. Absorbed dose rates (D) and annual effective dose equivalent s have been calculated for each sampling point. The average value of adsorbed dose rate and effective dose equivalent were found as 191 and 169 nGy/h; 2 and 2 mSv/y for the Maritza and the Tundja river sediments, respectively.

Modeling uranium biosorption by Cystoseira sp. and application studies

ABSTRACT The aim of the present work was to determine the applicability of raw and modified brown macroalga Cystoseira sp. as a biosorbent material for the sorption of uranium ions from aqueous solutions. Equilibrium of uranium biosorption was analyzed under isotherm models and thermodynamic parameters of the process. Recovery of uranium from acidic mine wastewater was also applied. The mechanism of biosorption was discussed considering experimental data and theoretical models. The bioremoval efficiency of modified biomass was higher than raw Cystoseira sp. and the theoretical biosorption capacity of modified biosorbent was calculated to be 468.01 mg U/g.

Recovery of Thorium by High-Capacity Biopolymeric Sorbent

The potential of prepared alginate biopolymers as a natural, economic, effective, non-toxic biosorbent was investigated for the recovery of thorium ions in this study. The experiments were carried out to study the effects of various physico-chemical parameters on biosorption and desorption of thorium. The biosorption process was examined by various isotherm models and equilibrium data were successfully described by a Langmuir model very well. The monolayer biosorption capacity was found as 169.50 mg/g. The thermodynamic parameters such as variations of enthalpy, entropy, and Gibbs free energy for thorium biosorption were also defined and the results suggest that endothermic nature of the process. The prepared alginate biopolymers exhibit high uptake capacity and regeneration potential for biosorption of thorium.