Cem Gok

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.

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.

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.

Preparation of Ca-alginate biopolymer beads and investigation of their decorporation characteristics for 85Sr, 238U and 234Th by in vitro experiments

The aim of this work was to investigate whether Ca-alginate biopolymer beads (CaABBs) can be used to reduce the bioavailability of radionuclides in the gastrointestinal tract of humans. The uptake of strontium, uranium and thorium from a simulated gastrointestinal system was studied by in vitro techniques using CaABBs. This agent was prepared from Na-alginate through cross-linking with divalent calcium ions according to the egg-box model. The effects of process variables such as pH of the gastrointestinal juice, incubation time and solid-to-solution ratio for the removal of radionuclides from the gastrointestinal juice were investigated. The results suggest that CaABBs are a potent material for reducing the bioavailability of radionuclides with a high uptake efficiency in the gastrointestinal tract.

Biosorption of Uranium and Thorium by Biopolymers

Abstract Biosorption can be defined as the removal of substances, such as metal or metalloid species, compounds, and particulates from solution by biological material or their products, especially bacteria, algae, yeast, and fungi by physicochemical binding. Among these biosorbents, biopolymers have been preferred over other materials because of their advantages, including biodegradability, hydrophilicity, and presence of carboxylic groups. The increase in the nuclear industry and other anthropogenic activities has intensified environmental pollution, with the accumulation of radioactive elements as uranium and thorium. Therefore, it is very important to identify potential effective and environmentally safe adsorbents for the removal and recovery of uranium and thorium. This chapter reviews the state of art of biosorption of uranium and thorium by biopolymers and compares the results found in the literature and the biosorption results on uranium and thorium by Ca-alginate biopolymer beads.

Separation of Uranium by an Extractant Encapsulated Magnetic Alginate Gels

The aim of this work is to prepare environmentally friendly and practically applicable alginate magnetic biopolymers encapsulated tri-n-butyl phosphate (TBP) for the removal uranium ions. Some important process parameters such as initial pH, initial U(VI) concentration, adsorbent dosage, time, temperature and sorption isotherms for uranium uptake were studied and the thermodynamic parameters for U(VI) were determined.

Characterization of Cystoseira sp. for the Isolation of Uranium

ABSTRACT Organic leaching is an important problem for the sorption of heavy metals and radionuclides by biological raw materials. In this work, various chemicals were used to modify the raw brown macroalga Cystoseira sp. to increase the capacity for uranium sorption and decrease leaching. The biosorption and desorption of uranium ions were optimized for various parameters using the unmodified and modified biosorbents. Surface properties and the binding sites of the macroalga were characterized by infrared spectroscopy, scanning electron microscopy, and X-ray diffraction. The maximum capacity for uranium of Cystoseira sp. modified with 0.2% glutaraldehyde in water was 428.4 mg/g and the percentage of desorbed uranium from the biosorbent was 99 ± 1% with elution by 1 mol/L HCl. This work represents the first report of Cystoseira sp. for biosorption and suggests its application for uranium ions.