JOURNAL OF HAZARDOUS MATERIALS

In performance assessment studies, the uptake of the radioactive elements by rock formations play an important role in retarding their aqueous phase migration. Sorption studies of radionuclides have been conducted to obtain data on the distribution coefficient (K-d) that is as an input parameter in the performance assessment of the geological disposal of radioactive wastes. In this work, sorption experiments were studied in a batch sorption system using Sr(NO3)(2) solution on non-treated and HCl-treated Kula volcanics. The distribution coefficient (K-d) values of Sr2+ derived from batch experiments were used to evaluate the migration behavior of Sr2+. Central Composite Design was used in the experiments. Sr sorption was studied as a function of pH, temperature, initial concentration of adsorbate and contact time. The results show that the K-d values are higher at pH 7-9 which is the pH range of the natural waters. The kinetic data conformed better to the pseudo-second-order equation. Thermodynamic parameters Delta H degrees, Delta S degrees and Delta G degrees were estimated and these parameters show that adsorption is endothermic. The correlation coefficients indicate that the Langmuir model fits better for the strontium sorption onto non-treated and HCl-treated Kula volcanics with monolayer capacities as 2.04 and 1.72 mg/g, respectively. (C) 2011 Elsevier B.V. All rights reserved

produced from textile sewage sludges

Different types of activated carbons were prepared by changing the activation temperatures (400-700 degrees C) and impregnation ratio (sewage sludge: KOH: 1:1, 1:2) and the removal of Sr+2 from aqueous solution was determined. The maximum adsorption yield (12.11 mg/g) was obtained at 500 degrees C for 1 h carbonization conditions with impregnation ratio of 1:1. The affecting parameters were analyzed by using central composite design method. The selected parameters were initial pH, temperature, initial strontium concentration and carbon dosage. The analysis of variance was performed in 95% confidence level and checked to fitting of experimental value and predicted value. The significant F was P < 0.05 with a model F value of 19.94 which revealed that this regression is statistically significant. The results of regression analysis indicated that pH and temperature parameters were not individually statistically significant for Se+2 sorption. However, the efficiency of strontium sorption increases with the increase in carbon dosage and decreases with the Sr+2 concentration. Influences of initial pH and temperature, pH and Sr+2 concentration, temperature and carbon dosage and Sr+2 concentration and carbon dosage on the adsorption process were considered statistically significant. Adsorption of strontium was described by Freundlich isotherm as a physical adsorption (E = 7.2 kJ/mol). The adsorption reactions were calculated as endothermic, spontaneous and favorable reactions. (C) 2012 Elsevier B.V. All rights reserved

Assessment of the adsorption of thorium onto styrene–divinylbenzene-based resin: Optimization using central composite design and thermodynamic parameters

Adsorption of thorium on styrene–divinylbenzene-based resin was investigated to obtain the optimum adsorption conditions by using the central composite design (CCD) method. This study was performed in 30 runs of experiments as a function of pH, thorium concentration, contact time and temperature. Adsorption performance of styrene–divinylbenzene-based resin was higher than 98%. The optimum adsorption of thorium using styrene–divinylbenzene-based resin can be successfully predicted statistically by the CCD method. In addition, sorption isotherm models such as Langmuir, Freundlich and Dubinin–Radushkevich were applied, and adsorption of Th(IV) was described most precisely by the Langmuir isotherm, which has the highest R2 (0.99) value. Thermodynamic parameters showed that the adsorption is an exothermic and spontaneous physical process. The results of this study reveal that this type of synthetic resin can be used as an effective sorbent material for the removal of Th(IV) ions from weakly aqueous solutions in remediation and nuclear wastewater treatment. © 2017 Institution of Chemical Engineer

Assessment of reaction between thorium and polyelectrolyte nano-thin film using Box–Behnken design

Sandwich type polyelectrolyte nano-thin films (PENTFs) were prepared by using polyallylamine hydrochloride and polyacrylic acid from layer-by-layer assembly process with spin coating system. Their nanostructures have been studied by scanning electron microscope, atomic force microscope, and attenuated total reflectance Fourier transform infrared spectroscopy. In order to understand the effects of the initial concentration of thorium, initial solution pH, temperature, and contact time on the reaction between thorium and PENTF, an experiment data set was designed according to Box–Behnken model. The analysis of variance calculations for regression model were carried out in 95% confidence level and were checked for fitting experimental data and predicted values. The correlation coefficient value (R2) obtained as 94% showed that there was a correlation between the predicted and the observed values. The optimum pH, temperature, initial concentration of thorium, and interaction time in studied ranges were found as 2.81, 35?, 160 mg·L-1, and 120 min, respectively. At these conditions thorium (IV) ions adsorption yield was obtained as 89 ± 2%. The Freundlich, Langmuir, and Dubinin–Radushkevich isotherms were used to investigate the characteristics of the process. These characteristics data imply that the Freundlich model fits better than the Langmuir model for the Th (IV) sorption onto PENTFs with KF and n values were found to be 20.6 mg·g-1 and 1.08 L·mg-1, respectively. The thermodynamic parameters were also computed as negative ?H value suggest that adsorption of Th (IV) is exothermic nature. The calculated negative and positive values of ?G indicate that the sorption process is favorable (energetically) while running below 40? and over this point the process status change to non-spontaneous, respectively. © 2017, © The Author(s) 2017