Sorption of uranium (VI) from aqueous solutions by DEEA organo-volcanic: Isotherms, kinetics and thermodynamic studies

Sorption of uranium (VI) from aqueous solutions by DEEA organo-volcanic: Isotherms, kinetics and thermodynamic studies 1 first-author 2 corresp Corresponding author, umran.hicsonmez@bayar.edu.tr Corresponding author, umran.hicsonmez@bayar.edu.tr umran.hicsonmez@bayar.edu.tr 3 2 Department of Primary School Science Teaching, Faculty of Education, Manisa Celal Bayar University, Demirci, Manisa 45900, Turkey Department of Primary School Science Teaching, Faculty of Education, Manisa Celal Bayar University, Demirci, Manisa 45900, Turkey Department of Chemistry, Faculty of Science and Art, Manisa Celal Bayar University, Manisa 45047, Turkey Department of Chemistry, Faculty of Science and Art, Manisa Celal Bayar University, Manisa 45047, Turkey Department of Physics, Faculty of Science and Art, Manisa Celal Bayar University, Manisa 45047, Turkey Department of Physics, Faculty of Science and Art, Manisa Celal Bayar University, Manisa 45047, Turkey The sorption of the uranium (VI) ions from aqueous solutions by DEEA organo-volcanics (Kula-TURKEY) was investigated under different experimental conditions. Diethylethanol ammonium (DEEA) was used to modify the surface of basaltic volcanics. The characteristic of basaltic volcanic was analyzed by XRF, SEM-EDS, FTIR, and XRD. The BET surface areas of unmodified volcanics and DEEA modified-volcanics were found as 2.265 m 2 /g and 3.689 m 2 /g, respectively. The volcanic samples were treated by using different concentrations of DEEA. The adsorption of U (VI) on natural and modified volcanics was examined as a function of the contact time, initial pH of the solution, initial U (VI) concentration, and temperature. Langmuir, Freundlinch, and D-R adsorption isotherms were used to describe the adsorption. While examining the adsorption percentage and distribution coefficient, these values for unmodified volcanics were found to be 25 % ±0.76, and 10.08 mL/g for the DEEA modified-volcanics were 88 % ±1.04 and 220 mL/g, respectively. The pseudo-first-order and pseudo-second-order kinetic model were used to describe the kinetic data. In this study, it can be seen that the adsorption process is suitable for the pseudo-second-order kinetic model. Various thermodynamic parameters (ΔG o , ΔH o , and ΔS o ) were calculated with the thermodynamic distribution coefficients obtained at different temperatures. The sorption process was a chemical adsorption process. The results indicated that the processes are spontaneous and endothermic. DEEA Kula volcanics Uranium Adsorption Isotherm 1. Introduction 1 Thorium and uranium mining, nuclear fuel cycle processes, nuclear power plant decontamination of nuclear facilities, and institutional uses of radioisotopes such as by agriculture, industry, research reactors, and medicine are among the main sources of radioactive wastes [ 1 1 ]. One of the most important heavy metals is uranium because it contains chemical toxicity and radioactivity [ 1 1 ]. It has been classified as a confirmed human carcinogen by the EPA (The Environmental Protection Agency). The only acceptable limit for the risk of cancer from uranium is zero tolerance. Moreover, the maximum contaminant level (MCL) was accepted as 30 mg/L by the EPA (The Environmental Protection Agency). The interim maximum acceptable level (IMAC) was proposed as 20 mg/L by Canada, and the reference level was recommended as 2 mg/Lby WHO [ 2 2 , 3 3 ]. Some methods, for example adsorption, biosorption, ion exchange, and solvent extraction have been developed to recover uranium from waste products [ 4 4 - 7 7 4-7 ]. Adsorption and ion- exchange are among the most used methods for the removal of uranium in industrial waste products. The clay and zeolite adsorbents known as natural adsorbent have sufficient sorption capacity. They are low cost, nontoxic, and abundant in nature. Further, the adsorption capacity of the clays is increased by expanding the clay pores and modifying various materials. In particular, the adsorption capacity of clays can be increased by using the calcinations technique, washing with acidic-alkali solutions, and affecting the inorganic cations [ 8 8 - 11 11 8-11 ]. The surface treatment of clay minerals with organic cations (usually quaternary ammonium compounds) can intensely modify the surface structures [ 12 12 , 13 13 ]. A number of studies have used HDTMA (hexadecyltrimethylammonium) modified clays and have shown their effectiveness in the removal of organic and metal ions such as phenol and Pb 2+ ions from aqueous solutions [ 14 14 - 16 16 14-16 ]. Majdan et al. [ 17 17 ] examined the uranium adsorption on organo bentonit treated with HDTMA and the structural properties of the adsorbent and adsorption products. Sprynskyy et al. [ 18 18 ] investigated the ability of natural and organic cation modified diatomite (HDTMA–diatomite) to remove U (VI) ions. The maximum sorption capacities in the natural and the modified diatomite for U (VI) were found as 25.63 µmol/g and 667.40 µmol/g respectively. Intensive magma and rock fragmentation are formed by volcanic eruptions. They produce volcanic ash. Volcanic ashes have particles with average diameters < 2 mm [ 19 19 ]. These volcanic ejecta, or tephras, contain various silicates and other minerals of different sizes such as volcanic glass, feldspar, quartz, hornblende, hypersthene, augite, magnetite, biotite, and apatite [ 20 20 ].Kula basaltic volcanics were selected because they are abundant in nature, cheap, and an accessible sorbent. Kula is one of the areas in which the young volcanic rocks are seen in Turkey. The Kula volcanics are situated in an area with a length of 30-35 km and a width of 10-15 km in the Manisa province, Turkey. These are quaternary alkali basaltic lava flows and tephra. Tephra is a general term for fragments of volcanic rock and lava regardless of size, which are blasted into the air by explosions or carried upwards by hot gases in the eruption columns or porous structure lava fountains [ 21 21 , 22 22 ]. In a study carried out by Kütahyalı et al. [ 22 22 ], the sorption of strontium ions on non-treated and HCl-treated with Kula volcanic were calculated as 2.04 and 1.72 mg/g, respectively. In this study, the adsorption behavior of U (VI) on Kula basaltic organo-volcanics modified by (DEEA) was investigated. The parameters affecting the uranium adsorption in aqueous solutions, such as the concentration of organic cation, contact times, initial pH, uranium concentration, and temperature were investigated, and the optimum conditions for the adsorption process were determined. 2 Materials and methods 1 2.1 Materials 2 The basaltic volcanics used in the present study were taken from the Manisa-Kula region of Turkey. Kula volcanics are classified as basic according to the rate of SiO 2 production, and basaltic according to their output temperature [ 23 23 ]. Kula basaltic volcanics were selected because they are abundant in nature, cheap, and an accessible sorbent. A cationing surface modifying agent (N,N-Diethylethanolammonium chloride DEEA-Cl (C 6 H 13 NO . HCl, WA 151.64 g/mol)), which is a quaterner ammonium salt, was used. A standard solution of 1000 mg/L U (VI) was prepared by dissolving a suitable amount of UO 2 (CH 3 COO) 2 2H 2 O (Merck, Germany) in ultrapure water. The initial pH solutions were changed by HNO 3 or NaOH. U (VI), and the concentrations were determined by Arsenazo III [ 24 24 ]. A PG (UK) instrument T80 UV-Vis Spectrophotometer was used. All reagents and solvents used were of an analytical grade. 2.2 Preparation of organo-volcanics 2 The organo-volcanics were prepared by treating the volcanics with an aqueous solution of DEEA) ( Fig 1 Fig 1 ). A total of 3 g of volcanics with 30 mL DEEA solution of different concentrations were added in a flask, which was gently shaken for 24 h at 20 o C. Then, the DEEA-modified volcanics were centrifuged at 4000 rpm, washed five times with ultrapure water, and dried at 60 o C [ 8 8 ]. Thus, the volcanics were modified with the addition of DEEA amounts of 5, 10, 15, and 20 mM. 2.3 Characterization of organo-volcanics 2 The surface structure of the made organo-volcanic was examined under a FEI QUANTA 400F SEM scanning electron microscope at 1.2 nm resolution. The dried powders (approximately 0.01 g) were placed on a sticky carbon tape on standard Al mounts, then sputter coated with a thin conductive layer of gold. The chemical composition of the basaltic original volcanic samples was analyzed by X-Rays Fluorescence Spectroscopy (XRF), using a Spectro IQ II instrument. The interactions between DEEA and the volcanics were examined by FTIR spectroscopy. The FTIR spectra was obtained by using KBr pellets with a Perkin Elmer FT-IR System/Spectrum BX. XRD patterns of the unmodified volcanite and the DEEA-uranium modified volcanite were obtained by using X-ray diffraction analyses (PANALYTICAL Emperian diffractometer), and the samples were scanned from 2 to 88 2-Theta in step sizes of 0.0130 and scanned at a step time of 148.92 s. The surface areas of the volcanics were found by using the BET equation to the physical adsorption data for the nitrogen at 77 K. The unmodified and DEEA-volcanic samples were degassed in a vacuum at 573 K and 323 K for 8 hours respectively. The (BET) analysis using the Autosorb 6 by Quantachrome Corporation was performed. The SEM-EDS images and BET were performed at the Central Laboratory of the Middle East Technical University in TURKEY. 2.4 Adsorption experiments 2 The uranyl acetate solution was added to the organo-volcanics. The sorption studies were carried out using the batch method. The mixture was shaken in a shaker (GFL 1083 model). The uranium (VI) percentage and adsorption uptake in the equilibrium, q e (mg/g) were found by using the following equations: <math display="block" id="M1"><mrow><mtext>removal efficiency     </mtext><mi>U</mi><mi>%</mi><mo>=</mo><mfrac><mrow><mo stretchy="false">(</mo><msub><mi>C</mi><mtext>o</mtext></msub><mo>−</mo><msub><mi>C</mi><mtext>e</mtext></msub><mo stretchy="false">)</mo></mrow><mrow><msub><mi>C</mi><mtext>o</mtext></msub></mrow></mfrac><mo>×</mo><mn>100</mn></mrow></math> <math display="block" id="M2"><mrow><msub><mi>q</mi><mtext>e</mtext></msub><mo>=</mo><mo stretchy="false">(</mo><msub><mi>C</mi><mtext>o</mtext></msub><mo>−</mo><msub><mi>C</mi><mtext>e</mtext></msub><mo stretchy="false">)</mo><mo>×</mo><mfrac><mi>V</mi><mi>m</mi></mfrac><mtext>     </mtext><mrow><mo>(</mo><mrow><mtext>mg/g</mtext></mrow><mo>)</mo></mrow><mo>,</mo></mrow></math> where, C o , is the initial concentration of U (VI) in the solution, (mg/L); C e is the equilibrium concentration of the uranium in the solution, (mg/L); V is the solution volume (L), and m is the dry adsorbent mass (g). The distribution coefficient, K d (mL/g), was calculated using Eq. (3): <math display="block" id="M3"><mrow><msub><mi>K</mi><mtext>d</mtext></msub><mo>=</mo><mfrac><mrow><mo stretchy="false">(</mo><msub><mi>C</mi><mtext>o</mtext></msub><mo>−</mo><msub><mi>C</mi><mtext>e</mtext></msub><mo stretchy="false">)</mo></mrow><mrow><msub><mi>C</mi><mtext>e</mtext></msub></mrow></mfrac><mo>×</mo><mfrac><mi>V</mi><mi>m</mi></mfrac><mo>.</mo></mrow></math> 3 Results and discussion 1 3.1 Characteristic analysis 2 The chemical composition of the original basaltic volcanic sample was found to be composed of SiO 2 , Al 2 O 3 , Fe 2 O 3 , MnO, MgO, CaO, Na 2 O, K 2 O, TiO 2 , P 2 O 5, and other trace elements at the percentages of 48.4%; 17.66%; 8.648%; 0.085%; 8.538%; 6.234%; 3.989%; 2.881%; 1.85%, 0.625%, and 1.09 %, respectively. The morphologies, as well as the structural ordering of the natural and modified volcanic, are presented in Fig. 2a Fig. 2a and Fig. 2b Fig. 2b , respectively. There are many crystals in the cavities of unmodified volcanics ( Fig. 2a Fig. 2a ). It was observed that the morphology of the surface was changed by the DEEA surfactant. The volcanic surface was covered with the DEEA organic. Carbon traces on the surface were seen, according to the findings of EDS ( Fig. 2b Fig. 2b ). The specific surface areas of the unmodified and DEEA modified volcanics were found as 2.265 and 3.689 m 2 /gby the multipoint BET method, respectively. The FTIR spectras of DEEA organo-volcanic and U (VI)-DEEA organo-volcanic are shown in Fig.3 Fig.3 . For the DEEA organo-volcanic, the broad band around 3385 cm -1 in the DEEA organo-volcanic was attributed to the O-H stretching vibrations. Generally, the C-H stretching bands of the alkylammonium cations are found in the 3020-2800 cm -1 area [ 25 25 ]. For the modified volcanic, two weak bands were noted at 2945 and 2845 cm -1 . The HOH deformation peak at 1654 cm -1 was present in the FTIR spectrum of the DEEA organo-volcanic. Generally, the adsorbed material was water contributing to the bending region in the 1600-1700 cm -1 area [ 24 24 ].The strong band around 1031 cm -1 was ascribed to the Si-O stretching vibration. The stretching and bending vibrations of the SiO 4 2- tetrahedral were the peaks at 537 and 471 cm -1 . The absorption band at 695 cm -1 was attached to the coupled Al-O and Si-O out of plane vibrations [ 26 26 ]. In the case of the U (VI)-DEEA organo-volcanic, peaks similar to that of the organo-volcanic structure were detected in the region of 3200-3600 cm -1 where it is indicated by Si-O, N-H and O-H stretching vibrations. It was observed that the H-O-H deformation peak shifted from 1654 cm -1 to 1641 cm -1 with adsorption. The changes of the absorption band related to the H-O-H deformation of water molecules adsorbed on the volcanic were shown by this band. The characteristic absorption peak of Si-O of the organo-volcanic was observed at 1031 cm -1 , and the Si-O of the uranium adsorption was expanded to the same range, which showed that the uranium is adsorbed on the volcanic surface. In additon, the peak at 695 cm -1 was shifted to the 654 cm -1 region. According to the XRD patterns of natural volcanics, such minerals as quartz (SiO 2 ), Coesite (SiO 2 ), potassium sodium alumosilicate (K .667 Na ..333 ) (AlSiO 4 ), magnesium iron alumosilicate (Mg 0.34 Fe 1.66 Al 4 ), Sekaninaite (Si 5 O 18 ), calsium magnesium catena-silicate diopside high (Ca Mg Si 2 O 6 ), and ferropargasite (NaCa 2 Fe 4 Al(Si 6 Al 2 )O 22 (OH) 2 were determined in the samples. The XRD patterns of the unmodified volcanite and the DEEA-uranium modified volcanite are shown in Figure 4 Figure 4 . The unmodified volcanite sample mostly consisted of the SiO 2 amorphous phases ( Fig.4 Fig.4 ). The X-ray pattern of the unmodified volcanite was different to the pattern of the treated one. A new few peaks of the organic cation are seen on the X-ray pattern of the DEEA-uranium modified material. They could originate from the DEEA cations and uranium deposited on the volcanite surface. Also, the uranium peak appeared on the pattern 34, 39 2-Theta o . The uranium peaks are similar to those in the literature [ 27 27 , 28 28 ]. The surface area was calculated by using the multipoint BET method. The BET surface areas of unmodified volcanics and DEEA modified-volcanics were found as 2.265 m 2 /g and 3.689 m 2 /g, respectively. The zeta potentials of the unmodified and modified volcanics were measured in the pH range of 3–8. The surfaces of both the volcanics were found to be negatively charged. We believe that there was an electrostatic attraction on the volcanic surface between the negative charge of the SiO and AlO groups and the positive charge of the organic chain. However, the volcanic surface was also negatively charged because the DEEA concentration was low. In the literature, it has been emphasized that cationic surfactants covered all the clay surfaces and displacing expanded by entering of the organic molecules between the sheet layers of the clay minerals [ 29 29 ]. 3.2 Batch adsorption experiment 2 3.2.1 Effect of different concentrations of organic cation 3 The effect of the organic cation concentration (5, 10, 15 and 20 mM)on the adsorption was examined in a media solution of 20 mg/L U(VI). The maximum U (VI) adsorption was found at 5 mM DEEA. When the organic cation concentration reached 5 mM micelle formation, it became more efficient than the interaction of the hydrocarbon chains. After this critical micelle point, the absorption capacity decreases [ 25 25 ]. 3.2.2 Effect of contact time 3 The time dependence of the U (VI) adsorption experiments is given in Fig. 5 Fig. 5 under the conditions of 1 g adsorbent, a volume of 30 mL, 20 mg/L U (VI), a pH of 3.5, and a temperature of 25 °C. The sorption of the U (VI) was increased from 61.15% to 76.30 % after 4 hours. Equilibrium was reached within 4 hours. 3.2.3 Effect of initial pH values 3 The effect of the initial pH on the U (VI) sorption was examined by adjusting it to different values ranging from 2.0 to 6.0 (30 mL solution and 20 mg/L U (VI)). The solution and volcanics were mixed at 25 °C for 4 hours. The U (VI) sorption strongly depended on the pH solution, and increased with the increasing pH ( Fig. 6 Fig. 6 .). When organic cation concentration reached 5 mM micelle formation, it is more efficient than the interaction of the hydrocarbon chains. After this critical micelle point, the absorption capacity decreases [ 24 24 ]. At a low pH (below pH 4), when the dissociation of the Si-OH bonds are suppressed, the adsorption of the U (VI) is low. The UO 2 2+ in the acidic solutions is the only complex-forming uranium species ((UO 2 ) 2 CO 3 (OH) 3 - , UO 2 OH + , UO 2 (OH) 2 , (UO 2 ) 2 (OH) 2 2+ , (UO 2 ) 3 (OH) 5 + and UO 2 CO 3 , etc) [ 14 14 ]. (UO 2 ) 2 (OH) 2 2+ ) and (UO 2 .OH) + hydrolysis species were found between pH 3.0 and 4.0. Also, the (UO 2 ) 3 (OH) 5 + forms at pH 4.0, and becomes dominant at the pH values exceeding 4.5 [ 30 30 ]. In this study, the optimum pH was found to be 5.0. 3.2.4 Effect of initial U (VI) concentration 3 The effect of the initial concentration of U (VI) was examined by contacting a mass of DEEA organo-volcanics (1 g) at 25 °C and an initial pH=5.0 using a range of U (VI) concentrations (20, 40, 60, 80, and 100 mg/L) ( Fig. 7 Fig. 7 ). The removal of the U (VI) was increased by increasing the initial U (VI) concentration between 20 mg/L and 40 mg/L. Moreover, the adsorption capacity of the DEEA-volcanics for U (VI) was decreased by increasing the initial uranium concentration (after 40 mg/L). The optimum concentrationwas found to be40mg/L. 3.2.5 Adsorption isotherms 3 Adsorption isotherms show the equilibrium relationships between the adsorbed ion concentrations and ion concentrations in a solution. In our work, the Langmuir, Freundlich, and Dubinin–Radushkevich isotherm adsorption models, the most commonly used models, were also employed to describe the sorption behaviors. The Langmuir isotherm model assumes that the sorption occurs on a homogeneous surface by the monolayer sorption. The Langmuir adsorption isotherm model is represented as Eq. (4), <math display="block" id="M4"><mrow><mfrac><mrow><msub><mi>C</mi><mtext>e</mtext></msub></mrow><mrow><msub><mi>q</mi><mtext>e</mtext></msub></mrow></mfrac><mo>=</mo><mfrac><mn>1</mn><mrow><msub><mi>K</mi><mtext>L</mtext></msub><msub><mi>q</mi><mtext>m</mtext></msub></mrow></mfrac><mo>+</mo><mfrac><mrow><msub><mi>C</mi><mtext>e</mtext></msub></mrow><mrow><msub><mi>q</mi><mtext>m</mtext></msub></mrow></mfrac><mo>,</mo></mrow></math> where, q m (mg/g) is the maximum amount of adsorption of U (VI) per unit mass of the adsorbent, and K L (L/mg) is the Langmuir affinity constant that represents the affinity between the adsorbent and the adsorbate. Freundlich isotherm, the linear equation is expressed by Eq. (5), <math display="block" id="M5"><mrow><mi>log</mi><msub><mi>q</mi><mi>e</mi></msub><mo>=</mo><mi>log</mi><msub><mi>K</mi><mtext>F</mtext></msub><mo>+</mo><mfrac><mn>1</mn><mi>n</mi></mfrac><mi>log</mi><msub><mi>C</mi><mtext>e</mtext></msub><mo>,</mo></mrow></math> where K F [(mg/g)(L/mg) 1/n ] is the constant related to the adsorption capacity of the adsorbent, and 1/ n is the constant related to the adsorption intensity of the adsorbent. The Freundlich isotherms were based on the adsorption on the heterogeneous solid surfaces. The Dubinin–Radushkevich isotherm is generally applied to express the adsorption mechanism with a Gaussian energy distribution onto a heterogeneous surface. The model has often successfully fit high solute activities and the intermediate range of concentrations data well. <math display="block" id="M6"><mrow><mi>ln</mi><msub><mi>q</mi><mtext>e</mtext></msub><mo>=</mo><mi>ln</mi><mo stretchy="false">(</mo><msub><mi>q</mi><mtext>s</mtext></msub><mo stretchy="false">)</mo><mo>−</mo><msub><mrow><mo stretchy="false">(</mo><msub><mi>K</mi><mrow><mtext>ad</mtext></mrow></msub><msup><mi>ε</mi><mn>2</mn></msup><mo stretchy="false">)</mo></mrow><mo>,</mo></msub></mrow></math> where q e is the amount of adsorbate in the adsorbent at equilibrium(mg/g); q s is the theoretical isotherm saturation capacity (mg/g); K ad is the Dubinin–Radushkevich isotherm and is constant (mol 2 /kJ 2 ), and ε is the Dubinin–Radushkevich isotherm and is constant. The approach is usually applied to distinguish the physical and chemical adsorption of metal ions with its mean free energy. The E per molecule of the adsorbate (for removing a molecule from its location in the sorption space to the infinity) can be computed by the relationship (7): <math display="block" id="M7"><mrow><mi>E</mi><mo>=</mo><msub><mrow><mrow><mo>[</mo><mrow><mfrac><mn>1</mn><mrow><msqrt><mrow><mn>2</mn><msub><mi>B</mi><mrow><mtext>DR</mtext></mrow></msub></mrow></msqrt></mrow></mfrac></mrow><mo>]</mo></mrow></mrow><mo>,</mo></msub></mrow></math> where B DR is denoted as the isotherm constant. Meanwhile, the parameter, ε, can be calculated by Eq. (8): <math display="block" id="M8"><mrow><mi>ε</mi><mo>=</mo><mi>R</mi><mi>T</mi><mi>ln</mi><msub><mrow><mrow><mo>[</mo><mrow><mn>1</mn><mo>+</mo><mfrac><mn>1</mn><mrow><msub><mi>C</mi><mtext>e</mtext></msub></mrow></mfrac></mrow><mo>]</mo></mrow></mrow><mo>,</mo></msub></mrow></math> where R , T , and C e represent the gas constant (8.314 J/mol K), the absolute temperature (K), and adsorbate equilibrium concentration (mg/L), respectively. We also tested the Langmuir, Freundlich, and D-R adsorption isotherms, and the results indicated that the D-R adsorption isotherm ( R 2 > 0.96) fitted the data better than the Langmuir and Freundlich adsorption isotherms . All the results are listed in Table 1 Table 1 . 3 1 Langmuir 3 1 Freundlich 4 1 D-R 1 1 q m (mg/g) 1 1 K L (L/mg) 1 1 R 2 1 1 K F (mg/g) 1 1 1/ n 1 1 R 2 1 1 q s (mg/g) 1 1 K ad (mol 2 /kJ 2 ) 1 1 E (KJ/mol) 1 1 R 2 1 1 400 1 1 0.0144 1 1 0.3131 1 1 2.2 1 1 0.9061 1 1 0.9564 1 1 74.24 1 1 0,0040 1 1 11,18 1 1 0.9646 From this research work, the maximum monolayer coverage capacity (qm) from the Langmuir Isotherm model was determined to be 400 mg/g, K L (Langmuir isotherm constant) is 0.014 L/mg, and the R 2 value is 0.31. The Freundlich isotherm constants k f and n were determined from the intercept and slope of a plot of log qe versus log C e ( Fig. 8 Fig. 8 ). From the data in Table 1 Table 1 , it can be seen that the value of 1/ n is 0.9061, the sorption of U(VI) on to DEEA organo-volcanics is favourable, and the R 2 value is 0.9564. Thus, the adsorption process is multilayered. In addition, from the linear plot of the D-R model, q s was determined to be 74.24 mg/g, the mean free energy, E was 11.18 KJ/mol indicating a chemical adsorption process, and the R 2 was 0.9646 higher than that of the Freundlich. Essentially, the DEEA organo-volcanic shows very good sorption performance for U(VI) in comparison with other adsorbents reported in the literature in Table 2 Table 2 . 1 1 Adsorbent 1 1 K F (mg/g) 1 1 pH 1 1 References 1 1 Wood powder 1 1 0,461 1 1 8 1 1 [ 31 31 ] 1 1 Wheat straw 1 1 0,346 1 1 7 1 1 [ 31 31 ] 1 1 Hematite 1 1 1,63 1 1 7 1 1 [ 2 2 ] 1 1 Talc 1 1 2,19 1 1 5 1 1 [ 32 32 ] 1 1 Natural clinoptilolite zeolite 1 1 0,087 1 1 6 1 1 [ 33 33 ] 1 1 Goethite-coated sand 1 1 0,064 1 1 9 1 1 [ 34 34 ] 1 1 Polyacrylamidoxime resin coated quartz sand 1 1 1,0 1 1 6 1 1 [ 35 35 ] 1 1 DEEA organo-volcanics 1 1 2,2 1 1 5 1 1 This Study Uranium adsorption onto DEEA organo-volcanics is shown schematically in Fig. 9 Fig. 9 . 3.2.6. Adsorption kinetics 3 The kinetics of adsorption is an important aspect in defining the efficiency of the adsorption process. The kinetic data in this study was modeled using pseudo-first-order [ 36 36 ] and pseudo-second-order [ 2 2 ] according to: <math display="block" id="M9"><mrow><mtext>Pseudo-first-order            </mtext><mi>ln</mi><msub><mi>q</mi><mtext>t</mtext></msub><mo>=</mo><mi>ln</mi><msub><mi>q</mi><mtext>e</mtext></msub><mo>−</mo><msub><mi>k</mi><mn>1</mn></msub><mi>t</mi><mo>,</mo></mrow></math> <math display="block" id="M10"><mrow><mtext>Pseudo-second-order            </mtext><msub><mi>q</mi><mtext>t</mtext></msub><mo>=</mo><mfrac><mn>1</mn><mrow><msub><mi>k</mi><mn>2</mn></msub><msubsup><mi>q</mi><mtext>e</mtext><mtext>2</mtext></msubsup></mrow></mfrac><mo>+</mo><mfrac><mn>1</mn><mrow><msub><mi>q</mi><mtext>e</mtext></msub><mi>t</mi></mrow></mfrac><mo>,</mo></mrow></math> where qe and qt are the adsorption capacity (mg/g) at equilibrium and time ' t ’, respectively, k 1 and k 2 are the pseudo-first-order and pseudo-second-order constants of the adsorption, respectively. The relationships of ln( qt - qe ) to t and t / qt to t were plotted according to the experimental values ( Fig. 10 Fig. 10 ). The adsorption kinetic data was ideally described by the pseudo-second-order equation (R 2 =0.9999). qe and k 2 were obtained and represented in Table 3 Table 3 . 1 1 Temperature (K) 1 1 q e (mg/g) 1 1 k 2 (g/mg min) 1 1 R 2 1 1 298 1 1 0.458 1 1 0.183 1 1 0.999 3.2.7. Thermodynamics studies 3 Entropy (ΔS o ) and Gibbs free energy (ΔG o ) factors were used to determine the processes occurring spontaneously. The thermodynamic data can be calculated with the thermodynamic distribution coefficient ( K d ). ΔG o , ΔH o (enthalpy change), and the ΔS o were calculated with the eq.11 [ 37 37 ]. <math display="block" id="M11"><mrow><mi>ln</mi><mtext>​</mtext><msub><mi>K</mi><mtext>d</mtext></msub><mo>=</mo><mfrac><mrow><mi>Δ</mi><msup><mi>S</mi><mi>o</mi></msup></mrow><mi>R</mi></mfrac><mo>−</mo><mfrac><mrow><mi>Δ</mi><msup><mi>H</mi><mi>o</mi></msup></mrow><mrow><mi>R</mi><mi>T</mi></mrow></mfrac><mo>,</mo></mrow></math> where T is the absolute temperature (K), and R is the gas constant (kJ/molK). ΔG o value was calculated from (Eq.12): <math display="block" id="M12"><mrow><mi>Δ</mi><msup><mi>G</mi><mi>o</mi></msup><mo>=</mo><mi>Δ</mi><msup><mi>H</mi><mi>o</mi></msup><mo>−</mo><mi>T</mi><mi>Δ</mi><msup><mi>S</mi><mi>o</mi></msup><mo>.</mo></mrow></math> The experiments were done at different temperatures for a solution concentration of 40 mg/L of uranium. The values of ΔH o and ΔS o were calculated from the slopes and intercepts of the linear regression of ln K d versus 1/ T . According to Table 4 Table 4 , the process is endothermic and the adsorbent adsorption capacity increases with increasing temperatures. 1 1 ∆ H o 1 1 ∆ S o 5 1 ∆ G o (KJ/mol) 1 1 (KJ/mol) 1 1 (KJ/(mol.K)) 1 1 293 K 1 1 303 K 1 1 313 K 1 1 323 K 1 1 333 K 1 1 2.2 1 1 0.05 1 1 -13.49 1 1 -14.02 1 1 -14.56 1 1 -15.09 1 1 -15.63 When the ions are adsorbed on the adsorbent surface, the water molecules that previously bonded onto the metal ion are released and dispersed into the solution. They lead to an increase in the entropy [ 38 38 ]. 4. Conclusion 1 The removal of U (VI) on DEEA organo-volcanics was examined as the parameters (times, initial pH, temperature, and initial concentration of U (VI)). The uranium adsorption and K d value of the natural volcanic after treatment with DEEA increased from 25 % ±0.76 to 88 % ±1.04 and from 10.08 mLg -1 to 220 mLg -1 , respectively. The studies on XRD and SEM analyses give characteristic results and indicated that DEEA penetrated into the clay interlayer. The data examined handling the adsorption models (Langmuir, Freundlich, and D-R) in the equilibrium. The Freundlich and D-R isotherms on heterogeneous surfaces provided the best correlation with the uranium adsorption. The rate of the process can be represented very well by the pseudo-second-order kinetic model. The temperature reliance of the U (VI) adsorption on DEEA organo-volcanic was examined, and the thermodynamic data ΔH o , ΔG o , and ΔS o were analyzed. The sorption process was a physical adsorption process for enthalpy exchange in 2.2 kJmol -1 . The result shows an endothermic heat of adsorption, but a negative free energy value, indicating that the process of uranium adsorption is favored at high temperatures. 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Mater . 186 , 458 - 465 ( 2011 ). doi: 10.1016/j.jhazmat.2010.11.029 http://doi.org/10.1016/j.jhazmat.2010.11.029 Kinetics and thermodynamics of cadmium removal by adsorption onto nano zerovalent iron particles A. Rahmati , A. Ghaemi , M. Samadfam , Kinetic and thermodynamic studies of uranium(VI) adsorption using Amberlite IRA-910 resin . Ann. Nucl. Energy 39 , 42 - 48 ( 2012 ). doi: 10.1016/j.anucene.2011.09.006 http://doi.org/10.1016/j.anucene.2011.09.006 Kinetic and thermodynamic studies of uranium(VI) adsorption using Amberlite IRA-910 resin The authors would like to thank the Central Laboratory of the Middle East Technical University for the analysis of the SEM-EDS and BET values in the samples. 10.1007/s41365-018-0359-3 This work was supported by the Manisa Celal Bayar University (No. BAP 2012-005). 2017-02-04 2017-04-20 2017-04-29 2018-02-13 2018-02-01 2021-04-11 © China Science Publishing & Media Ltd. (Science Press), Shanghai Institute of Applied Physics, the Chinese Academy of Sciences, ChineseNuclear Society and Springer Nature Singapore Pte Ltd. 2018 This is a post-peer-review, pre-copyedit version of an article published in Nuclear Science and Techniques. The final authenticated version is available online at: http://dx.doi.org/10.1007/s41365-018-0359-3 http://dx.doi.org/10.1007/s41365-018-0359-3 . 2018 Nuclear Science and Techniques 02 29