[en] The effects of pH, ionic strength, competing ions and initial metal concentrations on the uptake behavior and mechanism of radioactive Ni(II) onto MnO₂ was investigated using a combination of classical macroscopic methods and the extended X-ray absorption fine structure (EXAFS) spectroscopy technique. The results indicated that the uptake of Ni(II) on MnO₂ is obviously dependent on pH but independent of ionic strength, which suggested that the uptake of Ni(II) onto MnO₂ is attributed to an inner-sphere surface complex rather than an outer-sphere surface complex. EXAFS analysis shows that the hydrated Ni(II) is adsorbed through six-fold coordination with an average Ni-O interatomic distance of 2.04 ± 0.01 A. It can be inferred from the EXAFS analysis that the inner-sphere surface complex of Ni(II) onto MnO₂ is involved in both edge-sharing and corner-sharing linkages. Both the macroscopic uptake data and the molecular level evidence of Ni(II) surface speciation at the MnO₂-water interfaces should be factored into better prediction of the bioavailability and mobility of Ni(II) in soil and water environment. (author)

[en] An ammonium/hydroxyl-enriched p-BN microrods were synthesized and the adsorption behavior of uranyl on p-BN was systematically studied. The adsorption kinetic and isotherm studies revealed the adsorption behavior is independent on electrostatic attraction or chemisorption. The results demonstrate uranyl hydrolyzed precipitated crystals are formed on the surface of p-BN at an optimized pH of 2.86 and the maximum adsorption capacity can reach 413 mg g^-1 at T = 303 K. A hypothetical adsorption mechanism with a combination of surface adsorption and induced precipitation crystallization was proposed. (author)

[en] In this work, a series of batch experiments were carried out to investigate the effect of various environmental factors such as contact time, pH, ionic strength, coexisting electrolyte ions, humic substances and temperature on the sorption behavior of illite towards ⁶⁴Cu(II). The results indicated that ⁶⁴Cu(II) sorption on illite achieved equilibrium quickly. The pH- and ionic strength-dependent sorption suggested that ⁶⁴Cu(II) sorption on illite was dominated by ion exchange or outer-sphere surface complexation at pH < 7, whereas the pH-dependent and ionic strength-independent sorption indicated that the sorption process was mainly attributed to inner-sphere surface complexation at pH > 7. A positive effect of humic substances on ⁶⁴Cu(II) sorption was found at pH < 6.5, whereas a negative effect was observed at pH > 6.5. The Langmuir and Freundlich models were used to simulate the sorption isotherms of ⁶⁴Cu(II) at three different temperatures of 293, 313, and 333 K. The thermodynamic parameters (ΔH⁰, ΔS⁰, and ΔG⁰) of ⁶⁴Cu(II) sorption on illite were calculated from the temperature dependent sorption isotherms, and the results indicated that the sorption of ⁶⁴Cu(II) on illite was endothermic and spontaneous. From the experimental results, it is possible to conclude that illite has good potentialities for cost-effective treatments of ⁶⁴Cu(II)-contaminated wastewaters. (author)

[en] This work examines the sequestration of ⁶⁴Cu(II) by sorption process onto plasma-induced polyaniline (PANI)-grafted multiwalled carbon nanotubes (denoted as MWCNTs/PANI) prepared by an plasma-induced grafting technique. The role of a variety of environmental conditions such as pH, ionic strength, natural organic matter (NOM) in the sorption of ⁶⁴Cu(II) onto MWCNTs/PANI is studied. The results indicate that the sorption is strongly dependent on pH but independent of ionic strength. A positive effect of NOM on ⁶⁴Cu(II) sorption is found at pH <7.5, whereas a negative effect is observed at pH >7.5. The sorption isotherms in the absence and presence of NOM can be better described by Freundlich model than Langmuir model. Sorption isotherms of ⁶⁴Cu(II) at higher initial NOM concentrations are higher than those at lower NOM concentrations. The thermodynamic data calculated from temperature-dependent sorption suggest that the sorption is spontaneous and enhanced at higher temperature. Results of this work suggest that MWCNTs/PANI may be a promising candidate for cost-effective treatments of ⁶⁴Cu(II)-contaminated wastewaters. (author)

[en] Titanate nanotubes (TNTs) have attracted great interest in multidisciplinary study since their discovery. The adsorption of thorium [Th(IV)] onto TNTs in the absence and presence of humic acid (HA)/fulvic acid (FA) was studied by batch technique. The influence of pH from 2.0 to 10.0, ionic strength from 0.001 to 0.1 mol L^-1 NaClO₄, and coexisting electrolyte cations (Li⁺, Na⁺, K⁺) and anions (ClO₄^-, NO₃^-, Cl^-) on the adsorption of Th(IV) onto TNTs was tested. The adsorption isotherms of Th(IV) was determined at pH 3.0 and analyzed with Langmuir and Freundlich adsorption models, respectively. The results demonstrated that the adsorption of Th(IV) onto TNTs increases steeply with increasing pH from 2.0 to 4.0. Generally, HA/FA was showed to enhance Th(IV) adsorption onto TNTs at low pH values, but to reduce Th(IV) adsorption onto TNTs at high pH values. The adsorption of Th(IV) onto TNTs was also dependent on coexisting electrolyte ions in aqueous solution under our experimental conditions. The adsorption of Th(IV) onto TNTs is exothermic and spontaneous. The findings indicating that TNTs can be used as a promising candidate for the enrichment and solidification of Th(IV) or its analogue actinides from large volume solution in real work. (author)

[en] Herein, we used biochar pyrolyzed from rice straw to adsorb uranium (U) from aqueous solutions. The adsorption of U(VI) on biochar was strongly dependent on pH but independent on ionic strength. HA/FA enhanced the sorption at pH <6.8 while inhibited the sorption at pH >6.8. The sorption reached equilibrium within 3 h, which was not mediated by pH. The adsorption process was spontaneous and endothermic, and enhanced at higher temperature. However, the influence of temperature was negligible at low initial U(VI) concentrations. Therefore, biochar derived from rice straw may be a promising adsorbent for the removal of U(VI). (author)

[en] In our published paper entitled 'Sorption of radionickel to goethite: effect of water quality parameters and temperature' published in JRNC 285 (2010) 389-398 [1], the sorption of radionickel to goethite as affected by various environmental conditions such as pH, humic substances, ionic strength and temperature on radionickel sorption has been investigated by using batch technique. The sorption mechanism of radionickel on goethite was discussed according to the experimental data and the fitting results of sorption isotherms by Langmuir, Freundlich and D-R models. Kinetic sorption data was fitted by a pseudo-second-order rate equation. Ho et al. firstly reported the pseudo-second-order rate equation [2, 3], and then further developed this frame work in their following works [4, 5]. In our previous research, we had ever cited the original paper about the sorption isotherms such as Langmuir or Freundlich models. However, the reviewers gave the comments that the models had been widely used and it was not necessary for us to cite the original paper about the sorption isotherm. Similar condition can be also observed for carbon nanotubes that there are a lot of papers about carbon nanotubes not citing the original paper reported by Iijima [6]. In our published paper [1], we think that the pseudo-second-order rate equation has been widely applied and the equation is now a famous model to fit the sorption kinetic data. However, it is essential for us to cite all the relative references accurately so as to transmit scientific knowledge more effectively. We are so sorry to the fact that the original papers [2, 3] were not cited in our published paper [1], but it is not meant to show the disrespect to the author Ho [2]. In our future work, we wish to cite the papers published by Ho whose work are interesting and useful to simulate the sorption kinetic data of metal ions at solid-water interfaces. The physicochemical behavior of radionickel in environment is quite important to understand the potential pollution of radionickel in natural environment. In our published paper [1], the macroscopic data is helpful to understand the sorption mechanism of radionickel at solid-water interfaces. However, the information at microscopic level such as microstructures and chemical species of radionickel can be more accurate to assess the potential physicochemical behavior of radionickel in the environment. This information can be obtained from spectroscopy studies such as XPS, TRLFS and EXAFS. (author)

[en] In this work, sorption of Ni(II) from aqueous solution to goethite as a function of various water quality parameters and temperature was investigated. The results indicated that the pseudo-second-order rate equation fitted the kinetic sorption well. The sorption of Ni(II) to goethite was strongly dependent on pH and ionic strength. A positive effect of HA/FA on Ni(II) sorption was found at pH < 8.0, whereas a negative effect was observed at pH > 8.0. The Langmuir, Freundlich, and D-R models were applied to simulate the sorption isotherms at three different temperatures of 293.15 K, 313.15 K and 333.15 K. The thermodynamic parameters (ΔH⁰, ΔS⁰ and ΔG⁰) were calculated from the temperature dependent sorption, and the results indicated that the sorption was endothermic and spontaneous. At low pH, the sorption of Ni(II) was dominated by outer-sphere surface complexation or ion exchange with Na⁺/H⁺ on goethite surfaces, whereas inner-sphere surface complexation was the main sorption mechanism at high pH. (author)