Authors:D. Das, P. Pathak, S. Kumar, and V. Manchanda
Sorption behavior of 241Am (~10−9 M) on naturally occurring mineral pyrite (particle size: ≤70 μm) has been studied under varying conditions of pH (2–11),
and ionic strength (0.01–1.0 M (NaClO4)). The effects of humic acid (2 mg/L), other complexing anions (1 × 10−4 M CO32−, SO42−, C2O42− and PO43−), di- and trivalent metal ions (1 × 10−3 M Mg2+, Ca2+ and Nd3+) on sorption behavior of Am3+ at a fixed ionic strength (I = 0.10 M (NaClO4)) have been studied. The sorption of 241Am on pyrite increased with pH from 2.8 (84%) to 8.1 (97%). The sorption of 241Am decreased with ionic strength at low pH values (2 ≤ pH ≤ 4), but was insensitive in the pH range of 4–10, suggesting the
formation of outer-sphere complexes on pyrite surface at lower pH, and inner-sphere complexes at higher pH values. The sorption
of 241Am increased in the presence of (i) humic acid (5 < pH < 7.5), and (ii) C2O42− (2 < pH < 3). By contrast, other complexing anions such as (carbonate, phosphate, and sulphate) showed negligible influence
on 241Am sorption. The presence of Mg2+, Ca2+ ions showed marginal effect on the sorption profile of 241Am; while the presence of Nd3+ ion suppressed its sorption significantly under the conditions of present study. The sorption of 241Am on pyrite decreased with increased temperature indicating an exothermic process.
The sorption of Pu(IV), polymeric Pu(IV), Pu(V) and Pu(VI) from the 0.1 M NaClO4 solution onto multiwalled carbon nanotubes was investigated. The kinetic study of the sorption process have shown that the
polymeric Pu(IV) has the highest sorption rate, while decrease of sorption rate for plutonium aqua-ions in the order Pu(VI) > Pu(IV) > Pu(V)
was found. Strong dependence of sorption kinetics of ionic plutonium species on pH was shown, in contrast to polymeric species,
that were shown to quantitatively sorb (99%) in the wide pH range (pH 2–10). Two different sorption mechanisms for ionic and
polymeric plutonium species were proposed: on the bases of sorption isotherms chemisorptions of plutonium aqua-ions onto carbon
nanotubes and through intermolecular interaction for the polymeric plutonium species was defined. Distribution coefficients
of plutonium in various oxidation states were found to increase with pH, showing the highest values for polymeric plutonium
sorption (Kd = 2.4 × 105 mL g−1 at pH = 6).
Sorption of U(VI) from aqueous solution to decarbonated calcareous soil (DCS) was studied under ambient conditions using batch
technique. Soil samples were characterized by XRD, FT-IR and SEM in detail and the effects of pH, solid-to-liquid ratio (m/V), temperature, contact time, fulvic acid (FA), CO2 and carbonates on U(VI) sorption to calcareous soil were also studied in detail using batch technique. The results from experimental
techniques showed that sorption of U(VI) on DCS was significantly influenced by pH values of the aqueous phase, indicating
a formation of inner-sphere complexes at solid–liquid interface, and increased with increasing temperature, suggesting the
sorption process was endothermic and spontaneous. Compared to Freundlich model, sorption of U(VI) to DCS was simulated better
with Langmuir model. The sorption equilibrium could be quickly achieved within 5 h, and sorption results fitted pseudo-second-order
model well. The presence of FA in sorption system enhanced U(VI) sorption at low pH and reduced U(VI) sorption at high pH
values. In absence of FA, the sorption of U(VI) onto DCS was an irreversible process, while the presence of FA reinforced
the U(VI) desorption process reversible. The presence of CO2 decreased U(VI) sorption largely at pH >8, which might due to a weakly adsorbable formation of Ca2UO2(CO3)3 complex in aqueous phase.
Authors:Yalan Liu, Liyong Yuan, Yali Yuan, Jianhui Lan, Zijie Li, Yixiao Feng, Yuliang Zhao, Zhifang Chai, and Weiqun Shi
Uranium is one of the most hazardous heavy metal due to its long half-life radioactivity, high toxicity and mobility as aqueous
uranyl ion (UO22+) under ordinary environmental conditions. Herein, amino functionalized SBA-15 (APSS) was developed as a rapid and efficient
sorbent for removal of U(VI) from the environment. The APSS sample was synthesized by grafting method and was characterized
by SEM, NMR, SAXS, and N2 sorption/desorption isothermal experiments. The sorption of U(VI) by APSS was investigated under different conditions of
pH, contact time, initial U(VI) concentration, ionic strength and solid–liquid ratio. The results show that the sorption of
U(VI) by APSS is strongly dependent on pH but independent of ionic strength and solid–liquid ratios (m/V). The sorption is ultrafast with an equilibrium time of less than 30 min, and the sorption capacity is as large as 409 mg/g
at pH 5.3 ± 0.1. Besides, the U(VI) sorption by APSS from extremely diluted solution and the desorption of U(VI) from APSS
were also studied. It is found that 100 mg of APSS can almost completely remove the U(VI) ions from 4 L aqueous solution with
the U(VI) concentration as low as 4.2 ppb and the sorbed U(VI) can be completely desorbed by 0.1 mol/L nitric acid. The results
strongly reveal the high performance of the APSS material in the removal and preconcentration of U(VI) from the aqueous solution.
Authors:Sharayu Kasar, Sumit Kumar, Aishwarya Kar, K. Krishnan, N. Kulkarni, and B. Tomar
Sorption of Eu(III), an analogue of trivalent actinides (Am, Cm), by amorphous titania as well as different crystalline phases
of titania, namely anatase and rutile, have been studied as a function of pH, using 154Eu (half life = 8.8 yrs, Eγ = 123,247 keV) as a radiotracer. The objective of this study was to investigate the effect of the crystalline phase of the
titania on their sorption behaviour towards the metal ion. Amorphous titania was prepared by organic route and was converted
into anatase and rutile by heating at elevated temperatures based on the differential thermal analysis studies. Eu(III) sorption
by all forms of titania rises sharply with the pH of the suspension, with the sorption edge shifting to higher value in the
order; amorphous < anatase < rutile. However, the normalization of the sorption data to the surface area of the sorbents resulted
in the overlapping of the sorption curves for amorphous and anatase phases, with the data being higher for rutle in the lower
pH region, indicating the effect of the crystal phase on sorption behaviour of Eu(III).
The sorption of Co(II) on Na-montmorillonite was conducted under various conditions, i.e., contact time, adsorbent dosage,
pH, ionic strength, foreign ions, fulvic acid (FA), humic acid (HA) and temperature. Results of sorption data analysis indicated
the sorption of cobalt on Na-montmorillonite was strongly dependent on pH and ionic strength. At low pH, the sorption of Co(II)
was dominated by outer-sphere surface complexation and ion exchange with Na+/H+ on Na-montmorillonite, whereas inner-sphere surface complexation was the main sorption mechanism at high pH. The presence
of different cations influenced Co(II) sorption, while the presence of different anions had no differentiable influences on
Co(II) sorption. The presence of HA and FA decreased the sorption of Co(II) on montmorillonite. The sorption isotherms are
simulated well with the Langmuir model. The thermodynamic parameters (ΔH°, ΔS° and ΔG°) calculated from the temperature dependent isotherms indicated that the sorption reaction of Co(II) on montmorillonite was
an endothermic and spontaneous process. The sorption test revealed that the low cost material was a suitable material in the
preconcentration of Co(II) from large volumes of aqueous solutions.
Authors:Shitong Yang, Donglin Zhao, Guodong Sheng, Zhiqiang Guo, and Yubing Sun
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.
Authors:Mingming Wang, Jun Qiu, Xinquan Tao, Cuiping Wu, Weibing Cui, Qiong Liu, and Songsheng Lu
Multiwalled carbon nanotubes (MWCNTs) have attracted multidisciplinary study because of their unique physicochemical properties.
Herein, the sorption of U(VI) from aqueous solution to oxidized MWCNTs was investigated as a function of contact time, pH
and ionic strength. The results indicate that U(VI) sorption on oxidized MWCNTs is strongly dependent on pH and ionic strength.
The sorption of U(VI) is mainly dominated by surface complexation and cation exchange. The sorption of U(VI) on oxidized MWCNTs
is quickly to achieve the sorption equilibrium. The sorption capacity calculated from sorption isotherms suggests that oxidized
MWCNTs are suitable material in the preconcentration and solidification of U(VI) from large volumes of aqueous solutions.
Authors:Mingming Wang, Xingquan Tao, and Xiaoping Song
Oxidized multiwalled carbon nanotubes (MWCNTs) were characterized by SEM and FTIR. The sorption of Th(IV) on MWCNTs was studied
as a function of contact time, pH, ionic strength, Th(IV) concentration and temperature. The results indicate that the sorption
of Th(IV) on MWCNTs is strongly dependent on pH and weakly dependent on ionic strength. The sorption thermodynamics of Th(IV)
on MWCNTs was carried out at 293.15, 313.15 and 333.15 K, respectively, and the thermodynamic parameters (standard free energy
changes (ΔG0), standard enthalpy change (ΔH0) and standard entropy change (ΔS0)) were calculated from the temperature dependent sorption isotherms. The sorption of Th(IV) on MWCNTs is a spontaneous and
endothermic process. The oxidized MWCNTs may be a promising candidate for the preconcentration and solidification of Th(IV),
or its analogue actinides from large volumes of aqueous solutions.
Authors:Hui Zhang, Xianjin Yu, Lei Chen, and Jiaqiang Geng
The sorption of 63Ni(II) from aqueous solution using ZSM-5 zeolite was investigated by batch technique under ambient conditions. ZSM-5 zeolite
was characterized by point of zero net proton charge (PZNPC) titration. The sorption was investigated as a function of shaking
time, pH, ionic strength, foreign ions, humic acid (HA), fulvic acid (FA) and temperature. The results indicate that the sorption
of 63Ni(II) on ZSM-5 zeolite is strongly dependent on pH. The sorption is dependent on ionic strength at low pH, but independent
of ionic strength at high pH values. The presence of HA/FA enhances 63Ni(II) sorption at low pH values, whereas reduces 63Ni(II) sorption at high pH values. The sorption isotherms are simulated by Langmuir model very well. The thermodynamic parameters
(i.e., ∆H0, ∆S0 and ∆G0) for the sorption of 63Ni(II) are determined from the temperature dependent sorption isotherms at 293.15, 313.15 and 333.15 K, respectively, and
the results indicate that the sorption process of 63Ni(II) on ZSM-5 zeolite is spontaneous and endothermic.