In this work, Na-montmorillonite was used as a novel adsorbent for the sorption of Ni(II) from aqueous solutions. The sorption
and desorption of Ni(II) on Na-montmorillonite was investigated as the function of pH, ionic strength, Ni(II) concentrations
and temperature. The results indicated that the sorption of Ni(II) on Na-montmorillonite was strongly dependent on pH, ionic
strength and temperature. The sorption of Ni(II) increases slowly from 22.1 to 51.4% at pH range 2–6.5, abruptly at pH 6.5–9,
and at last maintains high level with increasing pH at pH > 9 in 0.1 mol/L NaNO3 solutions. The Ni(II) kinetic sorption on Na-montmorillonite was fitted by the pseudo-second-order model better than by the
pseudo-first-order model and the experimental data implies that Ni(II) sorption on montmorillonite were mainly controlled
by the film diffusion mechanism. The Langmuir, Freundlich and D–R models were used to simulate the sorption data at three
different temperatures (298.15, 318.15 and 338.15 K) and the results indicated that Langmuir model simulates the experimental
data better than Freundlich and D–R models. The sorption–desorption isotherm of Ni(II) on montmorillonite suggested that the
sorption is irreversible. The irreversible sorption of Ni(II) on montmorillonite indicates that montmorillonite can be used
to pre-concentration and solidification of Ni(II) from large volumes of solution and to storage Ni(II) ions stably.
Authors:Zhengjie Liu, Jianwei Yang, Zengchao Zhang, Lei Chen, and Yunhui Dong
Bentonite was investigated to remove Ni(II) from aqueous solutions because of its strong sorption ability. Herein, bentonite
was modified with sodium carboxymethylcellulose (CMC) and used as an adsorbent to remove Ni(II) from aqueous solutions. The
results indicated that CMC-bentonite had higher sorption capacity than bare bentonite in the sorption of Ni(II) from aqueous
solutions. Sorption of Ni(II) on CMC-bentonite was mainly dominated by ion exchange or outer-sphere surface complexation at
low pH values, but by inner-sphere surface complexation or surface precipitation at high pH values. The thermodynamic data
calculated from temperature dependent sorption isotherms indicated that the sorption of Ni(II) to CMC-bentonite hybrids was
an spontaneous process and enhanced with increasing temperature.
Effects of pH, Eu(III) concentration, ionic strength, temperature and humic acid (HA) on Eu(III) sorption to iron oxides were
investigated in detail. The sorption of Eu(III) to iron oxides was significantly dependent on pH and weakly dependent on ionic
strength, and higher temperature was gainful to Eu(III) sorption. In the presence of HA, Eu(III) sorption was enhanced significantly
at low pH; whilst obvious negative effect was observed in higher pH range. Below 12 mg/L HA, HA could obviously enhanced Eu(III)
sorption to iron oxides, nevertheless Eu(III) sorption decreased steeply with increasing HA while HA exceeded 12 mg/L. The
results were helpful for understanding radionuclides behaviors in natural environment.
Authors:Baowei Hu, Wen Cheng, Hui Zhang, and Guodong Sheng
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.
The sorption of radiocadmium on Ca-montmorillonite as a function of contact time, pH, ionic strength, foreign ions, humic
acid (HA) and fulvic acid (FA) was studied using batch technique. The results demonstrated that the sorption of Cd(II) was
dependent on ionic strength at pH < 9, and was independent of ionic strength at pH > 9. Outer-sphere surface complexation
and/or ion exchange were the main mechanism of Cd(II) sorption on Ca-montmorillonite at low pH, whereas the sorption at high
pH was mainly dominated via inner-sphere surface complexation. The sorption of Cd(II) on Ca-montmorillonite was dependent
on foreign ions at low pH values, but was independent of foreign ions at high pH values. A positive effect of HA/FA on Cd(II)
sorption was found at low pH values, whereas a negative effect was observed at high pH values. The thermodynamic parameters
(i.e., ΔH0, ΔS0, ΔG0) were calculated from the temperature dependent sorption isotherms, and the results indicated that the sorption process of
Cd(II) on Ca-montmorillonite was spontaneous and endothermic.
Sorption of thorium (IV) on goethite was investigated as a function of contact time, pH, ionic strength, anions, solid-to-liquid
ratio (m/V) and Th(IV) concentration using batch technique. The results showed that the sorption of Th(IV) was strong pH-dependence,
and increased from ~10 to ~100% over the pH range of 2.0–4.0, and then kept a constant level in the higher pH range. The sorption
of Th(IV) increased with increasing m/V and independent of ionic strength. It was clear that phosphate and FA significantly enhanced Th(IV) sorption on goethite.
The sorption and desorption isotherms were investigated at pH 2.90 ± 0.05 and analyzed with Freundlich and Langmuir models,
respectively. Compared to Langmuir model, Freundlich model could fit the experimental data better, according to the high relative
U(VI) sorption on kaolinite was studied as functions of contact time, pH, U(VI) concentration, solid-to-liquid ratio (m/V) by using a batch experimental method. The effects of sulfate and phosphate on U(VI) sorption were also investigated. It
was found that the sorption kinetics of U(VI) can be described by a pseudo-second-order model. Potentiometric titrations at
variable ionic strengths indicated that the titration curves of kaolinite were not sensitive to ionic strength, and that the
pH of the zero net proton charge (pHPZNPC) was at 6.9. The sorption of U(VI) on kaolinite increased with pH up to 6.5 and reached a plateau at pH >6.5. The presence
of phosphate strongly increased U(VI) sorption especially at pH <5.5, which may be due to formation of ternary surface complexes
involving phosphate. In contrast, the presence of sulfate did not cause any apparent effect on U(VI) sorption. A double layer
model was used to interpret both results of potentiometric titrations and U(VI) sorption on kaolinite.
Authors:Liang Chen, Shaoming Yu, Liming Zuo, Bin Liu, and Lingli Huang
In this study, a local bentonite from Gaomiaozi county (Inner Mongolia, China) was converted to Na-bentonite and was characterized
by FTIR and XRD to determine its chemical constituents and micro-structure. The removal of cobalt from aqueous solutions by
Na-bentonite was investigated as a function of contact time, pH, ionic strength, foreign ions and temperature by batch technique
under ambient conditions. The results indicated that the sorption of Co(II) was strongly dependent on pH. At low pH, the sorption
of Co(II) was dominated by outer-sphere surface complexation or ion exchange whereas inner-sphere surface complexation was
the main sorption mechanism at high pH. The Langmuir, Freundlich, and D-R models were used to simulate the sorption isotherms
of Co(II) at the temperatures of 293.15, 313.15 and 333.15 K, respectively. The thermodynamic parameters (∆G°, ∆S°, ∆H°) of Co(II) sorption on GMZ bentonite calculated from the temperature-dependent sorption isotherms indicated that the sorption
of Co(II) on GMZ bentonite was an exothermic and spontaneous process. The Na-bentonite is a suitable material for the preconcentration
and solidification of Co(II) from aqueous solutions.
Authors:S. Tripathi, R. Kannan, P. Dhami, P. Naik, S. Munshi, P. Dey, N. Salvi, and S. Chattopadhyay
The improvement and the refinement of non-viable Rhizopus arrhizus biomass were investigated via immobilization. Immobilization was carried out by using sodium alginate/CaCl2 solution and formaldehyde/HCl cross-linking with dead Rhizopus arrhizus biomass and were used for the sorption of radionuclides from low level effluent wastes. The sodium alginate/CaCl2 immobilized biomass (ratio 1:2) showed about 86% sorption for 241Am activity but due to its soft nature and tendency to undergo distortion in shape, is unsuitable for practical applications.
The biomass cross-linked with 15% formaldehyde/0.1 M HCl solution has a relatively high mechanical strength and rigidity.
It was showing a sorption of >99% for 241Am activity and has the sorption capacity of ~65 mg/g for americium and uranium. Hence, it can be utilized for the removal
of radionuclides from radioactive waste effluents.
Attapulgite has been applied in the sorption of metal and radionuclide ions since its discovery. Herein, radionuclide Am(III)
sorption onto attapulgite was carried out at 25 °C in 0.01 mol/L NaNO3 solutions. Effects of contact time, Am(III) initial concentration, pH, humic acid and temperature on Am(III) sorption onto
attapulgite were investigated. The sorption of Am(III) increases with increasing contact time and reaches a maximum value
within 24 h at different Am(III) initial concentration. The fast sorption velocity indicates that strong chemical sorption
or strong surface complexation contributes to the sorption of Am(III) onto attapulgite under the experimental conditions.
The experimental data can be described well by the pseudo-second-order rate model. The sorption of Am(III) onto attapulgite
is strongly dependent on pH values and surface complexation is the main sorption mechanism. The presence of HA enhances the
sorption of Am(III) onto attapulgite at pH < 8.5, whereas, at pH > 8.5, little effect of HA on Am(III) sorption is observed.
The Langmuir, Freundlich and D-R models were used to simulate the sorption data at different pH values and the results indicated
that Langmuir model simulates the experimental data better than Freundlich and D-R models. The thermodynamic parameters indicates
that the sorption of Am(III) onto attapulgite is an endothermic and spontaneous process. The results suggest that the attapulgite
is a suitable material as an adsorbent for preconcentration and immobilization of Am(III) from aqueous solutions.