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  • Author or Editor: Zhengjie Liu x
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Abstract  

Clay minerals have been widely used in wastewater disposal due to their strong sorption and complexation ability towards various environmental pollutants. In this study, the removal of Zn(II) from aqueous solution by natural halloysite nanotubes (HNTs) was studied as a function of various solution chemistry conditions such as contact time, pH, ionic strength, coexisting electrolyte ions and temperature under ambient conditions. The results indicated that the removal of Zn(II) by HNTs was strongly dependent on pH and ionic strength. Langmuir and Freundlich models were used to simulate the sorption isotherms of Zn(II) at three different temperatures of 293, 313 and 333 K. The thermodynamic parameters (ΔH 0, ΔS 0 and ΔG 0) calculated from the temperature dependent sorption isotherms indicated that the removal process of Zn(II) by HNTs was endothermic and spontaneous. At low pH, the removal of Zn(II) was dominated by outer-sphere surface complexation and/or cation exchange with Na+/H+ on HNT surfaces, whereas inner-sphere surface complexation was the main removal mechanism at high pH. From the experimental results, one can conclude that HNTs may have a good potentiality for the disposal of Zn(II)-bearing wastewaters.

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Abstract  

Bentonite has been studied extensively because of its strong sorption and complexation ability. Herein, GMZ bentonite from Gaomiaozi county (Inner Mongolia, China) was investigated as the candidate of backfill material for the removal of Th(IV) ions from aqueous solutions. The results indicate that the sorption of Th(IV) is strongly dependent on pH and ionic strength at pH < 5, and independent of ionic strength at pH > 5. Outer-sphere surface complexation or ion-exchange are the main mechanism of Th(IV) sorption on GMZ bentonite at low pH values, whereas the sorption of Th(IV) at pH > 5 is mainly dominated by inner-sphere surface complexation or surface precipitation. Soil fulvic acid (FA) and humic acid (HA) have a positive influence on the sorption of Th(IV) on bentonite at pH < 5. The different addition sequences of HA and Th(IV) to GMZ bentonite suspensions have no obvious effect on Th(IV) sorption to HA-bentonite hybrids. The high sorption capacity of Th(IV) on GMZ bentonite suggests that the GMZ bentonite can remove Th(IV) ions from large volumes of aqueous solutions in real work.

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Abstract  

The sorption of Cd(II) from aqueous solution on γ-Al2O3 was investigated under ambient conditions. Experiments were carried out as a function of contact time, solid content, pH, ionic strength, foreign ions, fulvic acid and temperature. The results indicated that the sorption of Cd(II) was strongly dependent on pH and ionic strength. At low pH, the sorption of Cd(II) was dominated by outer-sphere surface complexation and ion exchange with Na+/H+ on γ-Al2O3 surfaces, whereas inner-sphere surface complexation was the main sorption mechanism at high pH. The Langmuir, Freundlich and Dubinin–Radushkevich (D–R) models were used to simulate the sorption isotherms at three different temperatures. The thermodynamic data (ΔG 0, ΔS 0, ΔH 0) calculated from the temperature dependent sorption isotherms suggested that the sorption of Cd(II) on γ-Al2O3 was an spontaneous and endothermic process.

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Abstract  

In this paper, the sorption of Co(II) from aqueous solution to Ca-montmorillonite was studied under ambient conditions by using batch technique. The effects of contact time, solid content, pH, ionic strength and temperature on the sorption of Co(II) to Ca-montmorillonite was also investigated. The results indicated that the sorption of Co(II) was strongly dependent on pH values. The sorption was dependent on ionic strength at low pH values, but independent of ionic strength at high pH values. Outer-sphere surface complexes were formed on the surface of Ca-montmorillonite at low pH values, whereas inner-sphere surface complexes were formed at high pH values. The Langmuir, Freundlich and Dubinin–Radushkevich (D–R) models were used to simulate the sorption isotherms of Co(II) at three different temperatures. The thermodynamic parameters (ΔH 0, ΔS 0 and ΔG 0) were calculated from the temperature dependent sorption isotherms, and the results indicated that the sorption reaction of Co(II) to Ca-montmorillonite was an endothermic and spontaneous process. The high sorption capacity of Co(II) on Ca-montmorillonite suggests that the Ca-montmorillonite is a suitable material for the preconcentration and solidification of radiocobalt from aqueous solutions.

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Abstract  

Sorption of U(VI) from aqueous solution to Na-attapulgite was investigated at different experimental chemistry conditions by using batch technique. The attapulgite sample was characterized by FTIR and XRD. Sorption of U(VI) on attapulgite was strongly dependent on pH and ionic strength. The sorption of U(VI) on attapulgite increased quickly with rising pH at pH < 6, and decreased with increasing pH at pH > 7. The presence of humic acid (HA) enhanced the sorption of U(VI) on attapulgite obviously at low pH because of the strong complexation of surface adsorbed HA with U(VI) on attapulgite surface. Sorption of U(VI) on attapulgite was mainly dominated by ion exchange and/or outer-sphere surface complexation at low pH values, whereas the sorption was attributed to the inner-sphere surface complexation or precipitation at high pH values. The sorption increased with increasing temperature and the thermodynamic parameters calculated from the temperature dependent sorption isotherms suggested that the sorption of U(VI) on attapulgite was a spontaneous and endothermic process. The results indicate that attapulgite is a very suitable material for the preconcentration of U(VI) ions from large volumes of aqueous solutions.

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Abstract  

The sorption of Co(II) from aqueous solution on Na-rectorite was investigated under ambient conditions. Experiments were carried out as a function of contact time, solid content, pH, ionic strength, foreign ions, fulvic acid and temperature. The results indicated that the sorption of Co(II) was strongly dependent on pH. At low pH the sorption 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 Dubinin–Radushkevich (D–R) models were used to simulate the sorption isotherms at three different temperatures. The thermodynamic data (∆G 0, ∆S 0, ∆H 0) were calculated from the temperature dependent sorption isotherms and the results suggested that the sorption process of Co(II) on Na-rectorite was spontaneous and endothermic. Experimental results indicate that Na-rectorite is a suitable adsorbent for preconcentration and solidification of Co(II) from large volumes of aqueous solutions.

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Abstract  

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.

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Abstract  

The sorption of 60Co(II) on γ-Al2O3 was conducted under various conditions, i.e., contact time, adsorbent content, pH, ionic strength, foreign ions, humic acid (HA), and temperature. Results of sorption data analysis indicated that the sorption of 60Co(II) on γ-Al2O3 was strongly dependent on pH and ionic strength. At low pH the sorption was dominated by outer-sphere surface complexation or ion exchange, whereas inner-sphere surface complexation was the main sorption mechanism at high pH. The presence of different cation ions influenced 60Co(II) sorption, while the presence of different anion ions had no obvious influences on 60Co(II) sorption. The presence of HA decreased the sorption of 60Co(II) on γ-Al2O3. The sorption isotherms were simulated well with the Langmuir model. The thermodynamic parameters (ΔH 0, ΔS 0 and ΔG 0) calculated from the temperature-dependent sorption isotherms indicated that the sorption of 60Co(II) on γ-Al2O3 was an endothermic and spontaneous process. Experimental results indicated that the low cost material was a suitable material in the preconcentration of 60Co(II) from large volumes of aqueous solutions.

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Abstract

A new composite catalytic system of Pd/C, 2,4,6-trichloro-[1,3,5]-triazine and N,N-dimethylformamide was investigated in nitrocyclohexane hydrogenation to ∊-caprolactam. The Pd/C catalyst was prepared by the incipient impregnation method and characterized by BET, N2 adsorption–desorption, XRD, TEM and H2 chemisorption. The results indicate that 2,4,6-trichloro-[1,3,5]-triazine plays a key role in one step synthesis of ∊-caprolactam from nitrocyclohexane hydrogenation. Besides ∊-caprolactam, the products include cyclohexanone oxime, cyclohexamine, cyclohexanone and cyclohexanol. A possible mechanism for nitrocyclohexane hydrogenation in 2,4,6-trichloro-[1,3,5]-triazine and N,N-dimethylformamide complex was proposed.

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