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In this study, a novel dual-cation organomontmorillonites (OMt) nanocomposite was synthesized by two kinds of modifiers cetyltrimethylammonium chloride and cysteamine hydrochloride, and the adsorption behavior of modifiers into montmorillonite (Mt) has been investigated. The OMt were characterized by techniques, such as X-ray diffraction (XRD), Fourier Transform Infrared (FTIR) spectroscopy, and thermogravimetric and differential thermal (TG-DTA) analyses. The effects of temperature, contact time, the order of addition and the concentration of organic modifiers on the amounts of organics adsorbed were investigated. The adsorption amount of cetyltrimethylammonium chloride (CTAC) and cysteamine hydrochloride (CSH) increased with the increase of the added CTAC amount and contact time, while the addition order of modifiers and modification temperature had no significant effect on the actual adsorption amount of CTAC and CSH on Mt, as confirmed by the XRD patterns. The experimentally determined isotherms showed a good fit with the Langmuir adsorption models. The adsorption kinetics demonstrated that the adsorption of CTAC and CSH by Mt followed the pseudo-second-order model, and CTAC adsorption rate on Mt was faster than that of CSH. FTIR spectrum clearly revealed the incorporation of surfactant ions into the interlayer region. The TG-DTA analyses showed that the total mass losses of OMt strongly depended on the molecular volume of modifiers. [ABSTRACT FROM AUTHOR]

Montmorillonite (Mt) is proposed as a promising adsorbent for removing contaminants from water, yet it is unclear whether and how the layer charge density (LCD) of Mt. affects its hydration properties, especially for the capturing performance of anions by polyelectrolyte modified Mt. Here, the feasibility and performance of perchlorate uptake by poly-(diallydimethylammonium chloride) (PDDA) functionalized Mt. (PDDA-Mt x) with different LCD were investigated. PDDA species were loaded via partial intercalation or adsorption on the surface/end sites of Mt. The CEC of Ca-Mt x increased with increasing LCD, while on the contrary for colloidal valence. The perchlorate uptake by Ca-Mt x can be significantly improved by introducing PDDA species. As expected, the PDDA-Mt 0.3 showed superior perchlorate capture of up to 0.80 mmol/g due to the relatively high positive zeta potential and loading of un-ionized PDDA. The perchlorate uptake by PDDA-Mt x still maintained largely despite a slight decrease in the presence of co-competing anions NO-3, SO2–4 and PO3–4. The capture behaviors were well characterized by the pseudo-second-order and Langmuir isotherm models, and the natures of spontaneous and endothermic were demonstrated by thermodynamic analysis. Anion exchange and electrostatic were the dominant ways in which perchlorate was captured onto PDDA-Mt x. [Display omitted] • PDDA modified montmorillonites (PDDA-Mt x) are prepared for ClO− 4 capture. • Hydration property and PDDA loading are affected by layer charge density of Ca Mt. • A maximum ClO− 4 uptake capacity of 0.80 mmol/g was achieved by PDDA-Mt 0.3. • Ion exchange between ClO− 4 and PDDA-Cl species drives adsorption. [ABSTRACT FROM AUTHOR]

[Display omitted] • Polyelectrolytes were successfully loaded on Mt with a positive surface potential. • PDDA+ intercalation speed was fast (<0.1 h) and desorption ratio was < 10 % after 48 h. • The adsorption performance was as follow: PDDA x -Mt > CH-Mt > PAM-Mt > PQ28-Mt. • PMt showed a superior adsorption selectivity to ClO 4 -. • Anion exchange played a crucial role in the ClO 4 - adsorption processing onto PMt. Polyelectrolyte (with different unit structure or molecular weight) modified montmorillonite (PMt) was synthesized for perchlorate (ClO 4 -) removal. It was found polyelectrolytes were successfully loaded on montmorillonite (Mt), and the surface potential of most PMt changed from negative to positive. Polyelectrolyte desorption on Mt was < 10 % after 48 h. Poly(diallyldimethylammonium chloride) species modified montmorillonite (PDDA x -Mt) showed excellent adsorption performance for ClO 4 - with maximum adsorption amount over 2.78 mmol/g and equilibrium time within 10 min. The adsorption performance of PMt toward ClO 4 - followed this order: PDDA x -Mt > CH-Mt > PAM-Mt > PQ28-Mt. Moreover, PDDA x -Mt and CH-Mt showed a superior adsorption selectivity to ClO 4 - among competitive oxyanions in the quaternary-adsorbate system (ClO 4 - > PO 4 3- > SO 4 2- > NO 3 –). The enhanced ClO 4 - adsorption could be mainly attributed to the presence of anion exchange sites (−R 4 N+-Cl− or –NH 3 +-Cl−) provided by PDDA or CH, followed by electrostatic gravitation and weak hydrogen bonding interaction. Density functional theory (DFT) calculation revealed that ClO 4 - adsorbed on PMt is a process of electrons transferring from O atoms in ClO 4 - to H atoms on C in PDDA+ or N in CH+, PAM+ and PQ28+. The preparation method of PMt is simple with excellent adsorption performance and selectivity toward ClO 4 -, suggesting promising applications in anion wastewater treatment. [ABSTRACT FROM AUTHOR]

Hydroxy-Al pillaring agent was prepared and used to modify montmorillonite (Mt), and the effects of temperature, initial Al 3 + concentration and contact time were investigated by using a batch technique. The results showed that the uptake of Al 13 by Mt increased with increasing temperature, initial Al 3 + concentration and contact time. The adsorption equilibrium was achieved in 12 h as determined by kinetics. The adsorption kinetics demonstrated that the adsorption of Al 13 by Mt followed the pseudo-second-order kinetic model. The adsorption isotherms at the temperatures of 40, 60, 80 and 90 °C were determined and simulated using Langmuir, Freundlich and Redlich-Peterson models. The three kinds of isotherms could represent the experimental data well. The specific surface areas and pillar density increased while the total porous volumes slightly decreased with increasing Al 3 + concentrations. The XRD result showed that adsorbed Al 13 ions were located in the Mt interlayer spaces through monolayer adsorption. Thermodynamic analysis of adsorption process showed that the adsorption of Al 13 by Mt was spontaneous, endothermic with increasing disorder during the adsorption process and mainly physical in nature. [ABSTRACT FROM AUTHOR]

Various montmorillonite (Mt) nanocomposite adsorbents were prepared with Al 13 cations, dodecyl trimethyl ammonium chloride (DTAC) or dodecyl amine (DA) and characterized by Fourier transform infrared (FTIR) spectroscopy, X-ray diffraction (XRD) and BET surface area and pore size analyses. The adsorption of hexavalent chromium, Cr(VI) onto various Mt nanocomposites as a function of adsorbent dosage, initial Cr(VI) concentration, contact time and solution pH was investigated. The results showed that the obtained nanocomposites had large basal spacing and good porous structure, and the specific surface areas followed the order: OH-Al-Mt > DA-Al-Mt > DTAC-Al-Mt > Na + -Mt > DTAC-Mt > DA-Mt. The removal efficiency of Cr(VI) ions increased with increasing the adsorbent dosage and contact time, but decreased with increasing initial Cr(VI) concentration, as expected. The adsorption of Cr(VI) was highly pH-dependent and the maximum removal efficiency of Cr(VI) was found in the acid environment. The adsorption equilibrium time was 2 h and the adsorption kinetic data of Cr(VI) on various adsorbents were well described by the pseudo-second-order kinetics model, which indicated that the adsorption reaction of Cr(VI) ions with the adsorbents was mainly due to chemical adsorption. Both the Langmuir model and Freundlich model fitted the equilibrium data well, which suggested that the Cr(VI) adsorption onto various adsorbents was both as monolayer and on heterogeneous surface conditions. The adsorption results indicated that among all the adsorbents used in this experiment, the dodecyl amine and Al 13 cations composited with Mt (DA-Al-Mt) was the most effective for removing Cr(VI) from wastewater. [ABSTRACT FROM AUTHOR]

[Display omitted] • Triethylenetetramine functionalized montmorillonite (TTA-Mt) was synthesized. • TTA-Mt was tested for the immobilization of heavy metals in tailings. • Column simulation was carried out for 5 years using TTA-Mt. • Intercalation of TTA could remarkably enhance the immobilization property of Mt. • Complexation and precipitation were the immobilization mechanisms of heavy metals. The conventional environmental remediation materials, which are applied for the long-term treatment of mine tailings are easy to fail when affected by acid rain. Therefore, dynamic column simulation experiments were conducted to compare the immobilization persistence of As, Mn, Pb and Zn by the addition of triethylenetetramine modified montmorillonite (TTA-Mt) and calcium-based montmorillonite (Ca-Mt) in sulfide tailings during a simulated 5-year study of acid rain leaching. The structural and morphological characteristics of TTA-Mt were analyzed with FTIR, XRD, SEM, TEM and EDS. Results showed that the additions of TTA-Mt could persistently immobilize the heavy metal ions while Ca-Mt additions had little effect. After long-term simulated leaching for 5 years, TTA-Mt still had superior environmental stability for Zn and As with the immobilization rates of 96% and 86%, and the leaching amounts of Mn and Pb were less than 4.23 and 0.66 mg/kg, respectively. Morphology and chemical fraction analyses confirmed that the immobilization was mainly due to the formation of relatively stable phases by complexation and precipitation. Results presented here demonstrated the significant potential of TTA-Mt for long-term immobilization of heavy metals in tailings against acid rain and thus could provide guidance for remediation of tailings. [ABSTRACT FROM AUTHOR]

There are a large number of tailings left over by industrial development the world over and the tailings are harmful to the environment for a long time, so it is very important to study how to reduce environmental pollution from tailings. Here, the acid producing potential of three types of tin polymetallic tailings from the same locality with different degrees of weathering and the forms of heavy metals that exist in these tailings were studied. The effects of pH of simulated acid rain, temperature and time on the leaching of heavy metals from the different tailings were investigated along with their leaching characteristics. In addition, stabilization mechanism of heavy metals was analyzed from the kinetic and microscopic aspects. The potential application of sodium diethyldithiocarbamate intercalated montmorillonite (DDTC-Mt) was studied for stabilizing tin polymetallic tailings. The leaching of heavy metals in tailings is mainly due to the oxidation of tailings, which in turn is closely related to the acid producing potential of tailings and the existing forms of heavy metals in them. The stabilization of heavy metals by DDTC-Mt is mainly due to coordination between DDTC and heavy metals in the interlayer of montmorillonite. DDTC-Mt revealed a superior stabilization property in remediation of heavy metals from tin-polymetallic tailings with high acid producing potential by enhancing the stability of heavy metals in tailings, for example, the stabilization rates of Mn and Zn were 89.11% and 93.89%, respectively. [Display omitted] • Na diethyldithiocarbamate intercalated montmorillonite (DDTC-Mt) was prepared. • Studied DDTC-Mt for stabilizing tin tailings for remediating acid mine drainage. • Stabilization rates of DDTC-Mt for Mn and Zn were 89.11 and 93.89%, respectively. • Metal stabilization by DDTC-Mt is mainly by coordination between DDTC and metals. • Mn and Zn leaching with or without DDTC-Mt conforms to acid production of tailings. [ABSTRACT FROM AUTHOR]

Three types of alkyl-ammonium with different branching chains and three complexants with different functional groups were used to prepare alkyl-ammonium or complexant intercalated montmorillonite nanocomposite (A-Mt or C-Mt). In addition, synergistic intercalated montmorillonite nanocomposites (A/C-Mt) with alkyl-ammonium along with complexant were also prepared. The adsorption performance of the various nanocomposites toward Zn2+ and p-nitrophenol (PNP) from simulated binary wastewater containing both Zn2+ and PNP were systematically investigated. Characterization of Mt nanocomposites showed that both alkyl-ammoniums and complexants were successfully intercalated into the interlayers of Mt. The surfactant loading amounts of the various nanocomposites were also determined and correlated with the resulting expansion of the interlayer spacing. It was found that intercalation of alkane (OTAC) and –SH (CSH) were conducive to the adsorption of Zn2+ while –C 2 H 4 NH (TETA) and all alkyl-ammoniums were beneficial for PNP adsorption. The extent of adsorption was found to be controlled primarily by pH, i.e., the higher pH had a good effect on the adsorption of both Zn2+ and PNP. The adsorption process of Zn2+ onto Mt nanocomposites was more in line with the Freundlich model (R 2 = 0.99), while the Langmuir model described the adsorption of PNP well (R 2 = 0.99). The adsorption kinetics could be well described by the Elovich equation (R 2 = 0.98) and the double-constant model (R 2 = 0.89). Chemical adsorption was determined to be the dominant process between the contaminant and Mt nanocomposite surfaces. [ABSTRACT FROM AUTHOR]