Gemini surfactant-modified montmorillonite with tetrachloroferrate (FeCl4-) as a counterion simultaneously sequesters nitrate and phosphate from aqueous solution

Simple and scalable preparation of lignin based porous carbon coated nano-clay composites and their efficient removal for the diversified iodine

Here, lignin and nano-clay were used to prepare novel composite adsorbents by one-step carbonization without adding activators for radioactive iodine capture. Specially, 1D nano-clay such as halloysite (Hal), palygorskite (Pal) and sepiolite (Sep) were selected as skeleton components, respectively, enzymatic hydrolysis lignin (EHL) as carbon source, lignin based porous carbon/nano-clay composites (ELC-X) were prepared through ultrasonic impregnation, freeze drying, and carbonization. Characterization results indicated lignin based porous carbon (ELC) well coated on the surface of nano-clay, and made its surface areas increase to 252 m2/g. These composites appeared the micro-mesoporous hierarchical structure, considerable N doping and good chemical stability. Results of adsorption experiments showed that the introduction of ELC could well promote iodine vapor uptake of nano-clay, and up to 435.0 mg/g. Meanwhile, the synergistic effect between lignin based carbon and nano-clay was very significant for the adsorption of iodine/n-hexane and iodine ions, their capacity were far exceed those of a single material, respectively. The relevant adsorption kinetic and thermodynamics, and mechanism of ELC-X composites were clarified. This work provided a class of low-cost and environmentally friendly adsorbents for radioactive iodine capture, and opened up ideas for the comprehensive utilization of waste lignin and natural clay minerals.

Modification of ultrasound-pretreated montmorillonite using poly(diallyldimethylammonium chloride) for W and Mo separation and the sequential application in removal of heavy metals

The use of a resin to selectively separate thiomolybdate from a tungsten (W) feed solution is a well-known protocol for achieve high-purity W products; however, the regeneration of saturated resin is laborious. In this study, poly(diallyl dimethyl ammonium chloride) (PDADMA) was used to modify ultrasound-pretreated montmorillonite (Mt) for W and molybdenum (Mo) separation for the first time, and the resultant tetrathiomolybdate (MoS42-)-loaded composite was further tested to remove heavy metals instead of regeneration. Among the three variables of ultrasound pretreatment, that is, Mt concentration, ultrasound power, and treatment time, the Mt concentration exhibited the most significant influence followed by ultrasound power on the separation performance of W and Mo. Compared to the distance of the interlayer space and the surface charge of the modified Mt, the PDADMA content showed a closer correlation with the W/Mo separation coefficient. Assisted by Box-Behnken design, with Mt concentration of 6.9 g/L, ultrasound power of 593.8 W, and treatment time of 13.8 min, the composite with the greatest separation coefficient was obtained. The adsorption of Cu(II) on the optimal W/Mo separation-derived composite was ascribed to the formation of Cu-S complexes, while that of Pb(II) was attributed to complexation and surface precipitation. In contrast, ion exchange with the initially loaded anions, reduction by sulfide to Cr(III), and formation of Cr(III)-S complexes accounted for Cr(VI) removal. The adsorption of Cu(II) and Pb(II) equilibrated faster and showed higher acid-resistance than that of Cr(VI). The adsorption capacities for Cu(II), Pb(II), and Cr(VI) were 0.535, 1.398, and 0.882 mmol/g, respectively. Applying PDADMA to modify Mt as a reagent for W/Mo separation was feasible, and the derived composite was capable of removing cationic and anionic heavy metals.

Grafting of R4N+-Bearing Organosilane on Kaolinite, Montmorillonite, and Zeolite for Simultaneous Adsorption of Ammonium and Nitrate

Modification of aluminosilicate minerals using a R₄N⁺-bearing organic modifier, through the formation of covalent bonds, is an applicable way to eliminate the modifier release and to maintain the ability to remove cationic pollutants. In this study, trimethyl [3-(trimethoxysilyl) propyl] ammonium chloride (TM) and/or dimethyl octadecyl [3-(trimethoxysilyl) propyl] ammonium chloride (DMO) were used to graft three aluminosilicate minerals, including calcined kaolinite (Kaol), montmorillonite (Mt), and zeolite (Zeol), and the obtained composites were deployed to assess their performance in regard to ammonium (NH₄⁺) and nitrate (NO₃^-) adsorption. Grafting of TM and/or DMO had little influence on the crystal structures of Kaol and Zeol, but it increased the interlayer distance of Mt due to the intercalation. Compared to Kaol and Zeol, Mt had a substantially greater grafting concentration of organosilane. For Mt, the highest amount of loaded organosilane was observed when TM and DMO were used simultaneously, whereas for Kaol and Zeol, this occurred when only DMO was employed. ²⁹Si-NMR spectra revealed that TM and/or DMO were covalently bonded on Mt. As opposed to NO₃^-, the amount of adsorbed NH₄⁺ was reduced after TM and/or DMO grafting while having little effect on the adsorption rate. For the grafted Kaol and Zeol, the adsorption of NH₄⁺ and NO₃^- was non-interfering. This is different from the grafted Mt where NH₄⁺ uptake was aided by the presence of NO₃^-. The higher concentration of DMO accounted for the larger NO₃^- uptake, which was accompanied by improved affinity. The results provide a reference for grafting aluminosilicate minerals and designing efficient adsorbents for the co-adsorption of NH₄⁺ and NO₃^-.

Enhanced removal of fluoride, nitrate, and calcium using self-assembled fungus-flexible fiber composite microspheres combined with microbially induced calcium precipitation

Self-assembled fungus-flexible fiber composite microspheres (SFFMs) were firstly combined with microbially induced calcium precipitation (MICP) in a continuous-flow bioreactor and achieved the efficient removal of fluoride (F^-), nitrate (NO₃^-), and calcium (Ca²⁺). Under the influent F^- of 3.0 mg L^-1, pH of 7.0, and HRT of 8 h, the average removal efficiencies reached 77.54%, 99.39%, and 67.25% (0.29, 2.03, and 8.34 mg L^-1 h^-1), respectively. Fluorescence spectrum and flow cytometry analyses indicated that F^- content significantly affected the metabolism and viability of bacteria. SEM images showed that flexible fibers and intertwined hyphae provided effective locations for bacterial colonization in SFFMs. The precipitated products were characterized by XRD and FTIR, which revealed that F^- was mainly removed in the form of calcium fluoride and calcium fluorophosphate (CaF₂ and Ca₅(PO₄)₃F). High-throughput analysis at different levels demonstrated that Pseudomonas sp. WZ39 acted as the core strain, which played a crucial role in the bioreactor. The mechanism of enhanced denitrification was attributed to minor F^- stress and bioaugmentation technology. This study highlighted the superiorities of SFFMs and MICP combined remediation and documented a promising option for F^-, NO₃^-, and Ca²⁺ removal.

Immobilization of W(VI) and/or Cr(VI) in soil treated with montmorillonite modified by a gemini surfactant and tetrachloroferrate (FeCl4-)

The coexistence of highly toxic chromium (Cr) and the emerging contaminant tungsten (W) in the soil adjacent to W mining areas is identified. Immobilization of W and/or Cr is vital for the safe utilization of contaminated soil. In this study, the cationic gemini surfactant (butane-1,4-bis(dodecyl dimethyl ammonium bromide)) and tetrachloroferrate (FeCl₄^-)-modified montmorillonite (FeOMt) was applied to investigate the retention performance of W and/or Cr in the soil. Regardless of the initially spiked amount of WO₄^2- and/or CrO₄^2-, the W and/or Cr leached in soil solution was rapidly immobilized within 5 min. The immobilization rates of W and/or Cr in the single and binary soil systems were stably maintained against the variations in pH and coexisting anion. FeOMt showed more favorable performance in the retention of W and/or Cr with respect to the precursors (i.e., the original Mt and surfactant-modified Mt) and efficiently inhibited the phytotoxicity and bioaccumulation of W and/or Cr in mung beans. Due to the ion exchange, complexation, reduction, and flocculation, the addition of FeOMt transformed W and/or Cr from exchangeable/carbonate species to reducible/oxidizable fractions, reducing the environmental risk. FeCl₄^- complex, as a byproduct of the steel pickling process in industry, plays the pivotal role in the efficient retention of W and Cr. Based on the facile synthesis procedure and the efficient performance, the use of FeOMt for the amendment of W- and/or Cr-contaminated soil is feasible and promising.