Evaluation of phosphate removal from water by calcined-LDH synthesized from the dolomite

In the present study, the characteristics of the adsorption of phosphate on calcined layered double hydroxides (LDHs) from aqueous solution were evaluated under laboratory conditions. The anionic clays were Mg₃pH₁₀-LDH synthesized by co-precipitation and D ₁pH₁₀-LDH synthesized from the dolomite. The equilibrium isotherm showed that the uptake of phosphate ion by Mg₃pH₁₀(500)-LDH was in agreement with the Langmuir and Freundlich equations; the Langmuir model gave a better fit to the experimental data than the Freundlich one. The equilibrium isotherm showed, however, that the adsorption of the phosphate on D₁pH₁₀(500)-LDH was accompanied with precipitation reac tion of the phosphate salts. A mechanism proposed for the removal of phosphate ion has been confirmed by X-ray diffraction and FT-IR spectroscopy.     

Biosorbent for tungsten species removal from water: effects of co-occurring inorganic species

The effect of co-occurring inorganic species on the removal of tungsten from water was investigated using biosorbent (i.e., chitosan coated montmorillonite clay). Simulated natural water and well water from Fallon, NV were used for this study. The concentrations of tungsten (21-541 mg/L) and inorganic species ([H(2)CO(3)]=0-4.2 mg/L, [H(4)SiO(4)]=0-90 mg/L, and [SO(2-)(4)]=0-400 mg/L) in simulated feed water were varied. The concentration of tungsten in the well water was 26 microg/L. The pH level of simulated feed water and well water was adjusted to 4 since this pH was found to be the most effective pH for the tungsten removal using chitosan coated clay. Tungsten removal without the existence of co-occurring inorganic species decreases from 99.8 to 87.1% with an increase in initial tungsten concentration from 21 to 541 mg/L. It reduces further as the co-occurring inorganic species concentration increases. The percentage of the tungsten removal ranges between 68.2-93.8%, 66.7-94.2%, and 53.6-93.7% for simulated natural water containing varied amount of H(2)CO(3), H(4)SiO(4), and SO(2-)(4), respectively. The adsorption kinetic data could be best described by the pseudo second order expression. The adsorption equilibrium data was modeled with the Langmuir, Temkin, and Freundlich equations and was found to be represented well by the Langmuir equation. The essential characteristics of the Langmuir isotherm indicate that the adsorption of tungsten on chitosan coated clay is favorable regardless of the presence of interfering species. Compared to natural clay, chitosan coated clay has about 116 times larger adsorption capacity per gram of chitosan, which makes it a superior adsorbent. However, the maximum tungsten adsorption capacity decreases in the presence of co-occurring species since the co-occurring species suppress the adsorption. For the well water treated with biosorbent, the tungsten concentration in the product water was found to be lower than the detection limit (1 microg/L) of the inductively coupled plasma mass spectrometer (ICP-MS). The repeatable results obtained from the treatment of both simulated and well water suggest that using chitosan coated clay can be an efficient adsorbent for tungsten removal from contaminated sites.     

Water-insoluble cyclodextrin polymer crosslinked with citric acid for paraquat removal from water

The anionic water-insoluble cyclodextrin polymer (polyCTR-β-CD) was crosslinked between β-cyclodextrin (β-CD) and citric acid (CTR) at 180?°C during 30?minutes to eliminate paraquat (PQ) from water. The reaction yield was equal to 70.2%, the ionic exchange capacity corresponded to 3.29?mmol·g^?1 and the β-CD content was 0.29?mmol·g^?1. Then, samples were characterized by SEM, ATR-FTIR, TGA, BET and stereoscopic microscope. Adsorption experiments were investigated with different factors such as pH of the solution, contact time, initial concentration of paraquat and adsorption temperature. The relevant pH was equal to 6.5 and the optimal contact time was 120?minutes to attain adsorption equilibrium. At 30?°C, the adsorption capacity was increased (9.4, 17.4 and 20.8?mg·g^?1) when the initial concentration of paraquat was raised (25, 50 and 200?mg·L^?1 respectively). Adsorption kinetics was appropriated to the pseudo-second-order model and adsorption isotherm was fitted to the Langmuir model. For thermochemistry parameters at different temperatures, the negative ΔG° showed a spontaneous adsorption process, the negative ΔH° indicated an exothermic process and the positive ΔS° exhibited an increase disorder. Finally, the reusability of the insoluble polymer was reached 78.3% after four regeneration cycles in methanol.     

Adsorption of graphene for the removal of inorganic pollutants in water purification: a review

Graphene has aroused widespread attention as a new type of adsorbents due to its outstanding ability for the removal of various pollutants from aqueous solutions. This review summarizes the application of graphene-based nanomaterials as an advanced adsorbent for the removal of inorganic pollutants including anionic and cationic type. The adsorption properties, mechanisms, isotherms, kinetics, thermodynamics and regeneration of adsorbents are all summarized, and the further research trends on graphene-based nanomaterials in the removal of pollutants are also given.     

Preparation of Tetraethylenepentamine-Functionalized 4A Zeolite for effective removal of phosphate in water

Recently, the high-concentration phosphorus-containing wastewater has been caused lots of negative influences on aquatic environment and thus driven people to develop some effective methods to remove excess of phosphate in water. In order to solve these environmental problem, in this work, a tetraethylenepentamine (TEPA) modified 4A zeolite has been prepared and used for removing phosphate. Removal of phosphate by precipitation of 4A zeolite and electrostatic action of TEPA with phosphate were determined by scanning electron microscopy, X-ray powder diffraction and Fourier infrared spectrum, and morphology and characteristic peak of TEPA-4A zeolite before and after adsorption changed significantly. In addition, the results of batch adsorption studies showed that the pH of the solution have a significant influence on the adsorption of TEPA-4A and the biggest adsorption capacity was 23 mg/g at pH = 2.3 ± 0.2. Adsorption isotherms results showed that the process was consistent with Langmuir model and the maximum adsorption capacity could reach to 28 mg/g at 25 °C. TEPA-4A adsorption processes were spontaneous endothermic reaction, and elevated temperatures were conducive to the adsorption process through kinetics and thermodynamics results. The research of TEPA modified 4A zeolite and raw 4A zeolite provides technical support for the development of 4A zeolite instead of sodium tripolyphosphate as a new type of detergent ingredient.     

Facile synthesis of hydrous zirconia-impregnated chitosan beads as a filter medium for efficient removal of phosphate from water

The removal and recovery of phosphate from water using adsorption technology require that the adsorbent material is easily separable from treated water. Continuous efforts are still awaited to develop additional efficient phosphate adsorbents that are economical to fabricate. In this study, hydrous zirconia-impregnated chitosan beads (HZCB) containing different Zr/chitosan ratios were synthesized using a facile scheme. We found that HZCB with a Zr/amine molar ratio of?~?1 (HZCB-1) possessed excellent stability and phosphate removal performance. This optimized material was characterized with XRD, SEM, FTIR, XPS, specific surface area and point of zero charge measurements. The maximum adsorption capacity was 42.02 mg/g (at pH?~?6.7). The adsorption kinetics were best described by a pseudosecond-order model, and the rate constant of HZCB-1 was much lower than that of its powder but was similar to the commercial bead product Ferrolox. The removal of phosphate depended substantially upon pH and was enhanced by lowering the pH. Good selectivity of HZCB-1 for phosphate was observed, although the coexistence of sulfate produced a significant negative effect. Direct coordination of phosphate to Zr atoms by replacing hydroxyls was the dominant adsorption mechanism (~?85%), while chitosan also contributed to phosphate removal (~?15%). Adsorbed phosphate was successfully eluted by an NaOH solution, and the material obtained after desorption and regeneration was able to be repeatedly used. The results of column studies indicated that this material could be implemented in long-term application.

     

Use of triphenylmethane dyes for the spectrophotometric determination of polymer flocculants in aqueous solutions

The interaction of anionic forms of triphenylmethane dyes (TPM) with cationic polymer flocculants (e.g., with polydiallyldimethylammonium chloride (PC)) yields inextricable ion pairs. This leads to a shift of absorption bands or a redistribution of their intensities in the TPM spectra and can be used for the spectrophotometric determination of microgram amounts of flocculants in aqueous solutions. Among 14 studied TPMs, erythrosine is the most promising dye. The corresponding procedure allows the determination of PC at a level of the maximum permissible concentration. To decrease the effect of impurities, the use of the standard addition method is recommended.Translated from Zhurnal Analiticheskoi Khimii, Vol. 60, No. 3, 2005, pp. 278–283.Original Russian Text Copyright © 2005 by Antonova, Vershinin, Dedkov.     

Hybrid polymer inorganic materials prepared from ternary microemulsions

The microemulsion system containing vinyl acetate (Vac), silane derivatives tetraethoxysilane (TEOS), methacryloxypropyltrimethoxysilane (MPTS), vinyltriethoxysilane (VTES), methyltriethoxysilane (MeTES), octyltriethoxysilane (OTES), nonylphenol etoxylated with 25 mol of ethylene oxyde (NPEO₂₅) and water was studied. It was established that the probability of microemulsion formation increases with surfactant concentration. The microenviroment of the solubilization of the VAc and of silane derivatives in the aggregates of NPEO₂₅ was affected by their polarity. Hybrid materials were obtained by sol-gel reaction of silane derivatives combined with free-radical polymerization of VAc. The change of the glass transition temperature and of thermal stability of the polymer chains in the presence of the inorganic one proved the formation of simultaneous polymer inorganic hybrids.     

Effect of absorption of low-molecular-weight compounds by some polymer flocculants

The sorption properties of the intramolecular complex - poly(acrylamide) to poly(vinyl alcohol) grafted copolymer (PVA-PAA_N) in block state were investigated with respect to a number of compounds. The relatively small molecules of phenol, phenylalanine in water solution as well as nitrobenzene in hexane are strongly absorbed by PVA-PAA_N films. The large humine acid molecules (sizes are larger by more than ≈ 10 times) are absorbed by PVA-PAA_N very weakly. It was determined the absorption influence on the character of polymer film solution. In a number of cases the oscillation of the dilution and sorption were observed when determining the critical concentrations of guest molecules in the upper layer of polymer films were achieved. The possible mechanisms of absorption were discussed.     

Tamarindus indica mucilage and its acrylamide-grafted copolymer as flocculants for removal of dyes

The application of Tamarindus indica seed mucilage (Tam), a food grade polysaccharide, and its acrylamide grafted copolymer as flocculants was assessed for the first time for removal of various types of dyes from model textile wastewater containing azo, basic, and reactive dyes. Acrylamide grafted T. indica mucilage (Tam-g-PAM) was obtained by ceric ion initiated polymerization technique. A series of contact time experiments were conducted to assess the system variables such as concentrations of mucilage and dyes and pH. These flocculants reduce the dye concentration by flocculation and settling. The grafted copolymer, Tam-g-PAM showed better results for dye removal. The optimal flocculant concentration, which was required to effect flocculation, was independent of dye concentration within the range examined. Both the flocculants performed better for removal of azo dyes than for reactive and basic dyes.     

Iranian clinoptilolite-rich tuffs for radionuclide removal from water

Three Iranian natural zeolites were characterized and evaluated for their abilities to take up Ba⁺², Ca⁺², K⁺ and Na⁺ from radioactive waste waters. The distribution coefficient values (K _d ) of the cations were measured and investigated as a function of pH. Four different cationic forms (Na, K, NH₄, and Ca) were also prepared and theirK _d values were determined. Some cations such as potassium presented highK _d values both in natural and exchanged zeolites. In sodium and ammonium exchanged forms theK _d values increased between 7 to 100 times with respect to the untreated zeolite.     

Selective removal of amikacin from simulated polluted water using molecularly imprinting polymer: A column study

In the present work, antibiotic drug Amikacin has been used as template molecule to prepare poly(methacrylic acid) based molecularly imprinting polymer (MIP), using acetonitrile (Acn) as porogenic solvent. The MIP has been used for the selective removal of drug Amikacin (Amk) using column mode operation. The removal efficiency of the MIP was found to increase with the length of the column, while the increase in the flow rate was found to decrease the extent of removal. In addition, increase in the concentration of the feed drug solution also enhanced the extent of removal. The kinetic drug removal data was interpreted in the terms of various models such as Thomas and Yoon-Nelson models.     

Mineral sorbents for the removal of oil products from waste water

Properties of filtering-sorption materials based on basalt fibers and bentonite clays intended for the removal of oil products from water were studied. Optimal parameters of a feed providing the maximal purification efficiency with the minimal power consumption were determined.     

Selected hybrid photocatalytic materials for the removal of drugs from water

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Metallothionein-cross-linked hydrogels for the selective removal of heavy metals from water

The diverse functional repertoire of proteins promises to yield new materials with unprecedented capabilities, so long as versatile chemical methods are available to integrate biomolecules with synthetic components. As a demonstration of this potential, we have used site-selective strategies to cross-link polymer chains using the N- and C-termini of a metallothionein derived from a pea plant. This arrangement directly relates the swelling volume of the polymer to the folded state of the protein. The material retains the protein's ability to remove heavy metal ions from contaminated water samples, and can be regenerated through the subsequent addition of inexpensive chelators. The change in hydrogel volume that occurs as metal ions are bound allows the detection of contaminants through simple visual inspection. The utility of this bulk property change is demonstrated in the construction of a low-cost device that can report heavy metal contamination with no external power requirements. Most importantly, the generality of the protein modification chemistry allows the immediate generation of new hybrid materials from a wide range of protein sequences.     

Starch-modified filters used for the removal of dyes from waste water

The present article proposes the use of starch-enriched flour as low-cost adsorbent of dyes. The adsorbents have been prepared by reticulation of starch-enriched flour using epichlorohydrin as crosslinking agent. These starch-modified filters exhibit interesting properties in terms of sorption rate. Studies concerning the sorption capacity are presented. The influence of the amine groups and the chemical structure of dyes are also studied. The regeneration procedure of the filters is showed and discussed. In order to explain the results, an adsorption mechanism mainly based on physical adsorption and interactions such as hydrogen bonds and ion-exchange due to the nature of the polymer network is proposed.     

Effect of metal ions on the determination of polymer flocculants using triphenylmethane dyes

Transition and heavy metals interfere with the spectrophotometric determination of flocculants based on the formation of their ion associates with triphenylmethane dyes (TPM). The absorption band of metal complexes with these reagents overlaps the absorption band of the associates; moreover, metal ions enhance the absorption of the associate. The increase in sensitivity is accompanied by a decrease in repeatability; therefore, the detection limits of flocculants change insignificantly. In the determination of flocculants in water at a level of 1 mg/L and above, these metals should be separated or masked in advance.