Phosphorus fractions and phosphate sorption characteristics in relation to the sediment compositions of shallow lakes in the middle and lower reaches of Yangtze River region, China

Phosphorus is recognized as the most critical nutrient limiting lake productivity. The trophic status and development of lake systems are also influenced by the phosphorus content and fractions and phosphate sorption characteristics of the lake sediments. The phosphorus fractions and phosphate sorption characteristics of sediments in shallow lakes from the middle and lower reaches of Yangtze River region in China were investigated. The results show that the phosphorus contents in the sediments ranged from 217.8 to 1640 mg kg(-1); inorganic phosphorus (IP) was the major fraction of total phosphorus (TP); phosphorus bound to Al, Fe, Mn oxides, and hydroxides (Fe/Al-P), and calcium bound phosphorus (Ca-P) were the main fractions of IP. Phosphate sorption on the sediments mainly occurred within 2 h and then reached equilibrium in 10 h. The phosphate sorption rate was closely related to the concentration of fine particles. The phosphate sorption capacity ranged from 128.21 to 833.33 mg kg(-1), showing a significant correlation with the contents of Fe, Fe+Al, total organic carbon (TOC), cationic exchange capacity, total nitrogen, TP, Ca, IP, and the ratio of P/(Al+Fe), and it was higher in the sediments of eutrophic lakes than in mesotrophic lakes. Phosphate was mainly sorbed onto Fe and Al particles. The phosphate sorption efficiency ranged from 26.74 to 312.50 L kg(-1), and had a strong positive correlation with Fe content. For the eutrophic lake sediments, there were no significant relationships between the phosphate sorption efficiency and the selected physical and chemical parameters. But for the mesotrophic lake sediments, the phosphate sorption efficiency was found to be positively related to the contents of Al and Fe+Al.     

Development of Electroflotation Technology for Extraction of Anionic Surfactants and Nonferrous Metal Ions from Wastewater Produced at Electroplating Industries

Sorption extraction of anionic surfactants NaDDS and NaDBS on freshly formed iron(III) and aluminum(III) hydroxides and on a highly dispersed activated carbon of OU-B brand was experimentally studied. It was shown that NaDDS is the most fully sorbed on Al(OH)₃ and OU-B, whereas on Fe(OH)₃, the maximum sorption is observed for NaDBS. The electroflotation extraction of anionic surfactants and poorly soluble iron(III) and aluminum(III) hydroxides was examined and the influence exerted by the following factors (pH, nature of electrolyte, surfactant concentration) on the degree of extraction of these substances was analyzed. In addition, electroflotation extraction of OU-B in the presence on nonferrous metal hydroxides and surfactants of varied nature from aqueous solutions was performed. The results obtained were used to develop a technological scheme for electroflotation of complex-composition wastewater.     

Intraparticle phosphorus diffusion in a drinking water treatment residual at room temperature

Phosphorus (P) has been recognized as one of the major limiting nutrients that are responsible for eutrophication of surface waters, worldwide. Efforts have been concentrated on reducing P loads reaching water bodies, via surface runoff and/or leaching through a soil profile. Use of drinking water treatment residuals (WTRs) is an emerging cost-effective practice to reduce soluble P in poorly P-sorbing soils or systems high in P. Literature suggests that WTRs have huge P sorption capacities. We hypothesized that P sorption would be limited by diffusional constraints imposed by the WTR particles. Selected chemical and physical (specific surface area, particle size distribution) characteristics of an iron-based WTR were measured. Sorption P isotherms at room temperature were constructed, and sorption kinetics were monitored. An intraparticle diffusion model was utilized to fit the kinetic data. Results showed that the WTR dramatically reduced soluble P, showing nonequilibrium characteristics, even after 80 d of reaction. Specific surface area (SSA) measured with CO2 gas was significantly greater than the traditional BET-N2 value (28 versus 3.5 m2 g(-1)), suggesting that a large amount of internal surfaces might be present in the WTR. The intraparticle P diffusion model was modified to include the wide particle size distribution of the WTR. The intraparticle diffusion model fitted the data well (r2 = 0.83). We calculated a maximum apparent P diffusion coefficient value of 4 x 10(-15) cm2 s(-1), which agrees with published values for intraparticle diffusion in microporous sorbents. This work may be useful for predicting long-term sorption characteristics of WTRs, since WTRs have been suggested as potential long-term immobilizers of sorbed P in P-sensitive ecosystems.     

Influence of air on polybutadiene used in the preparation of stationary phases for high-performance liquid chromatography

A 100 ml bottle of polybutadiene, PBD, was repeatedly exposed to air over a period of 6 months. Samples were taken at time zero (PBD-0), after 3 months (PBD-3) and 6 months (PBD-6). These samples were sorbed onto HPLC silica by an open-air solution-evaporation procedure, which involved exposure to the atmosphere for 6 days. Portions of the three sets of samples were used to compare self-immobilization and the effects of 100 degrees C thermal treatments in air or nitrogen on HPLC performance of the resulting phases. It is concluded that self-immobilization is enhanced by prior exposure of sorbed PBD to air and subsequent heating at 100 degrees C further enhances column performance. The best performance (10(5) plates m(-1)) resulted from 4 h heating of PBD-6 material in nitrogen.     

Ceramic nanomaterials from aqueous and 1,2-ethanediol supersaturated solutions at high temperature

The aim of this study was the synthesis and physicochemical characterization of some nanosized hydroxides/oxides interesting in the field of ceramic materials with the aim of developing new materials for technological applications in the field of high-performance coatings. In particular, attention was focused on ZrO2nH2O, ZrO2, Zn(OH)2, ZnO, Al2O3nH2O, and Al2O3. The synthesis was carried out in 1,2-ethanediol at 150-160 degrees C or in water at 90 degrees C at a high degree of supersaturation in order to achieved nucleation rate much greater than the growth rate. The obtained ZrO2nH2O, Zn(OH)2, and Al2O3nH2O particles were peptized to eliminate possible agglomeration and then calcinated at a suitable temperature to allow the formation of the corresponding anhydrous oxides. The synthesized particles were characterized by scanning and transmission electron microscopy, X-ray diffractometry, and differential thermal analysis coupled with thermogravimetry and Fourier transform infrared spectroscopy. The study showed that all the products can be obtained in the nanostructured crystalline form; ZrO2 presented the interesting feature of different tetragonal/monoclinic ratios depending on the solvent used for the synthesis. Preliminary results on the potentialities of these ZrO2 particles as agents for ultrahard coatings on ceramic surfaces were encouraging and very promising.     

Adsorption of Cr(VI) and Se(IV) from their aqueous solutions onto Zr4+-substituted ZnAl/MgAl-layered double hydroxides: effect of Zr4+ substitution in the layer

Hydrotalcite-like compounds (layered double hydroxides, LDHs) containing varying amounts of Al(3+), Zr(4+), and Zn(2+) or Mg(2+) in the metal hydroxide layer have been synthesized and characterized by various physicochemical methods. The adsorption behavior of uncalcined (as-synthesized) and calcined LDHs have been investigated for Cr(2)O(7)(2-) and SeO(3)(2-). The mixed oxides, obtained on calcination at 450 degrees C, exhibit high adsorption capacities for Cr(2)O(7)(2-) (1.6-2.7 meq/g) and SeO(3)(2-) (1.1-1.5 meq/g), where adsorption occurs through rehydration. Substitution of Zr(4+) in the LDHs, for either M(2+) or Al(3+) ions, increases the adsorption capacity up to 20%, thus providing an alternative way to enhance the adsorption capacity of this type of material. The high adsorption capacity of these materials could be successfully used for removal of undesirable anions from water and also for synthesis of intercalated materials with tailored acidobasicity.     

Layered Double Hydroxides Intercalated by Polyoxometalate Anions with Keggin (alpha-H(2)W(12)O(40)(6)(-)), Dawson (alpha-P(2)W(18)O(62)(6)(-)), and Finke (Co(4)(H(2)O)(2)(PW(9)O(34))(2)(10)(-)) Structures

The pillaring of Mg(3)Al layered double hydroxides (LDHs) by the title polyoxometalates (POMs) was accomplished by ion exchange reaction of the LDH-hydroxide and -adipate precursors with the POM anion at ambient or refluxing temperatures. The structural, thermal and textural properties of the LDH-POM intercalates were elucidated based on XRD, FTIR, TEM, EDS, and N(2) adsorption-desorption studies. A gallery height of approximately 10 ? was observed for the LDH intercalated by the symmetrical Keggin POM, whereas two different gallery heights were found for the cylindrical Dawson (14.5 and 12.8 ?) and Finke (13.3 and 12.6 ?) anions, depending on the preparation temperature. The differences in POM orientations were rationalized in terms of different electrostatic and hydrogen-bonding interactions between the POM pillars and the LDH layers. Upon thermal treatment at >/=100 degrees C, the intercalated Dawson and Finke POM ions exhibited only one gallery orientation, regardless of synthesis conditions. The crystalline microporous structures were retained upon heating each LDH-POM intercalate in N(2) to 200 degrees C. Pillaring in all cases was accompanied by the formation of a poorly ordered Mg(2+)/Al(3+) salt impurity that formed on the external surfaces of the LDH crystals.     

Solid-state transformation mechanisms of associated minerals to aluminosilicates

Thermochemical and mechanochemical transformation mechanisms of associated minerals in clay (quartz, calcite, Al and Fe oxyhydroxides) are comparatively examined. The phase transformation sequence resulting from heating and, on the other hand from dry grinding of each of the associated minerals, depends on the structure and physicochemical properties of the starting materials.Grinding treatments may cause local heating and local pressure effects in some selective metal oxides and in calcite, respectively, accounting for their structural conversions.Dedicated to Dr. Robert Mackenzie on the occasion of his 75th birthday     

Fe-Al layered double hydroxides in bromate reduction: Synthesis and reactivity

This study presents a rare use of layered double hydroxides of Fe(II) and Al(III) (Fe-Al LDH), as reported for the first time for bromate removal from aqueous solutions. The Fe-Al LDH samples were prepared with Fe/Al molar ratios of 1-4 using a co-precipitation method at pH 7, with subsequent hydrothermal treatment at 120°C. The Fe-Al LDH (molar ratio of Fe/Al=1, 2) with a layered structure exhibited nearly complete removal of bromate from initial concentration of 100μmol/dm(3) at a wide pH range of 4.0-10.5 over a 2h reaction period; the residual bromate concentration in the solution was lower than the detection limit of 0.07μmol/dm(3) (9μg-BrO(3)(-)/dm(3)). During the reaction period, bromide was released into the solution via a reduction process. Reactivity of Fe-Al LDH with a Fe/Al molar ratio of 2 did not decrease the bromate reduction efficiency during 30days.     

Magnetic, luminescent Eu-doped Mg-Al layered double hydroxide and its intercalation for ibuprofen

A magnetic, luminescent Eu-doped Mg-Al layered double hydroxide with ibuprofen (IBU) intercalated in the gallery has been successfully prepared by a simple coprecipitation method. The physicochemical properties of the samples were well characterized by powder XRD, TEM, FTIR, TGA, inductively coupled plasma MS (ICP-MS), vibrating sample magnetometry (VSM), and fluorospectrophotometry. The results revealed that Fe(3)O(4) nanoparticles are coated on the surface of layered double hydroxides and the obtained (Mg(2)Al(0.95)Eu(0.05))(Fe)-(IBU) sample exhibits both superparamagnetic and luminescent properties, with a saturation magnetization value of 1.86?emu g(-1) and a strong emission band at 610?nm, respectively. Additionally, it was found that the ibuprofen loading amount is about 31?% (w/w), and the intercalated ibuprofen possesses sustained release behavior when the magnetic, luminescent composite is immersed in simulated body fluid (SBF).     

Toward a general strategy for the synthesis of heterobimetallic coordination complexes for use as precursors to metal oxide materials: synthesis, characterization, and thermal decomposition of Bi(2)(Hsal)(6).M(acac)(3) (M = Al, Co, V, Fe, Cr)

Bismuth(III) salicylate, [Bi(Hsal)(3)](n), reacts readily with the trivalent metal beta-diketonate compounds M(acac)(3) (acac = acetylacetonate; M = Al, V, Cr, Fe, Co) to produce trinuclear coordination complexes of the general formula Bi(2)(Hsal)(6).M(acac)(3) (M = Al, V, Cr, Fe, Co) in 60-90% yields. Spectroscopic and single crystal X-ray diffraction experiments indicate that these complexes possess an unusual asymmetric nested structure in both solution and solid state. Upon standing in dichloromethane solution, Bi(2)(Hsal)(6).Co(acac)(3) eliminates Bi(Hsal)(3) to give the 1:1 adduct Bi(Hsal)(3).Co(acac)(3). The 2:1 heterobimetallic molecular compounds undergo facile thermal decomposition on heating in air to 475 degrees C to produce heterometallic oxide materials, which upon annealing for 2 h at 700 degrees C form crystalline oxide materials. The synthetic approach detailed here represents a unique, general approach to the formation of heterobimetallic bismuth-based coordination complexes via the coordination of M(acac)(3) complexes to bismuth(III) salicylate.     

Studies on fluoride adsorption capacities of amorphous Fe/Al mixed hydroxides from aqueous solutions

This study evaluated the effectiveness of amorphous iron and aluminum mixed hydroxides in removing fluoride from aqueous solutions. A series of mixed Fe/Al samples were prepared at room temperature by co-precipitating Fe and Al mixed salt solutions at pH 7.5. The compositions (Fe:Al molar ratio) of the oxides were varied as 1:0, 3:1, 2:1, 1:1 and 0:1 and the samples were characterized by XRD, BET surface area and pH_ZPC. The XRD studies indicated the amorphous nature of the samples and Al(III) incorporation on Fe(III) hydroxides. Batch adsorption studies for fluoride removal on these materials showed that the adsorption capacities of the materials were highly influenced by solution pH, temperature and initial fluoride concentration. The rate of adsorption was fast and equilibrium was attained within 2 h. The adsorption followed first-order kinetics with intraparticle diffusion as the rate determining step for all the samples. The experimental data fitted well to both Langmuir and Freundlich adsorption isotherms. All samples exhibited very high Langmuir adsorption capacities; the sample with molar ratio 1 has shown maximum adsorption capacity of 91.7 mg/g. The thermodynamic parameters were determined to study the feasibility of the adsorption process.     

Sorption and Abiotic Redox Transformation of Nitrobenzene at the Smectite-Water Interface

The effect of the redox state of structural Fe on the surface reactivity of iron-bearing phyllosilicates in aqueous suspension was investigated using a molecular probe. For this purpose the structural Fe in montmorillonite and ferruginous smectite was chemically reduced by sodium dithionite in citrate-bicarbonate (CB) buffer solution under N(2) at 70 degrees C, with the excess reactants removed by washing and centrifugation. Nitrobenzene was chosen as an electron acceptor probe to react with unaltered and chemically reduced smectites. Nitrobenzene was transformed into aniline only in the presence of the reduced smectites. This abiotic reductive transformation depended on the concentration of the electron acceptor in solution and the total accessible structural Fe(II) in smectites. As much as 40% of the crystal layer structural Fe(II) of the reduced smectites was oxidized to Fe(III); these electrons migrated to the surfaces/edges and then were transported into the adjacent aqueous layer. No significant effect of the oxidation state of structural Fe on the sorption of nitrobenzene on smectites was observed, but the reduced smectites sorbed less aniline than the unaltered smectites. The electronic structure and molecular geometry of the probe were modified within the smectite-water interface. Reducing structural Fe in smectites perturbed the surface reactivity. Copyright 2001 Academic Press.     

P=N bond formation via incomplete N-atom transfer from a ferrous amide precursor

Incomplete N-atom transfer from Fe to P is observed when the ferrous amide complex (PNP)Fe(dbabh) (PNP-=N[2-P(iPr)2-4-methylphenyl]2, dbabh=2,3:5,6-dibenzo-7-azabicyclo[2.2.1]hepta-2,5-diene), prepared from salt metathesis of (PNP)FeCl and Li(dbabh), is thermolyzed at 70 degrees C over 48 h in C6D6. Several plausible reaction pathways resulting from the transformation of (PNP)Fe(dbabh) are discussed, including the possibility of an Fe(IV) nitride as an intermediate.     

Determination of uranium in technological waters by ion-pair liquid chromatography

U(VI) can be efficiently determined in the range 0.3-1OmM after its separation from Th(IV), Zr(IV), Al(III), Fe(III), lanthanides and other ions by ion-pair liquid chromatography on a 3 x 150 mm glass column packed with Separon SGX C18 modified with sorbed ammonium dodecyl sulphate. Traces of uranium can be preconcentrated directly on the analytical column from acidified water solutions and separated from Th, Zr, Al, Fe, lanthanides and other elements, with an enrichment factor of $ 100 and recovery of 98 +/- 8%, by isocratic or pH or concentration gradient elution with ammonium 2-hydroxy-2-methylpropionate or ammonium citrate solution. Post-column derivatization with 25muM Arsenazo III in 0.1M formate buffer at pH 2.7 is used for detection and quantification.     

Transmission electron microscopy and X-Ray diffraction analysis of aluminum-induced crystallization of amorphous silicon in alpha-Si:H/Al and Al/alpha-Si:H structures.

Solid phase crystallization of plasma-enhanced chemical-vapor-deposited (PECVD) amorphous silicon (alpha-Si:H) in alpha-Si:H/Al and Al/alpha-Si:H structures has been investigated using transmission electron microscopy (TEM) and X-ray diffraction (XRD). Radiative heating has been used to anneal films deposited on carbon-coated nickel (Ni) grids at temperatures between 200 and 400 degrees C for TEM studies. alpha-Si:H films were deposited on c-Si substrates using high vacuum (HV) PECVD for the XRD studies. TEM studies show that crystallization of alpha-Si:H occurs at 200 degrees C when Al film is deposited on top of the alpha-Si:H film. Similar behavior was observed in the XRD studies. In the case of alpha-Si:H deposited on top of Al films, the crystallization could not be observed at 400 degrees C by TEM and even up to 500 degrees C as seen by XRD.     

Spontaneous magnetization in Ni-Al and Ni-Fe layered double hydroxides

Layered double hydroxides containing paramagnetic Ni (II) and diamagnetic/paramagnetic Al (III)/Fe (III) ions have been prepared and characterized. Ni 2Al(OH) 6(NO 3). nH 2O ( 1), Ni 2Fe(OH) 6(NO 3). nH 2O ( 2), Ni 2Fe(OH) 6(C 6H 8O 4) 0.5. nH 2O ( 3), and Ni 2Fe(OH) 6(C 10H 16O 4) 0.5. nH 2O ( 4) were prepared by coprecipitation at controlled pH as polycrystalline materials with the typical brucite-like structure, with alternating layers of hydroxide and the corresponding anions, which determine the interlayer separation. Magnetic studies show the appearance of spontaneous magnetization between 2 and 15 K for these compounds. Interestingly, the onset temperature for spontaneous magnetization follows a direct relationship with interlayer separation, since this is the only magnetic difference between compounds 2, 3, and 4. Magnetic and calorimetric data indicate that long-range magnetic ordering is not occurring in any of these materials, but rather a freezing of the magnetic system in 3D due to the magnetic disorder and competing intra- and interlayer interactions. Thus, these hydrotalcite-like magnetic materials can be regarded as spin glasses.     

Layered Double Hydroxides with Hydrotalcite—type Structure Containing Fe^3＋,Al^3＋ and Mg^2＋

IntroductionLayered double hydroxides( LDHs) with hy-drotalcite ( HT ) - type structure are composed oftrivalent and divalent metal ions and have the gen-eral formula[1] ,[M2 + 1-x M3 + x ( OH) 2 ]x+ An-x/ n· m H2 O,where M3 + is a trivalentmental ion,such as Al3 + ,Fe3 + ,La3 + ,Ni3 + ,Mn3 + etc.,M2 + is a divalentmetal ion,such as Mg2 + ,Zn2 + ,Ca2 + ,Cu2 + ,Co2 +etc.,An-is a charge compensating anion,such asOH-,Cl-,NO-3 ,CO2 -3 etc.,m is the number ofthe moles of co- intercalat…     

Synthesis and characterization of new Mg(2)Al-paratungstate layered double hydroxides

Layered double hydroxides (LDHs, or hydrotalcites) with Mg(2+) and Al(3+) cations in the mixed metal hydroxide layer and paratungstate anions in the interlayer have been prepared. Different methods have been followed: anion exchange with Mg,Al LDHs originally containing nitrate or adipate, reconstruction of the LDH structure from a mildly calcined Mg(2)Al-CO(3) LDH, and coprecipitation. In all cases, the tungsten precursor salt was (NH(4))(10)H(2)W(12)O(42). The prepared solids have been characterized by elemental chemical analysis, powder X-ray diffraction (PXRD), FT-IR spectroscopy, thermogravimetric (TG) and differential thermal (DTA) analyses, scanning electron microscopy (SEM) with EDX (energy-dispersive X-ray analysis), and nitrogen adsorption at -196 degrees C for surface area and surface texture. Most of the synthesis methods used, especially anion exchange starting from a Mg(2)Al-NO(3) precursor at low temperature and short reaction times, lead to formation of a hydrotalcite with a gallery height of 9.8 A; increasing the reaction temperature to 70-100 degrees C and maintaining short contact times leads to a solid with a gallery height of 7.8 A. Both phases have been identified as a result of the intercalation of W(7)O(24)(6)(-) species in different orientations in the interlayer space. If the time of synthesis or the temperature is increased, a more stable phase, with a gallery height of 5.2 A corresponding to a solid with intercalated W(7)O(24)(6)(-), is formed, probably with grafting of the interlayer anion on the brucite-like layers. All systems are microporous. Calcination at 300 degrees C leads to amorphous species, and crystallized MgWO(4) is observed at 700 degrees C.     

燃煤飞灰中铁质微珠的显微结构及其组成研究

选用我国三个典型燃煤煤种的电厂飞灰中铁质微珠,进行显微结构与物相组成等方面的研究。揭示出铁质微珠中存在空心微珠、子母珠和实心微珠三种显微颗粒类型,在这些显微颗粒表面可识别出以微粒状和八面体自形晶两种方式存在的赤铁矿和磁铁矿析晶;元素分析表明,燃烧褐煤电厂铁质微珠主要由Fe、Ca、Al、和Si元素组成,燃烧烟煤和无烟煤的电厂铁质微珠主要由Fe、Al和Si元素组成;物相分析发现,Fe在铁质微珠中以四种存在形式：Fe3O4、α-Fe2O3、γ-Fe2O3和Fe3+-玻璃相。这些物相在三个电厂飞灰中呈现出不同的分布特征,反映出不同的燃煤煤种在锅炉中燃烧温度的差异。随着温度的升高,Fe3O4先氧化为γ-Fe2O3,或γ-Fe2O3与Fe3O4的固熔体,然后再转变为α-Fe2O3,当温度超过 1 400 ℃时,Fe2O3又转化为Fe3O4。