The coagulation of Ca3Al2(OH)12 in aqueous electrolyte solutions

Summary Coagulation rate measurements of Ca₃Al₂(OH)₁₂ in different aqueous electrolyte solutions (NaOH, NaNO₃, Ca(OH)₂) show that, at concentrations lower than 0.1 M NaNO₃ and 0.3 M NaOH respectively, the stability increases with increasing ionic strength. This fact cannot be explained as either primary or secondary coagulation according to the DLVO theory. However, polymeric ions such as poly-aluminate ions, present in the liquid phase can cause the observed coagulation behaviour at these concentrations. At NaNO₃ concentrations higher than 0.1 M NaNO₃ the coagulation behaviour can be explained as primary coagulation according to the DLVO theory assuming = withA ₁₍₂₎ = 0.03 X 10^–20J. Assuming a distance between the plane with average potentialgs and of 0.3 to 0.4 nm,A ₁₍₂₎ =0.28 -0.30 x 10^–20J depending on the conditions between these two layers.

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Zusammenfassung Koagulationgeschwindigkeitsmessungen an Ca₃ Al₂(OH)₁₂-Suspensionen zeigen, daß in wässerigen Elektrolytlösungen (NaOH, NaNO₃, Ca(OH)₂) bei Konzentrationen niedriger als 0.1 M NaNO₃ bzw. 0.3 M NaOH die Stabilität größer wird, wenn die Elektrolytkonzentration zunimmt. Weder primäre noch sekundäre Koagulation nach der DLVO-Theorie kann diesen Effekt erklären. Die Anwesenheit von polymeren Ionen (z. B. Polyaluminationen) in der Lösung kann das beobachtete Koagulationsverhalten bei diesen Konzentrationen aber deuten. Bei NaNO₃-Konzentrationen größer als 0.1 M kann das Koagulationsverhalten erklärt werden als primäre Koagulation nach der DLVO-Theorie mit der Annahme, daß= und A1(2)=0.03 X 10^–20 J. Nimmt man an, daß der Abstand zwischen den Flächen mit durchschnittlichen Potentialen und etwa 0.3–0.4 nm beträgt, so wird A1(2)=0.28–0.30 x 10^–20 J, abhängig vom Zustand zwischen diesen Flächen.

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With 8 figures and 1 table     

A kinetic study of the intercalation of lithium salts into Al(OH)3

The intercalation of five lithium salts into the gibbsite and bayerite polymorphs of Al(OH)3 has been studied using in situ energy-dispersive X-ray diffraction. The kinetics and mechanisms of the reactions have been modeled using the Avrami-Erofe'ev model. The kinetic data suggest that the reaction mechanisms are predominantly nucleation controlled, although the intercalation of LiNO3 into bayerite and of Li2SO4 into gibbsite proceed via two-stage mechanisms, one part of which is diffusion controlled. All the reactions proceed directly from the host to the product, except for the intercalation of Li2SO4 into gibbsite where a more hydrated intermediate form of [LiAl2(OH)6]2SO4 x yH2O is generated prior to the final product.     

DFT Study of Polymorphism in Al(OH)3: A Structural Synthon Approach

All the known polymorphs of Al(OH)₃ comprise a stacking of charge neutral layers having the composition [Al_2/3□_1/3(OH)₂] (□: cation vacancy) and designated by the symbol P. Employing a single Al(OH)₃ layer (layer group p12₁/a1) as a structural synthon, the energy profile computed for the translations of P and $\bar{P}$ ($\bar{P}$ : mirror image of P) layers relative to each other within a bilayer model, not only show minima corresponding to the four known polymorphs of Al(OH)₃ but also predict three new polymorphs with energy minima at the stacking vectors (7/10, 5/18, 1) (polymorph B1), (1/2, 0, 1) (polymorph B2) and (2/5, 1/9, 1) (polymorph B4). Of these B1 and B2 are 0.30 eV and 0.23 eV below the energy of bayerite (B3), but 0.30 eV and 0.37 eV above the global minimum which corresponds to gibbsite. B4 is only 0.08 eV above the energy of bayerite. This quantitative structural synthon approach offers B1, B2, and B4 as legitimate targets for future synthetic efforts.     

The influence of Al(III) supersaturation and NaOH concentration on the rate of crystallization of Al(OH)3 precursor particles from sodium aluminate solutions

The growth kinetics of colloidal Al(III)-containing particles (diameter<1000 nm), nucleated in optically clear, supersaturated sodium aluminate solutions as a precursor to Al(OH)(3) crystals, has been studied using dynamic light scattering. Two series of solutions were examined at 22 degrees C to determine the influence of Al(III) supersaturation and NaOH concentration on the initial particle growth behavior. One solution series consisted of solutions with constant Al(III) absolute supersaturation (DeltaC) of 1.48 M and [NaOH] range 1.83-4.00 M ([NaOH]/[Al(III)]=1.13-2.15) and Al(III) relative supersaturation (sigma)=3.86-10.36. The other solution series had a constant sigma of 7.55 and [NaOH] range of 1.50-4.27 M ([NaOH]/[Al(III)]=1.18-1.54) and DeltaC=0.86-3.19. The correlation between the initial particle growth rates and supersaturation (DeltaC or sigma) revealed marked anomalies over the entire supersaturation range studied. The growth rate remained substantially constant in the DeltaC range 0.86-2.55 M (for the constant sigma solution series), before increasing sharply upon a further increase of DeltaC beyond 2.55 M. The variation of the growth rate with sigma in the range 3.86-9.00 (for the constant DeltaC solution series) was remarkably weak, contrary to expectation. At higher sigma (>9.00), however, a marked increase in growth rate with increasing sigma was displayed. At constant DeltaC or sigma, the growth rate showed a strong variation with NaOH concentration, indicating that Na(+) and OH(-) species play a pivotal role in the Al(OH) precursor particles (nuclei) growth process. Furthermore, the kinetics of growth displayed by these nanosized particles are an order of magnitude slower than those observed for macroscopic gibbsite (gamma-Al(OH)(3)) crystals at similar supersaturations and temperature. The difference may be rationalized in terms of particle size and Al(OH)(3) dimorphic phase dependent solubility effects. An empirically adequate growth kinetics modeling was achieved when the growth rates were correlated with the Al(III) supersaturation (DeltaC or sigma) and the excess (free) NaOH concentration, rather than the former alone, as is commonly the case. A critical [NaOH]/[Al(III)] molar ratio of 1.27-1.35, below which the particle growth rate increased markedly and above which the rate was significantly reduced, was observed. This behavior is believed to be linked to solution speciation change that occurs at certain Al(III) and NaOH compositions.     

Radiation chemical investigations on aqueous solutions of C60(OH)18

The ultraviolet-visible absorption spectrum of C₆₀(OH)₁₈ in water showed an absorption band with λ_max = 215 nm and other characteristic absorption bands of C₆₀ are not observed. The singlet-singlet and triplet-triplet absorption bands are not observed in the 400–900 nm region. It has low reactivity with e_aq⁻ and formed an absorption band with λ_max = 580 nm. The hydroxyl radicals react with a bimolecular rate constant of 2.4×10⁹ dm³ mol⁻¹ s⁻¹ and showed an absorption band at 540 nm.     

Structural and electronic evolution of the As(OH)3 molecule in high temperature aqueous solutions: an x-ray absorption investigation

The geometrical and electronic structure of the arsenious acid molecule As(OH)(3) in aqueous solutions has been investigated by x-ray absorption spectroscopy (XAS) within extended x-ray absorption spectroscopy (EXAFS) and x-ray absorption near edge structure (XANES), using realistic first-principle calculations in the latter case. This investigation was performed on aqueous solutions of arsenious acid from ambient to supercritical conditions (P = 250 and 600 bars, T 相似文献   

Adsorption and desorption studies of radiocesium on Al2O3 from aqueous solutions

The adsorption and the desorption of radiocesium from aqueous solutions containing NaNO₃ or CaCl₂ on Al₂O₃ were studied over a wide range of background electrolyte concentration and solution pH by using batch techniques in polyethylene and glass test tubes. It was found that the wall of the glass test tubes has a great effect on the adsorption and desorption data, and the adsorption-desorption hysteresis on the same time scale is negligible by using the same aqueous solutions for both adsorption and desorption in the polyethylene test tubes. The dependences of the distribution coefficient on the pH and background electrolyte concentration and the adsorption mechanism were discussed.     

稀土对氢氧化铝凝胶加热转变过程的影响

采用TG DTG DSC热分析、X射线衍射物相分析等方法研究了稀土元素对氢氧化铝凝胶加热转变过程的影响。实验结果表明 :稀土的添加加速了非晶Al2 O3的形成 ;提高了非晶态Al2 O3的晶化温度 ;对γ Al2 O3向α Al2 O3转变的影响随稀土添加种类及添加量不同而不同 ,添加的 4种稀土元素对该转变的抑制作用由强到弱为 :La >(Y ,Nd) >Ce。对稀土作用机制的初步分析结果表明 :稀土添加减少了Al2 O3中残余的羟基 ,因而降低了晶化过程中铝离子的扩散速率 ,从而减少了γ Al2 O3的晶化速率 ;稀土对γ Al2 O3向α Al2 O3转变的抑制作用主要是由于稀土铝酸盐的形成 ,LaAl1 1 O1 8(磁铅石结构 )的形成能更有效地抑制γ Al2 O3向α Al2 O3的转变 ,而YAlO3和NdAlO3的抑制作用则较小 ,以氧化物形式沉淀出来的CeO2 对γ Al2 O3向α Al2 O3转变没有明显影响     

Mobilities and ion-pairing in LiB(OH)4 and NaB(OH)4 aqueous solutions. A conductivity study

The conductivities of aqueous solutions of sodium borate at 25°C and lithium borate at various temperatures are reported. The conductivity of the B(OH) ₄ ⁻ ion is 35.3 ±0.2 S-cm²-mole⁻¹ at 25°C. The electrolytes are both associated, the lithium salt being more associated than the sodium salt. The mobilities and association constants obtained from the conductivity data agree with a model recently proposed for the H₂O−B(OH) ₄ ⁻ interactions. A discrepancy in the reported thermodynamic behavior of NaB(OH)₄ aqueous solutions has been resolved by means of the association constants obtained in the present study. Thus the usefulness of the conductivity measurements to determine excess chemical potentials of binary electrolytes in dilute solution is again shown.     

Structural characterization of molybdenum(V) species in aqueous HCl solutions

Mo(V) aqua-chloro complexes in hydrochloric acid solutions have been studied by means of Mo K- and L2,3-edge X-ray absorption and Raman spectroscopic methods. The solid compounds (HPPh3)2[MoOCl5] (1), 6[MoOCl4(H2O)]-.10(pyH)+.4Cl- (2), and (pyH)2[Mo2O4Cl4(trans-OH2)2] (3) were used for structural comparisons. The compound 2 crystallizes in the orthorhombic space group Pmma (no. 51) with a=21.398(3), b=8.057(4), c=13.330(4) A, and Z=4. In 0.2 M solutions of MoCl5 in 7.4-9.4 M HCl the mononuclear [MoOCl4(OH2)]- complex dominates with the bond distances Mo=O 1.66(2) A, Mo-Cl 2.38(2) A, and Mo-OH2 2.30(2) A. Its Raman band at 994 cm-1 for the Mo=O symmetric stretching vibration is closer to that of 2 (988 cm-1) than of 1 (969 cm-1). The Mo K-edge EXAFS spectrum for 0.2 M MoCl5 in 1.7 M HCl solution reveals a dinuclear [Mo2O4Cl6-n(OH2)n]n-4 (n=2, 3) complex with a double oxygen bridge and the average distances Mo=O 1.67(2) A, Mo-(mu-O) 1.93(2) A, Mo-Cl 2.47(3) A, Mo-Mo 2.56(2) A, and a short Mo-OH2 distance of 2.15(2) A, which implies that at least one of the aqua ligands is in equatorial position relative to the two axial Mo=O bonds. This position differs from the Mo-OH2 configuration exclusively trans to the M=O groups of the isomeric (with n=2) dinuclear complex in 3. The difference in the ligand field is also reflected in their L2,3-edge XANES spectra. For 0.2 M MoCl5 solutions in intermediate HCl concentrations (3.7-6.3 M) the Raman bands at 802 cm-1 (Mo-O-Mo) and 738 cm-1 (Mo-(mu-O)2-Mo) verify three coexisting classes of Mo(V) complexes: mononuclear complexes together with dinuclear mono-oxo (e.g., [Mo2O3Cl6(H2O)2]2-) and dioxo bridged species, even though principal component analysis (PCA) of the corresponding series of EXAFS spectra only could distinguish two major components. By fitting linear combinations of the appropriate EXAFS oscillation components, dioxo-bridged dinuclear complexes were found to dominate at HCl concentrations相似文献   

Spectroscopy of lithium atoms sublimated from isolation matrix of solid Ne

We have studied, via laser absorption spectroscopy, the velocity distribution of (7)Li atoms released from a solid neon matrix at cryogenic temperatures. The Li atoms are implanted into the Ne matrix by laser ablation of a solid Li precursor. A heat pulse is then applied to the sapphire substrate sublimating the matrix together with the isolated atoms at around 12 K. We find interesting differences in the velocity distribution of the released Li atoms from the model developed for our previous experiment with Cr [R. Lambo, C. C. Rodegheri, D. M. Silveira, and C. L. Cesar, Phys. Rev. A 76, 061401(R) (2007)]. This may be due to the sublimation regime, which is at much lower flux for the Li experiment than for the Cr experiment, as well as to the different collisional cross sections between those species to the Ne gas. We find a drift velocity compatible with Li being thermally sublimated at 11-13 K, while the velocity dispersion around this drift velocity is low, around 5-7 K. With a slow sublimation of the matrix we can determine the penetration depth of the laser ablated Li atoms into the Ne matrix, an important information that is not usually available in most matrix isolation spectroscopy setups. The present results with Li, together with the previous results with Cr suggest this to be a general technique for obtaining cryogenic atoms, for spectroscopic studies, as well as for trap loading. The release of the isolated atoms is also a useful tool to study and confirm details of the matrix isolated atoms which are masked or poorly understood in the solid.     

Poly(acrylamide) grafts on spherical bead polymers for extremely selective removal of mercuric ions from aqueous solutions

Poly(acrylamide) grafted from solid polymer particles provides a simple solution for extremely selective removal of mercuric ions from aqueous solutions. The grafting of polyacrylamide has been performed, in high yields (164%), by redox initiation from iminoacetic acid groups created on crosslinked spherical beads (210–420 μm) of glycidyl methacrylate/methyl methacrylate/ethylene glycol dimethacrylate terpolymer. In the grafting, homopolymer formation has been reduced greatly (22%) by the treatment of the bead polymer with ceric ammonium nitrate before the addition of acrylamide monomer. The mobility of the graft chains provides nearly homogeneous reaction conditions and rapid mercury binding ability, as for low molecular weight amides [mercury sorption by a 0.105‐g polymer sample from 105 mL of a 7.74 × 10^?4 mol L^?1 (～155 ppm) Hg(II) solution shows first‐order kinetics with respect to the Hg(II) concentration, k = 1.1 × 10^?3 s^?1]. The mercury sorption capacity under nonbuffered conditions is around 3.6 mmol g^?1 (i.e., 720 g of mercury/kg) and mostly occurs with the formation of diamido–mercury linkages, which result in the crosslinking of polyacrylamide brushes outside the spherical beads. The crosslinks can be destroyed by treatment with hot acetic acid, without hydrolysis of the amide groups. This process allows a complete elution of the mercury as mercury acetate, and the overall result is reversible crosslinking of the outer shell by mercuric ions. The material presented is efficient in the removal of mercury at concentrations measured in parts per million, and the mercury sorption is extremely selective over some foreign ions, such as Fe(III), Cd(II), Zn(II), and Pb(II). © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 3068–3078, 2002     

A novel flocculant of Al(OH)3-polyacrylamide ionic hybrid

A novel flocculant based on hybrid Al(OH)(3)-polyacrylamide (HAPAM) has been synthesized using a redox initiation system ((NH(4))(2)S(2)O(8)-NaHSO(3)) at 40 degrees C in aqueous medium. The HAPAM was characterized by viscometry, IR spectroscopy, TEM, conductivity, and TGA. The flocculation behavior for 0.25 wt% kaolin suspension was evaluated by spectrophotometry and phase contrast microscopy. It was found that an ionic bond exists between Al(OH)(3) colloid and polyacrylamide (PAM) chains in the HAPAM and the flocculation efficiency of HAPAM is much better than that of commercial polyacrylamide (PAM) and PAM/AlCl(3) blend.     

New insights into the intercalation chemistry of Al(OH)3

This paper reports a number of recent developments in the intercalation chemistry of Al(OH)(3). From Rietveld refinement and solid-state NMR, it has been possible to develop a structural model for the recently reported [M(II)Al(4)(OH)(12)](NO(3))(2)·yH(2)O family of layered double hydroxides (LDHs). The M(2+) cations occupy half of the octahedral holes in the Al(OH)(3) layers, and it is thought that there is complete ordering of the metal ions while the interlayer nitrate anions are highly disordered. Filling the remainder of the octahedral holes in the layers proved impossible. While the intercalation of Li salts into Al(OH)(3) is facile, it was found that the intercalation of M(II) salts is much more capricious. Only with Co, Ni, Cu, and Zn nitrates and Zn sulfate were phase-pure LDHs produced. In other cases, there is either no reaction or a phase believed to be an LDH forms concomitantly with impurity phases. Reacting Al(OH)(3) with mixtures of M(II) salts can lead to the production of three-metal M(II)-M(II)'-Al LDHs, but it is necessary to control precisely the starting ratios of the two M(II) salts in the reaction gel because Al(OH)(3) displays selective intercalation of M nitrate (Li > Ni > Co ≈ Zn). The three-metal M(II)-M(II)'-Al LDHs exhibit facile ion exchange intercalation, which has been investigated in the first energy dispersive X-ray diffraction study of a chemical reaction system performed on Beamline I12 of the Diamond Light Source.     

Emission from the species CH3COC(OH)2CH3 in aqueous solutions of biacetyl

A previously unreported emission at 435 nm from solutions of biacetyl in water, methanol or ethanol has been observed. It results from excitation at the 280 nm absorption peak but not from excitation at the 405 nm absorption maximum; its intensity is proportional to the amount of water/acetonitrile mixtures, and is insensitive to air concentration. Comparison of the position and intensity of this new peak with the fluorescence maxima of simple ketones such as acetone suggest that it is emission from biacetyl hemi-hydrate or hemiketal, known to be the predominant species in aqueous solutions of biacetyl, and shown to be the predominant species in alcoholic solutions.     

Electrochemical behaviour of solid lithium nickelate (LiNiO2) in an aqueous electrolyte system

Lithium nickelate was synthesized by self-propagating high-temperature combustion. The electrochemical behaviour of the product was studied by cyclic voltammetry of microparticles immobilized on the surface of graphite electrodes. Whereas numerous previous studies have dealt with non-aqueous electrolyte solutions, here the behaviour of lithium nickelate in contact with aqueous electrolyte solutions was investigated. It could be shown that protons are intercalating upon reduction of the Ni(III) to Ni(II) and deintercalating upon oxidation. This insertion electrochemistry is chemically reversible. Within 1600 oxidation-reduction cycles, the response diminished only by about 10%. Scanning electron microscopy reveals a considerable recrystallization during the electrochemical cycles. Energy dispersive X-ray detection proved that no metal cations are intercalating. The electrochemical system is accessible only in very alkaline solutions as it shifts to more positive values with decreasing pH. Received: 18 February 1999 / Accepted: 5 May 1999     

Structural characterization and dielectric properties of the solid solutions AgPb(Sb,Bi)S3

The new solid solutions AgPbSb_1 − x Bi _x S₃ were prepared by solid state reactions. The phases were characterized by powder X-ray diffractions (XRD), scanning electron microscopy, and thermal analysis. The XRD patterns of different members (x = 0.5, 0.7, 0.8, and 1.0) are consistent with pure phases crystallizing in the cubic PbS-type structure. The electrical characterization was carried out using ac impedance spectroscopy and dc methods. The temperature dependence of the dc conductivity shows typical semiconductor Arrhenius behavior. The impedance measurements were performed in the frequency range of 0.1 Hz to 10 MHz and at the temperature range of 15 °C to 350 °C. The ac conductivity conforms to Jonscher’s universal power law. The frequency dependence of the dielectric permittivity follows the normal dielectric material behavior, and the relaxation is thermally activated. The frequency and temperature dependences of the electrical data are found to follow Summerfield scaling formalism.