Fixed pH Values Research Articles

The role of pH control on biohydrogen production by single stage hybrid dark- and photo-fermentation

The role of pH control on biohydrogen production by co-culture of dark-fermentative Clostridium acetobutylicum and photofermentative Rhodobacter sphaeroides was studied. Single stage dark fermentation, photofermentation and hybrid co-culture systems were studied at different values of controlled and uncontrolled pH. Increasing pH during dark fermentation resulted in lower hydrogen production rate (HPR) and longer lag time for both controlled and uncontrolled conditions. However, it only slightly affected cumulative H2 volume. Results have shown that pH control at pH 7.5 increased photofermentative hydrogen production from 0.966 to 2.502L H2/Lmedium when compared to uncontrolled process. Fixed pH value has proven to be an important control strategy also for the hybrid process and resulted in obtaining balanced co-culture of dark and photofermentative bacteria. Control of pH at 7.0 was found optimum for bacteria cooperation in the co-culture what resulted in obtaining 2.533L H2/Lmedium and H2 yield of 6.22mol H2/mol glucose.

Characterization of kinetic and thermodynamic parameters of cyanidin-3-glucoside methyl and glucuronyl metabolite conjugates.

The determination of rate and equilibrium constants of anthocyanin metabolites with in vivo occurrence, cyanidin-4'-O-methyl-3-glucoside (Cy4'Me3glc) and cyanidin-7-O-glucuronyl-3-glucoside (Cy7Gluc3glc), was carried out for the first time by means of direct and reverse pH jumps. The thermodynamics and kinetics of these compounds are similar to the anthocyanin monoglucosides in particular for the analogous cyanidin-3-glucoside (Cy3glc) and peonidin-3-glucoside (Peo3glc). The rate and equilibrium constants of metabolites were also compared with malvin (malvidin 3,5-diglucoside) and with a bioinspired compound 3',4'-dihydroxy-7-O-glucopyranosyloxyflavylium (DGF). In Cy4'Me3glc and Cy7Gluc3glc the rate of hydration for a fixed pH value is slower than in DGF and the dominant species at moderately acidic solutions is the hemiketal. Oppositely, in DGF trans-chalcone is the dominant species at moderately acidic solutions.

Effect of pH on the performance of olive pips reactive barrier through the migration of copper-contaminated groundwater

Adsorption data are modeled using the popular Langmuir and Freundlich isotherm models. These isotherms are primarily useful for simulating data collected at a fixed pH value. This study attempted to develop an adsorption isotherm based on the Langmuir model, to simulate pH-dependent adsorption effects. It is derived based on the results of a batch of experiments conducted under appropriate conditions using olive pips as the reactive bio-sorbent on a copper-contaminated solution. This isotherm is used as a linear correlation between the maximum adsorption capacity and the initial pH values of the feed solution, while a nonlinear power correlation is used to represent the affinity coefficient–initial pH relationship. This isotherm is integrated with the advection–dispersion equation for simulating the effect of the initial pH on the contaminant transport scenarios. The integrated model, solved numerically by the implicit finite difference method, is proven, in which the initial pH has a potential effect on the retardation factor and longevity of the bed of olive pips. This bed can be used as a permeable reactive barrier in the remediation of contaminated groundwater. A good concurrence between the integrated model predictions and experimental results for breakthrough curves was recognized with the index of agreement (d), as proposed by Willmott, not less than 0.999.

Electricity generation and COD removal of microbial fuel cells (MFCs) operated with alkaline substrates

The characteristics of electricity generation and COD removal of dual-chamber microbial fuel cells (MFCs) operated with alkaline substrates were studied. Substrates with constant pH of either 7 or 9 as well as varying pH in a cycle of 7-8-9-8-7 were used. MFCs operated with these substrates were denoted as MFC-pH7, MFC-pH9 and MFC-pHV, respectively. The experimental results indicate that the MFC-pHV can generate the highest performance of 2554 ± 159 mW/m2. Cyclic voltammetry (CV), active biomass and electrochemical impedance spectroscopy (EIS) measurements were conducted and these results suggested that the MFC-pHV had the highest electrochemical activity per unit biomass and the lowest internal resistance, which together contributed to the improved power output of the MFC-pHV. In addition, compared with the other two MFCs operated at fixed pH values, the COD removal efficiency of the MFC-pHV was improved due to the stronger adaptation to the varying pH-environment.

Mg-doped hydroxyapatite nanoplates for biomedical applications: A surfactant assisted microwave synthesis and spectroscopic investigations

Nanoplates of Mg doped hydroxyapatite (Mg-HAp) were derived successfully and rapidly via microwave irradiation technique. Hydroxyapatite (HAp) is the hard tissues and main inorganic component in mammals. Different nanostructures of HAp exist in different parts of human bone but nanorods are very common due to its intrinsic nature to grow in rode-like structure under physiological as well as under applied ambient conditions in laboratory. On the addition of Mg at very low level (0.06mol%) in pure HAp results the formation of 2-D plate-like nanostructures rather than rod-like which is the matter of interest. In this attempt our efforts have been focused on the study of effect of Mg incorporation on structural and spectroscopic properties of HAp prepared via microwave irradiation technique. This technique is preferred due to several advantages viz. very fast as well as homogeneous heating, time/energy saving and eco-friendliness. The calcium nitrate tetrahydrate (Ca(NO3)2⋅4H2O)) as a source of calcium, magnesium nitrate hexahydrate (Mg(NO3)2⋅6H2O) as a source of magnesium, disodium hydrogen phosphate dihydrate (NaH2PO4⋅2H2O) as a source of phosphorous and sodium ethylene diamine tetra acetate (NaEDTA) as a surfactant were used as starting reagents. Sodium hydroxide (NaOH) pellets were employed to adjust the pH value of final solution. The solution of fixed pH value was kept into the microwave oven generating waves of frequency 2.45GHz (water absorption frequency) and power 750W for 8min. The precipitate thus obtained was washed, centrifuged and then dried at 100°C for 2h. Dried powder was then calcined at 700°C for 2h. The bright white powder thus obtained was characterized structurally using X-ray diffraction and SEM techniques and spectroscopically by FT-IR and Raman techniques. Structural and spectroscopic analysis revealed the formation of Mg doped HAp [Mg-HAp: (Ca4.94Mg0.06) (PO4)3OH], nanoplates having average crystallite size of 26nm as estimated by Scherrer’s formula.

Porous Methyltrimethoxysilane Coated Nanoscale‐Hydroxyapatite for Removing Lead Ions from Aqueous Solutions

The aim of this study was to synthetize new porous nanoparticles based on methyltrimethoxysilane coated hydroxyapatite (MTHAp) for lead removal form aqueous solutions. The morphological and compositional analysis of MTHAp were investigated by X‐ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR) and scanning electron microscopy (SEM) equipped with an energy dispersive X‐ray spectrometer (EDS). Removal experiments of Pb2+ ions were carried out in aqueous solutions with controlled concentration of Pb2+ at a fixed pH value of 3 and 5 respectively. After the removal experiment of Pb2+ ions from solutions, porous hydroxyapatite nanoparticles were transformed into PbMTHAp_3 and PbMTHAp_5 via the adsorption of Pb2+ ions followed by a cation exchange reaction. The X‐ray diffraction spectra of PbMTHAp_3 and PbMTHAp_5 revealed that the powders, after removal of the Pb2+ ions, were a mixture of Ca2.5Pb7.5(PO4)6(OH)2, Pb2Ca4(PO4)2(SiO4), and Ca10(PO4)6(OH)2. Our results demonstrate that the porous hydroxyapatite nanoparticles can be used as an adsorbent for removing Pb2+ ions from aqueous solutions.

Photocatalytically active titanium dioxide nanopowders: Synthesis, photoactivity and magnetic separation

Two approaches were used to obtain nanocrystalline titanium dioxide (TiO2) photocatalyst powders. Firstly, low-temperature synthesis method and secondly liquid flame spraying. The structural properties of the produced powders were determined with X-ray diffraction, transmission electron microscopy and nitrogen adsorption tests. The photocatalytic properties of the powders were studied with methylene blue (MB) discoloration tests. After discolorations tests, TiO2 was coagulated with magnetite particles using FeCl3·6 H2O at a fixed pH value. Magnetic separation of coagulated TiO2 and magnetite was carried out by a permanent magnet. The obtained results showed that the particle size of the powders synthesized at low-temperature was very small and the specific surface area high. The phase content of the powder was also shown to depend greatly on the acidity of the synthesis solution. Powder synthesized by liquid flame spraying was mixture of anatase and rutile phases with essentially larger particle size and lower specific surface area than those of low-temperature synthesized powders. The MB discoloration test showed that photocatalytic activity depends on the phase structure as well as the specific surface area of the synthesized TiO2 powder. The magnetic separation of TiO2–magnetite coagulate from solution proved to be efficient around pH:8.

Isosaccharinate Complexes of Fe(III)

Prior to this study there were no thermodynamic data for isosaccharinate (ISA) complexes of Fe(III) in the environmental range of pH (>~4.5). This study was undertaken to obtain such data in order to predict Fe(III) behavior in the presence of ISA. The solubility of Fe(OH)3(2-line ferrihydrite), referred to as Fe(OH)3(s), was studied at 22 ± 2 °C in: (1) very acidic (0.01 mol·dm−3 H+) to highly alkaline conditions (3 mol·dm−3 NaOH) as a function of time (11–421 days), and fixed concentrations of 0.01 or 0.001 mol·dm−3 NaISA; and (2) as a function of NaISA concentrations ranging from approximately 0.0001 to 0.256 mol·dm−3 and at fixed pH values of approximately 4.5 and 11.6 to determine the ISA complexes of Fe(III). The data were interpreted using the SIT model that included previously reported stability constants for $$ {{\text{Fe(ISA}})_{n}}^{3 - n} $$ (with n varying from 1 to 4) and Fe(III)–OH complexes, and the solubility product for Fe(OH)3(s) along with the values for two additional complexes (Fe(OH)2(ISA)(aq) and $$ {\text{Fe(OH)}}_{ 3} ( {{\text{ISA}})_{2}}^{2 - } $$ ) determined in this study. These extensive data provided a log10 K 0 value of 1.55 ± 0.38 for the reaction $$ ({\text{Fe}}^{ 3+ } + {\text{ISA}}^{-} + 2 {\text{H}}_{ 2} {\text{O}} \rightleftarrows {\text{Fe(OH}})_{ 2} {\text{ISA(aq}}) + 2 {\text{H}}^{ + } ) $$ and a value of −3.27 ± 0.32 for the reaction $$ ({\text{Fe}}^{ 3+ } + 2 {\text{ISA}}^{-} + 3 {\text{H}}_{ 2} {\text{O}} \rightleftarrows {\text{Fe(OH)}}_{ 3} ( {\text{ISA}})_{2}^{2 - } + 3 {\text{H}}^{ + } ) $$ and show that ISA forms strong complexes with Fe(III) which significantly increase the Fe(OH)3(s) solubility at pH <~12. Thermodynamic calculations show that competition of Fe(III) with tetravalent ions for ISA does not significantly affect the solubilities of tetravalent hydrous oxides (e.g., Th and Np(IV)) in ISA solutions.

Role of various additives on the clouding phenomenon observed in imipramine hydrochloride solutions

The effect of various additives used in pharmaceutical formulations (inorganic salts, QABs, amino acids, sugars, alcohols, ureas) has been seen by studying the clouding phenomenon of imipramine hydrochloride (IMP) drug in solution. At fixed pH values, increasing inorganic salt concentrations caused an increase in the cloud point (CP) of 100mM IMP prepared in 1mM CTAB+10mM SP buffer solution; the magnitude of increase being dependent upon the position of the salts in Hofmeister series and hydrated radii. The addition of increasing amounts of quaternary ammonium bromides (QABs) also caused continuous increase in CP, which is explained on the basis of alkyl chain length of the particular QAB. All amino acids increased the cloud point but to different extent. While short chain alcohols affected the CP insignificantly, higher ones decreased it but medium chain alcohols showed maxima. All sugars caused a decrease in CP due to their water structure making property. Urea and alkylureas decreased the CP, which is explained on the basis of their water replacing ability from the micellar head group region. Thioureas increased the CP; however, the presence of an alkyl group had a similar effect as in alkylureas. The overall behavior has been discussed on the basis of electrostatic repulsion/interaction, micellar growth, and mixed micelle formation.

A modified Langmuir-Freundlich isotherm model for simulating pH-dependent adsorption effects

Analytical isotherm equations such as Langmuir and Freundlich isotherms are widely used for modeling adsorption data. However, these isotherms are primarily useful for simulating data collected at a fixed pH value and cannot be easily adapted to simulate pH-dependent adsorption effects. Therefore, most adsorption studies currently use numerical surface-complexation models (SCMs), which are more complex and time consuming than traditional analytical isotherm models. In this work, we propose a new analytical isotherm model, identified as the modified Langmuir-Freundlich (MLF) isotherm, which can be used to simulate pH-dependent adsorption. The MLF isotherm uses a linear correlation between pH and affinity coefficient values. We validated the proposed MLF isotherm by predicting arsenic adsorption onto two different types of sorbents: pure goethite and goethite-coated sand. The MLF model gave good predictions for both experimental and surface complexation-model predicted datasets for these two sorbents. The proposed analytical isotherm framework can help reduce modeling complexity, model development time, and computational efforts. One of the limitations of the proposed method is that it is currently valid only for single-component systems. Furthermore, the model requires a system-specific pH. vs. affinity coefficient relation. Despite these limitations, the approach provides a promising analytical framework for simulating pH-dependent adsorption effects.

Photocatalytic Degradation of Methylorange Using TiO&lt;SUB&gt;2&lt;/SUB&gt;, WO&lt;SUB&gt;3&lt;/SUB&gt; and Mixed Thin Films Under Controlled pH and H&lt;SUB&gt;2&lt;/SUB&gt;O&lt;SUB&gt;2&lt;/SUB&gt;

Wastewaters resulting from textile industry sector have a different chemistry compared with most of the other wastewaters. The different dyes in excess are usually very stable and even small quantities can have a major impact to the effluent. In order to treat these wastewaters, photodegradation is a largely investigated process that can be up-scaled. Photocatalysts based on wide band gap semiconductors can be used in heterogeneous photocatalysis and mostly reported are TiO2 and WO3. Under UV irradiation they form electron-hole pairs that produce active species that can oxidize the dye molecules. The electron-hole recombination represents the main cause for low efficiencies and is limited by the use of oxidant systems like H2O2. Doctor blade technique, a reproducible, up-scalable and low cost technique was used to obtain thin films. The reference dye, used in this experiment is methylorange in solution of 0.0125 mM, corresponding to average polluted water. In order to reduce the recombination in the catalysts, H2O2 is used. Another important aspect of the dye photocatalysis process, investigated in the paper is the adsorption of the dye molecule on the photocatalyst surface, strongly depending on pH which affects the dye's structure and the surface charge. Experiments are conducted at fixed pH values: 3, and respectively 7 covering values below and over the ZPC of the photocatalysts. The results show that TiO2/WO3 films have higher efficiency then the TiO2 and WO3 films, mainly due to the surface morphology of the films. By adding H2O2, higher efficiencies are obtained, confirming that the electron-hole pair recombination is reduced. From the point of view of pH, higher efficiencies are obtained in acidic solutions and the results are comparatively discussed considering the dye's ionic/neutral structure and the photocatalyst surface charge. The efficiency was calculated using UV-VIS spectrophotometer measurements of the solution and the thin films were characterized by AFM and XRD.

Hydrogen-Bonding-Induced Complexation of Polydimethylsiloxane-graft-poly(ethylene oxide) and Poly(acrylic acid)-block-polyacrylonitrile Micelles in Water

Polydimethylsiloxane-graft-poly(ethylene oxide) (PDMS-g-PEO) copolymers form micelles in water with PDMS as the core and PEO as the corona. The introduction of poly(acrylic acid)-block-polyacrylonitrile (PAA-b-PAN) block copolymers in water leads to the formation of micellar complexes due to the hydrogen bonding between carboxyl groups and ether oxygens among the PAA and PEO chains in the corona of the micelles. The effects of pH, molar ratios (r) of PAA/PEO, and the standing time on the directly mixing these two micelles in water have been investigated using laser light scattering (LLS) and transmission electron microscopy (TEM). Our results showed that the complexation between PAA and PEO in the corona was greatly enhanced at a pH below 3.5. For a fixed pH value, the interactions between these two micelles in water were governed by the value of r. At r < ∼0.6, mixing the two micelles in water resulted in a large floccule because the smaller PAA-b-PAN micelles act as physical cross-links, which are absorbed onto one PDMS-g-PEO micelle and simultaneously bonded to PEO chains on the other micelles, forming bridges and causing flocculation. At ∼0.6 < r < ∼1.2, the mixing led to stable micellar complexes with a layer of PAA-b-PAN micelles absorbed onto the initial PDMS-g-PEO micelles. At r > ∼1.2, the resultant micellar complexes first remained stable, but they precipitated from solution after a long time standing.

Combining Isoelectric Point-Based Fractionation, Liquid Chromatography and Mass Spectrometry to Improve Peptide Detection and Protein Identification

The off-line coupling of an isoelectric trapping device termed membrane separated wells for isoelectric focusing and trapping (MSWIFT) to mass spectrometry-based proteomic studies is described. The MSWIFT is a high capacity, high-throughput, mass spectrometry-compatible isoelectric trapping device that provides isoelectric point (pI)-based separations of complex mixtures of peptides. In MSWIFT, separation and analyte trapping are achieved by migrating the peptide ions through membranes having fixed pH values until the peptide pI is bracketed by the pH values of adjacent membranes. The pH values of the membranes can be tuned, thus affording a high degree of experimental flexibility. Specific advantages of using MSWIFT for sample prefractionation include: (1) small sample volumes (approximately 200 microL), (2) customized membranes over a large pH range, (3) flexibility in the number of desired fractions, (4) membrane compatibility with a variety of solvents systems, and (5) resulting fractions do not require sample cleanup before MS analysis. Here, we demonstrate the utility of MSWIFT for mass spectrometry-based detection of peptides in improving dynamic range and the reduction of ion suppression effects for high-throughput separations of tryptic peptides.

Thermodynamic Model for ThO2(am) Solubility in Isosaccharinate Solutions

Extensive studies on ThO2(am) solubility were carried out as functions of a wide range of isosaccharinate concentrations (0.0002 to 0.2 mol⋅kg−1) at fixed pH values of about 6 and 12, and varying pH (ranging from 4.5 to 12) at fixed aqueous isosaccharinate concentrations of 0.008 mol⋅kg−1 or 0.08 mol⋅kg−1, to determine the aqueous complexes of isosaccharinate with Th(IV). The samples were equilibrated over periods ranging up to 69 days, and the data showed that, in most cases, steady-state concentrations were reached in <15 days. The data were interpreted using the SIT model, and required the inclusion of mixed hydroxy-ISA complexes of Th(IV) [Th(OH)ISA2+, Th(OH)3(ISA)\(_{2}^{-}\), and Th(OH)4(ISA)\(_{2}^{2-}]\) with log 10 K 0=12.5±0.5,4.4±0.5 and −3.2±0.5 for the reactions: $$\begin{array}{l}\mathrm{ThO}_{2}(\mathrm{am})+3\mathrm{H}^{+}+\mathrm{ISA}^{-}\rightleftarrows \mathrm{Th}(\mathrm{OH})\mathrm{ISA}^{2+}+\mathrm{H}_{2}\mathrm{O}\\[3pt]\mathrm{ThO}_{2}(\mathrm{am})+\mathrm{H}^{+}+2\mathrm{ISA}^{-}+\mathrm{H}_{2}\mathrm{O}\rightleftarrows \mathrm{Th}(\mathrm{OH})_{3}(\mathrm{ISA})_{2}^{-}\end{array}$$ and $$\mathrm{ThO}_{2}(\mathrm{am})+2\mathrm{ISA}^{-}+2\mathrm{H}_{2}\mathrm{O}\rightleftarrows \mathrm{Th}(\mathrm{OH})_{4}(\mathrm{ISA})_{2}^{2-}$$ respectively.Predictions based on these Th-ISA complexes agreed closely with the extensive experimental data developed in this study as well as the very limited (only at pH=8.3) data from liquid-liquid extractions recently reported in the literature.

Effects of microstructure of mesoporous SnO 2 powders on their H 2 sensing properties

Various mesoporous tin dioxide (m-SnO 2) powders were prepared from two kinds of combination of a tin source and a surfactant template, and their H 2 sensing properties were investigated. The specific surface area and pore volume of the m-SnO 2 powder prepared from Na 2SnO 3·3H 2O as a tin source and n-cetylpyridinium chloride monohydrate (C 16PyCl; (C 5H 5NC 16H 33)Cl·H 2O) as a template under a fixed pH value of 10 (m-SnO 2(1)) were larger than those of the m-SnO 2 powders prepared from SnCl 4·5H 2O as a tin source and aerosol-OT (AOT; C 20H 37O 7SNa) as a template under different pH conditions (m-SnO 2(2)- n; n is the value of pH of the precursor solution). However, the specific surface area of m-SnO 2(1) decreased drastically by post-grinding, while m-SnO 2(2)- n powders with small secondary agglomerates showed only a slight decrease in specific surface area during post-grinding. In addition, m-SnO 2(2)- n sensors exhibited better H 2 response and lower resistance than those of m-SnO 2(1) sensor, especially at low operating temperatures, probably because of moderately developed mesopores which promoted easier diffusion of H 2 to the most sensitive region of the surface of SnO 2 particles.

In-vitro investigations of a pH- and ionic-strength-responsive polyelectrolytic hydrogel using a piezoresistive microsensor.

Environmental responsive or smart hydrogels show a volume phase transition due to changes of external stimuli such as pH or ionic strength of an ambient solution. Thus, they are able to convert reversibly chemical energy into mechanical energy and therefore they are suitable as sensitive material for integration in biochemical microsensors and MEMS devices. In this work, micro-fabricated silicon pressure sensor chips with integrated piezoresistors were used as transducers for the conversion of mechanical work into an appropriate electrical output signal due to the deflection of a thin silicon bending plate. Within this work two different sensor designs have been studied. The biocompatible poly(hydroxypropyl methacrylate-N,N-dimethylaminoethyl methacrylate-tetra-ethyleneglycol dimethacrylate) (HPMA-DMA-TEGDMA) was used as an environmental sensitive element in piezoresistive biochemical sensors. This polyelectrolytic hydrogel shows a very sharp volume phase transition at pH values below about 7.4 which is in the range of the physiological pH. The sensor's characteristic response was measured in-vitro for changes in pH of PBS buffer solution at fixed ionic strength. The experimental data was applied to the Hill equation and the sensor sensitivity as a function of pH was calculated out of it. The time-dependent sensor response was measured for small changes in pH, whereas different time constants have been observed. The same sensor principal was used for sensing of ionic strength. The time-dependent electrical sensor signal of both sensors was measured for variations in ionic strength at fixed pH value using PBS buffer solution. Both sensor types showed an asymmetric swelling behavior between the swelling and the deswelling cycle as well as different time constants, which was attributed to the different nature of mechanical hydrogel-confinement inside the sensor.

Environmental mobility of cobalt—Influence of solid phase characteristics and groundwater chemistry

The adsorption of cobalt on samples from a potential waste repository site in an arid region was investigated in batch experiments, as a function of various solution phase parameters including the pH and ionic strength. The samples were characterized using a range of techniques, including BET surface area measurements, total clay content and quantitative X-ray diffraction. The statistical relationships between the measured cobalt distribution coefficients ( K d values) and the solid and liquid phase characteristics were assessed. The sorption of cobalt increased with the pH of the aqueous phase. In experiments with a fixed pH value, the measured K d values were strongly correlated to the BET surface area, but not to the amount of individual clay minerals (illite, kaolinite or smectite). A further set of sorption experiments was undertaken with two samples of distinctive mineralogy and surface area, and consequently different sorption properties. A simple surface complexation model (SCM) that conceptualized the surface sites as having equivalent sorption properties to amorphous Fe-oxide was moderately successful in explaining the pH dependence of the sorption data on these samples. Two different methods of quantifying the input parameters for the SCM were assessed. While a full SCM for cobalt sorption on these complex environmental substrates is not yet possible, the basic applicability and predictive capability of this type of modeling is demonstrated. A principal requirement to further develop the modeling approach is adequate models for cobalt sorption on component mineral phases of complex environmental sorbents.

Thermodynamic Model for ThO2(am) Solubility in Alkaline Silica Solutions

No thermodynamic data for Th complexes with aqueous Si are available. To obtain such data, extensive studies on ThO2(am) solubility were carried out as functions of: (1) a wide range of aqueous silica concentrations (0.0004 to 0.14 mol⋅L−1) at fixed pH values of about 10, 11, 12, and 13; and (2) and variable pH (ranging from 10 to 13.3) at fixed aqueous Si concentrations of about 0.006 mol⋅L−1 or 0.018 mol⋅L−1. The samples were equilibrated over long periods (ranging up to 487 days), and the data showed that steady-state concentrations were reached in 10. The data were interpreted using both the Pitzer and SIT models, and required only the inclusion of one mixed-hydroxy-silica complex of Th [Th(OH)3(H3SiO4) 3 2− ]. Both models provided similar complexation constant values for the formation of this species. Density functional theory calculations predict complexes of this stoichiometry, having six-fold coordination of the Th cation, to be structurally stable. Predictions based on the fitted value of log 10 K 0=−18.5±0.7 for the ThO2(am) solubility reaction involving Th(OH)3(H3SiO4) 3 2− [ThO2(am)+3H4SiO4+H2O↔Th(OH)3(H3SiO4) 3 2− +2H+], along with the thermodynamic data for aqueous Si species reported in the literature, agreed closely with the extensive experimental data and showed that under alkaline conditions aqueous Si makes very strong complexes with Th.

Preparation and adsorptive application of novel superparamagnetic zirconia material

A novel superparamagnetic zirconia (ZrO 2/SiO 2/Fe 3O 4, SPMZ) material has been successfully synthesized via three sequential steps: chemical precipitation of magnetite, sol–gel coating of silica and sol–gel covering of zriconia. The physicochemical properties were characterized with N 2 adsorption at 77 K, scanning electron microscopy with energy-dispersive X-ray spectroscopy (SEM/EDX), superconducing quantum interference device (SQUID), powder X-ray diffraction (XRD), thermogravimetric analysis (TGA) and electrophoresis. SEM/EDX showed that zirconium is abundant on the surface with high atomic percent and the size of the aggregate is approximately smaller than 100 nm. Powder XRD illustrated the coexistence of tetragonal and monoclinic crystals. TGA indicated that conversion rate of pre-SPMZ before final calcination is affected by pyrolysis temperature. The adsorption behavior of sulfate on SPMZ from aqueous solution was examined as an index of adsorptive application. The removal efficiency of sulfate via adsorption is rather sensitive to the pH value of the solution in the range of 4–5.8. The further adsorption of sulfate on SPMZ is restrained as the pH value of solution reaches the point of zero charge pH PZC of SPMZ. The adsorption capacity of sulfate on SPMZ under a fixed pH value of 4 can be comparable to that of commercially nanopowder of zirconia. Furthermore, the adsorption rate of sulfate on SPMZ is rather fast in 1 min and then gradually slows down reaching the adsorption equilibrium. The liquid–solid separation can be easily carried out via the magnetic separation.

硫化カルシウムを用いた模擬めっき廃液中の銅，亜鉛，ニッケルの不均一系硫化反応特性

The present work is concerned with sulfidation of Cu, Zn and Ni containing plating wastewater with CaS. The sulfidation experiments were carried out by adding solid CaS (purity higher than 99%) to a simulated single-metal solution of NiSO4, ZnSO4 and CuSO4 solutions at a room temperature.At first, the experiments were conducted without pH adjustment and it was found that the complete sulfidation of Zn and Ni was achieved at an equimolar ratio of CaS to metal. For Cu, complete copper sulfidation was achieved at a CaS to Cu molar ratio of about 2 : 1. It was considered that CuS was almost instantly precipitated on the surface of un-dissolved CaS particles, which led to CaS being enclosed in CuS particles and it was thereby concluded that a higher CaS to Cu molar ratio was needed. This conclusion was further supported by a subsequent experiment, in which the sulfidation treatment was carried out using CaS solution. In this experiment, it was found that the concentration of Cu in the filtrate fell to below 1 mg/dm3 at an equimolar ratio of CaS to Cu.Finally, to investigate the possibility of selective precipitation, the experiments were conducted at fixed pH values and it was found that Cu was almost completely separated at pH = 1.8−2.0 when the CaS to Cu molar ratio was adjusted to 1 : 5. Further, almost 100% of Zn at pH > 4 and about 91% of Ni at pH = 7.5 was separated when an equimolar ratio of CaS to metal was used.