Amounts Of Metal Cations Research Articles

Elemental sulfur redox bioconversion for selective recovery of phosphorus from Fe/Al-bound phosphate-rich anaerobically digested sludge: Sulfur oxidation or sulfur reduction?

The biological oxidation of elemental sulfur (S0) to sulfate and the reduction of S0 to sulfide provide a potential route for extracting and reclaiming phosphorus (P) from anaerobically digested sludge (ADS). However, the treatment performance, stability, and cost-effectiveness of the two opposing bioprocesses based on S° for selective P recovery from ADS remain unclear. This study aimed to compare the roles of S0-oxidizing bacteria (S0OB) and S0-reducing bacteria (S0RB) in liberating insoluble P from ADS through single-batch and consecutive multibatch experiments. Changes in P speciation in the sludge during the biological extraction processes were analyzed by using complementary sequential extraction and P X-ray absorption near-edge spectroscopy. Results showed that S0OB treatment extracted more phosphate from the sludge compared with S0RB treatment, but it also released a considerable amount of metal cations (e.g., heavy metals, Mg2+, Al3+, Ca2+) and negatively affected sludge dewaterability due to intense sludge acidification and cell lysis. At pH 1.2, the S0OB treatment released 92.9% of P from the sludge, with the dissolution of HAP, Fe-PO4, Mg3(PO4)2, and P-fehrrihy contributing 26.8%, 22.1%, 12.8%, and 10.5%, respectively. The S0RB treatment released 63.6% of P from the sludge at pH 7.0, with negligible dissolution of metal cations, thereby avoiding costly purification of the extract and alkali neutralization for pH adjustment. This treatment involved the replacement of phosphates bounded with Fe-PO4 (FePO4 and P-fehrrihy) and Al–PO4 (P-Alumina and AlPO4) with biogenic sulfides, with contributions of 72.7%, and 20.9%, respectively. Consecutive bioprocesses for P extraction were achieved by recirculating the treated sludge. Both S0OB and S0RB treatments did not affect the extent of sludge dewatering but considerably weakened the dewatering rate. The S0OB-treated sludge exhibited prolonged filtration time (from 3010 s to 9150 s) and expressing time (from 795 s to 4690 s) during compression dewatering. After removing metal cations using cation exchange resin (CER) and neutralizing using NaOH, a vivianite product Fe3(PO4)2·8H2O (purity: 84%) was harvested from the S0OB-treated extract through precipitation with FeSO4·7H2O. By contrast, a vivianite product Fe3(PO4)2·8H2O (purity: 81%) was directly obtained from the S0RB-treated extract through precipitation with FeSO4·7H2O. Ultimately, 79.8 and 57.9wt% of P were recovered from ADS through S0OB extraction–CER purification–alkali neutralization–vivianite crystallization, and S0RB extraction–vivianite crystallization, respectively. Collectively, biological S0 reduction is more applicable than biological S0 oxidation for selectively reclaiming P from Fe/Al-associated phosphate-rich ADS due to better cost-effectiveness and process simplicity. These findings are of significance for developing sludge management strategies to improve P reclamation with minimal process inputs.

Structural, physical and magnetic evaluations of Ce-Zn substituted SrCo2 W-type hexaferrites prepared via sol gel auto combustion route

SrCo2 W-type hexagonal nanoferrites with composition SrCo2-xZnxCeyFe16-yO27 (whereas x = 0, 0.2, 0.4, 0.6, 0.8, 1.0 and y = 0, 0.02, 0.04, 0.06, 0.08, 0.1) were synthesized by sol-gel auto combustion method. X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), Field emission scanning electron microscopy (FESEM) and Vibrating sample magnetometer (VSM) were used to find out the structural, vibrational, morphological and magnetic properties of SrCo2 W-type hexagonal ferrites. Physical properties such as bulk density (Dbulk), X-ray density (Dxrd) and porosity (%P) of the SrCo2 W type hexagonal ferrites samples were calculated. Bulk density of the samples decreased whereas X-ray density increased with the Ce-Zn substitution in the W-type ferrites. Single phase samples of all the nanoferrites are achieved at the sintering temperature of 1050 °C. Structural parameters such as lattice parameters ‘a’ and ‘c’ were also calculated. Lattice parameter ‘a’ is found to be increased whereas ‘c’ is found to be decreased with the substitutions. Force constants at tetrahedral and octahedral sites are also evaluated which confirm the phase and substitution in W-type hexagonal ferrite. FESEM images showed homogenous and well crystallized at higher substitution of Ce-Zn in SrCo2 W-type hexagonal ferrites. Detailed magnetic parameters such as magnetic remanence coercivity, saturation, Bohr magneton, initial permeability, magneto crystalline anisotropy constant (K) and magnetic field anisotropy (Ha) were measured. Magnetic remanence decreased whereas coercivity, magneto crystalline anisotropy and field anisotropy increased in the SrCo2 W-type hexagonal ferrites samples. The dependence of Hc and Ha on the SrCo2 W-type hexaferrites may be due to the variations in the K and Ms of the substituted samples. Therefore, the prepared SrCo2 W-type nanoferrites with appropriate amount of metal cations are suitable candidate for the microwave devices and high frequency applications.

Dynamic Reference Electrode development for redox potential measurements in fluoride molten salt at high temperature

Measurement of redox potential in fluoride media is a major problem due to the difficulty to design a reference electrode with high stability, high mechanical resistance and high accuracy. In the frame of molten salt reactor studies, a dynamic reference electrode (DRE) is developed to measure redox potential in fluoride molten salt at high temperature. DRE is based on the in-situ generation of a transient redox system. The choice of the redox couple corresponds to the cathodic limit of the molten salt considered. As a preliminary step, the demonstration of feasibility of generating a DRE was done in LiF-NaF-KF (46.5–11.5–42mol%) media at 500°C. In this salt, the reference redox system generated by coulometry at applied current is KF/K, metallic potassium being electrodeposited on a tungsten wire electrode. The validation of the DRE response and the experimental optimization parameters for DRE generation were realized by following the NiF2/Ni redox potential evolution as a function of NiF2 concentration in the fused salt.The current value applied for DRE generation was optimized. It depends on the amount of metallic cations contained in the fused salt and which can be electrochemically reduced simultaneously during the DRE generation. The current corresponding to the DRE generation has to be 4 times greater than the current corresponding to the reduction of the other elements.

Adsorption of n-propyl mercaptan on Pb/LTA zeolites

In this study, we used Pb2+ cation exchanged zeolites as adsorbents due to their porous structure. Adsorption of n-propyl mercaptan on modified LTA and (3A, 4A) zeolites were studied by FTIR (Fourier Transform Infrared) Spectroscopy and AAS (Atomic Absorption Spectrometer) is used to measure the amount of metal cations on mentioned zeolites. SEM-EDX (Scanning Electron Microscope-Energy Dispersive X-Ray) graphics are used to monitor the differences on the surface. Cation modified zeolites change their characteristic properties for adsorption. LTA type zeolites when modified by Pb2+ cation tend to adsorb n-propyl mercaptan.

Usage of Layer-by-Layer Method for Obtaining Polyelectrolyte Multilayer Films Containing Transition Metal Cations

<p>The alternating layer-by-layer deposition of oppositely charged polyelectrolytes at solid substrates is an attractive technique for preparation of nanostructured surface coatings of controlled thickness. This paper reports the results of covalently binding of cobalt (II) and copper (II) ions within polyelectrolyte multilayers (PEMs). We have used polycation as polyethyleneimine (BPEI) and polyanion as poly(acrylic acid) (PAA) and the electrostatic layer-by-layer assembly technique to make uniform thin film coating on solid template with controllable thickness. Thermodynamic characteristics as stability constant, free Gibbs energy, enthalpy and entropy of complex forming processes of these polyelectrolytes with Co(II) and Cu(II) cations in solution were calculated by modified method of Bjerrum. The correlation between log β values and some of the fundamental properties of the metal ions are discussed. It was found that the ratio of Me:L in water solvent is 1:4 in the investigating systems Cu<sup>2+</sup>:BPEI and Co<sup>2+</sup>:BPEI and in the systems Cо<sup>2+</sup>:PAA and Cо<sup>2+</sup>:PAA - 1:2. PEMs were deposited onto silicon wafers, glass slides, or coated on silica oxide particles. Dipping solutions of different pH were used in order to find the optimum conditions for absorbing maximum amount of metal cations. These PEMs films are found to offer high capacity and selectivity for copper over cobalt in both acidic and alkaline media. Preliminary investigation have shown that metal containing PEMs has catalytic activity for oxidation of toluene with molecular in mild condition. The alternating layer-by-layer deposition of oppositely charged polyelectrolytes at solid substrates is an attractive technique for preparation of nanostructured surface coatings of controlled thickness. This paper reports the results of covalently binding of cobalt (II) and copper (II) ions within polyelectrolyte multilayers (PEMs). We have used polycation as polyethyleneimine (BPEI) and polyanion as poly(acrylic acid) (PAA) and the electrostatic layer-by-layer assembly technique to make uniform thin film coating on solid template with controllable thickness. Thermodynamic characteristics as stability constant, free Gibbs energy, enthalpy and entropy of complex forming processes of these polyelectrolytes with Co(II) and Cu(II) cations in solution were calculated by modified method of Bjerrum. The correlation between log β values and some of the fundamental properties of the metal ions are discussed. It was found that the ratio of Me:L in water solvent is 1:4 in the investigating systems Cu<sup>2+</sup>:BPEI and Co<sup>2+</sup>:BPEI and in the systems Cо<sup>2+</sup>:PAA and Cо<sup>2+</sup> :PAA - 1:2. PEMs were deposited onto silicon wafers, glass slides, or coated on silica oxide particles. Dipping solutions of different pH were used in order to find the optimum conditions for absorbing maximum amount of metal cations. These PEMs films are found to offer high capacity and selectivity for copper over cobalt in both acidic and alkaline media. Preliminary investigation have shown that metal containing PEMs has catalytic activity for oxidation of toluene with molecular in mild condition.</p>

Comparison of electrocoagulation using iron and aluminium electrodes with chemical coagulation for the removal of a highly soluble acid dye

The decolorization of a synthetic textile wastewater was investigated using electrocoagulation (EC) in a batch electrochemical cell. Orange II, a typical mono-azo acid dye, was used. Aluminum and iron electrodes were compared. The respective effects of operational parameters (initial dye concentration, current density, electrolysis time) and wastewater properties (initial pH and conductivity) were analyzed by comparing the performance of color removal, energy input, electrode mass consumption and the amount of sludge produced. Operating costs were deduced. A comparison with chemical coagulation (CC) using the same amount of metal cations as in EC was also carried out. Experimental results showed that EC maximized decolorization (up to 98%) in comparison to CC (limited to 53%). For EC, iron electrodes exhibited the highest decolorization yield and minimized simultaneously energy requirements, the amount of floc and operation costs in comparison to aluminium. As voltage vs. current curves did not differ significantly between Al and Fe, higher current was required with Al electrodes to achieve a similar decolorization yield. This was partly explained by differences in the decolorization mechanism, as Al electrodes seemed to promote the electroreduction of the azo bond of Orange II, contrary to Fe electrodes.

Rheological behavior of PMVE-MA aqueous solution with metallic cations

The rheological properties of aqueous solutions of poly(methyl vinyl ether-co-maleic anhydride) (PMVE-MA) upon addition of metallic cations at different pH values were investigated. Sol-gel transition and shear-thickening phenomena at moderate shear rate were observed upon increasing the amount of metallic cations, especially for cupric cation. At certain molar ratio (f gel) of added cupric cations to carboxyl groups in PMVE-MA, the system became gel-like, and the storage modulus (G’) and loss modulus (G") were parallel and exhibited a power-law dependence on the frequency, which is consistent with Winter’s hypothesis of determining the gel point of a crosslinking system. The shear-thickening behavior depends on f gel, pH, metallic valence, and temperature.

On the equivalence of acidic centers in H-beta zeolites tested by Fries rearrangement of phenyl acetate

The heterogeneously catalyzed liquid phase Fries rearrangement reaction of phenyl acetate was carried out on Beta zeolites reexchanged with different amounts of metal cations. The aim of this work was to determine the influence of the amount of Bronsted acid sites as the catalytic active centers on the conversion. Sodium and potassium ions as well as divalent calcium and zinc ions were used in the reexchange procedure. The conversion shows a linear dependency on the degree of ion reexchange following the theoretically expected values. So the results prove that the bridged hydroxyl groups are indeed the dominating active centers and that their strength seems to be independent of the degree of reexchange; consequently, their acidic strength should be identical. A special emphasis was placed on the reexchange with divalent metal ions. It was shown that one divalent ion is not able to replace two protons as is supposed to be necessary for the charge balance—so a 1:1 stoichiometry is needed to assume to explain the catalytic results.

Metal ion incorporation in the conducting polymer electrode matrix using an ‘active’ metal substrate

Abstract The incorporation of free transition metal cations (potential redox catalyst centers) into conducting organic films by electrodeposition is relatively rare due to the repulsive nature of the positive cation radicals of the polymer itself during polymerization. This paper shows that such metal cations can be trapped in the polymer matrix as it is being electrodeposited on a metal substrate electrode, which itself simultaneously electro-oxidizes (corrodes). The electropolymerizatiob of 3-methylthiopene on Mo(O), Ni(O) and Fe(O) substrate electrodes (‘active electrodes’) is reported. SEM, EDXRF, and XPS were used to demonstrate the amount of metal cations in and/or on the polymer matrix and to determine the valence states. The rates of diffusion of the incorporated metal ions into an LiClO 4 electrolyte solution were also studied. The presence of trace amounts of all three metal cations were sufficient to destroy the electroactivity of the polymer film electrodes for the oxidation of catechol.

Physiology of the Cell Surface of Neurospora Ascospores. III. Distinction Between the Adsorptive and Entrance Phases of Cation Uptake

The germination of ascospores of Neurospora tetrasperma has been shown to be inhibited by continual incubation in very small amounts of metal cations. Of these, Ag+, and p-chloromercuribenzoic acid...