Aqueous metal ion solution

Visser, A.E. et al.. Task-specific ionic liquids for the extraction of metal ions aqueous solutions, Chem. Commum., 135,2001. 

Acrylic acid-modified Ficus carica lignocellulosic fiber was used as adsorbent. And the removal of Cr(VI) was evaluated in the presence of various metal ions aqueous solutions [87]. The F. carica fibers were washed, dried at 50°C for 24 h, and soxhlet extracted with acetone for 12 h in order to remove waxes and lignin. Then it was dried at 50°C for 5h and then cut into pieces of 1.0-1.5mm-size. The F. carica fibers were immersed in 100 ml of double distilled water for 24 h in order to activate the reactive sites. A known amount of ceric ammonium nitrate, concentrated nitric acid, and acrylic acid was added to the flask containing the fiber. The mixture was heated to constant temperature for a definite time. The modified F carica fibers were washed with ethanol and dried at 50°C to a constant weight. The maximum adsorption capacity of Cr(VI) onto adsorbent was found to be 28.90 mg g". ... 

Because of ammine formation, when ammonia solution is added slowly to a metal ion in solution, the hydroxide may first be precipitated and then redissolve when excess ammonia solution is added this is due to the formation of a complex ammine ion, for example with copper(II) and nickel(II) salts in aqueous solution. 

Ion Removal and Metal Oxide Electrodes. The ethylenediamine ( )-functional silane, shown in Table 3 (No. 5), has been studied extensively as a sdylating agent on siUca gel to preconcentrate polyvalent anions and cations from dilute aqueous solutions (26,27). Numerous other chelate-functional silanes have been immobilized on siUca gel, controUed-pore glass, and fiber glass for removal of metal ions from solution (28,29). 

SEPARATION OF HEAVY METALS IN AQUEOUS SOLUTIONS BY A NEW ION EXCHANGER BASED ON CELLULOSE... 

A comprehensive list of standard potentials is found in Ref. 7. Table 2-3 gives a few values for redox reactions. Since most metal ions react with OH ions to form solid corrosion products giving protective surface films, it is appropriate to represent the corrosion behavior of metals in aqueous solutions in terms of pH and Ufj. Figure 2-2 shows a Pourbaix diagram for the system Fe/HjO. The boundary lines correspond to the equilibria ... 

Lower oxidation states are rather sparsely represented for Zr and Hf. Even for Ti they are readily oxidized to +4 but they are undoubtedly well defined and, whatever arguments may be advanced against applying the description to Sc, there is no doubt that Ti is a transition metal . In aqueous solution Ti can be prepared by reduction of Ti, either with Zn and dilute acid or electrolytically, and it exists in dilute acids as the violet, octahedral [Ti(H20)6] + ion (p. 970). Although this is subject to a certain amount of hydrolysis, normal salts such as halides and sulfates can be separated. Zr and are known mainly as the trihalides or their derivatives and have no aqueous chemistry since they reduce water. Table 21.2 (p. 960) gives the oxidation states and stereochemistries found in the complexes of Ti, Zr and Hf along with illustrative examples. (See also pp. 1281-2.)... 

Immersion plating Displacement of metal ions in solution by metal to be coated + M2 - M 1 + yMf. where xn =ym M, Cu from aqueous CuSO M2 Fe... 

The differential capacitance method cannot be used for reactive metals, such as transition metals in aqueous solutions, on which the formation of a surface oxide occurs over a wide potential re ion. An immersion method was thus developed by Jakuszewski et al. 3 With this technique the current transient during the first contact of a freshly prepared electrode surface with the electrolyte is measured for various immersion potentials. The electrode surface must be absolutely clean and discharged prior to immersion.182-18 A modification of this method has been described by Sokolowski et al. The values of obtained by this method have been found to be in reasonable agreement with those obtained by other methods, although for reactive metals this may not be a sufficient condition for reliability. 

It is very common for inorganic chemists to neglect or ignore the presence of solvent molecules coordinated to a metal centre. In some cases, this is just carelessness, or laziness, as in the description of an aqueous solution of cobalt(ii) nitrate as containing Co ions. Except in very concentrated solutions, the actual solution species is [Co(H20)6] . In other cases, it is not always certain exactly what ligands remain coordinated to the metal ion in solution, or how many solvent molecules become coordinated. Solutions of iron(iii) chloride in water contain a mixture of complex ions containing a variety of chloride, water, hydroxide and oxide ligands. 

A determination of dimethyl sulphoxide by Dizdar and Idjakovic" is based on the fact that it can cause changes in the visible absorption spectra of some metal compounds, especially transition metals, in aqueous solution. In these solutions water and sulphoxide evidently compete for places in the coordination sphere of the metal ions. The authors found the effect to be largest with ammonium ferric sulphate, (NH4)2S04 Fe2(S04)3T2H20, in dilute acid and related the observed increase in absorption at 410 nm with the concentration of dimethyl sulphoxide. Neither sulphide nor sulphone interfered. Toma and coworkers described a method, which may bear a relation to this group displacement in a sphere of coordination. They reacted sulphoxides (also cyanides and carbon monoxide) with excess sodium aquapentacyanoferrate" (the corresponding amminopentacyanoferrate complex was used) with which a 1 1 complex is formed. In the sulphoxide determination they then titrated spectrophotometrically with methylpyrazinium iodide, the cation of which reacts with the unused ferrate" complex to give a deep blue ion combination product (absorption maximum at 658 nm). 

Ion exchange (IX) is a very useful technique for the concentration, the purification and the separation of chemically similar metallic elements present in an aqueous solution. In its most popular form of application, the metal-bearing aqueous solution is passed through a bed of solid organic resin in a particulate form wherein the sorption of the metal ions on the resin takes place by ion-exchange reactions. The pregnant resin is washed free of the entrapped feed solution and then brought into contact with an eluant of suitable composition and volume so that the resin releases the metal ions back to the eluant. The ratio of the volume of the feed and that of the eluant determines the extent of concentration that can be achieved. Purification and separation are achievable if the resin is selective or specific with respect to the metal ions of interest in comparison to impurity ions. 

In Situ Mdssbauer Studies of Metal Oxide-Aqueous Solution Interfaces with Adsorbed Cobalt-57 and Antimony-119 Ions... 

In situ emission Mossbauer spectroscopy provides valuable information on the chemical structure of dilute metal ions at the metal oxide/aqueous solution interface The principles of the method are described with some experimental results on divalent Co-57 and pentavalent Sb-119 adsorbed on hematite. 

We now extend the work to in situ measurements on metal ions adsorbed at the metal oxide/aqueous solution interface. In this report, our previous results are combined with new measurements to yield specific information on the chemical structure of adsorbed species at the solid/aqueous solution interface. Here, we describe the principles of emission Mossbauer spectroscopy, experimental techniques, and some results on divalent Co-57 and pentavalent Sb-119 ions adsorbed at the interface between hematite (a-Fe203) and aqueous solutions. 

Abstract In this study, a new natural adsorbent (sumae leaves) for removing Cu (II) ion from the aqueous solutions has been investigated. Leaves of sumae were obtained from Siirt, Tmkey. The tannins were extraeted with acetone water (70 30, v/v) mixture from the leaves of sumac. For the total tannin determination Folin-Ciocalteu method was used and tannin content was found 27%. In batch experiments, pH profile, adsorption time, adsorbent/hquid ratio, initial concentration of metal ions, adsorbent amoimt, particle size of adsorbent and temperature were performed to determine binding properties of adsorbent for the Cu(II) ions. The concentrations of the metal ions in solutions before and after adsorption were measured with an atomic absorption spectrophotometer. 

Such experiments were repeated for eac compound at a variety of pH s and temperatures so that pH-rate constant profiles and activation energies could be obtained. Extraneous experimental complications such as sorption of the compound to container walls, incomplete extraction from aqueous solutions and possible catalysis by metal ions in solution were carefully monitored and accounted for in the final determination of aqueous phase hydrolysis rate constants. Of these possibilities, only sorption to container walls was observed to have a measurable effect on the experimental data. 

The high tension ion conduction agglomeration (INCA) system is an ex situ process for the recovery of soluble and particulate metals from aqueous solutions such as mining effluents, process waters, and wastewater. It is not known if the technology is currently commercially available. 

Figure 7.4. Schematic model of the Electrical Double Layer (EDL) at the metal oxide-aqueous solution interface showing elements of the Gouy-Chapman-Stern-Grahame model, including specifically adsorbed cations and non-specifically adsorbed solvated anions. The zero-plane is defined by the location of surface sites, which may be protonated or deprotonated. The inner Helmholtz plane, or [i-planc, is defined by the centers of specifically adsorbed anions and cations. The outer Helmholtz plane, d-plane, or Stern plane corresponds to the beginning of the diffuse layer of counter-ions and co-ions. Cation size has been exaggerated. Estimates of the dielectric constant of water, e, are indicated for the first and second water layers nearest the interface and for bulk water (modified after [6]).

In general, then, metal ions in solution form complexes (frequently six coordinate) with the solvent molecules, their counterions, and other donor molecules that happen to be in the solution. For example, in ammo-niacal aqueous solution, Ag+ forms Ag(NH3)2+ (as noted above), Cu2+ forms a series of aquaammines but most notably the royal blue trans-Cu(NH3)4(OH2)22+, and cobalt(II) forms Co(NH3)i(H20)6-i2+ complexes which react quite rapidly with oxygen in air to give the strawberry-red cobalt(III) complex Co(NH3)5OH23+ or (if much chloride ion is present) the Co(NH3)5C12+ ion mentioned above. 

To arrive at an understanding of the distribution of charge and potential near an interface, it is helpful to consider an electrode. A reversible electrode is one in which each of the phases contains a common ion that is free to cross the interface. The system Ag-Agl-aqueous solution is an example of a reversible electrode. A polarizable electrode, on the other hand, is impermeable to charge carriers, although charge may be brought to the surface by the application of an external potential. The system metallic Hg-aqueous solution is an example of a polarizable electrode we discussed the relationship among the applied potential, the interfacial tension, and the adsorption of ions in Chapter 7, Section 7.11. 

In fact, the converse is observed. The main features of the spectra of transition metal ions in solution are very similar to those for crystal lattices where the same donor atom is present as an anion. Further, the spectra differ little between solids provided the nearest-neighbour atom is unchanged, even if it is part of a multi-atom species and even if the symmetry of the crystal structure is low. The spectra of the first transition series carbonates, for example, are not markedly different from those of their oxides, nor from those of the ions in aqueous solution. In each case the nearest-neighbour atom is oxygen and six of these surround the metal atom in approximately octahedral positions. 

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