Teresa Soldi

Environmental vanadium distribution from an industrial settlement

The distribution of vanadium has been studied to evaluate the environmental pollution due to the combustion of fossil fuel and oil refinery processes. Vanadium is a useful marker for the potential release of toxic trace metals from fossil fuels, especially oils, as it is always present in these materials. Concentrations were evaluated in the area near the plant, in atmospheric particulate, meteoric water, soils and groundwaters. Vanadium can be derived from the industrial areas of the oil refinery processes or from domestic heating and automotive traffic. In order to differentiate the contributions of these immissions lead has also been determined and the lead/vanadium ratios have been considered.

Separation of vanadium(V) and -(IV) by sorption on an iminodiacetic chelating resin

Abstract The distribution of vanadium(IV) and vanadium(V) between an aqueous solution and the chelating resin Chelex 100 was investigated on the basis of the Gibbs-Donnan model. As expected from this model the thermodynamic equilibrium constant in aqueous solution and in the resin phase were found to be equal. The following values for the complexation constant and for the exchange coefficients in NaNO 3 0.1 M were found: log K = − 1.93 and log β 10 ex = −1.89 for vanadium(IV) and log K = 0.81 and log β 11 ex = 0.70 for vanadium(V). A complex VO 2 L (log β 10 ex = −1.48) was found to be formed inside Chelex 100 at pH higher than 3.5. The competition by the hydrolysis reactions in aqueous solution was quantitatively considered to explain the sorption curves of vanadium(V) in the acidity range up to pH 9. As vanadium(IV) is not desorbed at pH higher than 8 a separation method was proposed, based on a batch technique. It consists of sorbing both vanadium(V) and vanadium(IV) at a pH of about 4.5, and separating them by stripping vanadium(V) at a pH of about 10 and then vanadium(IV) at pH about 0.8. A preconcentration factor of 40 could be obtained in this way. The model was also used to predict conditions for separation by a column method. The interference of fulvic acid on the oxidation state of vanadium and on its sorption on Chelex 100 was examined.

Separation of trace amounts of aluminium on a strong anion-exchange resin loaded with a sulphonated azo dye

The sulphonated azo dye Chromotrope 2B is sorbed quantitatively by the strong anion exchanger AG 1-X8. A chelating resin is obtained, which is able to sorb aluminium from aqueous solutions selectively. The distribution equilibria were investigated under different conditions and interpreted on the basis of a Donnan equilibrium based model for the resin. A separation and pre-concentration method for aluminium in natural waters is proposed, based on the use of the modified resin in a column at ambient pressure. The selectivity with respect to other metal ions was good; this was to be expected because Chromotrope 2B in solution is also selective for aluminium. Recoveries of 100 ± 1% were obtained, with a pre-concentration factor of 50, at a total aluminium concentration of 2 × 10–6 mol kg–1.

Batchwise separation of gallium by an anion exchange resin loaded with a sulphonated azo dye

Gallium(III) is sorbed by a strong base anion exchange resin loaded with a sulphonated azo-dye, T-azo-R [1-(tetrazolylazo)-2-hydroxynaphthalene-3,6-disulphonic acid], which is able to complex it in aqueous solution. As sorption takes place at acidities at which the hydrolysis of gallium is not negligible, it must be considered as conconmitant equilibrium. The distribution equilibria depend on the amount of ligand sorbed, and on the volume, acidity and ionic composition of the aqueous solution, according to the Gibbs-Donnan model. The thermodynamic complexation constant in the resin phase can be calculated from the experimental distribution coefficients; the value of log K = -1.24(0.20) is in acceptable agreement with that in aqueous solution [log K = -0.75(0.33)] which was also determined in the present investigation. Two equations deriving from the Gibbs-Donnan model are used for predicting the conditions for sorption and elution of gallium by a batch procedure, and for separating it from aluminium.

Spectrophotometric study and analytical applications of the complexes of copper (II) and zinc (II) with some sulphonated azo dyes

The complexing ability of some water-soluble azo dyes towards copper(II) and zinc(II) were studied in 0.1 M sodium perchlorate and perchloric acid solutions, at 25.0 °C. Solutions with CM≫CL, where CM is the concentration of metal and CL the concentration of ligand, and CL≫CM(CM up to 10–3M, CL up to 2 × 10–4M and pH up to the precipitation of metal hydroxides) were investigated spectrophotometrically.The ligands T-azo-C and 3,6-disulpho-TAN are able to complex both copper(II) and zinc(II), but amaranth only copper(II). Besides the usual complexes having 1:1 metal to ligand molar ratios, a 2:1 complex has been detected in the system copper(II)- T-azo-C. The results are compared with others obtained previously. The copper(II) complexes are much more stable than those of zinc(II) and those of many other metal ions. Therefore, a method is proposed for the spectrophotometric determination of copper(II), which is almost free from interferences.

Voltammetric determination of some organic compounds of arsenic reduced at the mercury electrode

Abstract Cyclic voltammetric scans for methylarsonic acid, dimethylarsinic acid and 3-acetamido-4-hydroxyphenylarsonic acid at a mercury electrode in an acidic medium show anodic adsorption waves when the starting potential is sufficiently negative; the related arsines are formed on the electrode. Detection limits are at the micromolar level for the absorption peak found at about −0.1 V vs. SCE for all three compounds. Interferences are discussed.

Spectrophotometric investigation of the reaction of CU(II) and Cu(I) with 1-isonitroso-(1,2,3,4)-tetrahydrophenazine

The reactions of Cu(II) and Cu(I) with 1-isonitroso-(1,2,3,4)-tetrahydrophenazine (HITF) have been studied spectrophotometrically. Both ions form complexes with metal/ligand ratio 1:2. The complex of Cu(I) and ITF can be used for copper determination in the range 2-50 x 10(-6)M, and has been separated as the perchlorate in crystalline form. The spectrophotometric characteristics and the equilibrium constants for the ligand and for the complexes are reported.

Protonation and complex formation with heavy-metal ions of two tetrafunctional amines and of a new structurally related ion-exchange resin

The basicity and complexing ability towards copper(II) of two new tetrafunctional amines containing four basic aliphatic nitrogens (1) and two aliphatic and two heterocyclic nitrogens (2) have been investigated by potentiometric techniques. The basicity constants of the two compounds are different which indicates that the mechanism of protonation is different for the two amines. The presence of complexes [Cu(HL)], [CuL], [Cu(OH)L] for L =(1) and [Cu(H2L)], [Cu(HL)], [CuL], and [Cu(OH)L] for L =(2) could be detected in aqueous solution. A resin whose repeating unit is structurally related to (2) has been synthesized, and its basicity and stability constants have been compared with those of compound (2).