F. Corigliano

Study of the pre-crystallization stage of hydrothermally treated amorphous aluminosilicates through the composition of the aqueous phase

A detailed study of the parameters and phases involved in the pre-crystallization of the hydrothermal conversion of coal fly ash to zeolites has been performed. The study has also been extended to pumice, a natural glassy aluminosilicate.Dissolution of the main components, their concentration ratio in the solution phase, the re-precipitation in the form of an amorphous gel from which evolves zeolite crystals, and the compositions, occurrence times and degrees of completeness of the gel and zeolite crystals have been found to be strongly interrelated and all influenced by the temperature and alkali–metal content of the treatment.In the case of coal fly ashes, the halt occurring in the conversion to zeolites some time after its beginning has been shown to be due to the mullitic phase located inside the ash particles and containing most of the total aluminium content of the ashes. In contrast to the external amorphous phase, this phase is insoluble at the experimental conditions suitable for the conversion treatment.

Comparative IR study of solid hydrate decavanadates and polyvanadates in acidic aqueous solution

Abstract An attempt has been made to compare i.r. spectra of polyvanadate solutions with those of solid polyvanadates, in order to solve the problem if aqueous solution decavanadate species have the same structure as reported in solid hydrate decavanadates, and if hexavanadate species are coexisting with them. The i.r. spectra directly obtained from water solutions were unreliable; so, solution species have been extracted into a low absorbing organic phase. A previous control showed that no modifications of existing species were occurring for the phase transfer. In this way, evidence resulted for a complete identity between aqueous solution and solid decavanadate structure, and for a lack of hexavanadate species, at least within the sensitivity limits of the i.r. technique. These findings are in agreement with a recent Raman investigation, but appear in contrast with NMR and complexation data. A new interpretation of NMR data is suggested, leading to the removal of disagreement.

Possible alteration of monuments caused by particles emitted into the atmosphere carrying strong primary acidity

We discuss the effects of the presence in the atmosphere of acidic ashes originating from the burning of oil heavy fractions and of the damage they could cause to monuments if deposited onto them. After quantifying its load of potentially strong acidity, we studied the effect of this particulate coming into contact with samples of two of the most common types of calcareous materials used in the building of monuments in atmospheric conditions characterized by relative humidity values of between 0 and 94%. Visual examination of the surfaces of the calcareous materials revealed substantial alteration even after brief periods of exposure in atmospheres with relative humidity values above 40%. The transformation of calcium carbonate into bihydrate calcium sulphate and the release of coloured metal ions, both promoted by the humidity absorbed from the atmosphere, were evidenced by SEM images and confirmed by WDS probe investigation and XRD examination of the altered layers of material.

Sources of strong primary acidity in the atmosphere

Abstract The fly ashes produced by the burning of heavy oil have been identified in this study as carriers of strong primary acidity in the atmosphere in the form of sulphuric acidity and hydrolyzable metal ions. This is an acidity which is strong from the moment of its emission (strong primary acidity, SPA) and different from common sources of weak acidity (SO2 NO) which give rise to strong acidity only after some time in the atmosphere. The oil ash SPA is transmitted to water on impact resulting in highly acid pH values and high total acidity as well as significant concentrations of heavy metals. Here we present and discuss our results.

A selective reagent for the spectrophotometric determination of palladium

A spectrophotometric method for the determination of trace amounts of palladium(II) with ethyl 3-phenyl-5-isoxazolone-4-carboxylate was developed. With this reagent, palladium forms a yellow complex, stable in the pH range 1–6.5, which is extractable into 4-methylpentan-2-ol from 0.05–4 M perchloric acid medium. The coloured complex adheres to Beers law at 370 nm in aqueous and in 4-methylpentan-2-ol solutions, with molar absorptivities of 3.5 × 103 and 3.9 × 103 l mol–1 cm–1, respectively. Other platinum-group metals do not interfere. In the presence of highly coloured ions, extraction with 4-methylpentan-2-ol eliminates all interferences. Cyanide ions interfere in the method.

Influence of the calcium content on the coal fly ash features in some innovative applications

Despite a low chemical reactivity, recent trends in the innovative uses of coal fly ash based on the chemical properties have been successful. Lots of fly ash showing sharply alkaline reaction (water pH rising to 11-12 upon contact) usually are high-calcium (> 3-4%). most of which is present as CaO. These lots are suitable to be used as remotion agents of heavy metals in wastewater or retentive agents of them in polluted solids. Lots giving substantially neutral reaction are usually low-calcium (0.3%). They are suitable to be converted by hydrothermal treatments into zeolitic products where higher calcium contents interfere. A reverse destination is destitute of good results. Causes are discussed.

Dead-stop determination of EDTA and NTA in commercially available detergents

A rapid and selective method for the determination of ethylenediaminetetraacetic acid (EDTA) and/or nitrilotriacetic acid (NTA) in commercially available detergents has been developed. It is based on a titration with a standard solution of copper(II) in acetate buffer, where the end-point is revealed by means of a “dead-stop” system with two polarised copper electrodes. Furthermore, it is possible to determine in the course of the same titration the relative amounts of both chelating agents by using 4-(2-pyridylazo)-resorcinol (PAR), which changes colour at the end-point of the first reaction (copper-EDTA). Most detergent constituents, including polyphosphates, have been observed to have no effect on the determination; interference from some constituents (perborates and zeolites) can easily be removed. The method has been shown to give good results in the analyses of different commercially available products.

Formation of strong primary acidity in combustion particulate: causes and remedies

Abstract Having observed great variations in the strong primary acidity (SPA) content of the ash of fossil fuels with similar sulphur contents, we studied the chemical causes of the formation of SPA in ashes. The main factors behind these variations were found to be: (a) combustion conditions and the extent to which they favour or do not favour the formation of SO 3 (excess of oxygen, presence of suitable catalysts, etc.); (b) the amount of basic oxides present in the mineral fraction of the fuel in relation to the SO 3 produced; and (c) the basic strength of these oxides. The variable but, nevertheless, high SPA contents common only to oil ashes can be explained in the light of the modest values for factors (b) and (c) and the conditions favourable to factor (a) in this fuel. Remedies involve the in-flame addition of highly basic oxides in order to artificially increase factors (b) and (c).

Kinetics of the dissociation of decavanadate(6–) in neutral and weakly basic solutions

The kinetics of decomposition of [V10O28]6–(2 × 10–3– 9 × 10–5 mol dm–3) have been studied spectrophotometrically and pH-metrically within the range pH 6–12.5 at 25 °C, /= 0.1 mol dm–3, and 0.1 mol dm–3 Na+ cationic medium. A treatment of the pH dependence of the observed rate constants demonstrates the presence of fast acid-base pre-equilibria involving the reactive species [V10O28]6–. Protonation leads to the well known and stable species [HV10O28]5– and decreases the overall decomposition rate. Deprotonation gives rise to an unknown and more reactive [HV10O29]7– species, increasing the rate. The equilibrium constant for formation of the [HV10O29]7– species from hydrated [V10O28]6– and hydroxide is 1.06 × 105 dm3 mol–1 The rate of decom-position of decavanadate is given by the contributions from two first-order paths, k1[V10O286–]+k1′[HV10O297–], where k1= 1.6 × 10–5 and k1′= 1.02 × 10–4s–1.

Decavanadate protonation degrees in aqueous solution

Abstract Aqueous solutions of vanadium(V) have been prepared at different OH − vs. vanadium concentrations from both decavanadic acid and metavanadate solutions. These solutions have been extracted with an excess of tetraheptylammonium bromide in benzene. The bromide displaced has been determined in order to gain information on the average charge of the extracting species already known to be variously protonated decavanadate anions. The addition of a constant excess of supporting electrolytes has been avoided, as it is known it could affect the position of equilibria. Besides the already well known H 2 V 10 O 28 4− , HV 10 O 28 5− and V 10 O 28 6− species, strong evidence has also been obtained for the existence of H 3 V 10 O 28 3− . Moreover, a slow disproportionation of V 10 O 28 6− into HV 10 O 28 5− and V 2 O 7 4− (or HVO 4 2− ) during a first stage, and then into metavanadate, resulted. Therefore, H 6 V 10 O 28 proves a strong acid as triprotic instead of tetraprotic, as reported in the literature. Inconsistent results are almost certainly due to the high ionic media usually employed.