Paolo Aprea

Evaluation of an intermediate-silica sedimentary chabazite as exchanger for potentially radioactive cations

Intermediate-silica sedimentary chabazite contained in two chabazite-rich tuffaceous rocks has been evaluated as potential cation exchanger for radioactive cation removal from nuclear waste streams. Exchange isotherms have been obtained for the cationic couples Na/Ba, Na/Co, Na/Cs and Na/Sr and the relevant thermodynamic parameters calculated with the help of a computer program. Sedimentary chabazite turns out very selective for Cs þ , fairly selective for Ba 2þ and Sr 2þ , especially at low equivalent fraction of these cations in solution, and unselective for Co 2þ . An expla

Selective Laser Treatment on Cold-Sprayed Titanium Coatings: Numerical Modeling and Experimental Analysis

In this paper, a selective laser post-deposition on pure grade II titanium coatings, cold-sprayed on AA2024-T3 sheets, was experimentally and numerically investigated. Morphological features, microstructure, and chemical composition of the treated zone were assessed by means of optical microscopy, scanning electron microscopy, and energy dispersive X-ray spectrometry. Microhardness measurements were also carried out to evaluate the mechanical properties of the coating. A numerical model of the laser treatment was implemented and solved to simulate the process and discuss the experimental outcomes. Obtained results highlighted the key role played by heat input and dimensional features on the effectiveness of the treatment.

Data processing of cation exchange equilibria in zeolites: a modified approach

After reviewing the fundamental literature concerning the equilibrium of binary cation exchange reactions on zeolites, this paper provides a straightforward procedure of computation of their thermodynamic parameters, Kα and ΔGo, based on a method of evaluation of cations activity coefficients in solution, which is simple and accurate and is equipped with a sufficiently large data-base. The computation procedure was tested on isothermal equilibrium data of Cd2+ and Zn2+ exchange for Na+ in zeolite A at 25.0°C and 0.05, 0.10, and 0.50 total normality, by calculating their Ka and ΔGo and by comparing these results to those obtained evaluating the cations activity coefficients through a reference largely used method and to previous literature data. The results obtained show that the proposed methods give results in good agreement with those obtained with the reference method so that it appears to be a good alternative for the determination of cation activity coefficients in solution.

Iron-activated carbon nanocomposite: synthesis, characterization and application for lead removal from aqueous solution

The removal of Pb(II) ions from aqueous solution by adsorption on an Iron-Activated Carbon (IAC) nanocomposite was investigated. Removal studies were carried out in a batch system, and the effects of various operating parameters, such as solution pH, solid to liquid ratio and initial concentration were evaluated. Experimental design was carried out using central composite design (CCD) with response surface methodology (RSM). According to the RSM results, the optimum adsorption conditions for Pb(II) removal by IAC were pH = 6.5, solid to liquid ratio of 3 g L−1 and initial lead concentration of 10 mg L−1. Under these optimum operating conditions, 96.5% of Pb(II) was removed by the IAC nanocomposite. The equilibrium adsorption data were well described by the Freundlich isotherm. The maximum adsorption capacity of IAC was 121.9 mg g−1 for Pb(II). It was observed that the adsorption kinetics of Pb(II) on the IAC could be well analyzed with a pseudo-second-order model.

A chromium-based metal organic framework as a potential high performance adsorbent for anaesthetic vapours

In this work, a chromium-based metal organic framework (Cr-MOF) was synthesized, characterized and tested for the adsorption of a model highly ozone-depleting anaesthetic (sevoflurane). Adsorption isotherms were measured at different temperatures e.g., 283, 298, 313 and 328 K on both Cr-MOF and a conventionally used reference adsorbent. At the temperatures used in this study, the Cr-based MOF showed a significantly higher sevoflurane (selected anaesthetic) equilibrium adsorption capacity compared to the reference sample, although adsorption on the selected MOF did not take place on all active sites (i.e., it did not expose its coordinatively unsaturated sites). Moreover, sevoflurane adsorption on Cr-MOF was found to be fully reversible in the 283–328 K temperature range, and the adsorbent was fully regenerated by vacuum treatment at ambient temperature. The semiempirical Sips model was successfully used to fit sevoflurane adsorption data, substantially confirming the phenomenological aspects of the process inferable from the experimental results.

Study of the Linear Friction Welding Process of Dissimilar Ti-6Al-4V–Stainless Steel Joints

Linear friction welding (LFW) is an innovative joining method that can be used to obtain high-strength joints between dissimilar materials. A key factor that influences the joints performances are the intermetallic compounds that could be formed during the welding process. These intermetallics are brittle and could compromise the mechanical performances of the joint. This article deals with the analysis of the LFW process of dissimilar titanium–stainless steel joints. Two different types of joints were studied: AISI 304–Ti6Al4V and AISI 316–Ti6Al4V. Particular attention was paid to characterizing the intermetallic compounds using scanning electron microscopy, Electron probe microanalysis and X-ray diffractometry. Zones with different microstructure were observed. Due to the diffusive phenomena occurring during the welding, Kirkendall effect and occurrence of several intermetallics were observed. Moreover, it was found that the joint with AISI 316 formed brittle intermetallic compounds, which led to crack formation close to the weld line.

On the Interface Generated by Hot Isostatic Pressing Compaction Process Between an AISI 304 Container and the Ti6Al4V Powders

In this work, the interface between a Ti6Al4V component made by Hot Isostatic Pressing and the AISI 304 container was studied in detail. The interface is dominated by interdiffusion with evident Kirkendall effect. Different intermetallic phases have been recognized. In particular, on the AISI 304 side of the interface, both χ and σ phases have been identified, whereas on the Ti6Al4V side λ phase (Laves), FeTi, (Fe,Ni)Ti, Ti2Ni, and β-Ti are present.

Ion exchange kinetics and thermodynamics of hydrosodalite, a narrow pore zeolite

The ion-exchange properties of a synthetic hydrosodalite (Na-hS) have been investigated by kinetic and thermodynamic analysis of exchange reactions of the original sodium form for lithium, potassium and calcium forms. Kinetic curves, modelled by a Langmuir-type equation, revealed that exchange rate for lithium and for potassium are of the same order, whereas they are two order faster than for calcium. Thermodynamic analysis of the cation exchange isotherms pointed out that sodalite is selective for sodium over the other three cationic forms examined, which is consistent with the preference exhibited by the sodalite type for sodium environments, either in natural or in laboratory crystallization. Na/Li and Na/Ca exchanges are incomplete, whereas unexpectedly Na/K exchange turns out to be complete, even though K+ dimension exceeds the width of the access window to sodalite cages. The obtained results have been discussed in terms of Eisenman–Sherry theory, pointing out agreements and discrepancies.

An unconventional method for the recovery of caustic soda from spent Al-rich pickling solutions.

This work presents an unconventional procedure for the recovery of spent Al-rich caustic soda solutions from the pickling of dies for the production of aluminium extrusions. Caustic soda was regenerated at roughly 70%, by precipitating aluminate, after addition of a silica source, in the form of zeolite A, a microporous material that is widely used in many technological sectors. It was shown that the process is reliable and can be repeated for several cycles, provided the concentration of the caustic soda solution is suitably restored. The by-product obtained, zeolite A, proved to be a high-grade material with performance as a cation exchanger and physical sorbent that is certainly comparable to that reported in literature (e.g., cation exchange capacity equal to 5.14 meq g(-1) vs. 5.48 meq g(-1) and water vapour adsorption capacity of 26.5% vs. 27.6% at 16 torr and 298 K). The economics of the process, although not examined yet, would appear generally favourable, considering that zeolite A is a valuable by-product which widely covers the costs for the recovery of the spent solutions. There are, therefore, significant prospects for the use of zeolite A, particularly as a builder in detergent formulation.

Cation selectivity of a Ca2+ pre-exchanged clinoptilolite tuff

Abstract With the purpose to evaluate clinoptilolite for possible use in soil amendment strategies as a substitute of naturally occurring clay minerals, a marketed clinoptilolite-rich tuff coming from Anatolia, Turkey, was submitted, after exhaustive treatment with Ca 2+ solutions, to exchange tests towards some nutrient or noxious cations. Accordingly, time-dependant and equilibrium data of exchange reactions of Pb 2+ , Cu 2+ , Zn 2+ , Na + , K + and NH 4 + for Ca 2+ were collected and the corresponding thermodynamic and kinetic parameters were calculated following standard procedures. Results demonstrated an excellent to good propensity of Ca 2+ -clinoptilolite for K + , NH 4 + and Pb 2+ and a moderate affinity for the other three cations. The conclusion was that a Ca 2+ -rich clinoptilolite tuff can be considered as a good substitute for clay minerals to recover and/or rebuild degraded and depleted soils.