Feasibility of pyrohydrolysis as a clean method for further fluorine determination by ISE and IC in high purity nuclear grade alumina

Abstract

In this work, a method based on pyrohydrolysis of high purity nuclear grade alumina and subsequent F determination by ion chromatography (IC) and ion selective electrode (ISE) was developed. After pyrohydrolysis, F was absorbed in a suitable solution (50 mmol L−1 (NH4)2CO3, 50 mmol L−1 NH4OH, and also water were evaluated). Using the selected conditions, it was possible to digest a high sample mass (500 mg) in only 10 min. The following analytical parameters were evaluated: pyrohydrolysis temperature (550 to 1050 °C), time of reaction (2.5 to 20 min), air flow-rate (0.1 to 0.4 L min−1), water flow-rate (0.1 to 1.0 mL min−1), and the use of V2O5 (200 mg), as an auxiliary reagent. Quantitative F recoveries were obtained using air and water flow-rates pumped through the reactor at 0.2 L min-1 and 0.5 mL min−1, respectively. Only water was required as absorbing solution and the use of V2O5, generally recommended for inorganic matrices, was not necessary. Detection limits of 2.0 and 3.6 μg g−1 using IC and ISE, respectively, were obtained. Accuracy was evaluated by recovery tests and also by comparison with the results obtained by high resolution continuum source graphite furnace molecular absorption spectrometry (HR-CS GF MAS). Suitable recoveries for F were obtained (95%) and no statistical difference (95% of confidence level) was observed for the results obtained by HR-CS GF MAS. Pyrohydrolysis allowed the F volatilization in a relatively short time avoiding the use of concentrated reagents and making possible further determination by both analytical techniques (IC or ISE). The pyrohydrolysis method was considered suitable for further F determination, avoiding excessive dilution of digests or matrix matching approaches, making this method a suitable option for routine F determination in nuclear grade alumina samples.