Determination of As and Hg in acetic acid extract by vapor generation coupled to atomic spectrometry for solid waste classification

Abstract Methods for the determination of As and Hg by vapor generation atomic spectrometry in acetic acid leachates are proposed. The waste classification involves several tests, including the toxicity evaluation by which the solid waste is leached with acetic acid solutions according to procedures specified by Norms as for example USEPA, toxicity characteristic leaching procedure (TCLP). Some elements, such as As and Hg, are determined in the leachate, and if the concentration is higher than the limits of the Norms the waste is classified as hazardous. In this study, two wastes, a retorted shale and a catalyst from hydrothermal treatment, were submitted to the procedures. The reagents concentrations used to generate arsine for further determination by hydride generation atomic absorption spectrometry (HG AAS) were optimized: HCl (5% v/v), KI (3% m/v) and NaBH 4 (1.0% m/v containing 0.1% m/v NaOH). The previous addition of KI to reduce As(V) to As(III) was necessary to obtain accurate results. Mercury was determined by two techniques, cold vapor atomic absorption spectrometry (CV AAS), using NaBH 4 as reducing agent, and cold vapor atomic fluorescence spectrometry (CV AFS), using SnCl 2 as reducing agent. The reagents concentrations were also optimized, for AAS: HCl (0.5% v/v), KMnO 4 (0.25% m/v), hydroxylamine hydrochloride (0.02% m/v) and NaBH 4 (0.5% m/v containing 0.1% m/v NaOH); and for AFS: HCl (2% v/v), KMnO 4 (0.04% m/v), hydroxylamine hydrochloride (0.02% m/v) and SnCl 2 (3% m/v). Addition of KMnO 4 was used for an efficient vapor generation in the presence of acetic acid. The detection limit (3 s, n  = 10) for Hg using CV AFS was about two orders of magnitude lower than for CV AAS. All three proposed methods can be used for waste classification, considering that the limits of detection were in the order of ng L − 1 , much lower than the concentration limits of the Norm EPA, 5 mg L − 1 for As and 0.2 mg L − 1 for Hg. Accuracy for As was demonstrated by comparison with the results obtained by ICP-MS, and for Hg it was demonstrated by the recovery test. The results by CV AAS were below the detection limit. The analytes concentrations in the acetic acid leachates from both residues were below the concentration limits of the Norms, demonstrating that they are non-dangerous concerning As and Hg.