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Veröffentlichung Investigating reductive modification of granular ferric hydroxide for enhanced chromate removal(2019) Bahr, Carsten; Massa, Lukas; Stanjek, Helge; Ruhl, Aki SebastianRecent toxicological findings and expected lower regulatory limits for chromate (hexavalent chromium, Cr(VI)) in drinking water enforce the search for practical treatment options for efficient Cr(VI) removal. Cr(VI) adsorption and chemical reduction of highly soluble Cr(VI) to much less soluble Cr(III) are the main options that have already been experimentally investigated. Granular ferric hydroxide (GFH) is an established adsorbent for different pollutants but only to a limited extent for Cr(VI). The present study aimed at enriching ferrous iron (Fe(II)) as reducing constituent in the GFH to integrate reductive capabilities and thus to enhance Cr(VI) elimination. Three different batches were prepared and analyzed with regard to elemental and mineralogical compositions in comparison to conventional GFH. Long-term column tests showed enhanced Cr(VI) elimination in the modified materials with remarkably extended run-times until breakthrough. © 2019 Elsevier B.V. All rights reserved.Veröffentlichung Stabilization of chromium (VI) in the presence of iron (II): method development and validation(2020) El-Athman, Fatima; Polenz, Chantal; Mahringer, DanielThe presence of Cr (VI) in drinking water is mainly caused by leaching of chromium-containing aquifer material into groundwater. In contrast to Cr (III), it has been classified as highly toxic. For this reason, the WHO recommends the implementation of separate guideline values, instead of the so far used limit value of total chromium. The separate evaluation of Cr (VI) in raw water and during removal processes requires the Cr (VI) concentration to remain stable after sampling. In the presence of Fe (II), a stabilization of the samples is necessary to inhibit further reduction of Cr (VI) by Fe (II). In this study, two methods of Cr (VI) stabilization in Fe-(II)-containing water samples are investigated: Fe (II) oxidation by oxygen at high pH values in the presence of buffers and Fe (II) complexation by chelating agents. When adding hydrogen carbonate buffer, Cr (VI) recovery reached 100% at pH values of 10 to 12 in the presence of up to 3 mg L-1 Fe (II). Using hydrogen phosphate buffer, Cr (VI) recovery reached 100% only at pH 12 but for a Fe (II) concentration up to 6 mg L-1. Ammonium buffer was found to be less suitable for Cr (VI) stabilization. The addition of EDTA and citrate resulted in low recovery of Cr (VI), whereas citrate was found to accelerate the Cr (VI) reduction. Quelle: https://www.mdpi.com