Vol.:(0123456789) 1 3 Bulletin of Environmental Contamination and Toxicology https://doi.org/10.1007/s00128-020-02843-8 CONCEPT NOTE Continuous Flow Process for Cr(VI) Removal from Aqueous Solutions Using Resin Supported Zero‑Valent Iron A. Toli 1  · Ch. Mystrioti 1  · A. Xenidis 1  · N. Papassiopi 1 Received: 17 February 2020 / Accepted: 30 March 2020 © Springer Science+Business Media, LLC, part of Springer Nature 2020 Abstract The objective of the present study was to evaluate the performance of a nanocomposite material consisting of nano zero valent iron and a cation exchange resin, for the reduction of chromate, by conducting column tests. A cationic resin, Amberlyst 15, was selected as porous host material. The synthesis of the nanocomposite material (R-nFe) was carried out using Green Tea extract to obtain the reduction of adsorbed Fe(III) to the elemental state Fe(0). Three column tests were implemented with diferent dimensions, corresponding to variable contact times between the aqueous solution and the resin beads loaded with Fe(0), namely 168, 744 and 1260 s respectively for columns I, II and III. The results indicated that the removal of Cr(VI) follows a frst order kinetic law with a chemical constant equal to 0.0526 min −1 (8.8 × 10 –4  s −1 ). Keywords nZVI nanocomposite · Macroreticular resin support · Chromate reduction · Continuous fow tests Chromate is an environmental contaminant which is com- monly detected in groundwater and in drinking waters. Cr(VI) and Cr(III) are the most stable oxidation forms of chromium which occur in the environment. Trivalent chro- mium presents limited solubility and at low doses is consid- ered an essential nutrient element for metabolism. Contrary, hexavalent chromium is accused to be highly toxic (HCrO 4 − , CrO 4 2− ) and soluble. Despite the toxicity of hexavalent chro- mium, it is used in many industrial applications such as in metal electroplating, in wood preservation, in leather tan- ning and in pigments and dyes. Concentrations of hexavalent chromium can be detected in the environment accidently or due to inefcient waste treatment from industries. The most common technologies for water treatment for the Cr(VI) remediation are the chemical reduction and precipitation, adsorption, ion exchange, membrane fltration, biological and electrochemical remediation. Iron and sulphur based compounds are used as agents for the chemical reduction of Cr(VI) to Cr(III) (Chrysochoou et al. 2012; Di Palma et al. 2015). Nano ZVI is more efcient compared to micro or mil- limeter scale ZVI, due to the small particle size, large spe- cifc surface area and high reactivity (O’Carroll et al. 2013; Bavasso et al. 2016). Nanoscale ZVI is mainly applied for in-situ injection (Mystrioti et al. 2018). The use of nano zero valent iron (nZVI) for the reduction of Cr(VI) in the pres- ence of selected other heavy metals was proved to be fast and efcient (Gueye et al. 2016). However, nZVI presents limited mobility to calcareous aquifers and may be toxic for living organisms or cells. The incorporation of nZVI to inert materials are currently under investigation. In this category of technologies iron nanopar- ticles are fxed on a permeable matrix and this composite material is applied for the treatment of contaminated waters under fow conditions, such as a permeable wall underground or an appropriate flter in above ground installations. Solid porous materials, such as carbon, resins, zeolite etc., have been tested as support material for nZVI (Fu et al. 2014). The support material protects iron nanoparticles from rapid oxidation, hydrolysis in water and agglomeration. Cation exchange resins can be efciently used as a chemically inert medium, which simultaneously combines the chemical and the physical binding of iron nanoparticles without afecting their reactivity and allow the distribution of the pollutants through the porous matrix of the resin. Moreover cationic resins as supporting matrix can retain Fe(III) and Cr(III), which are produced during the chemical reaction between nZVI and Cr(VI). Studies involving the synthesis of resin supported nZVI are limited in number (Shu et al. 2010; Fu et al. 2013; Xie * A. Toli katerinatoli@metal.ntua.gr 1 Sch. of Mining and Metallurgical Eng., National Technical University of Athens, 15780 Athens, Greece