References
  -  F.C. Richard, A.C.M. Bourg, Aqueous geochemistry of
    chromium: a review, Water Res., 25 (1991) 807–816. 
-  J.P. Beukes, J.J. Pienaar N.G. Lachmann, E.W. Giesekke, The
    reduction of hexavalent chromium by sulphite in wastewater,
    Water SA, 25 (1999) 363–370. 
-  D.L. Sedlak, P.G. Chan, Reduction of hexavalent chromium
    by ferrous iron, Geochim. Cosmochim. Acta, 61 (1997)
    2185–2192 
-  J.W. Patterson, Industrial Wastewater Treatment Technology,
    2nd ed., Butterworth, Boston, USA, 1985. 
-  C.P. Huang, A.R. Bowers, The Development of an Activated
    Carbon Process for the Treatment of 
 Chromium VI-Containing
    Plating Wastwater, 2nd Conference on Advanced Pollution
    Control for the Metal Finishing Industry, EPA-6018-79-014,
    Cincinati, OH, 1979, pp. 114–122.
-  G. Vilardi, J. Rodríguez-Rodríguez, J. Miguel Ochando-Pulido,
    N. Verdone, A. Martinez-Ferez, L. Di Palma, Large laboratoryplant
    application for the treatment of a tannery wastewater
    by Fenton oxidation: Fe(II) and nZVI catalysts comparison
    and kinetic modelling, Process Saf. Environ. Prot., 117 (2018)
    629–638. 
-  L.E. Eary, D. Rai, Kinetics of chromium(III) oxidation to
    chromium(VI) by reaction with manganese dioxide, Environ.
    Sci. Technol., 21 (1988) 1187–1193. 
-  I.J. Buerge, S.J. Hug, Kinetics and pH dependence of
    chromium(VI) reduction by iron(II), Environ. Sci. Technol.,
    31 (1997) 1426–1432. 
-  Y.C. Shamra, B. Singh, A. Agrawal, C.H. Weng, Chromium
    removal of chromium by riverbed sand from water and
    wastewater: effect of important parameters, J. Hazard. Mater.,
    151 (2008) 789–793. 
-  M.S. Abdo, G.H. Sedahmed, A new technique for removing
    hexavalent chromium from wastewater and energy generation
    via galvanic reduction with scrap iron, Energy Convers.
    Manage., 39 (1998) 943–951. 
-  E. Demirbas, M. Kobya, E. Senturk, T. Ozkan, Adsorption
    kinetics for the removal of chromium(VI) from aqueous
    solutions on the activated carbons prepared from agricultural
    wastes, Water SA, 30 (2004) 533–539. 
-  A.H. El-Shazly, A.A. Mubarak, A.H. Konsowa, Hexavalent
    chromium reduction using a fixed bed of scrap bearing iron
    spheres, Desalination, 185 (2005) 307–316. 
-  S. Junyapoon, S. Weerapong, Removal of hexavalent chromium
    from aqueous solutions by scrap fillings, KMITL Sci. Technol. J.,
    6 (2006) 1–12. 
-  H. Qian, Y. Wu, Y. Liu, X. Xu, Kinetics of hexavalent chromium
    reduction by iron metal, Front. Environ. Sci. Eng. China,
    2 (2008) 51–56. 
-  S. Kang, G. Wang, H. Zhaoa, W. Cai, Highly efficient removal
    of hexavalent chromium in aqueous solutions via chemical
    reduction of plate-like micro/nanostructured zero valent iron,
    RSC Adv., 7 (2017) 55905–55911. 
-  J. Lv, X. Tong, Y. Zheng, Z. Lan, Kinetics of hexavalent chromium
    reduction by grey cast iron powder, Can. J. Metall. Mater. Sci.,
    58 (2019) 262–271. 
-  A.M. Ahmed, M. El Batouti, A.M. Darweesh, S.M. Said, The
    reduction of hexavalent chromium by ferrous ions to trivalent
    chromium in presence of organic acid additives, Asian J. Chem.,
    27 (2015) 3998–4006. 
-  P.D. Mackenzie, D.P. Horney, T.M. Sivavec, Mineral precipitation
    and porosity losses in granular iron columns, J. Hazard.
    Mater., 68 (1999) 1–17. 
-  M.M. Scherer, B.A. Balko, P.G. Tratnyek, The Role of Oxides in
    Reduction Reactions at the Metal-Water Interface, D. Sparks,
    T. Grundl, Eds., Mineral-Water Interfacial Reactions: Kinetics
    and Mechanisms, ACS Symposium Series 715, American
    Chemical Society, Washington, D.C., 1998, pp. 301–322. 
-  A.R. Pratt, D.W. Blowes, C.J. Ptacek, Products of chromate
    reduction on proposed remediation materials, Environ. Sci.
    Technol., 31 (1997) 2492–2498. 
-  T. Lee, H.Y. Lim Lee, J.W. Park, Use of waste iron metal for
    removal of Cr(VI) from water, Chemosphere, 53 (2003) 479–485. 
-  S.M. Ponder, J.G. Darab, T.E. Mallouk, Remediation of Cr(VI)
    and Pb(II) aqueous solutions using supported nanoscale iron,
    Environ. Sci. Technol., 34 (2000) 2564–2569. 
-  T. Kendelewicz, P. Liu, C.S. Doyle, G.E. Brown, Spectroscopic
    study of the reaction of aqueous Cr(VI) with Fe3O4(III) surfaces,
    Surf. Sci., 469 (2000) 144–163. 
-  M.T. Gueye, E. Petrucci, L. Di Palma, Chemical reduction of
    hexavalent chromium(VI) in soil slurry by nano zero valent
    iron, Chem. Eng. Trans., 43 (2015) 655–660. 
-  T.J. Gilmore, G.R. Holdren, D.I. Kaplan, Groundwater Well with
    Reactive Filter Pack, U.S. Patent 5,803,174, U.S. Patent Office,
    Washington, D.C., 1998. 
-  I.J. Buerge, S.J. Hug, Influence of mineral surfaces on chromium
    reduction by iron(II), Environ. Sci. Technol., 33 (1999) 4285–4291. 
-  V.G. Levich, Physiochemical Hydrodynamics, 2nd ed., Prentice
    Hall, New Jersey, U.S.A., 1962. 
-  A.M. Al Taweel, M. El-Ali, F. Azizi, B.O. Liekens, D. Odedra,
    A. Uppal, H.G. Gomaa, In-Line Processing for Intensifying
    Multi-Phase Contacting Operations, Proceedings of the 5th Inter.
    Conf. Process Intensification, Maastricht, The Netherlands,
    2003, pp. 59–73. 
-  M.S. El-Ali Al-Waqfi, B.A. Telfah, A novel technique for
    hexavalent chromium reduction, Jordan J. Earth Environ. Sci.,
    9 (2018) 13–20. 
-  J.P. Gould, The kinetics of hexavalent chromium reduction by
    metallic iron, Water Res., 16 (1982) 871–877. 
-  G. Vilardi, M. Stoller, L. Di Palma, N. Verdone, CFD model
    of agitated vessel for the removal of Cr(VI) by nano-hematite
    particles, Chem. Eng. Trans., 73 (2019) 157–162. 
-  M.M. Semary, A.A. Zatout, S.A. Nosier, M.S. Mansour,
	  Reduction of toxic Cr6+ ions using fluidized bed of iron particles,
    Ind. Chem., 2 (2016) 1000116, doi: 10.4172/2469-9764.1000116. 
-  N. Melitas, O. Chuffe-Moscoso, J. Farrell, Kinetics of soluble
    chromium removal from contaminated water by zerovalent
    iron media: corrosion inhibition and passive oxide effects,
    Environ. Sci. Technol., 35 (2001) 3948–3953. 
-  A.G. Williams, M.M. Scherer, Kinetics of Cr(VI) reduction by
    carbonate green rust, Environ. Sci. Technol., 35 (2001) 3488–3494. 
-  D. O’Carrol, B. Sleep, M. Kroll, H. Boparai, C. Kocur, Nanoscale
    zero valent iron and bimetallic particles for contaminated site
    remediation, Adv. Water Resour., 51 (2013) 104–122. 
-  M. Riviero-Huquet, W.D. Marshall, Reduction of hexavalent
    chromium mediated by micron- and nano-scale zero-valent
    metallic particles, J. Environ. Monit., 11 (2009) 1072–1079. 
-  M. Gheju, Hexavalent chromium reduction with zero-valent
    iron (ZVI) in aquatic systems, Water Air Soil Pollut., 222 (2012)
    103–148. 
-  J. Ye, Y. Wang, Q. Xu, H. Wu, J. Tong, J. Shi, Removal of
    hexavalent chromium from wastewater by Cu/Fe bimetallic
    nanoparticles, Sci. Rep., 11 (2021) 10848. 
-  C. Zhang, Q. Liu, R. Huang, W. Qi, Z. He, R. Su, Removal
    of hexavalent chromium using nanoscale zero-valent iron
    stabilized by poly(γ-glutamic acid), Chem. Eng. Trans.,
    81 (2020) 1285–1290. 
-  J.E. Yang, J.S. Kim, Y.S. Ok, S. Kim, Y. Kyung-Yoal, Capacity of
    Cr(VI) reduction in an aqueous solution using different sources
    of zerovalent irons, Korean J. Chem. Eng., 23 (2006) 935–939. 
-  P. Mitra, D. Sarkara, S. Chakrabartia, B. Dutta, Reduction of
    hexavalent chromium with zero-valent iron: batch kinetic
    studies and rate model, Chem. Eng. J., 171 (2011) 54–60. 
-  X. Tan, M. Shaaban, J. Yang, Y. Cai, B. Wang, Q. Peng, Efficient
    removal of hexavalent chromium from an aquatic system
    using nanoscale zero-valent iron supported by ramie biochar,
    Nanomaterials, 11 (2021) 1–15. 
-  S. Niu, Y. Liu, X. Xu, Z. Lou, Removal of hexavalent chromium
    from aqueous solution by iron nanoparticles, J. Zhejiang Univ.
    Sci., 6B (2005) 1022–1027. 
-  Y. Huang, T. Chen, J. Huang, Y. Chen, Effects of size and surface
    area of iron on reduction of hexavalent chromium, J. Univ. Sci.
    Technol., Beijing, 30 (2008) 53–57. 
-  Z. Al-Qodah, M. Al-Shannag, On the performance of free
    radicals combined electrocoagulation treatment processes, Sep.
    Purif. Rev., 48 (2019) 143–158.