Have a look at the article titled ''Kinetics and Products of Chromium(VI) Reduction by Iron(II/III)-Bearing Clay Minerals'' by Claresta Joe-Wong, Gordon E. Brown Jr, and Kate Maher. Environ. Sci. Technol., 2017, 51 (17), pp 9817–9825. DOI: 10.1021/acs.est.7b02934