Occurrence, release and alteration of chromite nanoparticles

Abstract

Many environmental risk assessments are based on the total concentration of elements in natural waters/ soils, ignoring that a significant proportion of elements is associated with nanoparticles. TEM analysis of the silicate minerals from a chromitite sample from the Mum and Alice June claims, California confirmed that Cr-rich silicates contained an abundance of chromite nanoparticles. Subsequently, the colloidal fraction of a Cr-rich silicate leaching experiment revealed that the chromite nanoparticles persist through the weathering of their host silicate, confirming that chromite nanoparticles can be a significant form of Cr in the environment. The oxidation of chromite nanoparticles in the presence of Mn-oxides (best known environmental oxidiser of Cr3+) was tested with 6 batch experiments at pH 5 over a 9-month period. These experiments reveal that the dominant redox reaction between chromite nanoparticles and Mn-oxides is the oxidation of Fe2+(rather than Cr3+) by Mn3+.