Chromium (Cr) is 21st most abundant element in the Earth's crust. Chromium is a transition metals and has a wide range of possible oxidation states. The most common oxidation states are +2, +3, and +6, with +3 being the most stable. In minerals, the predominant oxidation state is Cr3+.
The chromium content of natural waters is generally low and primarily controlled by mineral weathering. Like other multi-valence element, chromium is strongly controlled by redox and pH-Eh conditions. In aqueous solution, six different ionic forms of chromium may considered stable, Cr3+, CrOH2+, Cr(OH)2+, Cr(OH)4-, Cr2O72- and CrO42-.
Chromium is measured by inductively coupled plasma optical emission spectroscopy (ICP-OES) or inductively coupled plasma mass spectroscopy (ICP-MS)
The mobility of chromium is determined by the competition between complexation, dissolution/precipitation, redox processes and adsorption/desorption mechanisms. So the various species and concentrations may be used to indicate changing conditions in the aqueous environment. Chromium is typically enriched in oxidising groundwaters where it exists as Cr(III) anionic species. In reducing waters Cr may be lower due adsorption of the Cr(III) onto iron oxides.
References and Further Reading
- Davis, A. and Olsen, R.L., 1995. The Geochemistry of Chromium Migration and Remediation in the Subsurface. Ground Water, 33(5): 759-768.
- Hem, J.D., 1985. Study and interpretation of the chemical characteristics of natural water. U.S. Geological Survey Water-Supply Paper 2254, 263 p.
- Richard, F.C. and Bourg, A.C.M., 1991. Aqueous Geochemistry of Chromium - a Review. Water Research, 25(7): 807-816.
- Edmunds, W.M. & Smedley, P.L. (2000). Residence time indicators in groundwaters: The East Midlands Triassic Sandstone aquifer. Applied Geochemistry, 15, 737-752.
- Guendouz. A., Moulla, A.S. Edmunds, W.M., Zouari, K, Shand, P. & Mamou. A. (2003).Hydrogeochemical and isotopic evolution of water in the Complexe Terminal aquifer in the Algerian Sahara. Hydrogeology Journal, 11 483-495.