Thermodynamic metastability of chromium (III) and chromium speciation in natural waters

Abstract

Oxidation state diagrams and volt-equivalent values revealed the metastability of Cr(II) and Cr(III) states in aqueous solutions. The study also showed the (i) higher stability of Cr(III)-organic complexes over dissolved Cr)II) and Cr)III)-inorganic complexes (ii) strong tendency of Cr(III) to adsorb onto suspended particulate matter, (iii) feasiblity of reduction of CrO super(2)@)d4 super(−) species by organic ligands via complexation in natural waters and (iv) predominance of Cr(OH) super(+)@)d3 over Cr(OH) super(+)@)d2 above 40 plus or minus 1 degree C in seawater. Transformation of Cr(OH) super(2+) and Cr sub(2)O super(2)@)d7 super(−) (Stable species in river water having pH6 for Cr(III) and Cr(VI) states, respectively) to Cr(OH) super(+)@)d2 and CrO super(2)@)d4 super(−) (more stable species in seawater) occur during an estuarine mixing.