Thermodynamics Metastability of Chromium (III) and Chromium Speciation in Natural Waters

Abstract

Oxidation state diagrams and volt-equivalent values revealed the metastability of Cr(2) and Cr(3) states in aqueous solutions. The study also showed the (i) higher stability of Cr(2) - organic complexes over dissolved Cr(2) and Cr(3) - inorganic complexes, (ii) strong tendency of Cr(3) to adsorb onto suspended particulate matter, (iii) feasibility of reduction of CrO4 2 species by organic ligands via complexation in natural waters, and (iv) predominance of Cr(OH)3 over Cr(OH)2 + above 40 plus or minus 1 degree C in seawater. Transformation of Cr(OH)2+ and Cr2 O7 2- (stable species in river water having pH 6 for Cr(3) and Cr(4) states, respectively) to Cr(OH)2 + and CrO4 2 (more stable species in seawater) occur during an estuarine mixing.