THE KINETICS OF Cr(III) OXIDATION IN DOMINANT SOILS OF COIMBATORE DISTRICT, TAMILNADU, INDIA

Chromium has attained wide public and regulatory attention because of its toxicity to environmental ecosystem under certain oxidation state. An investigation was carried out with the main focus to find out whether irrigation of low concentration of Cr (III) containing treated tannery effluent to dominant soils of Coimbatore district favor oxidation of non-toxic Cr (III) to toxic Cr (VI). Significant transformation of Cr (III) to Cr (VI) in both soil types clearly indicate, that there was within shorter period of time. When the equilibration time, in batch study, was increased beyond 24 hours the oxidation of Cr (III) to Cr (VI) decreased which may be due to reduction of Cr (VI) to Cr (III) and adsorption of Cr (III) to nil minerals under the favorable soil pH conditions. Although the maximum concentration of water soluble Cr (VI) was only 5.3% of the spiked Cr (III) concentration at 5 mg L -1 the concentration of soluble Cr (VI) of 0.27 mg L -1 was beyond the critical limit of 0.05 mg L -1 for drinking water. Therefore it is essential imperative to exercise caution in the continuous application of Cr (III) containing tannery waste water to soils.