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Environ Chem Lett (2008) 6:235240 DOI 10.1007/s10311-007-0128-8
ORIGINAL PAPER
Removal of chromium (VI) from water streams: a thermodynamic study
George P. Gallios Miroslava Vaclavikova
Received: 26 April 2007 / Accepted: 8 October 2007 / Published online: 21 November 2007 Springer-Verlag 2007
Abstract The chemical speciation of water solutions containing chromium oxyanions in various ratios is calculated (with the aid of available computer code Mineql Plus, Geochemist Workbench and Visual Minteq) and discussed. The effect of solution pH, total concentration of each species studied, and the presence of other species in solution are calculated and presented in the form of thermodynamic speciation diagrams. Electrochemical diagram (correlating pH to Eh) has been calculated as well. The conditions of Cr(VI) reduction to Cr(III) and the subsequent solid phase precipitation are given as a function of redox potential and pH. Surface reactions that might occur between the chromate ions in the solution and redox couples as Fe2+/Fe3+ on the surface of sorbents are also discussed. Moreover, experimental sorption data of hexavalent chromium onto synthetic magnetite are presented and discussed with the aid of the calculated diagrams. A mechanism is elucidated for the efcient removal of Cr(VI) from water streams at low pH values, and zeta potential data of synthetic magnetite with and without Cr(VI) are presented, which agree well with the mechanism proposed.
Keywords Chromium Thermodynamic study
Chromium removal Sorption Iron oxide
Water treatment
Introduction
The presence of toxic metals in aqueous systems has become a problem due to their harmful effects on human health and other organisms in the environment. Among them, chromium is considered to be of high priority. Chromium is the 21st most abundant element in the earths crust and the 6th most abundant transition metal. It enters the environment from both natural and anthropogenic sources. The principal chromic ore is ferrous chromite, FeCr2O4. Plating and electroplating factories, leather tanneries, textile manufacturing facilities, cooling tower blowdown, rinse waters, steel producing factories, etc. are most often the anthropogenic sources. Chromium enters the air, water, and soil mostly in the chromium(III) and chromium (VI) forms. These two forms interact differently with living organisms. Chromium (III) is an essential nutrient and it is responsible (in addition to insulin) for reducing blood glucose levels. It has also been found to...