Modelling of chromium hexavalent reduction by ferrous ion in a batch stirred tank

In this paper mathematical models are proposed to simulate the dynamic behaviour of the reduction of Cr(VI) with Fe(II) in a batch stirred tank. Two approaches have been adopted to represent systems in non-equilibrium and quasi-equilibrium conditions. The models derived reflect the changes of the relevant reactant species concentration based on the Oxidation Reduction Potential (ORP) of the system. An automated pilot plant has been designed and commissioned to carry out on-line/real time data acquisition and control for this Cr(VI) reduction process experimentally. Both the quasi-equilibrium and non-equilibrium models were validated experimentally. Simulated and on-line results indicate distinctive ORP profiles pattern for these two processes. The ORP profiles for non-equilibrium processes show a distinctive pattern which indicates the complete reduction of Cr(VI) in the batch sample.