Kinetics of sodium ethylenediaminetetraacetate mineralization by cerium(IV) in nitric acid medium

Abstract

The process of sodium ethylenediaminetetraacetate (EDTA) mineralization by cerium(IV) in nitric acid medium was studied in batch and continuous feeding modes. In the batch mode EDTA solution was fed into the reactor in one stroke and in the continuous mode it was fed with a constant flow rate during a definite time interval. Cerium(IV) concentration was kept at high and constant level by selecting correct relation between cerium(IV) production in the electrochemical cell and the EDTA added. During the organic mineralization process cerium(IV) is reduced to cerium(III). The process was carried out at different temperatures, concentrations of nitric acid and cerium(IV). To obtain the limiting factors in the batch mode reaction, the dependence of CO2 evolution with time and carrier gas blowing rate was studied. Application of the model previously developed by us to the continuous process gave us the possibility to calculate pseudo first order kinetic constant on the basis of CO2 evolution data of both EDTA destruction regimes during feeding mode and after stopping organic addition. The efficiency of organic destruction estimated on the basis of CO2 evolved was in the range 75–95% and on the basis of liquid phase residual organic carbon analysis 95–99%.