Pages: 79-87

Authors: Aleksandra S. Milenković, Ivana D. Smičiklas, Jelena P. Marković,
and Nikola S. Vukelić

Abstract

The removal of ⁶⁰Co and ⁹⁰Sr from the aqueous phase was tested using red mud – the fine grained residue from bauxite ore processing. This industrial waste represents a mixture of numerous minerals, mainly oxides and hydroxides of Fe, Al, Si, and Ti. Experiments were conducted as a function of contact time, pH, and pollutant concentrations. Kinetic data were well fitted with a pseudo-second order equation. The calculated rate constants and initial sorption rates indicated faster sorption of Sr²⁺ ions. Removal of both cations rapidly increased with the initial pH increase from 2.5 to 3.5. With the further increase of pH, Co²⁺ sorption was nearly constant (98%-100%), whereas Sr²⁺ removal remained at the same level to initial pH~8 and gradually increased to 100% at pH 12. Equilibrium sorption data followed the Langmuir model, with the maximum sorption capacities of 0.52 mmol/g for Co²⁺ and 0.31 mmol/g for Sr²⁺. Sorbed cations exhibited high stability in distilled water. Desorption of Co²⁺ was also negligible in the presence of the competing Ca²⁺ cation, while 42%-25% of Sr²⁺ ions were desorbed depending on the previously sorbed amount. The results indicate that red mud is of potential significance as Co²⁺ and Sr²⁺ immobilization agent due to its high efficiency, abundance, and low-cost.

Key words: ⁹⁰Sr, ⁶⁰Co, immobilization, red mud

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