Water Supply Vol 5 No 5 pp 67–74 © IWA Publishing 2005
Ion exchange equilibria of arsenic in the presence of high sulphate and nitrate concentrations
R. Baciocchi*, A. Chiavola** and R. Gavasci***
*Department of Civil Engineering, University of Rome Tor Vergata, Via del Politecnico 1, 00133 Rome, Italy, (E-mail: baciocchi@ing.uniroma2.it; gavasci@ing.uniroma2.it)
**Department of Hydraulics, Transport and Roads, University of Rome La Sapienza, Via Eudossiana 18, 00184 Rome, Italy, (E-mail: agostina.chiavola@uniroma1.it)
***Department of Civil Engineering, University of Rome Tor Vergata, Via del Politecnico 1, 00133 Rome, Italy, (E-mail: baciocchi@ing.uniroma2.it; gavasci@ing.uniroma2.it)
ABSTRACT
The aim of this work was to develop a quantitative description of the ion exchange equilibria of arsenic on a strong anionic resin, in the presence of nitrates and sulphates. First, the ion exchange equilibrium data of As(V) and NO3− on a strong anionic resin in chloride form were obtained and described with a model based on the mass action law. Namely, assuming ideal behaviour for both solution and resin phase, the thermodynamic constant of the As(V)/Cl− and NO3−/Cl− ion exchange equilibria were estimated by fitting of experimental data. Then, these equilibrium constants were used to predict the ion exchange behaviour of the ternary system As(V)/NO3−/Cl−, providing a rather good agreement with experimental results. The ion exchange equilibria involving sulphate ions were also studied, showing a very high affinity to the resin phase. This behaviour did not allow a quantitative robust modelling of the equilibrium pattern. The results discussed in this paper represent a first step toward the development of a comprehensive modelling of the ion exchange process for the removal of As(V) from surface and groundwater in the presence of competitive, naturally occurring anions. Keywords Arsenic; ion exchange; nitrate; sulphate
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