Ion exchange model for reversible sorption of divalent metals on calcite: implications for natural environments

Environmental Science & Technology
Emmanuel TertreCatherine Beaucaire

Abstract

Most of the thermodynamic models available in the literature describing the speciation of the calcite surface do not predict a significant concentration of sorbed Ca(II), whereas previous electrokinetics studies clearly show that Ca(2+) is the main cation determining the potential of the calcite surface. This study proposes a new thermodynamic model based on ion-exchange theory that is able to describe the reversible sorption of Ca(2+) on calcite. To constrain the model, concentrations of Ca(II) sorbed reversibly on the mineral surface were obtained as a function of pH. Such experimental data were obtained using solutions in equilibrium with both calcite and fixed p(CO2(g)) values (from 10(-5) to 10(-2) atm). The concentration of (de)sorbed Ca(II) is almost constant in the [7-9.5] pH range, having a value of approximately 1.2 × 10(-6) ± 0.4 × 10(-7) eq·g(-1). Such a value agrees with total sorption site densities that were previously calculated by crystallography and is used to obtain a selectivity coefficient between H(+) and Ca(2+) species by fitting the experimental data. Then, selectivity coefficients between H(+) and different metallic cations (Zn(2+), Cd(2+), Pb(2+)) that are able to accurately describe previously publish...Continue Reading

References

Mar 2, 2002·Environmental Science & Technology·O S Pokrovsky, J Schott
Nov 23, 2010·Journal of Colloid and Interface Science·Frank HeberlingDirk Bosbach

Citations

Oct 10, 2014·Journal of Contaminant Hydrology·D A BelovaS L S Stipp

Related Concepts

Adsorption
Cadmium
Calcium
Vaterite
Carbonates
Cations, Divalent
Ion Exchange
Lead
Metals
Surface Properties

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