Hofmeister Effects on Cation Exchange Equilibrium: Quantification of Ion Exchange Selectivity

Abstract

The Hofmeister or specific ion effects are not involved in the existing ion exchange equilibrium theories. In this study, a new cation exchange model considering the specific ion effects was established. The relative adsorption ability was quantified through relative adsorption energy or selectivity coefficients of ions. The quantificational sequence of relative adsorption ratio ((relative adsorption energe for i ion)/(relative adsorption energy for j ion)) calculated from the new model was obtained: Ca > Mg ((Ca 2+ )/(Mg 2+ ) = 1.407) > K ((Mg 2+ )/ K 2+ = 1.467) > Na (K + /(Na 2+ ) = 1.646) > Li ((Na 2+ )/(Li 2+ ) = 1.110). It provided a new theory for quantificational description of ionic exchange adsorption selectivity for any ion pairs. The experimental data on various materials (montmorillonite, Illite, and Altamont soil) with very different charge densities agree well with each other. Thus we presume that the new model may apply to all charged surfaces.

Impact of electric field on Hofmeister effects in aggregation of negatively charged colloidal minerals

“…According to the calculated results from Liu et al, 11 the β values for K + and Na + were 1.244 and 0.756, and the β values for Mg 2+ and Ca 2+ were 0.831 and 1.169, respectively. a 0 (mmol/L) represents the equilibrium concentration in bulk solution,c(mmol/L) is the ionic concentration in the diffuse layer, which can be calculated as,c…”

“…However, further studies indicated that Hofmeister effects are also present at low electrolyte concentration (<100 mmol/L or even lower). 3,14,[28][29][30][31][32] In addition, Hofmeister effects are found to be more pronounced at very dilute concentration, 11,31,33,34 but classical theories including hydration effects, ionic size and dispersion force could not give a reasonable interpretation to this phenomenon. 34 Fortunately, several recent studies [33][34][35] have disclosed the essential role of polarization effect played in Hofmeister effects at interface surfaces, and these results provided motivation for us.…”

“…3 Following pioneering experiments conducted on the capacity of * For correspondence ions to stabilize protein solutions against precipitation by Franz Hofmeister in the late 19 th century, it was clear that aggregation and sedimentation of proteins in electrolyte solutions vary remarkably with ionic species, even if the valence and chemical nature of these ions are similar. 4 Over the last decades, Hofmeister effects have been observed ubiquitously in colloidal, nanocrystal and biological systems, including bacteria growth, 5,6 enzyme activity, [7][8][9] colloidal stability, 3,10 cation exchange equilibrium 11 and mineral dissolution. 12 These effects can influence the interactions of ions with different interfaces (metal/water, air/water, oil/water and water/solid), 13,14 as well as affect the physicochemical properties of the solution or colloids, such as activity coefficient, Zeta potential, freezing point, osmotic pressure, photoluminescence and catalytic properties.…”

The impact of the competitive adsorption of ions at surface sites on surface free energies and surface forces

“…It follows that ion site competition may help explain the relatively rare observations of Hofmeister series at low concentrations. [57][58][59] Hofmeister effects are more commonly observed in high salt conditions above 0.1M.…”

Principles for the determination of the surface potential of charged particles in mixed electrolyte solutions

“…The electrical potential at the solid-liquid interface is a fundamental parameter of electrochemical properties. The surface potential (potential at the original plane of the diffuse layer) of charged particles is a critical parameter for research into the transport [1] and electrical properties [2] of colloidal particles, the interactions between ions and surface [3] and interactions between particles [4,5].…”