Investigations of mechanism of Ca2+ adsorption on silica and alumina based on Ca-ISE monitoring, potentiometric titration, electrokinetic measurements and surface complexation modeling

Abstract

Research on Ca2+ adsorption onto the mineral surface is of significant importance with regard to geochemical processes. Sverjensky (Geochim Cosmochim Acta 70(10), 2427–2453, 2006) assumed that alkaline earths form two types of surface species on oxides: tetranuclear (> SOH)2(> SO−)2_M(OH)+ and mononuclear > SO−_M(OH)+. To look into the above assumption we investigated calcium adsorption on SiO2 and Al2O3 because they are the most widespread minerals in the environment. We have determined the proton surface charge, electrokinetic potential and metal adsorption as a function of pH. The Ca2+ uptake and concentration in the system were monitored by the calcium ion-selective electrode (Ca-ISE). The Ca-ISE measurements indicated a similar affinity of Ca2+ for both materials despite their differently charged surface, negative for silica and mainly positive for alumina. This may suggest that simple electrostatic interactions are not the primary driving force for calcium adsorption, and that solvation of calcium ions at the surface may be crucial. We have analyzed our experimental data using the 2-pK triple-layer model (2-pK TLM). Three calcium complexes on the mineral surface were reported. Two of them were the same for both oxides, i.e. the tetranuclear ($$>$$ > SOH)2($$>$$ > SO−)2_Ca2+ and mononuclear complexes > SO−_CaOH+. Additionally, minor contribution from >SOH…Ca2+ for silica was assumed. In the case of Al2O3 the hydrolyzed tetranuclear complexes ($$>$$ > SOH)2($$>$$ > SO−)2_CaOH+ at pH > 7.5 occurred based on the modeling results. Two types of surface complexes suggested by Sverjensky allowed for the correct description of proton and calcium uptake for alumina. However, the electrokinetic data excluded hydrolyzed tetranuclear surface species for this oxide.

Study on electrical double layer nanostructure on zeolitic materials’ surface in the presence of impurities of different nature

“…At pH equal or higher than 8.5, the zeta potential tends to increase in the systems containing zinc(II) ions. This is due to the overloading of the electrical double layer, i.e., charge reversal (Szymanek et al 2021). This phenomenon is related to the presence of more counterions within the inner part of the electrical double layer than on the surface of the solid.…”

A charge-free and membrane-free hybrid capacitive mixing system for salinity gradient energy harvesting

“…18,20 According to Gouy–Chapman–Stern model, 16,20,22,41 the diffuse layer potential ( φ d ) can be expressed as a function of the surface charge density ( σ ) of the electrode and the electrolyte concentration ( c ):where L , ε 0 , ε r , k , T , e and N A are the EDL effective thickness, the electric constant, the relative dielectric constant, Boltzmann constant, absolute temperature, electron charge and Avogadro constant, respectively. We used acid–base potentiometric titration 42–47 to determine the surface charge density of EDA-YP80F. Fig.…”

“…where L, 3 0 , 3 r , k, T, e and N A are the EDL effective thickness, the electric constant, the relative dielectric constant, Boltzmann constant, absolute temperature, electron charge and Avogadro constant, respectively. We used acid-base potentiometric titration [42][43][44][45][46][47] to determine the surface charge density of EDA-YP80F. Fig.…”

Influence of Charge Regulation on the Performance of Shock Electrodialysis

“…In this work, we considered the case of nonadsorbing ions in a shock ED process. However, it would be interesting to extend this modeling study to a feed with multivalent cations, since they are known to adsorb onto silica, 20,36 as well as mixtures. This could have large implications on the charge density of the porous medium, which is relevant to theoretically describe the behavior of shock ED process with complex feed streams, such as the recent experimental work of Alkhadra et al 6 ■ ASSOCIATED CONTENT * sı Supporting Information…”