Observation of the Unusual Aggregation Kinetics of Colloidal Minerals in Acidic Solutions

Abstract

Hofmeister (Specific ion) effects have been considered as important to chemical science as Mendel's work was to genetics. In this work, the aggregation kinetics of montmorillonite colloids in H + , Ag + , NH + 4 , K + and Na + solutions were measured in situ, detecting the unusual kinetics and ion specificity for H + . Activation energies that can quantitatively estimate the underlying specific ion effects change in the order of H + < Ag + < NH + 4 < K + < Na + . Meanwhile, it was found that although the aggregation of montmorillonite colloids with lower particle densities results in higher activation energies, Hofmeister series will not be affected. It was sufficiently testified that interaction energies of colloidal particles with adsorbed ions show fine correlation with activation energies for colloidal aggregation, and larger interaction energy corresponds to lower activation energy. An attempt was made to quantitatively estimate the ion specificity for H + , and it was substantialized that the unusual ion specificity of H + is caused by steric effect.

Adsorption of Ions at the Interface of Clay Minerals and Aqueous Solutions

“…As a matter of fact, ion-specific effects occur ubiquitously and play a vital role during a wide range of interfacial processes of clay minerals and salt solutions, and a number of these processes can be associated closely with the adsorption processes. We have clearly demonstrated the presence of Hofmeister series for both metal ions [12,[22][23][24] and anions [14,16] during the adsorption of ions onto clay minerals and the resulting aggregation of clay minerals; in addition, mechanism of ion-specific effects was explored and for metal ions, it can be ascribed to the difference of polarization effects responding to the electric field of colloidal particles [12].…”

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

“…Similarly, along with the concentration for 2:1 electrolyte solutions (Cu(NO 3 ) 2 , Mg(NO 3 ) 2 and Ca(NO 3 ) 2 ) increased from 1 to 2 mmol/L, the value ofṽ(Cu 2+ )/ṽ(Mg 2+ ),ṽ(Cu 2+ )/ṽ(Ca 2+ ) and v(Ca 2+ )/ṽ(Mg 2+ ) declined sharply from 433 to 2.11, 5.86 to 1.12 and 73.9 to 1.89, respectively (figure 3b).…”

“…1,2 According to the Derjaguin, Landau, Verwey and Overbeek (DLVO) theory, the aggregation processes of the charged colloidal particles are determined by the competition between long-range van der Waals force and electrostatic repulsion force, where the electrostatic repulsion force is dominated by the electrostatic field strength in the diffuse layer. The magnitude of the electric field strength in the diffuse layer are influenced by valence and concentration of the adsorbed counter-ions, ions with equal valence and concentration which would therefore exhibit identical capacity in precipitating charged colloidal minerals; this is in contradiction with our experimental observations that diverse aggregation kinetics were detected for different cation species.…”

“…Therefore, the present work aims to reveal Hofmeister effects on aggregation processes of negatively charged colloidal minerals at relatively low ionic concentrations and clarify the underlying impact of electric field around particle surface on Hofmeister effects. The aggregation kinetics were measured in the presence of various nitrate solutions (NaNO 3 , KNO 3 , NH 4 NO 3 , Ca(NO 3 ) 2 , Mg(NO 3 ) 2 and Cu(NO 3 ) 2 ) with different concentrations by the dynamic light scattering method. We found that pronounced Hofmeister effects were exhibited in colloidal mineral particles aggregation at dilute cationic concentration (<100 mmol/L) and electric field surrounding particle surface profoundly affected Hofmeister effects in aggregation of colloidal minerals.…”

Aggregation kinetics of binary systems containing kaolinite and Pseudomonas putida induced by different 1:1 electrolytes: specific ion effects

“…However, Tian et al (2014) observed more pronounced specific ion effects at lower electrolyte concentrations, which obviously cannot be explained by the ionic dispersion forces. A series of studies on the effects of ion interfacial reaction on colloidal particle aggregation have been carried out (Du et al, 2017;Gao et al, 2014;Hu et al, 2015;Li et al, 2015;Liu et al, 2014;Tian et al, 2015;Xu et al, 2015). They suggested that the strong non-classical polarization, which was caused by the strong electric field formed by the surface charge of clay minerals in water system, could give a rational explanation for specific ion effects on mineral colloids aggregation.…”