Detecting ion-specific forces between fatty acid colloids and salt crystals in brines using colloidal probe AFM

Area of Science:

• Colloid and Surface Chemistry
• Physical Chemistry
• Materials Science

Background:

• Ion-specific forces in concentrated salt solutions are crucial for applications in biology and engineering.
• Selective separation of minerals from brines, such as by flotation, relies on differences in colloidal interactions.

Purpose of the Study:

• To investigate and quantify the differences in colloidal forces between surfactant precipitates and NaCl vs. KCl crystals in concentrated brines.
• To elucidate the role of ion-specific interactions in enabling selective aggregation and flotation separation.

Main Methods:

• Fabrication of atomic force microscopy (AFM) probes using micron-sized lead laurate colloidal spheres.
• Performance of interaction force spectroscopy and force mapping on NaCl and KCl crystal surfaces in 7 M brines using AFM.
• Quantification of colloidal forces using numerical solutions of van der Waals and electrical double-layer theories.

Main Results:

• Significantly stronger attraction and adhesion were observed between the lead laurate colloidal probe and NaCl crystals compared to KCl crystals.
• These force differences explain the observed selective flotation separation of NaCl from KCl in brines.
• Theoretical analysis indicated the potential role of ion-specific interactions in predicting separation outcomes.

Conclusions:

• The study provides an innovative method for quantifying intermolecular interactions between surfactant colloids and salt crystals in brines.
• Findings offer new insights into colloid and surface chemistry concerning ion-specific forces governing aggregation and separation.
• The results support the selective separation of NaCl and KCl via flotation based on distinct colloidal forces.