Flotation surface chemistry of water-soluble salt minerals: from experimental results to new perspectives

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

HYPOTHESIS

Ion-specific forces in concentrated salt solutions play critical roles in many applications, ranging from biology to engineering, e.g., separating water-soluble minerals in brines by flotation using air bubbles. There should be some differences in colloidal forces between the surfactant precipitates in brines and NaCl crystals, and KCl crystals, making their selective aggregation and flotation separation possible.

EXPERIMENTS

Micron-sized spheres of fatty acid colloids were successfully prepared using lead laurate, characterized, and used to fabricate the AFM probes. Using a special AFM cell design and procedure, interaction force spectroscopy and force mapping on NaCl and KCl crystal surfaces using the probes were performed in their brines (7 M) and quantified using numerical solutions of advanced van der Waals and electrical double-layer theories to reveal valuable distributions of attractive, repulsive, and adhesive colloidal forces between the surfactant colloids and salt crystals.

FINDINGS

Attraction and adhesion between the lead laurate colloidal probe and the NaCl crystal surface were much stronger than those measured on the KCl crystal surface, explaining the selective separation between NaCl and KCl crystals by flotation in the brines. Theoretical analysis of the measured forces shows the potential role of ion-specific interactions in predicting selective aggregation and flotation separation. Our work provides an innovative approach to quantifying the intermolecular interactions between surfactant colloids and NaCl and KCl crystals, offering new theories on colloid and surface chemistry regarding ion-specific forces that underpin aggregation and separation in brines and beyond.

Crucial roles of ion-specific effects in the flotation of water-soluble KCl and NaCl crystals with fatty acid salts

HYPOTHESIS

Flotation of water-soluble KCl and NaCl minerals in brines is significant for K-fertilizer production, but its mechanism is controversial. Dissolved salt ions are expected to change the physicochemical properties of solvents, interfaces, and collector colloids, thereby affecting flotation significantly.

EXPERIMENTS

Flotation experiments of KCl and NaCl crystals in brines were conducted using potassium and sodium laurates as collectors. Contact angle (CA) and surface tension measurements, X-ray photoelectron spectroscopy (XPS) analysis, and molecular dynamics simulations (MD) were applied to gain a molecular understanding of changing interfacial properties and crystal-collector colloid interactions in the presence of dissolved ions in terms of salt flotation.

FINDINGS

While K⁺ ions activate the NaCl crystal flotation, Na⁺ ions depress the KCl crystal flotation, in agreement with the studies of CA, XPS, and MD results with these crystals. XPS results showed no collector adsorption at crystal surfaces which is a requirement of conventional flotation and presents a new theoretical challenge. We argue the crucial role of ion specificity: Na-laurate colloids adsorb at the bubble surface as a monolayer but solvent-separated from KCl crystals, inhibiting their flotation, or in interactive contact with NaCl crystals, enhancing their flotation. Increasing K⁺ concentration weakens NaCl crystal hydration, increasing Na-laurate colloid attraction with crystals for better flotation. The Contact Interactive Collector Colloid (CICC) and Solvent-separated Interactive Collector Colloid (SICC) hydration states are critical to salt crystal flotation via collector colloid-crystal attraction by dispersion forces.

Improvements in Visual Aspects and Chemical, Techno-Functional and Rheological Characteristics of Cricket Powder (Gryllus bimaculatus) by Solvent Treatment for Food Utilization

This study aimed to improve the visual aspects and chemical, techno-functional and rheological characteristics of Gryllus bimaculatus cricket powder through the use of different solvents, with the objective of using it as a protein source in food production. Four treatments (pH 5 aqueous solution, ethanol 20%, ethanol 99.5%, and hexane) were applied to the powder, and analyses were conducted to assess changes in the previously mentioned parameters. The results showed that the treatments led to an increase in protein concentration (from 55.4 to 72.5%) and a decrease in fat concentration (from 33.0 to 6.8%) in ethanol 99.5% treated powder, as well as a reduction in anti-nutritional compounds concentration, such as tannins (from 13.3 to 5.9 g/kg), in pH 5 treated powder, which is important for the nutritional value of the final product. The color of the powders was improved, being lighter after hexane and ethanol 99.5% treatments due to the removal of melanin with the defatting process. Flowability, water, and oil holding capacity were also improved in the defatted powders. All the results suggest that the main composition of the powder directly influences the analyzed parameters. These findings suggest that cricket powder treated with solvents can be used as a protein source in different food applications.