Hydrophilic Modification of Macroscopically Hydrophobic Mineral Talc and Its Specific Application in Flotation

Sodium diethyldithiocarbamate (DDTC), a common collector used to enhance the hydrophobicity of minerals in froth flotation, nevertheless weakens the hydrophobicity of the talc surface. To rationalize this anomaly, the interactions of a hydrophobic alkyl group and hydrophilic mineralophilic group (-NCS₂^-) of heteropolar surfactant DDTC, and a water molecule with the talc (001) surface, were investigated. Herein, DFT simulations found that the talc (001) surface features natural hydrophobicity determined by the competition between adhesion (surface water) and cohesion (water-water interactions). The interaction of the hydrophobic alkyl group of DDTC with the talc surface is more favorable compared to that of the -NCS₂^- group and H₂O, favoring the hydrophilic modification of the talc surface. Additionally, adsorption isotherms, time-of-flight secondary ion mass spectrometry (ToF-SIMS), microflotation tests, and contact angle measurements also indicate that the differences in adsorption orientation of the heteropolar surfactant DDTC on the talc surface enhance the hydrophilicity of the talc surface, leading to a decreased recovery of the talc. This study provides crucial surface chemistry evidence for the selective adsorption of heteropolar surfactants and contributes to the understanding of the mechanism for the efficient flotation separation of molybdenite from talc.