Utilization of Ammonium Chloride as a Novel Selective Depressant in Reverse Flotation of Potassium Chloride

The separation of sylvite (KCl) and halite (NaCl), two main minerals in potash ores, is difficult because of the high ion concentration, fine particles of NaCl, and aggregation of KCl and NaCl in the saturated system. This study employed ammonium chloride (NH4Cl) as a new depressant and dodecyl morpholine as a collector in the reverse flotation process. The depressing mechanisms were studied by adsorption capacity experiments, infrared spectral analysis, and molecular dynamics simulations. The flotation tests showed that NaCl recovery increased to 97% after the addition of NH4Cl, while KCl recovery was reduced to <1%. Notably, NH4Cl not only acted as a selective KCl depressant, but also activated NaCl flotation. The FTIR measurements showed that NH4Cl was physically adsorbed onto the KCl and NaCl surfaces. Adsorption capacity experiments and molecular dynamics simulations confirmed more favorable NH4Cl adsorption on the KCl surface than on the NaCl surface. Moreover, the KCl mineral surface was more hydrophilic, while that of NaCl was more hydrophobic. Relative concentration analysis revealed that >90% ammonium and chloride ions were distributed 2–10 Å away from the KCl surface but were dispersed on the NaCl surface, indicating that NH4Cl exhibited stronger intermolecular interactions with KCl than with NaCl