Flotation of halite and sylvite from carnallite with dodecyl morpholine

Carnallite recovery by reverse flotation of halite with dodecyl morpholine (DDM) as collector has been applied in industry. Despite successful use in industry, the surface chemistry for halite flotation with DDM collector is not clear. Therefore the major objective of this thesis research was to examine the flotation chemistry in detail and understand the nature of the interaction between the DDM collector and the soluble salt minerals, halite (NaCl), sylvite (KCl), and carnallite (KMgCl3.6H2O). After the introduction in Chapter 1, the flotation response of halite, sylvite and carnallite is reported as evaluated using microflotation. The results indicate that both NaCl and KCl can be floated using DDM as a collector from saturated solution. However, flotation of carnallite was not achieved at these or higher concentrations. FTIR analysis by the DRIFT technique showed that DDM selectively adsorbed at the surface of NaCl and KCl. In Chapter 3, the chemical features of dodecyl morpholine were evaluated by surface tension measurements for halite-, sylvite-, and carnallite-saturated solutions. The precipitation concentration was determined by turbidity measurements. In addition, the zeta potential of the collector colloid was also determined at different pH values. In Chapter 4, the wetting characteristics for NaCl, KCl and carnallite are reported. Contact-angle measurements as a function of DDM concentration indicate that, when the DDM concentration increased to 2 x 10-6 M, an increase in contact angle was observed at the surface of NaCl and KCl. Bubble attachment-time experiments indicate that there is a critical concentration at which effective attachment occurs. In Chapter 5, initial efforts to study the interfacial water structure using molecular dynamic simulation (MDS) are described. The simulation results indicate that the carnallite surface was completely hydrated. Therefore, the collector molecules or the collector colloid cannot replace interfacial water molecules at the surface of carnallite, and the carnallite particles remain hydrophilic during flotation with DDM. The water residence time at the NaCl surface, about 30 ps, is longer than the water residence time of 20 ps at the KCl surface but very small when compared with that of carnallite. The water resi¬dence time at the carnallite surface is longer than the simulation time of the water/carnallite system (1000 ps). This appears to be the major reason that carnallite cannot be floated using DDM or DDA as collector for that matter.