| Description |
Reverse flotation of silica from hematite is by far the most common strategy for the processing of iron ore containing silica gangue. In reverse flotation, quartz, the major impurity in the iron ore, is floated using ether amines, and iron oxide minerals are depressed using depressants such as starch. It is expected that improvement in grade and/or recovery may be possible from fundamental surface chemistry study of reverse flotation system for the processing of iron ore. Analysis of the wetting characteristics of hematite (Fe2O3) by contact angle, MDS, bubble attachment time and atomic force microscopy (AFM) surface force measurements show that the anhydrous hematite 001 surface is slightly hydrophobic at natural pH, in the absence of starch and other polysaccharides, with a contact angle of around 50. For alkaline pH, hydroxylation of the hematite surface occurs rapidly and the hematite becomes hydrophilic with a contact angle of 0⁰. In this regard the role of polysaccharides in reverse flotation is considered since hematite is already hydrophilic in alkaline pH solutions where reverse flotation is usually carried out. Contact angle, AFM and flocculation experiments suggest that the role of chemically adsorbed polysaccharides such as starch is to restrict the adsorption of amine at the hematite surface, hence preventing the creation of a hydrophobic surface state. It has been found that polysaccharides act both as a depressant and as a flocculant for fine hematite in the reverse flotation of iron ore. Also, in the present work, the depression of quartz at higher starch concentration has been investigated. Contact angle, bubble attachment time, quartz crystal microbalance with dissipation (QCM-D) and sum frequency vibrational spectroscopy (SFVS) measurements have been used to examine the interaction between mono ether amine and starch, and molecular dynamics simulation (MDS) was used to visualize the interaction between the amine and starch molecules. On the basis of these measurements it appears that a clathrate interaction takes place in such a way that the starch masks the hydrophobic tail of the mono ether amine, decreasing the contact angle at the quartz surface to 62° from 43° in the presence of excess starch. This research provides more understanding of the role of polysaccharides in the reverse flotation of iron ore. These findings should provide a foundation for improved operation in the reverse flotation of iron ore as it will help reduce reagent consumption and identify better operating conditions for improved grade and for recovery. |
