Variation in feed quality from day to day, shift to shift, even from dragline to dragline, represents a challenge to beneficiation plant operators and reagent suppliers. The overall goal of this project is to conduct a characterization study that involves as many samples as possible to cover such variations. The studies included fatty acid flotation to identify good and bad feeds, mineralogical characterization, encapsulation/ liberation determinations, heavy liquid separation as a diagnostic tool, and surface chemistry investigations.
Important ore characteristics were investigated using X-ray microtomography (XMT) to address encapsulation/liberation issues, including liberation-limited grade/recovery curves obtained for each sample. The liberation-limited grade recovery curve represents a boundary for separation efficiency. The grade and recovery for any actual separation cannot exceed the limit imposed by this curve. In the best case, the actual grade and recovery would fall on the curve and under these circumstances improved separation can only be achieved with further liberation by size reduction. If the grade and recovery for an actual separation falls below the curve, then the separation efficiency is limited by other factors (surface composition, slime coating, etc.) in addition to liberation limitations.
In addition to XMT, scanning electron microscopy (SEM), surface area measurements, energy dispersive spectroscopy (EDS) and X-ray photon spectroscopy (XPS), optical microscopy, infrared (FTIR), electrokinetics and adsorption measurements were used to address mineralogy, the chemical composition of particle surfaces and the surface properties controlling collector/phosphate interactions.
The obtained results are used to explain the flotation results in bench-scale Denver flotation cell experiments and important factors controlling the flotation response were identified. Even though there are reasons specific to some samples, general reasons have been identified that could explain the poor flotation behavior. In general, the flotation behavior is controlled by the differences in the physical and/or the surface chemical characteristics of the phosphate particles. For example, poor flotation could be attributed to one or more of the following characteristics:
- Encapsulation of phosphate particles in a thin or thick silica shell
- Heavy contamination of phosphate particles with contaminants like clay, gypsum, aluminosilicates, dolomite etc.
- The presence of phosphate as coarse and/or porous particles in the bad feed samples
- The presence of species such as silanol groups on the phosphate surface hindering adsorption of the collector
Examples of these characteristics of some bad samples (poor flotation behavior) and good samples are discussed in Volume I. Most importantly, a laboratory protocol has been developed to be used by the plant operators to diagnose the problem whenever a bad recovery feed is encountered. Such diagnostic tests will help the operators to take appropriate actions to deal with such problems.
More details about the studies dealing with many samples are reported by different team members: University of Florida in collaboration with ArrMaz Custom Chemicals and R Squared S Inc. (Volume II), University of Utah (Volume III), and Somasundaran Inc. (Volume IV).
Effect of Particle Characteristics on Fatty Acid Flotation of Florida Phosphate Rock.
FIPR Publication No. 02-173-236
Volume I: Project Summary
Volume III: Phosphate Encapsulation/Liberation Studies
Volume IV: Fundamental Studies
Hassan El-Shall, University of Florida with J.D. Miller, University of Utah; P. Somasundaran, Somasundaran, Inc.; R. Stana, R Squared S, Lakeland, FL; G. Wang, ArrMaz Custom Chemicals. April 2010.