This thesis aims to make a comparison between two types of grinding media, Cylpebs and conventional forged steel balls. The effect of grinding media type on the particle size distribution and ‘up-front’ flotation performance has been examined.
Cylpebs are essentially slightly tapered cylindrical grinding media, with a length to diameter ratio of approximately unity. There are varying reports from Cylpebs suppliers as to the comparative performance of Cylpebs as grinding media.
Based on findings from previous testwork and literature review, the following hypothesis is proposed:
For a set P80 of 150μm, Cylpebs will provide a tighter particle size distribution relative to steel balls, leading to increased flotation recovery for a given concentrate grade.
A sample of chalcopyrite ore from the Mt. Isa Copper Concentrator was used to conduct comparative grind and flotation tests using the two forms of grinding media.
A standard Bond ball charge was scaled in order to simulate a seasoned mill charge of appropriate volume for The University of Queensland’s laboratory mill. Doering Cylpebs of similar size were used to construct three different Cylpeb charges. In order to determine to best basis for substitution, for each Cylpeb/ball size the following properties were matched:
· •Cylpeb charge A: Same mass;
· •Cylpeb charge B: Same surface area and
· •Cylpeb charge C: Same bulk volume.
Laboratory scale batch grind tests using the various mill charges were conducted at 15, 20, 25 and 30-minute grind times. The resulting particle size distribution from each media charge, at each grind time, was compared. It was found that for the short 15-minute grind time, the heavier the Cylpeb charge, the finer the particle size distribution produced. However, there was very little difference in the particle size distributions produced for the 20, 25 and 30-minute grind times.From the tests in this thesis, reverse flotation was found to be feasible for the separation of naturally hydrophobic minerals from a chalcopyrite concentrate.
This observation is thought to be due to the decrease in breakage rate with decreasing particle size.
Laboratory scale batch flotation tests were conducted on the products from the 20-minute batch grind. A 20-minute grind time was used in order to achieve flotation feed with an 80% passing size of 150 microns. Physical and chemical conditions were maintained constant between tests. There was found to be no change in the position of the grade-recovery curve, no change in the flotation kinetics and no change in the selectivity of the copper over the iron or silica present in the system. The experimental results concluded that there was no significant change in flotation performance from the two grinding media types.
The electrochemical potential (Eh) of the pulp was measured after a 20-minute laboratory grind. The pulp potential was found to be lower for the Cylpeb batch grind relative to the forged steel balls, indicating that more reducing conditions were created by the Cylpeb grinding media. It is well known that wet grinding using Fe based media creates reducing conditions within a ball mill. For successful adsorption of collector to the surface of chalcopyrite, the electrochemical potential (Eh) of the pulp must be elevated to +50 to +100mV (Johnson, 2002). It is recommended that further testwork be conducted to look in more detail at the electrochemical conditions created by the Cylpeb grinding media.