Laboratory studies for improving green ball strength in bentonite-bonded magnetite concentrate pellets

The performance of bentonite binders in magnetite concentrate balling has been difficult to predict due to a lack of understanding of the binding mechanisms and of the effects of water chemistry. Results are presented that indicate that the most effective binding occurs when the bentonite platelets slide past one another to form sheet-like or fiber-like structures, which is produced by compressive shear mixing. It has also been determined that the effects of water chemistry on bentonite performance are much greater than had previously been believed. This is because the water retained in magnetite filter cake has been shown to have a considerably higher concentration of ions (particularly calcium and magnesium) than was present in the bulk solution, and these ions strongly impact the swelling behavior of the bentonite. Results showing the benefits of fiber development and showing the effects of the water chemistry are presented. By taking advantage of bentonite fiber development and dealing with the effects of water chemistry, the strength of bentonite-bonded magnetite concentrate pellets can be increased. These studies have brought to light a number of previously unsuspected effects, which are critically important for further improving the theories of bentonite-binding behavior. (C) 2003 Elsevier B.V. All rights reserved.