Bentonite binder effective strength (BESt) test for unfired iron ore pellets

Abstract

Iron ore pellets use bentonite clay as binder at dosages of from 0.5% to 1.0% of the moist iron ore concentrate weight. As a natural product, bentonite has variable water-absorption and binding properties depending on its source. Therefore, it is best to have a method for evaluating a given bentonite to determine how effective it would be before it is purchased for use to bind concentrate into pellets. Current tests of bentonite effectiveness include plate water absorption (PWA), methylene blue uptake, free swell, exchangeable cations and glycolated layer expansion. However, these tests have many disadvantages. First, they only measure the ability of a bentonite to expand, disperse or absorb, and they do not directly measure how well it will bond particles to form iron ore pellets. Second, most of the tests require up to 20 hours to perform. Bentonite only has a few minutes to interact within the concentrate before it is indurated (sintered). For this reason, these long-term tests may not reflect the true behavior of bentonite during iron ore pelletization. Third, the tests are tedious and the results are often inconsistent for different iron ore concentrates, laboratories and technicians. Fourth, some of the testing equipment is difficult to procure. Fifth, procedures are often difficult to standardize. In this paper, the binder effectiveness strength (BESt) test to evaluate binders for iron ore pellets is presented. This procedure directly measures the ability of bentonite to form interparticle bonds, requires only about two hours to complete, is simple and reproducible, and it uses readily available equipment that has been standardized for decades. In this paper, results are given that demonstrate that the BESt results correlate well with actual pelletization performance.