Natural Resources Research Institute Technical Report

Prepared for: Iron Range Resources and Rehabilitation BoardBentonite has been used by the taconite industry since commercialization of the process in the early 1950's. Although many alternate binders have been tested, including organic materials, bentonite still remains the preferred binder. Bentonite has the unique qualities that promote stable green balling conditions and provides acceptable strengths during drying, preheating, and contributes to the fired pellet strength at an acceptable cost. The incentive to consider other binders is based on such factors as improving the metallurgical properties of the pellets, decreasing their silica content, and lower overall costs. The USBM conducted a number of small scale tests using papermill sludge and other additives in place of bentonite as a binder for taconite pellets. Their balling tests indicated that acceptable green-ball strength could be achieved with papermill sludge. The fired pellet evaluations, however, were based on muffle furnace tests which do not accurately predict the fired pellet quality. Although the fired pellet data were also encouraging it was recognized that pot-grate tests were needed to obtain more definitive test data that could be directly related to commercial practice. Subsequently, the USBM recommended that the IRRRB fund an extension of the program to include pot-grate tests to verify the fired pellet quality obtained in the muffle furnace work. A test program was prepared by the Coleraine Research Laboratory of the Natural Resources Research Institute (NRRI) in cooperation with Dr. J. Nigro and Dr. L. Haas, USBM, and Mr. S. Dickinson, IRRRB. The contract proposal was submitted to the IRRRB January 27, 1988. The contract included evaluation of concentrate and sludge filtering and blending aspects, green-ball quality, and fired pellet quality based on pot-grate tests. This report presents data on all three aspects as stated in the contract and conclusions regarding future efforts in this area.University of Minnesota Duluth, Natural Resources Research Institute, 5013 Miller Trunk Highway, Duluth, MN 55811-144