The Effect of Fluorine and Chlorine on Fired Pellet Metallurgical Properties

To evaluate the effect of fluorine and chlorine on fired pellet metallurgical properties, specifically Reducibility (R40) and Low Temperature Disintegration (LTD). This will include the influence of halogenated process water for agglomeration and when applied to the surface of fired pellets for the purpose of pellet cooling, conveyor belt protection, and dust control.Several 5-gallon pails of fired acid pellets were collected from Minntac to be used in this project. Appropriate halogen-bearing reagents were also identified and located at the Coleraine Minerals Research Laboratory. The experimental plan, a 2^3 factorial with 2x replication and two center point trials, was also designed. Control factors include: chloride concentration of process water, chloride concentration of quench water, fluoride concentration of process water, fluoride concentration of quench water, and pellet temperature at time of quench. An infrared thermometer was purchased to be used to measure pellet temperature at quench. Execution of the test plan has been delayed due to limited technician availability.

Reducibility (R40) and Low Temperature Disintegration (LTD) are established metallurgical tests used to distinguish the quality of iron ore pellets for their performance in the blast furnace. Fired pellet quality has been historically influenced by chlorinated water when applied as dust control or cooling water. Process water containing high levels of chlorine has been shown to be detrimental to metallurgical properties when applied to the surface of cooled pellets. Quenching hot fired pellets for cooling or with conveyor belt protection water is known to degrade metallurgical properties due to the stresses created within the microstructure of the pellet. However, the impact of the chlorine levels in this water must be evaluated. The concentration of these halogens in process water used for agglomeration should also be included in this investigation for its effect on R40 and LTD.

Mini-pot and full pot-grate tests will be conducted to evaluate the effect of halogenated water to the balling process, as a dust control agent and as cooling water. Process water will be collected from Minntac and characterized for halogen content. CaCl, CaF2, HCl, and HF will be added to the water in small realistic quantities, and evaluated along with the process water collected from U.S. Steel Minntac and de-ionized water. A baseline test previously reported will be used as a baseline for comparison. Halogenated water will also be applied to pellets collected from the discharge of the furnace and compared to untreated pellets as well as stockpiled pellets for metallurgical quality. No work was done on this project for some time due to commitments of other projects. However, a new NRRI employee, Research Coordinator Kyle Bartholomew, has begun work on this project and will pursue future investigations.