Development of a Magnetite Content Analyzer for Iron Ore Pellets based on Magnetic Properties

摘要

This paper describes the development of an instrument for quick magnetite contents analysis in iron ore pellets through a non-destructive approach. Magnetite content affects the physical properties of pellets, such as cold crushing strength and tumbler index. Magnetite content in iron ore pellets may be increased during the induration stage of a pelletizing furnace by a reduction process that converts hematite into magnetite at high temperatures. In the mineral industry, conventional analysis techniques are mostly based on chemical methods. These methods are expensive and time-consuming, can expose people to chemical products and require a destructive sample preparation stage. Intervention in the process for correction is unfeasible due to the time required by chemical methods. The developed equipment performs an average content analysis of a pellets set with intact samples in a lower time interval than chemical tests. This paper analyzes samples by a mutual inductance principle according to the magnetic permeability of the pellets. The magnetic permeability of the pellets is highly influenced by the magnetite because magnetite has superior magnetic permeability compared with other components in the pellets. The structure of the equipment is similar to an electrical transformer, and the samples are inserted in a compartment between two coils. One coil generates an alternated magnetic flux that induces voltage on the other coil. The pellets modify the magnetic coupling between the coils, generating an induced voltage proportional to the samples magnetic permeability. This induced voltage is measured and converted by a calibration curve regarding magnetite contents. This paper presents the results obtained with iron ore pellets samples produced at the facility called Fabrica, Vale SA, Brazil. The results demonstrate a linear relationship between the induced voltage and magnetite content of the samples.