Beneficiation of Mishdovan Andalosite (Bafgh District) for Mullitization Purpose

Andalosite group minerals are the most suitable materials for refractories, which are mainly applied in furnace lines. Since these materials are currently used predominantly in alominosilicats refractories, then recognition and extraction of andalosite deposits, their processing studies and mullitization are important. In this research, the feasibility of the processing and mullitization of Mishdovan Andalosite ore were investigated. Semi-detail exploratory studies related to the Mishdovan ore have already been done in 2000 with more than 1.6 Mt reserve and 20% Al2O3 content. The primary samples were divided into two fractions based on crushing and thin section studies. In order to increase the Al2O3 content for 150 -355 µm fractions, the gravitational method (vibrating table) and for 75-150 µm fractions, the flotation method were employed. Also the Fe2O3 content was decreased to less than 1% by employing high intensity magnetic separator. Consequently, using of the mentioned techniques, it is possible to produce a concentrate with 56% Al2O3 content, which is suitable for mullitization. The mullitization process was studied at different temperatures (1400 – 1600 °C), periods of time (1- 3.5 hours) and grain sizes. Phase evolution was studied by XRD diffraction. Morphology, distribution and size of the grains were analyzed by means of SEM. The obtained results showed that the complete transformation of Andalosite group minerals to mullite takes place between 1500 – 1550 °C during 2hr for the grain size of 38 microns. At higher temperatures, the mullite grain revealed round and platelet morphology. Presence of the primary Corundum mineral in Andalosite sample caused a considerable decrease of the glass phase in the refractory.