Research On Processing Characteristic And Method Of High Phosphorus Oolitite Hematite

There are 3-4 billion tons of oolitic hematite ore reserves in western Hubei Province. Exploitation of these resources is a world class problem.The process mineralogy of oolitic hematite ores in western Hubei has been studied first in this dissertation. It is found that the major minerals in the ores are hematite, oolitic chlorite, and quartz, followed by limonite, mica, clay minerals and collophanite. The ore structures are mainly oolitic, stockwork, honeycomb, dominated by oolitic form. According to the core minerals, they can be divided into concentric ring structures with quartz as the core, oolitic chlorite as the core, collophanite as the core, limonite as the core, and oolitic chlorite-collophanite aggregates as the nucleus. Hematite interbeds with oolitic chlorite, quartz, clay and other gangue minerals as concentric rings. Most of the ring bands are very thin, and the ring boundaries are not smooth. These result in difficult dissociation of hematite from gangue minerals. Iron minerals existing in oolitic structure account for 75%, and the others existing in non-oolitic structure account for 25%.Gravity separation processes, including heavy liquid separation, jigging, chute separation, and tabling, have been investigated. For raw ore with iron content of 43%, the grades of iron concentrates obtained by gravity separation were usually lower than 51%. Some heavy products with iron grades above 54% had iron recoveries less than 36%. For high intensity magnetic separation, as the ore was crushed and ground to 95% of-0.045mm, the grade of iron concentrate could be increased to 54.20% Fe through roughing and cleaning, while iron recovery dropped to 36.31%. These iron concentrates had high phosphorus contents, generally 0.6% to 0.8%. In order to reduce phosphorus content, reverse flotation to remove phosphorus and high intensity magnetic separation to remove silicates were employed successively. Iron concentrate obtained had an iron content of 54.05% , and phosphorus content could be reduced to 0.20%. The iron recovery of iron concentrate was only 18.83%. In a word, for oolitic hematite ores with high phosphorus contents in western Hubei, qualified iron concentrates are hard to obtain using gravity separation, high intensity magnetic separation, and flotation processes. Generally, the grades of iron concentrates are below 55% Fe, and iron recoveries are also low. Magnetizing roasting using muffle furnace to convert hematite to magnetite has been investigated. For roasted ore with a grinding fineness of 85% below 0.045mm, iron concentrate with a production rate of 63.77%, iron content of 58.88%, phosphorus content of 0.712%, and iron recovery of 85.77% could be obtained by low intensity magnetic separation. As phosphorus content in this iron concentrate was high, iron concentrate with a production rate of 46.86%, iron content of 60.25%, phosphorus content of 0.31% , and iron recovery of 71.63% was obtained through dephosphorizing by reverse flotation. Comparative experiments were conducted to investigate the effects of dephosphorizing before roasting and dephosphorizing after roasting on the phosphorus contents of final iron concentrates. The results show that dephosphorizing before roasting was slightly better. Beneficiation indexes for magnetizing roasting-magnetic separation process were favorable, which indicates that iron minerals can be effectively recovered from oolitic hematite ores in western Hubei through magnetizing roasting-magnetic separation. However, effective industrial equipments for magnetizing roasting still need to be developed.Through the study and development of flash magnetizing roasting technology, expanded testing device has been built preliminarily. The raw ore was milled to-0.1mm. Then the ore powder was delivered into the reduction reactor after three stages of preheating in the cyclones. Hematite was almost completely transformed to magnetite in the reactor. Roasted ore was processed with low intensity magnetic separation, and iron concentrate with a production rate of 60.17%, iron grade of 58.32%, and iron recovery of 81.15% was obtained. The technical indexes of iron mineral concentration are excellent, which demonstrates that the roasting effect of flash magnetizing roasting equipment and technology is good, and conversion rate of hematite to magnetite is high.Finally, mechanism study has been conducted. The causes for oolitic hematite ores hard to be magnetized through roasting and solving approaches have been explained preliminarily.