Study On Dephosphorization Technology For High Phosphorus Oolitic Hematite By Coal-based Direct Reduction

With continuous expansion of our country's steel industry scal, our country has exceeded Japan and become the largest country of importing iron ore in the world. The total import of iron ore is 150 million ton in 2003, 208 million ton in 2004, 275 million ton in 2005, 326 million ton in 2006, and predicted that total import in 2007 will get to 355 million ton. The total import of iron ore makes up more than half of our country's iron ore demand volume. The large increase of import iron ore price after 2005 has created tremendous pressure on the development of our country's steel industry. So, this situation actively demands advanced technology to exploit the domestic available iron ore maximatily, especially the complicated and refractory ore. These iron ore have been not used due to the restriction of current mineral beneficiation technology . The increase in degree of self-sufficiency, alleviate the pressure of import and the maintenance of stable, enough, high quality iron ore supply to protect the persistent and stable development of steel industry.There are 3,000million ton High phosphorus Oolitic Hematite in our country. The phosphorus content of this iron ore is high(0.4～1.0%), the ore grade is low(35～50%), the grain size of iron oxide is minimum(1～3μm) and separation is very difficult, so these iron ore have been not used significantly. The phosphorus in these iron ore presents in collophanite, and mixes with chamosite containing iron oxide, forming a oolite texture in concentricity and layer check. If don't change the Fe's occurrence mode , Fe would be ineffectively selected and phosphorus would be ineffectively removed.The research makes use of iron ore coal mixed pellet self-reduction under high temperature reducing the hematite to metallic iron. Metallic iron will accumulate and grow up under high temperature, destroying the oolite structure of the green ore, changing the Fe's occurrence mode, and then getting the extra-high grade concentrate by magnetic separation. So, how to make the iron grain reconstruct and grow up during direct reduction of High phosphorus Oolitic Hematite is the premise of separating between metallic iron and gangue with rich phosphorus. So, study on the grain growth characteristics of metallic phase in direct reduction of high phosphorus oolitic hematite is partial content of this research.The influence of slag basicity, C/O mole ratio and reduction temperature on metallic iron reduction and the grain growth have been studied. The laws of collophanite and apatite reduction by controlling slag basicity, C/O mole ratio and reduction temperature are also researched. Finally, attain effective separation between metallic iron and gangue by magnetic separation. And simultaneously, make more phosphorus stay at the gangue. Exploring a new way to use High phosphorus Oolitic Hematite with rich storage capacity in our country.The analysis of agglomerate's mineral phase structure shows that iron ore coal mixed pellets of High phosphorus Oolitic Hematite destroy the the oolite structure of the green ore after reduction under high temperature, making the iron grain reconstruct and grow up successfully through metallic iron diffusion and gathering, and this makes a premise for separation between metallic iron and gangue with rich phosphorus. The size of iron grain is determined to C/O mole ratio , reduction temperature, slag basicity, reduction time and other technology factors.The results show that it is practicable to treat High phosphorus Oolitic Hematite using iron ore coal mixed pellet, the iron yield can be obtained more than 85%, dephosphorization rate can be obtained more than 80%.