Dissertation
Dissertation > Industrial Technology > Mining Engineering > Beneficiation > Metallic Ore Dressing > Black Metallic Ore Dressing

Study on the Process and Mechanism of Effective Beneficiation of Superfine Low Grade Hematite

Author ChunTieJun
Tutor ZhuDeQing;PanJian
School Central South University
Course Iron and steel metallurgy
Keywords superfine low grade hematite preliminarily upgrading direct reduction intensity magnetic separation grain growth
CLC TD951
Type Master's thesis
Year 2010
Downloads 208
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With the rapid development of iron and steel industry in China, the demand for imported iron ores has been greatly growing all over the country. In 2009,the import of iron ores was 628 Million tons and the dependence degree had increased to 69.2%.However, large quantities of low grade iron resources are not utilized by conventional beneficiation methods because of low grade iron, main valuable mineral hematite occurring at superfine size and disseminated with gangue minerals.It is significantly important to the development of China iron and steel industry to take the technology of preliminarily upgrade-direct reduction-intensity magnetic separation to treat those resources in the background of the price of iron ores increasing and the reserves of iron resources decreasing in China.In this paper, the process and mechanism of effective beneficiation on the superfine low grade hematite from Lianyuan steel have been studied.The results show that the final iron concentrate,assaying 88.31% Fe and 94.45% metallization degree was obtained at the iron overall recovery of 69.92% under the conditions of grinding fineness of reduced product at 89.20% passing 0.043mm and magnetic separation at 0.08T field intensity, and the reduced product was achieved under the conditions of rough concentrate at 12% with calcium containing complex additive,reducing for 120min at 1200℃and 2.5 coal-to-pellets mass ratio, and the rough concentrate under the conditions of pH=9.4, 100g/t starch,200g/t dodecylamine and grinding fineness of 88.72% passing 0.074mm of 27.23%Fe ROM ores.The results show that the calcium containing complex additive play an important role in enhancing the metallization degree of reduced product, the iron grade and recovery of the final iron concentrate.The isothermal reduction kinetics of pellets was studied. The results show that the reduction rate of pellets without additive and pellets with calcium containing complex additive are controlled by internal diffusion when the reduction temperature ranges from 900 to 1050℃,and reduction lasts for 120min in CO/N2=30/70 atmosphere.However, the calcium containing complex additive decreased the apparent activation energy of the pellets from 18.10 KJ-mol"1 to 10.15 KJ·mol-1, dropping 43.92% in reducing. The lower the apparent activation energy, the easier the reduction reaction takes place. So the reduction properties of pellets with calcium containing complex additives are better than that of pellets without additive.The kinetics of metal ferrous grains growth of pellets without additive and pellets with calcium containing complex additive were studied. The results show that the rate constant of grains growth of pellets without additive and pellets with calcium containing complex additive are 1.155(μm)2·min-1 and 1.397(μm)2·min-1 when reducing at 1000℃to 1200℃for 5min to 120min. The apparent activation energy of metal ferrous grains growth of pellets without additive is 132.53 KJ·mol-1,more than that of pellets with calcium containing complex additive with 93.27 KJ·mol-1.The calcium containing complex additive can effectively improve the growth of the metal ferrous grains.In reduction, the calcium containing complex additive can produce metal ferrous nucleus in the induction period, inducing the metal ferrous grains around nucleus diffusion and movement to the nucleus.In growing period, the metal ferrous grains move to the nucleus, producing the bigger size of metal ferrous grains.The lattice defects are improving and the lattice structures are tending to stability in the steady period. The growth of metal ferrous grains can effectively promote the iron grains liberated in milling, decreasing the cost of milling, upgrading the iron degree and the recovery of concentrate.

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