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Effect of Iron Ore Concentrate Morphology on Pellet Quality of Gol-e-Gohar Concentrate

Abazarpoor, Armin | 2017

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  1. Type of Document: Ph.D. Dissertation
  2. Language: Farsi
  3. Document No: 49479 (07)
  4. University: Sharif University of Technology
  5. Department: Materials Science and Engineering
  6. Advisor(s): Halali, Mohammad
  7. Abstract:
  8. In this study, the effect of iron ore concentrate morphology on green pellet quality was studied. In order to produce concentrate with different morphology using ball mill, ball charge (20-40 %V), grinding time (30-50 min) and ball distribution (15 mm, 23 mm, 15+23 mm) was varied. It was deduced that increasing grinding time and ball charge would result in reduction of D80 but would increase Blaine number. The interaction parameters of ball distribution-grinding time and ball distribution-ball charge had significant effect on Blaine and D80. It was also observed that mixed level of ball distribution would lead to higher Blaine numbers. The equation obtained by CCD was verified by the analysis of variance and calculation of correlation coefficient relating the predicted and experimental values. Operational parameters considered for HPGR included feed moisture (6-8 Wt %), specific pressure (3-5 N/mm2) and roller speed (0.5-0.6 m/s). It was deduced that increasing specific pressure and decreasing roller speed would result in reduction of D80 but would increase Blaine number. The response surface is used to show visually the effect of variable parameters on responses. The equation obtained by RSM was verified by ANOVA and regression coefficient.The effect of grinding method on the particle size, specific surface area and particle shape of an iron ore concentrate has been studied using optimum pellet feed ground by ball mill and HPGR. It was found that for samples having equal Blaine numbers, the amount of fine particles produced in HPGR was higher than that produced in a ball mill (Average= 3%). There is a visible difference between laser and other two particle size methods due to difference in basics of used mechanisms and fine particle adherence to coarse ones. A higher surface area was observed from HPGR treatment in compare to ball mill, provided by a higher porosity, cracks, roughness and new surfaces. Also, BET value was higher than Blaine method owing to Blaine assumption. Shape factor of particles was determined using three descriptors: circularity, roughness, and aspect ratio. It was also observed that HPGR produced particles that were more elongated, less circular and rougher than those processed by ball mill. The impact of ball to particle and attrition mechanism are responsible for particle reduction in ball mill, leaded to circular and less rough particles. However, compression between rolls and abrasion is created size reduction in HPGR.At the end of study, the effect of particle morphology on green pellet quality was investigated. It was found that pellet quality improved by Blaine increase due to improvement in capillary force and higher surface interface. The drop number and green compression quality of green pellets for HPGR particle is higher than those ground in ball mill because of higher inter-lock particles mechanism. However, the amount of green pellet with suitable size for ball mill is higher than HPGR. By dual comparison between HPGR and ball mill, it was deduced that the more important reason for different result of two grinding method stands for particle shape (resulted in better mechanicl-interlock between particles) and amount of fine particle. Also, bentonite consumption rate was decreased using HPGR method
  9. Keywords:
  10. Morphology ; Design of Experiments Method(DOE) ; Grain Shape ; Ball Mill ; High Pressure Grinding Roll (HPGR) ; Blaine ; Green Pellet

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