Fragmentation mechanism of low-grade hematite ore in a high pressure grinding roll

The fragmentation mechanism of low-grade hematite ore in a high pressure grinding roll(HPGR) was studied based on the characteristics of comminuted products at different specific pressure levels. The major properties included the reduction ratio, liberation, specific surface energy, and specific surface area. The results showed that the fracture of low-grade hematite ore in HPGR was an interactive dynamic process in which the interaction between coarse particles of gangue minerals and fine particles of valuable minerals was alternately continuous with increased compactness and compacting strength of materials. Within a range of 2.8–4.4 N/mm^2, valuable minerals were crushed after preferentially absorbing energy, whereas gangue minerals were not completely crushed and only acted as an energy transfer medium. Within a range of 4.4–5.2 N/mm^2, gangue minerals were adequately crushed after absorbing the remaining energy, whereas preferentially crushed valuable minerals acted as an energy transfer medium. Within a range of 5.2–6.0 N/mm^2 range, the low-grade hematite ore was not further comminuted because of the "size effect" on the strength of materials, and the comminution effect of materials became stable.

Low-Energy Multi-Impact Fracture Resistance of Cross Rolled Low Chromium Cast Semi-Steel Containing Rare Earth Grinding Ball

The low-energy multi-impact fracture resistance of the cross rolled low chromium cast semi-steel containing RE grinding balls was studied. Moreover, its damage mode was analyzed by means of metallographic examination, scanning electron microscopic examination and drop ball test. The results show that it can obtain extractive impact fracture resistance after proper heat treatment. More advantages were obtained for the ball worked in the condition of low-imp ductility act. The main reasons are the function of RE and the change in morphology of eutectic carbide network.

Instability of roll nonlinear system with structural clearance in rolling process

The vibration instability of the nonlinear dynamic system of the rolls considering the structural clearance was theoretically investigated,which is caused by the roll assembly accuracy deviation in the hot rolling process.Firstly,the dynamic rolling force model was established based on the Wekbrod model under the influence of the roll grinding deviation and the stability of the deformation zone.Further,the horizontal and vertical direction coupling dynamic model of the work roll was established considering the structural clearance between the roll and mill frame.Then,the nonlinear dynamic equation was solved by the Runge-Kutta method.The simulation results show that the dynamic system presents the nonlinear vibration characteristics,which shows that the instability of the system is a slowly varying response process with the characteristics of self-excited vibration and forced vibration.Finally,the comparison results show the consistency between the simulation and the test.

Roasting Properties of Pellets With Iron Concentrate of Complex Mineral Composition

Investigation was conducted on roasting properties of pellets with an iron concentrate of complex mineral composition. The results indicated that the pellets of complex mineral composition concentrate required higher pre- heating temperature and longer preheating time than that of single magnetite concentrate. Therefore, it is difficult for preheated pellets to withstand the mechanical collision in the roasting process in rotary kiln. It was found that after the iron concentrate being subjected to high pressure roll grinding, the specific surface area reached 2 029. i cm2/g. Consequently, the preheating and roasting temperature of pellets were decreased by 70 and 50 ℃ and preheating and roasting time were decreased by 2 and 4 min, respectively. Meanwhile, the compression strength of preheated and roasted pellets were increased by 200 N for a pellet and 220 N for a pellet, respectively. The mechanism lied in that the increase of specific surface area activated thermal reaction and promoted formation of inter-grain bridge.

Synthesis,characterization and properties of organically compounded bentonite by molecular intercalation process

A new process for manufacturing organically compounded bentonite was devcloped successfully based on the organic intercalation andlayered structure of bentonitc.The main steps in the proposed process included wet sodium activation of bentonite ore,organic com-pounding and high-pressure roll grinding.The optimum procedure is recommended as follows:5 mass%of sodium carbonate powderand 30 wt.%water are added to activate the bentonite ore for 24 h to prepare activated bentonice;0.5 wt.%of organic molecules are adiedinto the activated bentonite for organic compounding for 12 h:then,the high-pressure rollgrinding is followed to treat the organicallycompounded bentonice;:and finally,drying and fine prinding are performed for prenaring the final organically compounded bentoniteprodiuct with 10 wt.%moisture and 98% passing 0.074 mm.The obtained organically compounded bentonite was characterized usingan X-ray diffractometer,a scanning electron microscope and anX-ray photoelectron spectrometer.To confirm the effect of organicallycompounded bentonite on green balls,the pelletizing tests were carried out.The rexsults showed that high-pressure roll grinding can notonly enhance the ability of the crystal layer to hold the combined water.but also strengthen the intercalation compounding of the organicadditive,which is beneficial for the formation of a fiber-interlaced structure of the organically compounded bentonite and improvesthe quality index of the bentonite itself.Also,the organically compounded bentonite is helpiul to improve the indexes of green balls.

Influence of Mechanical Activation on Acid Leaching Dephosphorization of High-phosphorus Iron Ore Concentrates

High pressure roll grinding（HPRG）and ball milling were compared to investigate the influence of mechanical activation on the acid leaching dephosphorization of a high-phosphorus iron ore concentrate,which was manufactured through magnetizing roasting-magnetic separation of high-phosphorus oolitic iron ores.The results indicated that when high-phosphorus iron ore concentrates containing 54.92 mass% iron and 0.76 mass% phosphorus were directly processed through acid leaching,iron ore concentrates containing 55.74mass%iron and 0.33mass%phosphorus with an iron recovery of 84.64%and dephosphorization of 63.79% were obtained.When high-phosphorus iron ore concentrates activated by ball milling were processed by acid leaching,iron ore concentrates containing56.03mass%iron and 0.21mass% phosphorus with an iron recovery of 85.65% and dephosphorization of 77.49%were obtained.Meanwhile,when high-phosphorus iron ore concentrates activated by HPRG were processed by acid leaching,iron ore concentrates containing 58.02mass%iron and 0.10mass% phosphorus were obtained,with the iron recovery reaching 88.42% and the dephosphorization rate reaching 88.99%.Mechanistic studies demonstrated that ball milling can reduce the particle size,demonstrating aprominent reunion phenomenon.In contrast,HPRG pretreatment contributes to the formation of more cracks within the particles and selective dissociation of iron and P bearing minerals,which can provide the favorable kinetic conditions to accelerate the solid-liquid reaction rate.As such,the crystal structure is destroyed and the surface energy of mineral particles is strengthened by mechanical activation,further strengthening the dephosphorization.