Reaction characteristics of carbon-bearing pellets of Bayan Obo lean iron ores in a static magnetic field

The use of low-grade,refractory and composite paragenetic mineral resources is necessary for overcoming the shortage of iron ore resources in China.As a solution to the treatment of such iron ores,the direct reduction of carbon-bearing pellets can ensure complete iron removal and the effective enrichment of other high-value elements.Thus,this technology enjoys a broad application prospect.However,there are several problems with low-temperature reduction,such as low iron ore reaction efficiency,long reaction time,and high energy consumption.To improve the low-temperature carbothermic reduction efficiency of iron ores,a static magnetic field with magnetic induction intensity of 1.0 T was introduced.An isothermal reduction experiment was conducted at 1223 K to study the low-temperature self-reduction characteristics of carbon-bearing pellets of Bayan Obo lean iron ores in the static magnetic field.Also,the acting mechanism of the magnetic field was explored from the perspective of the reduction process,reaction efficiency,phase composition,microstructure changes,and dynamic behavior of iron ores.The results showed that the magnetic field can increase the low-temperature reduction rate of carbon-bearing pellets of Bayan Obo lean iron ores.Under the conditions of reduction temperature of 1223 K,magnetic induction intensity of 1.0 T,and reduction time of 60 min,the reduction degree was 92.42%,1.65 times that without a magnetic field.The magnetic field promoted the replacement of Ca^(2+)and Fe^(2+),so that the hard-to-reduce iron-bearing silicates were reduced in the order of Fe2SiO_(4)→(Ca,Na)FeSiO_(4)→FeO→Fe.The magnetic field enabled loose minerals,more pores and cracks,and changes in the growth morphology and distribution position of metallic iron.Compared with the case under the non-magnetic condition,the metallic iron precipitated from the slag phase in a foliated shape,separated from the matrix iron oxides,and grew up at the junction of the slag phase and coke.The magnetic field significantly increased the interfacial chemical reaction rate of the carbothermic reduction of iron ores and reduced the internal diffusion resistance of gas in the product layer.Specifically,the interfacial chemical reaction rate increased by 138%and the internal diffusion coefficient increased by 309%.Therefore,the effect of the magnetic field on the internal diffusion resistance was the main cause for strengthening the low-temperature reduction of iron ores.

Reduction of Carbon-bearing Pellets of Oolitic Hematite in a Shaft Furnace

When carbon-bearing pellets of oolitic hematite are treated in a shaft furnace,some problems are typically encountered：the metallization ratio of the metal pellets is low;the carbon-bearing pellets bond with each other at high temperatures;and the separation of phosphorus from iron is difficult.To solve these problems,experiments were conducted on oolitic hematite reduction in a resistance furnace and semi-industrial test shaft furnace.The results showed that the metallization rate reached 90% or greater under the conditions of a reduction temperature of 1 150℃,an atmosphere of simulated flue gas,and a reduction time between 1.5and 2.0h.The problem of high-temperature bonding among pellets can be solved by increasing the strength of the pellets,coating their surface with a surface transfer agent and maintaining an even temperature inside the shaft furnace.The basicity of the ore blend exerted no obvious effect on the magnetic concentrate and phosphorus content.The phosphorus content in the magnetic concentrate can be further reduced by improving the grinding capacity of the ball mills used in the experiments.On the basis of the experimental results related to oolitic hematite reduction with carbon-bearing pellets in a shaft furnace,the experimental requirements were satisfied with an average 88.27%total Fe content and 0.581% P content in the pellets.

Experimental study on smelting reduction of carbon-bearing manganese briquettes in slag bath

The reduction of carbon-bearing manganese briquettes in a slag bath was experimentally investigated at temperatures ranging from 1550 to 1650 ℃. Both the internal temperature and the microstructure evolution of the briquettes were analyzed by differential thermal analysis, scanning electron microscopy and energy-dispersive spectrum analysis, and the smelting reduction mechanism of the carbon-bearing manganese briquettes in the slag bath was further elaborated. The results indicated that the smelting reduction of the briquettes in the slag bath could be divided into three stages, and the aggregation and growth of the metallic particles during the reduction were significantly affected by the slag temperature. Under the experimental conditions, the reduction speed at the initial stage of the carbon-bearing manganese briquettes smelting reduction was controlled by the chemical reaction, whereas the reaction speeds at both the middle and following stages were limited by gaseous diffusion.

Effects of gangue compositions on reduction process of carbonbearing iron ore pellets

The influence of gangue compositions (mainly composed of SiO2,CaO,MgO and Al2O3)on the reduction kinetics of carbon-bearing iron ore pellets was estimated at 1373-1473 K in N2 atmosphere.The results showed that gangue content and each component distribution affected the pellets reduction process.The reduction rate was found to follow a linear correlation with quaternary basicity R4 [mass ratio of (CaO +MgO)to (SIO2 +Al2O3)]of the carbon-beating iron ore pellets;also,the content of SiO2 solid solution in iron oxide had a significant impact on the reduction rate.At the same reduction temperature,a higher R4 resulted in a lower SiO2 free content,weakening its inhibitory effect on the Boudouard reaction.The reduction temperature of Fe2SiO4 could be reduced by increasing the contents of CaO and MgO,improving the iron oxide reduction as well as the precipitation and growth of the iron grains.The g'angue content and .component distribution showed no effect on the rate-controlling step of the reduction;however,the apparent activation energy of reaction decreased with increasing quaternary basicity.When R4 increased from 0.15 to 0.67,the apparent activation energy decreased from 228.51 to 193.66 kJ/mol.