Selective Reduction of Niobium and Iron in Microwave Field
The reserves of niobium resources in Bayan Obo are abundant,but the niobium minerals in it have the characteristics of"multiple species,low grade,fine particle size and complex embedded relationships",as a result,in the traditional beneficiation pro-cess based on"iron and rare earth",niobium resources are scattered in all levels of beneficiation processes,and finally accumulated in tailings dams,with zero utilization rate.China is rich in non-coking coal resources,and the direct reduction technology does not de-pend on coke,eliminating the need for cooking equipment,and can also obtain high-grade iron concentrates.It is in line with Chinese resource utilization direction,and it is an effective method to deal with complex co-existing ores.However,the high reduction tempera-ture required by the direct reduction technology limits the selective reduction of valuable elements in the ore.Carbon can effectively ab-sorb microwaves.In the process of carbothermic direct reduction,microwaves are selected for heating,which can take advantage of the characteristics of bulk heating and selective heating of microwave heating to achieve rapid temperature rise.The coupling of microwave metallurgy technology and direct reduction technology can reduce the reaction temperature of direct reduction,speed up the reaction speed,and enhance the reduction ability.Based on this,this work proposed a new technology of"superconducting niobium separation-microwave iron removal-electrolytic niobium extraction"to deal with Bayan Obo tailings resources.Through the"permanent magnet-electromagnetic-superconducting"cascade magnetic separation technology and step-by-step flotation technology,the niobium was en-riched in the form of niobium-rich ore.Under the action of external field strengthening,the selective reduction of niobium-rich ore was carried out to remove iron to further realize the enrichment of niobium in niobium-rich ore.Finally,the selective reduction characteris-tics of electrochemical metallurgy were used to extract niobium in the form of ferroniobium alloy.In this paper,the low-temperature carbothermic reduction experiment of Bayan Obo tailings was carried out in the microwave field,optimize process parameters,achieve selective reduction of niobium and iron.The results showed that microwave could reduce the temperature of carbothermic reduction of Bayan Obo tailings and speed up the metallization rate.And with the increase of temperature,the prolongation of holding time and the acceleration of heating rate,the metallization rate of tailings increased.The reduction behavior of niobium minerals was related to the content and intercalation in the minerals.In the region rich in CaO and CaF2,iron niobate underwent the mineral phase transformation of FeNb2O6→Nb2O5→CaNb2O6→Ca2Nb2O6F;calcium niobate underwent the mineral phase transformation of CaNb2O6→Ca2Nb2O7→Ca2Nb2O6F.When total iron content of minerals(TFe)=10.60％and the temperature was less than 1100 ℃,niobium minerals could not be reduced by C,and were mainly distributed in the slag phase in the form of Ca2Nb2O6F;When TFe=29.20％,niobium minerals were reduced to NbO2 and NbC by C at 1000 ℃,and were closely adhered to Fe and FeS.The conditions for selective reduction of niobium and iron in microwave field were reduction temperature of 900 ℃,holding time of 40 min,heating rate of 30 ℃·min-1,the metalliza-tion rate of niobium tailings in Bayan Obo was 93.07％,and niobium minerals were not reduced,which could achieve selective reduc-tion of iron and niobium.
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