Oolitic hematite is an iron ore resource with rich reserves,complex composition,low grade,fine disseminated particle sizes,and a unique oolitic structure.In this study,a microwave-assisted suspension magnetization roa...Oolitic hematite is an iron ore resource with rich reserves,complex composition,low grade,fine disseminated particle sizes,and a unique oolitic structure.In this study,a microwave-assisted suspension magnetization roasting technology was proposed to recover and utilize the ore.The results showed that under the conditions of microwave pretreatment temperature of 1050℃ for 2 min,a magnetic concentrate with an iron grade of 58.72%at a recovery of 89.32%was obtained by microwave suspension magnetization roasting and magnetic separation.Moreover,compared with the no microwave pretreatment case,the iron grade and recovery increased by 3.17%and 1.58%,respectively.Microwave pretreatment increased the saturation magnetization of the roasted products from 24.974 to 39.236(A∙m^(2))/kg and the saturation susceptibility from 0.179×10^(−3) m^(3)/kg to 0.283×10^(−3) m^(3)/kg.Microcracks were formed between the iron and gangue minerals,and they gradually extended to the core of oolite with the increase in the pretreatment time.The reducing gas diffused from outside to inside along the microcracks,which promoted the selective transformation of the weak magnetic hematite into the strong magnetic magnetite.展开更多
Rare-earth(RE)rich intermetallics crystallizing in orthorhombic Ho_(6)Co_(2)Ga-type crystal structure exhibit peculiar magnetic properties that are not widely reported for their magnetic ordering,order of magnetic pha...Rare-earth(RE)rich intermetallics crystallizing in orthorhombic Ho_(6)Co_(2)Ga-type crystal structure exhibit peculiar magnetic properties that are not widely reported for their magnetic ordering,order of magnetic phase transition,and related magnetocaloric behavior.By tuning the type of RE element in RE_(6)Co_(2)Ga(RE=Ho,Dy or Gd)compounds,metamagnetic anti-to-paramagnetic(AF to PM)phase transitions could be tuned to ferro-to-paramagnetic(FM to PM)phase transitions.Furthermore,the FM ground state for Gd_(6)Co_(2)Ga is confirmed by density functional theory calculations in addition to experimental observations.The field dependence magnetocaloric and Banerjee’s criteria demonstrate that Ho_(6)Co_(2)Ga and Dy_(6)Co_(2)Ga undergo a first-order phase transition in addition to a second-order phase transition,whereas only the latter is observed for Gd_(6)Co_(2)Ga.The two extreme alloys of the series,Ho_(6)Co_(2)Ga and Gd_(6)Co_(2)Ga,show maximum isothermal entropy change(|ΔS_(iso)^(max)(5T)|)of 10.1 and 9.1 J kg^(-1)K^(-1)at 26 and 75 K,close to H_(2)and N_(2)liquefaction,respectively.This outstanding magnetocaloric effect performance makes the RE6 Co_(2)Ga series of potential for cryogenic magnetic refrigeration applications.展开更多
基金Projects(51874071,51734005,52104257)supported by the National Natural Science Foundation of ChinaProject(161045)supported by the Fok Ying Tung Education Foundation for Yong Teachers in the Higher Education Institutions of China。
文摘Oolitic hematite is an iron ore resource with rich reserves,complex composition,low grade,fine disseminated particle sizes,and a unique oolitic structure.In this study,a microwave-assisted suspension magnetization roasting technology was proposed to recover and utilize the ore.The results showed that under the conditions of microwave pretreatment temperature of 1050℃ for 2 min,a magnetic concentrate with an iron grade of 58.72%at a recovery of 89.32%was obtained by microwave suspension magnetization roasting and magnetic separation.Moreover,compared with the no microwave pretreatment case,the iron grade and recovery increased by 3.17%and 1.58%,respectively.Microwave pretreatment increased the saturation magnetization of the roasted products from 24.974 to 39.236(A∙m^(2))/kg and the saturation susceptibility from 0.179×10^(−3) m^(3)/kg to 0.283×10^(−3) m^(3)/kg.Microcracks were formed between the iron and gangue minerals,and they gradually extended to the core of oolite with the increase in the pretreatment time.The reducing gas diffused from outside to inside along the microcracks,which promoted the selective transformation of the weak magnetic hematite into the strong magnetic magnetite.
基金the National Natural Science Foundation of China(52071197)the Science and Technology Commission of Shanghai Municipality(19ZR1418300 and 19DZ2270200)+3 种基金AEI/FEDER-UE(PID2019-105720RB-I00)US/JUNTA/FEDER-UE(US-1260179)Consejería de Economía,Conocimiento,Empresas y Universidad de la Junta de Andalucía(P18-RT-746)the support provided by China Scholarship Council(CSC)of the Ministry of Education,China(202006890050)。
文摘Rare-earth(RE)rich intermetallics crystallizing in orthorhombic Ho_(6)Co_(2)Ga-type crystal structure exhibit peculiar magnetic properties that are not widely reported for their magnetic ordering,order of magnetic phase transition,and related magnetocaloric behavior.By tuning the type of RE element in RE_(6)Co_(2)Ga(RE=Ho,Dy or Gd)compounds,metamagnetic anti-to-paramagnetic(AF to PM)phase transitions could be tuned to ferro-to-paramagnetic(FM to PM)phase transitions.Furthermore,the FM ground state for Gd_(6)Co_(2)Ga is confirmed by density functional theory calculations in addition to experimental observations.The field dependence magnetocaloric and Banerjee’s criteria demonstrate that Ho_(6)Co_(2)Ga and Dy_(6)Co_(2)Ga undergo a first-order phase transition in addition to a second-order phase transition,whereas only the latter is observed for Gd_(6)Co_(2)Ga.The two extreme alloys of the series,Ho_(6)Co_(2)Ga and Gd_(6)Co_(2)Ga,show maximum isothermal entropy change(|ΔS_(iso)^(max)(5T)|)of 10.1 and 9.1 J kg^(-1)K^(-1)at 26 and 75 K,close to H_(2)and N_(2)liquefaction,respectively.This outstanding magnetocaloric effect performance makes the RE6 Co_(2)Ga series of potential for cryogenic magnetic refrigeration applications.
