Baotou mixed rare earth concentrate is a paragenetic mineral of bastnaesite(CeCO3F)and mona-zite(CePO4),with a complex structure that is difficult to decompose.Ca and Si impurities are embedded on the surface of the mineral,which affects the denitration activity of rare earth minerals.Consequently,it is essential to carry out impurity removal pretreatment before using natural minerals as catalysts.The spe-cific process for preparing denitrification catalysts from bastnaesite involves acid leaching,fluorine reten-tion and roasting,detailed as follows.In the first step,HCl is used to remove Ca,the concentrate of HCl is 6 mol/L and the mass ratio of bastnaesite to NaCl(fluorine retainer)is 1∶5.The mixture is stirred for 12 h before roasting at 500℃ for 2 h.In the second step,HF is employed to remove Si,with a concentra-tion of 13 mol/L.The mass ratio of Ca-removed powder to NaCl is 1∶5.The mixture is stirred for 12 h and subsequently roasted at 500℃ for 2 h.The Ca content in the catalysts prepared with Ca and Si-re-moved bastnaesite is reduced to 1.85%,while Si content decreases to 0.17%.Additionally,the concentra-tion of rare earth elements is increased by 22%compared with the raw ore.The removal of Ca and Si from bastnaesite results in the formation of a well-developed pore structure,which increases the specific surface area and active elements.Furthermore,the valence of some Ce ions transitions from+3 to+4,and lattice oxygen is formed.These structural changes provide more redox centers for the denitration process of the catalyst,significantly improving its denitration performance.Therefore,using bastnaesite after the removal of impurities as denitration catalysts has more advantages than directly using natural minerals.
关键词
氟碳铈矿/除杂/Ca/Si/酸浸/固氟/焙烧/脱硝催化剂
Key words
bastnaesite/removal of impurities/Ca/Si/acid leaching/fluorine retention/roasting/denitration catalyst
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