氟碳铈矿除Ca、Si制备脱硝催化剂及其脱硝性能的研究

Research on Preparation of Denitration Catalyst by Removal of Ca and Si from Bastnaesite and its Denitration Performance

包头混合稀土精矿是氟碳铈矿(CeCO_(3)F)和独居石(CePO_(4))的共生矿物,结构复杂,难以分解,且Ca、Si杂质嵌布在矿物表面,影响了稀土矿物的脱硝活性,因此在使用天然矿物作为催化剂之前,有必要对其进行除杂预处理。采用酸浸固氟焙烧方案将氟碳铈矿制成脱硝催化剂,具体工艺为:第一步,HCl除Ca,HCl浓度为6mol/L,氟碳铈矿与NaCl(固氟剂)质量比为1∶5,混合并搅拌12h后于500℃下焙烧2h;第二步,HF除Si,HF浓度为13mol/L,除Ca后粉末与NaCl质量比为1∶5,混合并搅拌12h后于500°C下焙烧2h。氟碳铈矿除Ca、Si后制备的催化剂中Ca含量降至1.85%,Si含量降至0.17%,稀土元素含量相比原矿提高了约22%。氟碳铈矿除Ca、Si后,表面形成了发达的孔结构,比表面积增大,活性元素增多,且部分Ce的价态由+3价转变为+4价,还形成了晶格氧,这些组织结构的变化为催化剂脱硝过程提供了更多的氧化还原中心,使得催化剂脱硝性能显著提高。因此,用除杂后的氟碳铈矿作脱硝催化剂比直接用天然矿物具有更大的优势。

Baotou mixed rare earth concentrate is a paragenetic mineral of bastnaesite(CeCO_(3)F)and mona-zite(CePO_(4)),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.