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采用高温直接还原-磁选-(NH4)2SO4焙烧-水浴浸出的工艺流程,从低品位含稀土尾矿中提取稀土。主要考察了(NH4)2SO4配量,焙烧温度和焙烧时间等实验参数对La,Ce,Nd浸出率的影响。通过SEM-EDS,XRD和TG-DSC表征了尾矿经高温直接还原后稀土的赋存状态、不同温度(NH4)2SO4焙烧富稀土渣过程中的物相变化和浸出渣及浸出液烘干后析出晶的物相成分。结果表明:稀土尾矿经高温处理后分别得到了高品位铁精粉和富稀土渣。稀土元素主要以Ca2RE8(Si O4)6O2,CaRE2(Si O4)2硅酸盐形式存在。优化实验条件下,(NH4)2SO4与富稀土按8∶1混匀,400℃焙烧45 min,80℃热水浴浸出时间1 h,浸出液液固比10∶1,La,Ce,Nd浸出率分别为96.13%,98.88%,97.10%。经(NH4)2SO4焙烧处理后,稀土元素的最终产物变为可溶性的(NH4)RE(SO4)2和RE2(SO4)3,萤石部分转变为Ca SO4。
Rare earths were extracted from low-grade rare earth-bearing tailings by high temperature direct reduction-magnetic separation- (NH4) 2SO4 roasting-water bath leaching process. The effects of (NH4) 2SO4 dosage, calcination temperature and calcination time on the leaching rates of La, Ce and Nd were investigated. The occurrence state of the rare earths after the direct reduction of the tailings at high temperature was characterized by SEM-EDS, XRD and TG-DSC. The phase transformation and the leaching residue and the leaching solution were precipitated after drying at different temperatures (NH4) 2SO4 Crystal phase composition. The results show that high-grade iron concentrate and rare-earth-rich slag have been obtained after the high temperature treatment of rare earth tailings. The rare earth elements are mainly in the form of Ca2RE8 (SiO4) 6O2, CaRE2 (SiO4) 2 silicate. Under the optimal experimental conditions, the leaching rate of La, Ce and Nd was 10: 1, the ratio of (NH4) 2SO4 to rare earth rich was 8: 1, calcined at 400 ℃ for 45 min, leached at 80 ℃ for 1 h, Respectively, 96.13%, 98.88%, 97.10%. After (NH4) 2SO4 calcination, the final products of rare earth elements become soluble (NH4) RE (SO4) 2 and RE2 (SO4) 3, and the fluorite partially transforms into CaSO4.