Abstract: As an important rare earth resource， sediments in the Indian Ocean basin have become an important way to guarantee the supply of rare earth in China. In order to explore the feasibility of the ultilization of the sediments in the Indian Ocean basin， the occurrence state of rare earth elements was characterized by means of MLA， chemical phase and SEM analysis ， and sulfuric acid was used as leaching reagent to investigate the effect of sulfuric acid concentration， ratio of liquid to solid， leaching temperature and time on the leaching rate of the rare elements. The purification of the leaching solution in the best condition was conducted by ammonia. The results showed that: ①sediment particles are extremely fine with a mean volumetric particle size of 4.47 μm， and mainly consist of clay， manganese oxide， quartz， feldspar， mica， chlorite and halite. Rare earth mainly occurs in apatite， accounting for 73.10%. ②The leaching efficiencies of La， Ce， Nd， Y， Gd， Dy and Er were 80.57%， 66.33%， 88.42%， 93.25%， 92.63%， 55.30% and 93.17%， respectively， under the best conditions of 2 mol/L H2SO4， ratio of liquid to solid of 7∶1， leaching temperature of 55 °C and leaching time of 120 min. ③The composition of rare earth leaching solution is complex， and the content of rare earth is low with only about 100 mg/L. Most of Al and Fe in the leaching solution was effectively removed when the pH of the leachate was controlled at 5.14 by adding ammonia water ， while the loss rate of rare earth was more than 30.85%. The research results is significant for the further development and ultilization of the deep-sea rare earth resources.

Key words: Indian Ocean, rare earths, occurrence state, leaching, purification