Abstract：A determination method of sulfur content in rare earth sulfides by indirect iodometry was proposed. The rare earth sulfides reacted with hydrochloric acid to form hydrogen sulfide, which could then react with iodine. The generated hydrogen sulfide gas was fully absorbed by iodine standard solution with known concentration and dosage. Then, the content of sulfur in rare earth sulfides could be indirectly calculated. The proper reaction conditions were obtained by the selection of solvents, the dosage of iodine standard solution and the shaking time of reaction. The results indicated that the optimal reaction conditions for the determination of 10%-25% (mass fraction) sulfur in rare earth sulfides were listed as follows: the hydrochloric acid was used as reaction reagent; the dosage of 0.1 mol/L iodine standard solution was 35 mL; the vigorous shaking time from reaction starting to titration was 2 min. The proposed method was applied to the determination of sulfur in three representative rare earth sulfide samples (Ce2S3, Sm2S3 and La2S3). The relative standard deviations (RSD, n=11) were less than 1%. The found results were consistent with those obtained by high frequency infrared absorption method and barium sulfate gravimetric method.
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