间接碘量法测定稀土硫化物中硫

试验提出了一种用间接碘量法测定稀土硫化物中硫含量的方法:稀土硫化物易与盐酸反应生成硫化氢,而硫化氢气体易和碘反应,故用已知浓度和用量的碘标准溶液完全吸收硫化氢气体,再用已知浓度的硫代硫酸钠标准溶液滴定出未反应的碘标准溶液,从而间接计算出稀土硫化物中硫含量。通过溶剂的选择、碘标准溶液用量及反应摇动时间的研究,确定了适宜的反应条件。结果表明,在稀土硫化物中硫质量分数为10%～25%时的最佳反应条件是:用盐酸作为反应溶剂,0.1 mol/L碘标准溶液用量为35 mL,反应开始至滴定前的剧烈摇动时间为2 min。采用实验方法对稀土硫化物中具有代表性的Ce₂S₃、Sm₂S₃及La₂S₃这3种样品中的硫进行了测定,结果的相对标准偏差(RSD,n=11)小于1%。测定结果与高频红外吸收法及硫酸钡重量法的测定值基本相符。

Determination of sulfur in rare earth sulfides by indirect iodometry

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.