通过控制不同的条件,先在铝酸钠溶液中加入过量的碘,使碘分别与铝酸钠溶液中的硫离子、硫代硫酸根和亚硫酸根反应,再用硫代硫酸根标准溶液返滴定过量的碘,最后,通过差减法得到硫离子、硫代硫酸根和亚硫酸根各自的含量,从而建立了间接碘量法测定铝酸钠溶液中硫离子、硫代硫酸根和亚硫酸根的方法.同时,运用碘酸钾与碘化钾在中性条件下不发生化学反应而在酸性条件下可反应生成碘的特性,在中性条件下使用基准碘酸钾与过量碘化钾配制了碘标准溶液,在实际测试时,只需通过向样品溶液加酸及碘标准溶液即可得到定量的碘,避免了由碘性状不稳定所带来的含量变化问题.将实验方法应用于不同生产流程中铝酸钠溶液(高压溶出液、粗液、种分母液)进行测定,5次平行测定硫离子、硫代硫酸根和亚硫酸根结果的相对标准偏差分别为0.68%~0.82%、0.26%~0.44%、0.38%~0.74%.按照实验方法对3种合成铝酸钠标准溶液中硫离子、硫代硫酸根和亚硫酸根进行测定,测定值均和理论值相符.
Excessive iodine was added into sodium aluminate solution to react with S2-, S2O and SO by controlling the different conditions.Then, the excessive iodine was back-titrated using thiosulfate standard solution.Finally, the content of S2-, S2O and SO was obtained by subtraction method.Thus, the determination method of S2-, S2O and SO in sodium aluminate solution by indirect iodometry was established.KIO3 did not react with KI under neutral condition, but the reaction occurred under acidic condition to form iodine.According to this characteristic, the iodine standard solution was prepared using reference KIO3 and excessive KI under neutral condition.During testing, the quantitative iodine could be obtained by adding acid and iodine standard solution into the sample solution,which avoided the concentration changing problem of iodine due to the instability.The proposed method was applied to the determination of sodium aluminate solution (high-pressure stripping liquid, crude liquid, seeded liquor) during different production processes.The relative standard deviation (RSD, n=5) for S2-,S2O and SO was 0.68%-0.82%, 0.26%-0.44% and 0.38%-0.74%, respectively.The content of S2-,S2O and SOin three synthetic standard sodium aluminate solutions was measured by experimental method.The found results were consistent with the theoretical values.
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