硫酸亚铁铵滴定法和高锰酸钾电位滴定法测定铝锰合金中锰

铝锰合金是炼钢用的元素添加剂和脱氧剂,对其中锰含量的准确测定能够更好地控制其产品质量。试料用王水溶解,在热的浓磷酸介质中,用高氯酸将锰(Ⅱ)氧化到锰(Ⅲ),以N-苯代氨基苯甲酸为指示剂,用硫酸亚铁铵标准溶液滴定锰(Ⅲ)至锰(Ⅱ),溶液颜色由紫色变为亮黄色,记为终点,建立了硫酸亚铁铵滴定法测定铝锰合金中锰的方法。在pH 6.0~7.0的焦磷酸钠介质中,采用复合式铂电极,用高锰酸钾标准溶液缓慢滴至电位突跃记为终点,建立了高锰酸钾电位滴定法测定铝锰合金中锰的方法。铝锰合金中常见的杂质元素铬、铜、铁、镁、钛、镍、硼、硅对两种方法的测定结果影响较小,可忽略。若存在钒和铈,在硫酸亚铁滴定法中需进行校正扣除。将两种方法用于铝锰合金样品分析,硫酸亚铁铵滴定法的相对标准偏差(RSD,n=11)为0.36%~0.50%,加标回收率为99.2%~100.8%。高锰酸钾电位滴定法的相对标准偏差(RSD,n=11)为0.39%~0.68%,加标回收率为99.2%~100.7%。选取AlMn20合金,采用标准方法GB/T 20975.7—2020进行方法验证,用F检验和t检验确定了两种方法都与标准方法有较好的一致性。

Determination of manganese in aluminium-manganese alloy by ferrous ammonium sulfate titration and potassium permanganate potentiometric titration

Aluminum-manganese alloy was an element additive and deoxidizer used in steelmaking. The accurate determination of manganese content in it was helpful to better control the quality of its products. After the sample was dissolved with aqua regia, manganese(Ⅱ) was oxidized to manganese (Ⅲ) with perchloric acid in the medium of hot concentrated phosphoric acid. Then, manganese (Ⅲ) was titrated to manganese (Ⅱ) by ferrous ammonium sulfate standard solution with N-phenylanthranilic acid as the indicator. The endpoint was achieved when the color of solution changed from purple to bright yellow. Thus, a determination method of manganese in aluminum-manganese alloy was established by ferrous ammonium sulfate titration. In the medium of sodium diphosphate solution at pH 6.0-7.0, the sample solution was slowly titrated with potassium permanganate standard solution. With the help of a composite platinum electrode, the endpoint was achieved when there was a potential jump. Thererfore, a determination method of manganese in aluminum-manganese alloy was established by potassium permanganate potentiometric titration. The common impurities in aluminum-manganese alloy such as chromium, copper, iron, magnesium, titanium, nickel, boron and silicon had little influence on the determination results of two methods, which could be ignored. If there were vanadium and cerium, the correction deduction should be conducted in ferrous ammonium sulfate titration. The two proposed methods was applied in analysis of aluminium-manganese alloy samples. The relative standard deviations (RSD,n=11) of ferrous ammonium sulfate titration were between 0.36% and 0.50%, and the recoveries of standard addition were between 99.2% and 100.8%. The relative standard deviations (RSD, n=11) of potassium permanganate potentiometric titration were between 0.39% and 0.68%, and the recoveries of standard addition were between 99.2% and 100.7%. The proposed methods were applied in determination of AlMn20 alloy, and the standard method GB/T 20975.7-2020 was used for method verification. Both F test and t test showed that the two methods had good consistency with the standard method.