EDTA滴定法测定铝灰中金属铝

铝灰是炼钢重要辅助材料之一,不仅能吸附钢水夹杂物而提高钢水质量,而且其中的金属铝能起到脱氧作用,从而降低钢中气体含量、减少钢中夹杂、提高钢的洁净度及机械性能。因此,将铝灰中金属铝与三氧化二铝物相分离,准确测定金属铝含量具有重要意义。采用三氯化铁溶液在电磁搅拌下溶解试样,将金属铝和三氧化二铝分离,金属铝以离子形式转入溶液中,强碱分离溶液中铁、锰等干扰元素,用过量的EDTA络合Al ³⁺,在pH 4.5～5.5以二甲酚橙为指示剂,用锌标准溶液滴定过量的EDTA后,用F^-置换出与Al ³⁺络合的EDTA,再用锌标淮溶液滴定释放出的EDTA,从而计算出金属铝含量。实验表明,通过正交试验,确定了三氯化铁溶液的质量浓度(100g/L)、用量(100mL)、样品质量(0.500 0g)、搅拌时间(60min)等溶样条件。结果表明,测得结果的相对标准偏差(RSD,n=8)为0.45%～0.78%;回收率为96%～101%。方法满足金属铝质量分数范围在10%～30%之间的铝灰检测要求。

Determination of metallic aluminum in aluminum ash by EDTA titrimetry

Aluminum ash was one of important auxiliary materials for iron making. It could absorb the inclusions in molten steel to improve the quality. Moreover, the metallic aluminum in aluminum ash played the role of deoxidization, thus reducing the gas contents and inclusions in steel, and also improving the cleanliness and mechanical property of steel. Therefore, the phase separation of metallic aluminum and aluminum oxide in aluminum ash had important significance for the accurate determination of metallic aluminum content. The sample was dissolved with ferric trichloride solution under electromagnetic stirring to separate metallic aluminum and aluminum oxide. Metallic aluminum was transferred into the solution in the form of ions. The interference elements such as iron and manganese were separated from the solution by strong base. Al³⁺ was complexed with excessive EDTA, and the excessive EDTA was titrated with zinc standard solution at pH 4.5-5.5 using xylenol orange as the indicator. Then F^- was added to complex EDTA to replace Al³⁺, and the released EDTA was titrated with zinc standard solution. Consequently, the content of metallic aluminum could be calculated. The sample dissolution conditions were obtained by orthogonal test as follows: the mass concentration and dosage of ferric trichloride solution was 100g/L and 100mL, respectively; the mass of sample was 0.5000g; the stirring time was 60min. The results showed that the relative standard deviations (RSD, n=8) of determination results were between 0.45% and 0.78%. The recoveries were between 96% and 101%. The proposed method could meet the determination requirements of aluminum ash with metallic aluminum in range of 10%-30% (mass fraction).