电位滴定法测定石灰中氧化钙和氧化镁

石灰以其优越的造渣性能而备受钢铁冶金行业青睐,石灰的主要成分为氧化钙和氧化镁,高效、准确测定石灰中氧化钙和氧化镁至关重要。采用国家标准GB/T 3286.1—2012中EDTA络合滴定法测定石灰中氧化钙和氧化镁,过程繁琐流程长,滴定终点通过肉眼判断容易产生视觉误差,因此不能满足冶炼过程工艺动态控制生产需求。实验使用盐酸溶解样品,在待测样品中加入三乙醇胺,掩蔽Fe³⁺、Al³⁺;加入糊精,抑制样品溶液中生成大量的氢氧化镁沉淀对Ca²⁺的吸附;用EDTA标准溶液在强碱介质下,电位滴定法测定氧化钙、氧化镁含量。对使用盐酸溶解石灰后的不溶物进行回收和不回收两种处理方法,并对氧化钙和氧化镁的测定结果进行t检验,结果无显著差异。按照实验方法测定3个石灰样品中氧化钙、氧化镁,结果的相对标准偏差(RSD,n=11)均小于0.5%。选择一批石灰试样,分别按照实验方法和GB/T 3286.1—2012测定氧化钙和氧化镁含量,两种方法测得的氧化钙和氧化镁差值分别小于±0.20%和±0.10%。通过电位突变来判断滴定终点,减少了人员判定滴定终点的视觉误差,能够满足冶炼过程工艺动态控制的测定需求。

Determination of calcium oxide and magnesium oxide in lime by potentiometric titration

Lime is favored by the iron and steel metallurgy industry for its superior slagging performance. The main components of lime are calcium oxide and magnesium oxide. It is very important to efficiently and accurately determine the contents of calcium oxide and magnesium oxide in lime. During the determination of calcium oxide and magnesium oxide in lime by complexometric titration method in national standard GB/T 3286.1-2012, the process is cumbersome and time-consuming. Moreover, the judgement of titration endpoint by eyes could easily cause visual error. Therefore, the method cannot meet the production requirements of dynamic process control in the smelting process. The sample was dissolved with hydrochloric acid. Triethanolamine was added into sample solution to mask the interference of Fe³⁺ and Al³⁺. Dextrin was added to inhibit the adsorption of calcium by a large amount of magnesium hydroxide precipitates in the sample solution. The contents of calcium oxide and magnesium oxide were determined by potentiometric titration using ethylenediaminetetraacetic acid (EDTA) standard solution in strong alkaline medium. Two treatment methods, i.e., recovering and not recovering the insoluble matter in the sample solution after dissolution with hydrochloric acid, were investigated, respectively. The t-test of determination results of calcium oxide and magnesium oxide was conducted, and it was found that there was no significant difference. The contents of calcium oxide and magnesium oxide in three lime samples were determined according to the experimental method. The relative standard deviations (RSD, n=11) of the results were all less than 0.5%. A batch of lime samples were selected for the determination of calcium oxide and magnesium oxide according to the method and GB/T 3286.1-2012, respectively. The differences of two methods were less than ±0.20% and ±0.10% for calcium and magnesium, respectively. The titration endpoint was judged by the potential jump, which could reduce the visual error of the personnel in judging the titration endpoint. The proposed method could meet the determination requirements of the dynamic control in smelting process.