碱熔-EDTA滴定法测定铬铁矿中钙和镁

用过氧化钠熔融分解试样,在强碱性条件下沉淀分离基体及铬、硅,控制溶液pH 6~7,用六次甲基四胺和铜试剂沉淀分离铁、铝、钛等干扰元素,再采用两种不同浓度的EDTA标准滴定溶液对滤液中的钙(以氧化钙计)和镁(以氧化镁计)分别进行滴定,建立了测定铬铁矿中钙和镁的方法。采用电感耦合等离子体原子发射光谱法(ICP-AES)对沉淀法分离铬后滤液中的钙进行了测定,结果表明,滤液中钙含量与样品中钙含量相比可忽略不计。干扰试验表明,试样中的共存元素均不干扰测定。按照实验方法对GTK-1铬铁矿样品、GBW 07820GCr-3铬铁矿标准物质和GSBD 33001-94铬铁矿标准物质中钙和镁进行测定,测定值与认定值一致,结果的相对标准偏差(RSD,n=8)在0.25%～4.9%之间,方法的极差在GB/T 24221-2009规定的允许差范围内。

Determination of calcium and magnesium in chromite by alkali fusion-EDTA titration

The sample was decomposed by sodium peroxide fusion method. The matrix, chromium and silicon were separated by precipitation under strongly alkaline conditions. Then, the pH of solution was controlled to 6-7 to precipitate and separate interference elements (such as iron, aluminum and titanium) by hexamethylenetetramine and copper reagent. The calcium (in calcium oxide) and magnesium (in magnesium oxide) in filtrate were titrated using EDTA standard titration solution with two different concentrations. The determination method of calcium and magnesium in chromite was established. The content of calcium in filtrate after separating chromium by precipitation method was determined by inductively coupled plasma atomic emission spectrometry. The results showed that the content of calcium in filtrate could be ignored compared with the content of calcium in sample. The interference test indicated that the coexisting elements in sample did not interfere with the determination. The calcium and magnesium in GTK-1 chromite sample, GBW 07820GCr-3 chromite standard substance and GSBD 33001-94 chromite standard substance were determined according to the experimental method. The found results were consistent with the certified values. The relative standard deviations (RSD, n=8) were between 0.25% and 4.9%. The range of method was allowable according to the specification in GB/T 24221-2009.