EDTA络合滴定法测定铁矿石中钙和镁

Determination of calcium and magnesium in iron ore by EDTA complexometric titration

在微氨性溶液中，采用硫化钠及铜试剂使铜、铅、锌、铁、钴、镍、锰、铬、镉、铋等生成硫化物沉淀和铜试剂内络盐沉淀与钙镁分离，然后以盐酸羟胺将微量的锰还原成低价消除其干扰，用三乙醇胺和L-半胱氨酸掩蔽残留的其他金属离子。在pH10氨水-氯化铵缓冲溶液中，以酸性铬蓝K-萘酚绿B为指示剂，用EDTA络合滴定法测定钙、镁合量；另在氢氧化钾溶液中，用钙试剂为指示剂，以EDTA络合滴定法测定钙量，用差减法计算镁的含量。该方法对铁矿石标准样品中的钙和镁进行多次测定，结果与认定值相符，相对标准偏差在0.99％—3.4％（n=6）之间，加标回收率在98％—101％之间。

In weak ammonia solution, sodium sulfide and cupral reacted with copper, lead, zinc, iron, cobalt, nickel, manganese, chromium, cadmium and bismuth to form a sulfide precipitatie and a eupral complex inner salt precipitate, realizing the separation of calcium and magnesium. Then, trace manganese was reduced to low valency by hydroxylamine hydrochloride to eliminate its interference, while other residual metal ions were masked by triethanolamine and L-cysteine. In ammonia water-ammonium chloride buffer solution at pHlO, total content of calcium and magnesium was determined by EDTA complexometric titration with acid chrome blue K-naphthol green B as the indicator. In addition, the content of calcium was determined by EDTA complexometrie titration with calcon as the indicator in potassium hydroxide solution. As a consequence, the content of magnesium could be calculated with difference subtraction method. Calcium and magnesium in iron ore standard sample were determined for many times by this method. The results were in agreement with the certified values, with the relative deviation of 0.99%-3.4%（n=6） and recovery of standard addition between 98%-101%.