磷矿及磷肥中氧化钙测定方法改进

Improvement of Determination Method of Calcium Oxide in Phosphate Rock and Phosphate Fertilizer

为了解决磷矿及磷肥中氧化钙酸溶不完全和消除测定过程中磷酸根、镁、铁等的干扰,对磷矿和磷肥中氧化钙的测定方法进行改进。对不同酸溶解体系选择、酸用量、加热时间、干扰掩蔽实验、pH值等条件进行实验,确定采用10 mL王水、3 mL氢氟酸分解试样,加入2 mL盐酸溶解盐类,加入10 mL糊精和5 mL三乙醇胺溶液掩蔽Mg^2+、Fe^3+、PO4^3-、Al^3+的干扰,无需过滤,在pH≈7时预加EDTA至溶液清亮,再加入KOH调节溶液pH>13,加入适量的钙黄绿素指示剂,用EDTA溶液滴定至绿色荧光消失,测定磷矿和磷肥中氧化钙。实验结果表明,三个磷矿石标准样品和磷肥监控样氧化钙测定的相对标准偏差(RSD,n=11)为0.21%~1.1%。实际磷矿和磷肥样品中氧化钙测定值与国家标准方法测定结果一致。

In order to solve the incomplete dissolution of calcium oxide in phosphate rock and phosphate fertilizer,and eliminate the interference of phosphate,magnesium and iron in the determination process,the determination method of calcium oxide in phosphate rock and phosphate fertilizer was improved in this paper.Condition experiments such as selection of different acid dissolution systems,acid dosage,heating time,interference masking experiment,and pH value were carried out.The experiment was established that 10 mL of aqua regia and 3 mL of hydrofluoric acid were used for decomposition,2 mL of hydrochloric acid was added to dissolve salts,10 mL of dextrin and 5 mL of triethanolamine solution were added to mask the interference of Mg^2+,Fe^3+,PO43-and Al^3+.The extract does not need to be filtered.EDTA was pre-added to clear solution at pH≈7 and KOH was added to adjust solution pH>13.Then an appropriate amount of calcein indicator was added,and titrated with EDTA until the green fluorescence disappears.Finally,calcium oxide in phosphate rock and phosphate fertilizer is obtained.The experimental results showed that the relative standard deviation(RSD,n=11)of calcium oxide in three phosphate rock standard samples and phosphate fertilizer monitoring samples were in the range of 0.21%—1.1%.The measured value of calcium oxide in actual phosphate rock and phosphate fertilizer samples were consistent with that of the national standard method.