自动电位滴定法测定工业氢氧化铝产品的纯度

氢氧化铝的纯度是工业氢氧化铝质量标准中重要的检测指标，建立一种准确的测定方法对工业氢氧化铝的质量控制具有重要意义。采用滴定法测定工业氢氧化铝产品的纯度时，Al³⁺易水解造成了Al³⁺的损失，且目视判断终点存在误差相对较大的问题，影响测定结果的准确度。通过控制前处理过程中溶液pH≤3,在pH≈3.0的乙酸-乙酸钠缓冲体系中，以EDTA络合Al³⁺,解决了Al³⁺水解易损失的问题；过量的EDTA以二甲酚橙为指示剂、用光度电极为指示电极，用氯化锌标准滴定溶液在590 nm波长下采用等步长滴定模式(MET)返滴定，建立了自动电位滴定法测定工业氢氧化铝产品纯度的方法。按照实验方法测定了阻燃剂氢氧化铝和水处理剂用氢氧化铝样品的纯度，测定结果的相对标准偏差(RSD,n=7)分别为0.06%和0.07%,结果与标准方法GB/T 4294—2010基本一致；测定阻燃剂氢氧化铝样品的加标回收率为99.66%～100.20%。

Determination of industrial aluminum hydroxide purity by automatic potentiometric titration

The purity of aluminum hydroxide is an important detection index in the quality standards of industrial aluminum hydroxide products. It is of great significance to establish an accurate determination method for the quality control of industrial aluminum hydroxide. During the determination of industrial aluminum hydroxide product purity by titration, the easy hydrolysis of Al³⁺ will cause its loss. Moreover, there is a relatively large error in visual judgment of the endpoint, which also affects the accuracy of determination results. The pH of solution in pretreatment was controlled to not more than 3. Al³⁺ were complexed with EDTA in acetic acid-sodium acetate buffer solution at pH≈3.0, which solved the loss problem of Al³⁺ due to hydrolysis. Excessive EDTA was back-titrated with zinc chloride standard titration solution at 590 nm by monotonic titration (MET) mode using xylenol orange as indicator and photometric electrode as indicating electrode. The method for the determination of industrial aluminum hydroxide product purity by automatic potentiometric titration was established. The purity of flame-retardant and water treatment agent samples of aluminum hydroxide were determined according to the experimental method. The relative standard deviations (RSD, n=7) of determination results were 0.06% and 0.07%, respectively. The found results were basically consistent with those obtained by national standard method of GB/T 4294-2010. The recoveries of flame-retardant sample of aluminum hydroxide were between 99.66% and 100.20%.