基于单因素结合Box-Behnken法的钨酸铵蒸发结晶提纯

Purification of Ammonium Tungstate via Evaporation Crystallization Based on Single Factor Combined with Box-Behnken Method

摘要:

采用单因素+Box-Behnken响应曲面法对钨酸铵溶液蒸发结晶法除杂工艺进行优化，以制备更高纯度的仲钨酸铵（APT）。首先，以降低APT中4种杂质（Na、K、S、Mo元素）总含量为出发点，利用单因素法初步确定结晶温度、搅拌线速度、钨酸铵溶液初始浓度的优选范围。其次，通过Box-Behnken响应曲面法对APT的蒸发结晶除杂工艺进一步优化，研究3种因素对APT中4种杂质总量的相互影响规律。结果表明，3种因素对4种杂质总量的影响顺序为：钨酸铵溶液初始浓度>蒸发温度>搅拌线速度；较佳工艺条件为蒸发温度94 ℃，搅拌线速度1.25 m/s，钨酸铵溶液初始浓度73 g/L。该实验条件下，制备所得APT 4种杂质总含量降低至39.351 mg/L，与响应曲面法模型的最优预测值的相对误差仅为4.110%，APT纯度达到4N；生成的APT晶体为伴生有少量碎晶的柱状长方体形貌，层状结构明显，粒径分布均匀，晶粒细化明显。

Abstract:

A combination of single factor and Box-Behnken response surface method was employed to optimize the impurity removal process during the evaporation crystallization of ammonium tungstate solution to prepare ammonium paratungstate (APT) with higher purity. Firstly, to reduce the total content of four impurities (Na, K, S and Mo) in APT, the preferred range of crystallization temperature, stirring speed and initial concentration of ammonium tungstate solution was preliminarily determined by single factor method. Secondly, the impurity removal process during the evaporation crystallization of APT was further optimized by Box-Behnken response surface method, and the interactive effects of three factors on the total amount of four impurities in APT was studied. The results show that the order of influence of three factors on the total content of four impurities is as follows: initial concentration of ammonium tungstate solution>evaporation temperature>stirring speed. The optimum process conditions are an evaporation temperature of 94 ℃, a stirring speed of 1.25 m/s, and an initial ammonium tungstate concentration of 73 g/L. Under the experimental conditions, the total content of four impurities in the prepared APT is reduced to 39.351 mg/L, which corresponds to a relative error of merely 4.110% compared to the optimal prediction value of the response surface method model. Consequently, the purity of APT reaches 4N level. The generated APT crystal is a columnar cuboid morphology with a small amount of broken crystals. The layered structure is obvious, the particle size distribution is uniform, and the grain refinement is obvious.