ADU 两步沉淀工艺应用过程中一级沉淀的结晶问题研究

INVESTIGATION OF CRYSTALLIZATION OF FIRST PRECIPITATION DURING APPLICATION OF ADU TWOSTAGE PRECIPITATION PROCESS

对重铀酸铵（ＡＤＵ）两步沉淀工艺应用过程中产生一级沉淀结晶的原因、过程以及解决这一关键技术问题的方法进行了分析和讨论，进行了模拟试验、一级沉淀槽结构分析和改进研究、工艺试验及产品质量分析等工作。研究结果表明，一级沉淀的ｐＨ≥４．０和一级沉淀搅拌能力不足是产生一级沉淀结晶的２个主要原因。当一级沉淀ｐＨ＜４．０时，主要形成可溶性的α－ＵＯ２（ＯＨ）２络合物；ｐＨ＝４．０—７．５，主要形成难溶的β－ＵＯ２（ＯＨ）２晶体；ｐＨ＞７．５，主要形成ε－ＵＯ２（ＯＨ）２晶体。控制ｐＨ＜４．０和强化搅拌可消除一级沉淀结晶，粉末产品性能满足技术条件要求。

he paper analyzes the reasons and the processes for which crystallization occurs at the first precipitation during application of ADU twostage precipitation process and discusses the ways,the means and the measures by which this key technical problem is dissolved. Such work has been developed as analogue experiment, analysis of the first precipitator structure and improvement research, process test as well as product quality analysis. The results demonstrate that the two main reasons for which the crystallization takes place at the first level precipitation are pH value equal to or greater than 4.0 and insufficient stirring capability. For first precipitation, at pH<4.0, the soluble complex αUO2(OH)2 is generated, at pH=4.0—7.5, the difficultly solved crystal βUO2(OH)2 created and at pH>7.5, the crystal εUO2(OH)2 formed. Therefore, the crystallization at the first precipitation can be eliminated by controlling pH<4.0 and strengthening stirring, and the characteristics of powder products can meet the requirements of technical specification.