磷酸二氢钾结晶的影响因素研究

Research on influencing factors of crystallization of potassium dihydrogen phosphate

采用间歇实验法研究了pH、降温速率等条件和铁(Ⅲ)、氟杂质对磷酸二氢钾结晶过程的影响。结果表明:在pH为3.0时,结晶析出温度和结晶析出量均最大,随着pH增加,颗粒聚集明显,表观粒径增大;随着降温速率的增大,结晶速度逐渐增大,晶体平均粒径减小,介稳区宽度逐渐增大,结晶的成核级数为4;杂质铁(Ⅲ)对结晶影响显著,随着铁(Ⅲ)质量分数的增加,晶体的长径比明显增大,晶形由棱柱状变为针状,介稳区明显变宽,结晶诱导期明显延长;杂质氟对结晶影响较小,随着氟质量分数的增加,介稳区宽度变宽,单晶长径比减小,晶形由长柱状变为方柱状,最后变为短粗状;在有氟存在时,比溶液中只掺杂铁(Ⅲ)时所得晶体的长径比减小,但结晶改善的效果并不理想。实验结果对磷酸二氢钾的生产过程有指导意义。

The effects of pH value and cooling rate, Fe^3＋ and F- impurities on crystallization of potassium dihydrogen phosphate （KDP） were studied by the batch crystallization experiments. Results showed that： when the pH value was 3. 0, the precipitation of crystals and crystallization temperature were both the highest. With the increase of pH value,the particle aggregation was obvious and the apparent size of crystals increased. With the increase of cooling rate, the metastable zone width and crystallization rate gradually increased,the average size of the crystals evidently reduced and the crystal nucleation rate was 4. The Fe^3＋ impurity had significant effect on crystallization process ： the morphology changed from prism to spiculate, with the increase of Fe^3＋ impurity, and the crystal slenderness ratio, crystallization inducement time and the metastable zone width increased obviously as well. The impurity of F - had little effect on crystallization. With the increase of Fimpurity, the slenderness ratio decreased, the metastable zone width increased slowly, but the crystal shape was changed from long prism to tetragonal prism and turned to podgy prism finally. The slenderness ratio decreased more in the presence of F - than just doping Fe^3＋ into the solution, but the effect of improving the crystallization was not up to much. Nevertheless, the experiment results have significance to direct the production of KDP.