二氧化硅对湿法磷酸中液相氟的脱除

Effect of silica on defluorination of wet process phosphoric acid

为充分回收利用湿法磷酸液相中的氟资源,以硫酸钾为脱氟剂,采用氟硅酸钾沉淀法回收利用湿法磷酸液相中的氟.首先比较了Ⅰ、Ⅱ、Ⅲ、Ⅳ型四种不同二氧化硅的脱氟性能,Ⅰ、Ⅱ型二氧化硅脱氟效果较差,Ⅲ、Ⅳ型二氧化硅活性较好,能有效提高脱氟率.然后实验采用Ⅳ型二氧化硅,研究二氧化硅和硫酸钾用量对反应的脱氟率、氟硅酸钾收率及反应选择性的影响,结果表明具有活性的二氧化硅具有良好的脱氟效果;二氧化硅和硫酸钾用量会显著影响反应的脱氟率和选择性,二氧化硅与氢氟酸的反应属于连串反应,反应先生成四氟化硅,然后生成氟硅酸.在二氧化硅和硫酸钾用量足够的情况下,氢氟酸几乎可以完全转化成氟硅酸钾沉淀,脱氟率可达79.59%.

To recover the fluorine effectively in the aqueous phase of wet-process phosphoric acid, the potassium sulfate was used as defluorination agent to transform the fluoride into potassium fluosilicate by the precipitation method. Firstly, by comparing the defluorination performance of four kinds of silicas, labeled as I, II, III and IV, the defluorination efficiency of I and II silica was poor, while III and IV had better activity and improved the defluorination performance effectively. Secondly, IV was chosen to study the effect of the dosage of silica and potassium sulfate on the defluorination efficiency, the yield of potassium fluorosilicate and the reaction selectivity. The results display that the activated silica obtains better defluorination efficien- cy, the dosage of silica and potassium sulfate clearly affects the defluorination efficiency and the selectivity, and the reaction between silica and hydrofluoric acid belongs to the consecutive reaction, in which tetrafluo- ride firstly forms and successively changes into hydrofluorosilicic acid. In the case of sufficient silica and potassium sulfate, the hydrofluoric acid is nearly transfbrmed into potassium hexafluorosilicate and its defluo- rination efficiency reaches 79.59%.