湿法磷酸制牙膏级磷酸氢钙中的脱氟工艺

针对由中低品位磷矿石制得的湿法磷酸，提出采用预脱氟和灰乳中和深度脱氟相结合的工艺路线，使净化后的湿法磷酸达到作为生产牙膏级磷酸氢钙原料酸的指标要求。实验表明，钾盐的脱氟效果与磷酸的浓度有一定关系，同时活性氧化硅有且于氟的进一步脱除；在进一步的净化过程中，用石灰乳中和至一定的ｐＨ值，绝大部分的氟及其它杂质沉淀析出脱除，净化酸达到了牙膏级磷酸氢钙的生产要求。

Defluorination of Wet-process Phosphoric Acid for Production of Toothpaste-grade Calcium Hydrogen Phosphate

Difficulties in defluorination and deep purification of wet process phosphoric acid bottleneck its use in the production of toothpaste grade calcium hydrogen phosphate. A two step process for purification of wet process phosphoric acid is proposed which utilizes pre defluorination by precipitation and deep defluorination by neutralization with slaked lime. The effect of defluorination is examined with the quantity of potassium chloride and the concentration of phosphoric acid. Moreover, active silicon oxide is of assistance to defluorination. The ratio of phosphorus pentoxide content to fluorine content in so treated that phosphoric acid can be more than 100. In a further purification step by neutralization with slaked lime, most of the fluorine and other impurities in the phosphoric acid deposit are separated at a definite pH value. The filtrated phosphoric acid, in which the ratio of phosphorus pentoxide content to fluorine content is more than 3 000, can therefore be employed to produce toothpaste grade calcium hydrogen phosphate. In the proposed process, about 30 percent of phosphorus pentoxide in the raw wet process phosphoric acid will come into the production of toothpaste grade calcium hydrogen phosphate.