两步法净化湿法磷酸及食品级磷酸氢钙的制备

采用两步脱氟和一步脱重金属与砷净化湿法磷酸 ,得到磷酸杂质含量为 :w(Pb) <0 0 0 1% ,w(F) <0 0 0 4% ,w(As) <0 0 0 0 2 % ,可作为食品添加剂使用。探讨了pH值、温度以及脱氟剂、脱重金属与脱砷剂用量等对净化效果的影响 ,得到第一步最佳净化工艺条件 :温度为 90～ 95℃ ,脱氟剂 (SiO2 )用量为磷酸中含F总质量的 12 0 % ;第二步最佳净化工艺条件 :pH值为3 0～ 3 2 ,温度为 10℃以下 ,脱氟剂 (SiO2 +Na2 CO3)组分SiO2 用量为第一步净化后磷酸中含F总质量的 2 5 0 % ,两组分的质量比m(SiO2 )∶m(Na2 CO3) =(5～ 10 )∶1,脱重金属与脱砷剂 (Na2 S)用量为磷酸中含重金属与砷总质量的 2 80 %。进一步净化磷酸制得了食品级磷酸氢钙。

Purification of Wet-way Phosphoric Acid by Two-step Method and Preparation of Food Grade Calcium Hydrogen Phosphate

Wet-way phosphoric acid is purified by two-step method.Impurity contents in the purified acid are fluorine content w(F)≤0.004%，heavy metal content w(Pb)≤0.001% and arsenic content w(As)≤0.0002%.It is suitable for food.Influences of pH value,temperature and amounts of defluorinating agent,demetalating-dearsenicating agent on the result of purification are investigated in detail.The optimal conditions for purification process are obtained.In the first step,the temperature is 90-95 ℃,amount of defluorinating agent(SiO2) is 120% of the mass of fluorine in phosphoric acid before purification.In the second step,the pH value is 3.0-3.2,the temperature is below 10 ℃,amount of defluorinating agent(SiO2+Na2CO3) is 250% of mass of fluorine in phosphoric acid after the first step purification and mass ratio m(SiO2)∶m(Na2CO3)=(5-10)∶1,and amount of demetaling-dearsenicating agent(Na2S) is 280% of the total mass of heavy metal and arsenic in phosphoric acid.Furthermore,food grade calcium hydrogen phosphate is prepared.