Technology Of Purification Of Wet-Process Phosphoric Acid By Solvent Extraction

Phosphoric acid is the second largest acid produced in the world and occupies an important position in our country.Phosphoric acid is extremely versatile and involves many industries.It also has different requirements for the purity of phosphoric acid.Wet-process phosphoric acid is gradually becoming the mainstream due to its advantages such as environmental friendliness,low cost,and sufficient raw materials,but the biggest disadvantage is that there are many types and high content of impurities in wet-process phosphoric acid.Therefore,it is necessary to develop a process for purifying wet-process phosphoric acid to meet the needs of phosphoric acid of various purities.The main research systems of thesis are water-kerosene-benzoic acid system,pure phosphoric acid-MIBK system,and crude phosphoric acid-MIBK system.The first two systems lay the foundation for the crude phosphoric acid-MIBK system experiment.The experiment detects the content of phosphoric acid and four impurities in the extraction phase,the washed extraction phase,and the stripping phase by changing the process conditions such as the ratio of different phases,rotation speed,vibration frequency,temperature,and acid concentration,etc.In addition,the extraction rate,phosphoric acid partition coefficient,selectivity coefficient,ion removal rate,back extraction rate,and back extraction acid concentration were calculated.Furthermore,the mass content of impurity ions in back extraction acid at 85 wt.% concentration was calculated and compared with the national standard to get the optimal process conditions.In the water-kerosene-benzoic acid system,the optimal operating conditions of the rotating disc tower are 1:2 and 400 rpm.The optimal operating conditions of the reciprocating plate column is 1:3 and 250 times/min.In the pure phosphoric acid-MIBK system,the maximum extraction rate of phosphoric acid in the rotating tower is 88.0 %,and the reciprocating plate column is 92.7 %.The extraction rate of phosphoric acid in the turntable tower increases with the increase of the rotation speed.When the ratio is more than 3,the extraction rate basically does not change.When the vibration frequency in the reciprocating plate column is 200 times/min,the extraction rate is the largest.With this vibration frequency,the greater the phase ratio,the higher the extraction rate.In the crude phosphoric acid-MIBK system,the optimal extraction conditions are at 40 ℃,with 72 wt.% original acid concentration,and MIBK-phosphoric acid ratio of 4.The optimal washing conditions are the conditions of40 °C,50 wt.% washing acid concentration,and washing acid-extraction phase ratio of15.The best stripping conditions are at 30 ℃ and the water-extraction phase ratio is 15.In the rotating disc tower,the extraction rate is the highest when the rotational speed is400 rpm and the phase ratio is 3.In the reciprocating plate column,the extraction rate is the highest when the vibration frequency is 400 times/min and the phase ratio is 4.