Separation of phosphoric acid and magnesium from wet process phosphoric acid by solvent extraction

Wet process phosphoric acid (WPA) contains a high concentration of metal cations. Our research group developed a P-15 extractant that can effectively remove metal cations in WPA. Different metal cations supported by the extractant are stripped and recycled by different stripping agents. In this study, ammonium sulfate is used as a stripping agent to separate magnesium ions from the extractant. So that phosphoric acid and magnesium ions can be separated and separately prepared into their own products. To determine the optimal operation parameters of the magnesium ion stripping process, single factor experiments are conducted. Under the reaction temperature of 333.15 K, stirring speed of 300 rpm, phase ratio (A/O) of 1/2, ammonium sulfate concentration of 3.305 mol/L, and reaction time of 30 min, the stripping efficiency reaches 75%. A stripping equilibrium curve at 333.15 K is plotted to determine the optimal reaction order for countercurrent stripping. Through two-stage countercurrent stripping, the magnesium ion concentration in the extractant could be reduced to approximately 0.0018 mol/L when A/O = 1/2. Magnesium ion concentration in extraction can be reduced from 0.0419 mol/L to 0.0026 mol/L through two-stage stripping countercurrent cascade. The concentration of each kind of impurity ion in ammonium magnesium sulfate crystals is all below 500 ppm.