Enhanced adsorption of potassium nitrate with potassium cation on H3PO4 modified kaolinite and nitrate anion into Mg-Al layered double hydroxide

Kaolinite modification by grinding with H3PO4 was conducted to introduce more H+ for potassium exchange, therefore to enhance largely the capacity of potassium fixation. The precursor of Mg-Al LDH by milling both Mg and Al hydroxides was used to incorporate nitrate anions. The modified kaolinite and the synthesized LDH precursor were simultaneously used to achieve synergistic effect to raise the removal efficiency of potassium nitrate. The neutralization action between H+ ions exchanged with potassium cations from the kaolinite and OH- ions exchanged with nitrate anions from the LDH allows the continuous exchanging to remove out potassium nitrate at high efficiency, achieving the desalination of the very difficult alkali metals salts. The process provides an effective way to desalinate the difficult alkali metal salts and recover potassium from some specific industrial wastewaters with the products serving as a slow-release fertilizer.