Konjac glucomannan/pectin/Ca-Mg hydrogel with self-releasing alkalinity to recover phosphate in aqueous solution

The combination of polysaccharides can obtain stable, degradable, and environmentally friendly hydrogels, which have broad application prospects in adsorbents assembly. With Ca²⁺ and Mg²⁺ as crosslinkers, a new pectin/Konjac glucomannan/Ca-Mg composite hydrogel was prepared for phosphate adsorption by the alkali-thermal co-reaction method. Since Mg(OH)₂ can create a suitable pH condition for phosphate adsorption by Ca, Ca and Mg synergistically promoted phosphate adsorption and remained stable in the pH range of 4 to 10. FTIR, SEM-EDS, XRD, XPS, and zero potential analysis corroborated that the hydrogel used Ca and Mg as active sites to trap pollutants by electrostatic adsorption and fix phosphate through complexation to form Mg₃(PO₄)₂·8H₂O and CaPO₃(OH)₂·H₂O. Furthermore, it is unnecessary to separate the recovered phosphate from the hydrogel, and it can be used directly as a fertilizer. By being reused in the soil, it promoted seed germination and seedling growth. This adsorbent has the potential for recovery as a phosphorus-containing organic fertilizer after phosphorus adsorption.