Synthesis of zeolite/geopolymer composite for enhanced sequestration of phosphate (PO₄³⁻) and ammonium (NH₄⁺) ions; equilibrium properties and realistic study

Zeolite impeded geopolymer (Z/G) was synthesized from natural kaolinite and diatomite. The structure (Z/G) was characterized as an enhanced adsorbent for PO₄³⁻ and NH₄⁺ ions from aqueous solutions, groundwater, and sewage water. The synthetic Z/G structure exhibits sequestration capacities of 206 mg/g and 140 mg/g for PO₄³⁻ and NH₄⁺, respectively which are higher values than the recognized results for the geopolymer and other adsorbents in literature. The sequestration reactions of PO₄³⁻ and NH₄⁺ by Z/G are of Pseudo-Second order kinetic behavior considering both the Chi-squared (χ²) and correlation coefficient (R²) values. The sequestration reactions occur in homogenous and monolayer forms considering their agreement with Langmuir behavior. The Gaussian energies (12.4 kJ/mol (PO₄³⁻) and 10.47 kJ/mol (NH₄⁺)) demonstrate the operation of a chemical sequestration mechanism that might be involved zeolitic ion exchange process and chemical complexation. Additionally, these reactions are exothermic processes of spontaneous and favorable properties based on thermodynamic studies. The Z/G structure is of significant affinity for both PO₄³⁻ and NH₄⁺ even in the existence of other anions as Cl⁻, HCO₃⁻, SO₄²⁻, and NO₃⁻. Finally, the structure used effectively in the purification of groundwater and sewage water from PO₄³⁻ and NH₄⁺ in addition to nitrate, sulfate, and some metal ions.