Insight into the CaO green decorated clinoptilolite as an effective adsorbent for nitrate and phosphate ions; equilibrium; kinetic, and safety studies

Natural clinoptilolite was decorated by green CaO nano-rods using green tea extract and in the existence of sonication waves producing nano-composite (CaO _(NRs)/Clino). The CaO _(NRs)/Clino was characterized as a potential adsorbent for nitrate (NO₄⁻) and phosphate (PO₄³⁻) with enhanced capacities. The estimated maximum CaO _(NRs)/Clino uptake capacities for NO₄⁻(141.4 mg/g) and PO₄³⁻ (200.7 mg/g) are higher than the detected values for the individual components (clinoptilolite and CaO). The kinetic behaviors of NO₃⁻ and PO₄^3- uptake reactions by CaO _(NRs)/Clino follow the Pseudo-Second order model (R² > 0.95) and the equilibrium time was detected after 300 min and 460 min, respectively. The equilibrium properties of the occurred reactions are of higher agreement with the isotherm assumption of the Freundlich model suggesting multilayer and heterogeneous adsorption processes. The estimated values of Gaussian energy (8.3 kJ/mol (NO₃⁻) and 9.4 kJ/mol (PO₄³⁻)) suggest a principal effect for the chemical processes including ion exchange and chemical complexes. The CaO _(NRs)/Clino is of significant affinity for NO₃⁻ and PO₄^3- ions even in the existence of SO₄²⁻, Cl⁻, and HCO₃⁻ as competitive anions as well as Zn (II), Pb (II), and Cd (II) as competitive cations during the adsorption processes. The recyclability studies declared significant stability for CaO _(NRs)/Clino as an adsorbent in five cycles of NO₃⁻and PO₄³⁻ adsorption tests. Moreover, the CaO _(NRs)/Clino adsorbent was used effectively in the decontamination of real sewage water from NO₃⁻ and PO₄³⁻ ions.