Phosphate removal by Ca(OH)2-treated natural minerals: Experimental and modeling studies

Adsorption of phosphate phosphorus (PO4-P) from wastewater onto eco-friendly geosorbents has gained great attention aiming at recovering an essential nutrient for crop production. Notably, the literature on PO4-P aqueous-phase adsorption kinetics is limited to application either empirical reaction-based models lacking a physical significance or over-simplified diffusion-based frequently used outside their applicability area. In this study, equilibrium and kinetic experiments are presented under wide range concentrations (50–500 mg P/L) using sustainable low-cost modified adsorbents. The aqueous solutions Ca(OH)2-treated zeolite (CaT-Z) bentonite (CaT-B) was analyzed by dimensionless two-phase homogeneous surface diffusion model (TP-HSDM) assuming constant diffusivity coupled with double selectivity isotherm equation (DSM). TP-HSDM fit data four initial P (50, 100, 200 300 mg/L) resulted in average relative error 14.6% 17.4% experimental CaT-Z CaT-B, respectively. coefficient (Ds) ranged 2.5 × 10-10 8.7 cm2/s 1.6 4.78 10-9 CaT-B. external mass transfer (kf) 2.72 10-4 8.38 cm/s 5.63 2.24 10-3 Biot (Bi) number exhibited values order magnitude 105 indicating that intraparticle controlling mechanism both materials.