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

Mitrogiannis, Dimitris and Psychoyou, Maria and Baziotis, Ioannis and Mavrogonatos, Constantinos and Koukouzas, Nikolaos and Anastopoulos, Ioannis and Fyrillas, Marios and Inglezakis, Vassilis J. (2023) Phosphate removal by Ca(OH)2-treated natural minerals : experimental and modeling studies. Colloids and Surfaces A: Physicochemical and Engineering Aspects, 660. 130805. ISSN 0927-7757 (

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Adsorption of phosphate phosphorus (PO 4-P) from wastewater onto eco-friendly geosorbents has gained great attention aiming at recovering an essential nutrient for crop production. Notably, the literature on PO 4-P aqueous-phase adsorption kinetics is limited to the application of either empirical reaction-based models lacking a physical significance or over-simplified diffusion-based models frequently used outside their applicability area. In this study, equilibrium and kinetic experiments are presented under a wide range of phosphate concentrations (50–500 mg P/L) using sustainable and low-cost modified adsorbents. The kinetics of PO 4-P adsorption from aqueous solutions onto Ca(OH) 2-treated zeolite (CaT-Z) and bentonite (CaT-B) was analyzed by a dimensionless two-phase homogeneous surface diffusion model (TP-HSDM) assuming constant diffusivity coupled with the double selectivity isotherm equation (DSM). The TP-HSDM fit to the data at four initial P concentrations (50, 100, 200 and 300 mg/L) resulted in an average relative error of 14.6% and 17.4% from the experimental data for CaT-Z and CaT-B, respectively. The average surface diffusion coefficient (D s) ranged from 2.5 × 10 -10 to 8.7 × 10 -10 cm 2/s for CaT-Z and from 1.6 × 10 -10 to 4.78 × 10 -9 cm 2/s for CaT-B. The external mass transfer coefficient (k f) ranged from 2.72 × 10 -4 to 8.38 × 10 -4 cm/s for CaT-Z and from 5.63 × 10 -4 to 2.24 × 10 -3 cm/s for CaT-B. The dimensionless Biot (Bi) number exhibited values in the order of magnitude of 10 5 indicating that the intraparticle diffusion is the controlling mass transfer mechanism for both materials.