White Cement as a Nontoxic and Eco-Friendly Adsorbent for Phosphate Adsorption/Desorption: Characterization, Optimization, and Modeling Studies

White cement (WC) represents a low-cost, sustainable, and nontoxic alternative adsorbent for phosphate (PO43–) adsorption from aqueous solutions. The composite central rotational design (CCRD) method was applied to optimize adsorption through kinetic, equilibrium, and thermodynamic batch studies. For fixed-bed column studies, the CCRD method evaluated the influent flow rate and adsorbent mass. The high levels of calcium oxide (CaO, 65%) observed in WC influenced the adsorption that achieved an efficiency of 97% under the optimal condition. Pseudo-first and pseudo-second order models better represented adsorption (54.68 mg g–1; pH 7.5). Redlich–Peterson, Freundlich, and Langmuir models better represented adsorption (59.53 mg g–1) at the equilibrium time (60 min). Adsorption showed spontaneous reactions of an exothermic nature. The proposed mechanisms are related to adsorption onto iron and aluminum hydroxides and oxides, precipitation of calcium phosphates, and electrostatic attraction. Non-PO43– desorption was observed under the evaluated conditions. In the fixed-bed column assays, an influent flow rate of 3.50 mL min–1 and an adsorbent mass of 0.27 g were verified as optimal conditions. WC exhibited phosphate removal efficiencies of 90% for raw effluent and 98% for primary-treated effluent from a corn flour processing industry with initial PO43– concentrations of 1.35 and 0.19 mg L–1, respectively. Finally, WC demonstrated a promising capacity as an adsorbent for phosphate removal.