Efficient phosphate removal using calcium hydroxide-modified natural zeolite: a sustainable solution for eutrophication control

Phosphate enrichment of aquatic environments is a primary cause of eutrophication, requiring cost-effective and sustainable treatment strategies. In this study, natural zeolite was modified with calcium hydroxide to enhance its phosphate adsorption capacity. Batch experiments were conducted to evaluate the effects of adsorbent dosage, initial phosphate concentration, solution pH, temperature, and modifier concentration on removal performance. The modified zeolite achieved removal efficiencies above 92% at concentrations up to 50 mg L-1, and adsorption capacities of 9.74 mg g-1 and 14.68 mg g-1 at 313 K for 100 mg L-1 and 200 mg L-1, respectively. Equilibrium data were best described by the Langmuir isotherm at 313 K (R2 approximate to 0.999) and by the Freundlich model at 293 K (R2 = 0.9635), while thermodynamic analysis confirmed a spontaneous and endothermic process. Mechanistic interpretation indicated that phosphate removal occurred through electrostatic attraction, ligand exchange, and calcium phosphate precipitation, with precipitation dominating under alkaline conditions (pH 7-9). Regeneration studies exhibited the progressive decline in adsorption efficiency due to calcium leaching, pore blockage, and irreversible phosphate binding. These results highlight calcium hydroxide-modified zeolite as a low-cost and environmentally friendly material for phosphate removal, while also emphasizing the need for further validation with real wastewater and pilot-scale applications.

Journal

INTERNATIONAL JOURNAL OF ENVIRONMENTAL SCIENCE AND TECHNOLOGY

Year

2025

Volume

23

Issue

2

ISSN

1735-1472

eISSN

1735-2630

DOI

10.1007/s13762-025-06961-w

WoS UID

WOS:001631464100005