Calcined natural limestone as a low‐cost adsorbent for municipal wastewater treatment: Synthesis, physicochemical characterization, and multi‐parameter pollutant removal performance

Abstract

The progressive deterioration of freshwater resources and the inadequacy of wastewater treatment infrastructure have intensified the demand for low‐cost, locally available adsorbent materials. While calcined calcium‐based minerals have been studied against single synthetic pollutants, their behavior in real, multi‐pollutant wastewater remains largely unexplored. This study addresses that gap through a calcium sulfate/calcium carbonate‐dominated mineral adsorbent, with minor silica content, derived from natural limestone via reagent‐free calcination at 500°C for 2 h, applied directly to real municipal wastewater across six quality parameters. Characterization by XRD, FTIR, UV–Vis, and SEM–EDX confirmed this multiphase composition, a direct optical band gap of 2.7 eV, and nanometric crystallite sizes of 21.37 ± 6.09 nm and 22.17 ± 5.34 nm before and after treatment. Calcination restructured the surface into a porous, acicular morphology with a higher density of active sites. Batch adsorption demonstrated high removal efficiencies for suspended solids (87.1%), chemical oxygen demand (91.0%), and biochemical oxygen demand (96.8%) at an optimal dose and contact time of 15 mg and 120 min, whereas phosphate, nitrite, and ammonium removal remained markedly lower (≤21%), revealing a clear divergence between organic and inorganic pollutant removal. This divergence reflects three concurrent mechanisms: physical adsorption, ionic interaction, and surface precipitation. These findings establish calcined limestone as a cost‐effective adsorbent for wastewater treatment, clarifying the pollutants for which it is best suited.