Upcycling coal fly ash and red mud into a magnetic zeolite composite for the efficient sequestration of ciprofloxacin

Abstract

The discharge of pharmaceutical pollutants, such as ciprofloxacin (CIP), into water bodies poses a significant threat to global water security. This research introduces a circular economy approach by synthesizing a magnetic cancrinite-type zeolite (MZ-3) from coal fly ash (CFA) and red mud (RM) via a streamlined alkali fusion-hydrothermal route (160°C for 9 h). The resulting composite exhibited high crystallinity, a mesoporous framework, and a strong negative zeta potential (-51 mV), which facilitates CIP adsorption. Experimental results demonstrated that MZ-3 can adsorb up to 62.75 mg g -1 of CIP at pH 7.1, where CIP predominantly exists in its zwitterionic form. The adsorption data were best described by the Sips isotherm (R 2 = 0.99087), indicating heterogeneous surface energy. The incorporation of magnetic iron oxide from red mud enabled efficient solid-liquid separation using a magnetic field, thereby eliminating the need for energy-intensive filtration. The adsorbent maintained structural stability during operation; regeneration with a saturated NaCl solution restored active sites, increasing removal efficiency to 93.2% by the second cycle. These findings establish MZ-3 as a high-performance, cost-effective, and sustainable material for the remediation of antibiotic-contaminated wastewater, thereby effectively converting industrial waste into a valuable water-treatment resource.