Synchronously efficient removal of ammonium and phosphate by organo-functionalized magnetic clinoptilolite: Insights into adsorption threshold and possible mechanism.

Aquaculture wastewater containing ammonium (NH4+-N) and phosphate (PO43--P) can lead to eutrophication of regional water bodies, which urgently requires new and cost-effective remediation strategies. In this study, a novel starch carbon functionalized magnetic clinoptilolite powder (SC/Fe3O4@CP) was prepared by sequential magnetization and starch carbonization. The results indicated that the adsorption thresholds of SC/Fe3O4@CP towards NH4+-N and PO43--P achieved 79.23 and 50.34 mg/g, which were 1.32∼2.72 and 1.38∼3.26 folds that of other functionalized clinoptilolites, respectively. Adsorption kinetics revealed that the removal of NH4+-N and PO43--P was predominantly governed by physisorption and chemisorption, respectively. In addition to increasing the specific surface area and porosity of clinoptilolite, magnetization and organo-functionalization also introduced more binding sites such as metal oxides and oxygen-containing groups, which significantly promoted the synchronous and efficient adsorption of NH4+-N and PO43--P. Two-dimensional correlation spectroscopy demonstrated that the CO groups generated during organo-functionalization exhibited the highest sensitivity toward the adsorption of NH4+-N and PO43--P, suggesting its significant involvement in the adsorption process. The possible adsorption mechanisms include physisorption, ion exchange, surface precipitation, ligand exchange, and electrostatic attraction. Actual aquaculture wastewater treatment showed that SC/Fe3O4@CP could remove more than 96 % of COD and all N and P species without regeneration in three consecutive treatments. Overall, SC/Fe3O4@CP has good application potential in the treatment of aquaculture wastewater.