Impact of concentrated acid, base and salt pretreatments on the characteristics of natural clinoptilolite and its ammonium uptake from model solution and real effluents

摘要

In this study the influence of highly concentrated reagents (NaCl, 22.36%; HCl, 20%; NaOH, 32%) on the mineralogy (e.g. structure and mineral chemistry) and NH4+-exchange capacity of a natural zeolite (clinoptilolite) is investigated. Treatment was executed in packed bed columns and accompanied by liquid and solid analytics (ICP-MS, XRD, EPMA, BET, ion exchange). Ammonium uptalce was tested in batch experiments with model solutions using different concentrations of NH4Cl and real effluents from mechanical sludge dewatering (sludge liquor). It turned out that the Sl/Al-ratio of the zeolite minerals measured by EPMA changes to some extent because of dissolution of Si and Al during treatment. Acid treatment leads to a remarkable increase in the specific surface (from 16 to 77 m(2) g(-1) after treatment). NH4+-exchange isotherms revealed a significant decrease in equilibrium loadings with HC1-treatment and an increase with NaOH-treatment (+ 250/0) at concentrations > 1300 mg NH4+ L-1 compared to untreated zeolite. At lower concentrations (< 1300 mg NH4+ L-1) treatment with NaCl is best. Basic treatment leads to the formation of an altered outer rim on zeolite particles enriched in Na and depleted in K. Compared to model solutions, ammonium uptake from sludge liquor (712 mg NH4+ L-1) was significantly lower for NaCl treated zeolite but higher for HCl and NaOH treated samples, probably as a result of the complex composition of real effluents leading to potential cross-interactions that influence NH4+ ion exchange on treated zeolites.