Using Raw and Thermally Modified Fibrous Clay Minerals as Low Concentration NH4+-N Adsorbents

Abstract

Raw and modified fibrous clay minerals palygorskite (Pal) and sepiolite (Sep) were tested for their ability to remove ammonium from ammonium polluted water. Palygorskite and sepiolite underwent thermal treatment at 400oC (T-Pal and T-Sep respectively). Raw and thermally treated samples were characterized using XRD, SEM, BET, FT-IR, TGA, zeta potential and XRF. The techniques verified the effect of thermal treatment on samples structures and the enhancement of negative charge. Both raw and thermally-activated materials applied in batch kinetic experiments, and found to be efficient adsorbents in their raw forms, since Pal and Sep achieved 60 and 80% NH4+-N removal respectively within 20 min of contact for initial NH4+-N concentration of 4 mg/L. Similar removal rates were gained for other concentrations representative of contaminated aquifers that were examined, ranging from 1 mg/L to 8 mg/L. Results for the modified T-Pal and T-Sep minerals showed up to 20% higher removal rate. Saturation tests indicated the positive effect of thermal treatment on the minerals since T-Pal and T-Sep removal efficiency reached 85% and remained stable for 24 h. However, competitive ions in real water samples can influence the NH4+-N removal efficiency of the examined samples. In all cases, the Freundlich isotherm and pseudo-second kinetic models showed better fitted all examined samples thus indicating heterogeneous chemisorption.