Adsorption studies using natural palygorskite for the treatment of real sanitary landfill leachate

The efficiency of a naturally occurring palygorskite as an adsorbent for the simultaneous removal of color, dissolved chemical oxygen demand (d-COD) and ammonium nitrogen (NH4+-N) from real, untreated sanitary landfill leachate (SLL) was investigated. Saturation and desorption studies of palygorskite were also performed for all three pollutants simultaneously. Optimal adsorption conditions were attained at palygorskite dosage of 133 g L-1 and suspension pH 8. In these conditions, color removal efficiency reached 85.4 +/- 1.4% within just 2.5 min of contact time with the natural palygorskite, while d-COD and NH4+-N removal was 54.7 +/- 0.6% and 41.9 +/- 0.5%, respectively, for 180 min residence time. Limited reuse of palygorskite for color uptake was possible. NH4+-N uptake on palygorskite was irreversible, while d-COD and color uptake were reversible. The combination of natural palygorskite with natural zeolite in series, in any order, doubled the overall removal efficiency of NH4+-N from raw SLL. Solid characterization of palygorskite confirmed the adsorption of NH4+-N, aromatic and aliphatic organic compounds. BET specific surface area (SSA) analysis showed significant changes of the solid upon saturation. Zeta potential measurements of the suspended particles after SLL treatment in combination with FTIR and XPS analyses suggested that SLL decolorization was due to the adsorption of anionic aliphatic and aromatic compounds. The results of this study indicate that adsorption on natural palygorskite is a viable option for the pre-treatment of untreated landfill leachate.