Nitrate removal from aqueous solution using fuller’s earth and modified fuller’s earth

Abstract

Water, a vital resource for ecosystems and human populations, is facing increasing nitrate contamination due to agricultural runoff, industrial discharge and improper waste disposal. The present study focuses on the efficacy of nitrate removal through adsorption using fuller’s earth (FE) and modified fuller’s earth (acid-treated) (MFE) as adsorbents. The impact of initial pH (2.0–7.0), contact time (5–240 min), adsorbent dosage (1–30 g/L), initial nitrate concentration (50–250 mg/L) and temperature (30–50°C) on nitrate removal using fuller’s earth were studied. The maximum nitrate removal was observed at pH 2.0, and equilibrium was reached in 120 min at 30℃. The Freundlich isotherm best fit the equilibrium data. The maximum nitrate uptake of fuller’s earth and modified fuller’s earth were 84.75 mg/g and 85.47 mg/g, respectively. Nitrate removal by FE and MFE followed a second-order kinetic equation. Thermodynamic studies showed spontaneity and the exothermic nature of the nitrate adsorption process. ∆H° values were −44.96 and −42.63 kJmol−1 for FE and MFE and ΔS° was −85.11 and −74.52 Jk−1mol−1 for FE and MFE, respectively. FE, known for its exceptional adsorption capacity owing to its porous structure and high ion-exchange capacity, has demonstrated a remarkable affinity for nitrate ions in batch studies.

Keywords

• Nitrate removal
• modified fuller’s earth
• adsorption isotherms
• kinetic models