Sorption Characteristics of Nitrogen Forms on Microporous Adsorbents for Novel Fertilizer

Abstract

Diffusion of nitrogen (N) on void pores determines the sorption capacity of microporous inorganic solid adsorbents. A laboratory study was undertaken to assess the sorption kinetics of N on adsorbents viz., zeolite, nano-zeolite, biochar and size reduced biochar in order to know the sorption efficiency and fabrication of novel N fertilizer. Adsorption and desorption pattern were examined using four forms of N viz., ammonium (NH4+), nitrate (NO3-), amide (NH2) and ammonium + nitrate (NH4++NO3-) were loaded at varying concentrations (100-700 mg L-1 (adsorption) and 20-200 mM (desorption)). Batch and contact time (0-8 h) experiments revealed that equilibrium time, equilibrium concentration and equilibrium percentage (NH4+-N; 5-7 h, 1.2-1.7 mg L-1, 46-73%) and (NO3--N; 6-7 h, 0.9-1.6 mg L-1, 40-70%), respectively. Nano-zeolite had the highest sorption capacity for 42.5, 40 mg g-1 after 6-7 h of shaking period of NH4+-N and NO3--N, respectively. Theoretical Freundlich adsorption isotherm equations predicted adsorption of N as 35.0, 48.5, 31.3 and 43.8 mg g-1 (NH4+) and 17.5, 28.2, 14.3 and 19.2 mg g-1 (NO3-) for zeolite, nano-zeolite, biochar and size-reduced biochar, respectively. Results of this study suggested that nano-zeolites are most suitable adsorbent to retain both forms of N which could be best adsorbent for fabrication of N fertilizer.