Effective adsorption of ammonium nitrogen by sulfonic-humic acid char and assessment of its recovery for application as nitrogen fertilizer

Abstract

Ammonium nitrogen (NH4+-N) is a form of N that is non-negligible in eutrophication water as well as an essential nutrient for plants growing. Carbon materials are considered superior for the adsorption recovery of excess NH4+-N in water bodies. The sulfonic-humic acid char (SHAC) was prepared from humic acid (HA) by pyrolysis and hydrothermal grafting with sodium allyl sulfonate. SEM-mapping, FTIR and XPS results indicated that sulfonic groups (-SO3H) were successfully grafted onto SHAC. The adsorption kinetic fitting displayed that the adsorption of NH4+-N by SHAC conformed to the pseudo-second-order kinetics and could reach equilibrium in about 100 min. The maximum adsorption of NH4+-N by SHAC was 77.24 mg/g, it was mainly contributed by electrostatic attraction, hydrogen bonding and pore volume sites. SHAC adsorption of NH4+-N resulted in the material SHAC-N, which desorption rate was considerably slower than that of commercially available ammonium chloride (NH4Cl) fertilizer and in accordance with the first order model. Wheat growth experiments revealed that the quality of wheat treated with SHAC-N (higher 100-grain weight and lower nitrate content) was better than that of NH4Cl fertilizer. In addition, the higher residual NH4+-N in the SHAC-N treatment soil facilitated subsequent crop planting. These results indicated that SHAC has excellent adsorption and slow release of NH4+-N, and has great potential application for N management in environment and agriculture.