Modification of oyster shell powder by humic acid for ammonium removal from aqueous solutions and nutrient retention in soil

Abstract

Oyster shell (OS) can be used as absorbent, building material, catalysts and agricultural supplement due to the specific physicochemical properties. To add to the value of this wild raw material, a novel humic acid-modified oyster shell (HAOS) was prepared by introducing humic acid (HA) onto the OS surface through a solid phase grafting method. Thermogravimetric analysis (TGA), scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS) and energy-dispersive X-ray (EDX) spectroscopy were performed to optimize the modification conditions. Batch adsorption experiments were designed to evaluate the effects of HA coating, pH, salinity, isotherm and kinetics on NH4+ adsorption. A soil column experiment was carried out to investigate the nitrogen release upon HAOS addition. The results showed that the adsorption capacity of HAOS for NH4+ increased by 43.5% compared with OS. The adsorption kinetics of NH4+ on HAOS could be explained by the pseudo-second-order kinetic model (R2 = 0.9864), and the maximum adsorption amount calculated from the Langmuir adsorption model (R2 = 0.9907) was approximately 56.1 mg g−1. Moreover, 5% HAOS addition could prolong the release time of NH4+ and decrease the amount of NO3- leaching from soil. The application of HAOS in the plant growth assay significantly increased the elongation and fresh weight of the test plants. Consequently, the novel HAOS had broad application prospects in ammonium treatment and soil fertility improvement.