Study on adsorption of nitrate in water by OTAC modified coal-based granular activated carbon

Abstract

In recent years, the problem of excessive nitrate in urban drinking water in China has seriously influence on the drinking water quality and threatened human health.In order to further improve efficiency of removal nitrate from water,this study herein developed an economic and efficient nitrate adsorbent-octadecyltrimethyl ammonium chloride modified coal-based granular activated carbon (OTAC-GAC).The optimal preparation conditions and the maximum nitrate adsorption capacity of OTAC-GAC were determined by orthogonal experiment method.The adsorption mechanism of nitrate on OTAC-GAC was investigated by dynamic adsorption modeling and surface characterization.The results show that the optimum condition of anchoring QA onto GAC is achieved at the OTAC concentration of 5 mmol/L, the reaction temperature of 20℃ and the reaction time of 2h, the optimized OTAC-GAC exhibits higher nitrate adsorption capacity (22.05 mg/g) than that of the pristine GAC (15.31 mg/g). The adsorption performance fits the pseudo-second-order model (R2=0.999), Langmuir adsorption model(R2=0.913) and D-R adsorption model very well.Besides, compared to the pristine GAC, the pore volume of the optimized OTAC-GAC decreased by 47%,the nitrogen amounts of increased by 44%, and the basic functional group increased by 3.4 times, indicating the OTAC that hosts positively-charged nitrogen successfully anchored into GAC pores.Therefore, it can be predicted that adsorption mechanism of nitrate on the OTAC-GAC includes ion exchange and electrostatic adsorption, which provid a theoretical support for maintaining drinking water safety.

Keywords

• coal-based granular activated carbon
• otac
• nitrate
• adsorption capacity
• mechanism study