3.1. Adsorption characteristics of

3.1. Adsorption characteristics of NH4+ onto NCM3.1.1. Adsorption kinetics As shown in Fig.1, the removal efficiency of NH4+ on all NCM increases with the increasing reaction time and reaches equilibrium in 30 min. The adsorption of NH4+ on NCM is very rapid and reaches equilibrium within 30 min. This may be attributed to the utilization of readily available adsorption sites of the NCM leading to a fast diffusion and rapid equilibrium attainment (Jha and Hayashi, 2009;Alshameri et al., 2014c). When the adsorption of the exterior surface of the adsorbent reaches a saturation point, NH4+ ions enter into the pores of adsorbent and are absorbed by the interior surface of particles (Zaghouane-Boudiaf and Boutahala, 2011; Sun et al., 2015; He et al., 2016). It has been widely proposed that fast adsorption kinetics play an important role in the efficiency and field deployment of adsorbents (Mohammadi et al., 2011; Alshameri et al., 2014b; Xia et al., 2016). To further investigate the adsorption behavior, pseudo-first order and pseudo-second-order kinetics models were used to analyze the obtained data and can be summarized as follows.