Arsenate removal from aqueous solution by siderite synthesized under high temperature and high pressure.

In present study, a novel method was developed to synthesize siderite under high temperature and high pressure (SID-HTP). SID-HTP was characterized by N2 adsorption-desorption isotherms (BET), XRD, SEM, and FTIR and utilized to remove arsenic(V) (As(V)) from aqueous solution. Results showed that, under oxic condition, pH had ignorable effect on As(V) adsorption. However, adsorption capacity increased with increasing pH from 2 to 7 and remained relatively constant at higher pH until 10 under anoxic condition. Higher adsorption was obtained in the presence of oxygen, showing oxygen-enhanced As(V) adsorption on SID-HTP. In both cases, adsorption equilibrium was achieved within 12 h and adsorption process was better described by pseudo-second-order kinetic model. The equilibrium data fitted well with Langmuir isotherm model for As(V) adsorption. The maximum adsorption capacity increased with increasing temperature, which was up to 42 mg g-1 at 55 °C in the presence of oxygen. Thermodynamic study revealed that the adsorption was a spontaneous and endothermic process. The mechanism of oxygen-enhanced adsorption was mainly ascribed to the -OH on the surface of FeOOH (goethite and lepidocrocite) in the SID-HTP. It suggested that SID-HTP would be a potentially attractive adsorbent for As(V) removal.