Removal of nitrate and phosphate from aqueous solution by modified corn straw: characteristics and mechanism

This study investigated the removal of NO3– and PO43– from eutrophic water by a new sorbent of modified corn straw which is low-cost and environmentally safe. The sorbent was characterized using element analyzer, spectrum and scanning electron microscopy, 13C nuclear magnetic resonance and Fourier transform infrared. Results suggest that the quaternary amino group and hydroxyl group are the main functional groups on the fibrous surface of the sorbent. The effects of contact time, initial concentration and pH on the removal of NO3– and PO43–, as well as adsorption isotherms at different temperature were investigated. Results showed that the adsorption of NO3– and PO43– by this sorbent can reach equilibrium within 10 min, which was highly efficient. The adsorption process could fit well with the pseudo-second-order reaction kinetic rate equation and the adsorption rate is positively correlated to the square of the adsorption process driving force. The equilibrium data fitted well with Langmuir adsorption model and the maximum NO3– and PO43– adsorption capacities at neutral pH were 19.9 and 0.164 mg/g at 30°C, respectively. A stability test was operated for three cycles. Results demonstrate that the adsorption capacity of this sorbent only loses 14.0%, indicating that the sorbent has good potential for reuse and recycle.