Removal of NO-N in alkaline rare earth industry effluent using modified coconut shell biochar.

Coconut shell biochar (CSB) was selected as raw material to obtain two kinds of modified biochars by pickling and iron modification. The pickling coconut shell biochar (PCSB) and pickling-iron modified coconut shell biochar (PICSB) were used as adsorbents to remove NO-N in alkaline rare earth industry effluent. The results showed that pickling smoothed the surface of CSB, and α-FeOOH was formed on the surface of PCSB because of FeCl solution modification. Suitable adsorbent dosages of PCSB and PICSB were both 2.0 g/L. The NO-N adsorption process by PCSB and PICSB both reached equilibrium at 30 min. The quasi-first-order kinetic model shows good fit to the NO-N adsorption by PCSB. Whereas, the quasi-second-order kinetic model is more suitable for PICSB adsorbing NO-N. The adsorption mechanisms of PICSB for NO-N removal were ligand exchange and electrostatic attraction, and that of PCSB for NO-N removal was electrostatic attraction. The NO-N adsorption amounts of PCSB and PICSB decreased with increasing adsorption temperature and pH. The maximum NO-N adsorption amounts of PCSB and PICSB were 15.14 mg/L and 10.75 mg/L respectively with adsorbent dosage of 2.0 g/L, adsorption time of 30 min, adsorption temperature of 25 ± 1 °C, and initial solution pH of 2.01.