Enhanced nitrate removal by physical activation and Mg/Al layered double hydroxide modified biochar derived from wood waste: Adsorption characteristics and mechanisms

The adsorption treatment of nitrate wastewater has attracted much attention worldwide. However, most of the currently enhanced adsorption methods used chemical modification, both physically activated and chemically modified to composite carbon material lacks attention. To investigate whether the composite biochar could enhance the removal of nitrates, woody waste of apple branch as biomass feedstock was pyrolysed and CO2 activated to obtain biochar (AB), which loaded with Mg/Al layered double hydroxide (Mg/Al-LDHs) to synthesis a novel Carbon-adsorbent (AMB). The adsorption characteristics and mechanisms of NO3- on AMB were inves-tigated by the batch experiment, adsorption models and various characterisation. The results showed that Mg/Al-LDHs are successfully modified on the surface of AB. The average adsorption capacity of AMB for NO3- is 7.43 times that of AB, and the average removal rate for NO3- improved from 13% to 83%. The theoretical maximum adsorption capacity of NO3- on AMB was 156.84 mg g(-1). The Pseudo-second-order and Freundlich models can well simulate the kinetics and isothermal process, implying that adsorption mechanisms of NO3- on AMB were multilayer physical-chemical composite adsorption, including surface physical sorption, intraparticle diffusion, electrostatic adsorption, ion exchange, and metal-bonded bridges. Therefore, the AMB could be used as a low-cost and high-efficiency adsorbent for removing nitrate in wastewater.

Automated summary

The study demonstrated that the modified composite biochar shows good adsorption performance for nitrate wastewater, with significantly increased adsorption capacity and removal rate. The adsorption mechanisms involve various physical-chemical composite processes such as surface adsorption, diffusion, and ion exchange.