[Adsorption Characteristics and Mechanisms of Phenol and Ammonia Nitrogen from Coking Wastewater by Modified Biochar]

Corn stalks were prepared into biochar （CSBC）， and modified biochar （MCSBC） was obtained by treatment with NaOH. The adsorption characteristics of phenol and ammonium nitrogen （NH₄⁺-N） on CSBC and MCSBC were studied using a batch equilibrium method. The effects of dosage and solution pH on the adsorption of phenol and NH₄⁺-N by MCSBC were investigated， and the adsorption mechanisms were explored based on the experimental results and characterization data. The results showed that the adsorption of phenol on CSBC and MCSBC was a diffusion process involving heterogeneous and multiple reaction synergistic effects. The adsorption of NH₄⁺-N was mainly governed by chemical adsorption， and the adsorption processes of phenol and NH₄⁺-N on CSBC and MCSBC were primarily monolayer adsorption. Isothermal adsorption data indicated that in the binary component system， the maximum adsorption capacities （q_m） of MCSBC for phenol and NH₄⁺-N were 415.81 mg·g^-1 and 287.73 mg·g^-1， respectively， which increased by 361.55% and 11.67% compared with those in the single-component system. The adsorption of phenol by MCSBC was more effective under acidic conditions， while the adsorption of NH₄⁺-N was more effective under alkaline conditions. When both components coexisted， the average pH value of 8 from coking wastewater could be adopted. The optimal dosage was 4 g·L^-1， and MCSBC demonstrated good recycling and regeneration capabilities. The adsorption mechanisms of phenol by MCSBC included π-π interactions， hydrogen bonding， and pore-filling effects. The adsorption mechanisms of NH₄⁺-N included pore filling， hydrogen bonding， ion exchange， and electrostatic attraction. In the binary component system， the preferential adsorption of NH₄⁺-N could significantly enhance the adsorption of phenol on MCSBC through charge-assisted hydrogen bonding. In summary， MCSBC shows high potential for treating phenol and NH₄⁺-N in coking wastewater.