Polycyclic Aromatic Hydrocarbon Adsorption By Coal-based Adsorbent:Materials Preparation,Adsorption Performance And Mechanism

The coking industry is an economic pillar industry in China,but the wastewater produced in the coking process is a kind of highly toxic wastewater that is difficult to degrade,and the near-zero discharge of wastewater has become a bottleneck for the sustainable development of the coking industry.The polycyclic aromatic hydrocarbons(PAHs)in coking wastewater are the main reason for the poor degradability and high biological toxicity of coking wastewater,and the trace amount of PAHs can cause serious food safety and ecological pollution problems.Therefore,how to solve the environmental pollution problems caused by PAHs efficiently and rapidly has become a hot research topic in recent years.In this study,CP was used for the adsorption and removal of PAHs from coking wastewater based on the consideration of in situ utilization of industrial by-product-coke powder(CP).The applicability of coke powder was investigated by changing the material dosage,solution environment and other conditions;the mechanism of CP adsorption of PAHs was clarified by characterizing the physicochemical information,analyzing the adsorption kinetics and adsorption isotherm fitting results,and simulating calculations.Based on the dominant adsorption mechanism of CP and PAHs,lignite activated coke(ABC)was prepared by hightemperature quenching and cooling activation method from the utilization of low-rank coal-lignite(BC)for quality improvement.The optimum preparation conditions were determined by varying the calcination temperature,dissolved oxygen content of the quencher and p H.The mechanism of PAHs removal by ABC adsorption was revealed by comparing the performance of ABC with BC adsorption of PAHs and the change of material structure before and after ABC adsorption of PAHs.It provides scientific basis and theoretical guidance for the preparation of a green,stable and inexpensive adsorbent and efficient treatment of coking wastewater.(1)CP achieved stable removal of PAHs at different p H and high concentrations of multiple species ions,and the removal rates were above 90%.In the saturation adsorption case,CP adsorbed naphthalene as a multilayer,which is consistent with the Frundlish isotherm model,and the removal rate was 83%.The saturation adsorption of naphthalene and naphthol by CP was in accordance with the quasi-secondary kinetic equation,and the saturation adsorption amounts were 23.83 mg/g and 8.08 mg/g,respectively.the saturation adsorption amount of naphthalene by coke powder hightemperature expanded pore material(CCP)was four times higher than that by CP,and the adsorption process was influenced by the porosity.the saturation adsorption amount of naphthol by CCP was only 1.5 times that by CP.The main mechanism of naphthalene and naphthol adsorption by CP is that multilayer adsorption of naphthalene and CP occurs due to hydrophobic effect and van der Waals interactions,and monolayer chemisorption of naphthol with CP surface is mainly attributed to the strong π-donor and π-π EDA effect in the polarized electron depletion region of CP surface.(2)High temperature can expand the pores of coal-based materials and increase the adsorption performance of naphthalene,but the performance of naphthol adsorption decreases significantly.ABC with good performance in naphthalene and naphthol removal was obtained by quenching and cooling at high temperature using BC as precursor,where high temperature increased the specific surface area of the material,changed the pore structure,removed the surface carboxyl groups and broke the ether bonds,which were the main reasons for naphthalene adsorption.The quenchant p H and the dissolved oxygen content in the quenchant can change the type and number of functional groups and defects on the surface of the material,which is the key to naphthol adsorption.The optimum preparation conditions were 0.04 mg/L of dissolved oxygen in the quencher,1000°C calcination temperature and neutral quencher p H,when the removal rates of naphthalene and naphthol reached 94% and 96%,respectively.The adsorption experiments showed that ABC could achieve high removal of naphthalene and naphthol in a wide p H range(3-11),and the removal rate was still more than 80%after five cycles.The isothermal adsorption results showed that naphthalene was adsorbed in multiple layers on the ABC surface with a saturation capacity of 112 mg/g due to hydrophobic effect and van der Waals interactions,while naphthol was adsorbed in a single layer on the ABC surface with a saturation capacity of 6.72 mg/g due to π-πEDA and hydrogen bonding.The capacity was significantly enhanced.