Adsorption And Removal Of Tetrakis (Hydroxymethyl) Phosphonium Chloride And Its Resource Utilization

Tetrakis（hydroxymethyl）phosphonium chloride（THPC）is widely used as flame retardant,chrome-free tanning agent,bactericide,etc.However,the direct or indirect THPC in wastewater will cause serious harm to the ecological environment.Therefore,Recycling THPC from wastewater and settling it in river and lake sediment for sterilization provides a new idea for THPC emission reduction and resource recycling.In this paper,grapefruit peel biochar prepared under different pyrolysis conditions(BC₃₀₀,BC₄₀₀,BC₅₀₀,BC₆₀₀,BC₇₀₀,and BC₈₀₀)was selected,at the same time,by one-step pyrolysis of biomass and KOH,Al Cl₃,ZnCl₂ to prepare KOH-activated biochar(KOH-BC₇₀₀),Al Cl₃-activated biochar(Al Cl₃-BC₇₀₀),ZnCl₂-activated biochar(ZnCl₂-BC₇₀₀)at 700℃.The materials were characterized and analyzed by XRD,FT-IR,SEM,BET,etc.,and were applied to simulated wastewater for adsorption of THPC.The bactericidal effects of BC₇₀₀(THPC-BC₇₀₀)and KOH-BC₇₀₀(THPC-KOH-BC₇₀₀)on Escherichia coli after adsorption of THPC were explored.The main findings are as follows:（1）The characterization results showed that BC₇₀₀ has a wrinkled fragmented structure with few surface pores.while KOH-BC₇₀₀ contains meso-microporous structure,with the higher specific surface area of 512 m²/g,as well as larger micropore and mesopore volume.The mesoporous pore volume of the Al Cl₃-BC₇₀₀ increased and weakly crystalline Al₂O₃ crystals were produced on the surface of the sorbent.The micropore volume of the ZnCl₂-BC₇₀₀ was increased,and Zn O crystals were produced on its surface.（2）Adsorption experiments showed that compared with biochar prepared at other pyrolysis temperatures,the pristine biochar prepared at a pyrolysis temperature of 700°C had the best adsorption effect on THPC.Compared with BC₇₀₀,the adsorption capacities of KOH-BC₇₀₀,Al Cl₃-BC₇₀₀,and ZnCl₂-BC₇₀₀ were significantly improved,and KOH-BC₇₀₀ revealed the best adsorption effect.The maximum adsorption capacities of BC₇₀₀,KOH-BC₇₀₀,Al Cl₃-BC₇₀₀ and ZnCl₂-BC₇₀₀ for THPC removal were 239.6 mg·g^-1,438 mg·g^-1,301.6 mg·g^-1 and278.9 mg·g^-1,respectively.The adsorption process of the four adsorbents toward THPC removal reached the adsorption equilibrium in about 720 minutes.The adsorption kinetic data of the four adsorbents are consistent with the adsorption pseudo-second-order kinetic model,and the adsorption isotherms are more fit with Langmuir adsorption isotherm model.Intraparticle diffusion is not the only controlling step,and adsorption thermodynamic models show that the adsorption process is spontaneous and endothermic.The adsorption mechanisms of these four biochar for THPC removal include pore filling,cation-πinteraction,hydrogen bonding interaction,and ion exchange.（3）The sterilization performance experiments showed that the sterilization effect of THPC-KOH-BC₇₀₀ is stronger than that of THPC-BC₇₀₀.When the dosage is 4 mg and the concentration of bacterial liquid is 5.225×10³ CFU/m L,the sterilization rate reaches 100%within 40 minutes.The bactericide kinetics of THPC-KOH-BC₇₀₀ acting on Escherichia coli suspensions are confirmed in the Weibull model.The bactericide kinetics of THPC-BC₇₀₀ acting on Escherichia coli suspensions fit with the First-order log-linear model.