Efficiency And Mechanisms For The Removal Of Ciprofloxacin In Water By Red Mud And Its Modification

Red mud is a solid waste produced in the process of industrial production of alumina.And 1?2 ton of red mud was produced with every 1 t of Al2O3.the world's Ted mud emission achieved 60 million t/a worldwidly,and it accounted for 1/15 in China.Due to its relatively low value of recycling,simple accumulation and deposition caused serious environmental problems.So it is of great scientific and practical value to study the recycling of red mud.So far,the adsorption of red mud for heavy metals,organic dyes and phosphates has been reported.In this paper,ciprofloxacin,a third-generation of quinolone antibiotic,was used as the target pollutant,the adsorption,catalytic oxidation and mechanism of red mud and its magnetic modification for ciprofloxacin were studied,and the main contents were as follows:(1)SEM,TEM,specific surface area and pore size analysis showed that red mud was composed of fine particles and dispersed irregular quadrilateral crystals,with the specific surface area of 10.96 m2·g-1 and the complex pore structure,with average pore size of 40.93 nm.BBD method was used to optimize the adsorption conditions of red mud for ciprofloxacin.And the model had significant adaptability to the adsorption amount and adsorption rate by the analysis of variance,K-S test and Pearson correlation.The fitted quadratic regression equation can reflect the relationship between the influence factors and the adsorption capacity/adsorption rate accurately and reasonably.The optimal adsorption conditions were as follows:adsorption temperature 25?,oscillation rate 247.87 r·min-1,pH=3.0,red mud dosage 3.46 g·L-1,ciprofloxacin initial concentration 29.44 mg·L-1,the predicted adsorption capacity was 7.50 mg·g-1,the adsorption rate was 97.48%.And the model satisfaction rate achieved 0.977.(2)The parameters affected adsorption showed that the optimal dosage of red mud was 3.5 g·L-1.The adsorption amount increased,adsorption rate changed slowly with temperature in range of 15-55? and ciprofloxacin initial concentration in range of 10-30 mg·L-1.pH value of 3.0 was more conducive to the adsorption.The adsorption process followed the pseudo-second-order reaction kinetics and the Langmuir-Freundlich isotherm model.The adsorption process contained various adsorption mechanisms,including fast,slow adsorption and intra particle diffusion.The adsorption mechanism showed that the-COO in ciprofloxacin molecule complexed with red mud surface,and C=O may have weak electrostatic or inner spherical bonding with red mud.Thermodynamic results showed that the adsorption is a spontaneous endothermic reaction.The saturated adsorption of red mud was more stable in the range of pH=9.0?11.0.(3)Red mud can effectively catalyze peroxymonosulfate(PMS)for the degradation of ciprofloxacin.Electron transfer of Al,Ti and Fe,Lewis acids such as Ca,Al and Na formed complexes with PMS,which generated more HO· and SO4-·,oxidized ciprofloxacin adsorbed on red mud surface.The reaction activation energy was calculated as 5.74 kJ·mol-1.The degradation rate maintained above 80%with pH value in the range of 5-11,which broadened the pH range of Fenton like reaction.Cl-?NO3-?HCO3-and H2PO4-inhibited or promoted ciprofloxacin degradation to a certain extent.After four repetitions,ciprofloxacin degradation rate decreased by 9.1%.The metal leach of red mud meet its safety standard.Eight byproducts were produced in red mud/PMS oxidation system and ciprofloxacin degraded in two ways.(4)Magnetic red mud CoFeRM was prepared by coprecipitation method.Compared with red mud,CoFeRM has larger specific surface area of 77.16m2·g-1,more complex pore structure with the average pore size of 10.75 nm,and excellent sedimentation performance.The adsorption capacity and adsorption rate red mud and CoFeRM on ciprofloxacin were 3.64 m2·g-1,42.53%and 4.25 m2·g-1 and 70.88%,respectively.The response surface optimization model can also reflect the relationship between the main factors and ciprofloxacin removal rate accurately.Similar to the adsorption of red mud on ciprofloxacin,CoFe2O4 adsorption on ciprofloxacin followed the pseudo-second-order kinetic,and was also a spontaneous endothermic reaction.(5)CoFeRM can effectively catalyze the ultrasonic/H2O2 degradation on ciprofloxacin,which was mainly due to the formation of HO·.Cl-?NO3-and HCO3-inhibited the degradation,while H2PO4-had rare effect.Ciprofloxacin degradation rate in lake and sewage water kept above 90%.CoFeRM still maintained good catalytic activity after four time of repetition.The ciprofloxacin TOC removal reached 50.03%,and 8 by-products were detected by UPLC-MS/MS.Ciprofloxacin was mainly degraded by piperazine ring cracking.The results of this paper had certain important reference value for the resource utilization of red mud and the treatment of ciprofloxacin-polluted wastewater..