Theoretical Basis And Application Demonstration On Advanced Treatment Of Electroplating Wastewater Based On Magnetic Exchange Resins Adsorption

Electroplating wastewater is a typical combined wastewater containing heavy metal ions,anionic surfactants,complexing agent,etc.It is difficult to remove a variety of pollutants effectively and simultaneously with conventional water treatment process.Heavy metal ions and organic compounds could interact with each other and change their existing forms,elevating the difficulty of its treatment,and thus pose a serious toxicological threat to the ecosystem and human health.In view of the serious environmental problems caused by electroplating wastewater,the Environmental Protection Ministry issued "GB21900-2008 plating emission standards",which was enforced on August 1,2008.Implementation of the new standards proposed more stringent requirements for heavy metals and COD.Conventional treatment methods cannot meet the increasing emission standards,therefore advanced treatment is indispensable.Various treatments such as membrane filtration,biotechnology,adsorption and ion-exchange have been employed to the advanced treatment of electroplating wastewater,but they all have their inherent advantages and limitations.Among these methods,ion-exchange is suitable for advanced wastewater treatment,especially for those laden with pollutants of low concentration.However,the diameter of conventional resin is about 0.3?1.2 mm,leading to the high investment of fix-bed equipment and complex operation.MIEX-Cl,a magnetic anion exchange resin developed by Orica,is the only commercial magnetic resin so far It has the characteristics of small size,fast kinetic and easy separation.Recently,MIEX-Na,a magnetic weak acid resin has been developed by Orica.Boyer combined MIEX-Cl and MIEX-Na in a full-mixed reactor for removal of organic matter and hardness,and further reduced the cost of investment in the construction of the water treatment.Based on the above background,this thesis employed magnetic weakly acid exchange resin NDMC and magnetic strongly anion resin NDMP developed by Nanjing University,to study their adsorption behavior and mechanism on the typical heavy metals and organic acid in electroplating wastewater.Base on the study,the advanced technology of combined magnetic resins was applied in practical projects.Cu(?)was chosen as the typical heavy metal because of its common use in electroplating industry.The adsorption behavior of Cu(?)on NDMC and commercial resins C106 and IRC-748 were deeply investigated.Resin structure(including pore size,particle size,and exchange capacity)was taken into account to explore the influence mechanism on the adsorption rate.It was deduced that the particle size and exchange capacity were the main factors in rate-controlling.The adsorption kinetics of Cu(?)onto the three resins fitted well with the pseudo-second-order equation.The initial adsorption rate h of NDMC was about 4 times that of C106 and nearly 8 times that of IRC-748.NDMC resin with the smallest bead radius possessed the largest external surface.The increase of contact surface area led to the decrease of effective distance between the adsorbent and the target ion.The acting force(F)between Cu(?)and NDMC was highest of all.Therefore,NDMC had the fastest kinetic property among three investigated resins.The effect of organic acid on adsorption showed that at pH lower than 4.5,the coexistence of citric acid and tartaric acid inhibited the adsorption of Cu(?)on the NDMC.At pH higher than 4.5,the presence of tartaric acid promoted the adsorption of Cu(?)on the resin.HCl solution(pH 2)could effectively desorb more than 95%of Cu(?).The adsorption properties of NDMP for sodium dodecyl benzene sulfonate(SDBS),oxalic acid(OA)and citric acid(CA)commonly used in electroplating were also studied.The adsorption isotherm of three kinds of organic acids onto the NDMP fitted well with Langmuir equation,indicating that the adsorption of organic acids on the resin was monolayer adsorption.The maximum adsorption capacity Q0 for SDBS,OA and CA were 2.97 mM/g,1.64 mM/g and 0.959 mM/g at 303 K,respectively.By studying the adsorption behavior of NDMP for SBDS-Cu,OA-Cu and CA-Cu composite components,it was demonstrated that NDMP can simultaneously adsorb OA-Cu and CA-Cu,and the adsorption amount increased with the increase of pH.When pH is higher than 3,Cu(?)was mainly present as[Cu-(Oxalate)2]2-in OA-Cu solution and then co-adsorbed onto the resin.In CA-Cu solution,Cu(?)was mainly in[Cu-Citrate]" form and was co-adsorbed to NDMP.NDMC and NDMP and their combined processes were employed to simultaneously remove such heavy metals(HMs)as Cu(?),Ni(?)and tannic acid(TA).Both NDMC and NDMP resins exhibited co-removal capability for Cu(?)and TA in binary solutions.Complexing-bridging was ascribed as the primary mechanism for the co-removal of TA and Cu(?).Moreover,hydrogen bond interaction between both nitrogen atom of the secondary amine(-NH-)and oxygen atom of carbonyl(C=O)with un-ionized TA,and quaternary ammonium(-N+(CH3)3)ion exchange with ionized TA were ascribed to the mechanism of TA adsorption onto NDMP.The novel integrative technique based on NDMP and NDMC mixed completely in the same reactor could simultaneously remove Cu(?),Ni(?)and TA with high efficiencies of 92.1%,94.8%and 88.4%,respectively.After the magnetic resin technology were applied to practical electroplating wastewater advanced treatment in north part of Jiangsu Province,the effluent can reach the GB21900-2008,surface water quality standard GB3838-2002 ? and the EPA833-B-94-002 toxicity limits requirements(chronic toxicity 1TUc,acute toxicity 0.3TUa).The fixed investment costs of 3600 yuan/m3 and the processing costs of 1.53 yuan/m3 demonstrated that the magnetic ion exchange treatment can be applied as advanced electroplating wastewater treatment processes.