Research On Deep Removal Of Acidity Complex Nickel By Using Magnetic Flocculation Coupled With Highly-efficient Heavy Metal Chelating Agent EDTC And Magnetic Seeds Recycle

As an important source of nickel containing effluent,electro-plating wastewater is both complex and uncontrollable.Nickel ion combines with complexing agents,forming different nickel complexes,to make electroplating wastewater more difficult to manage and treat.EDTC(N,N-bis-(dithiocarboxy)ethanedi amine),a highly-efficient heavy metal chelating agent,provided an enlightening insight to deal with electro-plating wastewater since it was able to attacked directly the complex heavy metal.Magnetic flocculation technology shows excellent settleability on account of enhancing the flocculation property and improving the structure of folcs.The paper aims to investigate the deep removal of complex nickel from wastewater by using magnetic flocculation coupled with EDTC,explore the the magnetic flocculation mechanism involved in the reaction and magnetic seed recycling.Firstly,CA-Ni(citric acid,CA),TA-Ni(tartaric acid,TA)and SP-Ni(pyrophosphate,SP)were dissolved in deionized water as the simulated wastewater.Important investigated parameters included EDTC dosage,magnetic seeding dosage,initial pH and sedimentation time.The results indicated the residual Ni concentration could be less than 0.1 mg/L from the initial concentration of 50 mg/L,under the conditions of 100 mg/L magnetic seeds(350 r/min,2 min),MEDTC/MNi=10(250 r/min,2 min),PAM I mg/L(50 r/min,3 min)and 5 min sedimentation time with unregulated pH.The residual Ni concentration met the requirement of the maximum allowed discharge concentration for nickel in the Discharge Standard of Electroplate Contaminant(GB21900-2008).The technology of magnetic flocculation coupled with EDTC performed better than EDTC used alone cause the former reduced 20%EDTC dosage and shorten the sedimentation time.Orthogonal test indicated the primary and secondary order of parameters that affected the complex nickel removal rates is pH,EDTC dosage,magnetic seeding dosage,sedimentation time.Secondly,the magnetic separation experiments on complex nickel were conducted based on above experimental design and results.Important investigated parameters included hydraulic retention time,magnetic seed dosage,and magnetic field strength.The experiment resulted in a residual Ni concentration of less than 0.1 mg/L compared to the initial concentration of 50 mg/L.The experimental conditions leading to these results were:70 mg/L magnetic seeds(350 rpm,2 min),3 min hydraulic retention time,and 3.5A electrical current.This demonstrated that magnetic separation was a promising technique due to its time saving.Orthogonal test indicated the primary and secondary order of parameters that affected the complex nickel removal rates by using magnetic separation technique is magnetic seed dosage,magnetic field strength and hydraulic retention time.Thirdly,magnetic seed recycling was examined systematically.Magnetic flocs were collected using a magnetic separation device and soaked in sodium hydroxide solution.Magnetic seed recovery reached 76.42%after 3 hr of stirring,and the recycled magnetic seeds were still effective in enhancing flocculation.The SEM and XRD of recycled and unused magnetic seeds showed no apparent variations in morphology,even the XRD of recycled magnetic seeds showed a high magnetite(Fe3O4)level.Zeta potentials,particle size distribution and fractal dimension were determined to probe into the magnetic flocculation mechanism.The Zeta potential results illustrated that magnetic seeds firmly combined with flocs when the pH ranged from 6.5-7.5,due to the electrostatic attraction.When the pH was less than 7,magnetic seeds and EDTC also combined due to electrostatic attraction.The particle size analysis and fractal dimension presented that it would decrease the micro flocs,increase the floc volume and density by loading the magnetic seeds.