Preparation Of Core-shell Structured Magnetized Water-clearing Agent And Evaluation Of Its Treatment Effect On Poly-containing Sewage

In order to meet the demand for crude oil,polymer flooding is widely applied to enhance the crude oil recovery at present.Although polymer flooding can effectively enhance the oil recovery,the problem of oily wastewater treatment is also brought about.Due to the presence of natural surfactants and residual polymers,oily wastewater is a kind of stable O/W emulsion.In order to make the oily wastewater reach the discharge standard,it is usually treated by chemical method.At present,the cationic water clarifier is widely applied,and novel nonionic water clarifier has attracted general attention.However,there are some deficiencies in both kinds of water clarifiers.Aiming at these deficiencies,a new kind of magnetic water clarifier was developed.The characterization of its properties,evaluation of performances and study of mechanism of the water clarifying process were carried out.First of all,a novel magnetic water clarifier was synthesized through the three steps reaction of a type of non-cationic water clarifier.The resultant products displayed excellent treatment effect for oily wastewater,and could be recycled for several times under an external magnetic field.A series of characterizations of the magnetic water clarifier were carried out,including scanning electron microscope,transmission electron microscope,Zeta potential,X-ray diffraction,infrared spectroscopy,thermogravimetric analysis,saturation magnetization and contact angle.It was found that the magnetic water clarifier was basically irregular solid particles with core-shell structure and the diameters were in the range of 160 to 260 nm,the saturation magnetization was about 55.2 emu/gThe performance of the magnetic water clarifier was evaluated.Specifically,the effects of the dosage,temperature,ultrasonic time,Fe3O4 particle size and the type of the nonionic polyether on its water-clarifying performance were studied.The results indicated that the optimum operation conditions of the resultant magnetic water clarifier was when the dosage was 2-2.5 g/L,the temperature was 65 ?,and the ultrasonic time was 6 min.Generally,smaller Fe3O4 nanoparticles had larger specific surface area,resulting in larger grafting ratios of the nonionic polyether water clarifier.Therefore,magnetic water clarifiers fabricated by smaller Fe304 nanoparticles usually had smaller size,stronger dispersibility and magnetization intensity and showed better water clarifying performance.The results also show the magnetic water clarifiers modified by different prepared polyethers have same good effect.The amount of nonionic polyether is similar to that of the surface of the magnetic water clarifier.The results show that the effect of the magnetic water clarifier depends on the nonionic polyether of the surface.When the effect of the polyether water clarifiers is good,the effect of magnetic water clarifiers is good.The removal rate of the recycled magnetic water clarifiers decreased.The experimental data showed that the particle size of the recycled magnetic water clarifiers increased.Moreover,the characteristic absorption peak of the polyacrylamide was found in the infrared spectra,which indicated that residual polymers in the oily wastewater was absorbed on the surface of the magnetic water clarifier,forming bridging materials and leading to the coalescence of the magnetic water clarifiers.Consequently,the specific surface area of the magnetic water clarifiers was reduced and the dispersibility was weaken,thereby the oil removal rate decreased.The results of the interfacial tension and adsorption experiments indicated that after added into the oily wastewater,the magnetic water clarifiers would spontaneously move towards the oil/water interface,decrease the interfacial tension,and adsorb the interfacial active substances there.The study of the three-phase contact angle suggested that the magnetic water clarifiers could not exist steadily at the oil/water interface.The microkinetics of the flocculation indicated that with the increase of both the concentration of the magnetic water clarifier and the operation temperature,the rate constant k increased and the half-time period t1/2 of the oil drop decreased.Therefore,the water clarifying mechanism was concluded as:after added into the oily wastewater,the magnetic water clarifiers moved towards the oil/water interface and absorbed the interfacial active substances which stabilized the oil/water interface.As the magnetic water clarifiers could not exist steadily at the oil/water interface,the adsorbed interfacial active substances were taken away from the interface,thus the interface was unstable,leading to the coalescence of oil drops and the ultimate demulsification.