Study on Behaviors of Scale Inhibition and Pollutant Adsorption in Circulating Cooling Water with the Synergy of Magnetic Field and Carbon Nanotubes
Author:Jiang Li Li
Supervisor:shen feng man zou zong shu
With the rapid development of iron and steel industry,the consumption of industrial water has increasedsharply.To save fresh water resources and reduce consumption in responding to an appeal by the national energy conservation and emissions reduction,the current iron and steel enterprises havewidely used the water supply mode of circulating cooling water and wastewater after treatment.But the resulting circulating water is easy to produce scale,corrosion,andheavy metals and organic pollution.Therefore,it is necessary to develop a method withnon-pollution,low cost,stable treatment effect to achieve inhibition of scaling,and removal of heavy metal and organic compound polutants.Based on the above reason,the present workproposed a new water treatment processthat utilize the synergic effect of magnetic field and carbon nanotube.The scale formation in the process of circulating cooling water treatment,pollutant adsorption behavior and mechanism of scale inhibition and decontamination effect,especially the synergic behavior of magnetic field and carbon nanotubes,including the mechanism and effect,were experimentally studied,to provide theoretical and technical supports for the technology development and application of new method.The main research contents and results are as follows.(1)Experiment of circulating water treatment with soly magnetic fieldwas conducted to determine the mechanism and effect of scale inhibition by magnetic field.The results show that,without magnetic treatment(0 T),the conductivity of circulating water changes slightly,showing that the number of ions in circulating water tends to be stable.The conductivity of circulating water with magnetic treatment increases gradually.When magnetic field intensity is 0,5 T,the conductivity is the greatest,showing that the ion content in the water is the greatest and the scale inhibition effect is the best.The optimum magnetic treatment conditions are:ion concentration of K4(900 mg/L),magnetic field intensity of K3(0.5 T),temperature of K2(303 K),time of K3(54 h),and water flow velocity of K1(0.17 m/s).Without magnetic treatment,the scale inhibition rate of circulating wateris 0 all the way,showing that calcium and magnesium ions in the circulating water have reacted with carbonate ions to form calcium carbonate and magnesium carbonate precipitation.When the magnetic field intensity is 0.5 T,the scale inhibition rate is the maximum,attaining 38%at 54 h.With increasing of magnetic field,the relative variation of the molecular internal energy of circulating water decreases,and the change of molecular activation energy increases,showing that the water tends to be stable,reaction between cations and anions is difficult,and thus scale formation is inhibited.The scales in circulating water without magnetic treatment are mainly composed of calcite,and scales with magnetic field are mainly aragonite and vaterite.(2)Fe3O4/MW CNTs composite material was prepared and adsorption experimentfor Pb2+ and Zn2 in circulating water was conducted.The TEM images of the prepared samples showed thata large number of Fe3O4 nanoparticles attached on the surface of carbon nanotubes.The particles are superparamagneticand the particle size is about 10 nm.The infrared spectraofFe3O4/MWCNTsshoweda Fe-O vibration peak at 599 cm-1.The XPS spectra showed that there were C,O and Fe elementsin the Fe3O4/MWCNTs,and atomic ratio was C:O:Fe = 0.82:0.11:0.07,showing that the mass fraction of Fe3O4is 14.20%.The hysteresis loop of Fe3O4/MWCNTs appeared as S type with saturation magnetization intensity of 50.10 A·m-2/kg.The residual magnetism and coercive force were both 0,showing its superparamagnetism.With the increase of solution pH,the adsorption capacityof Fe3O4/MWCNTsfor Pb2+o and Zn2+ increased significantly and the maximumwas achieved at pH=5.The adsorption kinetic experiment results show that the adsorption reached equilibrium at 6 h,and the equilibrium adsorption capacities of Pb2+ and Zn2+were 48.29 mg/g and 2.55 mg/g,respectively.The adsorption process follows the pseudo-second-order kinetic model.The adsorption process of Pb2+ and Zn2+ornto Fe3O4/MWCNTs follows the Langmuir isotherm model,and the maximum adsorption capacities of Pb2+ and Zn2+are 69.25 and 3.979 mg/g,respectively.(3)NH2-SH-Fe3O4/o-MWCNTs composite material was prepared as adsorbent and adsorption experiment for organic pollutants in circulating water was conducted.The TEM images of the samples showed that a thin film of about 6.5 nm was formed on the surface Fe3O4/o-MWCNTs.The surface of carbon nanotubes was covered uniformly by uniform Fe3O4 nanoparticles of about 10 nm.The VSM spectra showed that the adsorbent was superparamagnetic,and the saturation magnetization intensity was 32.8yAm2/kg.The infrared spectra showed that amine and thiol groups were loaded on the surfaces of carbon nanotubes.The TGA results showed that the mass fraction of amino group was about2.25%and that of thiol was about 14.6%.The adsorption experiment results show that,when pH is 6,the maximum adsorption capacities of NH2-SH-Fe3O4/o-MWCNTs for lead ions,zinc ions and phenolare 199.6,179.8 and 56.2 mg/g,respectively.The removal ratesof lead ions and zinc ions reached 98%and 94%,respectively.The adsorption kinetic results show that the adsorption process follows the pseudo-second-order kinetic model.The isothermal adsorption results show that the adsorption process of NH2-SH-Fe3O4/o-MWCNTs for Pb2+,Zn2+ and phenol followsmore closely with Freundlich model.The thermodynamic results show thatthe adsorption processes of NH2-SH-Fe3O4/o-MWCNTs for lead ions,zinc ions and phenol are spontaneous.The adsorption of lead and zinc ions is the combination of physical and chemical adsorptions.The adsorption of phenol is physical adsorption.All the adsorption processes are endothermic.(4)We performed the experiment that magnetic field and carbon nanotubes effecting circulating water.The results show that purified multi-walled carbon nanotubes inserted into the layer of graphene oxide and graphene oxide and carbon nanotube connected together to form a three-dimensional structure in TEM images.Fourier infrared spectrum of NH2-SH-GO/o-MWCNTs showed that Si-O and C-H stretching vibration peak was presented at 1106 cm-1 and 1445 cm-1,respectively.The appearance of absorption peak of Si-C,Si-O,Si-N,S-H,-NH2 groups directly proved amino and sulfydryl loaded successfully on the surface of GO/o-MWCNTs.XPS results showed that there were C,O,N,S and Si element in the adsorbent,and atomic percentage was 82.55%,11.76%,2.76%,1.56%and 1.37%,respectively.Conductivity of circulating water without magnetic field fluctuated slightly,and conductivity of circulating water quickly increased to 285 μs/cm at 15 min under 0.27 T.Variation of molecules activation energy without magnetic field is almost the same.The change of molecules internal energy slightly reduced at 0.27 T.Under synergy of magnetic field and carbon nanotubes,magnetic field can still have the effect of scale inhibition.And the effect was not weaker because of addition of carbon nanotubes.At the same time the existence of magnetic field can promote metal ions adsorption,inhibite phenol adsorption.The increase of temperature promotes the increase of conductivity of circulating water.The effect is not obvious for molecules internal energy,but reduced the activation energy.Besides the increase of temperature improve performance of lead ion and phenol adsorption.