Preparation Of Novel Polycarboxylate-chitosan Based Flocculant And Application Performance

The key to strengthening wastewater treatment and reuse is to effectively control pollutants in water.Flocculation is the most important first grade treatment in water pollution control.It can be targeted to remove a variety of pollutants with complex components in the water,and its removal efficiency mainly depends on the performance of the flocculant.The traditional flocculants have few active sites,which leads to its very limited ability to remove inorganic ions and organic macromolecules in water.To breakthrough the limitations,this study selected the natural aminopolysaccharide chitosan as the grafting backbone and the bio-based itaconic acid as the polycarboxylic acid monomer for the purpose of enhancing the adsorption capacity of the floccualnt,thereby preparing an organic/organic composite polycarboxylic acid-chitosan based flocculant CS-g-P?AM-IA?.Combined with the carrier flocculation technology and magnetic separation technology,an inorganic/organic composite polycarboxylic acid-chitosan based magnetic composite flocculant Mag@PIA-g-CS was prepared by graft copolymerization on the surface of a vinyl magnetic core.The two flocculants were systematically investigated by a series of characterization methods and applied to various water pollution areas.The action mechanism buried in the flocculant and different pollutants was revealed.The main research contents and conclusions are as follows:?1?The results of fourier transforms infrared spectroscopy?FTIR?,magnetic resonance spectrometer?¹H NMR?and X-ray diffraction patterns?XRD?indicated that the targeted flocculant CS-g-P?AM-IA?was successfully synthesized.The introduced polymer molecular side chain made the ordering of the whole structure collapsed by weakening the hydrogen bond on the main chain of chitosan.Compared with CS and CS-g-PAM,the surface structure of CS-g-P?AM-IA?is relatively irregular,with more pore structure and larger fractal dimension of 1.329.In addition,the solubility of the grafted product CS-g-PAM and CS-g-P?AM-IA?is greatly improved,and can be dissolved well within the pH range of 2.0¹2.0.The effect of total incoming mass fraction,CS accounted for the total feed mass fraction,monomer mole ratio n_?AM?:n_?IA?,initiator concentration,pH value and ultraviolet illumination time on the product viscosity and grafting efficiency was studied,thus the optimum synthesis conditions were obtained.?2?The flocculant CS-g-P?AM-IA?was used for the treatment of kaolin wastewater,crystal violet?CV?dye wastewater and actual papermaking wastewater.During the flocculation process,CS-g-P?AM-IA?fully exerted its bridging effect of polymer chains and the characteristic adsorption of all active groups.Under the optimimmum conditions such as dosage and pH,CS-g-P?AM-IA?presented excellent removal efficiency in the application of kaolin suspension particles and CV dyes.The CV dye removal efficiency of CS-g-P?AM-IA?was better than that of CS-g-PAM,and with relatively larger kaolin floc size.In the actual papermaking wastewater treatment,CS-g-P?AM-IA?combined with CaCl₂ has significantly better COD removal rate and turbidity removal rate than the commercial CPAM,and the supernatant of treated wastewater was clear.?3?The solvothermal method was used to successfully synthesize Fe₃O₄ magnetic nanoparticles with good morphology,crystal shape and magnetic response.The magnetic composite flocculant Mag@PIA-g-CS was prepared by graft copolymerization on the surface of vinyl-modified Fe₃O₄ magnetic nanoparticles.The chemical composition,structure and morphological characteristics of Mag@PIA-g-CS were characterized using a variety of characterization methods.The results of fourier transforms infrared spectroscopy?FTIR?,magnetic resonance spectrometer?¹H NMR?and thermogravimetric analysis?TGA?indicated that IA and CS was successfully grafted into the magnetic product Mag@PIA-g-CS,and the product still maintained good crystal structure and with good thermal stability.The saturation magnetization value of Mag@PIA-g-CS and Mag@CS are significantly lower than magnetic core Fe₃O₄ particles,but still have good magnetic response performance.In addition,the scanning electron microscopy and transmission electron microscopy analysis show that the Fe₃O₄ magnetic nanoparticles are well dispersed and relatively uniform in size,while the magnetic particle surface of Mag@PIA-g-CS is surrounded by a thin layer of translucent organic matter and forms a clear class core-shell structure.?4?Due to the effect of a large number of carboxyl active groups,Mag@PIA-g-CS showed significantly better flocculation performance in removal of heavy metal Ni?II?ions and cationic malachite green?MG?dyes than Mag@CS.The removal of Ni?II?ions and MG dye molecules by Mag@PIA-g-CS was greatly affected by the ionic strength of the water and the presence of coexisting cations,which indicates to some extent that the interaction process mainly occurs through ion exchange and electrostatic interactions.The morphology of Mag@PIA-g-CS after attached with contaminants has undergone great changes.The structure of Ni?II?-containing flocs is relatively loose,whereas the structure of MG-containing flocs is relatively dense and the magnetic nanoparticles contained therein are encapsulated more compact,but both flocs maintained good magnetic separation performance.X-ray photoelectron spectroscopy was used to analyze the binding state of C 1s and N 1s peaks for Mag@PIA-g-CS and flocs.After flocculating the target pollutants,the binding energy and relative content ratio of each binding state of the C 1s and N 1s peaks changed significantly,with the appearance of new peaks.Mag@PIA-g-CS has good acid stability and recyclability.After five consecutive cycles of flocculation/regeneration,the flocculant's absorption capacity was still slightly reduced but it still maintained good removal efficiency.?5?The coagulants PAC/PFS loading magnetic powder were used to compare with the laboratory-made magnetic composite flocculant Mag@PIA-g-CS.In the treatment of highly turbid organic micro-polluted water,Mag@PIA-g-CS showed a significantly superior removal effeciency of turbidity and UV₂₅₄ than conventional PAC/PFS loading magnetic powder,and the treatment effect was more stable over a wide p H range.