Preparation, Characterization And Applications Of New Inorganic Polymer Composite Flocculant PPFS

Currently, flocculation has already become an inportent part of water treatment process. The core technology of flocculation process was the development of flocculants. It was the characteristics of flocculant which determined not only the flocculation effect but also the overall water treatment effect. The floc and precipitation produced by interaction between flocculant and colloidal particles and suspended matter contained in aqueous solutes were the key to remove various contaminants in water through flocculation. Development of new high quality flocculant was an important task of water treatment to improve the coagulant effect in water treatment, to reduce costs and to explore new application area. At present, one of water environment status was the continuous decrease of water resources, two issues were significant in water science, one of which was the limited water supply, and the other of which was the problem of wastewater. To be specific, the volume of wastewater was increasing dramatically with more and more kinds of pollutants and increasing complexity of the composition. Therefore, the difficulty of further treatment was increasing. Because the traditional flocculant could not meet the requirements of flocculation technology any longer, new research and development of flocculants has already been one of the important research topics.Because PO₄^3- played an important role to increased accumulation of Polymeric Ferric Sulfate (referred to as PFS), a certain quantity of PO₄^3- was introduced into the preparation of PFS and the Polymeric Phosphate Ferric Sulfate (referred to PPFS) and a new type of multi-core highly charged intermediate complex was produced. Compared to traditional inorganic flocculants, it possessed such characteristics as faster floc formation, higher particle density, higher settlement rate and higher removal rate of TP. In addition, it had numerous advantages such as safety, no secondary pollution, high efficiency, low consumption, low cost, high added value, adaptation to a wide range temperature and pH value. It could be used to replace expensive organic polymer flocculant partially. Nowadays, PPFS is a kind of inorganic polymer iron flocculants which has excellent prospects for development and application, which could be used in the treatment of a variety of industrial wastewater, sewage and drinking water.The main contents and conclusions in this study were as following:(1) By one factor analysis of PPFS preparation conditions, it was indicated that the product was most stable and the effect of flocculation was the best when the preparation temperature was 80℃, preparation time was 60min and the molar ratio nPO₄^3-/nFe³⁺ was 0.3 and B was 20%. On this basis mentioned above, the orthogonal was carried out with nPO₄^3-/nFe³⁺, B and preparation temperature as the three factors. The results showed that the treatment effect was the best when nPO₄^3-/nFe³⁺ was 0.3, B was 30% and the preparation temperature was 80℃.The B value obtained from the two experiments were different, indicating that there were certain interactions between preparation factors.(2) Stability of the PPFS was studied. Compared with the PFS, due to the introduction of PO₄^3-, the form of Fe in the aggregate was changed and the hydrolysis ability of Fe was weakened, which made PPFS more stable.(3) Advantagous form of the hydrolysis process of PPFS was studied, and the changes in the structure, composition and surface topography of PPFS after the introduction of PO₄^3- was investigated. Through timed spectrophotometry of Fe-ferron complexation, it was showed that the amount of Fea and Fec in Polymeric Phosphate Ferric Sulfate (PPFS) flocculants were the important factors in the three, while Feb was the transition states and the amount of Feb was small which had no significant effect. Play good flocculation mainly high polymer which exists with the forms of Fec. The Ultraviolet-visible spectrum showed that main forms of iron were Fe5(OH)96+,Fe5(OH)87+,Fe5(OH)78+,Fe6(OH)126+,Fe7(OH)129+å’ŒFe7(OH)1110+ in PPFS. Compared with the UV absorption spectra of PFS, a new absorption peak of PPFS generated at the 450nm, indicating that the introduction of phosphate changed the form of iron in PFS, [Fex (OH)y]2H2PO₄(6x-2y-1)+,[Fex (OH)y]2HPO₄(3x-y-1)+,[Fe_x (OH)_y]₂PO₄^(6x-2y-3)+ and other macromolecular complexes might be generated, the specific structure of which should be studied furtherly. The high-polymeric of PPFS was more when nPO₄^3-/nFe³⁺ was 0.3 and B * was 0.2. Infrared spectra showed that PPFS had similar characteristic absorption peak at 3400cm-1 and 1640cm-1, but peak area and the wave number were changed, which could be considered as elements of the-OH stretching vibration and the combination of H-OH bending vibration of water molecules. The peak shape changed more obviously in the wave number of 900 1200cm-1 and these peaks might be Fe-OH-Fe or Fe-PO₄ vibration, indicating that the polymer reaction occurred between the coexistence of iron ions in PFS and PO₄^3-, and Fe-PO₄ was formed after PFS being combined with PO₄^3- . X-ray diffraction analysis showed that the forms of iron in PPFS were mainly Fe4.67(SO₄)6(OH)2·20H₂O, FeHSO₄·4H₂O, Na₂HPO₄·2H₂O and so on. XRD analysis showed that a new phase of phosphate iron polymer was formed after the introduction of PO₄^3-. It was also indicated that PPFS was a new inorganic polymer composite flocculant based on the synthesis of PFS. SEM characterization showed that a large number of side chains on the surface of PFS polymer were formed because of the introduction of PO₄^3-, which gave excellent role of bridging to PPFS and enhanced flocculation performance dramatically.(4) Using PPFS in the treatment of urban domestic wastewater and it was found that it showed good removal effect for SS, COD and TP, among which, removal of TP was the most significant. The main influence factors for treatment of urban sewage by PPFS based on one-factor experiments with removal rate of COD and TP in sewage as the measurable indicators, were nPO₄^3-/nFe³⁺,Band dosage. Through Box-Behnken experiment design and Response Surface Analysis (RSA), optimization grouping of these 3 main influence factors was realized; a quadratic response surface model and optimum level values were obtained. It was found that the optimization grouping of the main influence factors for the removal of COD were as following: nPO₄^3-/nFe³⁺ being 0.28,B being 18.76% and dosage being 77.57mg/L, and under the optimum conditions, the removal rate of COD was 75.98%. The optimization grouping of the main influence factors for the removal of TP were as following: nPO₄^3-/nFe³⁺ being 0.36,B being 18.26% and dosage being 7.37mg/L, and under the optimum conditions, the removal rate of TP was 93.64%.A regression analysis was utilized to evaluate the fitness of the model. However, the relevance of COD was lower than that of TP, which was mainly due to the error of flocculation experiments and COD determination, especially in low concentrations of COD. In addition, comparing the effects of urban sewage treatment by PFS and PPFS, the results showed that the removal effects of turbidity, COD and TP by PPFS were better than that by PFS, and the pH value of the former was also more stable. Flocculation was realized by the effects of adsorption and bridging comprehensive role when treating sewage by PPFS.(5) Through experiments of treating micro-polluted water by PPFS, taking TOC removal and UV absorbance at a wavelength of 254nm as general indicators of organic matter removal, and six kinds of PAEs and 15 kinds of PAHs compounds as refinement indicators, application of PPFS was studied thoroughly.. The results of TOC removal and UV254 showed it had a certain remove effect in organic compounds of micro-polluted water by PPFS. The results of PAEs and PAHs showed that there was a more significant removal effect of these two types of organics by PPFS. The main influence factors for the treatment of micro-polluted water by PPFS based on one-factor experiments with removal rate of TOC in water as the measurable indicator were nPO₄^3-/nFe³⁺,Band dosage. Through Box-Behnken experiment design and Response Surface Analysis (RSA), optimization grouping of these 3 main influence factors was realized; a quadratic response surface model and optimum level values were obtained. It was found that the optimization grouping of the main influence factors to TOC were as following: nPO₄^3-/nFe³⁺ being 0.30,B being 28.54% and dosage being 16.35mg/L, and under the optimum conditions, the removal rate of TOC was 21.71%.A regression analysis was utilized to evaluate the fitness of the model. Flocculation was realized by the effects of adsorption and bridging comprehensive role when treating sewage by PPFS.