Preparation And Properties Of Magnetic Polysilicate Metal Salt-polysaccharide Composite Flocculant

The progress of science and technology has improved productivity,however,every coin has two sides,while we enjoy the various conveniences they bring us,we must also pay attention to the damage and threat to the water environment in the production process.Flocculation technology has been widely used in the treatment of municipal wastewater and industrial wastewater due to its advantages of high efficiency,simple operation and low cost.The flocculation process relies on the action of contact and adhesion,so that the suspended particles in wastewater could form larger aggregates gradually through charge neutralization,bridging and cleaning.The selection of flocculant will directly affect the flocculation effect.This paper mainly studied the application of magnetic polysilicate metal salt-polysaccharide compound flocculant in the field of water treatment.Three magnetic composite flocculants were prepared,including magnetic polysilicate aluminum-ferrosilicate sodium carboxymethyl cellulose（Fe₃O₄-PSAF-CMC）,magnetic polysilicate aluminum-zinc chitosan（Fe₃O₄-PSAZ-CTS）and magnetic polysilicate aluminum-titanium sodium alginate（Fe₃O₄-PSAT-SA）.Fe₃O₄magnetic nanoparticles were prepared with ferric chloride and ferrous chloride as raw materials,and then Fe₃O₄and sodium silicate,aluminum sulfate,ferric chloride and sodium carboxymethyl cellulose were used to prepare Fe₃O₄-PSAF-CMC flocculant.Taking turbidity removal rate as the measurement index,the preparation conditions of flocculant were optimized,and the optimization results were as follows:the p H value of magnetic polysilicic acid was 3.0,the molar ratio of aluminum and iron to silicon was 1.0,the molar ratio of aluminum to iron was8/2,the mass ratio of sodium carboxymethyl cellulose to silicon was 0.2,the concentration of Fe₃O₄was 1.75 g/L,the reaction temperature was 40℃,the stirring time was 2 h,the stirring speed was 500 rpm,the curing time of magnetic polysilicic was 2 h,and the curing time of Fe₃O₄-PSAF-CMC was 18 h.X-ray diffraction analysis,fourier transform infrared spectroscopy,transmission electron microscopy,scanning electron microscopy,thermogravimetric analysis and vibrating sample magnetometer analysis were used to investigate the structure and morphology of the flocculant.The prepared Fe₃O₄-PSAF-CMC was used to conduct flocculation experiments on Songhua River water,and the optimal flocculation conditions were investigated by single factor experiment.The results showed that the flocculation effect was best when the normal temperature and neutral water sample were treated,the dosage of flocculant was 2 m L/L,and the sedimentation time was 30 min.Separate 50%of the precipitates produced after flocculation,and add Fe₃O₄-PSAF-CMC at the best dosage of 50%to flocculate the new Songhua River water sample.The turbidity removal rate could still reach more than 96%.Fe₃O₄nanoparticles,sodium silicate,aluminum sulfate,zinc sulfate,chitosan as raw materials to prepare Fe₃O₄-PSAZ-CTS flocculant,and explore the best preparation conditions,the best conditions for the preparation of flocculant:the p H value of magnetic polysilicate and Fe₃O₄-PSAZ-CTS was 1.0,the molar ratio of aluminum and zinc to silicon was 0.8,the molar ratio of aluminum to zinc was 8/2,the mass ratio of aluminum and zinc to chitosan was 8/2,and the concentration of Fe₃O₄was 1.45 g/L.The bonding structure and surface morphology of Fe₃O₄-PSAZ-CTS were analyzed by scanning electron microscopy,fourier transform infrared spectroscopy,X-ray diffraction and thermogravimetric analysis.The suitable flocculation conditions for Songhua River water samples were studied.When p H=8.0,Fe₃O₄-PSAZ-CTS dosage was 1.5 m L/L and sedimentation time was 20 min,the treatment effect was better.50%of the precipitate produced after flocculation was separated and 50%of the optimal dosage of Fe₃O₄-PSAZ-CTS was added to conduct flocculation experiment on the new Songhua River water sample,the turbidity removal rate was still above 95%.Fe₃O₄-PSAT-SA flocculant was prepared from Fe₃O₄nanoparticles,sodium silicate,aluminum sulfate,titanium sulfate and sodium alginate.The preparation conditions of the flocculant were optimized as follows:when the p H value of magnetic polysilicate was 3.0,the molar ratio of aluminum and titanium to silicon was 1,the molar ratio of aluminum to titanium was 8/2,the mass ratio of sodium alginate to silicon was 0.04,and the concentration of Fe₃O₄was 1.45 g/L,the performance of the prepared flocculant was the best.Scanning electron microscopy,fourier transform infrared spectroscopy,X-ray diffraction and thermogravimetric analysis were used to investigate the morphology and structure of the flocculant.The optimal flocculation conditions of Fe₃O₄-PSAT-SA for water samples from Songhua River were investigated by single factor experiment.The results showed that when 1m L/L flocculant was added to neutral water samples and the sedimentation time was20 min after flocculation,the turbidity removal rate could reach about 95%.Separate the flocs produced,and add 50%magnetic flocs（50%of all flocs separated）and 50%Fe₃O₄-PSAT-SA（50%of the optimal dosage of flocculant）to the new Songhua River water sample,and the turbidity removal rate was still about 95%.Polysilicic acid was easy to gelate,and the coordination and complexation of metal ions with silicate neutralizes the adsorption and bridging ability of polysilicic acid and the electric neutralization ability of metal salts,thus improving the stability of flocculant.At the same time,the participation of Fe₃O₄nanoparticles also made it possible to recycle the precipitate produced by magnetic flocculant.The flocs produced by the three flocculants prepared in this paper could be reused.Therefore,this will improve the economic benefits of the flocculant.Among them,Fe₃O₄-PSAF-CMC flocculant has the characteristics of strong stability,low preparation cost,and has the potential of long-term storage and conversion into powder sample storage.Fe₃O₄-PSAZ-CTS flocculant has the advantages of less dosage and better flocculation effect.Fe₃O₄-PSAT-SA flocculant has the characteristics of low preparation cost and less dosage.