Preparation Of Polysilicate Metal Salt Flocculants And Research On Fluorine Removal Performance

As water environment becomes worse,fluorine pollution is increasing in the water.People are easy liable to disease,such as dental fluorosis and fluorosis of bone,that drinking excessive fluoride water in the long term.Fluorine pollution has been one of the most recognized problems in the world.Coagulating precipitation is the most economical method of eliminating fluorine.The traditional flocculant has a large amount of flocculant and a lot of sludge applied in the treatment of fluoridated water.So it is imperative to study an efficient defluorination agent.Poly-silicate-aluminum-calcium(PSAC)flocculant is established by sodium silicate,aluminium chloride and calcium chloride as the raw material.Residual F^-concentration is as to evaluation index.In experiments,optimal preparation conditions of PSAC are studied by the single factor and orthogonal test method.The experimental results show that the optimal preparation conditions for the PSAC are that n(Si O₂)is 0.3 mol/L,the polymerization of p H is3,n(Al)/n(Ca)is 7:3,n(Si)/n(Al+Ca)is 1:4.The influence sequence of various factors on the fluoride removal effect of flocculant is this:n(Si)/n(Al+Ca)>n(Al)/n(Ca)>p H>n(Si O₂).Poly-silicate-aluminum-magnesium(PSAM)flocculant is established by using sodium silicate,aluminium chloride and magnesium chloride as the raw material.Residual F^-concentration is as to evaluation index.In experiments,optimal preparation conditions of PSAM are studied by the single factor and orthogonal test method.The experimental results show that the optimal preparation conditions for the PSAM are that n(Si O₂)is 0.3 mol/L,the polymerization of p H is 4,n(Al)/n(Mg)is 4:1,n(Si)/n(Al+Mg)is 1:4.The influence sequence of various factors on the fluoride removal effect of flocculant is this:n(Si)/n(Al+Mg)>n(Al)/n(Mg)>p H>n(Si O₂).According to the representation of the SEM,FTIR and XRD,the chemical reaction of the mixed solution generates a new substance(polysilicate metal salt flocculant)during the preparation of flocculant.It is not just a mix of chemical solution.PSAC and PSAM have chain,ring and network structures with large specific surface area.They can effectively adsorb and complexity F^-in water,and play a significant role in adsorption and bridging.The chemical bonds of Si-O-Al,Si-O-Ca and Si-O-Mg are discovered in the flocculant.Flocculant and F^-band together by forming Si-F,Al-F,Ca-F,Mg-F and other chemical bonds in water.Compared with the traditional flocculants of fluorine removal mechanism,polysilicate metal salt flocculants can remove F^-from water through chemical action.It makes the polysilicate metal salt flocculant achieve an ability better than the traditional flocculant that fluorine removal performance.In the process of coagulation and precipitation,appropriate flocculation conditions can improve the fluorine removal performance of flocculant.The optimum flocculation conditions of PSAC are as follows:p H is 8,water temperature is 25?,the rapid stirring time is 2 min,the rapid stirring speed is 240 r/min,the slow stirring time is 14 min,the slow stirring speed is10 r/min,the settling time is 20 min.The flocculant amount of 1.8 mmol/L can be reduced the F^-from 5 mg/L to 1.10 mg/L in water.Compared with the same weight traditional flocculant of PAC,the increased effect of PSAC is closer to 40%.The optimum flocculation conditions of PSAM are as follows:p H is 8.5,water temperature is 20?,the rapid stirring time is 1.5min,the rapid stirring speed is 280 r/min,the slow stirring time is 10 min,the slow stirring speed is 10 r/min,the settling time is 25 min.The flocculant amount of 1.8 mmol/L can be reduced the F^-from 5 mg/L to 0.9 mg/L in water.Compared with the same weight traditional flocculant of PAC,the increased effect of PSAM is closer to 45%.Polysilicate metal salt flocculant is an inorganic polymer flocculant.It has strong adsorption electric neutralization and adsorption bridge capacity,and the flocs formed are large and dense.It gets good defluorination and precipitation properties.It can remove fluoride from water quickly and effectively.Compared with the traditional flocculant,it has the advantages of less dosage,lower sludge moisture content,higher fluoride removal rate,and has broad application prospects.