Preparation Of Flocculant Cationic Metal-polysilicate From Fly Ash And Its Application In Wastewater Treatment

Nowadays,water pollution is serious in all parts of the world,and the treatment and purification of waste water is one of the problems have catched every country's attention.Flocculation sedimentation technology,one of the most popular water treatment methods,can not only be directly used in wastewater treatment,but also can be used as a pretreatment method and remove the pollutants in the water by other methods.Fly ash is the main solid waste discharged from coal-fired power plants and coal-fired boilers.China is a big coal-burning country and produces a large amount of fly ash every year.Because the fly ash has a large number of silicon,aluminum,iron and other materials which can be used for the preparation of flocculant,in this paper,fly ash has be used to produce a new flocculant,cationic metal-polysilicate.The research work and achievements of this paper are as follows:1.The preparation of cationic metal-polysilicate flocculant by using fly ash is mainly divided into three processes,roasting,acid leaching and aging.Firstly,fly ash mixed with cosolvent sodium carbonate will be roasted at a high temperature.Then use concentrated hydrochloric acid to leach silicon,aluminum,iron element.Add metal salt into the pickling liquid in proportion,polymerize and age together to get flocculant.During roasting process,the ratio of the sodium carbonate and the amount of Si substance in the fly ash is 1:2,roasting tempreture is 900 ? and roasting time is 60 min.During acid leaching process,the concentration of hydrochloride acid is 4 mol/L,leaching tempreture is 110 ? and leaching time is 1 hour.At this time,the leaching rate of Al3+ was 72.1%,the leaching rate of Fe3+ was 78.5%,and the leaching rate of Si was 66.2%.2.The best preparation conditions for the flocculant are:SiO2 concentration 2.5%,mole ratio of metal ions and Si is n(M):n(Si)= 1:1,molar ratio of aluminium,iron,magnesium ions is n(Al):n(Fe):n(Mg)= 3:1:4,pH value of 3.0,then aged under 40 ? for 2 h.3.Flocculant's optimum processing conditions are:dosing quantity 8 ml/L,wastewater pH around 11,temperature 30? or so,flocculating settling 2 h.At this time,the removal rate of COD in wastewater can reach 77.8%,the chroma removal rate can reach 94.8%,the total nitrogen removal rate is about 33.4%,the total phosphorus removal rate can reach 95.3%,the ammonia nitrogen removal rate was 45.2%.4.The cationic metal-polysilicate flocculant compared with PFS,PAC,the removal rates of COD,total nitrogen,total phosphorus in waste water is better,the chroma removal rate is close to the PAC,the removal rate of ammonia nitrogen is close to PFS and better than PAC obviously.