Preparation Of Polysilicate Flocculant From Fly Ash And Its Application

Fly ash is a kind of solid waste produced by coal-fired power stations.The main components of fly ash are silica and some metallic oxides.It can be used to prepare high-performance polysilicate flocculants.In this experiment,polysilicate flocculant was prepared by using fly ash and salt with high temperature roasting and acid leaching.The magnetic separation wastewater generated during the iron ore beneficiation process contains a lot of suspended ore powder particles,heavy metal ions and organic agents.Using the flocculants prepared with fly ash to treat the iron ore magnetic separation wastewater can achieve‘treatment of wastes with processes of wastes against one another'and the purpose of energy conservation and environmental protection.Firstly,the fly ash raw material from Kunming Power Plant in Yunnan Province was analyzed and characterized.Most of its granules is irregular particles with smooth surfaces and some particles approximately sphere.The main components are quartz,limonite,mullite and some amorphous substances.The chemical composition is mainly O,Si,Al,Fe.The particle size distribution is between 0.16 and 100?m,and the average particle size is 13.31?m.Secondly,Na₂CO₃ and Na HCO₃ were used to modify fly ash.It was found that the prepared flocculants had higher removal rates of iron ore magnetic separation wastewater turbidity and COD,reaching more than 90%,and the results were similar.The sintering degree of the products modified with Na HCO₃ are less severe as those obtained with Na₂CO₃.Therefore,using Na HCO₃ to modify fly ash was decided,the optimal experimental conditions were alkali-ash ratio as 0.75,roasting temperature as800?and roasting time as 60 min.Thirdly,the optimal process conditions for preparing polysilicate flocculant were hydrochloric acid concentration as 18%(mass fraction),liquid-solid mass ratio as 12,reaction temperature as 20?,stirring speed as 100 r/min,stirring time as 5min,and aging time as 60min.Under these conditions,the effluent turbidity removal rate was95.89%,and the COD removal rate was 99.16%.Then,the obtained polysilicate flocculant was characterized by infrared spectrum,X-ray diffraction,scanning electron microscope–energy dispersive spectrometry,Zeta potential,and particle size distribution.The results show that the main phase composition of polysilicate flocculant is Si-O,Si-O-metal and Si-Cl bond compounds.It is a cationic flocculant.Microscopic morphology is rough,porous irregular particles on the surface.The particle size is mainly concentrated between 2?m-100?m,and the average particle size is 15.32?m,which is basically normally distributed.The polysilicate flocculant prepared by the optimal process conditions is used to treat the iron ore magnetic separation wastewater.The optimal process conditions were the flocculant dosage as 10 m L/L,p H as 9,temperature as 80?,fast stirring speed as400r/min,fast stirring time as 2 minutes,slow stirring speed as 120 r/min,slow stirring time as 25 minutes and settling time as 60 minutes.Under these conditions,the turbidity removal rate of iron ore magnetic separation wastewater was 97.30%,and the COD removal rate was 99.10%.Finally,the turbidity-time relationship of the water treatment sediment ation process was fitted with second-order reaction kinetic model and hyperbola model.It was found that the second-order kinetic model has a greater correlation coefficient and can better describe the edimentation process of polysilicate flocculant treating iron mine magnetic separation wastewater.The research on the storage stability of polysilicate flocculants found that compared with the polysilicate flocculants that prepared just before use,the water treatment performance of polysilicate flocculants that had been storage for a long time had a significant decline,but it still remained within the 91-day inspection range Higher flocculation performance.Low p H is beneficial to keep the flocculant with high flocculation performance for a long time.High p H will destroy the molecular structure of the flocculant and cau se the flocculation performance and storage stability to decrease.Properly increasing the liquid-solid ratio of the flocculant,that is,increasing the water content of the flocculant is conducive to maintaining high flocculation performance for a long ti me.Too low or too high liquid-solid ratio will lead to poor storage stability.