Preparation Of Polysilicate Metal Salt Flocculant From High Silicon Aluminum-based Solid Waste And Its Performance Researc

Every year,a large amount of solid waste rich in silicon and aluminum（such as coal gasification ash and foundry dust）are produced around the world.Solid waste posed the serious threats to the ecological environment and human health if they not effectively managed and recycled.However,little research has been conducted on the resource utilization of coal gasification ash and foundry dust,as well as on the preparation of coagulant from coal gasification ash and foundry dust.In this paper,polysilicate aluminium ferric coagulant was prepared from coal gasification ash and foundry dust by copolymerization method.The main research contents include the efficient leaching of Si,Al and Fe from coal gasification ash;the effects of（Fe+Al）/Si molar ratio,p H,polymerization temperature and polymerization time on the performance of coagulants;the coagulation performance of coagulants on steel industry wastewater and breeding wastewater and their coagulation mechanism.The main results are as follows:（1）The roasting activation and alkali leaching conditions were optimized by orthogonal experiments,and the best acid leaching conditions were also investigated by response surface methodology to achieve efficient leaching of Si,Al and Fe from coal gasification ash.The optimized parameters of roasted coal gasification ash were included the roasting temperature of 900℃,mass ratio of raw material to co-solvent of 4.6:1,and roasting time of 2h.Acid leaching conditions were included the acid leaching temperature of 95℃,acid leaching time of 1.4h,and hydrochloric acid concentration of 5 mol/L.alkali leaching conditions were included sodium hydroxide concentration of 5 mol/L,alkali leaching temperature of 75℃,liquid-solid ratio of 10,and alkali leaching time of 0.5.The dissolution rates of Si,Al and Fe in coal gasification ash were 41.44%、53.61%and53.35%,respectively.（2）The factors influenced preparation of polysilicate aluminum ferric from leachate of coal gasification ash were investigated.The best performance of the polyaluminosilicate iron flocculant was obtained under the conditions of（Fe+Al）/Si molar ratio of 4.3 and p H at 2.The maximum removal rates of turbidity,COD,color and UV₂₅₄ from the steel wastewater were93.69%,62.66%,54.54%and 24.51%,respectively,which were significantly better than those of the commercial coagulants.Results of the polysilicate aluminum ferric by FT-IR,XRD and SEM showed that amorphous silica-aluminium-iron polymers were generated in the coagulant and formed a dendritic structure at a（Fe+Al）/Si molar ratio of 4.3.（3）The process of preparing polysilicate aluminum ferric from foundry dust by copolymerization was explored,and its coagulantion performance were evaluated.The optimum preparation conditions of polysilicate aluminum ferric from foundry dust contained the（Fe+Al）/Si molar ratio 5.4,polymerization temperature 50℃,polymerization time 2h and p H 2.Compared with commercial PSAF,the removal rates of COD,chroma,turbidity and phosphate in breeding wastewater are respectively increased by 8.93%,25.5%,30.6%and45.9%when the dose is 10 m L/L.（4）The content of Fe_b in polysilicate aluminum ferric flocculant is 24%on initial stage,but the content of Feb will decrease slowly with increasing time.Results from Zeta and particle size analysis show that polysilicate aluminum ferric has strong adsorption and electric neutralization,and the average particle size of wastewater can reach 2138 nm after it is added to the breeding wastewater.In the range of p H 1-3.5,the higher the p H,the better the stability of coagulant,and the best coagulation performance and good stability for coagulant occurred at p H at 2.