Preparation Of Composite Coagulant And Coagulation Performance With Coal Fly Ash And Iron Scale

Fly ash is a typical industrial solid waste.For a long time,the huge stockpiles of them have not only seriously threatened the ecological balance,but also wasted such high-value renewable resources.At present,the utilization of fly ash is mostly concentrated on the fields of building materials and backfilling,but the utilization rate of chemical products is still relatively low.Iron scale is the scrap produced in the process of rolling,the content of ferrum is very high,generally returned to metallurgy process.In this paper,polysilicate aluminum chloride(PASC)and polysilicate aluminum ferrite(PSAF)coagulants were prepared by activation extraction of aluminum ferric and silicon from Jungar high alumina fly ash and Laigang Group iron scale,in addition,their microstructure characterization and coagulation mechanism were studied.The optimum experiment conditions of fly ash-sodium carbonate were below:the calcination temperature was 900 ?,the calcinations time 3 hours,the n(Na2CO3):n(SiO2)was 0.8,the hydrochloric acid concentration was 3 moL/L,the dosage of HC1 was 120 mL,the leaching time was 0.5 hours,the leaching temperature was 40 ?.The dissolution rate of aluminum,ferrum and silicon were 96.4%,97.64%and 98%,respectively,and the residual rate was only 2.6%.Characterization for calcination clinker and leaching residue at 700 ??900 ?were studied:X-ray diffraction analysis shows that the refractory phase of fly ash reacted with sodium carbonate successively to produce nepheline and sodium aluminate acid.The patterns of scanning electron microscope show that porous structure was formed on the surface of spherical vitreum in fly ash.The results of fourier transform infrared spectroscopy show that the chemical bonding structure corresponding to the peak position was consistent with the phase analysis.The kinetic process of aluminum and ferrum indicated the leaching rate of them were controlled by both boundary layer diffusion and chemical reaction.Coagulants of PASC and PSAF were prepared by copolymerization.The optimum synthesis scheme of PASC were below:the n(Si):n(Al)was 6,the basicity was 1,the polymerization temperature was 45 ?,and the reaction time was 2.5 hours.Response surface methodology was used to optimize the synthesis scheme of PSAF:the n(Al):n(Fe)was 1.38,the basicity was 0.5,the polymerization temperature was 39.2 ?,the reaction time was 1.36 hours.X-ray diffraction test shows that polysilicic acid reacted with metal ion and its hydrolysate to form a new amorphous polymers.The results of fourier transform infrared spectroscopy show those characteristic absorption peaks of Si-O-A1 and Si-O-Fe at 1037 cm-1 and 950 cm-1.The patterns of scanning electron microscope and energy dispersion spectrum show that the aggregation and dendrification degree of the product are strong at appropriate molar ratio of A1 Fe and Si or basicity.The patterns of transmission electron microscope and energy dispersion spectrum show that the product has abundant spatial network structure.The analysis of thermogravimetry show that each weightless region corresponds to the corresponding endothermic peak in the differential scanning calorimetry diagram,and the chemical bond breaks near 750 ?(PASC)or 700 ?(PSAF).The residual weight of the product is nearly 50 percent,which indicates that the product is stable.The research of Me-Ferron time by time complexation colorimetry shows that the content of Alb in PASC was 54.57%,the content of Alb and Feb in PSAF were 53.58%and 44.82%,respectively,and the content of Alb+Feb was 98.4%.It can be seen that the introduction of ferrum reduces the content of Alb,but the total effective component was increased significantly,so the coagulation effect was enhanced.The results of coagulation experiment demonstrate that the removal rate of turbidity and organics increases first and then tends to be stable with the increase of coagulant dosage,increases first and then decreases with the increase of the pH of wastewater and time,the order of performance of the three coagulants is PSAF>PASC>PAC,and the coagulation process was controlled by multiple coagulation mechanism.The fractal dimension and particle size of those flocs is proportional to the former coagulation index,the height of sedimentation is inversely proportional to the fractal dimension.The absolute value of zeta potential of the flocs decreases first and then increases after the zero point.