Study On Synthesis Of Zeolite From Fly Ash And Adsorption/Electric Field Assisted Adsorption Properties For Ni²⁺

Power plant coal ash is a solid waste formed by coal combustion in thermal power plants.It is rich in silicon and aluminum sources and is an important substitute for molecular sieves.as raw material for treating heavy metal wastewater,the zeolite molecular sieves prepared from fly ash?CFA?can not only realize the utilization of solid waste,but also serve as an efficient and cheap adsorption material for the treatment of heavy metal-containing wastewater,which has important economic and environmental benefits.In this paper,NaA zeolite molecular sieves were prepared by alkali fusion hydrothermal synthesis using solid waste fly ash fromthermal power plant as raw material.The synthesized products were characterized by SEM,XRD,FT-IR and TG.When treating Ni²⁺-containing wastewater with the synthesized molecular sieves as adsorbent,the effect of adsorption time,ion concentration and zeolite dosage on the adsorption performance of Ni²⁺simulated wastewater and actual wastewater was studied,respectively.The adsorption process and behavior of the productswere analyzed.Besides,the effect of electric field on the adsorption of Ni²⁺by synthesized zeolites and its influence mechanism were studied.The main findings are as follows:?1?The NaA zeolite molecular sieve was synthesized by alkali fusion hydrothermal method.The optimized synthesis parameters were alkali-to-ash ratio 1:1,calcination temperature 650°C,liquid-to-solid ratio 7:1,and crystallization temperature 100°C.The phase analysis showed that the synthesized NaA zeolite molecular sieve had a regular cubic structure with uniform particle distribution and a specific surface area of 90.043 m²/g.The thermogravimetric analysis showed that the synthesized NaA zeolite molecular sieve had good thermal stability.?2?The synthetic NaA zeolite showed good Ni²⁺adsorption performance in the case of Ni²⁺simulated wastewater.The optimized adsorption treatment process was as follows:when the initial Ni²⁺concentration was 100 mg/L,the addition amount of synthetic zeolite was 2 g/L,and the solution pH was 7,the adsorption time was 3 h,the nickel removal rate was 94%,and the maximum Ni²⁺adsorption amount was48.150 mg/g.At the same time,the NaA zeolite had good regeneration performance/When it was treated for desorption by 1 mol/L HCl solution and repeated for 5 times,the amount of adsorption still reached 41.55 mg/g.The adsorption rate of synthetic zeolite to Ni²⁺was controlled by chemical adsorption process,and the adsorption model is basically consistent with the Langmuir isotherm adsorption model.The kinetic adsorption of Ni²⁺satisfies the quasi-second-order kinetic equation.?3?As an adsorbent for the treatment of Ni²⁺-containing wastewater,the fly ash-synthesized zeolite exhibits excellent Ni²⁺adsorption performance with an additional electric field.In the case of treating the simulated wastewater with Ni²⁺concentration of 100 mg/L,at when the electric field voltage was0.8 V/cm,the NaCl concentration was 1 g/L,and the initial pH of the solution was6,the zeolite could adsorb Ni²⁺for 64.44 mg/g.Compared to the case in open circuit,the adsorption amount increased by 53.17%and the saturated adsorption time was shortened by 50%.Among them,electric field strength,electrolyte concentration and solution pH had an important influence on zeolite adsorption performance.When the electric field was applied,the structure of NaA zeolite did not change significantly,but it could effectively increase the electromigration of heavy metal Ni²⁺,accelerate the adsorption rate.The electric field could also revitalize the zeolite adsorbent,increase the specific surface area and the pore volume of the adsorbent,synergistically improving the adsorption performance of Ni²⁺.?4?The actual electroplating wastewater was treated by fly ash synthetic zeolite molecular sieve.When the addition amount of synthetic zeolite was 8 g/L and the pH value of electroplating wastewater was 7,the removal rate of Cu²⁺,Zn²⁺,Ni²⁺and Cr³⁺in electroplating wastewater after 240 min adsorption were 73.1%,61.4%,50.3%,and50.3%,respectively.At the same time,the HCl solution could regenerate the synthesized zeolite very well.After 5 cycles of adsorption and regeneration experiments,the synthesized zeolite still showed good adsorption performance for each metal ion,indicating that the fly ash synthesized zeolite was promising for treating the actual electroplating heavy metal wastewater.