Comprehensive experimental design on the preparation of zeolite from fly ash and its performance in removing ammonia nitrogen from water
[Objective]Ammonia nitrogen in wastewater and fly ash is harmful to aquatic life and human health,conflicting with the sustainable development concept of preserving"Lucid waters and lush mountains are invaluable assets".This study presents the design and synthesis of a fly ash-based zeolite molecular sieve with good ammonia nitrogen adsorption performance,which was applied to the treatment of ammonia nitrogen wastewater.[Methods]This approach embodies the"green chemistry"principle by"treating waste with waste",thereby promoting the coordinated development of economic and environmental benefits.Fly ash primarily comprises silicon oxide and alumina,which are essential raw materials for zeolite molecular synthesis.Focusing on efficiently treating ammonia nitrogen wastewater,we conducted comprehensive experiments to prepare zeolite from fly ash and assess its performance in removing ammonia nitrogen from water.The methodology included the synthesis of sodium aluminosilicate(NaA)zeolite using fly ash as a raw material,testing its ammonia nitrogen adsorption performance,and analyzing the adsorption mechanism.The optimizations led to the optimum preparation parameters for Zeolite A(LTA),featuring a calcination temperature of 600 ℃ and alkali/oxide(silica and alumina)ratio of 1∶1.2 for fly ash pretreatment,and a Si/Al ratio of 0.50 in the synthesis gel.A series of different products were characterized,using X-ray diffraction,scanning electron microscopy,electron dispersive spectroscopy,nitrogen physisorption,and thermogravimetry to confirm their structure and molecular formula.The NaA zeolite synthesized under the above optimal conditions displayed cubic morphologies with uniform sizes,which increased with the Si/Al ratios.[Results]The Si/Al ratio of the synthesized LTA was 1,and the external specific surface area was found to be up to 22 m2 g-1.The saturated adsorption capacity for ammonia nitrogen was also measured to be as high as 18.59 mg·g-1,with a removal efficiency of 58％.The adsorption mechanism was systematically investigated via adsorption kinetic experiments,revealing that the process is dominated by chemical adsorption,involving three stages where intra-particle diffusion is not the only rate-controlling step.[Conclusions]This comprehensive experiment integrates concepts from physical chemistry,materials chemistry,and instrumental analysis,offering hands-on experience in zeolite molecular operation and testing,product characterization,and mechanism exploration.Furthermore,it enhances students'basic experimental operation skills and broadens their horizons through literature review in the early stage.Innovative experiments,when combined with self-learning theoretical knowledge and cutting-edge content,can facilitate the cross-integration of knowledge.This approach helps in cultivating students'hands-on experience and their ability to apply professional knowledge to analyze and solve complex problems,thereby improving their scientific literacy and innovation capabilities.The integration of the green development concept and professional experimental teaching should deepen students'learning and exploration of molecular sieve synthesis and preparation process,aiding in cultivating well-rounded professionals".
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