Utilization of NaP zeolite synthesized with different silicon species and NaAlO₂ from coal fly ash for the adsorption...

NaP zeolite was successfully synthesized by using various commercial silicon sources and NaAlO₂ extracted from coal fly ash as raw materials. Multiple characterization methods were employed to investigate the effect of silicon sources on NaP zeolite. Adsorption performance and mechanism of NaP zeolite for Rhodamine B were surveyed. The product synthesized by fumed SiO₂ at n(Na₂O)/n(SiO₂) = 0.70 presented single spherical morphology with the average grain size of 3.22 µm. The shearing of NaOH resulted in the formation of silicates with different polymerization degrees and silicates occurring in the forms of monomeric, dimeric, trimeric, long-chain, and cyclic oligomers, initiating an improvement in pore structure and morphology. The introduction of dynamic crystallization mode (with the rotating speed of 150 r/min) not only reduced grain size (from 3.22 µm to 1.78 µm) but also shortened crystallization time (from 12 h to 10 h) of NaP-fumed SiO₂. NaP zeolite had excellent adsorption performance for Rhodamine B with the removal rate of 98.26%. Adsorption behavior fitted well with pseudo-second-order kinetics and Langmuir isotherm adsorption equations. Adsorption process was endothermic and feasible. NaP zeolite had good regeneration and alkali resistance capacities. Adsorption manners mainly contained pore filling, electrostatic attraction, and hydrogen bonding, focused on physisorption.