Effect of Alkalinity on Zeolite LTN Formation under Bayer Process Pre-desilication Conditions

There is limited research about the formation of zeolite LTN under Bayer process pre-desilication conditions. Here, we report on the effect of alkaline (2-8 M NaOH) and aluminate concentrations (0.125-0.75 M) using 0.1 or 0.2 M soluble silicate with respect to its effect on zeolite crystallization within a pre-desilication time range of 4 h. Whether the LTA or LTN phase forms first is found to depend on both the aluminate and alkaline concentrations. With a 2 M NaOH initial concentration, only an amorphous-to-LTA-phase transformation is observed. For 4 and 6 M NaOH, decreasing the aluminate concentration increases the proportion of the LTN phase compared to that of LTA. The phase transformation between LTA and LTN was also observed. However, only LTN transformed into SOD at 8 M NaOH. Select pure phases obtained from the experiments were characterized by NMR and thermal gravimetry. Amorphous, LTA, and LTN phases transformed into a low-camegieite phase, while SOD remained unchanged when heated to 850 degrees C. These findings on zeolite LTN provide information on the further development of the previously proposed Bayer sandy desilication product process.

Automated summary

Limited research exists on the formation of zeolite LTN under Bayer process pre-desilication conditions. The effect of alkaline and aluminate concentrations on zeolite crystallization was investigated, with LTA and LTN phases forming depending on the concentrations. Experimental results showed phase transformations and characterization of pure phases through NMR and thermal gravimetry, providing information for further development of the Bayer sandy desilication product process.