Alkali Treatment of Commercial Silicoaluminophosphate Molecular Sieves (SAPO<sub>-</sub>34) Enhances the Water Adsorption and Desorption Properties

Abstract

Commercial silicoaluminophosphate molecular sieves (SAPO-34) received alkali treatment with either NaOH (0.2, 0.01, 0.005, or 0.001 M) or NH 4 OH (0.005 M). Treatment with NaOH (0.005 M) increased the water adsorption initial rate of SAPO-34 by 1.4-fold. The alkali treatment introduced Na + adsorption sites into the SAPO-34. The desorption ratio (adsorption at 30˚C and desorption at 100˚C) was 88.2% higher than the original rate (84.3%). On the other hand, after alkali treatment of SAPO-34 using NH 4 OH (0.005 M), calcination resulted in the highest desorption ratio at 91.3%. When combined with calcination, alkali treatment with NH 4 OH introduced H + adsorption sites into SAPO-34, H + adsorption sites feature low levels of interaction with water, which enhanced the desorption ratio, but decreased the initial adsorption rate. These results indicate that treating commercial SAPO-34 with 0.005 M NaOH enhances both the adsorption and desorption behaviors.

Sorption of Heavy Metal Ions of Chromium, Manganese, Selenium, Nickel, Cobalt, Iron from Aqueous Acidic Solutions in Batch and Dynamic Conditions on Natural and Synthetic Aluminosilicate Sorbents

“…The phenomenon of ion exchange is facilitated by internal cavities and interconnected channels of molecular size, present in the structure of zeolites [ 31 ]. Natural zeolites occur in hydrated forms, such as clinoptilolite (K 2 Na 2 Ca) 2 [(Al 6 Si 30 )O 72 ]·24H 2 O [ 32 , 33 ]. Their sorption abilities have already been extensively studied by many authors [ 34 ].…”