Improvement in the Synthesis Conditions and Studying the Physicochemical Properties of the Zeolite Li-A(BW) Obtained from a Kaolinitic Rock

Abstract

crystallization of zeolite Li-A(BW) from kaolinite (Standard porcelain by the iMeRYS Minerals Ltd) through a conventional hydrothermal treatment is here achieved for the first time with no additives as reported in the literature. Moreover lower kaolin calcination temperatures and lower synthesis temperatures are tested and verified in this work. The synthesis process is rather simple as the reaction of kaolinite with alkali occurs very readily after calcination of at 650 °C. Metakaolin is mixed with calculated amount of aluminum hydroxide and lithium hydroxide and the experiment is performed at ambient pressure and 180 ± 0.1 °C. Li-A(BW) is characterized by powder X-ray diffraction, high temperature X-ray diffraction, scanning electron microscopy, inductively coupled plasma optical emission spectrometry, thermal analysis and infrared spectroscopy. calculation of cell parameters (through Rietveld Refinement) and density, specific surface and pore size are also achieved. The amount of amorphous phase in the synthesis powders is estimated with quantitative phase analysis using the combined Rietveld and reference intensity ratio methods. The results become notably attractive in view of a possible industrial transfer of the synthesis protocol. Zeolites are a group of tectosilicates of about 50 minerals with synthetic analogues. Their structure is made of three-dimensional networks of Al/Si tetrahedra arranged to form channels containing water and exchangeable alkaline or alkaline earth cations. Zeolite Li-A(BW) is a synthetic low silica zeolite, which possesses the ABW framework topology. Low silica zeolites such as Li-A(BW), are widely involved in several technological applications, such as ion exchangers, adsorbents and catalysts, in radioactive-waste water treatments, sewage effluent treatments, agricultural-waste water treatments, as materials for ferroelectric devices 1. Zeolite Li-A(BW) was first synthesized by Barrer and White 2 and the framework structure and water positions were later determined by Kerr 3 by X-ray powder diffraction (Pna2 1 , a = 10.31, b = 8.18; c = 5.00 Å). Krogh Andersen & Ploug-Sorensen 4 confirmed this structure by X-ray single crystal refinement and later Norby et al. 5 gave the lithium and hydrogen positions by neutron powder diffraction. From the above structural investigations, it results a framework characterized by 4-, 6-, and 8-rings of TO 4 tetrahedra and a fully ordered Si/Al distribution. The result is a zigzag chain of 4-rings running along the c-axis. These chains are linked together, forming 8-ring channels, in which water molecules and lithium ions are situated. Li-A(BW) is characterized by limited reversible rehydration 5 and undergoes to a displacive transition collapsing into the anhydrous phase γ-eucriptite at 650 °C 6. The response to compression of Li-A(BW) zeolite was explored by synchrotron X-ray powder diffraction experiments in the range P amb-8.9 GPa resulting in a cell volume decrease of 12% 7 .

Green and low-cost synthesis of zeolites from kaolin: a promising technology or a delusion?

“…According to some reports, phase purity should be at least 90%. 32,50,51 Detergents require zeolites with the following properties: relative crystallinity of about 100%, Ca 2+ cation exchange capacity of 560 meq/100 g, average particle size of 4 μm, while 99% is within the range of 1 to 10 μm, and whiteness of more than 90%. 52…”

On the suitability of phillipsite-chabazite zeolitite rock for ammonia uptake in water: a case study from the Pescara River (Italy)

“…Zeolitic water content (Table 2 ) was calculated by differential thermal analysis (DTA) and thermogravimetry (TG) (Fig. C3 , Appendix C) using a Mettler TGA/SDTA851e instrument (10°/min, 30–1100 °C, sample mass of ~ 10 mg, Al 2 O 3 crucible) according to the method proposed by 71 .…”

Synthesis and characterization of Na-P1 (GIS) zeolite using a kaolinitic rock

“…The scope of the present work is to test a natural rock, i. e. a kaolinitic rock coming from Romana (Italy) in the synthesis of monomineralic powders of Na-P 1 . Among clay minerals, in fact, kaolinite is the most common phyllosilicate involved in successful zeolitic synthesis because of its particularly ample/large supply and availability and the well-known reactivity of thermally treated kaolin clays (metakaolin) with alkali 3 , 27 – 31 .…”