Synthesis and Characterisation of LTA Zeolite from Angren Kaolin: Evaluation of a Regional Feedstock for Zeolite Production

Linde Type A (LTA) zeolite was synthesised from purified Angren kaolin (Uzbekistan) by a metakaolin route. Raw kaolin was beneficiated by dispersion–decantation to reduce iron, calcined at 700 °C, and crystallised in NaOH solution at 100 °C. Products were characterised by powder X-ray diffraction (PXRD), X-ray fluorescence (XRF), Raman spectroscopy, N2 physisorption and thermal analysis (TGA/DTA). PXRD confirmed crystalline LTA as the major phase (cubic lattice parameter a = 24.68 ± 0.02 Å), with residual quartz from the precursor. XRF gave a near-ideal bulk composition (Si/Al = 1.07, Na/Al = 0.98), confirming sodium incorporation, and Raman corroborated minor quartz and anatase impurities. The very low N2 uptake at −196 °C reflects the restricted access of the 4 Å LTA windows rather than an absence of microporosity. Thermogravimetric analysis showed a ~13 wt% loss of zeolitic water below 300 °C, consistent with substantial hydration of the LTA framework. Locally sourced Angren kaolin can thus be converted into crystalline LTA, establishing a viable regional feedstock for a framework whose potential for molecular-sieve and ion-exchange applications remains to be evaluated by dedicated adsorption measurements.

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