Synthesis and Characterization of Na-X Zeolite Using a Natural Opaline Diatomite Rock from SE Spain

A natural diatomite was used to hydrothermally synthesise Na-X zeolite. Albacete diatomite from southern Spain (mainly constituted by opaline silica) was chemically treated with HCl and NaOH to obtain sodium silicate, a reagent necessary for zeolitic synthesis. The experimental synthesis protocol was performed at 75 °C by mixing the obtained silicatic solution with chemical reagents represented by soda and alumina. Na-X zeolite begins to appear after only 1.5 h and reaches its crystallisation climax at 11 h. Hydroxisodalite appears at 40 h. Synthesized phases were subjected to chemical-crystallographical and mineralogical-textural characterisation. The thermal behaviour and infrared response have also been investigated. The purity of the synthesized zeolite, verified through quantitative phase analysis using the combined Rietveld and reference intensity ratio methods, opens the way to a possible industrial transfer of the experimental procedure.