The present work deals with the hydrothermal synthesis of Na zeolites (Na-A, Na-X and Na-P) and hydroxysodalite using kaolinite calcined at 650°C as starting material. The focus was on definition of the most favourable conditions for the synthesis of zeolite Na-A and Na-X from metakaolin in order to economize on both energy (i.e. synthesis temperatures) and reaction time and to enlarge the field of pure and isolated synthesized phases. Metakaolin was mixed with calculated amounts of NaOH solution and sodium silicate and five sets of experiments were carried out at ambient pressure and 68±0.1°C varying the SiO2/Al2O3 ratio from 2.2 to 7. Optimal conditions for crystallization of Na-A zeolite from kaolinite were reached with a SiO2/Al2O3 ratio of 2.2 plus 4 M NaOH without adding sodium silicate; transformation into hydroxysodalite develops after ∼8 h. For SiO2/Al2O3 ratios between 4 and 7, crystallization of the separate Na-X zeolite phase could be achieved and transformation into Na-P and hydroxysodalite occurred after 382 h and 190 h, respectively. For SiO2/Al2O3 ratios between 5 and 6, transformation of metakaolin into Na-X plus Na-A, hydroxysodalite and Na-P occurred, and the field within which Na-A and Na-X zeolite exists overlapped that of the other zeolites.The products of synthesis were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), inductively coupled plasma optical emission spectrometry (ICP-OES), infrared spectroscopy (IR) and thermal analyses (TG-DTG-DTA).Obtaining pure Na-A and Na-X zeolite from kaolinite treated at low metakaolinitization temperature (650°C) and low hydrothermal synthesis temperature (68°C) represents a considerable economic advantage in terms of both energy and time.

Zeolites K-F and W (EDI and MER types) were synthesized hydrothermally using a natural rock as raw material. Chemical treatments were carried out on a diatomitic rock (containing opaline silica) from Crotone (Calabria, Italy) in order to separate/obtain potassium silicate, a reagent necessary for synthesizing zeolites. Synthesis experiments were performed by mixing the obtained siliceous solution with potassium hydroxide and alumina in varying proportions at 150°C and room pressure. Four synthesis series were performed to form zeolite K-F (EDI) and zeolite W (MER).The chemical-physical and morphological characterization of the zeolite phases were carried out. Cell parameters were calculated using the Rietveld method. Infrared, thermal and nuclear magnetic resonance (29Si) experiments confirmed the high quality of the zeolite products. The amorphous phase in the synthesis powders was estimated with quantitative phase analysis using the combined Rietveld and reference intensity ratio methods.

Solid phase reaction synthesis of wollastonite-2Mby a natural rock precursor as the source of amorphous silica and CaCO3is reported. Chemical treatments were carried out on a diatomitic rock from Crotone (Calabria, Italy) in order to measure its reactive silica and CaCO3contents. Four series of synthesis were performed at 1000°C at ambient pressure by mixing, at different stoichiometry, the diatomitic rock with a natural limestone as a source of additive CaCO3, and sodium carbonate (Na2CO3) as triggering agent.Wollastonite-2Mwas characterized by chemo-physical, crystallographical and morphological-microtextural analyses. All these characterizations, together with infrared and nuclear magnetic resonance (29Si) responses provide values comparable to literature data. Estimation of the amorphous phase in the synthesis powders was performed through quantitative phase analysis using the combined Rietveld and reference intensity ratio methods, resulting in a final product of 96.3% wollastonite-2M.