## 2 Materials and Methods  
The diatomite residue used in this investigation came from the filter earths used in the beer brewing process of the Heineken company at its plant located in Jaen (Spain). Once dried in an oven at 105 \({}^{\circ}\)C, this material was ready to be used without the need for grinding, since its particle size presented a high fineness (all the material passed through the 63-um sieve). Thus, the energy and economic costs of milling would be eliminated, an aspect that is especially positive if the zeolitization protocol described were to be scaled up to an industrial level. The diatomite's chemical composition (obtained by X-ray fluorescence using a Thermo ARL ADVANT'XP Sequential XRF equipment) is shown in Table 1.  
The high percentage of loss on ignition (LOI) is attributable to the organic matter retained in the diatomic mineral matrix during the filtration process in beer production. Accordingly, the diatomic waste was calcined at 550 \({}^{\circ}\)C for 5 h in a muffle to remove the organic matter. On the other hand, as expected, the SiO\({}_{2}\) content is predominant, reaching a value of almost 90% after calcination (Table 1), since silicon is the main component of diatomaceous earths. Far below, the second element present is aluminum (\(\sim\)4%), followed by lower proportions of iron and alkali and alkaline earth metals, among others. The presence of these elements could be due to impurities in the diatomic itself, as well as to substances retained in its structure during filtration. Despite this, the chemical composition of Table 1 is in the same order as others found in the literature for diatomaceous earths from different sources and countries [12]. As a result, the Si/Al molar ratio of the raw material is high (Si/Al = 17.4). After that, the clean diatomite (Dt) was subjected to hydrothermal treatment with a 3M NaOH solution. The liquid (NaOH solution)/solid (mass of Dt) ratio used was 10, specifically 10 g of Dt in 100 mL of NaOH solution. The mixture was kept under constant magnetic stirring for 24 h at 80 \({}^{\circ}\)C in a closed Erlenmeyer flask [7]. On completion of the 24 h of hydrothermal stirring, the suspension was filtered and washed with distilled water until a neutral pH was reached. The sediment finally obtained was dried at 105 \({}^{\circ}\)C in an oven and subsequently characterized. The sample obtained after this treatment was named Dt-Z. The quantitative mineralogical composition of the original Dt and the phases formed from it was determined by X-ray diffraction (XRD) using a PANalytical(r) diffractometer X'Pert Pro model. For this analysis, polycrystalline powder diffractograms were obtained after adding \(\sim\)25 wt.% alumina to the sample in order to determine both the crystalline and amorphous phases by Rietveld refinement [13; 14]. The measurement conditions were as follows: 45 kV, 40 mA, Cu radiation, solar slit of 0.04 rad, antiscattering slit of 1/2\({}^{\circ}\), divergence slit of 1/8\({}^{\circ}\), step size of 0.0167, counting time (s) of 130, Bragg-Brentano HD module and X'celerator detector. The Rietveld analysis of the sample was carried out with the HSP program of Panalytical. It is important to note that the quantification of mineral/amorphous phases is not an aspect usually addressed in other studies shown in the literature, which are limited exclusively to phase identification, making this a point of special interest in this research. The N\({}_{2}\) adsorption-desorption isotherms at 77 K of both Dt and the resulting zeolites (Dt-Z) were obtained using Surface Area and Porosity Analyzer-Model ASAP 2420 manufactured by Micromerities Instrument Corporation, deducing the Brunauer-Emmett-Teller (BET) surface area, the Barrett-Joyner-Halenda (BJH) mesopore characteristics, as well as the micropore volume based on the Density Functional Theory (DFT).