Synthesis of zeolitic materials from solid residues of the Argentinian brewing industry

MILAGROS OTEGUI ALEXENICER,; FERNANDO IVORRA; FUCHS, VANESA M.; CARLA DI LUCA; PAOLA MASSA

Buenos Aires

Congreso; 11 World Congress of Chemical Engineering; 2023

Asociación Argentina de Ingenieros Químicos

Natural diatomaceous earth is fossilized silicon-rich sediment from algae. They have diverse industrial applications due to their high porosity and adsorption capacity. Most diatomite global exploitation is used as a beverage filter aid.The brewing industry, with strong local development in Mar del Plata (Argentina), generates a significant volume ofsolid waste. It is estimated that, for every liter of filtered beer, 1-2 g of diatomite is consumed, and 18 g of sludge is generated. The sludge contains spent diatomite, water, vegetable remains, yeasts, and trapped solids. Currently,these residues are dumped in landfills, spread over large expanses of farmland, or used as direct feed for livestock, mixed with other process residues (spent grains). These final disposal practices are not sustainable and can bedangerous to mammals due to the presence of crystalline silica.Research on diatomite reuse is still scarce, although there is a growing interest in developing more sustainablematerials and processes. In this context, we are investigating the application of these solid wastes in the preparation of adsorbent and/or catalytic materials, such as zeolites of commercial interest.The industrial sludge was first conditioned through different thermal treatments to remove moisture and organic matterfrom the residual sludge. X-ray diffraction (XRD) measurements verified that the conditioned residue is mainly composed of crystalline silica, phase cristobalite (SiO2: 90,8%; Al2O3: 4,9%). According to selected data from the literature, a starting molar ratio SiO2/Al2O3=11 was defined to obtain Faujasite-type zeolites. Technical grade Al2(SO4)3 was used as a complementary source of aluminum. The precursors were mixed and subjected to alkaline hydrolysis inan aqueous NaOH solution, followed by an activation/ageing time (Na2O/SiO2=0.9; H2O/Na2O=40). Finally, the hydrothermal stage was carried out in an autoclave reactor at 100 ºC. The synthesis variables that were investigatedwere the ageing time/temperature of the precursor gel and the crystallization time and temperature. For the experimental series reported in the present work, the activation was set at 70 ºC for 4 h (to favor the complete dissolution of the residue). The crystallization was performed at 100 ºC, during 1 -24 h. Finally, the solid was washeduntil neutral pH, filtered, and dried.The XRD analysis confirmed the disappearance of the cristobalite signal, for crystallization times above 4 h, and the preferential formation of a Gismondine-type zeolite (phase NaP). For crystallization times between 1 and 4 h, mixtures with NaA zeolite and sodalite were detected.Exploratory adsorption tests were carried out with Cu2+ and Zn2+ cations, with promissory results. Based on these results, we plan to continue exploring the operating conditions that allow directing the synthesis toward the formation of zeolites with greater commercial interest (FAU type or NaA). We will focus on the reproducibility of the procedures, the yield of the synthesized product, and the properties associated with higher efficiency of adsorption of contaminantsfrom water.