# Valorization of Ornamental Stone Processing Waste for the Synthesis of LTA- and SOD-Type Zeolites

## TL;DR

This paper shows how waste from ornamental stone processing can be turned into useful zeolites, offering a sustainable and cost-effective method for producing materials with applications in catalysis and gas separation.

## Contribution

The study demonstrates a novel, environmentally friendly method to synthesize LTA and SOD zeolites from ornamental stone waste using alkaline activation and hydrothermal crystallization.

## Key findings

- LTA zeolite with 99.94% crystallinity was synthesized in 6 hours from ornamental stone waste.
- The LTA zeolite transformed into SOD phase with 87.56% crystallinity over 48 hours.
- 29Si and 27Al NMR analyses confirmed structural changes and the basic nature of the synthesized zeolites.

## Abstract

The conversion of ornamental stone waste, rich in quartz
and potassium
feldspar, into precursors for LTA and SOD zeolite synthesis was investigated
via alkaline activation at 850 °C, followed by hydrothermal crystallization
without autoclaves. This approach promoted complete amorphization
of the material, facilitating the breakdown of the original crystalline
framework and the incorporation of sodium ions, which are essential
for structural rearrangement during zeolite formation. LTA zeolite
was obtained after 6 h of crystallization, reaching 99.94%
crystallinity, and progressively transformed into the SOD phase over
48 h, achieving 87.56% crystallinity. This phase transition
was closely related to variations in the Na2O/Al2O3 molar ratio and the conditions governing nucleation
and crystal growth. Solid-state 29Si NMR analyses revealed
local rearrangements in the aluminosilicate framework during the LTA
→ SOD transformation, highlighting the key role of Na+ redistribution in structural evolution. Complementary 27Al NMR confirmed the exclusive presence of tetrahedrally coordinated
aluminum and the absence of Brønsted acid sites, indicating a
basic character of the synthesized zeolites. These results demonstrate
the technical and environmental feasibility of using ornamental stone
waste as a raw material, providing a sustainable and economically
competitive route to produce functional zeolites with potential applications
in catalysis, adsorption, sensing, and gas separation technologies.