# Thermally Induced Phase Transformation of Ni-Exchanged LTA Zeolite as an Alternative Route of Obtaining Stable Ni-Spinel Pigment

## TL;DR

This study shows how heating nickel-exchanged LTA zeolite creates stable blue pigments, offering a sustainable method for ceramic pigment production.

## Contribution

A novel dual-purpose method for nickel immobilization and pigment synthesis using thermally induced phase transformation of Ni-LTA zeolite.

## Key findings

- Ni-exchanged LTA zeolite transforms into NiAl2O4 spinel at 900–1300 °C, confirmed by XRPD and FTIR.
- Pigment color intensifies with higher temperatures, reaching over 99% crystalline phase at 1300 °C.
- SEM analysis shows morphological changes to sintered agglomerates, improving pigment stability and hardness.

## Abstract

This study investigates the thermally induced phase transformation of Ni-exchanged LTA zeolite as a dual-purpose method for nickel immobilization and the synthesis of stable ceramic pigments. The process describes a cost-effective and sustainable alternative to conventional pigment production, aligning with circular economy principles. Upon thermal treatment at temperatures ranging between 900 °C and 1300 °C, Ni-exchanged LTA zeolite undergoes a transformation to NiAl2O4 spinel, confirmed by XRPD, FTIR, and thermal analysis. Initially, NiO is formed, but as the temperature increases, it dissolves and transforms into NiAl2O4. Colorimetric studies revealed intensified blue pigmentation with increasing temperature, correlating with crystallite growth and structural evolution. SEM analysis showed morphological changes from cubic particles to sintered agglomerates, enhancing pigment stability and hardness. The Ni-LTA sample calcined at 1300 °C showed the highest hue angle, which was consistent with the formation of over 99 wt.% of the nickel aluminate crystalline phase at this temperature. The results demonstrate that Ni-LTA zeolite can be effectively transformed into durable greenish-blue pigments suitable for application in porcelain. This transformation is especially evident at 1300 °C, where a spinel phase (NiAlSi2O4) forms, with colorimetric values: L = 58.94, a* = –16.08, and b* = –15.90.