Silica-free zirconia from zircon mineral by thermal plasma processing

ABSTRACT

Experimental and thermodynamic studies on thermal plasma processing of zircon-carbon mixtures are reported in this paper. Plasma processing of zircon-carbon mixtures to convert the silicate mineral to zirconium dioxide with concurrent removal of silica was studied. Zircon sand was mixed with carbon powder and processed in a specially designed nontransferred arc plasma reactor operated using air as plasma medium. Addition of carbon to zircon facilitated in situ reduction of silica to SiO gas, which escaped with the exhaust gas. More than 96% product purity could be obtained by in-flight removal of silica by processing zircon mixed with sufficient amount of carbon at 25 kW input power. Microstructure analysis showed that in-flight removal of silica facilitated the hexagonal growth pattern and irregularly shaped bulk zirconia crystal structures of monoclinic zirconia. Thermodynamic analysis of in-situ removal of silica by carbo-thermal reduction showed that the amount of carbon had a significant effect. The studies showed that controlled addition of carbon could lower the reaction temperature by more than 500 K and facilitated in situ removal of silica. The studies are technologically relevant and offer useful guidance for making the plasma process economically viable.

KEYWORDS:

• zircon
• dissociation
• air-plasma
• zirconia
• torch
• in-flight
• reaction
• silica

Acknowledgments

The authors gratefully acknowledge the financial support received from DST.

Additional information

Funding

The work was funded by Department of Science and Technology, Government of India under the DST-TSDP for the characterization and instrument facility (Sanction order no: DST/TSG/AMT/2015/604).