Spectroscopic investigations on different grade samples of Talc

Abstract

Three grades of Talc, Mg₃[Si₄O₁₀](OH)₂, collected from Kurnool district of Andhra Pradesh, India have been investigated by spectrochemical analysis, Optical and EPR spectroscopy. All these samples contain iron as major impurity and trace amounts of Al, Ca, Cr, Cu, Mn and Ni. The Optical absorption spectrum of the high grade Talc sample exhibit six bands at 29403, 26308, 24993, 22720, 20613 and 17090 cm⁻¹, ascribed to Fe³⁺ impurity, substituted for Mg ion. Low grade Talcs show edge absorption at 27500 and 22750 cm⁻¹, due to higher content of iron. The crystal field parameters evaluated are B = 700, C = 2800 and Dq = 700cm⁻¹. In addition, the presence of Fe³⁺ and Mn²⁺ impurities have been confirmed by EPR spectroscopy. Heating the samples to 850°C in steps yielded spectra corresponding to stabilization of iron centres only, at the expense of Mn²⁺ ones.

Key Words:

• talc
• optical spectroscopy
• electron paramagnetic resonance
• impurity ion
• iron
• manganese
• crystal field parameters