A novel fractional crystalisation-based method for the purification of tellurium to 5 N purity

Separation and Purification Technology, vol. 409, pp. 139242

Abstract

The purification of Tellurium to ultra-high purity levels using multi-pass zone melting remains as state-of-the art method, but it is very time-intensive as slow and repeated processing are required. In this study, a rotational Cooled Finger crystallisation approach is investigated as a pre-purification step to accelerate the purification process prior to zone melting. A systematic experimental study was conducted using 4 N (99.99%) tellurium as feed material, examining the combined effects of rotation rate (25–200 RPM) and cooling gas flow rate (20–120 L/min) on refining performance. Under favourable conditions, the Cooled Finger process achieved purification to 5 N (99.999%) within a single crystallisation step of 30 min. Total impurity concentrations were reduced from 100 ppm to ranges of 5-60 ppm, corresponding to refining efficiencies of 42–90%, with material yields ranging from 8% to 25%. The results show that the refining performance is governed by the interplay between solidification dynamics, temperature gradient and solute transport, which are collectively controlled by the applied rotation and cooling conditions. Compared to conventional zone melting, the Cooled Finger process provides significantly faster impurity reduction. Using it as a supplementary method to zone melting substantially lowers the impurity burden, and may reduce overall processing time required for achieving ultra-high purity tellurium.

Authors 3

1. Hanwen Chung Aachen IME Process Metallurgy and Metal Recycling

   RWTH Aachen University

   Affiliation as printed

   IME Process Metallurgy and Metal Recycling, RWTH Aachen University, 52072 Aachen, Germany

2. Semiramis Friedrich corresponding Aachen IME Process Metallurgy and Metal Recycling

   RWTH Aachen University

   Affiliation as printed

   IME Process Metallurgy and Metal Recycling, RWTH Aachen University, 52072 Aachen, Germany

3. Bernd G. Friedrich Aachen IME Process Metallurgy and Metal Recycling

   RWTH Aachen University

   Affiliation as printed

   IME Process Metallurgy and Metal Recycling, RWTH Aachen University, 52072 Aachen, Germany