1. Department of Physical Chemistry, Sofia University, 1 James Bourchier Blvd, 1164 Sofia, Bulgaria
2. School of Minerals and Energy Resources Engineering, University of New South Wales, Sydney, NSW 2052, Australia
3. Department of Medical Physics and Biophysics, Medical Faculty, Medical University–Sofia, Zdrave Str. 2, 1431 Sofia, Bulgaria
4. Department of Mineral Processing Engineering, Istanbul Technical University, Istanbul 34469, Turkey