INVESTIGATION OF SURFACE PROPERTIES AND FLOATABILITY OF CdTe
SEMICONDUCTOR FOR THE SAKE OF RECYCLING OF OBSOLETE SOLAR ELEMENTS
Ljudmilla BOKÁNYI1 – Szilvia SZABÓ2 – József PAULOVICS3
1
Associate Professor, Head of Department
Institute of Raw Materials Preparation and Environmental Processing, University of Miskolc, Hungary
Miskolc-Egyetemváros 3515, Hungary, ejtblj@uni-miskolc.hu
2
Managing Director, Kiss Analitika LTD, Sajóbábony, Gyártelep Pf. 4. 3792, Hungary
szabo.szilvia@kisanalitika.hu
3
Project Manager, ÉMK LTD, Sajóbábony, Gyártelep 3792, Hungary
paulovics.jozsef@emkkft.hu
ABSTRACT
Waste recycling is one of the most important challenges of the XXI century. The recycling of wastes is
closely related to and bases on the mineral processing. Many mineral processing techniques and equipment
are applied in this field. The principles of the characterisation of wastes and design of technologies is rather
similar to the classic mineral processing’s. Nevertheless, the diversity of the wastes and their complex
composition and properties, as well as their environmental impact requires a special approach.
Solar elements have sandwich structure of glass substrate and cover, as well as very thin semi-conductor
layer. CdTe semi-conductor can be recycled by flotation. Within the RESOLVED (LIFE European
Framework) R&D project on the recycling of solar elements the surface properties of pure semiconductor
CdTe and pure glass were investigated by the measurement of zeta-potential using Zeta PALS Brookhaven
instrument at University of Miskolc. Applied surfactants were: potassium ethyl xanthate; the anionic
oxhydryl Aero Promoter 825 or Flotinor SM 35; the cationic Armoflote 43 or Armoflote 64, as well as
Hostaflot LET (dithiophosphoric acid diethyl ester) and Hostaflot M91 (mercaptobenothiazole). The tested
electrolytes were sodium-sulphide and sodium-silicate. Zeta-measurements were carried out at full pHrange. Interfacial interactions were detected and interpreted. The basic results were verified by the flotation
kinetic tests.
Finally, the flotation technological experiments were carried out at a semi-technical scale using the real
obsolete solar elements. The particle size at the liberation degree of 98% was as fine as below 5
micrometer. A special flotation cell was built with a very fine air bubbles generation and distribution.
The pre-concentrate for the manufacturing of the test solar module was performed and transported to the
BAM Institute (Berlin), the principal co-ordinator of the Project, and then further to the First Solar (USA)
where a new panel was manufactured using recycled semi-conductor.
KEYWORDS
Solar elements, recycling, cadmium telluride, surface properties, zeta-potential, flotation.