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Author(s)

Denise Crocce Romano Espinosa

• Document type: Doctoral Thesis
• Press: São Paulo.
• Institution: Universidade de São Paulo (USP). Escola Politécnica (EP/BC)
• Defense date: 2002-11-29

Examining board members

Jorge Alberto Soares Tenório; Andrea Moura Bernardes; Arthur Pinto Chaves; Claude Henri Paul Lupis; Arlindo Philippi Junior

• Advisor: Jorge Alberto Soares Tenório

Abstract

The use of batteries is increasing in the last decade along with the use of portable devices. Batteries may contain heavy metals, so their disposal must be controlled. Conama (Conselho Nacional do Meio Ambiente - part of the Brazilian Environmental Agency) formulated a law that rule the disposal of batteries. Brazil is the only country in the Latin America that has a law concerning the disposal of batteries. The consumer batteries cannot be disposed of along with the municipal waste and their recycling is encouraged. This thesis\' objectives are to characterize spent NiCd batteries (used in mobile telephones), to study the pyrometallurgical processes for the recycling of this kind of battery through cadmium distillation under different conditions (vacuum, nitrogen atmosphere and reductor addition to the charge) and, to compare the cadmium distillation results for the studied conditions. The characterization was carried out, initially, through the manual dismantling of some batteries and the separation of the internal components of the batteries. The electrodes were characterized by chemical analysis, specific surface area analysis, size separation, X-ray diffraction and scanning electronic microscopy with microprobe analysis. The spent batteries were prepared to the cadmium distillation process using unit operations of mining treatment. An experimental set-up was build to distillate the cadmium from NiCd batteries under vacuum and under nitrogenatmosphere. This set-up is composed essentially of an electric furnace, a stainless steel retort, a cooper water?cooled condenser attached to the retort and a vacuum pump. In the tests with nitrogen atmosphere, a flange that allowed the nitrogen into the chamber was attached to the set-up, the vacuum pump was detached and a second water?cooled condenser was inserted into the chamber. The cadmium distillation was also studied by thermogravimetric tests was the material ) of the electrodes. The results showed that the organic material that is an internal part of the NiCd batteries acted as reductor in the distillation tests. The material that remained in the crucible at the end of the distillation tests was composed of metal fragments (steel) and metal dust (Ni-20% Co). The cadmium purity was higher than 99,95%. Cadmium distillation from its oxide is a temperature dependent process, however the temperature effect was stronger for temperatures lower than 900°C. (AU)